Pacific Section AAPG, SPE and SEPM Joint Technical Conference

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A Geochemical Investigation Of The Suitability Of Oil Reservoirs In The Southern San Joaquin Valley Of California For Carbon Sequestration And Enhanced Oil Recovery


Carbon capture and sequestration (CCS) is one approach to reduce emissions of the greenhouse gas CO2 into the atmosphere. CCS involves capturing CO2 emissions from power plants, compressing it to a supercritical state, and injecting it into an underground reservoir. The San Joaquin Valley (SJV) is being investigated as a possible location for CCS combined with enhanced oil recovery (EOR) to help reduce greenhouse gas emissions as well as increase oil production within depleted oil fields. The three formations studied for this project are the three most likely targets for CCS within the SJV: the Stevens Sandstone (Elk Hills, North Coles Levee oil fields), the Temblor Formation (McKittrick oil field), and the Vedder Formation (Rio Bravo oil field). Before CCS can go forward, a geochemical analysis of potential water-rock interactions due to exposure to supercritical CO2 must be completed. Core samples from the three target formations were acquired from the California Well Sample Repository. Sample mineralogy was examined by X-ray diffraction (XRD) and scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS) analysis. Potential dissolution/precipitation reactions were examined by identifying changes in solution chemistry during high pressure/temperature (250 bars, 110oC) autoclave reaction experiment in which the formation samples were exposed to supercritical CO2 for 12 days under the conditions in the proposed storage formations. The experiments showed an immediate drop in pH to 5.63 and then a slow rise back up to 6.25. Alkalinity increases more than 10-fold and dissolved Ca, Mg, and K increase by a factor of 4, indicating dissolution of carbonate minerals and possibly feldspars. After the experiments, the formation samples are examined by SEM-EDS to identify changes in mineralogy and texture due to exposure to supercritical CO2. Potential future dissolution/precipitation reactions are identified through geochemical modeling of changes in solution geochemistry, using the PHREEQ-C interactive geochemical modeling program.