The GEODISC Program: Research into Geological Sequestration of CO2 in Australia

© 2001,

AAPG/DEG

, 1075-9565/00/$15.00/0Environmental Geosciences, Volume 8, Number 3, 2001 166–176

166

E N V I R O N M E N T A L G E O S C I E N C E S

The GEODISC Program: Research into

Geological Sequestration of CO

2

in Australia

JOHN BRADSHAW* and ANDY RIGG

‡

*

Australian Petroleum Cooperative Research Centre, Australian Geological Survey Organisation, GPO Box 378, Canberra ACT 2601, Australia

‡

Australian Petroleum Cooperative Research Centre, GPO Box 463, Canberra ACT 2601, Australia

ABSTRACT

The GEODISC research program is being jointly funded by the

Australian government and several of the nation’s gas producers.

It is designed to address key technical, commercial, and envi-

ronmental issues associated with geological sequestration of CO

2

in Australia. Some of the largest point source emitters of CO

2

in

Australia are liquefied natural gas (LNG) plants. As some of the

gas fields to be developed in the near future have higher CO

2

content than currently producing fields, emissions are projected

to increase. GEODISC is currently in year two of its planned

4-year program. The results of the research will have application

both within Australia and internationally. The work is being done

initially at a regional scale, examining all potential sedimentary

basins in Australia, followed by detailed analysis at the most

promising sites. Comparison of the sites at the regional scale is

being done using deterministic risk analysis. Data from Austra-

lian reservoirs show large variance to that used in the published

reservoir simulations from Europe. As such, research is being

focused into topics, such as storage efficiency, that are consid-

ered critical to the successful implementation of the findings

from GEODISC. Results to date indicate that there is excellent

potential to sequester CO

2

in all of the major sedimentary basins

of Australia. Estimates to date from only 49 sites (ignoring the

specific economic viability of individual sites), indicate that

there is a risked total pore volume capacity to store 1000 times

the annual (1998) emissions of CO

2

for Australia. The actual

total capacity value of sedimentary basins to sequester CO

2

is

likely to be several orders of magnitude higher than this figure.

Key Words:

Australia, GEODISC, sequestration, CO

2

, storage

efficiency, risk.

INTRODUCTION

Following the Conference of Parties to the FrameworkConvention on Climate Change in Kyoto in December1997, the outcome for Australia’s commitment to green-house gas emissions was an allowance of 8% growth in totalemissions (expressed as CO

2

equivalents) above 1990 lev-els. Despite being an increase, this allowance represents aconsiderable challenge and requires Australia to implement

•

•

strategies for reducing emissions from existing operationsand to restrain those for planned developments. The Austra-lian Greenhouse Office (AGO) has indicated on their web-site that Australia’s net greenhouse gas emissions in 1990were 389.8 million tonnes CO

2

equivalent, growing to455.9 million tonnes CO

2

equivalent in 1998. With the addi-tion of emissions due to land clearing, these numbers are493.3 and 519.9 million tonnes CO

2

equivalent, respec-tively.

GEODISC is a jointly funded program between the Aus-tralian government and most of the major gas producers inAustralia, and is examining the potential for geological se-questration of CO

2

in Australia. Cook et al. (2000) providesa detailed description of the objectives of GEODISC andthe rationale for considering geological sequestration inAustralia. GEODISC is being conducted through the Aus-tralian Petroleum Cooperative Research Centre (APCRC),which comprises both government and university geologi-cal research centers. Funding for GEODISC comprises al-most A$2.5 million per annum of cash and in-kind contribu-tions.

PROGRAM OUTLINE

GEODISC commenced on July 1, 1999 after extensiveconsultation with industry regarding the issues, priorities,and available data. Wherever possible international researchand development experience is being applied and modifiedto suit the conditions that prevail in Australia. An exampleof this is the current reexamination of the critical factor ofstorage efficiency that will be discussed in detail later.

The first phase of the program is the identification ofthose geological formations in each sedimentary basin withthe most appropriate parameters to sequester large volumesof CO

2

. The parameters include the physical characteristicsof the target reservoir and seal formations, and also the tem-perature, structural setting, stress regime, and hydrogeologyof the surrounding basin that directly affects those forma-tions. The major output from this work will be injectivitymaps for each sedimentary basin.

The second phase of GEODISC will involve more de-tailed studies at specific sites within key basins. This willinclude prediction of CO

2

-trapping mechanisms from mod-eling of the water-CO

2

-rock interactions, economic model-

B R A D S H A W A N D R I G G : T H E G E O D I S C P R O G R A M

167

ing for transportation, compression and injection, examin-ing technology for monitoring the movement of the CO

2

,and investigation of any environmental or safety issues.Physical and chemical attributes of Australia’s naturally oc-curring CO

2

accumulations will also be studied in supportof these predictions.

GEODISC thus comprises 10 specific projects, being:

1. regional analysis2. site-specific analysis3. CO

2

reactions and coupled model development (masstransport)

4. petrophysics and geomechanics5. reservoir simulation (mass flow)6. monitoring7. risk and uncertainty8. economic model9. international collaboration

10. natural analogs

As can be seen from Figure 1 the main projects that havebeen operating to date and producing results includeProjects 1, 2, 3, 8, and 9. This article will focus on some ofthe general outcomes from the existing research, but willnot deal with specific sites that have been examined as thesecurrently are subject to confidentiality arrangements withthe sponsoring group.

Geological Options for CO

2

Sequestration

Figure 2 shows the various geological settings where CO

2

might be sequestered. The options include the use and stor-age of CO

2

in

1. enhanced oil recovery2. enhanced coal seam methane recovery3. depleted oil and gas reservoirs4. deep unmineable coal seams5. large voids and cavities6. deep unused saline water saturated reservoir rocks

For various reasons, described below, some of these op-tions have no or limited application within the geologicalsettings in Australia. The application of each concept fo-cuses on the technical, social, environmental, and economicviability as it relates to Australian conditions.

Enhanced Oil Recovery

Enhanced oil recovery (EOR) using injected CO

2

hasbeen practiced in the oil industry for several decades. Inplaces such as the Permian Basin in Texas, CO

2

is a valu-able resource that is piped hundreds of kilometers from Col-orado to be injected into oil fields to increase the recoveryof oil (Holtz et al., 2001; Stevens et al., 2001). However, inAustralia most of the crudes are light with good reservoircharacteristics, strong water drives, and high recovery fac-

FIGURE 1: GEODISC project timetable.

168


tors, thus reducing the potential target volumes left in theground. In 1990, the volume of remaining oil that could berecovered in Australia using CO

2

floods was estimated asbeing 709 million barrels at oil prices of US$20 per barrel(Wright et al., 1991). The amount of CO

2

that would be re-quired to recover this 709 million barrels of currently eco-nomically recoverable oil would be of the order of 100–200million tonnes CO

2

. The actual sequestration capacitywould depend on the details of each CO

2

EOR flood and onwhether an economic credit was available for CO

2

seques-tration.

To recover the additional technically feasible but cur-rently uneconomic EOR potential (1733 million barrels;Wright et al., 1991) would more than double the amount ofCO

2

that could be sequestered in the process of EOR. AfterEOR flooding was complete, additional CO

2

might be se-questered by continuing to flood the depleted reservoirs totheir spill point. To realize this sequestration potentialwould require access to major sources of CO

2

for Austra-lia’s larger oil fields. This would include capture of CO

2

from flue stacks from La Trobe Valley coal-fired power sta-tions for injection into the Gippsland Basin oil fields and re-injection of CO

2

from Gorgon and other gas fields into oilfields in the Carnarvon Basin.

Enhanced Coal Seam Methane

Enhanced coal seam methane (ECSM) is an industry thatis rapidly developing in North America (Gale and Freund,2001), but in Australia it is still is in its infancy. When CO

2

is injected into coal beds containing methane, the CO

2

willpreferentially adsorb onto the coal, theoretically releasing

two methane (CH

4

) molecules for each CO

2

molecule. In pi-lot studies this has been shown to be at least three methanemolecules for each CO

2

molecule (Gale and Freund, 2001).In this way, injected CO

2

can enhance methane productionfrom coal seams while sequestering CO

2

at the same time.Stevens et al. (1999, 2001) reported that the Bowen Basin inAustralia rated highly in the world for ECSM.

However, most of the ECSM activity is along the easterncoast of Australia, whereas the majority of CO

2

productionfrom the liquefied natural gas (LNG) industry is on the west-ern coast, which are thousands of kilometers apart. There iscertainly potential for ECSM to become a viable option forsequestering CO

2

; however, it will rely on technology to re-move CO

2

from coal-fired power plants (Holtz et al., 2001),and the potential storage volumes may be small comparedto the supply. Early investigations suggest that there may beproblems with the economic viability of projects wherelarge numbers of wells (hundreds) would be required tomatch the supply of CO

2

from coal-fired power plants.

Deep Unmineable Coal Seams

In a similar way to ECSM, CO

2

can be injected at depthinto coal seams that are unlikely to be mineable in the nearto long-term future. The CO

2

will adsorb onto the coal andbe stored. Australia is richly endowed with coal, especiallythroughout eastern Australia, and potentially this is a viableoption (Figure 3). However, discussion with state geologi-cal agencies suggest that the depths required to inject theCO

2

without potentially sterilizing the future mining poten-tial of the coal resource will, in some basins such as theSydney Basin, be in the order of 600 to 1000 m. At the up-

FIGURE 2: Options for the geological disposal of CO2 (from Cook, 1998).


169

per range of depths it is dubious as to whether there will besufficient permeability in the coal seams to allow injectionof the CO

2

at either a rate to match the supply of CO

2,

or at acost that would be economic. Injection into sandstone unitsunderlying coal seams in this situation, however, may be anoption requiring further study.

Depleted Oil and Gas Reservoirs

As documented in the Joule II report (Holloway et al.,1996; also see “Storage Efficiency”), depleted oil and gasreservoirs offer one of the more viable and secure optionsfor sequestration of CO

2

. Depleted fields have a known vol-ume of recovered hydrocarbons, thus allowing accurate esti-mates of the maximum available pore volume into whichCO

2

can potentially be stored, and they are known to havebeen successful in securely storing hydrocarbon gases andfluids over geological time periods (millions of years). Tomaximize the storage potential, it is probable that there willbe a benefit from injecting CO

2

into fields that are pressure-depleted rather than water drives. Pressure-depleted fieldsprovide the opportunity to inject CO

2

into lower pressurereservoirs than would exist under normal geological condi-tions. During depletion of water drive fields, the pressurereequilibrates to normal geological conditions as groundwater flows in to replace the produced hydrocarbons, thusmaking injection pressures higher than in pressure depletionfields. Reservoir simulation in GEODISC will enhance theunderstanding of the way the various parameters and per-mutations of injection and storage capacity interact.

Unfortunately for CO

2

sequestration, Australia has a pre-ponderance of water drives in many of its largest hydrocar-bon accumulations. However, there are many viable loca-tions such as the Cooper Basin in South Australia wherepressure depletion is normal and many fields such as Gidgealpa

are near or already depleted. In terms of volume, however, Fig-ures 4 and 5 (gas and oil depletion curves for Australia) showthat Australia does not have many large fields (either gas or oil)that will be depleted in the near future, and those that will be-come depleted are not near major CO

2

sources.

Large Voids and Cavities

In Australia there are no mining activities for salt thatwould produce large voids in salt caverns, such as exist inNorth America. Calculations for voids in abandoned under-ground coal mines suggest that the volumes available permine are very small (

�

0.5

�

10

6

T of CO

2

), and hard rockmines are even smaller. When combined with their often iso-lated location, they are not considered likely to be economic.Of greater concern, however, is that many underground min-ing activities in Australia use long-wall techniques, which bydesign fracture the roof during collapse. The issue of CO

2

containment risk due to fracturing would pose significantproblems, as would the shallow depth of the mines and manyadits and drill holes that penetrate them, all of which couldprovide conduits for CO

2

to escape to the surface.

Deep Unused Saline Water-SaturatedReservoir Rocks

Deep saline reservoirs are widely recognized as being themost viable option for sequestration of CO

2

in terms of costand capacity in Australia, as well as internationally (Linde-

FIGURE 3: All basins with reported coal seams in Australia.

FIGURE 4: Gas depletion curves for Australia, both onshore and offshore (suppliedby AGSO—Petroleum Technical Advice Group, D. Wright and S. Le Poidevin).

FIGURE 5: Oil depletion curves for Australia, both onshore and offshore (suppliedby AGSO—Petroleum Technical Advice Group, D. Wright and S. Le Poidevin).

170


berg and Holloway, 1999). It utilizes existing experienceand technology developed in the oil and groundwater indus-tries for modeling the behavior of fluids in the subsurface.Australia has over 300 known sedimentary basins, of whichat least 200 are over 1000 m thick (Figure 6). Of these over50 could be considered viable sites for study in terms of lo-cation (near CO

2

source and acceptable water depth) andgeological characteristics.

GEODISC has completed preliminary analysis of the 17most significant petroleum provinces from both onshoreand offshore Australia, and by mid-2001 will have exam-ined the remaining basins with CO

2

sequestration potential.The initial results indicate that many of the reservoirs inAustralia have very favorable characteristics when com-pared to other petroleum provinces of the world (Figure 7).The risked total available pore volume of CO

2

for the 49 in-dividual sites from the 17 basins studied from Project 1 (i.e.,the summed capacity of local sites, not total basin wide ca-pacity, and risked for uncertainty and chance of success andignoring the economic viability of individual sites) is ap-proximately 4.5

�

10

11

T (

�

8400 Tcf) of CO

2

. The total ca-pacity available, if basin wide sites are considered, will bemany orders of magnitude higher than this figure. Giventhat Australia’s net total annual CO

2

emissions are in the or-

der of 500

�

10

6

T (

�

9.3 Tcf), it is apparent why this op-tion is attractive.

TERMINOLOGY, METHODOLOGY, AND FURTHER RESEARCH

In the course of establishing GEODISC and Project 1across a vast and diverse geological province like Australia,numerous conceptual issues and problems required resolu-tion. These included:

•

how to describe suitable sites for study;

•

how to compare and contrast each of the sites for thepurpose of ranking them; and

•

identifying and addressing critical factors that were un-certain or unknown, and that had the potential to limitthe implementation of the findings of GEODISC.

Following are three brief examples of what has been donein GEODISC so far on these issues:

•

establishing appropriate terminology (ESSCIs);

•

modifying oil industry methodology (prospect and playrisk assessment); and

•

research that needs verification (storage efficiency).

FIGURE 6: Sedimentary basins map of Australia showing sites that have been examined in stages 1 and 2 of Project 1, and basins being examined in stage 3.


171

Terminology: Environmentally Sustainable Site for Carbon Dioxide Injection

The literature on geological sequestration sometimes has dif-ficulty describing the various conceptual options (as outlinedabove) as to what type of site is being described, be it either areservoir, aquifer, or coal seam. Different authors alternate be-tween these descriptions depending on what they believe to be

the natural resource into which they are considering injectingCO

2

. For this reason, and to minimize potential communityconcern that an established resource may be sterilized, a neutralterm, “environmentally sustainable site for carbon dioxide in-jection” (ESSCI), has been used as described below.

Within the oil exploration industry the term “prospect”relates to an individual site where hydrocarbons are be-

FIGURE 7: Kv vs. Kh for Australian reservoirs. Data is from 1626 data points from core plugs from 52 wells from Papuan, NW Shelf, and Gippsland Basins (from AGSORESFACS database).

172


lieved to have accumulated. The term “play” is used to de-scribe the interaction of reservoir, seal, source, trap, and rel-ative timing, which combine to create a variety of similarhydrocarbon accumulations across a region. A group ofclosely related plays are also referred to as a hydrocarbon orpetroleum system, often being described as the source rockand all its known hydrocarbon accumulations (Magoon andDow, 1994). Within the groundwater industry, “reservoirs”are referred to as “aquifers.” For the purpose of sequesteringCO

2

, it was thought inappropriate to use the terms “play,”“reservoir,” or “aquifer” as it may give the false impressionthat an existing resource was potentially going to be com-promised. As such the term ESSCI was derived. HenceESSCI can be used in the same way for grouping the vari-ous components of a CO

2

injection site, as “play” or “pros-pect” is used for the oil exploration industry.

Methodology: Risking

To assess the potential ESSCIs over an area the size ofAustralia at a regional scale, it was necessary to develop amethodology that would allow both the capture of detailedanalyses for each ESSCI site, as well as maintaining rigorand consistency to allow comparison between ESSCIs. Theapproach adopted was to modify the “play and prospect”risk assessment that has been used in the oil exploration in-dustry for many decades. This risking scheme follows thewell-documented principles of White (1987). It has beenmodified in a similar fashion to that documented in Austra-lia in an example by Bradshaw et al. (1998). In this exam-ple, the risking approach was applied to both the conven-tional area of petroleum exploration, as well as to anexample of site selection for quarries in the hard rock indus-try. Despite that the factors that needed to be assessed werecompletely different, and included social and environmentalissues, the consistent approach required by the methodologymeant that it was readily adaptable and meaningful resultscould be used to compare and contrast each site. For theESSCIs, a similar approach was adopted to that used for thehard rock industry, with a mix of geological, engineering,economic, and social factors being assessed.

Five factors were chosen to describe an ESSCI, each ofwhich have subelements that are considered when assessingthe risk, mostly from a geological viewpoint. The factorsused are all rated between 0 and 1, with 0 meaning that thefactor fails and 1 meaning that the factor works. The factorsare as follows.

1.

Storage capacity.

The chance that the reservoir willmeet the volume requirements of neighboring, currentlyidentified CO

2

sources, given consideration of tempera-ture, pressure, capacity, radius of 1 Tcf (53.65

�

10

6

T)of CO

2

if injected at the site, area, pore volume.

2.

Injectivity potential.

The chance that the reservoir con-ditions will be viable for injection given considerationof porosity, permeability, thickness.

3.

Site details.

The chance that the site is economically andtechnically viable given consideration of distance toCO

2

source, water depth, ESSCI depth, overpressure.4. Containment. The chance that the seal and trap will

work for CO2 given consideration of seal capacity andthickness, trap, faults.

5. Existing natural resources. The chance that there areno viable natural resources in the ESSCI that may becompromised, such as proven or potential petroleumsystem, groundwater or coal, or other natural resource(e.g., national park).

These ESSCI factors are mostly independent of one an-other, but each is a required condition to successfully se-quester CO2. This means that if one of them does not work(fails) then none of the others are relevant, as the chancethat the ESSCI will fail is certain. Because the ESSCI fac-tors are independent, they can be multiplied through to getvarious factors, and then multiplied against the estimatedstorage volume or capacity to get a risked capacity. This is avaluable tool in comparing different ESSCIs in different ba-sins. An example may be where two ESSCIs have the samerisk capacity, with Site A having a low geological risk andsmall capacity, whereas Site B has a high geological riskand a high capacity. In such a case, provided the high geo-logical risk in Site B was not due primarily to containment,then Site B may be the preferred site for further study as itwould offer the largest potential. The multiplied factorsused in this study are as follows.

ESSCI chance: product of all five individual ESSCI factorsrisked capacity: ESSCI chance � total estimated storage

capacity of CO2

ESSCI rating: ESSCI chance/radius of 1 Tcf (53.65 � 106 T)CO2 at the site

The ESSCI chance is the product of all five ESSCI fac-tors. The lower the ESSCI chance the greater likelihood thatit will fail. Thus an ESSCI chance of 0.2 means that it has aone in five chance, or 20% chance, of working. It is impor-tant to remember that these riskings are not actual but rela-tive and are used to create a seriatim of what is best andwhat is worst among a variety of ESSCIs. When doing therisk assessment, it is important to distinguish at which scaleattributes are being risked: whether they are from the viewof a regional concept of the ESSCI, or the play level, or atthe local or prospect level.

The risked capacity is a product of the ESSCI chance andthe total estimated storage capacity of CO2 that is likely tooccur at the site or across the region that the ESSCI can bedefined within.

B R A D S H A W A N D R I G G : T H E G E O D I S C P R O G R A M 173

The ESSCI rating utilizes a calculation made at the sitethat determines the radius out from the injection site that 1Tcf (53.65 � 106T) of CO2 will disperse, given factors suchas the reservoir quality and thickness, depth, pressure, andtemperature. This is simply an estimate of the theoreticalcylinder that the injection bubble would form, not the actualshape of the bubble at each site, and is used only for com-parison purposes. Where the radius is low, this means it is abetter result as there is less likelihood of the CO2 spreadingfar from the site. This in turn means there is less chance ofCO2 spilling away from and outside closure of the trap, orencountering lateral variations in reservoir conditions orseal, or intersecting fault planes that may act as conduits tothe surface and breach the trap. Thus where there is lesschance of the ESSCI failing (a high ESSCI chance number)and a low radius, the ESSCI rating will be very high. There-fore, the higher the ESSCI rating, the better the sequestra-tion potential of the site.

Further Research: Storage EfficiencyAs was predicted in the initial planning of GEODISC,

many topics surfaced at the beginning of the project that hadthe potential to influence a successful outcome. One criticaltopic is that of rates, be it either rates of migration, mineral-ization, or injection. However, at this stage in GEODISC,the largest uncertainty is that of storage efficiency and theactual volume of CO2 that can be injected into a reservoir.

The Issuevan der Meer (1993, p. 966) stated that:

it is extremely difficult to predict any total CO2 storagevolume. . . . Present calculations regarding the storageefficiency of an aquifer are subjective due to the lack ofdefinition of the total pore volume available for CO2

storage.

and van der Meer (1995, p. 513)

There are two problems associated with the storage effi-ciency of aquifers. The main one is the impossibility ofarriving at one number that is universally valid, becausethe conditions in the subsurface are too diverse. Theother problem is that even if such a number is arrived at,people are likely to misuse it.

However, despite these warnings, numerous reviews ofCO2 sequestration potential have simply requoted the earlywork with no apparent case-specific analysis of the actualreservoirs at their proposed site. This raises a concern thaterroneous assumptions potentially may have been made insome CO2 injection scenarios. Because the early work pro-duced very low (2%) percentages (van der Meer, 1993,1995), this could mean that the volume of CO2 that can besequestered in the subsurface is vastly underestimated. Forvery large gas fields with high CO2 contents, such as thosecontaining over 1 Tcf/53.65 � 106 T of CO2, it could lead to

the assumption that no single structure will be capable of se-questering the CO2 that it produces. Such an analysis couldaffect the viability of an entire project, as multiple injectionsites for a single CO2 source in an offshore setting, wouldmake projects cost-prohibitive.

Storage Efficiency FactorsMost analyses of CO2 storage efficiency are based on res-

ervoir simulation modeling with several factors affectingthe result to varying degrees, including the following.

• Reservoir properties: porosity, permeability (horizontaland vertical)

• Reservoir conditions: temperature, pressure, depth• Mobility ratio of CO2 vs. water: the greater the depth

the lower mobility ratio and the higher the storage effi-ciency (van der Meer, 1995)

• Open or closed hydrological regime: affects ability toinject CO2

• Injection rate: the slower the rate the higher the storageefficiency (modeled on dipping reservoirs, 10�) (Holt etal., 1995)

• Supply rate from source: impacts on the number ofwells and the injection rate

• Number of wells used for injection: requires trade-offof cost vs. injection rate vs. supply rate vs. storage effi-ciency

• Gravity segregation: relates to dip and height of closureon structure

• Type of trap: the higher the dip the greater the storageefficiency (Holt et al., 1995), four-way dip anticlinesimply shallow dip, fault-related structures imply higherdip, salt piercement features imply higher dip, hydrody-namic (no meaningful assessment of storage efficiencycan be made especially if the system is open)

• Type of drive: water (lower storage efficiency), pres-sure depletion (higher storage efficiency and preferred)

• Residual water saturation

Simulation Resultsvan der Meer (1992, 1993, 1995) and Holt et al. (1995)

documented a series of reservoir simulations. The principalresult from van der Meer (1992), using geological parame-ters from the Netherlands, was an estimate that only 2.28%of pore space (product of 3.05% 2-D volumetric sweep effi-ciency and 75% horizontal sweep efficiency) would be oc-cupied by CO2 before it escaped through the spill point of atrap. The simulations were work undertaken in conjunctionwith the Joule II Project (Holloway et al., 1996). From theresults of these studies the Joule II report applied a series ofconstraints for their assessment of the sequestration capac-ity of reservoirs/aquifers, being

174 E N V I R O N M E N T A L G E O S C I E N C E S

For aquifers: Unless known otherwise, the storage effi-ciency of the aquifer is assumed to be 6% in aquifersthat are in open communication with the ground sur-face, and 2% in aquifers that are closed (commonly butnot in every case, identified by overpressure). A storageefficiency of 4% will be used where it is not knownwhether the reservoir is open or closed.

For gas fields: The volume of the initially recoverable re-serves is available for storage of CO2.

For oil fields: The volume of the initially recoverable re-serves can be replaced by CO2.

While it is apparent that the 2% value comes from van derMeer (1992), it is not immediately obvious from where 6%is derived. A range of 1–6% is mentioned in van der Meer(1995), but the 6% figure only appears in the conclusion andnot in the substance of the paper. A possible implicationfrom the wording in the Joule II report is that the work con-ducted by van der Meer was on closed systems rather thanopen systems. If they were closed, as many North Sea fieldsare, then low rates of storage efficiency would be expected.If that is the case then the upper range of 6%, and how itwas derived, assumes considerable importance.

Holt et al. (1995) simulated work associated with EORusing CO2 in a water-flooded reservoir. In contrast to thework of van der Meer (1992, 1995), they obtained storageefficiency rates of 13–68% of pore volume (PV). Their sim-ulation examined varying injection rates, permeability, anddip of the reservoir. Injection rates of 0.4% PV/year gavehigh storage efficiency (�30%) and at 1.6% PV/year gave16% storage efficiency. By varying the absolute permeabil-ity, Kv/Kh, and relative permeabilities, while keeping theinjection rate constant (1.6% PV/year), they achieved arange of 13–26% storage efficiency (Figure 8)

Simulation Assumptions vs. Australian ConditionsNumerous assumptions were made in the documented

simulations, including reservoir conditions where Kv/Kh ra-tio ranged from 0.01 to 0.1 (van der Meer, 1992, 1995) and0.04–0.004 (Holt et al., 1995). This implied that CO2 wouldmigrate laterally rather than vertically after injection intothe reservoir. The properties for Australian reservoirs indi-cate that the modeled Kv/Kh ratio represents the lower 2%of Australian reservoir conditions (Figure 7).

Some of the simulation studies have highlighted a prefer-ence for steeper dips to maximize storage efficiency; how-ever, in practice such structures will normally be fault-re-lated features not four-way dipping anticlines. Fault-relatedstructures have a risk of loss of containment because of thepotential for leakage of CO2. Even in depleted gas fieldswith faults in the trapping style, uncertainty exists as towhether the fault systems will seal CO2, especially if car-

bonate cements are present in the fault zone. This will bespecifically addressed during the GEODISC program.

From these simulations a number of questions requireconsideration in terms of how the various studies should beinterpreted, being either mutually exclusive or complemen-tary. Perhaps more importantly for GEODISC, how do theyapply to Australian reservoir examples given the large vari-ance in permeability? The answer we believe is to do ourown specific reservoir modeling.

Reservoir simulation is a case-specific task and no uni-versal number for storage efficiency can be derived. Numer-ous factors including depth, reservoir parameters, supplyand injection rate, remaining fluids, and pressure regimewill all influence the result of the simulation.

CONCLUSIONSThe work being undertaken in GEODISC will develop a

portfolio of potential CO2 sequestration sites for the majorsedimentary basins of Australia. Fundamental research top-ics that are critical to successful sequestration of CO2 willbe undertaken as detailed work is conducted in the more fa-vorable locations. To adequately assess the sequestrationpotential at a continent-wide scale, methodologies such asrisk assessment are being applied with development of a se-riatim for the most favorable locations. The results of thesestudies will have both local and international impact on theviability of CO2 sequestration. Results to date indicate thatthere is excellent potential to sequester CO2 in all of the ma-jor sedimentary basins of Australia. Estimates to date fromonly 49 sites (ignoring the specific economic viability of in-dividual sites) indicate that there is a risked total pore vol-ume capacity to store over 1000 times the annual (1998)emissions of CO2 for Australia. The actual total capacityvalue of sedimentary basins to sequester CO2 is likely to beseveral orders of magnitude higher than this figure.

•

FIGURE 8: Adapted from Figure 3 of Holt et al. (1995) showing the equivalent CO2saturation versus injection rate. Note Holt et al.’s (1995) Figure 3 has x-axis as log10but it is actually log normal.

B R A D S H A W A N D R I G G : T H E G E O D I S C P R O G R A M 175

ACKNOWLEDGMENTSThe authors would like to acknowledge the sponsors of

GEODISC: Australian Greenhouse Office (AGO), BHP Pe-troleum (BHPP), BP, Chevron (Aust.), Chevron (Interna-tional), Shell, and Woodside. The agencies contributing toGEODISC include: Australian Geological Survey Organisa-tion (AGSO), Australian Petroleum Cooperative ResearchCentre (APCRC), Commonwealth Scientific Industrial Re-search Organisation (CSIRO), Curtin University, NationalCentre for Petroleum Geology and Geophysics (NCPGG),and the University of New South Wales (UNSW). Consider-able contributions and discussions were provided from re-searchers from the agencies named above, who are currentlyworking on the GEODISC program, including; Barry Brad-shaw, Jonathon Ennis-King, Steven le Poidevin, VictoriaMackie, Lincoln Paterson, Lynton Spencer, and Denis Wright.

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176 E N V I R O N M E N T A L G E O S C I E N C E S

ABOUT THE AUTHORS•John Bradshaw

John Bradshaw is project manager of

Project 1 (Regional Analysis) in the GEO-

DISC research project at the Australian Pe-

troleum Cooperative Research Centre. He

has a B.Sc. (Honors) and Ph.D. in Applied

Geology from the University of New South

Wales. John is an exploration technologist

with a regional knowledge of Australian

sedimentary basins and is employed as a principal research scientist

at the Australian Geological Survey Organisation. He has also

worked for Esso (Aust.) and on staff exchange for a year with WMC

Petroleum and Ampolex/Mobil. He has extensive fieldwork experi-

ence throughout central Australia and Papua New Guinea, where he

consulted for several years. John has previously run major industry-

funded research projects examining the petroleum systems of Austra-

lia. He is a member of GSA, PESA, and AAPG.

Andy RiggAndy Rigg is the program manager for

the GEODISC research program with the

Australian Petroleum Cooperative Re-

search Centre (APCRC) and is based in

Sydney. He has a B.Sc. andB.Sc. (Honors)

in Geology (University of Sydney and Uni-

versity of Tasmania). He has 30 years of

experience in the oil and gas industry. He

was geological manager for Esso Australia before becoming general

manager of exploration with Santos. From 1985 to 1997 he was gen-

eral manager of exploration for Ampolex Limited. He has been non-

executive director for several listed Australian oil and gas companies

and occupies this position for Timor Sea Petroleum NLNatural Gas

Australia Ltd. and Methanol Australia Pty Ltd. He is a member of

PESA (past federal president and distinguished member).

The GEODISC Program: Research into Geological Sequestration of CO2 in Australia

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