基于状态方程的溶解气回注油藏物质平衡计算方法

Material Balance Equation Calculations for Solution Gas Reinjection Reservoir with the Equation of State

传统物质平衡方程(material balance equation,MBE)计算溶解气回注的过程中,油气体积系数和溶解气油比等物性参数难以准确测定,当分离器温度、压力等计算条件变化时又需重新进行高压物性实验,过程烦琐且成本较高。针对以上问题,从物质平衡原理出发,分别在油藏压力高于和低于饱和压力条件下推导出物质的量形式的溶解气回注物质平衡方程,同时给出油藏采出程度和含油饱和度表达式;结合Peng-Robinson(PR)状态方程和闪蒸计算方法编制了相应的程序,预测了实际油藏地层压力和平均流体饱和度等开发动态特征,并运用组分模型对计算结果进行验证。结果表明:该物质平衡方法能够准确预测溶解气回注开发特征;对于异常高压油藏,原油主要的可采储量来自弹性气驱开发阶段,应保持地层压力高于原油泡点压力。

Some property parameters,for example the volume factors of oil and gas and solution gas-oil ratio,are often inaccurate for traditional material balance equation(MBE)to forecast the performance of solution gas reinjection.Furthermore,these data are from PVT test and should be updated with new test when the calculation condition changes,which results in low efficiency and high cost.Aiming at the limitation of traditional MBE,the MBE in mole form and the expressions of oil recovery degree and saturation for solution gas reinjection at pressures above and below the bubble point were developed respectively.The reservoir performance,such as reservoir pressure and average fluid saturation,was also predicted by the Peng-Robinson(PR)equation of state and flash calculation with corresponding computing program for a real case.All results were validated by compositional simulator.The results show that this new MBE method can forecast the reservoir performance accurately.For abnormal high pressure reservoir,pressure should be maintained above the bubble point to produce the most recoverable reserve.