The Effect of Formation Water Salinity on the Minimum Miscibility Pressure of CO2-Crude Oil for Y Oilfield

CO2 miscible flooding is an important technology for enhancing oil recovery and greenhouse gas storage in the world. However, as a tertiary recovery technology, it usually occurs after water flooding development. Therefore, the actual reservoir usually contains a lot of injected water in addition to bound water.The salinity of these formation waters varies from place to place.However, CO2 is a kind of gas with strong activity. After it is injected into the reservoir, it is easy to react with formation water and rock and affect the physical properties of the reservoir. Does this reaction affect the minimum miscible pressure (MMP) of CO2-crude oil, a key parameter determining miscible flooding in formation water with different salinity?How?There is little coverage of this. Therefore, based on the CO2-formation water-rock interaction experiment, this paper uses the core displacement method to measure the MMP of CO2-crude oil with different salinity in formation water. The experimental results show that CO2 dissolved in formation water and acidified it，which caused that the PH of formation water decreased from 7.4 to 6.5. At the same time, CO2 reacted with formation water and albite, potassium feldspar and carbonate minerals in the core to generate silicate and carbonate precipitates, which migrated to the pore throat together with the released clay particles. Ultimately, it increased the porosity of the core by 5.63% and reduced the permeability by 7.43%. In addition, when the salinity of formation water in core was 0mg/L, 4767 mg/L and 6778 mg/L, the MMP of CO2- crude oil was 20.58MPa, 19.85MPa and 19.32MPa respectively.In other words, with the increase of salinity of formation water, the MMP of CO2- crude oil decreased gradually.