乌石凹陷M油田低对比度油藏成因机理及渗透率评价

乌石凹陷M油田主力油组砂体规模较大, 岩性主要为含砾中粗砂岩和砂砾岩, 其次为细砂岩。砂砾岩油层由于受特殊沉积和成岩作用影响, 浅层油层表现为高阻特征, 中深层部分油层电阻率与水层相差不大, 为测井流体性质识别及渗透率定量评价带来较大困难。以核磁、压汞、铸体薄片等实验资料为基础, 从微观研究高阻油层与低对比度油层储层特征的差异, 并且将储层按粒间孔、混合孔、铸模孔分为3类, 建立了M油田储层类型划分标准及渗透率预测模型。结果表明: 孔隙结构的复杂性造成的高束缚水饱和度是导致区域低对比度油层形成的主要原因; 储层分类后渗透率计算精度明显提高, 为油田开发方案的制定与实施及钻后评价奠定了坚实的基础。 

Genetic mechanism and permeability evaluation of low contrast oil reservoirs in M Oilfield of Wushi Sag

The sandstone body of the main oil layer of M oilfield in Wushi Sag is large, and the lithology is mainly gravelly medium-coarse sandstone and sandy conglomerate, followed by fine sandstone.Due to the influence of special sedimentation and diagenesis, the shallow buried oil layer shows the characteristics of high resistivity, while the resistivities of some middle and deep buried oil layers are very close with that of the water layers, which brings great difficulties to the well logging based identification of fluid properties and quantitative evaluation of permeability.Based on the experimental data of NMR, mercury injection and cast thin sections, this paper analyzed the difference in reservoir characteristics between high resistivity reservoirs and low contrast reservoirs from the microscopic view.Then, based on the pore types (intergranular pores, mixed pores and mold pores), the resevoirs were diveded into three types, and the reservoir type classification standard were established. At last, the reservoir type-based permeability estimation models were proposed.The results show that the high irreducible water saturation caused by the complexity of pore structure is the main reason of the low contrast reservoirs. The accuracy of the estimated permeability is significantly improved after reservoir classification, which lays a solid foundation for the formulation and implementation of the oilfield development plan and post drilling evaluation.