多级水力压裂应力阴影效应的数值分析

Numerical analysis of the stress shadowing effects in multistage hydrofracturing

多级水力压裂作为储层改造的主要技术手段,广泛用于提高致密油气藏的气体产量。裂缝在扩展过程中的应力阴影效应对于有效连通储层的天然裂缝并形成有利于油、气体流动的复杂裂缝网络至关重要。本研究采用了自适应的有限元-离散元方法,通过改进网格自动细化和识别多个裂缝扩展模拟含天然裂缝储层的多级水力压裂。数值模型中考虑了水力裂缝、天然裂缝和微观孔隙结构的相互作用,整合了非线性的Carter滤失模型来描述多级压裂过程中压裂液的滤失效应。引入了理想平行板流的支撑剂运输方程,并采用了达西定律来分析裂缝网络中的流体渗透效应。通过比较无裂缝均质模型和天然裂缝模型的裂缝网络和流体流动,评估了天然裂缝对多级压裂裂缝行为和气体产量的影响。研究为确定和优化致密气藏中压裂簇间距提供了一种新的方法。

Multistage fracturing is a commonly-used method to improve gas production in tight hydrocarbon reservoirs.Stress shadowing effect among multi-fractures is crucial in effectively connecting the pre-existing natural fracture of reservoir and forming a complex fracture network that facilitates gas flow.Challenges remain in accurately characterizing the fracture structure and propogation patterns of naturally fractured reservoirs.In this study,we adopt an adaptive finite-discrete element method to simulate the multistage fracturing of a naturally fractured reservoir by improving the mesh auto-refinement and identification of multiple fracture propagation.The numerical model covers interactions among hydraulic fractures,pre-existing fractures,and microscale pores,while integrates the nonlinear Carter leak-off criterion to describe fluid leak-off and hydromechanical coupling effects during multistage fracturing.We introduce the proppant transport equation for idealised parallel plate flow in fractures,and Darcy's law is adopted to analyse the seepage flow in the fracture network and determine gas recovery.We then compare the fracture network and consequent fluid flow induced by the hydrofracturing of unfractured and naturally fractured models to assess the influence of pre-existing fractures on multistage fracturing behaviour and gas production.This study provides a new approach to determine and optimize fracturing cluster spacing in tight gas reservoirs.