应用分形理论研究鄂尔多斯MHM油田低孔渗储层孔隙结构

基于岩样的毛管压力分析数据,讨论了岩石孔隙结构的分形特征。用孔径小于某一值r的孔隙体积百分比S与r的拟合关系,计算了鄂尔多斯盆地西部MHM油田三叠系延长组和侏罗系延安组低孔、低渗储层孔隙结构的分形维数。计算结果表明,两个层段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表现出分形特征。同一块样品的大孔隙段与小孔隙段表现出多重分形,延10段储层孔隙结构的分形维数在大孔隙段比小孔隙段小,而长6段储层的分形维数分布特征却与延10段储层相反。在大孔隙区间延10段的分形维数比长6段小,反映出长6段储层孔隙结构比延10段复杂。研究分析认为,利用孔隙结构分形维数并结合其他孔隙特征参数,可以很好的反映出储层微观孔隙结构的复杂性,为研究储层孔隙结构微观非均质性提供了一个方便有效的手段,并为进一步的储层评价奠定了基础。

Pore structure study of low porosity and permeability reservoirs in MHM oilfield of Ordos Basin with fractal theory

Fractal features of pore structure are studied by using analytic data of capillary pressure of core samples.The fitting relationship between the volume percentage(S)of pores with pore diameter smaller than a given value(r)and the pore diameter(r)is used to calculate the fractal dimension of pore structure of the low porosity and permeability reservoirs in the Triassic Yanchang Formation and Jurassic Yan'an Formation of MHM oilfield,Ordos basin.The capillary pressure curves of both formations have a scale interval,in which pore structure shows fractal features.The macropore and micropore intervals of same core sample show multi-fractal features.For the 10th member of Yan'an Formation(Yan 10 reservoir),the fractal dimension of pore structure in macropore interval is larger than that in micropore interval,while for the 6th member of Yanchang Formation(Chang 6 reservoir),the distribution of fractal dimension is just the opposite.In macropore interval,the fractal dimension of Yan 10 reservoirs is smaller than that in Chang 6 reservoirs,indicating that the pore structure of the latter is more complex than that of the former.Fractal dimension of pore structure,in conjunction with the other pore characteristic parameters,can well reflect the complexity of microscopic pore structure.It provides a convenient and effective method for study on the microscopic heterogeneity of reservoir pore structure,and a solid basis for further reservoir evaluation.