基于实测数据及数值模拟断层对地应力的影响

STUDY ON INFLUENCE OF FAULTS ON GEOSTRESS BY MEASUREMENT DATA AND NUMERICAL SIMULATION

以松辽盆地北部某油区为背景,采用差应变及波速各向异性法对4口井两主力油层进行地应力测量,结果表明:对于同一区块相距仅2000m左右的4口井,其地应力状态存在较大的差异,尤其是地应力方向更是如此,影响因素分析进一步表明,地应力状态的差异是由于断层影响所致。为此,基于有限元软件ANSYS进行二次开发,利用三维有限元数值模拟方法,结合优化反演技术,对研究区地应力场进行反演,研究表明:由于断层影响以及复合断层的叠加扰动,研究区地应力状态表现出复杂的非均匀分布特征,断层附近应力方向发生转向,其中断层端部应力方向偏转超过40°,因此,离散"实测点"不能反映断块区地应力场全貌,三维数值模拟是定量分析地应力场的有效方法。

Taking one oil region in the northern Songliao Basin as engineering background of the research, the geostresses of the two oil layers in four boreholes have been measured by the methods of differential strain analysis（DSA） and anisotropic of wave velocity. The results reveal that there exist considerable differences between the geostress states of four boreholes which are only 2 000 m away from each other, and especially the differences of orientation. The analysis of affecting factors on the geostress states show that the differences are due to the influence of faults. With the aid of three-dimensional finite element simulation techniques and the theory of optimization, analysis of the distribution of geostresses in the study area has been carried out by the secondary development of ANSYS. It is found the heterogeneity and aeolotropism of geostress states are caused by faults or superposition of action of faults. The results show that the deviation in the orientation of the maximal horizontal stress exists in the adjacent zone of the faults, and the deviation angle near the end of the fault is more than 40°. So the distribution of the geostresses can not be generated by limited discrete measuring points. The 3D numerical simulation is an effective method for geostresses research.