COALBIOREACTOR FOR IN-SITU COAL BIOMETHANATION

FIELD OF INVENTION

This invention “CoalBioreactor for in-situ coal biomethanation” relates to a bioreactor (unregistered trade name

CoalBioreactor), invented for accelerated natural or imitated biomethanation of all types of coal in-situ to

biogenic methane (biomethane) for its recovery at surface; having an impermeable enclosure in subsurface

target coal formation, the in-situ biomethanation operation area, and connected to surface by a central well,

passing through subsurface formations overlying the target formation, for recovery at surface the subsurface

biomethane generated, and injection of CO2 in the subsurface impermeable enclosure; to make feasible

utilization of all types of coal, especially those that are non-extractable/un-mineable, as a sustainable source of

energy and sink for CO2 sequestration at industrial (large) scale and commercial rate.

Coal’s natural or imitated biomethanation stimulation to a commercial rate and industrial scale needs

incorporation of local strategies to deal with associated bottlenecks that are usually specific to microbial

geological biomethanation conditions (MGBC) of a target coal formation and its ecosystems. Therefore the

subsurface construction of the impermeable enclosure (either on a piece of the target coal formation, one after

the other or in multiple numbers simultaneously covering whole of the target formation and all coal seams, or a

single one covering whole of the target formation and all coal seams), the connecting well to surface, and

facilities at surface for monitoring, control and regulation of in-situ biomethanation process in the subsurface

impermeable enclosures properly, are engineered meticulously to have features suited to MGBC character of the

target coal formation. The surface facilities facilitate injection of designer bio-stimulants or/and

bioaugmentation of a set of designer anaerobic microbial consortia in the subsurface impermeable enclosure for

stable and prolonged in-situ biomethanation of a substantially very high percentage of substrate (coal carbon

polymer) present therein, without contaminating the subsurface surroundings.

Once biomethanation of all the substrate present within the subsurface impermeable enclosure is over (using all

the permutations and combinations of injection of designer bio-stimulants or/and bioaugmentation of a set of

designer anaerobic microbial consortia and control and regulation of subsurface in-situ biomethanation

operational and environmental parameters critical for a stable process for a prolonged period) and the

biomethane generated therein recovered at the surface using primary conventional extraction methods, then CO2

(generated subsurface during in-situ biomethanation process and recovered along with generated biomethane as

a byproduct at surface and also emitted due to combustion of recovered biomethane at surface) gets injected in

the subsurface impermeable enclosure for enhanced recovery of subsurface biomethane generated. The injected

CO2, first, pushes out most of those biomethane that were generated but remained trapped in the coal formation

itself for their recovery at surface. Secondly the sequestered CO2 acts as a green solvent, usually in those

formations that are more than about a km deep, and therefore dissolves some more substrate (a fraction of

leftover coal carbon polymer in the residual coal formation that were not hydrolyzed initially by designer bio-

stimulants and microbial consortia, in addition to a substantially very high percentage of coal carbon polymer

hydrolyzed earlier before CO2 sequestration) and makes them bioavailable for biomethanation, and thus some

additional biomethane gets generated for its recovery at surface. Thirdly, the sequestered CO2 gets utilized as a

substrate by bioaugmentation of another set of designer anaerobic microbial consortia in the subsurface

impermeable enclosure.

The continued biomethanation of CO2 in the subsurface impermeable enclosure makes possible repeated

sequestration of CO2 in the subsurface impermeable enclosure that leads to in-situ biomethanation process and

generation of biomethane in the subsurface impermeable enclosure for a very prolonged period, till

biomethanation process is techno-economically feasible. Thereafter, lastly, for extraction of geothermal energy

from the CO2-filled reservoir, CO2 geothermics is used for extraction of geothermal energy on sustainable basis.

Thus this invention transforms the target coal formation in a sustainable CO2 sequestration sink and source of

sustainable energy (in biomethane and geothermal form).

BACKGROUND/PRIOR ART OF INVENTION

All coal contains a huge quantity of energy in solid coal carbon form. Some of them contain a bit varying

quantity of energy in gaseous methane hydrocarbon form also. Traditional coal mining operation of coal

extraction makes possible commercial use of the energy available in solid coal carbon polymer form whereas

energy available in gaseous hydrocarbon form usually vents out. Out of total coal geological resources, only

about 22% of the resources are extractable under BAU (business as usual) scenario in India. Even under

envisaged BCS (best-case scenario), the percentage of extractable coal reserves are likely to enhance say by

another 50%, though it is an optimistic estimate but even after that extraction of only about 30% of the total coal

geological resources would be possible, and 70% of the coal geological resources would remain non-extractable

(un-mineable). Thus the huge energy contained therein in solid coal carbon polymer form and gaseous methane

form would remain untapped and unrecovered forever. With a bit changed percentage of non-extractable coal

geological resources, the scenario is likely to be the same worldwide.

Coalbed Methane (CBM) recovery technology extracts energy available in gaseous hydrocarbon form, mainly

methane form, from both extractable and non-extractable coal. Extraction of energy available in solid coal

carbon polymer form in non-extractable coal is possible through application of thermal underground coal

gasification (UCG) technology. Under UCG operation, solid coal carbon polymer gets converted into synthetic

or syn gas, which contains mainly CH4, H2, CO and CO2. However, UCG is only suitable for those non-

extractable coal deposits that have low water content and are available at relatively sallower depth. It is not

suitable for aquatic coal deposits. Its suitability and applicability is narrow and limited due to depth

consideration, seam thickness, ash content, discontinuities in coal deposits, over dependence on geological

factors, chances of aquifers contamination, subsidence, roof failure, extremely high operating temperature, etc.

All combined result in running of the gasifier without having proper control over the gasifier and produced syn

gas. All of the engineering cannot account for unpredictability associated with opening a hole up under the

ground and all technologies alone cannot create stability in UCG; and therefore, though this technology is on

trial run here and there for last more than 100 years, however, its application, as a large-scale coal to synthetic

gas conversion technology

for energy extraction at industrial scale and commercial rate, proves to be more

difficult. Moreover, apart from extracting effectively only a low percentage of the energy contained therein in

the solid coal carbon polymer form that too in form of syn gas, which is not as clean and quality fuel as

methane, an UCG operation spoils the target coal formation completely, and thus the residual coal loses its

further utility fully.

Realizing that more than 70% of the natural coal resources across the globe are non-extractable and coal is not a

green fuel, its combustion produces CO2 and pollutes environment; commercial extraction of energy from 70%

of the non-extractable coal and utilization of its main associated pollute CO2 (produced during energy extraction

and emitted due to combustion of energy extracted) for value addition so that the energy extraction process

becomes almost carbon-neutral and sometimes even carbon-negative is the central idea behind present invention

of “CoalBioreactor for in-situ Coal Biomethanation”. Application of this invention is equally relevant for

extraction of energy available in solid carbon polymer form from any and all other non-extractable carbonaceous

materials in almost carbon-neutral and sometimes even carbon-negative way.

Biomethanation is a natural, slow process and complex phenomenon of bioconversion of coal to biogenic

methane (biomethane) by indigenous microbes undergoing in some coal continuously that have favourable

microbial geological biomethanation conditions (MGBC). This natural slow ongoing biomethanation process

can be accelerated up to an extent using biostimulation or/and bioaugmentation in those coal that have

favourable MGBC. A number of approaches have been made and developed for biomethanation of

carbonaceous materials on surface as well as in-situ in subsurface. The subsurface accelerated in-situ

biomethanation mainly has been proposed for fossil fuels target formations by suggesting monitoring, control

and regulation of a highly complex biomethanation phenomenon and its critical parameters in its existing natural

environment that is likely to be open and permeable, and likely to be fully or fairly open to its surrounding for

to and fro movement of bio-stimulants and microbial consortia, waste and toxic materials, pathogens, etc to

surrounding formations, unless otherwise surrounded from all the six sides by fully impermeable cap rocks

existing naturally. For instance,

PATENT CITATIONS

Cited Patent Filling

Date

Publication

Date

Applicant Title Features

1. IN2580/DEL/2004* 28.12.2004 09.02.2007 Aqua Technos Asia

Co. Ltd.

A Biomethanation Plant and a

Process for Treatment of Spent Wash using the

Biomethanation Plant

Plant is at surface. Substrate is liquid

(soft) and therefore, biomethanation process simple, easy and different.

2. WO2009148569* 02.06.2009 10.12.2009 Ciris Energy, Inc. The Stimulation of Biogenic

Gas Generation in Deposits of

Carbonaceous Material

Treating of subterranean formation by

injecting two types of chemicals,

microbial consortia, and utilizing indigenous consortia. Moreover,

claiming for hydrolysis using chemicals

rather than using microbial Acidogens. No mention of CO2 sequestration and

fracturing of coal. In-situ but suggesting

in acceleration and control of processes utilizing its existing natural that is

usually an open and permeable

environment.

3. US2010/0093049A1* 04.09.2004 15.04.2010 Rathin Datta Biological Methane Production from Coal, Manure, Sludge,

Wastes or Other Carbonaceous

Feed Stocks with Simultaneous Sequestration of CO2

Plant is at surface. Substrate is particulate and/or dissolved

carbonaceous feed stocks, therefore

biomethanation process is simple, easy and different. Use of alkaline earth metal

salt as divalent for utilization of

generated CO2 as a part of biomethanation process itself, not a

sequestration in true sense.

4. US20010045279 20.02.2001 29.11.2001 Converse David R. Converting Hydrocarbons to

Methane

MEOR by generating CO2 gas to build

up pressure in reservoir to enhance recovery. No fracturing.

Characterization is based on one

microorganism identification, not complete MGBC. In-situ but suggesting

in acceleration and control of processes

utilizing its existing natural that is usually an open and permeable

environment.

5. US20060254765 30.01.2006 16.11.2006 Luca Technologies, Lic Biogenic Fuel Gas Generation

in Geologic Hydrocarbons

Process of stimulation by injecting only

water, no growth medium, microbes, nutrients and other chemical

amendments. In-situ but suggesting in

acceleration and control of processes utilizing its existing natural that is

usually an open and permeable

environment.

6. US20070261843 05.04.2006 15.11.2007 Luca Technologies, Lic Providing Acetic Acid or Potassium Acetate Activator to

a Microorganism in a

geological formation from outside to Activate the

Microorganism which Metabolise Carbonaceous

Material in the Formation to

Methane

Process of stimulation by injecting chemicals, no microbes, nutrients, etc.

In-situ but suggesting in acceleration

and control of processes utilizing its existing natural that is usually an open

and permeable environment.

7. WO2005115649A1 27.05.2005 08.12.2005 Michael Endmon Process for stimulating production of methane from

petroleum in subterranean

formations

Only acceleration of process by identifying ecological environment

suitable for microbial growth and trying

to modify that by adding chemicals, etc. In-situ but suggesting in acceleration

and control of processes utilizing its

existing natural that is usually an open and permeable environment.

8. PCT/US01/32635 24.10.2001 02.05.2002 Guyer J E Method of generating and

recovering gas from subsurface

formations of coal,

carbonaceous shale and organic rich shales

CO2 and CO sequestration in the

beginning that attract coal matrix

swelling, reduction in permeability,

Injectivity loss, cap rock deformation and CO2 sequestration in a limited

quantity. Apart, biomethanation process

associated with disadvantages of the coal swelling process, besides

suggesting in acceleration and control of

processes utilizing its existing natural open that is usually a permeable

environment.

* Cited by examiner

Both the above citations (1) & (3) are biomethanation plant at surface, not in-situ, treating comparatively very

soft substrates available either in liquid or particulate state compared to in-situ coal (a solid, dry, insoluble and

thus a complex substrate for biomethanation that too in-situ), therefore the biomethanation process is quite

different.

Citation (1) recommends thermophilic digestion over mesophilic digestion and mainly deals with conversion of

mesophilic digesters to thermophilic digesters for higher reduction of BOD, COD, TDS and TSS. Therefore the

plant and the biomethanation process deal with altogether different concept than the CoalBioreactor and the

biomethanation process therein.

Citation (3) anaerobically incubate a particulate alkaline earth metal salt in contact with a particulate and/or

dissolved carbonaceous feedstock in contact with a neutral or alkaline aqueous consortium of methanogenic

bacteria; where as in the CoalBioreactor the biomethanation process would be accelerated preferably utilizing

indigenous biomethanation microbial consortia itself by adding most suitable growth medium, nutrients and

other chemical amendments (to be determined only after MGBC characterization of target hydrocarbon) of

proper quality and in appropriate quantity. Injection of suitable microbial consortia would only be considered in

absence of indigenous biomethanation microbial consortia. Moreover, CO2 sequestration, which is part of

process in citation (3) that would comparatively reduce the ratio of CO2 in produced biogas, that would take

place only at end of the biomethanation of maximum fraction of the target hydrocarbon present therein would

consider sequestration of CO2 produced, CO2 emitted due to combustion of biomethane harvested at surface as

well as sometimes may even CO2 from external sources depending on volume of the void created inside the

CoalBioreactor due to in-situ biomethanation of coal. Therefore the plant, the biomethanation process as well as

CO2 sequestration process are altogether totally different in citation (3) than in the present invention.

Citations (2), (4), (5), (6), (7) and (8) are about acceleration of in-situ biomethanation of various carbonaceous

materials including coal and lignite, using a number of schemes in the target blocks, where natural in-situ

biomethanation is already undergoing. Except for citation (8) and perhaps citation (2) also, none of them

consider in-situ biomethanation of carbonaceous materials in blocks where there is no trace of natural in-situ

biomethanation (blocks that lack natural favourable environment for in-situ biomethanation). Citation (2) and

(8) suggests injections of microbial consortia from surface, but only in targeted carbonaceous materials

subsurface a formation that is open fairly permeable and likely to be fully or fairly open/expose to surrounding

formations, unless otherwise surrounded from all the six sides by fully impermeable cap rocks existing naturally.

Moreover, except for citation (8), none of the aforementioned citations disclose their deployment pathways i.e.

schemes of injection of microbes, growth medium, nutrients and other chemicals, recovery of gas generated, in-

situ bioconversion process, monitor, control and maintenance of the accelerated in-situ biomethanation process.

None of them discloses their operational plan including how they would accelerate ongoing biomethanation

process at a commercial rate safely in a controlled, regulated and cost-effective manner, that too following a

preferred bioconversion pathway, in a target subsurface formation having fully or fairly open/exposed

subsurface surroundings.

A bioconversion process taking place in a target formation having even a bit of open permeable surroundings

cannot be monitored, controlled and regulated properly. Any and all efforts put to tame the microbial consortia

and control the in-situ biomethanation process critical parameters would be inadequate. Further, unrestricted

movements of injected ingredients (nutrients, chemical amendments and microbial consortia) beyond the target

formation through the permeable surroundings would drain and waste the ingredients and the process would not

be cost-effective. Besides, chances of competitive microbial consortia entering in target formation can’t be ruled

out that would further drain the scares resources and would add in making the in-situ biomethanation process

less cost-effective. Chances of entry of toxic materials and pathogens from the surrounding formations may even

completely ruin the ongoing in-situ biomethanation process. Apart, unrestricted movements of associated

metabolic wastes and other toxic materials would likely contaminate the subsurface surroundings, therefore,

none of the citations (2), (4), (5), (6), (7) and (8), due to carrying out their in-situ biomethanation process in a

formation that has unregulated openness, would be able to obtain the mandatory environment permit needed, to

carry out the in-situ biomethanation of carbonaceous materials operations, from their respective Governments.

Moreover, none of these citations except citation (8) support additional benefit of CO2 sequestration. Though

citation (8) suggests use of CO2 as a nutrient to be injected in the coalbed prior to injection of microbial

consortia and other nutrients, however, it is well established that about 98% of CO2 sequestered in coal

formations is stored in adsorbed state on surfaces of coal matrix and hardly 2% in Free State in naturally

fractured cleat system. Adsorption of CO2 in a coal matrix causes strain to be induced between the adsorbing

CO2 molecules and the coal matrix surface, known as coal matrix swelling, that starts usually within an hour of

CO2 sequestration and reduces the natural permeability (pore space available through cleat system for gas

movement in coal mass, usually not adequate) further. CO2 sequestered, depending on depth of target coal

formation, either would be in sub-critical conditions for depth less than 1000 meter or super-critical conditions

for dept more than 1000 meter. Due to higher viscosity and swelling associated with super-critical CO2; super-

critical CO2 exhibits significantly lower permeability value than the sub-critical CO2. Therefore, high coal

matrix swelling is expected in non-extractable coal (mostly at a very high depth with poor natural permeability)

that would lower the permeability further. Apart, matrix swelling also causes loss of injectivity due to cap rock

deformation; of course depending on pressure and duration of CO2 injection. It has been observed that CO2

migrates into the overlying units even when a cap rock is directly overlying the coal. Therefore, CO2

sequestration in natural coal formations not only suffers a serious setback in terms of injectivity loss, cap rock

deformation, lowering of the permeability and opening path through cap rock for migration of CO2 sequestered

but would also open path even for generated biomethane, which is lighter than CO2. Besides, it is understood

that CO2 sequestration process in coal releases some toxic metals originally tapped in the coal (beryllium,

cadmium, mercury and zinc) that would likely contaminate the formation water and other liquids used in in-situ

biomethanation operation; even it may contaminate the surrounding water. Therefore, the suggested repeated

CO2 sequestration as nutrient in the beginning, before actual in-situ biomethanation process takes place in coal

target formation, may cease the generation and recovery of gas operation completely.

Besides, none of the citations (2), (4), (5), (6), (7) and (8) support the further benefit of CO2 geothermics for

extraction of geothermal energy from the target formation.

Hence, the present invention has been proposed.

OBJECTIVE OF INVENTION

The primary objective of the present invention is to overcome disadvantages associated with prior art of in-situ

biomethanation of subsurface carbonaceous formations including coal, by creating a bioreactor for carrying out

in-situ biomethanation process within a subsurface impermeable enclosure, which is constructed subsurface,

either on a piece of the target coal formation (one after the other or in multiple numbers simultaneously,

ultimately covering whole of the target coal formation) or a single one covering whole of the target formation

and enclosing all of its coal seams, and meticulously engineered for incorporating very specific features suitable

to microbial geological biomethanation conditions (MGBC) character of the target coal formation.

Another objective of the present invention is to make the bioreactor suitable for in-situ biomethanation of any

and all types of coal to biogenic methane (biomethane) without contaminating the subsurface surroundings.

Another objective of present invention is to make the bioreactor suitable for acceleration of process of

biomethanation, existing naturally in a target coal formation or imitated in a target coal formation that lacks

natural process of biomethanation, to a commercial rate and industrial scale.

Another objective of present invention is to make the bioreactor suitable for utilization of a substantially very

high percentage (up to a maximum extent possible) of coal carbon polymer (substrate) present within the

bioreactor for its biomethanation to biogenic methane (biomethane).

Further objective of present invention is to make the bioreactor suitable for utilization of a substantially very

high percentage (up to a maximum extent possible) of coal carbon polymer (substrate) present within the

bioreactor for its biomethanation to biogenic methane (biomethane) cost-effectively.

Another objective of the present invention is to make the bioreactor suitable for recovery, at surface, using

primary conventional recovery methods of a substantially very high percentage of subsurface biomethane

generated in the subsurface impermeable enclosure.

Further objective of the present invention is to make the bioreactor suitable for recovery, at surface, using

primary conventional recovery methods, of a substantially very high percentage of subsurface biomethane

generated in the subsurface impermeable enclosure cost-effectively.

Further objective of the present invention is to make the bioreactor suitable for enhancing the recovery

percentage further, by injecting CO2 (generated subsurface during in-situ biomethanation process and recovered

along with generated subsurface biomethane as a byproduct at surface and also emitted due to combustion of

recovered biomethane at surface) in the residual coal, leftover in the subsurface impermeable enclosure after full

(up to a maximum extent possible) utilization of substrate for biomethanation, to push out a substantially very

high percentage of those subsurface biomethane that were generated earlier but remained trapped in the coal

formation, for its collection at surface.

Another objective of the present invention is to make the bioreactor suitable for enhancing the substrate

utilization percentage further, by injecting CO2 (generated subsurface during in-situ biomethanation process and

recovered along with generated subsurface biomethane as a byproduct at surface and also emitted due to

combustion of recovered biomethane at surface) in the residual coal, leftover in the subsurface impermeable

enclosure after full (up to a maximum extent possible) utilization of substrate for biomethanation. The

sequestered CO2 acts as a green solvent usually in those target formations that are more than about a km deep,

and dissolves some more substrate (a fraction of leftover substrate in the residual coal formation that could not

be hydrolyzed initially by injecting bio-stimulants and microbial consortia, in addition to a substantially very

high percentage of substrate hydrolyzed earlier before CO2 sequestration) to make it bioavailable for further

biomethanation.

Another objective of the present invention is to make the bioreactor suitable for utilizing the sequestered CO2 as

a substrate in the subsurface impermeable enclosure by bioaugmentation of another set of designer anaerobic

microbial consortia in the subsurface impermeable enclosure.

Further objective of the present invention is to make the bioreactor suitable for extraction of energy (in form of

biomethane) for a very prolonged period, by injecting CO2 repeatedly in the subsurface impermeable enclosure

for its continued utilization as a substrate for biomethanation by set of designer microbial consortia already

injected in the subsurface impermeable enclosure, till biomethanation process is techno-economically feasible.

Further objective of the present invention is to make the bioreactor suitable for extraction of almost carbon-

neutral energy, by injecting CO2 generated subsurface during in-situ biomethanation process and recovered

along with generated subsurface biomethane as a byproduct at surface and also emitted due to combustion of

recovered biomethane at surface.

Further objective of the present invention is to make the bioreactor suitable for extraction of fully carbon-neutral

energy provided earlier biomethanation of coal carbon polymer has created/resulted in enough voids in the coal

formation to accommodate all CO2 generated subsurface during in-situ biomethanation process and recovered

along with generated subsurface biomethane as a byproduct at surface and also emitted due to combustion of

recovered biomethane at surface.

Another objective of the present invention is to make the bioreactor suitable for extraction of carbon-negative

energy, and in-situ biomethanation of coal in the CoalBioreactor may qualify as a clean development

mechanism (CDM) project. When CO2 is being utilized as a substrate then there is a scope of repeated CO2

injection at rate more than CO2 generated subsurface during in-situ biomethanation process and recovered along

with generated subsurface biomethane as a byproduct at surface and also emitted due to combustion of

recovered biomethane at surface, CO2 even from outside sources may also get accommodated in the voids in the

residual coal.

Another objective of the present invention is to make the bioreactor suitable for extraction of geothermal energy

on sustainable basis using CO2 geothermics.

Thus the main objective of the present invention is to utilize any and all types of coal formation, especially those

that are otherwise non-extractable/un-mineable, as a sustainable sink for CO2 sequestration and sustainable

source of carbon-neutral energy extraction to provide energy and environment security to economies, and extend

application of this invention to utilize any and all types of carbonaceous materials, having energy stored in solid

carbon form, as a sustainable sink for CO2 sequestration and sustainable source of carbon-neutral energy

extraction.

STATEMENT/ SUMMARY OF INVENTION

CoalBioreactor is a simple and easy to construct in-situ, low operational cost, single stage, mesophilic, slow rate,

heterogeneous, and over pressured batch bioreactor, having commercial life of about 50 years, operation in

which is carried out in one or two stages of 25 years each. In-situ coal biomethanation operation starts usually in

2 weeks to 6 months time and completes mostly within 25 years time. It considers hydrolysis as the rate limiting

step in in-situ biomethanation of solid, dry, insoluble complex coal substrate. Hydrolysis gets accelerated

through maximization of coal surfaces exposed to Acidogens (one of the species of coal biomethanation

microbial consortia) that is responsible for hydrolysis of substrate (coal carbon polymer) by secreting hydrolytic

enzymes on exposed coal surfaces. Biostimulation or/and bioaugmentation of other Acetogenic and

Methanogenic species of the anaerobic microbial consortia, as and when required accelerates the in-situ

biomethanation process. It has arrangements for injection of CO2, at the end of the coal biomethanation period.

CoalBioreactor can be constructed either on a piece or covering the entire target coal formation, enclosing a

single, multiple or all coal seams of the target coal formation using multiple seam completion (MSC)/ horizontal

multi-lateral multi-seam well (HMMW) technology. If the CoalBioreactor initially being constructed only on a

piece of the target formation block, in that case, once the commercial life of the CoalBioreactor is over, the new

CoalBioreactor would be constructed just adjacent to the old one or/and above the previous seam. In this way

construction sites for the CoalBioreactor would advance till biomethanation of entire target coal formation is

over.

The in-situ biomethanation and its rate depend on chemical and physical composition of the target coal

formations, presence of biomethanation microbial consortia, and environment for its growth i.e. on microbial

geological biomethanation condition (MGBC) of the target coal formations. The natural, slow, anaerobic, and

complex process of biomethanation by native (indigenous) anaerobic microbial biomethanation consortia are

evident in some of the target coal formations. These formations are supposed to have favourable natural MGBC

(FNMGBC). For industrial exploitation, this process needs to be accelerated at industrial scale and commercial

rate in coal formations having FNMGBC, and imitated and accelerated in those that lack FNMGBC.

Manipulation of MGBC, especially taming the microbial consortia and creating desired environment favourable

for their growth, in a coal formation that has open/exposed surroundings (at the most surrounded by parting

rocks that may not be fully impermeable and at the same time may not surround the targeted formation

completely) is not be feasible. Chances of anaerobic microbial biomethanation consortia useful and responsible

for in-situ biomethanation of coal carbon polymer (substrate) migrating outside the targeted formation, resulting

in presence of a very thin population of biomethane producing microbes in the target coal formation, nutrients

and other chemical amendments injected for use of these microbes for their accelerated growth are spreading

and leaking outside the targeted formation, infiltration of other unwanted competing microbes and pathogens

from outside (surrounding environments/formations), and biomethane generated migrating and accumulating

outside the targeted coal formation are very high. Apart from affecting the in-situ biomethanation process,

biomethanation rate and the cost-effectiveness of the in-situ biomethanation process adversely; the

measurement of pH, temperature, pressure, redox potential and other parameters critical for acceleration and

imitation of biomethanation process in the target coal formation using biostimulation or/and bioaugmentation

would be difficult, and their control and regulation impossible. Obviously, optimization of biomethanation rate,

and effective recovery or harvesting of maximum biomethane generated at surface would not be possible in the

target coal formation that has unregulated openness. Apart, unrestricted movements of associated metabolic

wastes and other toxic materials would likely contaminate the subsurface surroundings, which is undesirable

and moreover would not be acceptable to Government Environment Authorities during grant of the mandatory

environment permit needed to carry out subsurface in-situ biomethanation of carbonaceous materials operations.

Efficient, cost-effective in-situ biomethanation process without contaminating the subsurface surroundings is

only possible in a regulated close environment. Apart, prolonged biomethanation for biomethanation of a

substantially very high percentage of substrate into biomethane is only feasible within a regulated impermeable

enclosure.

Parting rocks surrounding the targeted coal sedimentary formation may be highly porous (sandstone and

limestone beds) or highly impermeable (clay bands) or may have varying degree of porosity (shale). Therefore,

chances of having a natural impermeable enclosure surrounding the target coal formation fully from all the six

sides are very remote; and in absence of natural impermeable boundaries fully or partly across all the six sides

of the targeted coal formation, a regulated impermeable enclosure surrounding the six sides of the targeted coal

formation needs to be constructed. The initial size of the regulated impermeable enclosure would mainly depend

on presence and location of natural impermeable rocks within and adjacent to the targeted formation, size of the

target coal formation block, its MGBC characterization, techno-economics of construction of impermeable

enclosure and impact of enclosure size on in-situ biomethanation project, available infrastructure, biomethane

market and initial budget available for this endeavor. Depending on these there may be either only one enclosure

for the entire target formation exploiting only a single or multiple or all seams of the target formation in one go

or through a number of enclosures of varying sizes constructed on pieces of suitable sizes and operating in a

series one after the other or simultaneously in parallel.

Coal within regulated impermeable enclosure would be fully fractured by injecting site specific correctly

formulated and tested hydraulic fluids compatible with the target formation. The hydraulic fracturing fluids

would be a well designed synthetic growth medium in fresh water and nutrients including selected species of

Acidogens or/and designer microbes in case bioaugmentation is imperative ( a study conducted indicates that

microbes sustain very high pressure even up to 1000 atmospheres i.e. 14696 psi, therefore, it is expected that

Acidogens or designer microbial consortia to be injected with fracturing fluid would sustain the injection

pressure that is usually up to 9000 psi, especially for a very short duration without getting affected adversely),

prepared in a biotech laboratory using reasonably well defined ingredients including traditional but microbes

friendly fracturing substances, wetting and dispersing agents, solvents and surfactants, and alkaline agents and

chealators. The injected fluids would be non-toxic, containing coal and microbes friendly liquids passing

through toxicity testing for both target coal formation and microbes. It would likely penetrate very deep in the

coal with likely induced multiple horizontal and vertical fractures. Acidogens (the hydrolyzing microbes) would

attach to all exposed surfaces on coal matrix blocks and even in some of the larger macropores that are available

through natural and induced fractures and nutrients would support accelerated growth of Acidogens patches on

the coal surfaces and growth of patches of other microbial species of anaerobic consortia, namely Acetogens

patch over Acidogens patch and Methanogens patch over Acetogens patch. Microbes, coal particles and growth

medium themselves would act as proppants. However, in compelling situations and circumstances, even

commercially available fracturing techniques like wave or hydraulic fluids, air, air mist, foam, air foam, etc.

along with microbe’s friendly wetting and dispersing agents would be used as fracturing fluids first; and growth

medium, microbes, nutrients and other chemical amendments would be pushed in the fractures (natural and

induced) thereafter subsequently.

All the fractures, natural and induced (using wave or hydraulic fluids) fractures, would remain within the

impermeable enclosure of the CoalBioreactor itself that would facilitate free flow and spread of injected

microbes, growth medium, nutrients and other chemical amendments inside the subsurface impermeable

enclosure; so that microbial population gets attached to farthest coal matrix blocks surfaces (may even in some

larger macropores of matrix blocks), grow and cover maximum coal surfaces exposed to them resulting in

accelerated in-situ biomethanation of natural substrate (coal carbon polymer); and biomethane generated flow

freely and accumulates in the production well for its maximum primary recovery and once biomethanation of all

(up to a maximum extent possible) the substrate present within the CoalBioreactor is over (using all the

permutations and combinations of injection of designer bio-stimulants or/and bioaugmentation of a set of

designer anaerobic microbial consortia and control and regulation of subsurface in-situ biomethanation process

and the biomethane generated therein recovered at the surface using primary conventional extraction methods)

then sequestration of CO2 (generated subsurface during in-situ biomethanation process and recovered along with

generated biomethane as a byproduct at surface and also emitted due to combustion of recovered biomethane at

surface) back in the highly porous residual coal itself for enhanced recovery; but at the same time, not to allow

flow and spread of growth medium, microbes, and biomethane outside the impermeable enclosure and flow of

other materials including pathogens, competing microbial consortia and other contaminants inside the

impermeable enclosure from the surroundings. Apart from sequestration of CO2 generated subsurface during in-

situ biomethanation process and recovered along with generated biomethane as a byproduct at surface and also

emitted due to combustion of recovered biomethane at surface, if biomethanation of substrate has

created/resulted in enough voids in the coal then it may accommodate CO2 even from outside sources also. As

large volume of void created due to biomethanation of coal, the resulting coal matrix swelling caused by

sequestered CO2 would get adjusted and nullified in the created void itself, and therefore there would be no

effective reduction in the natural permeability of coal formation, deformation in the surrounding cap rocks, and

the toxic metals released due to CO2 sequestration would accumulate in the sump due to gravity and would be

pumped out to surface with the spent growth medium.

Thus, this invention relates to construction of a custom designed and subsurface constructed bioreactor, based on

MGBC characterization of the target coal formation, in-situ in the target coal formation situated subsurface at

any depth, whether on a piece or the entire target coal formation, having an impermeable enclosure covered

from all the six sides by impermeable walls enclosing fully fractured coal formation within it, and an

impermeable sump constructed in the parting rock just below the bottom of the constructed impermeable

enclosure, and connected with fractured coal formation within the impermeable enclosure internally having full

permeable connectivity; connected to surface through a single vertical hole running from surface to down below

in the sump, passing through which would be the three injection pipes (one of them work as injection pipe for

hydraulic fracturing of targeted coal formation initially and as a production pipe for recovery of biomethane

generated at surface later on, second of them supply the requisite ingredients including growth medium,

nutrients, microbial consortia and other chemical amendments and third of them for injection of CO2 from

surface after full utilization of substrate for in-situ biomethanation within the impermeable enclosure) and a

collection pipe (running from sump to surface) to remove the metabolic wastes and toxic materials and spent

growth medium accumulated in the sump to surface to analyze it for understanding operational and

environmental health of the in-situ biomethanation process within the subsurface enclosure, and treatment

or/and replenishment of the growth medium for reinjection along with nutrients, other chemical amendments

and microbes in right quantity, quality and sequence for its spray on the fractured coal within the subsurface

impermeable enclosure as and when required, individually or in any combinations, in controlled and regulated

manner for continued maintenance of unhindered in-situ biomethanation operations in the subsurface

impermeable enclosure for a prolonged in-situ biomethanation process till (usually well below 25 years)

biomethanation of almost all the coal carbon polymer (substrate) present therein the subsurface impermeable

enclosure is over, and subsequently after that using sequestered CO2 as a substrate till repeated CO2

sequestration and its in-situ biomethanation operation can be supported commercially; and thereafter, use of CO2

geothermics for extraction of geothermal energy on sustainable basis.

This custom designed and in-situ constructed (based on MGBC characterization of the target coal formation),

properly engineered cost-effective construction with accelerated in-situ biomethanation rate for a very prolonged

period and use of CO2 geothermics for extraction of geothermal energy on sustainable basis, has been termed as

a CoalBioreactor (unregistered commercial trade name).

BRIEF DESCRIPTION OF THE ACCOMPNAYING DRAWINGS

Further objects and advantages of this invention will be more apparent from the ensuring description when read

in conjunction with the accompanying drawings and wherein:

Fig.1 is a: Schematic and Pictorial Diagram of a CoalBioreactor indicating a Subsurface Impermeable

Enclosure construced subsurface on a piece of the target coal formation, a few hundred meters to a

few kilometers deep, with completely fractured (natural and induced) coal within the Subsurface

Impermeable Enclosure, a Central Vertical Hole (Central Vertical Well) encompassing an injection

pipe (Hydraulic Fracturing cum Production pipe) passing through that is a Spent Growth Medium

Collection pipe, and an impermeable Sump, constructed in the parting rock just below the target coal

formation.

Fig. 2 is a: Schematic and Pictorial Diagram of a CoalBioreactor indicating a Central Vertical Well and three

Injection pipes (first, a Hydraulic Fracturing cum Production pipe used for hydraulic fracturing of

coal within subsurface impermeable enclosure initially and recovery of subsrface biomethane

generated at surface later on; second, a Spray Injection pipe used for spray of growth medium,

micobes, nutrients and other chemical amendments in the subsurface impermeable enclosure, and

third, CO2 Injection pipe for injection of CO2 for sequestrationin the subsurface impermeable

enclosure) and one Spent Growth Medium Collection pipe (passing through the 1st injection pipe and

used for collection of spent growth medium, metabolic wastes and othe toxic materials accumulated

in the sump at surface), and all the four passing though the central vertical well.

Fig. 3 is a: Pictorial Diagram of the target coal formation after different stages of fracturing within a Subsurface

Impermeable Enclosure.

Fig. 4 is a: Pictorial Diagram of the target coal formation after different stages of fracturing and microbial

growth (forming biofilm) on the Coal Matrix Block Surfaces in a Subsurface Impermeable

Enclosure.

Fig. 5 is a: Schematic and Pictorial Diagram of Pushing of Growth Medium, Microbes, & Nutrients to the

Farthest Fractured Point in a Subsurface Impermeable Enclosure when Growth Medium, Microbes,

& Nutrients that themselves are acting as a Fracturing Fluid to fracture target coal formation.

Fig. 6 is a: Schematic and Pictorial Diagram of Pushing of Growth Medium, Microbes, & Nutrients to the

Farthest Fracture Point in a Subsurface Impermeable Enclosure when Traditional Hydraulic

Fracturing Fluids first are used for Fracturing of the target coal formation and the Growth Medium,

Microbes & Nutrients are pushed at later on.

Fig. 7 is a: Pictorial Diagram of the target Coal formation after Different Stages of Fracturing and Different

Stages of Microbial Growth (forming biofilm) on the Coal Matrix Block Surfaces within a

Subsurface Impermeable Enclosure.

Fig. 8is a: Schematic and Pictorial Diagram of a Subsurface Impermeable Enclosure indicating Flow of Growth

Media and Gases Generated within the Subsurface Impermeable Enclosure.

Fig. 9 is a: Schematic and Full Pictorial view of the CoalBioreactor indicating Surface and Subsurface facilities

including Line Diagram of Measurement and Regulation of ingredients for Control of Parameters

Critical to in-situ biomethanation of coal.

DETAIL DESCRIPTION OF THE INVENTION

Collating published information (geological maps, topographic and cadastral maps, scientific papers and reports,

land records, air photographs, satellite imagery, etc.), constructing photogrammetric maps and using modern

techniques like remote sensing and global positioning system (GPS); detailed information about the target coal

formation and surrounding parting/cap rocks are gathered, analyzed and worked out; coal characteristics mainly

rank or maturity, type and grade, and potential reservoir properties mainly reservoir geometry (a conceptual

model of reservoir visualized in 3D space and conforming to natural boundaries of reservoir), coal seam

thickness, natural gas content, gas pressure (saturated or under saturated), natural fractures or permeability (cleat

network whether mineralized or potentially open), geological barriers (depositional or structural), compressive

stress regimes (impacting permeability), coal fabric preserved or destroyed (to ascertain risk of fine production)

and basin hydrology influence on gas storage, etc. are determined. Collecting fresh coal sample, preferably

pressurized core sample, microbial geological biomethanation conditions (MGBC) characterization of the target

coal formation gets carried out in a fully equipped laboratory and based on that a bioreactor for the target coal

formation gets custom designed i.e. main constructional features like size, site, depth and construction

technologies to be applied and main operational features like ingredients to be injected and its type, quantity,

sequence, etc. are ascertained. Based on size of the target coal formation, number of coal seams and their depth,

geology of target formation, available infrastructure at target site, construction cost, biomethane market,

economics of the biomethanation project, and initial budget available for development of the in-situ

biomethanation project; size (either a piece of the target block or the entire target block, exploiting only a single

or multiple or all seams in one go) and initial site (with an intention to utilize maximum of the surrounding

natural impermeable parting rocks to construct a subsurface impermeable enclosure) of the bioreactor gets

decided. If situation permits, a single bioreactor using horizontal multi-lateral multi-seam well (HMMW)

technology or a number of bioreactor simultaneously, may be of different sizes, needs to be constructed for

taking up in-situ biomethanation of the entire target coal formation in one go. However, if the bioreactor is

initially being constructed only on a piece of specific size and site of the target formation at a specific depth, not

exploiting the entire target formation (entire area of the target formation with all the seams) in one go, in that

case, once the commercial life of the first bioreactor is over, the new bioreactor of next appropriate specific size

gets constructed just adjacent to the old one or/and above the previous site, and in this way construction sites for

a number of bioreactor to be constructed

would advance to cover the entire target coal formation.

Parting rocks surrounding the size, site and depth of the subsurface impermeable enclosure to be constructed,

may be highly porous (sandstone and limestone beds) or highly impermeable (clay bands) or may have varying

degree of porosity (shale). All efforts are made to identify and utilize, as far as possible, the natural impermeable

parting rocks, whether fully or partly impermeable for creating a fully subsurface impermeable enclosure around

the proposed size and site of construction. However, in absence of existence of natural impermeable barriers

fully surrounding all the six sides of the proposed subsurface impermeable enclosure to be constructed; an

impermeable wall, utilizing surrounding rocks and/or peripheral target coal formation of varying

impermeabilities, of appropriate thickness and strength (worked out considering size of the proposed subsurface

impermeable enclosure, MGBC characterization of the target coal formation and geology of the adjacent

parting rocks) gets constructed using all available technologies including cementing, plug in technology,

grouting conventional placement design or remote placement design, and grouting technology, individually or in

any combinations, as and where required, by filling completely or partly fissures, fractures or joints in

surrounding parting rocks mass and peripheral coal, without creating new or opening existing fractures. The

impermeable enclosure would be properly engineered by applying individually or any combinations of well

technologies like vertical or/and horizontal, horizontal multi-lateral multi-seam well (HMMW); drilling

technologies like conventional, unconventional, horizontal, directional, air coiled tubing, and others; fracturing

technologies like horizontal, vertical, directional, hydraulic or wave or gas fracturing; well completion

technologies like open hole cavity or/and cased, cemented, perforated, fracture stimulated completion using

most appropriate drilling, jetting, fracturing, and cementing technologies.

Physical construction of a bioreactor (See Fig.1) of specific size and at a specific site in a subsurface at any

depth 1(usually ranging from a few hundred meters to a few kilometers deep) in a target coal formation 2 starts

start with construction of a subsurface impermeable enclosure 3 (demarked by red lines), the sole operational

area. Coal within impermeable enclosure is fractured in-situ in such a way that all the induced and natural

fractures remain within the subsurface impermeable enclosure with highly porous and permeable central or

operational region 4. All the six impermeable sides 5,6,7,8, 9 and 10 (between red and ash colour outlines) of

the impermeable enclosure, whether available naturally or created, completely isolate the highly porous and

permeable operational region 4 of the subsurface impermeable enclosure from the rest of the subsurface

surroundings. A central vertical well 11, from surface to subsurface target coal formation, developed several

month in advance (in due consultation with drilling contractors, service company representatives, and well

operators who are experienced in drilling, stimulation and completion) of appropriate diameter (depending

mainly on volume of the coal formation within the impermeable enclosure, casing program, depth, geology of

strata overlying the target coal formation, MGBC characterization of target coal formation, drilling rig, fracture

design, fracturing equipment; typically of 121

4 inch hole size), internally connected (through perforations) to

the impermeable enclosure, and passes through its centre. The well passing through a number of parting

formations connects to a single, multiple or all coal seams of target block using multiple seam completion

(MSC) technology that facilitates optimum utilization of the target coal formation in one go thus having a higher

industrial scale operation commercially. A rat hole of few inches diameter in the bottom parting rock 12 (the

exact size and design of which mainly depends on size of the bioreactor, MGBC characterization of the coal

formation and geology of the parting rock), down just below the centre of the impermeable enclosure and in full

alignment with the well, of about a few hundred feet depth having an impermeable membrane is created as a

sump. This sump 13 provides adequate sump/space for logging, and accumulation of spent growth medium,

wastes and toxic materials. An electric submersible pumping system 14 consisting of a down hole electric

powered motor and centrifugal pump assembly is fitted in the sump to lift the materials accumulated therein to

surface through spent growth medium collection pipe 15 passing through the well. Electricity is supplied to the

motor through a cable 16 clamped to the spent growth medium collection pipe. Operational region within the

subsurface impermeable enclosure and sump are connected internally and are fully permeable to allow

accumulation of wastes and toxic materials and spent growth medium from the operational area to sump (usually

due to gravity but some time also may due to sucking) to be pumped to surface, as and when necessitated, for

analysis to monitor the operational and environmental health of the operational area and control the operational

and environmental critical parameters for regulation of unhindered cost-effective operation of the bioreactor.

Three injection pipes (See Fig. 2), passing through the central vertical well, would run from surface to down

below subsurface constructions. The first injection pipe (hydraulic fracturing cum production pipe) 17, in

housing spent growth medium collection pipe, runs from surface to subsurface sump (indicated with larger

diameter) being used initially for hydraulic fracturing of coal within the subsurface impermeable enclosure by

injecting, through all its perforations 18 (initially throughout the length within subsurface impermeable

enclosure and later on most of the perforations gets plugged in properly after the fracturing and well cleaning

operations except for upper 19 and lower perforations 20), high pressure (usually up to 9000 psi depending on

depth and MGBC character of the target coal formation) hydraulic fracturing fluids. Coal within subsurface

impermeable enclosure is fractured fully by the site specific correctly formulated and tested hydraulic fluids

compatible with the target formation injected. The hydraulic fracturing fluids are a well designed synthetic

growth medium in fresh water and nutrients (including selected species of Acidogens or/and designer microbes

in case bioaugmentation is imperative - a study conducted indicates that microbes sustain very high pressure

even up to 1000 atmospheres i.e. 14696 psi, therefore, it is expected that Acidogens or designer microbial

consortia getting injected with fracturing fluid will sustain the injection pressure that is usually up to 9000 psi,

especially for a very short duration without getting affected adversely), prepared in a biotech laboratory using

reasonably well defined ingredients including traditional but microbes friendly fracturing substances, wetting

and dispersing agents, solvents and surfactants, and alkaline agents and chealators. The injected fluids are non-

toxic, containing coal and microbes friendly liquids passing through toxicity testing for both target coal

formation and microbes. Fluids penetrate very deep in the coal with multiple horizontal and vertical fractures.

Acidogens (the hydrolyzing microbes) attach to all six surfaces of coal matrix block available through natural

and induced fractures and may even enter into some of the larger macropores of the block. Nutrients support

accelerated growth of Acidogens in patches on the surfaces of coal matrix block and growth of other microbial

species of consortia (namely Acetogens over patch of Acidogens and Methanogens over patch of Acetogens).

Microbes, coal particles and growth medium themselves act as proppants. However, in compelling situations

and circumstances, even commercially available fracturing techniques of wave or hydraulic fluids, air, air mist,

foam, air foam, etc. along with microbe’s friendly wetting and dispersing agents are used as fracturing fluids

first; and growth medium, microbes, nutrients and other chemical amendments are pushed in the fractures

(natural and induced) subsequently later on. The same pipe later on is used for recovery of biomethane

generated in the subsurface impermeable enclosure, and hence is termed as a production pipe.

Biomethane generated accumulates in upper part of the subsurface impermeable enclosure and enters, due to

pressure difference (gradient), in the production pipe through upper perforations 19. The lower perforations 20

allow, due to gravity, accumulation of spent growth medium, washed out microbes, metabolic wastes, and other

toxic materials including toxic metals originally tapped in the coal (beryllium, cadmium, mercury and zinc) in

the sump for transfer of this accumulation to surface by spent growth medium collection pipe.

The second injection pipe 21 (spray pipe indicated yellow in the Fig.2) runs from surface to just below the top

impermeable wall of subsurface impermeable enclosure and is being used for spraying/injecting 22 requisite

ingredients (growth medium, microbes, nutrients, and other amendments) in upper part of the subsurface

impermeable enclosure, as and when require, to support prolonged in-situ biomethanation.

Once biomethanation of all the substrate (up to a maximum extent possible) present therein the subsurface

impermeable enclosure is over and the biomethane generated therein recovered at the surface using the primary

conventional extraction methods; CO2 (generated subsurface during in-situ biomethanation process and

recovered along with generated biomethane as a byproduct at surface and also emitted due to combustion of

recovered biomethane at surface) is injected in the residual coal in the subsurface impermeable enclosure

through the third injection pipe, the CO2 injection pipe 23 (indicated green in the Fig. 2), runs from surface to

lower part of the subsurface impermeable enclosure, and releases CO2 at bottom 24, just above the bottom

impermeable wall of the subsurface impermeable enclosure.

Facilities for monitoring, control and regulation of biomethane generation rate and other parameters critical to

subsurface in-situ biomethanation operation are at surface and are conducted by analyzing the spent growth

medium in fully equipped laboratories at surface. However, if absolutely necessary, probes are placed suitably

in the well, impermeable enclosure and sump through these injection pipes.

Microbial accessibility to substrate (See Fig. 3) is through fractures. Natural porosity 25 of coal (usually due to

cleats of sizes 7 to 30 µm in which microbes of usually 2 to 6 µm size could enter easily) is very small ranging

from 0.1 to 0.59% only. Though the effective surface area of coal, depending on its rank, ranges from 150 to

more than 500 square meters per gram, however, this surface area is located inside the coal matrix blocks in 3

size of pores, ranging from macropores (d > 30ƞm), mesopores (1.2 ƞm < d < 30 ƞm) to micropores (d < 1.2

ƞm). Obviously, most of the microbes, due to their size bigger than pores, are not able to enter into these pores,

however, occasionally some may enter into macropores that are larger than microbe’s size, and thus come in

contact with exposed coal surfaces within those pores. Thus microbial accessibility to coal surfaces and hence to

coal carbon polymer (substrate) usually is limited, only in natural fractures of coal formation. However,

microbial accessibility is improved by inducing new fractures in coal. This improvement is proposed through

fracturing the coal contained within the subsurface impermeable enclosure. Usually one stage fracture with a

reasonable fracturing pressure is sufficient to fracture the coal enough 26 to make it sufficiently porous to

initiate or/and accelerate biomethanation operation in the subsurface enclosure at commercial rate. However, if

impermeable enclosure has been constructed using week parting rocks available and coal inside the subsurface

impermeable enclosure is highly impermeable, recalcitrant and hard in that case, to achieve the same desired

porosity, the original coal within the subsurface impermeable enclosure may have to be fractured in a number of

attempts (maximum 5 stages as indicated in Fig. 3) applying mild fracturing pressure each time to fracture the

coal sufficiently to make the bioreactor operational but at the same time avoiding damage to the subsurface

impermeable enclosure. In this way, accelerated in-situ biomethanation of the target coal formation having even

the worst MGBC (WMGBC) is possible at commercial rate. Apart, fracturing target coal formation in series is

also helpful in using different alternatives, even after start/initiation of in-situ biomethanation, for avoiding

impacts of common apprehensions like reduced bioavailability of substrate in a highly crystalline coal and coal

macerals, inhibitions like de-acceleration or retardation of in-situ biomethanation process or complete seizure of

biomethanation process (though with a very-very remote chance in a highly engineered bioreactor that operates

in completely regulated, measured and controlled manner with proper arrangements for biostimulation and

bioaugmentation, as and when required) and implementation of hopes like having a preferred biomethanation

pathway in the bioreactor to make in-situ biomethanation of even WMGBC coal techno-economically feasible.

The basic purpose of fracturing is to enhance exposed surface area to microbes by enhancing the porosity by

inducing engineered fractures, and for that fracturing pressure would be so adjusted that each stage of fracturing

enhances the porosity of coal inside the subsurface impermeable enclosure. Microbial accessibility (See Fig. 4)

to exposed coal surface 27 thus increases through 28, 29, 30, and 31 to 32 with increase in induced fractures

just after each stage of fracturing and microbes and other ingredients (growth medium, nutrients and other

chemical amendments) get pushed to the farthest end 33 (See Fig. 5, if growth medium, microbes, & nutrients

themselves are acting as a fracturing fluid) and 34 (See Fig. 6, if initially traditional hydraulic fracturing fluids

are used for fracturing of target coal formation and growth medium, microbes, & nutrients are being pushed

later on) through natural and induced fractures in target coal formation within the subsurface impermeable

enclosure.

Contact inhibited growth of microbes take place on exposed coal surfaces. As coal surfaces gets exposed in an

aqueous medium (growth medium), it inevitably and almost immediately become conditioned or coated by

polymers from that medium, and the resulting chemical modification will affect the rate and extent of microbial

attachment to the coal surfaces. It is known that the extent of microbial colonization appears to increase as the

surface roughness increases. Moreover, microbes attach more rapidly to hydrophobic surfaces, and therefore

both these findings indicate favourable conditions for attachment of microbes to exposed coal surfaces. Most

normal anchorage-dependent cells are contact inhibited. Surface associated microbes (biofilms) exhibit a distinct

phenotype with respect to gene transcription and growth rate. As they approach confluence or cover the surface

on which they are growing completely, they stop growing. Individual cells seeded at low density grow at a

normal rate until they form a patch of cells. In that patch, the cells at the perimeter continue to grow at the

normal rate, but the cells in the centre completely be surrounded by other cells and consequently are to some

extent is contact inhibited. Moreover, the confluent patch of cells is not a static system. Therefore, it is expected

that Acidogens growing into patches initially have exponential growth. However, once the patches are large

enough to encircle or surround some Acidogens or get surrounded by Acetogens, they have contact inhibited

growth. In a patch, the Acidogens at the perimeter continue to grow at the normal rate, having sufficient

availability of substrate, growth medium, and nutrients, but the Acidogens in the centre that are completely

surrounded by other microbes (Acidogens and or Acetogens), do not have sufficient accessibility to growth

medium and nutrients, and consequently they are contact inhibited. Since these Acidogens do not grow as

rapidly or at all, the apparent growth rate for the Acidogens patch decreases. Acidogens, hydrolyzing species

present in anaerobic microbial biomethanation consortia, attach to the six surfaces of a coal matrix block and

larger macropores of coal matrix blocks and grow in a patch (micro colony). Other microbial species of

consortium like Acetogens and Methanogens also form their patches. Acidogens patch is over conditioning film

attached to the exposed coal surfaces whereas Acetogens patch is over Acidogens patch and Methanogens patch

is over Acetogens patch. After sufficient lateral growth, patches of individual species merge to cover the entire

exposed coal surfaces with cells of their respective species. Confluent patch forms monolayer of Acidogenic,

Acetogenic and Methanogenic biofilm. Biofilm formed, initially, is not a continuous monolayer surface

deposits, rather it is expected to be very heterogeneous (in space and time), containing patches of microbes

encased in an extracellular polymeric substance (EPS) matrix and separated from other patches by interstitial

voids (water channels), however there may be migration of microbes from one patch to other. At last each

monolayer biofilm gets fully packed with their respective microbial species, and all mono layers combined form

a multi-layers microbial biofilm, attached to exposed coal surfaces (See Fig. 7) in the subsurface impermeable

enclosure.

Hydrolases (hydrolytic enzymes) secreted by Acidogens accumulate in the hydrodynamic boundary layer

between biofilm and coal surfaces exposed to microbes. Though it appears that hydrolysis of substrate available

only on exposed surfaces of coal/lignite takes place, nevertheless, as coal in its pores (macro, meso, and micro)

has a very large effective water surface area, therefore, water molecules, invariably seep even in the narrowest

micropores and cover the entire effective water surface area available in pores, whereas hydrolases get able to

seep only into macro pores and some of the bigger mesopores. Hydrolases depolymerize substrate present

therein in all possible manners and solubilize the resulting monomers/ oligomers in water. The crystalline coal

macerals present in pores of coal matrix embed substrate so tightly that normally it do not allow penetration of

enzymes, and even relatively small molecules of water inside the macerals crystals; however, following C1-CX

model of amorphogenesis, it is considered that hydrolases penetrate crystalline macerals and hydrolyze

substrate embed therein.

Synergistic and syntrophic relations among Acidogens, Acetogens and Methanogens convert the hydrolyzed

substrate into biogenic methane (biomethane). Biomethane generated (See Fig. 8) in the subsurface impermeable

enclosure accumulates in upper part 35 (indicated through brown arrows) of the subsurface impermeable

enclosure. It enters in the production pipe through upper unplugged perforations and reaches to surface due to

pressure gradient. Biomethane generation rate is measured at surface. With envisaged frequent process

instabilities and just in time subsequent remedies for stabilizing the process, that biomethane generation rate

after bioreactor starting period (2 to 6 months) increase slowly and gradually throughout the buildup phase

(about 10 years) and reaches to a steady plateau state once exposed coal surfaces are fully covered with the

biofilms. Spent growth medium, traversing through fractures and larger pores, and taking metabolic byproducts

and toxic materials produced during biomethanation process along with it 36 (indicated through blue arrows),

passing through lower perforations in hydraulic fracturing or production pipe, accumulates in sump, and there is

complete wash out of these waste and toxic materials. This is because access of most of the microbes are

confined to induced and natural fractures only, therefore these waste and toxic materials are being produced

only in wider fracture openings, which becomes wider and wider with increase of biomethanation time, and

would be washed very effectively by regular flow of spent growth medium. It also takes care of one of the much

talked and apprehended problems of paraffin obstruction. Clearing of the paraffin obstruction, accumulated in

fractures and not in pores (except some bigger pores having microbial accessibility), accomplished with regular

spraying of growth medium washes the coal surfaces of fractures regularly. Paraffin accumulates in sump along

with spent growth medium that is taken to surface for its removal. All the accumulation in sump including spent

growth medium is pumped to surface (See Fig. 9) at regular interval, analysis of which helps in knowing the

growth medium parameters, and thus the operational and environmental parameters and conditions of the

bioreactor. As anaerobic digestion process is sensitive to environmental factors and growth medium parameters

and prone to instability, therefore continuous measurements 37 of environmental parameters like pressure, redox

potential, waste & toxic materials concentration; and growth medium parameters like pH, temperature, VFAs

concentration, etc. are imperative. Biomethane generated is measured 38 continuously either by using orifice

meter or turbine meter, however as turbine meter provides quick, easy, and highly accurate instantaneous

readings, this is preferred. Measurement of biomethane generation rate, analysis of spent growth medium to

know the concentration of supporting and inhibitory substances, and measurement of environmental parameters

determine the time, quantity and sequence 39, 40, 41 and 42 of spraying individual microbial species and or

consortium, nutrients, and other requisite chemical amendments in the bioreactor. This would likely keep the

environmental factors and growth medium parameters of bioreactor under control and anaerobic biomethanation

process stable.

Samples of spent growth medium are collected at surface. Initially the collection frequency is high, say every

few hours, and later on at a reduced frequency, say once in a week or month, as the biomethanation process

stabilizes. Apart, whenever there is an unexpected drop in biomethane generation rate, at that time also samples

are collected for analysis. Based on measured environmental and spent growth medium parameters, a routine

control actions, individually or in any combination and sequence are taken. As most of the microbes found in

nature are mesophilic, and at the same time the process stability of thermophilic reactor is poor, therefore,

temperature of the bioreactor is maintained in the range of 30 to 350C for growth of mesophilic microbes by

making proper arrangements for heating and or cooling of growth medium at surface. Operating pressure inside

the bioreactor likely remains constant; however, through addition or removal of growth medium fluids,

operating pressure in the CoalBioreactor is regulated. As anaerobic process is energetically favourable only at

stable redox potentials below -200 mv, it is maintained at that level. Though different microbial species of

consortium work well at different pH (for methanogens and acetogens, optimum pH is 7.0, methanogens at pH <

6.6 grow very slowly, whereas acidogens work even with pH 6.0), however, pH of media is maintained at

neutrality through pH buffer arrangements. An increased concentration of VFAs indicates a change in process

balance that could lead to failure of coal biomethanation process. Appropriate VFAs concentration is regulated

by adding methanogens or microbial consortium in the bioreactor. Apart, methanogens, microbial consortium,

nutrients, and other chemical compounds would be sprayed in the subsurface impermeable enclosure, as and

when required, to maintain proper microbial environment and appropriate growth medium parameters to

accomplish stable bioreactor operation for a prolonged period for optimum biomethane generation rate and

conversion of maximum substrate to biomethane. However, if application of the above steps, individually or in

all possible combinations and sequences, fails to improve biomethane harvesting rate or maintain commercial

biomethane recovery rate then this indicates inhibition of biomethane process by accumulation of higher

concentration of waste and toxic materials in the subsurface impermeable enclosure. At this point of time,

bioreactor’s entire growth medium along with metabolic waste products and other toxic materials get collected

in the sump by sucking or lowering the sump pressure. These are pumped to surface for removal of accumulated

waste and toxic materials as well as pathogens, if present any. Growth medium is treated properly. Even

selective removal of waste products is considered through integrated membrane separation or using advanced

toxic waste removal technology. Treated growth medium or fully replenished growth medium or treated growth

medium with some replenished medium is re-circulated for its spraying in the subsurface impermeable

enclosure. With application of above suggested steps, it is likely that biomethane generation becomes

sustainable with appropriate rate, and entire substrate available in CoalBioreactor gets utilized by microbes for

its bioconversion to biomethane. Failure in improvement of biomethane generation rate, even after repeated

application of above control measures, clearly indicates non availability of substrate to microbes for

biomethanation. At this point of time, economics of bioreactor decides the next course of action. Either it is re-

fracturing of coal inside the subsurface impermeable enclosure or injection of CO2 for sequestration. In case of

first option, the above steps are repeated, once again.

In case of going for second option, CO2 is injected from the bottom of the subsurface impermeable enclosure,

just after biomethanation of coal present therein is over. CO2 enters into voids in residual coal and displaces

generated biomethane remaining there. It also enters into micropores of coal matrix and displaces generated

biomethane as well as natural methane adsorbed on coal in these pores. Moreover, CO2 attains super critical

condition usually in those coal formations that are more than 1 km deep. As supercritical CO2 is a very effective

green solvent that is capable of metabolizing (extracting) hydrocarbons from coal matrixes; therefore CO2

injected not only flushes out the remaining biomethane (may be as high as 40% of biomethane generated) but it

acts as a green solvent for residual coal and a fraction of residual substrate gets bioavailable further. Thus,

biomethanation of a fraction of residual coal takes place further. Apart a fraction of injected CO2 acts as a

substrate for biomethanation, by another set of designer microbial consortia injected, especially under enhanced

CO2-H2 reduction methanogenesis pathways (ECHRMP). Repeated sequestration of CO2 in the CoalBioreactor

for its continued utilization as a substrate for biomethanation makes the biomethane energy extraction from the

bioreactor sustainable. This repeated sequestration activity is carried out till operation remains commercially

feasible. Thereafter, CO2 geothermics extracts geothermal energy on sustainable basis.

The operation of bioreactor gets abandoned permanently, once CO2 sequestration in the residual coal in the

bioreactor operation loses its commercial viability. The remaining, CO2 as per Intergovernmental Panel on

Climate Change (IPCC) special report on carbon dioxide capture and storage, would remain in the pores and

void created due to biomethanation of non-extractable coal for at least 1000 years. Moreover, as injection is in

fully porous residual coal, apprehensions regarding coal swelling or/ and reaction with coal are not of much

significance in this case. However, if the bioreactor was constructed only in a part of the targeted coal initially,

in that case, the new bioreactor gets constructed just adjacent to the old one or above the worked out seam, and

in this way the bioreactor’s construction sites advance till biomethanation of the entire targeted coal is over.

I claim,

1. A CoalBioreactor for in-situ coal biomethanation that is a bioreactor mainly comprising of:

a subsurface impermeable enclosure in the target coal formation of appropriate size (either on a piece of the

target coal formation, one after the other or in multiple numbers simultaneously covering whole of the target

formation and all coal seams, or a single one covering whole of the target formation and all coal seams,

using multiple seam completion/ horizontal multi-lateral multi-seam well technology) and at an appropriate

site (aiming to have a natural subsurface impermeable enclosure formed by utilizing maximum of the

surrounding natural impermeable parting rocks to surround all the six sides or otherwise engineered one by

applying technologies like grouting, plug in, cementing, etc. in existing permeable/semi permeable

surrounding parting rocks and/or peripheral target coal to create six sides of impermeable walls/ barriers)

allowing free flow and spread of injected microbes, growth medium, nutrients and other chemical

amendments inside the impermeable enclosure but at the same time, not to allow flow and spread of growth

medium, microbes, and biomethane outside the impermeable enclosure and flow of other materials including

pathogens, competing microbial consortia and other contaminants inside the impermeable enclosure from

the surroundings. The subsurface impermeable enclosure is the main operational area of the CoalBioreactor

that consists of:

fully fractured coal within impermeable enclosure by injecting site specific correctly formulated and

tested hydraulic fluids compatible with the target coal formation, a well designed synthetic growth medium

in fresh water and nutrients including selected species of Acidogens or/and designer microbes in case

bioaugmentation is imperative, prepared in a biotech laboratory using reasonably well defined ingredients

including traditional but microbes friendly fracturing substances, wetting and dispersing agents, solvents

and surfactants, and alkaline agents and chealators that are non-toxic, containing coal and microbes friendly

liquids passing through toxicity testing for both target coal formation and microbes; however in compelling

situations and circumstances, even commercially available fracturing techniques like wave or hydraulic

fluids, air, air mist, foam, air foam, etc. along with microbe’s friendly wetting and dispersing agents to be

used as fracturing fluids first, and growth medium, microbes, nutrients and other chemical amendments

would be pushed in the natural and induced fractures subsequently thereafter,

microbes, growth medium and nutrients penetrating very deep in the coal within subsurface microbial

enclosure through natural and likely induced multiple horizontal and vertical fractures,

Acidogens (the hydrolyzing microbes) attaching to all exposed surfaces on coal matrix blocks and

even in some of the larger macropores that are available through natural and induced fractures,

nutrients supporting accelerated growth of Acidogens patches on the coal surfaces and growth of

patches of other microbial species of anaerobic consortia, namely Acetogens patch over Acidogens patch

and Methanogens patch over Acetogens patch,

microbes, coal particles and growth medium themselves are acting as proppants,

facilitating prolonged stable in-situ biomethanation of a substantially very high percentage of substrate

(coal carbon polymer) present therein to biogenic methane (biomethane), and preventing contamination of

the subsurface surroundings;

a central well passing through all the subsurface parting rocks formations overlying the target coal

formation that connects subsurface impermeable enclosure to surface;

a sump in the bottom parting rock just below the subsurface impermeable enclosure, having adequate sump

and logging space, interconnected to subsurface impermeable enclosure internally to accumulate spent

growth medium and wastes and toxic materials generated due to in-situ coal biomethanation, for their

removal to surface using an electric submergible pumping system fitted in the sump;

a spent growth medium collection pipe for transfer of spent growth medium, wastes and toxic materials from

sump to surface;

facilities at surface for monitoring of biomethane generation rate and operational and environmental

parameters, critical to prolonged stable subsurface in-situ biomethanation operation, analysis of the spent

growth medium to get insight of operational and environmental health of the subsurface impermeable

enclosure for deciding prudent implementation steps of injecting through spray pipe requisite ingredients in

right quantity, of right quality, at right time and in right sequence in the subsurface impermeable enclosure

to control and regulate the stable and prolonged biomethanation operation in the subsurface enclosure;

three injection pipes running from surface to subsurface impermeable enclosure and passing through the

central well,

a hydraulic fracturing cum production pipe, running from surface to sump and in housing spent growth

medium collection pipe within it, used for hydraulic fracturing of target coal formation initially and later on

for recovery of subsurface biomethane generated at surface,

a spray injection pipe running from surface to just below the top impermeable wall of subsurface

impermeable enclosure for spray of requisite ingredients in the impermeable enclosure, as and when

required, and

a CO2 injection pipe running from surface to lower part of the subsurface impermeable enclosure to

inject CO2; once in-situ biomethanation of almost all the substrate (up to a maximum extent possible due to

prolonged stable biomethanation operation in the subsurface impermeable enclosure, and injection of

ingredients in any and all permutations and combinations unable to boost or even maintain the

biomethanation operation) present within the subsurface impermeable enclosure is over and the subsurface

gas generated has been recovered at the surface using primary and conventional gas recovery methods; to

enhance recovery of subsurface biomethane already generated, make additional percentage of substrate

bioavailable for in-situ biomethanation mainly in deep (about a km) target coal formation, and using

sequestered CO2 as a substrate for its biomethanation by injecting another set of requisite designer microbial

consortia in the subsurface impermeable enclosure; and

probes, if otherwise absolutely necessary, placed suitably in the well, subsurface impermeable enclosure

and sump through these injection pipes and collection pipe.

2. The CoalBioreactor, as set forth in claim 1, for in-situ biomethanation of any and all types of coal to

biomethane without contaminating the subsurface surroundings.

3. The CoalBioreactor, as set forth in claim 1, in which repeated injection of CO2 in subsurface impermeable

enclosure, for its use as a substrate for continued biomethanation for generation of biomethane on

sustainable basis, makes the in-situ biomethanation operation within the bioreactor highly carbon-neutral

and sometimes even carbon-negative.

4. The CoalBioreactor, as set forth in claim 2 and claim 3, for an existing Coalbed Methane (CBM) block for

enhanced generation and recovery of CBM (ECBM) as well as sustainable generation and recovery of CBM

(SCBM) and for any and all carbonaceous materials formations including coal formations, having energy

stored in solid carbon form, independently as an energy extraction technology (EET) for extraction of a

very high percentage of energy contained therein in highly carbon-neutral and sometimes even carbon-

negative way and on sustainable basis.

5. The CoalBioreactor, as claimed in claim 3, for producing and recovering hydrogen from carbonaceous

materials formations including coal, by injecting a different set of designer microbial consortia to follow

hydrogen generating bioconversion pathway.

6. The CoalBioreactor, as set forth in claim 3, in which CO2 geothermics extracts geothermal energy on

sustainable basis.

Figure 1.

Surface

Subsurface

(Underground)

(5, 6, 7, 8,

9 and 10)

(1) Different Layers of Parting

Rocks (a few hundred meters to a few kilometers deep)

(2)

(4) (3)

(11)

(13) (12) (14)

(15)

(16)

Figure 2.

(17)

(21)

(18, 19

and 20)

(22)

(23)

(24)

Figure 3.

.

(25)

(26)

Figure 4.

Figure 5.

(27) (28) (29)

(31) (32) (30)

(33)

Figure 6.

(34)

Figure 7.

Figure 8.

(35)

(36)

Figure 9.

(37)

(39)

(40)

(38)

(42)

(41)