Abstract

A series of laboratory investigation on factors affecting Enhanced Oil and Gas Recovery and CO<sub>2</sub> geo-sequestration were conducted. The coreflooding experiments were done using a relatively heavy crude oil (18& API), a number of brines of 0.18%-2.5% NaCl and varieties of cores with a range porosity and permeability from 15% and 17 mD to 19% and 330 mD under some typical reservoir pressure-temperature condition of 1164-3300 psi and 50-83 &C. Factors affecting CO<sub>2</sub> enhanced oil and gas recovery including the effects of the petrophysical properties of the reservoir rocks, formation water salinity, reservoir pressure, the Minimum Miscibility Pressure (MMP), total volume (PV) injected and injection rate and gravity segregation.

Excellent recovery factors in the range of 27%-34% Original Oil In Place (OOIP) and almost 100% gas recovery were achieved through immiscible and miscible CO<sub>2</sub> flooding. Some of the coreflooding experiments were monitored with a medical CT in real time. The coreflooding experiments have shown that (1) reservoir petrophysical properties with permeability difference of up to an order of magnitude do not affect the CO<sub>2</sub> EOR factor; (2) variable EOR can be achieved both at reservoir pressures below or above the CO<sub>2</sub>-oil MMP; (3) Incremental oil recovery is proportional to the pore volume (PV) of CO<sub>2</sub> injected up to 3PV; (4) No significant additional recovery was observed beyond the MMP; (5) CO<sub>2</sub>-Water alternating gas (WAG) flooding can be quite effective in EOR in terms of the less amount of CO<sub>2</sub> injected as compared to that for the single CO<sub>2</sub>-water flooding to achieve the same EOR; (6) there is no benefit to use low-salinity CO<sub>2</sub> WAG flooding; (7) the optimum injection rate in the laboratory is around 1 cc/minute. These finding may provide some useful insight and guide for the field application of CO<sub>2</sub> enhanced oil and gas recovery; (8) During enhanced gas recovery using supercritical CO<sub>2</sub>, gravity segregation may occur in some porous-permeable reservoir with denser supercritical CO<sub>2</sub> preferentially enter through the bottom of the reservoir.

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