渤南洼陷古近纪早中期应力场数值模拟及其与断层发育的关系

Tectonic Stress Field Simulation of Early-Middle Paleogene and Its Relationship with Fault Development in Bonan Sub-sag

以地震、地质、测井等资料为基础,通过构造演化及断层落差法,分析渤南洼陷断层的分布及活动特征,为数值模拟提供地质模型。古近纪早中期是渤南洼陷断层的主要形成时期,发育NWW向、NEE向、NE向断层,断层组合以伸展构造样式为主,兼具走滑构造样式。运用ANSYS软件对渤南洼陷古近纪早中期构造应力场进行有限元数值模拟,模拟结果显示,古近纪早中期,最小主应力为张应力,断裂带内部为应力的低值区,断层上盘附近应力集中;差应力的高值区与断层分布一致;平面剪应力为右旋剪切特征,高值区主要发育NWW向、NE向断层,低值区以NEE向断层为主。模拟结果显示,构造应力场与断层的关系主要表现在2个方面:一方面,构造应力场控制断层的发育及分布,即差应力决定断层的优势发育区,平面剪应力控制断层发育的走向;另一方面,断层活动可以改变局部构造应力场大小,主要影响断层上盘附近一定距离内的应力场,造成应力集中,进而影响次级断层的形成。

On the basis of the seismic,geological and logging data,the distributions and activities of faults were analyzed through structural evolution and fault throw calculation,which provides the geological model for simulation.Faults in Bonan Sub-sag are mainly developed in Early-Middle Paleogene,with NWW,NEE and NE orientations.Structural patterns exhibit predominantly extensional characteristic,and shear structural patterns are secondary.The finite element numerical simulation of Early-to-Middle Paleogene in Bonan Sub-sag was conducted using ANSYS software.The simulation results show that：In Early-to-Middle Paleogene,the minimum principal stress is tensile stress,exhibiting low values in fault zones and high values in the hanging wall near the fault zones.The high differential stress area is in accordance with the distribution of faults.The planar shear stress behaves as dextral shearing,with high value areas distributed by NWW and NE faults,and low value areas distributed by NEE faults.It is concluded from simulation results analysis that the relationships between tectonic stress field and fault development are demonstrated in two aspects.On one hand,the development and distribution of faults are mainly controlled by the tectonic stress field.The differential stress determines the distribution of faults,while the planar shear stress controls fault orientation.On the other hand,the tectonic stress field is locally influenced by fault activities to some extent.The tectonic stress field is more likely to concentrate in the hanging wall near the fault zones,which can cause the formation of little faults.