川东南石龙峡背斜区奥陶系五峰组页岩顶面现今应力场数值模拟研究

Numerical simulation of present-day stress field on the top surface of Ordovician Wufeng Formation shale in the Shilongxia anticline area,Southeast Sichuan, China

近年来川东南地区页岩气勘探取得重大突破,勘探领域进一步向深层、超深层迈进。受多期构造运动及多套滑脱层影响,川东南地区表现出具有多层滑脱的复杂构造样式,深层现今地应力分布特征存在争议,局部应力场方位变化尚不明确,为深层页岩气开发带来巨大挑战。本文基于钻测井资料和高精度三维地震资料,建立石龙峡背斜地质模型,根据岩石力学参数及边界条件确定研究区力学模型,利用二维有限元数值模拟方法,对石龙峡背斜区奥陶系五峰组页岩顶界面现今应力场分布进行模拟研究。在此基础上,结合研究区石页1井实钻资料对模拟结果的合理性进行验证。研究结果表明:1)石龙峡背斜区现今应力场分布受先存构造、岩石力学差异性等多种因素影响。模拟结果显示在断层带周围,特别是断层带的转折端及末端,表现出应力集中现象,该区域应力值较高,分布范围在-81.85~-80.95 MPa;而断层带本身处于破碎状态,应力值较低,应力分布范围在-77.8~-49.74 MPa;背斜核部为能干性较强区域,处于应力集中状态,应力值较高,应力分布在-113.2~-81.85 MPa。2)石龙峡背斜奥陶系五峰组顶界面现今最大主应力方向呈近南北向展布,主要受控于后期来自大娄山方向的挤压作用影响。川东南地区应力场受多期构造作用叠加,早燕山期主要受控于东部雪峰山弧形构造带的推覆作用等,形成石龙峡背斜构造形态。而现今应力场分布主要受控于晚燕山期—喜马拉雅期来自南侧大娄山推覆的作用,使得现今研究区最大主应力方向呈近南北向。

In recent years,significant breakthroughs have been made in shale gas exploration in the Southeast Sichuan area,and the exploration field has further advanced to the deep and ultra-deep layers.Under the influence of multi-phase tectonic movement and multiple sets of sliding layers,the Southeast Sichuan area shows a complex tectonic style with multi-layer sliding,and the present distribution characteristics of the geostress in the deep layer are controversial,and the orientation change of the local stress field is still unclear,which brings a great challenge to the development of deep shale gas.In this paper,based on the drilling and logging data and high-precision 3D seismic data,a geological model of Shilongxia anticline is established,the mechanical model of the study area is determined according to the rock mechanical parameters and boundary conditions,and the distribution of the present stress field in the top interface of Ordovician Wufeng Formation shale in the Shilongxia anticline area is simulated using the 2D finite element numerical simulation method.On this basis,the reasonableness of the simulation results is verified by combining the actual drilling data of SY1 well in the study area.The results show that:1)the distribution of the present stress field in the Shilongxia anticline area is affected by the pre-existing tectonic structure,rock mechanical variability and other factors.The simulation results show that around the fault zone,especially at the turning end and the end of the fault zone,there is a stress concentration phenomenon,and the stress value in this area is high,with a distribution range of-81.85~-80.95 MPa;while the fault zone itself is in a broken state,with a low stress value,with a distribution range of-77.8~-49.74 MPa.The core of the anticline is an area of strong dryness and is in a state of stress concentration with higher stress values and the stress distribution ranges from-113.2~-81.85 MPa.2)The present maximum principal stress of the top interface of Ordovician Wufeng Formation of Shilongxia anticline is spreading in a near-north-south direction,which is mainly controlled by the influence of extrusion from the direction of Daloushan Mountain in the late stage.The stress field in Southeast Sichuan is superimposed by several periods of tectonic effects,and the Early Yanshan Period is mainly controlled by the thrusting and overturning effects of the Xuefengshan Mountain arc tectonic belt in the east,forming the tectonic morphology of the Shilongxia anticline.Nowadays,the distribution of the stress field is mainly controlled by the thrusting and overturning of the southern Daloushan Mountain during the Late Yanshan and Himalayan periods,which makes the direction of the maximum principal stresses in the study area nowadays nearly north-south.