Characterization of a potential CO2 storage complex in the Cambay Basin, India

Williams, John; Roy, Somali; Pal, Nabarun; Vishal, Vikram. 2024 Characterization of a potential CO2 storage complex in the Cambay Basin, India. [Lecture] In: Society of Exploration Geophysicists. Role of Geosciences in Carbon Storage., Mumbai, India, 19-21 Mar 2024. (Unpublished)

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Introduction High-level studies have identified that there is potential for subsurface storage of CO2 in India (Holloway et al., 2009; Vishal et al., 2021). A major challenge to the deployment of CO2 storage in India is the lack of detailed technical appraisals aimed at understanding and de-risking the storage resource. The vast majority of India’s CO2 storage resource is therefore considered to be undiscovered as per the Society of Petroleum Engineers CO2 Storage Resource Management System (SRMS) scale (SPE, 2017). Given the need to rapidly appraise India’s storage resource to support emission reductions targets, one pragmatic approach would be to first define representative storage complexes in key regions of interest for future CO2 storage developments. Theory and/or Method The notion of a CO2 storage complex is embedded in European legislation, where it provides a means of defining the storage site and surrounding geological domain which can have an effect on overall storage integrity and security, including secondary containment formations (EC, 2009). Defining a storage complex can therefore be a key starting point in identifying the specific site appraisal studies required to gain insight into the likely dynamic behavior of sites during CO2 injection, including the long-term post-injection period. This presentation will investigate how storage projects developed in NW Europe have considered the subsurface lithostratigraphy and structure to define storage complex boundaries. Through interpretation of legacy datasets acquired during legacy oil and gas exploration and development, these principles will then be applied to an area on the flank of the brownfield Gandhar Oil Field in the Cambay Basin, Gujarat. Example The lithostratigraphic determination of a potential storage complex within the Anklesvar Formation is illustrated in Figure 1. The stratigraphy of the Cambay Basin presents the possibility for several different storage concepts. Firstly, hydrocarbon-bearing sandstones of the Mid-Eocene Hazad Member may be suitable for CO2 storage, either following cessation of production, and/or as a beneficial by-product of CO2-enhanced oil recovery. The Hazad Member is sealed by shales of the Kanwa Member. Secondly, marine shales of the overlying Ardol Member provide an additional top seal, while deltaic sandstones are also present over part of the area which present an opportunity for saline aquifer storage. The sand-prone sequences within the Ardol Member may be considered as a storage opportunity in their own right, or in the context of secondary storage in the event of CO2 storage in the Hazad Member. The storage complex is capped by shales of the Telwa Member, which exhibits a variable thickness distribution across the region. The regionally extensive Y Marker in the Upper part of the Cambay Shale provides a reliable seismic reflector which can conveniently be used to define the lower storage complex boundary. In this way, thin impersistent sandstones in the upper part of the Cambay Shale are also incorporated within the storage complex. Evaluation of legacy oil and gas datasets have enabled mapping of the distribution, thickness and structural disposition of the reservoir and top seal units. This has enabled a high-level assessment of the storage potential and associated storage risks to be determined. The spatial arrangement of reservoir sands in the Hazad and Ardol Members is controlled by frequent fluctuations between transgressive and regressive sequences, and the direction of sediment input. The deltaic sands of the Hazad Member are mainly sourced from the Northeast, and are covered by transgressive shales of the Kanwa Member. Changes in baselevel and sediment input direction have influenced the distribution of the Ardol Member, leading to an uneven distribution of sands. The Telwa shale, acting as the regional seal, experiences occasional erosion beneath a second-order erosional unconformity. No major faults offset the storage complex in the study area, with the primary risk being the presence of down-cutting sandstone units affecting the Kanwa and/or Telwa member top seals. A number of key recommendations for further detailed appraisal have been identified, including the requirement to accurately determine the volumes of sandstone available for CO2 storage capacity estimations, and the requirement to carefully characterize the thickness of the Telwa Member as the ultimate top seal. Finally, the high number of legacy oil and gas wells in the region will necessitate detailed well integrity studies. Conclusions We have demonstrated for the first time how application of the storage complex concept can be applied to an onshore sedimentary basin in India. The study has enabled identification of specific activities that will be required to fully understand the CO2 storage potential of the region. These measures relate to the quantification of storage capacity, the likely dynamic behavior of the site, and the understanding of containment risk and natural barriers.

Item Type: Publication - Conference Item (Lecture)
Additional Keywords: IGRD
Date made live: 03 Apr 2024 14:36 +0 (UTC)

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