鄂尔多斯盆地致密油藏天然裂缝与人工裂缝特征及开发意义

Characteristics of natural and hydraulic fractures in tight oil reservoir in Ordos Basin and its implication to field development

裂缝特征参数是致密油藏开发方式及井网优化的依据;针对致密油藏体积压裂下如何确定开发方式,通过对矿场测试的人工裂缝、天然裂缝和地应力方向采用高斯函数拟合,研究三者之间优势方向的耦合关系。针对致密油藏体积压裂人工裂缝有效参数的认识,提出以自然能量开发井网为研究对象,依据人工压裂缝控制区域和非控制区域压力变化规律的差异性,通过建立水平井分区渗流模型及拟合水平井生产数据,确定人工裂缝有效缝长;在此基础上,建立典型井精细地质模型及数值模型,对比不同裂缝有效宽度下数值模拟平均单段产量与实际统计单段平均产量,观察水平检查井取芯结果。结果表明:人工裂缝的优势方向与地应力优势方向基本一致;地应力的优势方向与天然裂缝优势方向差异较大的致密油藏,采用准自然能量开发,基本一致或差异小的致密油藏,具有注水补充能量的潜力;人工裂缝平均有效宽度小于等于10m。

The characteristics of the fractures in a tight oil reservoir are the basis for the selection of oil exploitation modes and well pattern optimization.In this study,a Gauss function fitting method was adopted to investigate the coupling relationship among the natural fractures,fractures generated by hydraulic fracturing and in-situ formation stress.Using the effective parameters of the hydraulic fracturing via volumetric fracturing in the tight oil reservoirs,the effective length of the hydraulic fractures can be identified through the analysis of the pressure difference between fracture controlled and uncontrolled zones by fitting the production data of the horizontal wells according to the established flow model based on the natural energy development mode.On this basis,a numerical simulation model of typical wells can be established.By comparing the production predicted by the numerical simulation and the actual field data,the reliability of the above analysis method can be verified along with the coring observation from the inspection wells between the horizontal wells.The results show that the dominant direction of the hydraulic fractures is basically the same as that of the in-situ stress,and these reservoirs can be produced via a natural energy development mode.For the tight oil reservoirs with the dominant direction of the in-situ stress different from that of its natural fractures,water injection technique can be considered.For the cases studied in this paper,the average effective fracture width is less than or equal to 10 m.