考虑水力压裂缝和天然裂缝动态闭合的三维离散缝网数值模拟

Numerical Simulation of 3D Discrete Fracture Networks Considering Dynamic Closure of Hydraulic Fractures and Natural Fractures

基于嵌入式离散裂缝模型,提出一种可在三维空间中考虑应力状态影响的裂缝动态闭合表征方法。将任意方向裂缝的开度和渗透率考虑为作用在裂缝平面法向有效应力的函数,同时用裂缝传导率变化表征支撑剂充填的水力压裂缝与被开启的天然裂缝由于油藏开发过程中地层流体压力下降而发生的动态闭合行为。研究表明:致密油藏开发以缝控储量为主。对压裂水平井进行产能评价时,裂缝动态闭合会导致产能的部分损失,其影响不可忽略;水力压裂缝的支撑剂材料属性及天然裂缝的刚度是其中的主控因素。因此需要增大支撑剂的浓度、粒径大小并改善支撑剂的性质,在最大程度上降低裂缝闭合对生产的不利影响。

A characterization method for fracture dynamic closure considering influence of stress state in three-dimensional space is proposed based on an embedded discrete fracture model.Aperture and permeability of fractures in any direction are considered as functions of normal effective stress acting on the fracture surface.Meanwhile,the change of fracture conductivity is used to characterize dynamic closing behavior of proppant-filled hydraulic fractures and opened natural fractures due to the decrease of formation fluid pressure during reservoir development.It shows that the development of tight oil reservoirs is dominated by“fracture-controlled reserves”.In evaluating productivity of fractured horizontal wells,the dynamic closure of fractures lead to a partial loss of production,and its influence can not be ignored.Proppant material properties of hydraulic fractures,and stiffness of natural fractures are the main controlling factors.To minimize adverse impact of fracture closure on production it is necessary to increase the concentration and particle size of proppant and improve proppant properties.