The Geological Potential of the Arabian Plate for CCS and CCUS - An Overview
12 Pages Posted: 9 Apr 2021
Date Written: April 8, 2021
Given allowable carbon emissions for reaching climate targets, CCS and CCUS are without alternatives to simultaneously maintain a supply of sufficient energy for the world and preventing stranded subsurface assets for hydrocarbon producing countries. Permanent storage of carbon dioxide (CO2) in deep subsurface formations is acknowledged as a scalable and achievable technology to contribute to the ongoing efforts of limiting CO2 emissions and possibly lead to the use of stored CO2 for geothermal energy generation. The sequestration processes include entrapping CO2 in saline aquifers and hydrocarbon reservoirs in its mobile phase and in basalts as carbonate minerals. So, what are then the geological subsurface opportunities in Arabia for CO2 sequestration? A high level assessment has been conducted to identify geological formations suitable for storing and utilizing CO2 on a large scale. Over the Arabian peninsula four significantly different geological terrains are likely suitable for CCS & CCUS: (1) An Eastern section of stacked Mesozoic aquifers along the coast and inland of the Arabian Gulf, (2) rift basins with deep saline aquifers along the Red Sea, (3) Cenozoic volcanic rocks inland of the Red Sea coast, and Proterozoic ultramafic rocks in the Arabian Shield, and (4) a fringe of Cretaceous obducted marine crust (ophiolites) in Northeastern Oman and the UAE.
The potential of the North-Eastern section for retaining CO2 in the subsurface is essentially manifested by the presence of many super giant oil reservoirs in stacked, layered limestone sequences of mainly Mesozoic age. During this time period the eastern part of the Arabian plate was at a passive continental margin in a near-equatorial location resulting in mainly limestone deposition over very large areas. The overall architecture of cyclic carbonate deposition, interrupted by the incursion of thick layers of evaporites (e.g. Tithonian Hith Anhydrite) and shales (e.g. Albian Nahr Umr FM), has produced an ideal combination of multiple stacked reservoirs/aquifers overlain by seals. Gentle folding has created numerous structures for the permanent entrapment of migrating hydrocarbons but also light fluids such as supercritical CO2. Aquifer porosity and permeability are typically around 20% and 10mD - 100mD respectively, but can reach up to 40% porosity and Darcy-scale permeability. Aquifer fluids are typically highly saline reaching concentrations of 5 times seawater or more. The favorable conditions of relatively high porosity and permeability can exist to several km depth at which the formation temperatures reach 150°C and sometimes beyond. This not only offers the possibility for CO2 storage but also utilization as a geothermal source for electricity generation and other heat-energy utilization processes, such as desalination and district cooling. Similar favorable geological conditions for CCS and CCUS are likely present in the rift basins along the Red Sea Coast albeit at a smaller scale and less well explored. Rift basins reach 6km in depth and are filled with continental and marine clastic and carbonate sediments, salt and shale layers can provide seal capacity. Opportunities for CCUS and geothermal energy generation are likely to exist near the populated and industrialized centers along the Red Sea.
Thick stacked basaltic lava flows inland of the Red Sea coast (Harrats) and ophiolites associated with seafloor obduction along the North-Eastern margin of the plate in Oman and the UAE offer opportunities for CO2 sequestration in its solid phase.
Keywords: Arabian Peninsula, CCS, CCUS, subsurface CO2 storage, deep aquifer, seals, stacked basalts, geothermal energy
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