Net fluid production and pressure data were gathered to estimate the amount of CO2 storage space available and the potential for additional oil recovery using CO2-enhanced oil recovery (EOR) in the Phacoides sandstone, McKittrick oilfield, San Joaquin Valley, California. The Phacoides reservoir has produced 61.5 million reservoir barrels of fluid, a volume equivalent to the subsurface capacity of 9.8 million metric tons of CO2. Reservoir pressure changes with fluid production suggest that injecting 1 million metric tons of CO2 may raise reservoir pressures by 2 MPa (255 psi). We assume that the sealing capacity of the reservoir for CO2 injection is equivalent to the conditions controlling the original hydrocarbon accumulation. If injection pressures exceed this limit, the CO2 could leak through the caprock, from aging wellbores or along faults in the reservoir.

Faulting has compartmentalized the reservoir into six major blocks with varying degrees of hydraulic communication. Injection wells will be required within each sealed fault block, resulting in additional costs for implementing a carbon capture and sequestration (CCS) project.

Through CO2-EOR, an additional 17 million bbl of oil may be recoverable, thereby offsetting the cost of carbon storage. This is equivalent to 1.4 million metric tons of additional storage space. However, assuming that none of the carbon is captured, combustion of this additional oil will add approximately 7 million metric tons of CO2 to the atmosphere, negating the available storage space in the reservoir and resulting in a net carbon gain to the atmosphere of 700,000 metric tons.

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