Compositional Simulation of CO 2 Huff-n-Puff Processes in Tight Oil Reservoirs with Complex Fractures Based on EDFM Technology Considering the Threshold Pressure Gradient

Although tight oil reservoirs have abundant resources, their recovery efficiency is generally low. In recent years, CO 2 injection huff-n-puff has become an effective method for improving oil recovery on the basis of depleted production of volume-fracturing horizontal wells in tight oil reservoirs. In order to study the effects of CO 2 huff-n-puff (CO 2 -HnP) on production, a compositional numerical simulation study of CO 2 huff-n-puff (CO 2 -HnP) was conducted in tight oil reservoirs with complex fractures. Embedded discrete fracture model technology was used in the simulations to characterize complex fractures. The process of CO 2 huff-n-puff (CO 2 -HnP) was simulated, which consists of CO 2 injection, CO 2 soaking, and CO 2 production. Taking into account the threshold pressure gradient and stress sensitivity in the model, we conducted a series of numerical simulations with different production condition parameters, such as bottom-hole pressure, CO 2 injection rate, injection time, soaking time, and the number of cycles of CO 2 huff-n-puff (CO 2 -HnP). Then, the effects of these sensitivity parameters on the cumulative oil production (COP) were studied. The results indicate that the threshold pressure gradient and rock stress sensitivity factors greatly affect the pressure field of tight reservoirs and the cumulative oil production (COP) of multistage-fracturing horizontal wells. The production parameters all have an impact on the COP. The injection rate and circulation number both have optimal values, and the injection time and soak time tend to have less significant effects on the growth of cumulative oil production over time. According to the numerical simulation, the optimal solution is 5 × 10 4 m 3 /day injection rate per cycle, 25 days of injection time, 35 days of soaking time, three cycles, and production for 5 years, which can obtain the optimal cumulative oil production.