The Influence of Fracture Network Geometry on Production from Unconventional Reservoirs

Abstract:

While the general principles of hydraulic fracturing are well known, there are many aspects of the process that require further understanding, particularly the role of natural fractures both as part of the stimulated fracture network and as background, unstimulated fractures. Discrete fracture network (DFN) models are useful experimental tools for testing hypotheses about fracture controls on production. DFN numerical experiments use a range of fracture network geometries from simple parallel fractures, to complex networks that incorporate stimulated natural fractures. The results of models and comparisons with production data provide constraints on the geometries and properties of the stimulated fracture networks.

The geometries of matrix blocks and fractures have a strong influence on the pressure and rate declines during production. Simple fracture networks consisting of parallel, equally-spaced hydraulic fractures produce pressure and flow transient behaviors that range from linear (square-root) to bilinear (fourth-root) with distinct fracture and matrix dominated stages. The transition times between these stages depend on the fracture sizes and properties and the matrix-block sizes and properties. Unlike the simple systems, which have only a single matrix block size, complex networks contain a distribution of block sizes. The complex systems produce early time behaviors that lie between the linear and bilinear cases until the small blocks within the stimulated volume are depleted and the overall stimulated volume behaves as a single linear source. An inspection of production data, which has been deconvoluted to produce an equivalent constant-rate signature, suggests behaviors that are consistent with complex fracture-network behaviors.