超深油藏物质平衡方程修正及应用

Modification and application of material balance equation for ultra-deep reservoirs

压缩系数是影响油藏物质平衡方程准确性的关键参数,其大小与地层压力密切相关,超深油藏地饱压差、油藏压降较大,但传统超深油藏物质平衡方程忽略压缩系数随地层压力的变化。为完善超深油藏物质平衡方程,考虑岩石孔隙体积压缩系数、地层水压缩系数、地层原油压缩系数、地层原油的两相体积压缩系数以及气体压缩系数随地层压力的变化,修正不同驱动方式(弹性驱、水压驱动、气顶驱、溶解气驱、综合驱动)传统超深油藏物质平衡方程。研究结果表明:传统油藏物质平衡方程未考虑压缩系数随地层压力的变化、未采用微分或积分法求解,不适合超深油藏;传统油藏物质平衡方程均是近似方程。若忽略压缩系数随地层压力的变化且做进一步近似处理,修正后超深油藏物质平衡方程可转化成传统油藏物质平衡方程,证实超深油藏物质平衡方程的修正过程及最终表达式可靠。利用修正后超深油藏物质平衡方程计算得到塔里木盆地超深油藏G-02井动态地质储量为188.65×10^(4)t,而传统油藏物质平衡方程计算结果偏大,相对误差为19.19%;随油藏压降增加,修正后超深弹性驱油藏物质平衡方程计算动态地质储量逐渐减小。

Compressibility coefficient is a key parameter that affects the accuracy of material balance equation,and its value is closely related to formation pressure.Ultra-deep reservoirs are characterized with large pressure difference between initial reservoir pressure and saturation pressure,and large reservoir pressure drop,but traditional material balance equations for ultra-deep reservoirs ignore the change of compressibility coefficient with formation pressure.In order to improve material balance equations for ultra-deep reservoirs,the variation of the compressibility coefficient of pore space of rock,water compressibility,oil compressibility,oil-gas two phase volume compressibility and gas compressibility with formation pressure are all considered,respectively,and the traditional material balance equations aimed at different types of drive(elastic drive,hydraulic drive,gas cap drive,dissolved gas drive,combination drive)are modified.It is concluded that the traditional material balance equations fail to consider the change of compressibility coefficient with formation pressure and does not use differential or integral method to solve,which is not suitable for ultra-deep reservoirs.Also,the traditional material balance equations are all approximate equations.If the change of compressibility coefficient with formation pressure is ignored and approximate treatment is further made,the modified material balance equations for ultra-deep reservoir becomes the traditional material balance equations,which proves that the revision process and final expressions of material balance equation for ultra-deep reservoir are reliable.The dynamic geological reserve of Well G-02 in ultra-deep reservoir in Tarim Basin is 188.65×10^(4) t using the modified material balance equation,but the calculated results using the traditional material balance equation is relatively high,and the relative error is 19.19%.The dynamic geological reserve calculated from the modified elastic drive material balance equation decreases with reservoir pressure drop.