2.2 Potential geological CO2 storage sites in India
The potential geological CO2 storage sites inconsidered in detail in this report are divided into three categories:
- oil and gas fields
- coal seams
- saline water-bearing rocks
The potential for storage in basalt rock formations is not quantified in this report as this storage concept is not considered to be mature at present (IPCC 2005). However, it is noted that two extremely large areas in India are covered by thick basalt formations, the largest of which is known as the Deccan Traps and the smaller as the Rajmahal Traps. If the concept of CO2 storage in basalt formations can be advanced into a mature option, it may have great potential in India (Singh et al. 2006).
2.2.1 Estimated CO2 storage capacity in oil and gas fields in India
The methodology used to calculate the CO2 storage capacity of oil and gas fields is given in Appendix 1.
The location of oil and gas fields in India is shown in Figure 2.3. They occur in three areas: Assam and the Assam-Arakan Fold Belt (NE India), the Krishna-Godavari and Cauvery Basins (SE Indian coast), and the Mumbai/Cambay/Barmer/Jaisalmer basin area (NW India).
Initial in-place and ultimate oil and gas reserves in India as of 01/04/2006 are as shown in Table 2.3 (DGH 2006).
|Initial in place||Ultimate reserves|
|Gas (109 cubic metres)||Oil (106 tonnes)||Gas (109 cubic metres)||Oil (106 tonnes)|
It has been assumed, but not confirmed, that Initial in-place = Oil initially in place, and ultimate reserves = ultimately recoverable reserves as defined in Appendix 1. Based on this assumption, the storage capacity of the oil fields of India is estimated to be 1.0 to 1.1 Gt CO2, approximately one year’s emissions from major point sources. The storage capacity of the gas fields and gas caps on oil fields is estimated to be 2.7 to 3.5 Gt CO2.
Field-by-field reserve information is not available in the public domain, but some basin-by-basin estimates of oil reserves and thus oil field storage capacity, gleaned from a variety of sources, are given in Table 2.4.
|Basin||URR Oil mmbbls||URR Oil 106 tonnes||URR Oil 106 m3||CO2 density reservoir conditions (default = 0.6 t m-3)||FVF (default = 1.2)||Estimated CO2 storage capacity106 tonnes|
|Barmer Basin (Rajasthan)||322||42.9||51||0.6||1.2||24|
|Mumbai Basin (offshore|
|Mumbai and Gujarat)||6300||840.0||1001||0.6||1.2||469|
|India total (DGH 2006)||12395||1652.77||1970||0.6||1.2||1000 – 1100|
URR data for Assam from USGS, data for Barmer and Cambay Basins from Cairn Energy, data for Mumbai offshore = USGS – Cairn Energy estimate for Cambay. N.B. data for the productive Krishna-Godavari, Jaisalmer and Cauvery basins is not included.
The reserves of the Mumbai High field are estimated to be approximately 4 billion barrels of oil and 7.4 tcf gas, http://www.hubbertpeak.com/laherrere/GPPI200701.pdf. Production data from the Ankleshwar field (Cambay Basin) suggest that it may have ultimately recoverable reserves of about 400 million barrels of oil.
The figures quoted for CO2 storage capacity in oil fields are necessarily crude and should be regarded as highly provisional. They do not explicitly include additional potential that might be obtained through(EOR); however, they are possibly overoptimistic in the sense that they are based on the assumption that all the pore space in the field formerly occupied by produced oil and associated gas can be filled by injected CO2. Any (EGR) resulting from CO2 injection into depleted gas fields is likely to be marginal in terms of additional storage space as >90% of the gas found in gas fields is commonly recovered in primary production, leaving little scope for EGR.
2.2.2 The coalfields of India
The coalfields of India are described briefly in Appendix 2.
The majority of coalfields in India are of Permian age. Geologically, the vast majority of this Permian coal is located in the Raniganj and Barakar Coal Measures, in the lower part of the Gondwana Supergroup. Nearly 90% of India’s total coal resources are in the Barakar Formation.
India also has some resources of lignite and sub-bituminous coal. This is much younger than the Permian hard coals, being of Cainozoic age.
The Gondwana coalfields of India are found in fault-bounded troughs (graben) that overlie either Precambrian igneous and metamorphic basement rocks or Proterozoic sedimentary rocks. The continuity of these troughs has been disturbed by post-depositional folding and faulting such that the coalfields now form a number of separate rather than continuous outcrops within them (shown in grey in Figure 2.4).
More than 99% of the bituminous to sub-bituminous coal is found in eastern India, in the states of West Bengal, Jharkhand, Madhya Pradesh, Chhattisgarh, Orissa, Andhra Pradesh and Maharashtra.
2.2.3 Coal resources of India
The data tabulated below is based on the Coal Inventory of India. This is a resource evaluation that covers all known coal seams over 0.5m thickness and down to the depth of 1200m. It was constructed from data made available by the Geological Survey of India, Central Mine Planning and Design Institute, Mineral Exploration Corporation Ltd., Singareni Collieries Co. Ltd and Department of Mining and Geology, Maharashtra. The steps involved in production of the inventory were: regional mapping of major basins, regional exploration of basins considered to have coal-bearing potential and detailed exploration of individual coal-bearing blocks. The resource is categorized by coalfield, State and depth. It is further divided into the following categories: proved (typically explored by boreholes <400 m apart), indicated (typically explored by boreholes 1-2 km apart) or inferred (typically explored by boreholes >1-2 km apart).
A resource evaluation, by State, of coal seams >0.5 m thick at depths <1200 m (GSI 2007) is given in Table 2.5.
|State||Resource estimate as on 1.1.07 under depth:||Total Resource (Mt)|
|N E States||787||155||942|
** Jharia coalfield resource position is available only in 0-600m depth range and has been included within 300-600m depth account. The reserve position within 300m depth over is found in all the active coalfields except a few hidden pockets under basaltic flow or soil cover.
Coal resources in the inventory are further divided into three categories: proven, indicated and inferred (Table 2.6).
|State||Coal resources in Million tons (Mt)|
Cenozoic coals contribute an estimated 946 Mt to the totals in Tables 2.5 and 2.6. They are found in 67 fragmented coal-bearing pockets principally in Assam, Meghalaya, Nagaland and Arunachal Pradesh. Cenozoic coals in general have low ash and high sulphur.
Additionally, a few thin coal seams occur in pockets of Upper Gondwana strata – at Guneri in Gujarat, and Kota and Chikiala in the Satpura and Godavari Valley basins respectively.
Lignite fields are also present. The major fields are given in Table 2.7. Total resources amount to some 25000 Mt but, with the exception of the Neyveli field, a field-by-field breakdown of resources was not available for the study. The Neyveli lignite field produces 24 Mt lignite annually, and feeds three power stations with a combined capacity of 2490 MW.
|Name of lignite field||State||Area km2||Reserves Mt|
|Upper Assam||Assam/Arunachal Pradesh|
126.96.36.199 MAJOR COAL FIELDS OF INDIA
|Coalfield||Area km2||Reserve109 tonnes||Coal quality|
|S. Karanpura||195||6.0||Non coking-Superior|
|N Karanpura||1230||15.9||Medium coking|
|W Bokaro||259||5.0||Medium coking|
|E Bokaro||208||7.1||Medium coking|
|Jharia-Barakar -Mahuda||21058||19.4||Prime and medium coking|
|Raniganj -Barakar -Raniganj||1530||25.5||Medium coking, Non coking, Superior|
|Rajmahal||208||14.1||Non coking -Inferior|
|Singarauli||2202||12.9||Non coking -Inferior|
|Sohagpur-North -South||3000||4.5||Medium coking Non coking -Superior|
|Bisrampur||1036||1.5||Non coking -Superior|
|Hansdeo-Arand||154||5.0||Non coking -Superior|
|Tatapani-Ramkola||12||2.4||Non coking -Superior|
|Mand Raigarh||500||19.1||Non coking -Inferior|
|Pench Kanhan||12||2.4||Non coking-Superior|
|Wardha valley||4130||5.7||Non coking-Superior|
|Kamptee||95||2.9||Non coking -Superior|
|Nand Bander||0.8||Non coking –Superior|
|Godavari valley||17000||17.5||Non coking-mainly superior grade|
|Talcher||1813||39.6||Non coking –Inferior|
|Ib River||1375||22.4||Non coking –Inferio|
From the surveys undertaken so far, the area of the major coalfields totals nearly 37000 km2. Of this, approximately 8000 km2 has been explored in detail, the majority of which contains coal seams at depths of 300-600m. An additional 14500 km2 has been established as potentially coal-bearing as a result of regional exploration.
188.8.131.52 MINOR COAL FIELDS OF INDIA
Resources of coal in the minor coalfields of India are shown in Table 2.9.
|State / Coal Field||Coal reserve within||Area-sq.km|
2.2.4 Coal quality
Reserves of the various qualities of coal found in India are shown in Tables 2.10 and 2.11.
|State/Coalfield||Superior grade||Inferior grade||Total|
|Tata Pani Ramkola||0||843||0||573||202||1617|
Limited coking coal is available, mainly within Damodar Valley, in the E &W Bokaro, N & S Karanpura, Raniganj and Jharia coalfields, and a small fraction in Sohagpur and Kanhan Valley coalfields. Very little prime coking coal is available: it is found only in the Jharia coalfield in upper coal seams IX to XVIII - the lower seams have medium- to non-coking properties.
Superior grade non-coking coals of A to D grade with ash and moisture below 34 % are also limited in quantity and available mainly in the Damodar Valley coalfields, with a small fraction of the reserves in Raniganj, South Karanpura and the Central India coalfields.
Inferior grade coal (E to G grade) with ash plus moisture content over 34% is available in the Son Mahanadi Valley, Pranhita Godavari Valley, Wardha Valley, Singarauli, Rajmahal and North Karanpura coalfields. Coal of this grade is primarily used for thermal power generation. Distribution of the different grades of Gondwana coal to 1200m depth is given in Table 2.12.
|Type of coal||Proved||Indicated||Total||% share|
|Grade E +F+G||48166||102591||150757||55.2|
|Subtotal non coking||75212||138404||213616|
2.2.5 Undiscovered and deep coal resources
Additional as yet undiscovered coal resources may be present outside the explored areas. Moreover there are areas within the well-delineated coalfields where coal occurs at depths beyond the resource estimation and eventual mining limits. These blocks are of interest because they may be available for underground gasification, coal bed methane production and possibly for carbon dioxide storage – if it proves possible to store CO2 at these depths. As examples, in the East Bokaro coalfield, approximately 3.2 billion tonnes of coal may be below 1200 m depth. Approximately 6.7 billion tonnes of Barakar coal may be beyond mining depths in the Jharia coalfield, and 0.97 billion tons of mainly of superior quality coal may be below minable depths in the Raniganj coalfield. Coal reserves at depths below 1200 m are expected in the South Karanpura and Sohagpur coalfields.
Additional deep coal resources are also widespread, for example beneath western parts of the Bengal Basin. However these are too deep to be of interest for CO2 storage in coal at present, although the sandstones in the succession may have potential.
2.2.6 Demand for coal in the Indian market
India’s population already exceeds 1 billion and, according to the United Nations, is expected to reach 1.33 billion in 2025 and 1.53 billion in 2050 (World Resources Institute 1998-99). Clearly, India will need electricity, steel, cement, and other industrial products to meet the rising demand. Because of limited indigenous petroleum and natural gas, coal has become the main source of energy.
Indicative future demand for coal (Chaudhary 2000) is summarized as follows in Table 2.13. Demand projection is just indicative because of delay in setting up planned capacity of power stations and other industrial units.
|Power plants - Power grade||222 Mt||288 Mt||500 Mt|
|Steel Industry - Coking coal||41 Mt||52 Mt||68 Mt|
|Cement industry - Superior grade non-coking||18 Mt||21 Mt||37 Mt|
|Other industry - Superior grade non-coking||41 Mt||51 Mt||85 Mt|
|Total demand for coal||323 Mt||412 Mt.||90 Mt|
Coal-based thermal power plants are spread all over India whereas coal is confined to 8 eastern states. Therefore coal has to be transported over 1000 km to feed some of the remote power stations. The average distance of coal transport to power plants is 675km.
In view of reducing pressure on the railways, environmental protection, control over generation ofand overall economics, there is currently a restriction on transport of low grade coal to remote power plants. The Ministry of Environment and Forest declared that after 1st June, 2001, all coal used more than 1000 km away, or in environmentally sensitive and metropolitan cities power plants, will be washed / processed to an ash content not exceeding 34% (Varma 1999). The restriction clearly demands high production of A to D grade coal or processing of inferior E/G grade coal to reduce ash content to 34%. Obviously, superior grade non-coking coal will be preferred by the remotely located power stations and hence its mining feasibility will improve further in the future.
2.2.7 Estimated CO2 storage capacity in coal fields in India
Carbon dioxide storage in coal beds is a technology that is only in the demonstration phase (IPCC, 2005), and the evaluation of demonstration projects will affect its perceived applicability and, consequently, the capacity for CO2 storage in coal beds not only in India but worldwide. The methodology used for estimating the CO2 storage capacity of coalfields is given in Appendix 1.
A key issue for India’s CO2 storage capacity in coal seams is to what extent mining will take place in each coalfield. It is considered likely that open cast mining and selective underground mining to 600m depth will take place in all major fields irrespective of coal quality, reserve position and distribution pattern, even in basins with only power grade coal. Selective underground mining of superior grade non-coking coal and coking coal is likely to take place down to 1200m in the Jharia, Raniganj, Bokaro, Karanpura and Sohagpur coalfields.
Selective underground mining is likely to lead to the development of fissures and fractures in the overburden above mined seams, and may also enhance theof the Coal Measures below the mined seam. Thus the only areas where CO2 storage is actually likely to be practical in India are areas of the major coalfields either not subject to selective underground mining or significantly (say 100 m) below mined seams.
Bachu et al. (2007) state that: “Permeability is a determining factor in the viability of a CO2 storage site, and currently it is considered that coal permeability has to be greater than 1 mD for successful CO2 injection and/or coalbed methane (CBM) production. Coal permeability is affected by physical (mechanical) and chemical factors. It varies widely and generally decreases with increasing depth as a result of cleat closure with increasing effective stress. The permeability of shallow coals (a few hundred metres deep) is on the order of millidarcies (mD) and higher, while the permeability of deep coals is on the order of microdarcies (μD), which is too low to allow CO2 injection and flow without fracturing. Coalbed methane cannot be produced if permeability is less than 1 mD (Zuber et al., 1996), and this is generally reached in the depth range 1300-1500 m. It is for this reason that most of the coalbed methane producing wells in the world are less than 1000 m deep (IPCC, 2005), and why 1300-1500 m is considered as the depth limit of possible CO2 storage in coals. Coal is a polymer-like substance that is often affected by the gas with which it is in contact.
Coal swells as CO2 is adsorbed, which further reduces permeability and(IPCC, 2005). Coal swelling generally increases with increasing gas affinity to coal (e.g., CO2 versus methane), and may reduce permeability by two orders of magnitude or more (Shi and Durucan, 2005). In addition, the injected CO2 may react with the coal and/or formation water, leading to solids precipitation and further permeability reduction (Reeves and Schoeling, 2001; Zhang et al., 1993). Carbon dioxide is a “plasticizer” for coal, lowering the temperature required to cause the transition from a glassy, brittle structure to a rubbery, plastic structure (IPCC, 2005). Coal plasticization destroys the permeability that would allow CO2 injection. Thus, these combined effects on permeability caused by the presence of CO2 reduce the depth limit for CO2 storage in coals to approximately 1,000 m.
The process of CO2 trapping in coals at temperatures and pressures above the critical point is not well understood, and it seems that adsorption is replaced by absorption and the CO2 diffuses into coal (Larsen, 2003). The transition from one process to the other is not sharp, but rather gradual. At the high temperature and pressure conditions that correspond to supercritical CO2, it is not clear whether CO2 is adsorbed by coal, occupies the pore space like a fluid with very low viscosity, or infuses into the coal matrix. Under these conditions coals are not a good storage medium because CO2 might be highly mobile and migrate out of the coals into the adjacent strata or within the coals themselves, with the potential for leakage into shallow groundwaterand even to the surface. Thus, until the basic science of CO2 storage in coal advances to clarify these points, it seems that it would be safe to consider that CO2 should be stored only in coal beds that are at such temperature and pressure conditions that CO2 is in the gaseous phase. For hydrostatic conditions and average geothermal gradients this would correspond to depths in the 700-800 m range”.
Therefore it is possible to consider a position in which:
- selective mining takes place in all major fields to depths of 600 m, and more in Jharia, Raniganj, Bokaro, Karanpura and Sohagpur
- CO2 storage is not likely to take place <100 m below a mined seam, and
- CO2 storage in coal seams should only take place where CO2 is in the gaseous phase, i.e. above 700-800 m depth
If such a position indeed arises, there may prove to be very little scope for CO2 storage in India’s major coalfields. However, CO2 storage may prove to be possible down to depths of 1000 m or more, so an indicative storage capacity calculation was made on the following basis, see also Table 2.14:
- All beds with coal of any grade to depth of 300m will not be available for storage of CO2 as these are stipulated to be within the range of surface mining
- All coal beds with coking coal - prime, medium or semi coking - will not be available for CO2 storage irrespective of depth
- All coal beds with superior grade non coking coal (Grade A to D) will not be available for storage of CO2 irrespective of depth
- A parting of 100m undisturbed formation has to be maintained below the 300m depth floor
- On average, 30% of power grade non coking coal (Grade E-G) beds at depths between 400m (i.e. 300m less 100m barrier) and 600m will be available for CO2 storage*
- On average, 10% of coal beds in coalfields where variable grades of coal occur at depths of 400m-600m depth will be available for CO2 storage, in view of the selective mining of superior grade (A to D) coal beds
- On average 50% of inferior grade non coking coal under thick basalt / intertrappean cover and or geologically disturbed beds at depths of 400-600 m will be available for CO2 storage
- 50% of coal within basins with coal beds of different grades at depths between 600-1200m will be available for CO2 storage
- 100% of coal beds of inferior grade coal (E, F, G) at depths between 600 and 1200m will be available for CO2 storage
- 100% of inferior grade non coking coal at depths of 600-1200 m under thick basalt / intertrappean cover and or geologically disturbed beds will be available for CO2 storage
- Average CO2 storage capacity of India’s coal resources is 0.02 tonnes of CO2 per tonne of coal
* with the exception of Godavari and Wardha Valley E Grade coal beds, which will be included in superior grade coal due to premium pricing.
|Depth of coal beds||Coal grade/category||CO2 storage Capacity|
|0-300m||All grades of coal||Nil|
|Superior grade non coking coal||Nil|
|Mixed (Superior: Inferior 1:1)||10%|
|Inferior (E-G) grade||30%|
|Inferior under thick trap||50%|
|Superior non coking coal||Nil|
|Mixed grade (1;1 ratio)||50%|
|Inferior grade under trap||100%|
On the basis of these assumptions, the CO2 storage capacity of the coalfields of India is estimated to be approximately 345 Mt CO2. A more detailed breakdown is shown in Table 2.15.
|State /Coalfield||Reserve at 300-600 m depth (Mt)||Reserve available for CO2 storage 300-600m (Mt)||Est. CO2 storage capacity 300-600 m (Mt)||Reserve at 600-1200 m depth (Mt)||Reserve available for CO2 storage 600-1200m (Mt)||Est. CO2 storage capacity 600-1200 m (Mt)||Estimated total CO2 storage capacity (Mt)||Coal bed Quality|
|Raniganj||519||0||0||see above||see above||see above||0||Superior|
|North East Region|
** Jharia coalfield reserve is estimated within 0-600m depth cover.
Note that only eight of the coalfields have the capacity to store >10 Mt CO2 and none have the capacity to store >100 Mt CO2. Thus, in practice, it appears that storage in coal seams can make little contribution to reducing India’s CO2 emissions.
A more rigorous approach to calculating India’s CO2 storage capacity in coal seams could be undertaken but is beyond the scope of this study.
2.2.8 Estimated CO2 storage capacity in deepin India
The CO2 storage capacity in the deep saline water-bearing reservoir rocks (deep saline aquifers) of India is described qualitatively on a sedimentary basin-by-basin basis in Appendix 3. Areas not described in this analysis were not examined in detail because a first-pass assessment suggested that they may have little realistic CO2 storage potential.
As expected in a country study (Bachu et al. 2007), insufficient geological information was available to determine the saline aquifer CO2 storage capacity of any of the basins. However, a qualitative comparison of the saline aquifer storage capacity with that of the European sector is given in Appendix 4. This employs the same methodology as used in the IEAGHG European sector study (Wildenborg et al. 2006).
For assessment purposes, the basins were divided into categories of good, fair and limited saline aquifer CO2 storage potential, as below. This process inevitably involved a degree of geological judgement and it is felt that the classification could be significantly refined with further work. Indeed, with further work, some basins are likely to be raised to categories of higher potential.
184.108.40.206 BASINS WITH GOOD POTENTIAL
Basins falling into this category contain hydrocarbon fields (proving containment of buoyant fluids over geological timescales) and there is expectation of good reservoir and seal quality at depths below 800 m over at least a significant part of the basin. They are:
- Assam Basin
- Assam-Arakan fold belt
- Mahanadi basin (deep water part)
- Krishna-Godavari Basin
- Cauvery Basin
- Mumbai Basin
- Cambay Basin
- Barmer Basin
- Jaisalmer Basin
The locations of these basins in relation to India’s major sources of CO2 are shown in Figure 2.6
A summary of their perceived CO2 storage potential is given below:
The Assam Basin
The presence of oil fields in the area south of the Brahmaputra River, at several stratigraphic levels in the Cenozoic section, indicates that this part of the Assam Basin has good potential to store buoyant fluids such as supercritical CO2. Several apparently well-sealed reservoir horizons are present. The area north of the Brahmaputra lacks hydrocarbon fields, possibly because the seals are poorer but more likely due to lack of migration across the anticlinal Brahmaputra Arch that lies beneath the Brahmaputra. If the latter is the case, this area may also have potential.
The Assam Basin is remote from the main part of peninsula India and thus any CO2 transport to Assam from peninsular India would have to be by pipeline, either around the ‘chicken neck’ to the north of Bangladesh, or across Bangladesh, or across Bangladeshi territorial waters.
The area is prone to some of the largest earthquakes ever recorded.
The Assam-Arakan Fold Belt
Gas fields are present in the outer parts of the fold belt itself, e.g. in the Surma Basin (NE Bangladesh), the Chittagong Hill Tracts (SE Bangladesh), Tripura and Mizoram. The presence of the Surma, Barail and Tipam groups in the Cachar-Tripura-Mizoram region, all of which contain sandstones, suggest that potential for CO2 storage exists in these areas as well, at least west of the outcrops of Disang Shales. The main drawback is geographic: the Indian parts of the fold belt are remote from both major CO2 sources and the main part of India. Overpressure may also be an issue.
The Mahanadi Basin
Good potential exists in deep water (i.e. water depths below 200 m), where there has been a major gas discovery, but this would likely be expensive to access. Both the onshore and shallow offshore basins should have some CO2 storage potential, but the lack of hydrocarbon discoveries shoreward of the 200 m isobath (and thus a lack of proven containment of buoyant fluids) means that the potential in these areas is classified as only fair. Nevertheless, there is a potential regional seal in the Miocene-Pliocene section both onshore and offshore. In the offshore area, the most promising reservoirs may be the Palaeogene sandstones.
The Krishna-Godavari Basin
The Krishna-Godavari basin has excellent CO2 storage potential both onshore and offshore, as the numerous hydrocarbon fields indicate the presence of traps that can retain buoyant fluids at several stratigraphic levels. Goodand permeability are present in some of these fields, e.g. the Ravva field, which is offshore. Further potential undoubtedly exists in deep water further offshore.
The Cauvery Basin
The presence of oil and gas fields in the Cauvery Basin indicates that the potential to store CO2 in this area is high. This is particularly so in Mid- to Upper Cretaceous sequences where reservoir quality is good and there are interbedded seals.
The Mumbai Basin
The Mumbai Basin is a huge offshore area which appears to have good potential for CO2 storage. The majority of reservoirs in this region are carbonates, so CO2/water/rock reactions need to be considered. Moreover, reservoir properties can be quite variable. Post-Miocene shales form a regional cap rock over the whole Mumbai Offshore, except for the Ratnagiri Block. Overpressured formations may have to be avoided.
The Cambay Basin
There is good CO2 storage potential in the Cambay Basin, demonstrated by the presence of numerous oil and gas fields. The Tarapur Shale is a regional cap rock that lies above the main reservoir rocks, which are of Middle-Upper Eocene age. Offshore, in parts of the Gulf of Cambay, hydrocarbons have been trapped in domal structures capped by the overlying Miocene Kand Shale. There is good potential for EOR in the oil fields of the Cambay Basin.
The Barmer Basin
The Barmer Basin is the northwards continuation of the Cambay Basin into the state of Rajasthan. There is likely to be excellent future potential for CO2 storage in the Barmer Basin, both for EOR in the oil fields once these are developed, and in the aquifers. Projected secondary recovery by waterflooding in the main fields is predicted to be only in the order of 10-30% of oil in place.
The Jaisalmer Basin
The Jaisalmer Basin has potential for CO2 storage, particularly in the western Kishangarh and Shahrgarh sub-basins where gas fields prove the potential to contain buoyant fluids.
220.127.116.11 BASINS WITH FAIR POTENTIAL
These contain one or more potential regional seals, underlying reservoirs at depths >800 m and potential structural closures. However, in these basins, containment of buoyant fluids over geological timescales is not yet proven by the discovery of hydrocarbon fields. These basins are:
- Mahanadi Basin (onshore and nearshore part)
- Bikaner-Nagaur Basin
- Kutch Basin
The location of these basins, the basins with good potential and the major sources of CO2 are shown in Figure 2.7 Summaries of the potential of these basins follow:
The Mahanadi Basin (onshore and shallow water offshore)
Both the onshore and shallow offshore basins should have some CO2 storage potential, but the lack of hydrocarbon discoveries shoreward of the 200 m isobath (and thus a lack of proven containment of buoyant fluids) means that the potential in these areas is classified as only fair. Nevertheless, there is a potential regional seal in the Miocene-Pliocene section both onshore and offshore. In the offshore area, the most promising reservoirs may be the Palaeogene sandstones.
The Bikaner-Nagaur Basin
Some CO2 storage potential may exist in the Proterozoic reservoirs beneath the Hanseren Evaporite Formation, i.e. the Jodhpur Sandstone and the Bilara Dolostone. However, this cannot be quantified at present.
The Kutch Basin
In the Kutch Mainland, the Upper-Jurassic top Jhuran sandstones are potential reservoir rocks which are buried to depths of around 800-1295 m therefore potentially suitable for CO2 storage. In the Pacham Island area, Mesozoic cover is possibly too thin to be of interest for CO2 storage. In eastern Kutch, sands of the Lower Khadir Formation are at sufficient depth to be considered for CO2 storage and capped by shales. Further study is required to firm up the storage potential in this basin.
18.104.22.168 BASINS WITH LIMITED POTENTIAL
Porous and permeable reservoir are absent or not sealed in these basins, or the basins lack structural closures, or are in structurally complex fold belts, or they face major potential conflicts of use. Basins in this category are:
- Ganga Basin (and Punjab Shelf)
- Bengal Basin (Indian part)
- Vindhyan Basin
- Cuddapah Basin
- Chhatisgarh Basin
- Konkan-Kerala Basin
- Narmada Basin
- Saurashtra Basin
- Rajmahal Basin
- Pranhita-Godavari Basin
- South Rewa Basin
- Satpura Basin
- Damodar Valley Basins
These are shown in Figure 2.8. The reasons that these basins are considered to have limited potential at present are given below. It is probably premature to write any of them off completely however, given the current state of knowledge about CO2 storage and the fact that many of them are relatively poorly explored due to a perceived lack of hydrocarbons.
The Ganga Basin and Punjab Shelf
The Ganga Basin, which lies beneath the densely populated agricultural region of the Ganges Plain, is considered to have limited potential because there is a potential conflict of interest between groundwater supply and CO2 storage. This may be controversial because geologically the Ganga Basin contains 4-6 km of Cenozoic and Quaternary alluvium that thins southwards and eastwards onto older sedimentary rocks. Were it not for the potential conflict of interest, this basin could have significant CO2 storage potential. Fewer wells have been drilled in the Ganga basin and Punjab Shelf than in prospective areas elsewhere in India and hence some areas and sequences are still poorly known. By 1991, only 15 deep exploration wells had been drilled.
The Bengal Basin
The western (Indian) part of the Bengal Basin may have some CO2 storage potential, but the lack of proven seal and closure means that prospects are classified as limited at present. There is excellent potential in the eastern part of the basin, in eastern Bangladesh, where there are gas fields in the basin both onshore and offshore.
The Vindhyan, Chhatisgarh and Cuddapah Basins
The Vindhyan, Chhatisgarh and Cuddapah Basins are Proterozoic basins – the sedimentary rocks within them are generally about 1500-500 million years old. Such information as is available at present suggests that these rocks are highly indurated and have insufficient permeability for large-scale CO2 storage.
The Konkan-Kerala Basin
The Konkan-Kerala Basin is perceived to have poor reservoir potential and may lack structural closures.
The Narmada and Saurashtra Basins
The Narmada and Saurashtra basins may have potential beneath the Deccan Trap, but this is unproven and this part of the succession is likely to be difficult to image seismically.
The Prahnita-Godavari, Satpura, Rajmhal, Damodar Valley and South Rewa Basins
The Prahnita-Godavari, Satpura, Rajmahal, Damodar Valley and South Rewa Basins are Gondwana Basins some of which are relatively restricted in size and depth. Nonetheless, some are large, contain significant thicknesses of sandstone and may have storage potential at depth (Mondal 2006). For example sandstones in the Rajmahal coalfields, which continue at depth beneath the Rajmahal Traps, and sandstones within the Lower Gondwana succession in the Pench-Kanhan-Tawa valley area may have potential at depth in the centre of the Satpura Basin. It is definitely too early to write off the CO2 storage potential of some of these basins, but further investigation is required to prove up potential.
Some of the Gondwana Basins are actively being mined for coal. These coal-bearing areas may have potential to store limited amounts of CO2 adsorbed onto coal (see section 2.2.2 above).