ABSTRACT: Pre injection of CO2 before main fracturing can effectively increase oil production and store CO2. SEM scanning showed that complex cross fracture structure is formed on the rock surface, and the permeability of the core is significantly improved after CO2 soaking. According to the experimental data and production history fitting, the permeability of fractures and matrix affected by CO2 are established. The temperature of CO2 along wellbore was calculated to determine the phase state of CO2. We compared the effects of CO2 injection amount, shut in time and injection mode on fracturing stimulation. The results show that: for Mahu conglomerate reservoir in Xinjiang, pre injection of CO2 can increase oil production by more than 15% compared with direct fracturing in the first year; continuous injection is recommended to developing the reservoir, which can contact larger reservoir area; single fracture injection of 60 tons CO2 and shut in time of 15 days can achieve good results in reservoir development. For refractured well, CO2 + fracturing fluid is preferred due to low viscosity of CO2 and weak capability to propagate the fracture.

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