Problems like small sweeping volume, short stimulating period and poor producing performance challenge the effectiveness of single horizontal well CO2 huff ‘n’ puff in the fault-block reservoirs with edge water. The effect of CO2 volume on multiple horizontal wells CO2 huff ‘n’ puff has been studied in this paper to investigates the feasibility of CO2 huff ‘n’ puff by horizontal well group. Studies on both isothermal property of CO2 and the CO2-crude oil properties under reservoir conditions offer the possible basis for this work. A 3D edge water model with three horizontal wells, which was designed and produced according to geological data, was used to simulate the process of CO2 huff ‘n’ puff by horizontal well group. Subsequently, experiments were carried to investigate the impact of CO2 volume on water control and oil stimulation. Results show the CO2 isothermal compressibility under certain pressure make it possible to inject gas with relatively low energy loss and to enlarge sweeping volume. Meanwhile, with more CO2 mole composition in the crude oil, the mixture intends to be more flowable. Consequently, as the gas volume increases from 0.07PV to 0.13PV, the comprehensive water cut rate drop from 0.72% to 5.93%, and both oil and gas production increase accordingly. However, the gas use ratio dwindles as the volume exceeds 0.13PV.

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