Experimental studies on CO2 foam performance in the tight cores

Enhanced oil recovery for tight reservoirs with extremely low permeability and porosity is becoming the new routine for reservoir engineering research. Foam flooding has already been proven as an effective approach to enhance the oil recovery in conventional reservoirs. However, limited research has been done on the phenomena and mechanism of foam performance in the tight porous media. In this study, a series of core flooding tests are performed to investigate the foam performance in the absence and presence of oil in tight core samples with different permeabilities from 0.1mD to 3.3 mD. The foam resistance factor, mobility reduction factor, and relative mobility of the displacing fluid are investigated by comparing the foam flooding processes with waterflooding and the co-injection processes of brine and gas. The effectiveness of applying foam flooding as a tertiary recovery method in the tight core samples is studied by comparing the production data, pressure drop data, and relative mobility of displacing fluid between foam flooding and waterflooding. Unlike conventional foam injection process, the increase of foam quality will not create more stable foam flow that gives significant higher foam resistance factor and much better mobility control as expected in the tight core samples. Also, the foam resistance factors even decrease with increasing injection rates at such a low permeability. These results suggest the foam with low foam quality and low injection rate may be the answer to tight reservoir EOR application. As for the oil production test, the experimental results support the effectiveness of foam flooding on reducing mobility compared with waterflooding and the co-injection of brine and gas. An additional 15-22% oil recovery factor is achieved by introducing foam flooding after waterflooding has done. Surprisingly, comparing with a long period of waterflooding without any oil production, the additional oil was successfully produced at a much lower pressure drop during the early stage of foam injection. Since extremely high pressure drop may not be a necessary constraint on foam flooding EOR process in tight reservoirs, it suggests the potential solution on questionable injectivity issue during foam flooding in the tight reservoirs by introducing an optimized discontinuous surfactant-alternating-gas gas process. Also, the relative mobility of displacing fluid is lowered by one order of magnitude compared with waterflooding in the presence of oil.