压裂裂缝网络不稳态流动半解析模型

摘要

Comparing with the flow in single and multiple fractures, the flow behaviors in hydraulic fractured networks that consist of interconnected fractures are featured of flow redirection and flux redistibution at fracture intersections. In this paper, the flow behavior in fractured networks was modeled and the numerical solution was given by combining star-delta transformation and finite difference methods. An analytical solution for the flow in reservoir matrix was obtained based on source functions in Laplace domain and superposition principles. A semi-analytical model for the transient flow in hydraulic fractured networks was derived by dynamically coupling these two flow processes. The model was verified with a field case study. The results show that the semi-analytical model can be applied to fracture networks with arbitrary geometry and variable fracture conductivity. The transient bottomhole pressure and production rate can be solved along with reservoir pressure distribution during different pro-duction periods. In an infinite slabed reservoir, the flow in hydraulic fractured networks can be classified into five flow re-gimes, including the fracture linear flow, bilinear flow, formation linear flow, transient flow and pseudo-radial flow. The after-flow caused by wellbore storage effect may overshadow the fracture linear flow. For the reservoirs with permeability of 1×10-7μm2 , the fluid drainage occurs primarily in the vicinity of the fractures with large density and higher conductivity at the early-middle production periods. However, the ultimate depletion ( e. g. after 30-50 years of production) is still limited to the region of the stimulated reservoir volume and the fluid flow beyond the stimulated region makes little contribution to the total produc-tion.%与压裂单条缝及多条缝的流动模式不同，包含相互交错裂缝的压裂裂缝网络流动会在裂缝交汇处产生流向重定向和流量重分配的过程。通过引入星三角变换法，并结合有限差分方法对这一特殊流动过程进行描述，推导裂缝网络内部流动数值解。基于Laplace空间源函数及叠加原理建立油藏流动解析解。耦合该两部分流动，给出一个压裂裂缝网络不稳态流动半解析模型，并利用现场实例验证模型的实用性。结果表明：该模型可以处理裂缝空间位置和导流能力任意分布的裂缝网络，能够预测生产井的压力、产量动态及不同生产阶段的油藏压力分布；在上下封闭无界储层中，压裂缝网存在裂缝内部线性流、裂缝与地层双线性流、地层线性流、过渡流以及拟径向流；受井筒存储效应的影响，观测不到裂缝内部线性流；渗透率为1×10-7μm2级别的储层在生产早、中期流体流动主要集中在密度大及导流能力高的裂缝附近，但最终(生产30~50 a)的泄流区域都局限在压裂改造范围内，改造区外的储层流体很少流动。