鄂尔多斯盆地合水地区长6致密砂岩储层现今地应力分布特征及其开发建议

致密油藏物性差，非均质性强，现今地应力分布特征影响着致密油藏钻井施工、井网部署、压裂改造和注水管理等方面。文章根据微地震监测法分析了鄂尔多斯盆地合水地区长6储层单井现今地应力的方向，利用水力压裂资料分析了研究区单井现今地应力大小。在单井现今应力分析的基础上，结合合水地区长6储层构造、沉积、岩相特点建立了三维非均质地质模型，通过室内三轴岩石力学试验与施工数据，得到不同岩相的岩石物理参数，由此建立三维力学模型。利用Ansys进行有限元数值模拟，得到了研究区长6储层三维现今地应力分布模型，模拟结果表明水平最大主应力范围为34~42 MPa；水平最小主应力范围为25~36 MPa；水平差应力范围为3~10 MPa，并将结果与实际测量的井点应力大小进行对比，误差小于10%，模拟结果可信。分析模拟结果可知研究区现今地应力的分布主要受到了岩石物理力学性质差异的影响，而构造格架的影响较小。在结果分析的基础上，建议研究区布井时，不仅考虑地应力的影响，还应将天然裂缝作为影响因素考虑，同时，为尽可能地降低开发成本，在差应力相等的区域，油气工业井一般部署在应力值低的地方。 

Distribution characteristics of the present-day in-situ stress in the Chang 6 tight sandstone reservoirs of the Yanchang Formation in the Heshui Area, Ordos Basin, China and suggestions for development

Tight reservoirs feature poor physical properties and strong heterogeneity. The distribution of present-day in-situ stress affects tight reservoirs in the drilling operation, well pattern deployment, fracturing transformation and water injection management. The microseismic monitoring method and the hydraulic fracturing data were used respectively to analyze the direction of present in-situ stress of single well in the Chang 6 reservoirs and the magnitude of present-day in-situ stress of single well in the study area. Combining the analysis with the characteristics of structure, sedimentation and lithofacies in the study area, we built a three-dimensional heterogeneous geological model. Based on the triaxial rock mechanics test and operation data, we identified the physical parameters of different facies, and built a three-dimensional mechanical model. Also the Ansys finite element numerical simulation was applied to build a three-dimensional present-day in-situ stress distribution model of the Chang 6 reservoirs. The simulation results showed that the maximum horizontal principal stress ranged from 34 MPa to 42 MPa, the minimum from 25 MPa to 36 MPa, and the horizontal differential stress from 3 MPa to 10 MPa. The simulation results of the wellpoint stress had a less than 10% margin of error compared with the actual measurement, proving the simulation results are reliable. It was inferred from the simulation results that the present-day in-situ stress distribution in the study area was mainly affected by the difference in rock physical and mechanical properties, but less by the tectonic framework. On the basis of the result analysis, it is suggested that natural fracture should also be considered as an influencing factor when wells are deployed in the study area. Meanwhile, in order to reduce development cost as much as possible, industrial wells should be generally deployed in the place with low stress as for the area with equal differential stress.