gastips-winter04.pdf

Reducing the Risk of Exploring ForAnomalously Pressured Gas AssetsInnovative Discovery Technologys newly developed diagnostic tools are helping Wind River Basinoperators find and produce the basins large anomalously pressured gas resources.

Coalbed Natural Gas Resources:Beneficial Use AlternativesThe final article in this series discusses treatment technologies and alternative uses for coalbednatural gas produced water.

Tight Gas Sands DevelopmentHow toDramatically Improve Recovery EfficiencyIntegrated application of joint DOE/NETL and industry-sponsored intensive resource developmenttechnology could double the volume of natural gas considered technically recoverable from tight gas sands in Rocky Mountain basins. This is the first of a three-part series.

Gas Potential of Selected Shale Formationsin the Western Canadian Sedimentary Basin A preliminary study by Gas Technology Institute evaluated the geochemical, geological and structuralcharacteristics of the shale packages in the Western Canadian Sedimentary Basin.

Large-Scale Sulfur RecoveryRecovery methods become more critical as gas production encounters more sulfur.

New High-Power Fiber Laser Enables Cutting-Edge ResearchThe recent commercial availability of high-power fiber lasers presented a timely opportunity for Gas Technology Institute to enhance ongoing research of laser applications for well construction and completion.

Continuing Development of LNG Safety ModelsGas Technology Institute and the University of Arkansas are soliciting interest from organizations toparticipate in research to further expand the capabilities of modeling tools used to assess potentialhazards associated with liquefied natural gas terminal and shipping operations.

TECHNOLOGY DEVELOPMENTS IN NATURAL GAS EXPLORATION, PRODUCTION AND PROCESSINGA Publication of Gas Technology Institute, the U.S. Department of Energy and Hart Publications, Inc.

GasTIPS

Items of Interest 03 Editors Comments34 Briefs and New Publications35 Events Calendar and Contacts

Winter 2004 Volume 10 Number 1

GTI-03/0207

Basin CenterGas

Produced Water

UnconventionalResources

CanadianResources

Gas Processing

LaserTechnology

Liquified Natural Gas

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Managing EditorsMonique A. BarbeeRhonda DueyHart Publications

Graphic DesignLaura WilliamsHart Publications

EditorsJames AmmerDOE-NETL

Joseph HilyardGas Technology Institute

Subscriber ServicesJacquari HarrisHart Publications

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C O N T E N T SEditors Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Basin Center Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Produced Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Unconventional Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Canadian Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Gas Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Laser Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Liquified Natural Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Briefs and New Publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Events and Contact Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

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GasTIPS (ISSN 1078-3954), published four times a year by Hart Publications, a divisionof Chemical Week Associates, reports on research supported by Gas Technology Institute,the U.S. Department of Energy, and others in the area of natural gas exploration, formationevaluation, drilling and completion, stimulation, production and gas processing.

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2 GasTIPS Winter 2004

In March 2002, SpencerAbraham, Secretary of theU.S. Department of Energy(DOE), requested that theNational Petroleum Council(NPC) undertake a study onnatural gas in the United States.The study was to examine theimplications of increasingdemand, new sources of supply,new technologies, and evolvingmarket conditions for naturalgas prices and deliveryreliability through 2025.Abraham was particularlyinterested in actions that industry andgovernment could take to ensure adequate andreliable supplies of energy for U.S. consumers.

The NPC on Sept. 25, 2003 unveiled asummary of its findings and recommendations. Itwas a result of more than a year of work by threetask groups Demand, Supply, and Transmission& Distribution with representatives from largeand small gas producers, transporters, serviceproviders, financiers, regulators, local distributioncompanies, power generators and industrialconsumers of natural gas.

These findings, essentially the informed,collective view of the U.S. gas industry, state thatpolicies that continue to encourage the use ofnatural gas but discourage access to additionalsupplies will result in undesirable impacts toconsumers and the economy.

In the study, the NPC developed twoscenarios of future supply and demand that movebeyond the status quo: a Reactive Path and aBalanced Future. Both require significantactions by policy makers and industrystakeholders, but the Balanced Future scenariobuilds in additional supportive policies for supply

development and allows greater flexibility in fuelchoice by power producers.

The report recommends more than 50 specificactions that government can take to improve thelikelihood that the lower-gas-price environmentof the Balanced Future scenario is the path thecountry travels during the next 20 years. Theserecommendations include: removal of barriers to energy efficiency

improvements in power plants (New SourceReview reforms);

providing certainty regarding Clean Air Actprovisions;

enabling legislation for an Alaskan gaspipeline;

encouraging the construction of liquefiednatural gas terminals;

streamlining permitting for drilling in theRocky Mountains;

removal of Outer Continental Shelf leasingmoratoria; and

a more efficient review process for proposedpipeline projects.An important assumption in the NPCs

Balanced Future scenario is that the DOE

continues initiatives thatcomplement privately fundedresearch efforts.

On the supply side, the NPCsupports a significant DOE rolein upstream research, particularlywhere it complements privatelyfunded research efforts. TheNPC also recommends a re-evaluation of the technologyresearch funding levels fornatural gas relative to other fuelsin light of the increasingchallenges facing natural gas.

The importance of therelationship between new technology researchand development (R&D) and future gas supply ismore fully discussed in the Supply Chapter ofVolume II of the NPC report. According to thechapter, by the year 2025, a difference in the rateof development and application of newexploration and production (E&P) technologiescould mean the difference between 25 Tcf/yearand 30 Tcf/year for the combined U.S. andCanada natural gas production capability.

The NPC study is encouraging because itoutlines a path for increased domestic use ofclean-burning natural gas within the context of athriving economy and the security of a range ofdomestic and non-domestic supply alternatives.However, it is also sobering in its recognition ofthe effort needed to keep us on that path. TheNational Energy Technology Laboratory, alongwith other research partners such as the GasTechnology Institute, is proud to be a part of thatbalanced effort.

For more information, visit www.npc.org.

Winter 2004 GasTIPS 3

Commentary

A Balanced Future for Natural Gas ResearchThe National Petroleum Councils report on natural gas describes a difficult but necessary path forfuture gas development.

Anomalously pressured gas accumulationsin the Rocky Mountain LaramideBasins (RMLB) are a large gas resource,but one that has been difficult to exploit.The goalof this work is to maximize exploration riskreduction when exploring for such gasaccumulations in the RMLB or anywhere in theworld by gaining a better understanding of therock/fluid characteristics of the RMLB generallyand the Wind River Basin specifically. Critical tothis effort, funded by the U.S. Department ofEnergy/National Energy Technology Center, arethe evaluation of gas distribution in the fluidsystem, and prediction of enhanced porosity andpermeability in the rock system.

Detailed sonic and seismic interval velocityanalyses were used to evaluate the spatialdistribution of water- and gas-rich fluid-flowdomains. The basinwide fluid-flow regime in theWind River Basin was determined in thefollowing steps: a detailed velocity model was established from

sonic logs, 2-D seismic lines and, if available,

3-D seismic data. Automatic pickingtechnology using continuous, statisticallyderived seismic interval velocity selection and conventional graphical interactivemethodologies were used to construct theseismic interval velocity field;

velocities calculated from the constructed idealregional velocity/depth function thevelocity/depth trend resulting from theprogressive burial of a rock/fluid system ofconstant rock/fluid composition, with all otherfactors remaining constant were removed from the observed sonic or seismic intervalvelocity/depth profile; and

removal of these velocities allowed: (1)evaluation of the regional velocity inversionsurface (for example, the pressure surfaceboundary separating normally pressured rocksabove from anomalously pressured rocks below,either under- or over-pressured); (2) detectionand delineation of gas-charged, multiphasefluids domains beneath the velocity inversionsurface (for example, volumes characterized by

anomalously slow velocities); (3) evaluation ofvariations within the internal fabric of thevelocity anomaly, which thereby isolatedintense, anomalously slow velocity domains; and(4) determination of the distribution of single-phase, water-rich fluid-flow regimes undermeteoric water drive.

Anomalous velocity model for the Wind River BasinUsing this procedure, an anomalous velocity(AV) volume can be constructed for a particulararea or, in the case of the Wind River Basin, forthe whole basin. The AV volume constructedfor the Wind River Basin was based on about2,000 miles of 2-D seismic data and 175 soniclogs, for a total of 132,000 velocity/depthprofiles. The technology was tested byconstructing 10 cross-sections through the AV volume coincident with known gas fields.In each cross-section, a strong, intense,anomalously slow velocity domain coincidedwith the gas productive rock/fluid interval.


BASIN CENTER GAS

By Ronald C. Surdam, Zunsheng Jiao

and Yuri Ganshin, Innovative Discovery

Technologies LLC

Reducing the Risk of Exploring for AnomalouslyPressured Gas AssetsInnovative Discovery Technologys newly developed diagnostic tools are helping Wind River Basinoperators find and produce the basins large anomalously pressured gas resources.

Figure 1. Anomalous velocity model of the Wind River Basin,Wyoming, showing the relief on the regional velocity inversionsurface and the gas-charged rock/fluid domain below thissurface.

Figure 2. Velocity model of the Wind River Basin, Wyoming,showing the base of the water-charged rock/fluid volume. In theLower Fort Union, Lance, Meeteetse and Mesaverde units,relatively small, discontinuous, water-rich domains occur awayfrom the basin margins. These laterally discontinuous domains arenot connected to the updip meteoric water fluid-flow system.

The AV volume for the Wind RiverBasin can be used to: delineate the regional velocity

inversion surface (Figure 1; theregional pressure surface boundary), orthe depth at which the observedvelocity value begins to becomesignificantly slower than predicted atthat depth by the ideal regionalvelocity/depth function;

easily isolate gas-charged rock/fluidsystems characterized by anomalouslyslow velocities (Figure 1) and water-richrock/fluid systems characterized by normalvelocities (Figure 2), which fall along theregional ideal velocity/depth trend.

Regional velocity inversion surfaceThe regional velocity inversion surface is animportant boundary with respect to the fluid-flowand rock/fluid regimes. This pressure surfaceboundary separates normally pressured, water-rich(typically single-phase) fluid-flow systems abovefrom anomalously pressured (under- or over-pressured), multiphase, gas-charged fluid-flowsystems below. The surface is characterized by: a steepening of the vitrinite reflectance

(Ro)/depth gradient at the boundary, whichsuggests a significant difference in the thermalregime above and below the regional velocityinversion surface;

a significant change in formation waterchemistry within individual stratigraphic units,which suggests an individual marine unit abovethe boundary is more likely to be flushed withmeteoric water than the same unit occurringbelow the boundary;

acceleration of the reaction rate of smectite-to-illite diagenesis in mixed-layer clays; and

an increase in bitumen and remnant liquidhydrocarbons below the surface.Capillary properties are one of the most

important rock/fluid attributes that change inrelation to the regional velocity inversion surface.An increase in capillary displacement pressuresoccurs across the regional velocity inversionsurface from a few hundred pounds per square

inch (psi) above to a few thousand pounds persquare inch below the surface. This change isimportant because of its effect on sealing capacity.Above the regional velocity inversion surface,certain fine-grained lithologies in individualstratigraphic units are capable of supporting gascolumns a few hundred feet high, whereasbeneath this surface, the same lithologies arecapable of supporting gas columns severalthousand feet in height. Rock/fluid systems belowthe surface are dominated by capillarity, whichmakes it difficult for fluid to move across low-permeability boundaries and increases thepotential for compartmentalization of the fluid-flow systems. In summary, all the changes inrock/fluid characteristics associated with theregional velocity inversion surface are compatiblewith a significant reduction in the convection offluids across this surface or boundary.

Regional velocity inversion surfaces have beendetected in more than 30 basins (Table 1) aroundthe world using the techniques discussed above.The most detailed evaluations of lithologiesassociated with the regional velocity inversionsurface have occurred in the RMLB. In each ofthese basins, the regional velocity inversion surfaceis commonly associated with a low-permeabilitylithology, which has often been modified to evenlower permeability values through diagenesis. Insome cases, the inversion surface cuts acrossstratigraphic boundaries, typically along a near-vertical fault. Where this occurs, the inversionsurface follows the low-permeability stratigraphicunit laterally until it intersects a fault and jumps up

or down to another low-permeabilitystratigraphic/lithologic unit and againcontinues laterally. Note that thedistribution of regional velocity inversion surfaces in the RMLB istypically associated with low-permeability lithologic units such asshales, paleosols, and diagenetically andpedogenetically modified siltstones andsandstones, among others.

Topographic relief on a regionalvelocity inversion surface can occuralong faults, fracture swarms, stacked

sandstones or other stratigraphic/structuralelements that result in permeability chimneys. Inthe Wind River Basin, many of the topographichighs on the regional velocity inversion surface are3,000ft higher than the surrounding areas. Each ofthe highs represents the vertical migration of gas gas chimney for example; thus, these areasrepresent conduits characterized by enoughpermeability to allow vertical migration of gas.

Gas-charged domainsOther features of the fluid-flow system that canbe detected and the distribution delineated arethose domains beneath the regional velocityinversion surface that are intensely slow, whichare interpreted to be those domains where theprobability of high gas saturation is highest.These domains are characterized by AV valuesgreater than 1,000 m/sec. The minus sign on theAV value indicates the velocity is anomalouslyslow. Such an AV value indicates that, at thatpoint, the velocity falls 1,000 m/sec below orslower than predicted for that depth by the idealregional velocity/depth function. Anomalousvelocity values can vary between regions becauseof variations in seismic acquisition parametersand overall seismic data quality. In the RMLB,intensely slow velocity (gas-charged) domainstend to be highly compartmentalized.

Basinwide rock/fluid systems:Wind River BasinSome locations in the Wind River Basin havecolumns of rock/fluid systems more than 5,000ft


BASIN CENTER GAS

Table 1. List of basins in which the Innovative DiscoveryTechnology exploration strategy and associatedtechnologies have been successfully applied.

thick characterized by continuous, anomalouslyslow velocities. If anomalously slow velocitiesequate to gas-charge in the RMLB, these areas inthe Wind River Basin contain thick rock/fluidcolumns that have no connection to meteoricwater. In other words, the velocity analysisstrongly suggests the occurrence of regionallysignificant fluid-flow compartments, with a gas-charge in the fluid phase (a water-gas-oil system),that are isolated from meteoric water recharge.This configuration does not eliminate thepossibility that trapped water is present, perhapseven substantial, smaller water-dominateddomains within the large regional gas-chargedcompartments. However, if such water-rich fluiddomains exist, they are not being recharged fromthe meteoric water system. Most importantly,even in intensely slow velocity (gas-charged)domains, fluid-flow systems are water-gas-oil,such as in the lower Fort Union, Lance,Meeteetse and Mesaverde units, where relativelysmall, discontinuous, water-rich domains occuraway from the basin margins.

Anomalously slow velocities do not exclude thepresence of water. The most significant decrease invelocity occurs when the gas phase reaches about20%. Knight et al. (1998) have shown there is arelationship between gas saturation distribution

and velocity. The group conclude that in a water-gas saturated reservoir, a patchy distribution of thedifferent lithologic units is found to cause P-wavevelocity to exhibit a noticeable and almostcontinuous velocity variation [decrease] across theentire saturation range. These findings areimportant, the group notes, because they indicatethat in many of the reservoir intervals of interest inthe RMLB, where the distribution of lithologies ispatchy, a relationship between increasing gassaturation and decreasing velocity is different fromthe response of a homogeneous reservoir, where asingle large drop in velocity occurs in the 15% to20% saturation range. The work of Knight et al.explains why, in some relatively thick andheterogeneous reservoir intervals like the LanceFormation, there is nearly a continuous decrease invelocity as the gas-charge, as reflected by theestimated ultimate recovery of wells, increases.

This relationship between velocity and gassaturation is the main diagnostic tool used hereinto evaluate the distribution of gas in the RMLB.Thus, in the anomalously slow velocity domains, asignificant gas phase exists (as a gas-charged andmultiphase fluid flow system), and any waterpresent is isolated from the meteoric water flowsystem. Note that gas production from reservoirintervals characterized by intensely slow velocity

domains in the RMLB commonly have very lowinitial water production.

The Wind River Basin on a regional scale isdivided into at least two regionally prominentfluid-flow compartments separated by a velocityinversion surface. The upper compartment iswater-dominated, probably under strong meteoricwater drive, whereas the lower compartment is gas-charged, isolated and anomalously pressured. Thelower boundary of the regionally gas-chargedcompartment was not observed in the presentwork, but generally it must be at a depth equivalentto 3-sec two-way travel time or greater (more than15,000-ft depth). Based on earlier work in thePowder River Basin, there is a strong possibility thelower boundary of the regional gas-chargedcompartment in the Wind River Basin will beassociated with the lowermost organic-rich shale inthe Mesozoic section.

Judging from cross-sections through the AVvolume, numerous fluid-flow sub-compartmentsoccur within the regionally prominent gas-chargedcompartment beneath the regional velocityinversion surface. The geometries and boundariesof these sub-compartments are controlled by faults,other structural elements, low-permeability rocksresulting from the stratigraphic framework, such assandstone distribution and petrophysical character,depositional setting and diagenetic history.

Distribution of potential gas-charged reservoirsDetermining the distribution of gas-charged and water-charged domains significantly reducesexploration uncertainty (risk) in Laramidebasins. Even more risk reduction can be achievedby determining where targeted reservoir intervalswith enhanced porosity and permeabilityintersect and penetrate anomalously slow velocity domains. Well log data and seismicattributes can be used to evaluate the distributionof sandstone-rich intervals within targetedreservoir units (stratigraphic units withcommercial gas production potential) within theWind River Basin.

The Frenchie Draw gas field in the WindRiver Basin provides a good illustration of

BASIN CENTER GAS

Figure 3. Seismic data display superimposed on a frequency attribute section at FrenchieDraw field. Shaded region shows anomalous velocity overlap.


the difficulties associated withdetecting and delineating gasassets beneath the regional velocityinversion surface. The field wasoriginally drilled because of astratigraphic trap, consisting oflenticular fluvial sandstone in the lower Fort Union/Lancestratigraphic interval, on a north-plunging structural nose. But thetrapping mechanism and gasdistribution pattern have proven tobe complex, and the exploitationof this gas asset by conventional technologies hasbeen fraught with significant risk, as iscommonly the case in gas fields in the basin.Surdam (2004) has demonstrated a goodcorrelation between seismic frequency andgamma ray logs, such as lithology, through thelower Fort Union/Lance strati-graphic interval atFrenchie Draw. It is concluded that seismicfrequency can be used to distinguish sandstone-rich from shale-rich stratigraphic intervals in theFrenchie Draw field in the Wind River Basin.

Figure 3 shows sandstone-rich intervals withlow seismic frequency (blue areas outlined bywhite dots and denoted by arrows) within thelower Fort Union/Lance stratigraphic sectionthat intersect anomalously slow velocity domains(shaded area outlined by red dots) within theFrenchie Draw. The graphic shows that not onlydoes a north-plunging structural nose occur inthis area, but at the boundary between the Upperand Lower Fort Union stratigraphic units (nearthe upper limit of gas production) a shale-richsequence (orange) serves as a regional seal. Also,the distribution of sandstone-rich intervals (blue)stands out against the shale-rich intervals (orange,yellow and green). The lenticular aspect of thefluvial sandstone-rich intervals is apparent. Inconclusion, the distributional pattern oflithologies shown in Figure 3 corresponds with initial interpretations of geologists andgeophysicists who discovered the field.

This example further illustrates the complexnature of compartmentalization of productionpotential within anomalously slow, gas-charged

domains. The distributions of production sweetspots in this example are controlled by a variety offactors, including, but not limited to, stratigraphicand structural frameworks, all below a regionalvelocity inversion surface (see red line; Figure 3)and within the regionally anomalously slowvelocity volume.

Figure 4 is the pressure data for the Fort Union,Lance and Mesaverde stratigraphic units from theWind River Basin. The Fort Union Formationpressure data were originally from 297 wells and1,212 tests; the Lance Formation data were from129 wells and 611 tests; and the Mesaverde Groupdata were from 132 wells and 323 tests. The datashown were edited according to the followingscheme: the initial shut-in pressure (ISIP) and final shut-

in pressure (FSIP) had to be reported or the testwas discarded;

the ISIP and FSIP values had to agree within10% or the test was discarded; and

all pressure data characterized by gradients lessthan 0.1 psi/ft (for example, gas gradient) were eliminated.The observed pressure regimes in the lower

Fort Union, Lance and Mesaverde units are nearly identical. Most of the observed pressuremeasurements are near the hydrostatic gradient(about normal) or are significantly under-pressuredfor each unit from near surface to 12,000-ft depth.Only when these units approach 12,000-ftpresent-day depth are over-pressured values(significantly >0.43 psi/ft) observed (Figure 4).From the regional velocity inversion surface

(usually encountered at 6,000-ft to8,000-ft depth) down to 12,000-ftdepth, the observed pressuregradients typically are less or slightly greater than the regionalhydrostatic pressure gradient (i.e.,about 0.43 psi/ft). Much of thedrilling activity for these units is fortargets in the 8,000-ft to 12,000-ftdepth window.

The pressure data providesubstantial evidence that significantportions of the lower Fort Union,

Lance and Mesaverde units are under-pressured ornormally pressured. When Figure 4 is combinedwith Figure 1, it can be concluded that few of theserocks are in fluid-flow communication with themeteoric water system. The rock/fluid systems inthe lower Fort Union, Lance or Mesaverde unitsbelow the regional velocity inversion surface aretypically not under strong water drive. If exceptionsto this statement exist, they will be on a local andsmall scale and will not be detectable on the scaleof seismic data. Instead, the normal and under-pressured rock/fluid systems below the regionalvelocity inversion surface and above 12,000-ftdepth are compart-mentalized and gas-charged,with multiphase fluid systems dominated bycapillarity. Below about 12,000ft, the rock/fluidsystems for all these units will likely becompartmentalized and over-pressured.

Commonly, the best gas production inLaramide basins is beneath but within 2,000ft ofthe regional velocity inversion surface. Typically,reservoir rocks in this area of the pressure transition(i.e., regional velocity inversion surface) haveundergone less burial and diagenesis than reservoirrocks occurring deeper in the anomalouslypressured rock/fluid column; they have relativelygood porosity and permeability. If the rock/fluidsystem within this depth interval is under- or evennear normal pressure, it can be easily bypassed or badly damaged.

Recent work has shown that in all the RMLB,the transition at the regional velocity inversionsurface is commonly from a normally pressuredto an under-pressured fluid-flow system. The

BASIN CENTER GAS

Figure 4. ISIP (left) and FSIP (right) vs. depth for the Lower Fort Union,Lance and Mesaverde stratigraphic units from the Wind River Basin.For each unit from near surface to 12,000ft, most of the observedpressure measurements are near the hydrostatic gradient (i.e.,normally pressured) or significantly under-pressured.



potential for drilling damage to under-pressuredreservoir rock in the RMLB, and probablyelsewhere in the world, is universal, particularly ifthe under-pressured zone or interval is relativelythin and adjacent to over-pressured rock/fluidsystems. The potential for yet unrecognizedunder-pressured gas resources in many of theRMLB is significant (excluding the Alberta andSan Juan basins, where large under-pressured gasresources have been recognized and exploited).Ironically, under-pressured gas resources containsome of the best-quality reservoirs within theanomalously pressured portion of the WindRiver Basin.

ConclusionsThe rock/fluid characteristics of the RMLBdescribed in this work demonstrate the potentialfor significant, relatively unconventional, so-called basin-center hydrocarbon accumulations.The rock/fluid systems characterizing the RMLBdictate that if such accumulations occur, they willbe characterized by several critical attributes aspreviously noted.

Because some of these critical attributes are not associated with conventional hydrocarbonaccumulations, a new set of diagnostic tools isrequired for efficient and effective explorationand exploitation of these types of gas prospects.

To maximize exploration risk reduction whenexploring for these types of gas accumulations inthe RMLB, or for anomalously pressured gasaccumulations anywhere in the world, it isrecommended that highest priority be given toevaluating gas distribution in the fluid system, andpredicting enhanced porosity and permeability inthe rock system.

For more information about InnovativeDiscovery Technologys (IDT) exploration toolsand technologies, contact Ronald Surdam,president. IDT, 1275 N. 15th St., Ste. 121,Laramie, WY 82072; Tel: (307) 745-4464; e-mail: [email protected].

AcknowledgmentsIDT would like to thank the U.S. Department of

Energy (Contract No. DE-FC26-01NT41325)for supporting this work. Gary Covatch, ourprogram officer, and his colleagues at the NationalEnergy Technology Laboratory have been veryhelpful. Also, we acknowledge the support andcooperation of Echo Geophysical of Denver. Lastly,we acknowledge the support and encouragementoffered by industry.

References1. Chen, W., A. Park, and P.J. Ortoleva, 1994,

Role of Pressure-Sensitive Reactions in SealFormation and Healing: Application of the CIRF.AReaction-Transport Code, in P. Ortoleva, ed., BasinCompartments and Seals: American Association ofPetroleum Geologists Memoir 61, 1994, Tulsa,O.K., p. 417-428

2. Heasler, H.P., R.C. Surdam, and J.H. George,1994, Pressure Compartments in the Powder RiverBasin, Wyoming and Montana, as Determined fromDrill-Stem Test Data, in P. Ortoleva, ed., BasinCompartments and Seals: AAPG Memoir 61, p.235-262

3. Knight, R., J. Dvorkin, and A. Nur, 1998,Acoustic Signatures of Partial Saturation,Geophysics, Vol. 63, No. 1 (January-February1998), pp. 132-138

4. MacGowan, D.B., Z.S. Jiao, R.C. Surdam,and F.P. Miknis, 1994, Formation WaterChemistry of the Muddy Sandstone, and OrganicGeochemistry of the Mowry Shale, Powder RiverBasin, Wyoming: Evidence for Mechanism ofPressure Compartment Formation, in P. Ortoleva,ed., Basin Compartments and Seals: AAPG Memoir61, p. 321332

5. Maucione, D.T., and R.C. Surdam, 1997,Seismic Response Characteristics of a Regional-Scale Pressure Compartment Boundary, AlbertaBasin, Canada, in R.C. Surdam, ed., Seals, Traps,and the Petroleum System: AAPG, Memoir 67, p.269-282

6. Surdam, R.C., 1997, A New Paradigm forGas Exploration in Anomalously Pressured TightGas Sands in the Rocky Mountain LaramideBasin, in R.C. Surdam, ed., Seals, Traps, and thePetroleum System: AAPG, Memoir 67, p. 283-298

7. Surdam R.C., 2001a, Anomalously Pressured

Gas Resources in Rocky Mountain LaramideBasins, World Oil, Vol. 222, No. 9, p. 80-82

8. Surdam, R.C., 2001b, AAPG is a Huge,Undeveloped Resource, The American Oil & GasReporter, Vol. 44, No. 12, pp. 68-71

9. Surdam, R.C., 2001c, Sweet Spot of Success:Velocity Analysis Maps Sweets Spots in Tight GasReservoirs, New Technology Magazine, Vol. 7, No.3, p. 32-33

10. Surdam, R.C., Z.S. Jiao, and H.P. Heasler,1997, Anomalously Pressured Gas Compartmentsin Cretaceous Rocks of the Laramide Basins ofWyoming: A New Class of HydrocarbonAccumulation, in R.C. Surdam, ed., Seals, Traps,and the Petroleum System: AAPG, Memoir 67, p.199-222

11. Surdam, R.C., J. Robinson, Z.S. Jiao, N.K.Boyd, 2001, Delineation of Jonah Field UsingSeismic and Sonic Velocity Interpretations, in D.S.Anderson, J.W. Robinson, J.E. Estes-Jackson, E.B.Coalson,, ed., Gas in the Rockies, Rocky MountainAssociation of Geologists, Denver, p. 189-208

12. Surdam, R.C., Z.S. Jiao, and Y. Ganshin,2003a, Anomalously Pressured Gas Distribution inthe Wind River Basin, Wyoming, DOE TopicalTechnical Progress Report under Contract No. DE-FC26-01NT41325, p. 22

13. Surdam, R.C., Z.S. Jiao, and Y. Ganshin,2003b, Rock/Fluid System Characteristics of theWind River Basin, Wyoming, DOE TopicalTechnical Progress Report under Contract No. DE-FC26-01NT41325, p. 18

14. Surdam, R.C., Z.S. Jiao, and Y. Ganshin,2004, Reducing Risk in Low-Permeability GasFormations: Understanding the Rock/FluidCharacteristics of Rocky Mountain LaramideBasins, DOE Final Technical Progress Reportunder Contract No. DE-FC26-01NT41325, p. 39

15. Surdam, R.C., Z.S. Jiao, and R.S.Martinsen, 1994, The Regional pressure Regime inCretaceous Sandstones and Shales in the PowderRiver Basin, in P. Ortoleva, ed., BasinCompartments and Seals: AAPG, Memoir 61, p.213233.

16. Timur, A., 1987, Acoustic Logging, in H.Bradley, ed., Petroleum Engineering Handbook,Dallas, Dallas Society of Petroleum Engineers.

BASIN CENTER GAS


Coalbed natural gas production,commonly called coalbedmethane or CBM, is of vitalinterest in the search for new naturalgas resources in the United States.Coalbed methane resources in theRocky Mountain states have generatedan industry drilling boom during thepast decade. The output reached 4billion cf/d in 2002 with productionfrom 20,000 wells. This represents 8%of all natural gas produced in theUnited States. Interest in CBMdevelopment is high, particularly inWyoming, Montana and New Mexico.However, development brings with it agrowing concern about how to handlethe produced water. Argonne NationalLaboratory estimates for 2002 indicate morethan 14 billion bbl/year of produced water mustbe handled in the United States, with anincreasing amount coming from coalbed naturalgas development.

Economics of CBM production depend onreducing the cost of handling produced water.Beneficial uses for produced water offer the bestalternative to high-cost re-injection procedures.Various treatment or pretreatment applications(see Coalbed Natural Gas Produced Water: WaterRights and Treatment Technologies, GasTIPS, Fall2003, Vol. 9, No. 4, p. 13-18) may be necessarybefore produced water can be funneled foralternative uses. However, much of the waterfrom CBM development in the RockyMountain region is of high quality and requires

no or only moderate treatment prior toagricultural or industrial use.

Alternatives to re-injection of CBMproduced water fall in five main categories:water impoundments for stock and wildlife,irrigation, surface discharge, and recreationaland industrial uses. These categories have someoverlap because of drainage characteristics andstorage requirements.

Water impoundmentsWildlife and Livestock Water ImpoundmentsWildlife watering ponds are perhaps one of thesimplest alternative uses for CBM and benefitsthe general public most. Wildlife wateringponds provide adequate drinking water duringdrought periods, create or expand suitablehabitat for wildlife and may improve water

quality. Because the arid western stateshave broad areas with inadequatesurface water and prolonged periodsof drought, creation of ponds usingCBM produced water can be highlybeneficial to resident species of deer,pronghorn, coyotes, bobcats, uplandgame and shore bird species. Pondsalso can be constructed to providebreeding areas for waterfowl orwintering areas for migratorywaterfowl and other transient birdspecies. The ponds also can providehabitat for fish. Ponds can be used toincrease the range of certain wildlifespecies into areas that previously didnot have sufficient surface water.

The Natural Resource Conservation Service(NRCS) has nationwide standards and designguidelines for wildlife watering facilities.Simple water tanks for remote areas whereproduced water of acceptable quality is availablecan be constructed from PVC pipe and a small tank or impoundment pit. Ponds for year-round water impoundment for wildlife,migratory birds and fish must be at least 40 acres in size with 25% of the area more than 9ft deep. Other requirements, such asfencing to protect livestock, water valves and maintenance, are provided by the NRCS. Construction and maintenance ofCBM produced water wildlife wateringimpoundments are low-cost, and benefitprivate land owners as well as federal and statelands and services.

PRODUCED WATER

By: Viola Rawn-Schatzinger,CDO Technologies, Inc.;

Dan Arthur and Bruce Langhus,

ALL Consulting

Coalbed Natural Gas Resources: Beneficial Use AlternativesThe final article in this series discusses treatment technologies and alternative uses for coalbed naturalgas produced water. Information in this article is based on a research guide funded by the U.S.Department of Energy/National Energy Technology Laboratory, the Bureau of Land Management and the Grand Water Protection Research Foundation.

Figure 1: The quality of coalbed methane produced water inmuch of the Rocky Mountain region meets standards forwildlife and livestock watering.


Livestock watering practices often rely onaccess to natural streams and lakes. In manyareas, this has caused erosion anddestabilization of stream banks, increasedsediment load and contamination caused byincreased nutrients and resulting algae bloom.Using off-channel watering facilities andCBM produced water ponds could provideadditional water sources, allow the expansionof livestock grazing to areas otherwise notsuitable because of limited surface water andreduce negative impacts of livestock on naturalstreams. Figure 1 shows a simple stockwatering setup using a large equipment tire.

FisheriesConstruction of fisheries isanother beneficial use for CBM producedwater related to wildlife impoundments and recreational uses. Off-channel ponds ofsufficient size to be maintained as fishbreeding habitat range in size from smallprivate ponds to large reservoirs and lakes.When conditions of size, depth andaccessibility are met, state agencies will stockthe ponds with the appropriate species of fishfor the region. State, federal and commercialfisheries are established to provide fish for

restocking as well as commercial resale andconsumption. The state and federal fisheriesare an important aspect of recreationalprograms. Location of fishponds is dependenton available quantities of useable water. TheBureau of Land Management manages morethan 85,000 miles of fishery habitat on publiclands in the United States. Coalbed methaneproduced water has the potential to expandthe number of fisheries and areas where theycan be established.

Requirements for fishponds differ fromstate to state but primarily specify pond size,depth, year-round water capacity, erosionprevention, livestock fencing and control offlow. Consideration of CBM produced waterfor fishponds and hatcheries depends ondissolved oxygen and nutrient content.Coalbed methane produced water is typicallylow in dissolved oxygen, but the content maybe increased through surface water transport,agitation or aeration. High salt or metalcontent could be harmful to fish populationsand if present must be removed prior to use inponds. Untreated CBM produced water inWyoming has been used to establish ponds forrainbow trout, blue gill and small-mouth bass.Some previous stocking operations inWyoming were halted because there was alack of available water, but CBM producedwater is used to supplement natural water inthese ponds.

Recharge PondsRecharge ponds arereservoirs constructed as off- or on-channelholding ponds, frequently called storm waterponds, retention ponds or wet extendeddetention ponds. Recharge ponds function asa permanent water management effort forseasonal surface water discharge. They mayserve to restore depleted groundwater by waterinfiltration into the subsurface or primarily toimprove water quality or minimize peak flow periods and flooding. Recharge pondslower the total dissolved solid (TDS) contentand thus can serve as a CBM produced watertreatment in addition to beneficial use of theimpounded water.

Design of recharge ponds has five areas of specification: pretreatment, treatment,conveyance, maintenance reduction andlandscaping. Pretreatment involves filtrationor an interval to allow the sediment to settleprior to input into the recharge pond. Varioustreatments may be used to eliminatepollutants. Control of water flow and volumein the pond, pond size and spillway designfalls into the conveyance category.Landscaping ponds increase the aestheticappeal and may contribute to improvedmaintenance of slopes and reduced erosion.They often also improve local wildlife habitat.Because CBM development has the potentialto draw down local aquifers, it is vital tomaintain surface impoundments to supportlocal water use.

RecreationRecreational use of largemanmade water bodies has become animportant secondary function of lakes andwater sources created or expanded for urban and industrial water supplies. Fishing,swimming, boating and camping facilities arethe most common recreational uses forimpounded water. Coalbed methane water canbe used to supply artificially constructedimpoundments or supplement natural lakesduring seasonal low periods. Wildlife habitatfor migratory birds also may be classified asrecreational use for hunters. A potentialproblem with constructing large recreationallakes is the relatively short-term nature (10years to 20 years) of CBM development,which could result in water starved lakes.

Evaporation PondsEvaporation pondsconstructed in off-channel areas providestorage for CBM water. As evaporationoccurs, the remaining water becomesconcentrated into high TDS brine. The pondmay need to be lined with bentonite clays toprevent water infiltration into the soil. In aridclimates in the West, evaporation rates from28 in. to 52 in. annually have been recorded. Inthe Gulf Coast region, evaporation rates mayreach 48 in. to 70 in. per year. Evaporativeponds provide a relatively low-cost disposal

PRODUCED WATER

Figure 2: Wetlands may have anadditional benefit in sequesteringcarbon dioxide, and in a minor wayhelp moderate global climatic changes.


method for CBM produced water if theproper stratigraphic layers of sediment arepresent. These include layers of sand andshales, which form impermeable seals orbarriers to infiltration.

Constructed WetlandsWetlands aredesignated by saturated soil conditions,which determine the vegetation that maygrow in a given region. Wetlands can beconstructed in areas where frequent and longperiods of soil inundation occur using CBMproduced water to soak the site in arid off-channel areas. Wetland systems providedual benefits as a means of naturally treatingCBM produced water and to enhance and increase wildlife habitat. Wetlandconstruction requirements are specific tolocality but in general require a gentlegradient to prevent water runoff and soilswith silt, loam, clay and fine sand that areable to hold water. Plant species should beselected given consideration to the localclimate, tolerance levels to possible TDSconcentration in the CBM produced water,and their value as food and habitat for fishand wildlife. Early stages in wetlandconstruction and the resulting increasedvegetation are shown in Figure 2.

Surface dischargeThe release of CBM produced water intosurface water may be considered a beneficialuse to augment stream water flow. The key tosurface discharge is management of dischargeamounts, timing and impact on the surfacestreams. The Clean Water Act requirespermits for all water discharges. Permits todischarge water, including CBM producedwater, specify the requirements on each siteincluding volumes of water, TDS content andthe body of water receiving the discharge. Theeffluent content of water discharged must bedetermined prior to discharge, and the periodof discharge time is controlled to protectseasonal requirements of local streams,fish and wildlife. Surface discharge of CBM produced water can be intertwined

with water rights issues. After discharge,the water becomes part of the waters of thestate and is subject to all regulationsapplicable to surface water. Federal, state andIndian lands water rights must be consideredfor any use of the water once it has beendischarged into a stream.

Individual states have specific regulationsfor discharge of water, which were discussed inarticle 2 of this series. Some of the typicalconsiderations require: characterization of the stream; the total maximum daily load of pollutants

in a stream segment; the base flow; the biological environment potentially

affected; the primary source of water; the type of point source for any pollutants; the size and type of stream (perennial,

intermittent or ephemeral); and the effect of snowmelt on stream flow.

There are three methods of surfacedischarge: discharge to surface water;discharge to land surface, with possible runoff;

and discharge to land surface, with possibleinfiltration into subsurface aquifers. Directdischarge by pipelines avoids the potentialerosion affects of open-channel discharge.Erosion causes local problems and increasesthe sediment load of the stream. The volumeof direct discharge must also be considered soabrupt changes in the height of the water in achannel does not cause adverse effects on plantlife, bank stability, aquatic vegetation, fish orinvertebrates all of which have particulardepth and flow requirements.

Water discharge to land surfaces iscommonly used for irrigation. Center-pivots,side-rolls and fixed or mobile water guns areirrigation systems used in the arid westernstates to spread water over a maximum area.All three have been used with CBM producedwater in the Powder River Basin of Wyoming.Figure 3 shows the side-roll irrigation system.

Discharge of CBM produced water tosurface impoundments having the potential ofinfiltration into subsurface aquifers requiresdetermination of on- or off-channel waterbodies. On-channel discharge includes ponds

PRODUCED WATER

Figure 3: Local soils, pasture and agricultural needs must be considered before settingup coalbed methane irrigation systems.


or dry drainages managed to encourageinfiltration into alluvial channel fill. Thevolume and TDS content of the CBM watercan easily be monitored. Discharge into off-channel constructed containment structures isdesigned to reduce the volume of producedwater through infiltration and evaporation,leaving remaining water for beneficial use likestock or wildlife watering or fisheries.

Agricultural Uses In addition to livestockand wildlife watering, CBM produced waterfor crops or to support pasture growth is aneffective use in the arid western states whereCBM produced water is normally highquality. Agricultural water sources in the westare limited by low rainfall and snowmelt,normally a cumulative amount of less than 20in. per year. The runoff into ephemeralstreams is seasonal, and marginal dry landfarming can be improved with increased watersupplies. Storage of CBM produced water inimpoundments can alleviate the seasonalproblems and provide irrigation water asneeded for crops.

Coalbed methane produced water often hashigh sodium adsorption ratio (SAR) values the ratio of sodium, calcium and magnesiumconcentrations high concentrations ofmetals iron, manganese and barium andvariable salt content. These minerals mayaffect soil permeability or be toxic to certainplant species. Ideal conditions for CBMproduced water for irrigation are areas withcoarse-textured soil and salt-tolerant crops.Several studies have been conducted andcomparisons made to other arid parts of theworld to identify the plants best suited toCBM irrigation.Use of salt-tolerant speciesutilizing CBM produced water is a landmanagement option. Cooperation with CBMproducers, land owners and mineral rightsholders is necessary to optimize managementof produced water for agricultural uses.

The suitability of saline water for irrigationis dependent on numerous factors, includingthe type and relative abundance of ions insolution, soil texture and mineralogy,

sensitivity threshold and growth stages ofplant species, as well as the amount of CBMproduced water during each irrigation event.Plant sensitivity research can be used to selectagricultural crops, which grow in areas oflimited rainfall, colder temperatures andshorter growing seasons found in most of theRocky Mountain states. The U.S. Departmentof Energy-sponsored studies at MontanaState University have found barley, wheat,sugar beets, sorghum and cotton are bestsuited to irrigation by CBM produced waterin the Powder River Basin. Native high salt-tolerant grasses and forbs can be plantedaround impoundments and discharge sites tomaximize the use of CBM produced waterand reduce erosion, as well as being used inbioremediation of brine contaminated soils.

Irrigation in the Powder River Basin usingCBM produced water began in the 1990s.However, produced water from coalmines inportions of the Powder River Basin has beenused for livestock and human consumption formore than 100 years. Sprinkler systems areused to provide a slow discharge of water overa wide area. Selection of the best irrigationsystem for a given area looks at several criteria: soil type (infiltration rate); system size or length; sprinkler head and capacity (spray nozzle or

oscillating); area of coverage; elevation differential from pivot point to

end of system; water pressure (pump capacity); speed of rotation; and peak daily evaporation.

Flood irrigation, using a series ofconstructed channels to divert water to nativegrass pastures, also has been applied. Oneadvantage of flood irrigation is that less wateris lost through evaporation, but it is moredifficult to spread the effects of the water overwide areas.

Mixing CBM produced water with naturalrunoff may improve the quality of irrigationwater. Use of on-channel and off-channel

impoundments for storage and mixing canimprove the suitability of irrigation water bybalancing the levels of salts and mineral insubsurface and surface waters. Soilamendment procedures may be used toimprove soils prior to irrigating with CBM produced water. Additives includecultivating gypsum or sulfur compounds intothe soil to reduce clays and minimize theprecipitation of calcite. Cultivation furtherencourages the growth of microbial bacterial,which are beneficial to the soil whensufficient water is available.

Industrial useWater management options for CBMproduced water include use in the operationalactivities of industries in the producingregion. Common industrial uses include coal mines, animal feedlots, cooling towers,car washes, enhanced oil recovery and fire protection.

Coal Mines As CBM produced water isfrequently available close to coal miningoperations, coalmines are a prime industrialuser of CBM produced water. Coalmines canuse CBM water for drilling operations, dustabatement, support on conveyor belts,crushing and grinding, assistance in restoringabandoned mine sites, and preventingspontaneous combustion of coal in thesubsurface and storage areas.

Animal FeedlotsUsing CBM producedwater for animal feedlots has two applications,livestock watering and management of animalwastes. Water is used to dilute animal wastesprior to discharge or disposal. The U.S.Environmental Protection Agency regulatesthe disposal of animal waste streams based onthe number of animals held in a given facility.If the pollutants are discharged into navigablewaters, the waste stream must be reduced tospecified limits by adding fresh water.

Cooling TowersNumerous industries,chemical plants and municipal powergenerating plants require large quantities of water as a cooling agent. Cool water enters

PRODUCED WATER


the system and is recycled throughheat exchanges and cooling ponds,removing heat generated by theactivities of the industrial complex.Constant input of water isnecessary because of loss byevaporation. Only CBM producedwater with relatively low TDScontent can be used because highTDS content could result inmineralization, which would clogthe cooling system.

Field and Car Wash FacilitiesConstruction activities requirewashing vehicles to avoidspreading noxious plants to other areas. Thisis particularly important when equipment isbeing used for reclamation of disturbed sites.Field sites and car washes in rural areas can besupplied with CBM produced water. Becausethere is a discharge of water to the soil, onlyCBM produced water with acceptable TDSand SAR levels can be used for this purpose.

Enhanced Oil Recovery When oil andgas fields are in proximity to CBM producingareas, the use of produced water from CBMactivities for waterflooding or secondaryrecovery is possible. Waterfloods are acommon practice that can be performed withvarying quality water and may be able to uselow-quality CBM produced water.

FisheriesCommercial fisheries in thewestern United States obtain water rights todivert water into their operational ponds fromsurface waters, and CBM produced watercould be economically used in place ofdiverted surface or groundwater. This optionis applicable if the fisheries are in or near theCBM fields where water can be easilytransported or accessed through naturaldrainage systems. The water must be ofsufficiently high quality not to be toxic orhazardous to the fish.

Fire ProtectionSupplies of water fornearby municipal fire hydrants and sprinkler systems are a valuable use of CBMproduced water. Fighting fires does not

require high quality water and could benefitfrom the use of CBM produced water by notdepleting drinking water supplies. Wildfires inthe western United States are becoming largerand more dangerous because of the droughtconditions that exist in many states, andnormal supplies of water for fire fighting are becoming depleted. Supplies of CBM produced water stored inimpoundments could provide accessible waterfor fighting fires in remote western areas.

Other Industrial UsesIn some of thewestern states, CBM produced water isbeginning to be used in industries like sodfarming, solution mining for minerals,production of bottled drinking water andwater for breweries. Sod farming using CBMproduced water in the San Juan Basin ishelping supply the publics increasing demandfor sod in new developments in municipalareas. Uranium mines in Wyoming are usingCBM produced water in solution mining ofuranium ore, and companies in Nebraska,Texas and Oklahoma have submitted permitsfor similar operations. Some CBM producedwater already falls into the range of bottleddrinking water and can be sold in stores, whileother CBM water would require minimaltreatment to make it suitable for drinkingwater. Drinking water quality CBM water canbe used in breweries, and less high-qualityCBM water can be used to irrigate barley,

hops and other grains used in themanufacturing process.

Domestic and Municipal WaterUseCoalbed methane producedwater that meets drinking waterstandards can be used for public,residential and municipal water useand supply. Many of the westernstates have a rural population inwhich individual landowners couldbenefit from a residential supply ofCBM produced water, while otherstates have large municipalities inor near existing and potentialCBM development. Coalbed

methane produced water may also be used forwatering lawns and in swimming pools,washing machines and plumbing.

ConclusionsMany coalbed natural gas operators arepursuing beneficial uses for CBM producedwater where they are producing. Thedevelopers are undertaking a variety of newwater management feasibility studies for newuses for CBM produced water that meet stateand federal regulations and provide cost-effective water management for the CBMproducers as well as low-cost, readily availablewater for public, residential and industrial uses.The handbook provides several case studies,which discuss strategies used for managingCBM produced water in the western United States. The strategies often employ acombination of several methods includingimpoundment, livestock and wildlife watering(Figure 4), irrigation and dust abatement.

AcknowledgementThe information in this article is based on

a research guide, Handbook on Coal Bed Methane Produced Water: Management and Beneficial use Alternatives by ALLConsulting, Tulsa, Okla., funded by the U.S.Department of Energy, the Bureau of LandManagement and the Ground Water ProtectionResearch Foundation.

PRODUCED WATER

Figure 4: This figure shows a pond in the Powder River Basinsupplied by coalbed methane produced water that facilitieswildlife and recreational uses.


PRODUCED WATER

Multi-Seam Well Completion Technology: ImplicationsFor Powder River Basin Coalbed Methane ProductionBy John R. Duda, U.S. Department of Energy, NETL

The Powder River Basin coalbed methane (CBM) play is in northeasternWyoming and southeastern Montana. Covering 12,000 sq miles, the CBM playencompasses parts of seven counties in the two states and targets natural gas lockedin Tertiary-age Fort Union Formation coals (see map). Depths for the play rangefrom 300ft to more than 2,500ft and include a series of distinct coal seams,including the Anderson, Wyodak and Big George.

During the past 5 years, CBM development has increased in the basin. As ofJuly 2003, nearly 1 Bcf/d of natural gas and 1.5 million bbl of water were beingproduced from about 12,000 wells.

More than 3,000 additional wells have been drilled but await utility andgathering line hookups and water discharge permits, among other things.

Thus far, development has generally targeted the shallow, thick, easy-to-reachcoal seams along the eastern edge of the basin. However, with depletion ofgeologically more favorable areas, development is moving toward the deeper andsomewhat thinner coals in the central and northern portions of the basin. In theseareas, single-seam well completion technology may no longer prove adequate.

Coalbed methane operators in the Powder River Basin have long recognizedthe potential utility of multi-seam completions (MSC). Several operators havehighlighted areas where such technology would be advantageous or vital forfurther development. A handful of operators have tried MSC. Because of theunique geological and reservoir properties of Powder River Basin coals shallow,underpressured, low-rank (low strength) coals surrounded by water-bearingaquifers the application of MSC technology has been largely unsuccessful.

Task descriptionAt the request of the U.S. Department of Energy (DOE), Advanced ResourcesInternational Inc. undertook an analysis designed to evaluate the potential impactsof MSC technology for CBM development in the Powder River Basin. The studywas a natural outgrowth of an earlier DOE analysis, which evaluated the economicimpacts of produced water management alternatives on CBM development in the basin.Objectives of the MSC study include: to estimate how much additional CBM resource would become accessible and

technically recoverable, compared with drilling one well to drain a single coal seam; to determine whether there are economic benefits associated with MSC

technology utilization (assuming its widespread, successful application) and ifso, quantify the gains;

to briefly examine why past attempts by Powder River Basin CBM operators touse MSC technology have been relatively unsuccessful; and

to provide the underpinnings to a decision as to whether an MSC technologydevelopment and/or demonstration effort is warranted.

Summary of findingsThe Powder River Basin has numerous sequences of thin coal seams that extendover major areas of the basin, particularly along the northern portion of the basinand in Montana. Whenever these thin (


Three case studies are presented in thisarticle to demonstrate the application of Intensive Resource Development(IRD). The first case study discusses how IRD isconverting the Williams Fork/Mesaverde gasplay in the Rulison field of the southern PiceanceBasin of Colorado from a modest 100 Bcfaccumulation into what is potentially a multi-Tcfgas field. The second case study examines theapplication of IRD in the Jonah field of theGreater Green River Basin of Wyoming, a fieldonce labeled uneconomic and now the No. 1producing field in the basin. The third case studydescribes how application of the lessons learnedfrom the IRD experience in the Rulison field hashelped change the Cave Gulch/Waltman field inthe eastern Wind River Basin of Wyoming from a four-well prospect into a major gas field. One common thread in these examples isthat the technologies and insights applied in each grew out of research and development (R&D) efforts supported by the U.S.Department of Energy/National EnergyTechnology Laboratory (DOE/NETL) duringthe 1980s and early 1990s. Figure 1. Gas fields in the southern portion of the Piceance Basin are experiencing

active tight gas sands drilling.

UNCONVENTIONAL RESOURCES

by Vello A. Kuuskraa, Advanced Resources

International, Inc.;and James Ammer,

NETL

Tight Gas Sands DevelopmentHow to Dramatically ImproveRecovery EfficiencyIntegrated application of joint DOE/NETL and industry-sponsored intensive resource developmenttechnology could double the volume of natural gas considered technically recoverable from tight gassands in Rocky Mountain basins. This is the first of a three-part series.

This three-part series of GasTIPS articles on tight gas sand resource developmentfocuses on the application of advanced exploration and production technology in low-permeability sandstone reservoirs to increase domestic natural gas supplies and lowertheir finding and production costs. IRD is the integrated application of a series ofcomplementary resource assessment, reservoir characterization and field developmenttechnologies designed to optimize recovery. It is particularly applicable to low-permeability reservoirs with thick but discontinuous pay zones and anisotropic flowbehavior settings where a wells drainage area is low but numerous productiveintervals are penetrated.

The suite of technologies IRD encompasses includes: natural fracture identification technologies to delineate high-productivity

sections within a multi-township tight gas accumulation; well logging technologies that reliably distinguish between gas- and water-

bearing sands, and can identify and quantify volumes of secondary porosity; multi-zone completion technologies that can efficiently stimulate multiple zones

without damaging a formation; and well testing technologies to establish drainage volumes, well-to-well

communication and anisotropic flow patterns.


Case Study No. 1SouthernPiceance Basin, ColoradoThe Piceance Basin is in northwest Colorado.Gas fields in the southern portion of the basin(Rulison, Grand Valley, Parachute and MammCreek) are experiencing active drilling for tightgas sands in the Upper Cretaceous-ageMesaverde Group (Figure 1). Historically, thetight lenticular Mesaverde sands in the WilliamsFork have been viewed as a massive but low-productivity natural gas resource. However, field-based research has provided a more rigorousgeologic understanding of these tight gasreservoirs and the appropriate technologies forproducing them.

The Mesaverde tight gas sands in the PiceanceBasin are estimated to hold more than 300 Tcf ofgas. This resource is most highly concentrated inthe southern portion of the basin, particularly inthe stacked, lenticular sands of the Williams ForkFormation being developed in the Rulison field. Inrecent presentations to the Colorado Oil and GasCommission (COGC), Williams RMTconcluded the gas-in-place per section was 135 Bcf at Rulison, 120 Bcf at Parachute and 105 Bcf at Grand Valley. At traditional wellspacings of 160 acres per well (four wells persection), 5% to 6% of this resource is in contactwith a wellbore and recoverable. Based on theresults of the MWX research (see sidebar), twonew IRD strategies have been pursued in theRulison field: intensive infill drilling and extensivevertical sand development. As documented inBarrett Resources and Williams RMTsubmissions to the COGC, these companies creditthe DOE/NETL-sponsored MWX and its otherR&D projects for developing the knowledge baseand science for much of the IRD technology atRulison field.

Geologic Basis for IRD StrategyOutcropstudies of the lenticular Mesaverde sands haveshown that wells separated by only 1,000ft willnot be in communication, except in a handful ofthe more continuous sand intervals. Wells spacedas close as 1,100ft (28 acres per well) show littleto no pay correlation from well to well (Figures 2and 3). Even the three closely spaced MWX wells


NETL Intensive Resource Development R&DThe DOE/NETL sponsored three major research and development (R&D) activities in the Piceance Basin duringthe 1980s that helped establish a foundation for IRD technology. First was a series of resource assessments for thePiceance, Greater Green River and Wind River basins completed during a 15-year period (1980 to 1995). Theseassessments drew attention to large, high-concentration, Cretaceous-age unconventional gas accumulations andestablished the need for their thorough characterization. The National Energy Technology Laboratory (NETL)recently completed reassessments of the Greater Green River and Wind River basins, and is working on the Uintaand Anadarko basins (seee GasTIPS Summer 2002, Vol. 8 No. 3).

Second was the Multiwell Experiment (MWX) in the southern Piceance Basin.This R&D project produceda comprehensive, well-documented description of the geologic controls on gas productivity in the Williams Forkand Iles Formations of the Mesaverde Group.

The third effort was an initial field test and demonstration of geomechanical-based natural fracture predictiontechnology in the Rulison field of the southern Piceance Basin. This test drew on prior work at the MWX siteto develop technology for locating the higher productivity areas within tight gas sand accumulations. Whilethese U.S. Department of Energy (DOE)-fostered research efforts were not the only drivers for the developmentof IRD technology, they were important catalysts.

The MWX in the Rulison field in Garfield County, Colo., began in 1980 and was completed in 1988. Threevertical wells, (MWX-1, 2 and 3) were drilled only a few hundred feet apart to provide a laboratory forproduction and stimulation experiments. The bulk of the work was performed in MWX-1, with holes two andthree serving as observation wells for interference tests. An additional slant hole well was completed in 1990 aspart of a joint DOE/Gas Research Institute (GRI) field research project.

The wells targeted the Mesaverde Group, Iles and Williams Fork Formations, which together encompass fourdifferent depositional environments. A geologic characterization of the Williams Fork Formation establishedthat the sand bodies are compartmentalized fluvial point bars, with extremely tight matrix permeability (


(about 150ft apart) showed poor well-to-well log correlation for the Williams Fork lenticularsands (Figure 4). Reservoir simulation (by Barrett Resources and Advanced ResourcesInternational) incorporating the low magnitude,anisotropic permeability and compartmentalizedgeometry of the lenticular Williams Fork sandbodies, has shown such wells have limited arealdrainage. These studies helped operators view theWilliams Fork as primarily a vertical rather thanareal reservoir. This led operators to pursue moreintensive development closer well spacing andcompletion of all potentially productive sandintervals than had been traditional in thePiceance Basin.

Infill Well Tests Support Tighter SpacingWell tests also supported the idea of limitedcommunication. During the initial infill-drilling program at Rulison, bottomholepressure tests on new wells drilled adjacent tohighly productive older wells showed essentiallyno communication-related depletion. Morerecent bottomhole pressure build-up data

Barrett Resourcesperformed on 80-acre and 40-acrespaced wells in 1994and 1995, and

subsequently on 20-acre spaced wells drilled in1996 at Rulison and Grand Valley fields,indicated essentially no well-to-well pressurecommunication.

Reservoir Simulation and Analyses QuantifiesBenefitType curve matching performed on aseries of representative Mesaverde tight sand wellsin different portions of the Rulison field showedthe average outer limit of pressure depletion for atypical 1.8 Bcf well in the Williams Fork, after 20years of production, is about 12 acres. Reservoirsimulation and production data showed thattraditional 160-acre spacing wells would onlyrecover about 7% of the gas-in-place, but thisvalue would climb to 21% at 40-acre spacing.Modeling also showed that when permeability,anisotropy and depositional direction areaccounted for, drainage takes on a preferentialeast-west direction, calling for wells to be spacedon a rectangular rather than a square grid.

Barrett Infill Program Shows IRD BenefitThe traditional field development practice for theWilliams Fork (Mesaverde) Formation had been

to space wells at 160 acres or more. In 1994,Barrett Resources took the initial steps towardIRD, requesting approval for first 80-acre andthen 40-acre spacing from the COGC. In 1996,Barrett requested approval to drill four wells in a20-acre spacing pilot. The 20-acre spaced wellsperformed as well as the older, more widelyspaced offset wells. Based on these promisingresults, the field operator continued with itsintensive infill-drilling program.Twelve new infillwells were drilled in Section 20 of the Rulisonfield between 1998 and 2000, bringing the sectiontotal to 30 wells (effectively 20-acre spacing). Theperformance of these wells continued to beencouraging, with initial gas rates of 1 MMcf/d to2 MMcf/d and estimated ultimate recoveries of1.4 Bcf to 2.5 Bcf per well. Analysis of currentlyavailable data shows: the reserves per well remained relatively

constant as the well density in Section 20 hasprogressively increased, indicating additionalgas is being recovered vs. faster depletion; and

intensive development of the Williams Forksands at 20 acres per well may result in therecovery of 50 Bcf to 60 Bcf of gas reservesfrom this single section. Based on previousexperience, bottomhole pressure testing on the20-acre spaced wells at Rulison revealed that


Figure 2. Even closely spaced wells often show little continuity.

Figure 3. This figure shows the location of the cross-sectionoutlined in Figure 2.



only three of the 72 sands tested in the fourwells exhibited pressure communication andpossible partial pressure depletion.The field operator (now Williams

Production RMT) took the IRD concept to thenext level by applying for permission to drillSection 20 in the Rulison field, and anadditional section at Grand Valley field, at aspacing of 10 acres per well. Starting in late2001 and continuing through early 2003, theoperator added 10 additional infill wells toSection 20, bringing the total to 40 wells. Whileproduction data are still limited and several ofthe wells are still cleaning up, preliminaryanalysis shows the most recent group of wellshave exhibited initial production rates of 1MMcf/d to 2 MMcf/d, comparable or superiorto the previously drilled 20-acre and 40-acrespaced wells. Seven of the 10 wells, after about1 year of production, have performed such thattheir ultimate recoveries can be estimated in therange of 2 Bcf per well. Pressure testing in thenewly drilled 10-acre spaced infill wellsdetected partial reservoir pressure depletion insix of 98 individually tested sand bodies. Thetotal gas recovery from this section of the field,albeit with favorable reservoir properties and ahigh concentration of gas in-place, is expectedto be more than 100 Bcf per section if fullydeveloped with 64 wells (Table 1). Based onestimates by Williams, gas recovery in this

section may reach 75% of gas-in-place vs. lessthan 10% on 160-acre spacing.

Vertical Completion and RestimulationThelenticular sands in the Rulison field areseparated into a series of packages, each ofwhich comprise 400ft to 500ft of gross interval,and most wells penetrate four to six packagesacross more than 3,000ft of gas-saturatedinterval. Historical practice, given thedifficulties with then-current log interpretationtechnology, had been to complete one or twosand packages to avoid wet, unproductive sands.This conventional practice resulted in per-wellreserves averaging 0.5 Bcf, effectively renderingthe wells and the gas play uneconomic.

Starting in 1994, Barrett Resources began toaggressively develop the total stack of lenticularsands intersected by each wellbore. The newapproach included completing and independentlystimulating each of the sand packages, increasingthe size of the proppant load, and using moresophisticated fracturing fluids and procedures.

With improved core and log data, and a betterunderstanding of lenticular sands, and basin-centered gas plays, Barrett also began to re-examine the potential for recompleting theseolder wells. An early recompletion demonstrationtook place in 1990 in the No. 1 well at the DOEsMWX field research site. The recompletion,which involved perforating and stimulating threeadditional uphole Williams Fork/Mesaverde sand

packages, exhibited an excellent initial productionresponse. As of early 2003, it had produced 1.4 Bcf of incremental production, validating this more aggressive recompletion approach.Following this demonstration, the operatorlaunched a program to recomplete bypassed sands in older wells. Overall, the recompletionprogram has been successful, adding more than80 Bcf of low-cost natural gas reserves. Thecumulative effect of completing four to five payzones in a single well and recompleting the olderwells has been to raise the average wellperformance for new and old wells in Rulisonfield to 1.5 Bcf per well.

Based on the Rulison field example, IRDtechnology, with 10-acre well spacings andvertical completion of the full stack of sand, offersthe promise of providing about 100 Bcf ofrecoverable resource per section and recovery of80% of gas-in-place. IRD could transform atownship-sized, basin-centered tight gas fieldfrom a 100-Bcf prospect into a major field withmultiple Tcf of reserves. Other operators in theSouthern Piceance Basin are applying the lessonslearned at Rulison for optimally developingmassively stacked tight sand accumulations inother Williams Fork Formation tight gas fields.Successful application of this technology holds

Figure 4. Outcrop studies have indicatedthe individual point bar deposits are inirregular vertical contact with thesequence of deposits that comprise thelarger sand lenses in the fluvial channel.

Figure 5. The Lance Formation is emerging as a significant producing horizon in the Jonahand Pinedale fields in the Greater Green River Basin.



the potential for converting this previouslyuneconomic tight gas play into a world classnatural gas accumulation.

Case Study No. 2Northwestern Greater GreenRiver Basin, WyomingThe Greater Green River Basin (GGRB) is thedominant natural gas-producing basin in theRocky Mountains. Gas in this basin is found inthe Tertiary and Cretaceous-age Fort Union,Lance, Mesaverde Group, Frontier, Muddy andDakota formations. Recently, the 8,000-ft to12,000-ft Lance Formation has emerged as asignificant producing horizon in the Jonah andPinedale fields in the northwestern portion of theGGRB. Development of an extensive stack oftight, over-pressured sandstones is underway inboth fields (Figure 5).

The township-sized Jonah field is estimated(by industry) to hold nearly 10 Tcf of gas-in-place; a resource concentration of 250-Bcf to 300-Bcf per section. A unique geologic settinginvolving the local uplift of the over-pressuredLance section and a series of lateral sealing faultshas enabled gas to accumulate and remaintrapped in the Jonah field area (Figure 6).

Completion Inefficiencies Set the Stage forIRDPrior to 1992, completion attemptsemployed relatively small amounts of proppant(80,000 lb to 200,000 lb) and cross-linked water-based gel or carbon dioxide foam as the transportfluid. These ineffective fracturing fluids, coupledwith poor proppant placement, failed to establishcommercial production. Between 1992 and 1995,nine wells were stimulated with high-qualitynitrate (N2) foam and an average proppant load of550,000 lb. Most of these new stimulations,

limited to the thicker (250ft to 300ft) sandstoneintervals, resulted in successful wells but withsteep annual declines in gas production.Engineering analyses of the wells completedusing N2 foam highlighted several factors thatpotentially limited well performance: significant vertical growth of hydraulic

fractures outside of the pay interval; creation of multiple fractures with a resultant

reduction in propped fracture length; and inefficient lateral transfer of proppant away

from the wellbore.Beginning in 1994, a new completion

approach was initiated using water-based fluidswith borate cross-linkers and a modifiedperforation technique designed for flexibletreatment of multiple intervals. Wells where thisnew approach was employed exhibited initial gasflow rates comparable to the earlier completionsbut with shallower gas production declines,which, from improved lateral and verticalproppant placement, have led to greater ultimategas recoveries.

With new well completion practices, gasproduction rates have improved significantly froman average of 2 MMcf/d to 3 MMcf/d, to 5MMcf/d to 7 MMcf/d. One of the best earlywells was found to be productive from as many as17 separate sandstones distributed across all fourlower pay intervals (Lower-Middle Lance) andhas been completed in an additional 11 zones inthe Upper Lance.

Evolution of IRD in Jonah FieldAggressivevertical completion of the full stack of gas-charged net pay in the Lance Formation has

Figure 6. This cross-section shows the Jonah and Pinedale fields relative to thesurrounding tectonic features.

1. Estimated based on history matching with ARI-tight type curve model for wells drilled through 1997.

Table 2: Evolution of well completion practices, Jonah field, GreaterGreen River Basin.

Table 1: Expected results from intensive field development (Sec. 20, T6S, 94W, Rulison).

FirstGeneration

SecondGeneration

Third Generation Current

Pre-1990 1992-1993 1994-1995 2000+Pay

Selection Bottom 40% Bottom 20-50% 50% 50% to 100%

Frac Stages 1 1 3 Up to 10

Frac Fluid X-Link Gel N2 N2/Gel Borate Gel

IP(MMcf/d) 1.4 1 to 4 3 to 5 5 to 15

EUR (Bcf ) 1.5 2.0 3.0 5 to 10+

Date Wells and Spacing Reserves/Well1

(Bcf )Total Gas

Recovery (Bcf )Initial First 2 wells @320A/W 2.1 41994 Next 2 wells @160 A/W 2.2 41995 Next 4 wells @80 A/W 1.9 8

1996-1997 Next 8 wells @40 A/W 1.8 14 1997 Pilot 4 wells @20A/W 1.7 7

1998-2000 Next 12 wells @20 A/W 1.7 20 Latest Next 32 wells @ 10 A/W 1.7 55

TOTAL (64 wells) 1.75 112



converted the Jonah field from a bypassed areawith low productivity wells to a highly productivegiant gas field. The realization that past payselection procedures were inadequate and pastwell stimulation practices were damaging led tochanges in well completion practices (Table 2).The current IRD approach is to attempt to link awellbore to as much of the vertical net pay aspossible, using a dozen or more stimulations inindividual Lance zones. With IRD, the estimatedreserves per well in the Jonah field have increasedfrom 1 Bcf to 2 Bcf per well in the early 1990s to5 Bcf to 10 Bcf per well currently. As of mid-2003, Jonah is the largest natural gas field in theGGRB, producing 670 MMcf/d from 484 wells,compared with 15 MMcf/d in 1995.The field hasproduced more than 800 Bcf and is on its way tobecoming a multi-Tcf gas field. Recently, theoperators in the Jonah field and in the adjoiningPinedale area have begun development on 40-acre spacing, with indications of closer spacings tocome. The coupling of intensive areal resourcedevelopment with successful intensive verticalresource development should continue to improve

the size and economics of this major newtight gas sand field.

Case Study No. 3Eastern Wind River Basin,WyomingThe Wind River Basin is one of the least developed of the high-potentialnatural gas basins in the RockyMountains. Gas in this basin exists in anextensive stack of Tertiary- throughCretaceous-age formations. Recently, thetight gas sands in the Fort Union/LanceFormation have become targets of activetight gas development. The primary FortUnion/Lance Formation natural gas fieldsin the Wind River Basin are FrenchieDraw, Madden, Muddy Ridge/Pavilionand Waltman/Cave Gulch. The largest ofthese, Waltman/Cave Gulch, is on thenortheast flank of the basin, about 50miles west-northwest of Casper, Wyo.(Figure 7). Although the field was

discovered in 1959, the Cave Gulch Unitremained undeveloped and its true potentialunrealized until Barrett Resources rediscovered it.For nearly 35 years, the Cave Gulch Unit wasjudged to be a modest, marginally productivenatural gas field, having recovered less than 5 Bcfand producing only a few MMcf/d. Recognitionthat the Cave Gulch Unit held a massive stack ofgas-saturated sands led to the application of IRDin this field starting in 1994.

The Bureau of Land Management (BLM)estimates the Waltman/Cave Gulch field areacontains at least 1.6 Tcf of gas-in-place, primarilyin a four-section area on the western edge of thefield and in two sections on the eastern edge ofthe field.The BLM estimates the Fort Union andLance Formations in this area contain an average885ft of net pay within a 4,000-ft gross interval,holding from 450 Bcf to 680 Bcf per section.Assuming the reservoir sands are truly gas-(instead of water-) saturated, this would make thearea one of the most highly concentrated naturalgas accumulations in the Rocky Mountain region.

Evolution of Intensive Vertical Resource

Development at Cave GulchIntensive verticalresource development, completing as much of thevertical sand interval as possible (between four andfive stimulation stages per well on average) usinglarge volumes of proppant (about 200,000 lb ofsand per stage on average) has improved theperformance of Cave Gulch wells. A total of 28IRD wells completed between 1994 and 1998exhibited initial flow rates as high as 10 MMcf/d,some with estimated reserves of 20 Bcf per well.Although there is considerable variability in theperformance of the wells, particularly recent wellsdrilled along the edge of the Cave Gulch Unit, theaverage ultimate recovery for 43 successful LanceFormation IRD completions (excluding threeeconomic dry holes) is estimated at 9 Bcf per well.The average of 18 successful, shallower Fort UnionIRD completions in the Cave Gulch Unit is anestimated 5 Bcf per well, excluding four dry holes.

This example illustrates how the combined useof vertical development of the full stack of tightsands and optimum well spacing can lead torecovery of large volumes of natural gas from arelatively limited portion of the tight gas resource base.Together, these examples show howfundamental research and careful characterizationof an apparently uneconomic resource bygovernment and industry can reveal opportunitiesfor new approaches to unlocking tight gas.

References1. Finch, R.W., W.W. Aud and J.W. Robinson, 1997,

Evolution of Completion and Fracture StimulationPractices in Jonah Field, Sublette County, Wyoming,Rocky Mountain Association of Geologists Guidebook ofOilfield Technologies in the Rocky Mountains, in press.

2. Kuuskraa, V.A., Produced Massively StackedLenticular Sands of Colorados Piceance Basin,GasTIPS, Spring 1997, p 4.

3. Law, B.E., and C.W. Spencer, eds., 1989, Geologyof Tight Gas Reservoirs in the Pinedale Anticline area,Wyoming, and at the Multiwell Experiment Site,Colorado U.S. Geological Survey Bulletin 1886.

4. Lorenz, J.C., 1990, Geology, MultiwellExperiment Final Report, Part IV. The FluvialInternal of the Mesaverde Formation, Sandia NationalLaboratories, Report SAND 89-2612/A.

Figure 7. Although the Cave Gulch field wasdiscovered in 1959, only recently has it beenrecognized as a significant gas accumulation.


Unconventional gas resources includecoalbeds, shale formations and low-permeability sandstone. Gas fromfractured shales is a burgeoning element of thisunconventional gas mix. To better understandthe exploration potential of this play, modelshave been developed that better characterizethe geological setting and the geochemicalframework of shale gas production in thecontinental United States. This study wasconducted to better characterize the shale gaspotential of five formations in western Albertaand eastern British Columbia within theWestern Canadian Sedimentary Basin(WCSB) that conform to these models.

The formations

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