Ma Yuhua, Kang Zhihong, Lei Xin, Chen Xiaodong, Gou Congbo, Kang Zhijiang, Wang Shuoliang
School of Energy Resources, China University of Geosciences, Beijing, 100083, China.
Research Institute of Exploration and Development of Changqing Oilfield, PetroChina, Xi'an, 710000, Shaanxi Province, China.
Heliyon. 2023 Apr 23;9(5):e15675. doi: 10.1016/j.heliyon.2023.e15675. eCollection 2023 May.
Critical properties shift and large capillary pressure are important contributors for the phase behavior altering of nanopore fluid. However, the effects of critical properties shift and large capillary pressure on the phase behavior are ignored in traditional compositional simulators, leading to inaccurate evaluation results of tight reservoirs. In this study, phase behavior and production of confined fluid in nanopores are studied. First, we developed a method for coupling the effect of critical properties shift and capillary pressure into the vapor-liquid equilibrium calculation base on Peng-Robinson equation of state. Second, a novel fully compositional numerical simulation algorithm considering effect of critical properties shift and capillary pressure on phase behavior is accomplished. Third, we have discussed the alterations of critical properties shift effect, capillary pressure effect and coupling effect on the composition of oil and gas production in detail. The critical properties shift and capillary pressure effects on oil and gas production in tight reservoirs are analyzed quantitatively through four cases, and the influences of the two effects in oil/gas production are compared. Based on the fully compositional numerical simulation, the simulator can rigorously simulate the impacts of component changes during production. The simulation results show that both the critical properties shift effect and the capillary pressure effect reduce the bubble point pressure of Changqing shale oil, and the influence are more prevalent in pores of smaller radius. In pores is larger than 50 nm, the phase behavior altering of the fluid can be ignored. In addition, we devised four cases to comprehensively investigate the effects of critical properties shift and large capillary pressure on production performance of tight reservoirs. The comparisons between the four cases show that the capillary pressure effect impacts the reservoir production performances greater than the critical properties shift effect, such as higher oil production, higher GOR, and lower content of lighter component and higher content of heavier component in the residual oil/gas. The results of coupling effects indicate that the critical properties shift effect would suppress the effect of the capillary pressure effect. In particular, the difference between the simulation results of the coupling effects and the base case is smaller than that between the simulation results of the capillary pressure effect and the base case.
临界性质偏移和大毛细管压力是纳米孔隙流体相行为改变的重要因素。然而，传统的组分模拟器忽略了临界性质偏移和大毛细管压力对相行为的影响，导致对致密油藏的评价结果不准确。在本研究中，对纳米孔隙中受限流体的相行为和产量进行了研究。首先，基于彭-罗宾逊状态方程，开发了一种将临界性质偏移和毛细管压力的影响耦合到气液平衡计算中的方法。其次，完成了一种考虑临界性质偏移和毛细管压力对相行为影响的新型全组分数值模拟算法。第三，详细讨论了临界性质偏移效应、毛细管压力效应和耦合效应在油气产量组成上的变化。通过四个案例定量分析了致密油藏中临界性质偏移和毛细管压力对油气产量的影响，并比较了这两种效应在油气产量中的影响。基于全组分数值模拟，该模拟器可以严格模拟生产过程中组分变化的影响。模拟结果表明，临界性质偏移效应和毛细管压力效应均降低了长庆页岩油的泡点压力，且在半径较小的孔隙中影响更为普遍。在半径大于50nm的孔隙中，流体的相行为改变可以忽略不计。此外，设计了四个案例，全面研究临界性质偏移和大毛细管压力对致密油藏生产性能的影响。四个案例的比较表明，毛细管压力效应比临界性质偏移效应更能影响油藏的生产性能，如更高的产油量、更高的气油比，以及剩余油/气中较轻组分含量更低、重组分含量更高。耦合效应的结果表明，临界性质偏移效应会抑制毛细管压力效应的影响。特别是，耦合效应与基础案例的模拟结果差异小于毛细管压力效应与基础案例的模拟结果差异。
