The Study On The Increasing Recovery Ratio Technology By Low Temperature Liquid CO₂ Huff-and-Puff

As a kind of oil displacement agent CO2 is used widely in the petroleum industry. It is proved in both lab and field tests that using CO2 to displace oil is an effective method of greatly increasing well productivity. With the discovery of CO2 source and the development of match technology in the home country , low temperature liquid CO2 huff and puff is widely used as a new formation improvement technique applicable to low permeability reservoir and is with good prospect in field application.CO2 huff and puff technology, intending to increase single well recovery, is independent on the fluid displacement (driving) from adjacent well and is confined in a small area. Comparing with the other methods of recovery-enhancing its advantages are less fund, short operating cycle, fast reclaiming cost and applicable in wide scope. It is particularly superior to single wells in small and poorly-connected reservoirs once used other recovery-enhancing methods but less-effective in productivity increase.In this paper we mainly study, analyze and bring forward a solution for the problems induced by pumping low temperature liquid CO2, which once impacted the operating effect when conducting CO2 huff and puff in Jilin Oil Field. Based on information investigation and field data analysis we study all kinds of factors which will influence the operating effects, such as the higher oil viscosity, difficulties in producing oil etc. resulting from changes in temperatures in both well-bore and formation during CO2 injection. We also develop a temperature field model of low temperature liquid CO2 huff and puff. Using this model we calculate the tendency of temperature change in well-bore during different periods as a function of CO2 injecting rate, pumping rate and shut-in time. We provide optimal treatment design parameters and well selection basis. Anexperimental method is also presented here to test the properties of CO2 dissolution in oil and its rheology. During low temperature liquid CO2 huff and puff the rheology of formation oil and property of low temperature liquid CO2 dissolution in oil are varied as the temperature field changes. We have extensively studied these properties and the effect of CO2 injection on surface tension. The preliminary achievements are as the following:① developing a temperature field model of low temperature liquid CO2 huff and puff and a software of technique design for CO2 huff and puff② presenting an experimental method in order to test the rheology of oil during low temperature liquid CO2 huff and puff③ analyzing and determining the rate and volume of CO2 injection in order to control reservoir temperature decrease caused by liquid CO2 and the change in oil viscosity④ determining a proper shut-in time and production pressure difference in order to resume temperature and reduce gas slippage, avoid increasing oil viscosity, enhance CO2 huff and puff effectiveness⑤ giving a conclusion of the more the C02 volume, the longer the shut-in time required in order to resume temperature according to the corresponding relationship between CO2 volume and shut-in time⑥ indicating that at the CO2 critical temperature oil viscosity is the highest.In this paper we analyze the influences of low temperature liquid CO2 huff and puff, in addition present treatment principles of low temperature liquid CO2 huff and puff, therefor our study will provide practical implications.