分段压裂诱导地热储层应力场响应的单连通解析模型分析

Single-connected analytical model analysis of stress field response of geothermal reservoirs induced by staged fracturing

分段压裂诱导地热储层应力场响应将对地热储层井筒完整性和套管变形产生直接影响,研究分段压裂诱导地热储层应力场响应对指导现场压裂具有重要意义。现阶段普遍采用断裂力学对水力压裂诱导的应力场响应进行求解,然而分段压裂诱导地热储层应力场响应本质为热流固耦合作用下缝间应力干扰问题,使得这一问题的断裂力学求解异常复杂。鉴于此,引入连续性假设将此断裂力学问题转化为弹性力学问题,建立分段压裂诱导地热储层应力场响应的单连通解析模型,极大降低了求解难度,同时可以更加简便有效地对现场压裂后的应力场响应进行分析。并基于ABAQUS软件建立地热储层分段压裂热流固耦合数值模型,通过对比x、y方向平均应力验证解析模型误差在5%以内。进而利用解析模型,讨论簇数、温差和天然裂缝对地热储层应力场的影响,结果表明:随着簇数增加,地热储层内x方向应力分量随之增大,y方向应力分量随之减小;随着温差增大,地热储层内x、y方向应力分量均随之增大;随着天然裂缝密集程度增加,地热储层内x方向应力分量随之增大,y方向应力分量随之减小。

The stress field response of the geothermal reservoir induced by staged fracturing will have a direct impact on the wellbore integrity and casing deformation of the geothermal reservoir.Studying the stress field response of the geothermal reservoir induced by staged fracturing is important to guide the field fracturing.significance.At present,fracture mechanics is generally used to solve the stress field response induced by hydraulic fracturing.However,the stress field response of geothermal reservoirs induced by staged fracturing is essentially the problem of stress interference between fractures under the action of heat-fluid-solid coupling,which makes this problem difficult to solve.Fracture mechanics solutions are extremely complex.In view of this,the continuity assumption was introduced to transform this fracture mechanics problem into an elastic mechanics problem,and a single-connected analytical model of the stress field response of geothermal reservoirs induced by staged fracturing was established,which greatly reduced the difficulty of solving,and the stress field response after field fracturing can be analyzed more simply and effectively.Based on ABAQUS,a staged fracturing thermal-fluid-solid coupling numerical model for geothermal reservoirs was established,and the error of the analytical model was verified to be within 5%by comparing the average stress in the x and y directions.Then,using the analytical model,the effects of cluster number,temperature difference and natural fractures on the stress field of geothermal reservoirs are discussed.The results show that as the number of clusters increases,the stress component in the x-direction increases and the stress component in the y-direction decreases in the geothermal reservoir;as the temperature difference increases,the stress components in the x and y directions in the geothermal reservoir increase accordingly;as the density of natural fractures increases,the stress component in the x-direction increases and the stress component in the ydirection decreases in the geothermal reservoir.