Scholarly article on topic 'CO2 storage capacity estimates for selected regions of China - results from the China-UK Near Zero Emissions Coal (NZEC) Initiative'

CO2 storage capacity estimates for selected regions of China - results from the China-UK Near Zero Emissions Coal (NZEC) Initiative Academic research paper on "Earth and related environmental sciences"

CC BY-NC-ND
0
0
Share paper
Academic journal
Energy Procedia
Keywords
{"CO2 storage capacity" / Songliao / Subei / China}

Abstract of research paper on Earth and related environmental sciences, author of scientific article — J.M. Pearce, M. Li, S. Ren, G. Li, W. Chen, et al.

Abstract This paper presents an overview of some recent CO2 storage capacity assessments in the Songliao and Subei Basins in China, and a discussion of some of the specific challenges that must be addressed to further assess the feasibility of CO2 storage in China. Geological CO2 storage associated with CO2-EOR is of significant interest in these basins as it offers potential to increase oil production and provide additional fuel to meet China’s increasing energy consumption. Although some CO2 is stored during such flooding projects, the greatest storage potential is only realised at the end of a field’s productive life, when a depleted field can be used as a dedicated CO2 storage reservoir. The Songliao Basin, in North-eastern China has been the largest oil and gas producing province in China. The oilfields of the Daqing and Jilin oil provinces are estimated to have effective CO2 storage capacities of 593 Mt and 71.2 Mt respectively. Extrapolation of data from around the oilfields to the whole basin suggests that the most promising saline aquifer in the basin has a theoretical storage capacity of 692 Mt CO2: Its effective storage capacity (which cannot be estimated due to lack of data) is likely to be considerably smaller however. Limited data availability means the estimate of storage capacity in this saline aquifer is based on gross simplifications and extrapolation across large areas (e.g. basin-scale) but could provide a basis for comparison with the potential for CO2 storage in other regions in China, or to help prioritise more detailed analysis. Although smaller, the onshore oilfields of the Subei-Yellow Sea Basin were also assessed, as the presence of mature oil and gas fields and natural CO2 accumulations, suggest suitable targets for storage may be found. The total effective storage capacity of the 108 hydrocarbon fields in this basin are estimated to be only 21 Mt CO2. While small, these fields may offer niche storage options for smaller industrial CO2 sources, but if CCS is to contribute to reducing China’s growing CO2 emissions, then further evaluation and development of storage in saline aquifers is likely to be needed at the same time as storage in oil or gas fields.

Academic research paper on topic "CO2 storage capacity estimates for selected regions of China - results from the China-UK Near Zero Emissions Coal (NZEC) Initiative"

Available online at www.sciencedirect.com

ScienceDirect

Energy Procedía 4 (2011) 6037-6044

Energy Procedía

www.elsevier.com/locate/procedia

GHGT-10

CO2 storage capacity estimates for selected regions of China - results from the China-UK Near Zero Emissions Coal (NZEC) Initiative

J.M. Pearcea*1Li, Mb, Ren, S.c, Li, G.d, Chen, W.e, Vincent C.J.a and Kirk, K.L.a

aBritish Geological Survey, Keyworth, Nottingham, NG12 5GG, UK

China University of Petroleum, Changping, Beijing 10224, PRC cChina University of Petroleum, DongYing Shandong 257061, PRC Insitute of Geology and Geophysics, CAS, Beijing 100029, PRC, e3E Research Centre, Tsinghua University, Beijing 100084, PRC

Abstract

This paper presents an overview of some recent CO2 storage capacity assessments in the Songliao and Subei Basins in China, and a discussion of some of the specific challenges that must be addressed to further assess the feasibility of CO2 storage in China. Geological CO2 storage associated with CO2-EOR is of significant interest in these basins as it offers potential to increase oil production and provide additional fuel to meet China's increasing energy consumption. Although some CO2 is stored during such flooding projects, the greatest storage potential is only realised at the end of a field's productive life, when a depleted field can be used as a dedicated CO2 storage reservoir.

The Songliao Basin, in North-eastern China has been the largest oil and gas producing province in China. The oilfields of the Daqing and Jilin oil provinces are estimated to have effective CO2 storage capacities of 593 Mt and 71.2 Mt respectively. Extrapolation of data from around the oilfields to the whole basin suggests that the most promising saline aquifer in the basin has a theoretical storage capacity of 692 Mt CO2: its effective storage capacity (which cannot be estimated due to lack of data) is likely to be considerably smaller however. Limited data availability means the estimate of storage capacity in this saline aquifer is based on gross simplifications and extrapolation across large areas (e.g. basin-scale) but could provide a basis for comparison with the potential for CO2 storage in other regions in China, or to help prioritise more detailed analysis. Although smaller, the onshore oilfields of the Subei-Yellow Sea Basin were also

* Corresponding author. Tel.: +44 (0)115 9363222; fax: +44(0)115 9363200. E-mail address: jmpe@bgs.ac.uk.

doi:10.1016/j.egypro.2011.02.608

assessed, as the presence of mature oil and gas fields and natural CO2 accumulations, suggest suitable targets for storage may be found. The total effective storage capacity of the 108 hydrocarbon fields in this basin are estimated to be only 21 Mt CO2. While small, these fields may offer niche storage options for smaller industrial CO2 sources, but if CCS is to contribute to reducing China's growing CO2 emissions, then further evaluation and development of storage in saline aquifers is likely to be needed at the same time as storage in oil or gas fields.

© 2011 Published by El sevier Ltd.

Keywords: CO2 storage capacity, Songliao, Subei, China

1. Introduction

China's expected reliance on coal as a principal fuel for power generation over the next few decades suggests that the potential for carbon capture and storage (CCS) as a future option to mitigate China's CO2 emissions should be evaluated. Establishing China's potential CO2 storage capacity would be a key element of this evaluation. Previous estimates of theoretical storage capacity [1] have been reconnaissance estimates at a basin-scale, simply allowing those basins with higher prospectivity to be targeted for further investigation. This paper summarises more detailed assessments of the carbon dioxide storage potential in oilfields and one saline aquifer in north-eastern China (Figure 1), which were undertaken as part of the Near Zero Emissions in China (NZEC) initiative.

The potential for CO2 injection to contribute to increased production from mature and depleting oilfields is a clear priority for field operators, both to maximise revenues (thus offsetting some of the costs of CCS) and to meet China's increasing energy demands. While CO2-EOR may store some CO2 during the flooding project, most storage potential is only realised at the end of a field's productive life, when a depleted field can be used as a dedicated CO2 storage reservoir.

Storage potential has been evaluated at two scales: firstly at a regional basin scale and secondly at a site-specific scale. At both scales, we have calculated the potential storage capacities in CO2-EOR schemes, and also by direct storage into saline aquifers. In order to ensure that the calculated storage capacities can be compared with other regions of China, and more widely, a consistent if simplistic, calculation method has been applied, based on that published by the Carbon Sequestration Leadership Forum [2].

Figure 1: Locations of the Songliao and Subei basins.

2. Methodologies

This study is based on public domain data acquired as result of oil and gas exploration and production. Consequently, in the Songliao Basin, data is limited to the hydrocarbon-bearing regions around Daqing and Jilin in the centre of the basin, and the immediately adjacent saline aquifers. Therefore, in order to estimate the saline aquifer CO2 storage capacity of the Songliao basin, a detailed capacity estimate was made for the best potential storage formation in terms of reservoir characteristics, in the area where most data is available. The results were then extrapolated to provide an estimate of capacity for the one aquifer in the whole basin - with corresponding significant uncertainty.

The storage capacity potential of the oilfields has been estimated using a Carbon Sequestration Leadership Forum (CSLF)-derived methodology [2]. This calculation assumes that the volume of recoverable oil reserves can be largely replaced with CO2. This is generally valid for pressure-depleted reservoirs that are not subject to water drive from surrounding aquifers, and/or where water-flooding has not been applied. Where water has invaded the reservoir, it is assumed that CO2 can displace some but not all of this fluid, and so in such fields the estimated storage capacity is reduced. For the simple calculations performed here, it was assumed that the reservoir pressure could be returned to the initial pressure as a result of CO2 injection. Though it can be assumed that CO2 will be injected into depleted reservoirs until the initial reservoir pressure is restored, in some cases it may be safe to increase the pressure beyond the initial reservoir pressure. However in other fields, reservoir damage during depletion may limit injection and prevent reservoir pressures returning to original values. The formula used here, including a discount to allow for irreversible water invasion, is as follows:

MC02D = Voil(SIP) X Bo X PCO2 X Scoeff (1)

MCO2D = estimated storage capacity (Mt)

VOiL(stp) = Volume of oil at STP (Mt converted to m3 using API value of oil which is typically 33API in the Jilin oilfield) Bo = Formation volume factor (Assumed to be 1.1) pCO2 = Density of CO2 in the reservoir (0.6 t/m3)

Scoeff = storage coefficient to discount for water invasion etc is assumed to be 0.4

The calculation of storage capacity for aquifers mainly depends on the estimated volume of the aquifer which lies within closed traps. The theoretical CSLF calculation assumes the pore space can be filled, except that occupied by irreducible water. The effective capacity considers the volume of closed traps, trap heterogeneity, irreducible water saturation and buoyancy coefficient. These capacity limiting factors were amalgamated into a single storage coefficient. The Carbon Sequestration Leadership Forum (CSLF)-based methodology [2] for storage capacity in aquifers is calculated using the following formula:

MCo2C = A X h x®x(1 - Swirr )

MCO2C = estimated storage capacity (Mt) A = area of the aquifer

h = average height of the aquifer x net:gross ratio ® = average porosity of the aquifer Swirr = irreducible water saturation

For the basin-scale assessments this was simplified to

MCO2C = A X h X®X Scoeff (3)

Where Scoeff is an estimated storage coefficient, which for regional scale calculations was assumed to be 2% [4].

3. Songliao Basin

The Songliao Basin is located predominantly within the Heilongjiang and Jilin provinces in Northeastern China. The Songliao Basin has been the largest oil and gas producing province in China for over 40 years with a current annual oil production of around 350 million Bbl. The potential for CO2 storage within oilfields of two large hydrocarbon provinces within the basin, the Daqing and Jilin oil

provinces, was determined. In addition, the regional storage capacity of a selected saline aquifer, the Qingshankou Formation, was estimated. Installed generating capacity in the area of this basin in 2005 was 6.4 GW. A total of 78 sources, including all power plants, iron and steel plants, oil refineries, ammonia plants and the largest cement plants, produce total annual emissions of around 70.5 Mt CO2.

3.1. Geological overview

The Songliao Basin is one of the largest Jurassic-Cenozoic continental rift-basins in China, comprising a central depression with an area of about 39265 km2. Initial rifting, characterised by intense volcanic activity, began during the Late Jurassic Period, and was followed by formation of fault-bounded grabens and half grabens. During the post-rift phase, the basin formed a broad lacustrine depression which contains the Jilin Oil province. Subsequent compression led to some structural inversion [3]. The central depression fill comprises over 11km of Mesozoic sedimentary rocks, underlain by a basement of Palaeozoic-Pre-Palaeozoic igneous and metamorphic rocks. The basement is overlain by 1.5-2 km of Jurassic sediments, followed by a Cretaceous sedimentary fill with a thickness of over 7 km (Figure 2). The Lower Cretaceous largely comprises sandstone, shale and mudstone deposited in fan-delta, deltaic and lacustrine environments. The Upper Cretaceous comprises lacustrine sediments.

Q Quaternary K,qJ Quantou, Member II

Kjm-N Mingshui Formation M1 Quantou, Member I

Nenjiang Formation K,d Denglouku Formation

KjV Yaojia Formation K,vc Yingdieng Formation

K*qn Qingshankou Formation K,sh Shahezi Formation

Quantou Formation, Member III+IV

Figure 2: Schematic cross-section showing principle reservoir and seal strata. 3.1. Jilir Oil Province

The Jillin oil province comprises 25 individual oilfields. Of these, five fields were selected for further evaluation of their storage potential: Hingang, Xinli, Mutou, Qian'an and Yingtai. Others were not considered further either due to data limitations, or because the reservoirs were too shallow for supercritical CO2 injection) or because they were too small. The oil-bearing reservoirs in these five fields lie in the Lower Cretaceous Quantou, Qingshankou, Yaojia and Nenjiang Formations (Figure 2), at depths ranging from 1500 to 3430 m and comprise siltstones to fine carbonate-cemented greywacke sandstones. Reservoir permeabilities are quite low in the Xinli and Qian'an fields (5-20 mD) and even the more permeable Honggang and Xinli oilfield siltstones and sandstones have limited permeability of up to 275 mD (Table 1), which may reduce their injectivity. .The oilfields are generally compartmentalised and bounded by laterally discontinuous lithologies and faulting. For example, the depth of the oil-water contact in the Xinli and Mutou fields varies across the field indicating that the reservoir compartments are not in communication and so would have to be tapped individually to fully exploit the available pore space for CO2 storage and/or EOR.

Seals to these reservoirs are provided by the Nen I and Nen II mudstones, which have not been strongly compressed and trap hydrocarbon in the Heidimiao and Sa'ertu payzones (Figure 3). The mudstones within the Qingshankou Formation range between 100 to 400 m in thickness, with small pore sizes (average 3 - 5 nm), high capillary entry pressure and high plasticity. The Qingshankou mudstones form the seal for the

Fuyu and Yangdachengzi payzones. The sealing capability of these strata are proven by the oil and gas trapped in the reservoirs. Few faults extend above the Qingshankou and Nenjiang Formations, which should enhance potential containment of CO2 in these reservoirs. However, the isolation of pay zones has led to a high density of production boreholes penetrating the hydrocarbon reservoirs, which present potential leakage pathways.

Age Formation Member oilfield payzone Thickness Litholoyy

Quaternary 0-143

Ceno-zoic Talkang 0-135

Da'an 0-125

Upper Cret- Mingshul Ming II Mingshui^ 0 - 357

Ming l o-2sa

aceous Sifangtai 0-410

Men V 0-500 mudstone, argillaceous siltstone and fine sandstone

Nenjiang (k2rt) Nen IV • •

Nen III Heidlmiao 50-120

Nen II 00-213

Nen I Sa'ertu 27-120 black + green mudstone

Yao III Sa 1 a Sa II Sa Iii interbedded with siltstone and fine sandstone

Yaojia (k2y) Yao II 10 - 200

Yao I Putaohua Pu 1 A Pu II sandstone, siltstone, black + green mudstone

Lower Qingshankou Qlng lit Gaotaizi Gao 1 a Gaoll w Gao Iii Gao IV 80 - 600 sandstone and

Crel-aceous (k2qn) Qing II siltstone and interbedded siltstone and mudstone

Qlng I 40 - 100

Quan IV Fuyu 0 0-120 siltstone + fine

Quantou (k2q) Quan III Yang-# dachengzi 0-500 sandstone

Quan II 0-480

Quan I 0-890

□englouKu (k1d> calcareous shale.

Middle Bai Cheng Nong'an fine to coarsegrained

Jurassic Upper Yaonan sandstones

Sahez I

Ylng cheng

Palaeozoic

0 Oil-bearing 0 Gas-bearing 9 Some oilfields have a gas cap

Figure 3: Schematic stratigraphic section highlighting principle reservoir formations in Jilin oilfields.

The five large fields, the Honggang, Xinli, Mutou, Qian'an and Yingtai oilfields, have a total estimated effective storage capacity limited to 71.2 Mt CO2 (Table 1). The additional oil which could be recovered through EOR from these five fields is estimated to be 46 - 230 million barrels. Two of these fields, the Honggang and Xinli oilfields, were selected for more detailed assessment of storage potential to assist a source-sink matching exercise which is not reported here which only slightly altered their estimated capacities from those in Table 1 to 5 and 13 Mt respectively.

3.3. Daqing Oil Province

The Daqing oil province is located around Daqing city, in Heilongjiang Province. The length of the province from south to north is 138 km and width from east to west is 73 km. It has an oil-bearing area of about 4,103 km2. The largest fields in the Daqing oil province are the Lamadian, Sa'ertu, Xingshugang, Gaotaizi, Taipingtun, Putaohua and Aobaota oilfields (Table 2).

The hydrocarbon-bearing layers are grouped into 'payzone strata' and sub-stratum layers named after the largest fields. Hydrocarbons in the fields have accumulated in faulted anticlinal structures. The oil-bearing reservoirs in the Daqing oil province, which lie within the Cretaceous Qingshankou, Yaojia and

Nenjiang formations, at depths of between 800-1200 m, can be divided into six payzones: the Heidimiao, Sa'ertu, Putaohua, Gaotaizi, Fuyu and Yangdachengzi payzones. The Sa'ertu and Putaohua payzones are feldspar-lithic sandstones, with typical compositions of 40-50% feldspar, 30-40% quartz and 10-15% lithic clasts. There is a lower percentage of feldspar and quartz in the south of the complex and a higher percentage of volcanic lithic clasts. A clay matrix is the predominant cement in the sandstones, comprising 5-12% of the total rock and with the clay content increasing to the south of the oil field complex. The calcium carbonate content is about 2%. The reservoirs in the Sa'ertu, Putaohua and Gaotaizi payzones are in one connected pressure system. The initial reservoir pressure in the Daqing oil fields was 10.5-12.0 MPa with a pressure gradient of 1.05-1.13 MPa/100m. The initial reservoir temperature in the Daqing Oilfield Complex was about 45-53°C. The total theoretical storage capacity of these fields was calculated as 593 Mt (Table 2).

Table 1: Summary data and effective storage capacity estimates for five oil fields of the Jilin province.

Oilfield Honggang Xinli Mutou Qian'an Yingtai

Discovery year 1961 1973 1973 1979 1982

Oil-bearing formations Yaojia Quantou. No gas cap or edge aquifers. Quantou. Gas and underlying aquifer present. Qingshankou. No gas cap or underlying aquifer. Yaojia and Qingshankou. Gas cap and underlying aquifer present.

Burial depth of oil-bearing reservoir (m) 1200 1200-1500 500-600 1820 1384-1440, 15501690

Lithology of oil-bearing layer Siltstone interbedded with argillaceous layers Siltstone, fine sandstone and argillaceous siltstone Mudstone and siltstone mudstone, siltstone and coarse siltstone Siltstone, fine sandstone

Total thickness of oil bearing interval (m) 120 240+ 85-100 360 - 410 16

No. of oil layers 16 -

Net thickness (m) 4.6 7.9 6.9 8.8 30

Area (km2) 49.4 120.6 20 170.5 51.7

Average porosity (%) 22 16.3 23.5 15 22

Average permeability (milliDarcies) 132 - 172 20 205 5 - 11 37 - 86, 249 - 275

Original pressure (MPa) 12.25 12.2 6.5-7.0 19.29 15

Temperature °C 55 66 40 76 65

Estimate theoretical storage capacity (Mt)1 6 12.5 3.9 27 21.8

Estimate based on volumetric replacement of oil reserves using CSLF Eq1

3.4. Saline aquifer storage capacity estimates in Jilin

Saline aquifers around the Jilin oil complex were selected for storage capacity assessment as a limited amount of deep geological information about these aquifers was available from oilfield exploration. Initial site screening indicated that the deep saline aquifers suitable for CO2 storage are mainly located in the Qingshankou Formation. Using the CSLF-based methodology and a 2% storage coefficient, the effective storage capacity is estimated to be 692 Mt CO2 in the Qingshankou Formation across the basin. Detailed assessment of this Formation at one site in the Daqingzi area of the Jilin Oilfield complex indicated a storage capacity of 288 Mt CO2. However, significant further characterisation, including primary site exploration, would be needed to reduce the uncertainties associated with these estimates.

Table 2: Summary data and estimates of effective storage capacity for 7 fields of the Daqing oil province.

Oilfield Lamadian Sa'ertu Xingshugang Gaotaizi Taipingtun Putaohua Aobaota

Discovery year 1959 1959 1959 1959 1960 1959 1959.12.

Oil-bearing formations Qingshankou Yaojia & Nenjiang Qingshankou Yaojia & Nenjiang Nenjiang Yaojia & Qingshankou Yaojia Yaojia Yaojia Yaojia

Depth of reservoir (m) 920-1208 660-12001 850-1190 1080-1115 1895-1165 916-1250 916-1250

Lithology of oil-bearing layer Sandstone interbedded with mudstone Sandstone interbedded with mudstone Sandstone interbedded with mudstone Sandstone interbedded with mudstone Sandstone interbedded with mudstone Sandstone interbedded with mudstone Sandstone interbedded with mudstone

Total thickness ofpayzone (m) 390 30-60 300 65 60 65

No. oil layers 97 135 69 5 4 6 - 11 920~1230

Net thickness (m) 72 35-62 13-20 4.4 2.9 - 3.3 2.0 - 4.5 1.0 - 1.5

Area (106 m2) 100 200 216 9.5 61 95.2 40

Porosity (%) 23.7 - 26.7 23-26.3 21.4-25.0 23 23 23 - 24 23

Permeability (Darcies) 0.23 - 1.3 D 0.15 - 3.65 D 204 - 569 mD 86 - 258 mD 135 - 506 mD 89 - 370 mD 115 (117 mD)

Original pressure (MPa) 11.33 11.1 11.49 11.98 10.5 - 11.7 10.7 - 11.6 11.57

Storage capacity2 (Mt CO2) 187.4 308.1 83.4 1.0 4.3 7.4 1.1

Reservoirs with suitable T & P considered only. 2 Estimate based on volumetric replacement of oil reserves using CSLF Eq1.

4. Subei Basin

The Subei Basin is a Mesozoic-Cenozoic continental onshore hydrocarbon-bearing basin that contains many small oil and gas fields. The basin lies on Proterozoic basement rocks and contains three broad stratigraphic units: Middle Palaeozoic marine carbonates, and clastic and volcanic rocks formed during the

Middle-Upper Triassic and Cretaceous. During the Mid-late Triassic, the basin was uplifted, creating a

continental sedimentary environment. The basin as a whole originally contained 1472 million barrels of oil

and up to 8 billion m3 (2823 bcf) of gas. The region within which it lies is heavily developed with many medium to large cities and there is a high density of significant industrial sources of CO2 in this area. The small and strongly compartmentalised oilfields provide limited CO2 storage potential. As part of the regional assessment, 108 individual oil reservoirs have been evaluated, of which 75 reservoirs are

considered to be suitable for CO2-EOR. However, the estimated CO2 storage capacity using EOR is

limited to approximately 16 Mt CO2, and the expected incremental oil production is 35 million barrels of

oil. The remaining 33 reservoirs are suitable for CO2 storage without EOR and have an estimated total CO2 storage capacity of around 5 MtCO2. There are also many aquifers that formed in similar faulted structures associated with the oil reservoirs which may be considered as sites for CO2 storage. Little is currently known about the aquifers because they haven't been as intensively examined as the hydrocarbon bearing reservoirs. There are however many oil reservoirs which have large associated (or connected) lateral or underlying aquifers. To some extent, these aquifers can be considered as good targets for further characterisation because they occur below proven seals and data has been collected by oil companies, providing a certain amount of knowledge of their physical properties. There are also many natural CO2

reservoirs within the Subei Basin, which in the last ten years have been used to support CO2 flooding pilot projects. The natural CO2 reservoirs can be considered as analogues for CO2 storage, giving confidence in the potential of the area to store CO2; these might even be used for storing captured CO2 if they are depleted by oil industry use.

5. Conclusions

Active oil producing fields where CO2-EOR is technically possible provide credible opportunities to initiate CO2 storage demonstration projects in China. However, our estimates have shown that even when they have been depleted, individual reservoirs in the Songliao and Subei Basins have relatively low storage capacities. Moreover, storage capacities in these oilfields are generally small compared to emissions from power stations. The hydrocarbon reservoirs are typically geologically complex with moderate porosity and permeability and have high well densities. Consequently, high injection well densities are likely to be needed to access all the available pore space. The high well densities also suggest that containment risks due to potential well leakage will be a significant issue. In some of the fields examined here, individual pools are too small to provide potential storage capacity for even one power plant and may therefore only be utilised in opportunistic situations where a smaller source is located close by. The typically small storage capacities in these oilfields also mean that for CO2 volumes greater than those that can be accommodated in oilfields, more saline aquifer storage will be required relative to other oil-producing areas internationally, if CO2 emissions from larger coal-fired power plants are to be stored underground. For example the emissions from the 78 largest sources (predominantly coal-fired power plants but also industrial sources) within the Jilin Province have been estimated at around 71 Mt/a [5]. Our estimates suggest that oilfields will not provide enough storage capacity to meet the required volumes over the lifetimes of these sources and that saline aquifers would need to be utilized almost from the start of any large scale CCS implementation. Results from the other basins, examined here and elsewhere, indicate that elsewhere in China saline aquifers will need to be extensively utilized in parallel to any projects combining CO2-EOR and subsequent reservoir storage.

However, as in other parts of the world, the lack of data available to assess saline aquifers has forced us to provide a grossly simplified estimate of one specific aquifer in the Songliao Basin that occurs at the top of the oil-bearing formations. It can be assumed that the structural and stratigraphic compartmentalisation observed in underlying reservoirs may equally pertain to this aquifer and it is therefore suspected that better constrained storage capacities in this aquifer could well be significantly lower than the large theoretical capacity reported here. Although in this study, we have not assessed in detail the injection strategies that would be necessary for CO2 storage in these reservoirs and associated aquifers, the relatively small and compartmentalised nature of some of these fields suggest it may be likely that injection of significant volumes of CO2 may require a higher density of injection infrastructure together with active and careful pressure management, than is anticipated in other target storage areas such as the North Sea.

6. References

[1] Asia Pacific Economic Cooperation.. Assessment of Geological Storage potential of carbon dioxide in the APEC region - phase 1. CO2 storage prospectivity of selected sedimentary Basins in the Region of China and South East Asia. 2005. APEC Energy Working Group EWG Project 06/2003. 232pp.

[2] Bachu, S., Bonijoly, D., Bradshaw, J., Burruss, R., Christensen, N.P. Holloway, S., & Mathiassen, O.M. Estimation of CO2 Storage Capacity in Geological Media - Phase 2. Work under the auspices of the Carbon Sequestration Leadership Forum (www.cslforum.org). Final Report from the Task Force for Review and Identification of Standards for CO2 Storage Capacity Estimation. 2007.

[3] Huang, H.P., Yang, J., Yang, Y.F., Du, X.J., Geochemistry of natural gases in deep strata of the Songliao Basin, NE China. Int. J. Coal Geol. 2004: 58: 231-244.

[4] Vangkilde-Pedersen, T., Neele, F., van der Meer, B., Egberts, P., Wojcicki, A., Bossie-Codreanu, D., Le Nindre, Y.M. and Barthélémy, Y. Storage capacity standards. EU GeoCapacity deliverable D24. 2008:39 pp.

[5] Chen, W. Huang, L., Xu, R., Xiang, X. and Chen, J. 2009 Carbon emission sources estimation and mapping of sources and sinks in Jilin Province. NZEC internal report 28 pp.