RockMech – CO2

MBDCI

Geology and COGeology and CO22 Sequestration Sequestration in Kuwaitin Kuwait

Maurice B. Dusseault – U. of Waterloo

Reza Oskui – KISR Roman Bilak – Terralog Technologies

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KuwaitKuwait

Oil Energy CO2

Reservoirs EOR Technical issues… Economics?

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Geological COGeological CO22 Sequestration Sequestration

Suitability of target reservoir Volume and storage capacity Permeability and continuity Quality of long-term geological seal Existing access (wells) or easy access Location (near CO2 source?)

Availability of “pure” CO2

Technical issues arising Reservoir: fluids, flow, rates… Geomechanics: stresses, pressures,

seals…

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Stratigraphy…Stratigraphy…

The sequence of strata and their physical properties constitute the base information

Then, the structural aspects are incorporated

Heterogeneity and other factors can be included

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Some Sealing Issues for COSome Sealing Issues for CO22

Reservoir spill point, structure Quality of stratigraphic seal against

CO2 diffusion and percolation Existence of potential breaches

Penetrating faults, not fully sealed Sinkhole structures from carbonate karst

features or salt dissolution Fracture pathways through cap rock

And, of course, the wellbores…

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Structure and Unconformities…Structure and Unconformities…

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Spill Point Seal…Spill Point Seal…

U of Saskatchewan

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Complex Fault StructuresComplex Fault Structures

Stresses can change among fault blocks

Pressures as well (e.g.: compartments)

Fault mechanical, transport properties are different

Faults may affect CO2 strategies

Essential inputs for sequestration

Venezuela example

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Fault Structures…Fault Structures…

fold

faul

t

flat

U of Saskatchewan

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Stratigraphic TrapsStratigraphic Traps

U of Saskatchewan

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Geological Complexity…Geological Complexity…

Wara

Mauddud3SU3SM

3SL

4S

Original oil -water contact

Wara

Mauddud3SU3SM

3SL

4S

Combined structural and stratigraphic traps in Kuwait

Original oil -water contact

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Capillary Isolation of OilCapillary Isolation of Oil

p+Δpp

Capillary barriers and swept zones are created during high Δp displacement. These lead to severe difficulties in viscous oil development

Oil zone, capillary barrierZone swept by water

r

2p ow

capillary force barrier to water displacement

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Are Fractures Open or Closed?Are Fractures Open or Closed?

Sou

rce:

N. B

arto

n an

d A

. Mak

urat

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Rough or Smooth Joints?Rough or Smooth Joints?

Sou

rce:

N. B

arto

n an

d A

. Mak

urat

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MBDCI

Different Joint SetsDifferent Joint Sets

Sou

rce:

N. B

arto

n an

d A

. Mak

urat

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MBDCI

Limestones and SandstonesLimestones and Sandstones

These are generalizations only: specific rocks must be measured

character Sandstone Limestone

porosity generally 15%~30% generally 5%~15%

permeability 50-5000 md 10-100 md

pore patterns all interparticle poresmainly interparticle, but other patterns also very important

impact of fractures not important very important

the relation between porosity and permeability

high agreement generally no agreement

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Closure & HysteresisClosure & Hysteresis

Slate

Dolomite

Limestone

Continued closure with cycles

Hysteresis

No

rma

l Str

ess

- M

Pa

Mechanical aperture - micrometers

-What is the behavior of a joint under normal loading?-Is the joint rough or smooth?-How is the permeability changed?

Bandis - 1990

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Deep Fractured CarbonatesDeep Fractured Carbonates

Kuwaiti fractured carbonates reservoirs for CO2 sequestration are of interest

World distribution of carbonate rocks

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Depth range is also excellent…Depth range is also excellent…

To 10 km depth Fractured

carbonates Sandstones Huge storage

volumes exist EOR potential as

well…

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High porosity clastics (sandstones)}Fractured carbonates}

} Too deep and low porosity?

} Too shallow?

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COCO22 in the Lower Fars? in the Lower Fars?

Shallow reservoir – 100 – 250 m

CO2 will be a gas, not a liquid

After thermal EOR, CO2 can be used for inert gas injection, enhancing drainage, but…

Storage capacity is small

IRAQ

KUWAIT

Border

Lower Fars: Total Net Pay

Ratqa Field

0’

10’

20’

50’

30’

40’

Pilot 1

Pilot 2

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Inert Gas Injection (Inert Gas Injection (ΔρΔρ process) process)

dm

oil

gas

waterp

Generally, it is a top down displacement process,

gravitationally assisted and density stabilized

Note: in a water-wet reservoir,a continuous 3-D oil film exists,

providing that wg > og + wo

Gas is injected high in the reservoir to move the oil

interface downward

Recovery % can be high

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IGI, With Reservoir StructureIGI, With Reservoir Structure

oil bank, two-phase zonewater-wet sand

horizontal wellsparallel to structure

inert gas injection

keep p to a minimum

gas rates are controlled toavoid gas (or water) coning

three-phase zone

if coning develops,drop pressures!

best to monitorthe process;

mainly gas

water,one phase

p

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Zubair SandZubair Sand

Top = -1500 m Pressure = 15 MPa Storage capacity is

vast Good porosity,

good permeability

ShuaibaShuaiba

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Zubair SandstoneZubair Sandstone

Although it is a huge reservoir, it may not be a candidate everywhere for large-scale CO2 sequestration. Why?

-There is no oil in the Zubair, but there is oil above (Burghan) and below (Ratawi)

-Apparently, the upper shaley sand & thin Shuaiba carbonate are fractured

-Hence, we would have to rely on seals at the top of the Burghan sandstone

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SabiriyahSabiriyah

RaudhatainRaudhatain

N

KUBER ISLAND

UMM AL-MARADEM ISLAND

QAROH ISLAND

Bahrah

Khashman

Medina

Abdali

Dharif

Wafra

Umm Gudair

Abduliyah

Minagish

AL-KHIRAN

SE Ratqa

Ratqa

GreaterBurgan

FAILAKA ISLAND

Saudi Arabia

Iraq

Kuwait

Arabian Gulf

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How do We Rank Candidates?How do We Rank Candidates?

Kuwait has many options for CO2

Geological data varies from highly quantitative to qualitative

Some scheme is needed to rank reservoirs as candidates

A methodology is presented here The variables and weighting factors

must be chosen appropriately…

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Limestones – Fabric - ScaleLimestones – Fabric - Scale

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DisqualifiersDisqualifiers

A set of absolute disqualifiers is chosen An open fault at the crest of the structure Too shallow for SC-CO2 placement No top seal (e.g. fractured cap rock) Other criteria as well…

If the candidate fails on any disqualifying factor…

It is rejected for CO2 placement Uncertain cases are downgraded

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Important Parameters - PImportant Parameters - Pii

Volume (porosity), thickness, dip… Permeability Depth and temperature Presence of oil (EOR) Proximity to CO2 source Stress conditions (reservoir, cap rock) Reservoir condition

Penetrating wells and seal quality (t, k…) And so on…

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Geomechanical Earth ModelGeomechanical Earth Model

Yo

ung

’s M

od

ulu

s -

MP

a

FaultsHeterogeneity

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EXAMPLE ONLY!

PPii - Parameter Classification - Parameter Classification

Z - Depth Range Class Value

Less than 800 m 0

800 – 1200 m 1

1200 – 2000 m 3

2000 – 3000 m 5

> 3000 m 2

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Sandstones - HeterogeneitySandstones - Heterogeneity

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Weighting Coefficients…Weighting Coefficients…

Each parameter is weighted according to its importance

For example, 2 will have a high weight (1.0) because its impact is great

D – distance from CO2 source – might be weighted as 5 = 0.2

Then, W is calculated = ∑ i·Pi ...DEORVkZW 654321

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Weighting Coefficient Choice…Weighting Coefficient Choice…

Choices for i will be different for different areas

One way to choose values is… Convene a small panel of experts

(geology, reservoir, geomechanics…) Let them choose a set of i values

Now, using the i values, we can look at the robustness of the classification (candidate ranking outcomes)…

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Statistical EvaluationStatistical Evaluation

Values of i are statistically varied (e.g. i = 0.5, varied from 0.3 to 0.7

Also, different parameter classes can be chosen (see depth example…)

Then, the robustness of the outcomes can be studied

This allows the best candidates for CO2 use to be identified

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COCO22 Hydrates… Hydrates…

T.H

. Kw

an

, Geo

gia

Tec

h

What about phase changes?

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Final CommentsFinal Comments

The geological model is fundamental to the choice of sequestration candidate

Many geological factors are difficult to quantify (e.g fracture intensity)

A scheme was presented to extract a semi-quantitative ranking of candidates

Of course, Kuwait is blessed with many excellent candidates…

Let the studies begin…