A Utility Discrete Fracture Network Model for Field-Scale Simulation of Naturally Fractured Shale Reservoirs

Abstract

Multi-scale fracture distribution is a unique feature in shale gas reservoirs development. For a reservoir engineer, establishing a utility method which can be both numerically efficient and practically accurate is the greatest challenge of shale gas reservoirs numerical simulation. Naturally fractured shale gas reservoirs, which must be fractured before production, include many complex fracture networks (natural fracture and hydraulic fracture) that cannot be easily modeled by the simple continuous medium model (CMM), the discrete fracture model (DFM) or the discrete fracture network (DFN) model. In this paper, we propose a utility discrete fracture network (UDFN) model in which natural fractures are modeled by an analytic correction to matrix permeability, and hydraulic fractures are modeled by the DFN in which fractures are modeled explicitly. The partial differential equations are solved by Newton Raphson method through the C Sharp programing. Case studies reveal that the UDFN's computational speed improves orders of magnitude than those of the DFN and DFM when dealing with the same problem, while the numerical result from UDFN method keeps enough accuracy to match the production curves as well as the results from the DFN. Meanwhile, the UDFN not only can simulate individual fracture's effects explicitly like DFM, but also can match up better to the field production than the DFM. The method developed in this paper improved the simulation of multiple stage fractured horizontal wells performance in naturally fractured formations. It also makes the naturally fractured shale gas reservoirs numerical model much more concise and practical to the field case appplication.

Shale gas apparent permeability model coupling the transport mechanisms in matrix and natural fractures

“…能够综合反映基质-天然裂缝共同作用的页岩气表观 渗透率模型. 但通常情况下, 一方面, 页岩岩芯渗流 能力由基质孔隙和天然裂缝共同作用 [16,17] , 单一的 基质渗透率模型或裂缝渗透率模型无法描述岩芯中 气体实际流动过程, 同时计算结果难以通过实验验 证; 另一方面, 由于天然裂缝开度大小和基质孔隙直…”