Mutual Interactions of CO2/Oil and Natural Gas/Oil Systems and Their Effects on the EOR Process

Mutual interactions between oil and gas are critical factors affecting the gas enhancing oil recovery (EOR) process. Focusing on CO2/oil and natural gas/oil systems, their interactions are researched and compared by extraction capacity and solubility measurement experiments. Core flood tests are also implemented to determine the effects of interactions on oil recovery. Results show that CO2 can extract more light oil from the original and its extraction efficiency can reach 59.3% at 46 MPa, whereas that of natural gas is only 7.3%. However, heavy components content and viscosity of the residual oil processed by CO2 increases significantly because of extraction, while natural gas does not affect the composition of the residual so remarkably. With increased pressure, solubility of CO2 and natural gas in a light oil present a linear growth trend with similar rate, but the former is greater than the latter by about 130m(3)/m(3). Core flood tests show that, for the continuous gas injection in the secondary oil recovery process, recovery of CO2 flood is about 20% higher than that of natural gas due to the late breakthrough of CO2, as most of the crude oil is produced before breakthrough.