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2 Sequestration
Published in S. Komar Kawatra, Advanced Coal Preparation and Beyond, 2020
Caprock failures refers to fractures, whether naturally occurring or as a result of CO2 injection, in the rock above the CO2 reservoir by which the CO2 can escape. Most rock formations which have been considered suitable at all for use as a CO2 reservoir, particularly shale and evaporates, are understood to be fully up to the task of containing CO2 (Pawar et al., 2015). However, it is not necessarily the case that these rock formations are actually present across the entirety of any given reservoir. The laboratory determination of caprock quality largely depends on the permeability and capillary pressures: low permeability and high capillary entry pressures are correlated with high-quality caprock (Pawar et al., 2015). However, practical field concerns require determining whether or not the caprock is actually intact, based on the ductility of the rock and previous seismic history, along with the overall geometry of the reservoir (Pawar et al., 2015). Based on these parameters, risk assessment models can be developed.
Petroleum Migration and Accumulation
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
Trap rocks are of two type named according to their trapping functions. ‘Cap rock’ is a trap rock of low-permeability found at the top of the reservoir rock to prevent the upward leakage of oil/gas.‘Seal rock’ is a trap rock of low-permeability and functions to seal or block fluid in carrier bed and reservoir rock.
Optimization of injection-withdrawal schedules for underground gas storage in a multi-block depleted gas reservoir considering operation stability
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
Jun Zhou, Jinghong Peng, Guangchuan Liang, Jianhua Sun
UGS in a depleted gas reservoir mainly consists of underground system and aboveground system (Figure 1). The underground system includes reservoir, caprock and faults. The reservoir is a rock layer with certain porosity and permeability that can store natural gas. Caprock is the low permeability rock layer above the reservoir that protects the gas from escaping upward. Fault refers to the structure in which the earth’s crust is fractured by force, and the rock blocks are relatively displaced along both sides of the fault surface. Faults disrupt the continuity of the rock layer, so they prevent the flow of natural gas in a reservoir. According to the location of faults in the reservoir, they can be divided into boundary faults and internal faults. Due to the existence of internal faults, a complete reservoir can be divided into several disconnected RBs. Besides, the aboveground system has valve groups, gathering pipeline, compressor unit and dehydration unit. Injection-withdrawal wells connect the underground system and the aboveground systems.
Origin of the Neoproterozoic rim dolomite as lateral carbonate caprock, Patawarta salt sheet, Flinders Ranges, South Australia
Published in Australian Journal of Earth Sciences, 2020
R. A. Kernen, K. A. Giles, P. L. Poe, C. E. Gannaway Dalton, M. G. Rowan, J. C. Fiduk, T. E. Hearon
Salt diapir caprocks form by dissolution of halite and the cross flow of halite-undersaturated waters that leaves an insoluble residue of the non-halite minerals accreting along the salt–sediment interface (Figure 3; Kyle & Posey, 1991). The insoluble residue is dominated by sulfate minerals (anhydrite and gypsum) that progressively accrete downward with ongoing halite dissolution during diapiric inflation, a process referred to as ‘underplating’ (Kyle & Posey, 1991). Early in this process, microbe sulfate reduction (up to 85°C) or thermochemical sulfate reduction (100–135 °C) reduce organic compounds such as dead organic matter, carbohydrates, kerogen, crude oil, bitumen, dissolved or gaseous organic compounds (Machel, 1989). Sulfate is reduced to sulfide (H2S, HS–, and S2–) and to elemental sulfur while the organic compounds are oxidised to bitumen, bicarbonate, and/or carbon dioxide (Machel, 1989). A number of minerals may precipitate if the specific cations are available in sufficient amounts: these include calcite, dolomite, siderite, ankerite, pyrite, sphalerite, galena, and other minerals (Machel, 1989). Secondary and tertiary porosity, as well as solution-collapse brecciation, may occur owing to the dissolution of solid sulfates and/or carbonates (Machel, 1989). As a result, a vertically zoned sequence of anhydrite, gypsum, and/or limestone is formed along the salt–sediment interface and referred to as caprock (Figure 3; Kyle & Posey, 1991). Caprock associated with salt bodies can be found in both crestal or lateral positions adjacent to salt bodies (Evans, Nunn, & Hanor, 1991; Giles et al.,2012; Jackson, & Lewis, 2012; Kyle & Posey, 1991; Mast, 2016; Schwerdtner & Troeng, 1978).