应用分形理论研究鄂尔多斯ZJ油田长6段储层孔隙结构的非均质性

利用薄片资料分析了鄂尔多斯ZJ油田长6段储层的孔隙结构类型和组合特征.用岩样毛管压力数据讨论了岩石孔隙结构的分形特征.用小于某一孔隙半径r的孔隙体积百分比s与r的拟合关系,计算了ZJ油田延长组长6段储层的孔隙结构分形维数.计算结果表明,长6段储层的长62-1小层及长62-2小层的毛管压力曲线都存在一个标度区间,在该区间内孔隙结构才具有分形特征.同一岩样中,大孔隙与小孔隙呈多重分形特征,且对应于不同的标度区间.对于62-1小层,大孔隙段和小孔隙段的分形维数分别为2.58和2.85,表明长62-1小层小孔隙发育段的孔隙结构更复杂.对于长62-2小层,大孔隙段和小孔隙段的分形维数分别为2.71和2.83,同样,小孔隙段的孔隙结构复杂、非均质性强.对比长62-1和长62-2的大孔隙段分形维数知道,前者孔隙结构相对简单.对比测试结果知道,孔隙结构与含油性关系密切,孔隙结构简单的长62-1小层的含油性明显好于长62-2小层,而且孔喉相对分选系数与分形维数呈正相关关系.

Study on the heterogeneity of the pore structure of Chang 6 reservoir in ZJ oilfield, Erdos Basin using fractal theory

The type and the combination characteristics of the pore structure in the studied reservoir are analyzed by means of thin-section data.And the fractal characteristics of the pore structure are studied according to the capillary pressure analysis data from core samples.The fractal dimension of the pore structure of the reservoir is calculated according to the fitting relationship between the volume percent of the pore less than some radius and the radius.The results show that there is a scale range on the capillary pressure curves of both Chang 62-1 and Chang 62-2,and only in the scale range,pore structure has evident fractal character.In a sample,micro-pore and macro-pore present different fractal characteristics and scale ranges.In both sub-sections,fractal dimension of macro-pore is less than that of the micro-pore.For Chang 62-1 sub-section,the fractal dimension of the macro-pore is 2.58,whereas that of the micro-pore is 2.85.This result suggests that the structure of the micro-pore is more complex than that of the macro-pore.With respect to Chang 62-2 sub-section,the fractal dimension of the macro-pore is 2.71,whereas that of the micro-pore is 2.83.It also indicates that the structure of the micro-pore is more complex than that of the macro-pore and the micro-pore shows stronger heterogeneity.The fact that the fractal dimension of the macro-pore in Chang 62-1 is less than that of the macro-pore in Chang 62-2 implicates that the storage and flow capability of Chang 62-1 is better.Test data shows that there is a closed correlation between pore structure and hydrocarbon saturation,and formation Chang 62-1 has higher hydrocarbon saturation than Chang 62-2.Statistical result also indicates that there is a positive relationship between sorting coefficient of the pore throat and the fractal dimension of the pore structure.