OPTIMIZING CO2 EOR REAL TIME MANAGEMENT TO INCREASE "GREEN OIL" PRODUCTION THE ELK HILL CASE STUDY

The ability of CO2 to cause swelling, favorable mobility and relative permeability alteration made it an attractive EOR choice. It has gained importance over steam injection for deeper heavy oil reservoirs where steam operation is economically unviable due to depth limitation and/or potential excessive heat losses. A recent study on CO2‑EOR in the U.S. indicated that a production of 88 billion bbl of oil is technically feasible, while 39‑48 billion bbl are economically recoverable with current CO2 EOR technologies. However, with several ongoing projects all over the U.S. only 2.3 Billion bbl have been produced so far. Elk hills oilfield has been selected for the optimization study due to its wide range of net thickness, with 80% of its oil coming from zones between 5,000 ft and 10,000 ft, its mature condition and environmental sensitivity. Its 1,100+ wells and light oil gravity (38o API on average) plus extensive data are already available in the public domain make it a favorable candidate. In this paper we propose a new methodology to alter the MMP by optimizing the CO2 purity with varying mol fractions of hydrocarbon gases to effectively enhance the mobility ratio. We emphasize on maximizing reservoir contact to minimize the effects of viscous fingering and gravity override, while effectively increasing well operating pressure. The optimum distribution and count of vertical injectors, sufficient CO2 volumes and maintaining favorable fluid balance are key parameters used in the study. The paper elaborates an optimized next generation CO2‑EOR real‑time management approach for Elk hills oilfield, which would require a zonal allocation program, formal CO2‑EOR tracking system using observation wells allowing the precise targeting of the main pay zone, the residual oil zone and continuous CO2 injection.