Testing Method Study On Relative Permeability Of CO₂ Flooding

There were rich resources of low permeability oilfields in China,whose proven geological reserves has amounted to more than 70 million tons at present. Because low permeability oilfield had characters of low permeability, low porosity, low natural capacity, poor reservoir property, high interlayer heterogeneity, and non-Darcy seepage, the effect of water flooding development was poor. Limited by the current theoretical and technical conditions, its recovery can only reach about 20%, which was far lower than the recovery after water flooding & chemical flooding in medium of high permeability reservoirs. Through practice and research, CO₂ was injected into reservoir as oil flooding agent, which could greatly enhance the oil recovery of low permeable oil fields.The technology of improving oil and gas recovery using CO₂ flooding has been done a great deal of researches at home and abroad. The relative permeability curve had an important role on the research of fluid distribution, recognizing correctly CO₂ flooding characteristics under the condition of immiscible phase and miscible flooding and obtaining the exact relative permeability curve was the base of the research of swept volume, flooding effect, fine reservoir description and program optimization design. Research showed that the general relative permeability curves measuring method of CO₂ immiscible flooding was non-steady state in domestic at present, but considering non comprehensive affecting factors, whereas researches on the test method of CO₂ miscible flooding was less.Based on the enhanced oil recovery mechanisms of CO₂ flooding and the theoretical analysis on the affecting factors of CO₂ flooding relative permeability curve, the relative permeability curve measuring method of CO₂ immiscible flooding and miscible flooding has been studied by laboratory experiment in low permeability core. At last, the measuring method of CO₂ immiscible flooding has been improved,and the relative permeability curve of CO₂ miscible flooding was measured by the steady state method. According to the comparison and analysis on the obtained relative permeability curve, the changes of low permeability core actuating pressure, gas slippage effect, CO₂ solubility, and fluid viscosity had effect on test results of CO₂ flooding. Among them, low permeability core actuating pressure gradient mainly affected the of oil relative permeability values, gas slippage had certain effect on the gas phase relative permeability values, and higher values of relative permeability curves could be gained without considering these two factors. CO₂ solubility mainly affected the calculation results of core gas saturation, but we found after much research that fluid viscosity changed with the change of CO₂ content and the curve shape would generate certain deviation if ignore this factor. Comparing with miscible flooding and immiscible flooding, two phase area span was bigger and the end point value of gas phase relative permeability was higher.