致密油藏溶解气驱产能计算模型

A prediction model of well productivity for dissolved gas driving in tight oil reservoirs

针对致密油藏体积压裂水平井,考虑启动压力梯度和溶解气析出,引入新的拟压力和启动压力系数,运用稳定状态逐步替换法处理模型的非线性,改进三线流数学模型。结合物质平衡方法和牛顿迭代法求取不同时间下的地层压力和含油饱和度,获得致密油藏油气两相流产能半解析解,并运用矿场实际生产数据验证模型的准确性和实用性。结果表明:所建立的致密油藏油气两相产能计算模型模拟结果与现场数据吻合度高,可用于矿场实际进行产能预测;溶解气驱对产能的贡献显著,矿场实际中可通过超前注气等方式提高原始地层压力和溶解气油比提高产能;累积产油量随着启动压力梯度、井底流压的增加而减小,随着岩石压缩系数、溶解气油比、压裂段数、裂缝导流能力、半缝长的增大而增大。

A prediction model of well productivity for dissolved gas driving in tight oil reservoirs with hydraulic fracturing was figured out in this study.A new pseudo-pressure and threshold pressure coefficients were introduced using a steady-state gradual replacement method to deal with the nonlinearity of the model,considering the threshold pressure gradient and dissolved gas evolution,and the trilinear flow mathematical model was improved for stimulated volume fracturing in horizontal wells of tight oil reservoirs The model was solved combining the material balance and the Newton iteration methods to calculate the evaluation formation pressure and oil saturation at different times,and a semi-analytical solution of the two-phase flow productivity of the tight reservoir can be obtained.The accuracy of the model was verified using the actual production data of typical wells.The results show that the prediction results using the new model have a high precision match with the field data,and dissolved gas driving has a significant contribution to the well productivity.In practice,the original formation pressure and the dissolved gas-oil ratio can be increased by means of advanced gas injection in tight oil reservoirs in order to enhance the dissolved gas driving.It is also found that the cumulative oil production decreases with the increase of the threshold pressure gradient and bottom hole flowing pressure,while it increases with the increase of rock compressibility,dissolved gas-oil ratio,number of fracture sections,fracture conductivity,and half fracture length.