顺北油田碳酸盐岩地层天然裂缝分布及其造山运动力学特征

Distribution of Natural Fractures and Mechanical Characteristics of Orogenic Movement in Carbonate Formations in Shunbei Oilfield

对顺北油田顺8B区块奥陶系碳酸盐岩的天然裂缝进行研究,总结了研究区内天然裂缝的分组以及碳酸盐岩地层天然裂缝的分布规律。结合损伤和有限元数值模拟技术,开发了损伤模拟碳酸盐岩的模型工具,确定了与天然裂缝发育所对应的造山运动的位移方向及应变量。根据研究区地震波得到的地层构造,结合沉积和造山运动史,分析了石炭系卡拉沙依组-中奥陶统一间房组7个层位的天然裂缝/断层,归纳为5组天然裂缝体系;上奥陶统恰尔巴克组-中奥陶统一间房组储集层中的天然裂缝对应着加里东运动中期Ⅰ幕和加里东运动中期Ⅱ幕的造山运动,主要为贯通的张开裂缝和走滑裂缝/断层;根据地震层位信息,建立三维有限元模型,进行三维损伤有限元数值分析,正演数值计算结果给出了在加里东运动中期造山运动作用下研究区内损伤局部化带表示的天然裂缝/断层的三维空间分布,数值计算结果验证了加里东运动中期应力对奥陶系碳酸盐岩地层挤压的主方向为15°,地层受挤压程度相当于2.4%的应变量。

Natural fractures in the Ordovician carbonate formations in the Shun 8B block in Shunbei oilfield were investigated,and the clas⁃sification and distribution laws of the natural fractures were summarized.Then through damage and finite element numerical simulation,a theoretical tool for simulating the damage to the carbonate formations was developed,and the displacement direction and strain of orogenic movement corresponding to the development of natural fractures were determined.The results are as follows:①Based on the stratigraphic structure from seismic waves and the histories of sedimentation and orogenic movement in the study area,the natural fractures/faults in 7 sections in the Carboniferous Kalashayi formation to the Middle Ordovician Yijianfang formation are divided into 5 natural fracture sys⁃tems;②The natural fractures in the Upper Ordovician Qarbag formation to the Middle Ordovician Yijianfang formation correspond to the orogenic movement of the middle Caledonian PhaseⅠand the middle Caledonian PhaseⅡ,and they are mainly open fractures and strike⁃slip fractures/faults penetrating the formations;③Based on seismic horizons,a 3D finite element model was established and 3D damage fi⁃nite element numerical analysis was carried out.Forward numerical calculation provided the 3D distribution of the natural fractures/faults represented by localized damage zones under the action of the middle Caledonian orogenic movement in the study area.Numerical calcula⁃tion verified that the mechanics of the middle Caledonian orogenic movement extruded the Ordovician carbonate formation at the azimuth of 15°,and the extrusion degree of the formation is equivalent to 2.4%of the strain.