缝洞型碳酸盐岩油藏新型油藏生产指示曲线

弹性驱动油藏的生产指示曲线一直被看作是一条直线,由于原油压缩系数是一个随着地层压力增大而减小的变量,因此其并非一条直线,而是一条曲线,并且油藏压降越大,曲线偏离直线越明显,尤其是对于埋藏较深、地层压力与饱和压力差值较大的缝洞型碳酸盐岩油藏来讲,该油藏生产指示曲线会产生明显误差,需要进行改进。通过建立原油体积系数、原油压缩系数与地层压力的幂函数关系式,简化缝洞型油藏弹性驱动物质平衡方程,建立了新型的油藏生产指示曲线。研究与实例计算表明:地层压力大于饱和压力时,原油体积系数与地层压力不符合线性关系,而是符合幂函数关系,新建立的原油体积系数、原油压缩系数与地层压力的幂函数关系式,不仅符合实际变化规律,并且具有很高的计算精度;原油压缩系数的使用存在2种情况:一是某一地层压力对应的原油压缩系数;二是某一地层压力区间对应的平均原油压缩系数,两者不能混用,物质平衡方程应使用后者;新型的弹性驱动油藏的生产指示曲线始终为一条直线,直线的斜率即为原油地质储量。利用该新型油藏生产指示曲线可以更加准确地进行油藏驱动类型判断、储量计算等油藏研究。

New production index curve of fractured-vuggy carbonate reservoirs

The production index curve of elastic drive reservoir has always been regarded as a straight line.Because oil compressibility is a variable that decreases as formation pressure increases,the production index curve is not a straight line but a curve,which deviates from straight line more significantly as reservoir pressure drop increases.Especially for deep buried fractured-vuggy carbonate reservoirs which have large pressure difference between formation pressure and oil saturation pressure,the production index curve of reservoir will produce obvious error,hence it needs to be improved.By creating the power function relationship between oil volume factor,oil compressibility and formation pressure,the material balance equation of elastic drive fractured-vuggy carbonate reservoir was simplified,and a new production index curve of reservoir was established.The results show that the relationship between oil volume factor and formation pressure above saturation pressure is not linear but accords with power function,and the power function relationships between oil volume factor,oil compressibility and formation pressure not only conform to the actual law but also have high computational accuracy.There are two cases for using oil compressibility:one is the oil compressibility at a certain formation pressure,the other is the average oil compressibility in a certain formation pressure range,the two cases cannot be mixed,and material balance equation should adopt the latter.The new production index curve of elastic drive reservoirs is always a straight line,and the slope of the line is just original oil in place.Therefore,the new production index curve of reservoir is conducive to reservoir research,such as accurately judging the driving type of a reservoir and calculating the reserves.