Technique Uses Multilateral, Multisegment Wells To Represent Hydraulic Fractures

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 163644, ’Representing Hydraulic Fractures by Use of a Multilateral, Multisegment Well in Simulation Models,’ by D.A. Edwards, SPE, Schlumberger; N. Cheng, SPE, Statoil; T.P. Dombrowsky (now with Longhorn Technologies) and G. Bowen, SPE, Schlumberger; and H. Nasvik, SPE, Statoil, prepared for the 2013 SPE Reservoir Simulation Symposium, The Woodlands, Texas, USA, 18-20 February. The paper has not been peer reviewed. Simulating fractured wells is challenging and impractical with local grid refinement (LGR) in full-field models with a large number of wells each with multiple fractures. This paper describes a modeling technique by which hydraulic fractures are represented as part of the well model rather than as any form of refinement in the simulation grid. In this approach, a planar fracture is modeled by the mesh formed from the interconnected branches of a multilateral, multisegment well (MSW). Introduction Hydraulic fracturing can dramatically change the flow dynamics of a reservoir, so its correct modeling in reservoir simulation can be critical. However, the presence of hydraulic fractures presents a challenge in flow simulation. This is because these fractures introduce effects that operate on different length and time scales than do usual reservoir dynamics. To overcome this problem, a multitude of modeling techniques and workarounds has been developed. These include the use of dual-porosity models, enhancement of the productivity index of the fractured wells, virtual well perforations to simulate the fractures, and explicit fine-scale gridding. In full-field simulations, where an entire reservoir with complex geometry, multiple wells, and possible faults is modeled, LGR is a popular method representing hydraulic fractures. However, this approach introduces its own set of problems. For example, in structured grids, the overall orientation of the grid may not easily accommodate fractures, particularly if they are at arbitrary angles. This paper investigates the modeling of hydraulic fractures as part of the well model. MSWs are a discretized model of a well where fluid flow inside the wellbore is computed by solving physical flow model equations in one dimension. This domain is made up of the segments of the well that consist of nodes, which are connected by pipes. MSWs allow for lateral branches off the main stem and for looped flow paths; both features are employed here for the modeling of hydraulic fractures.