Representing Hydraulic Fractures Using a Multilateral, Multisegment Well in Simulation Models

Abstract

Abstract Hydraulic fracturing is a stimulation treatment routinely performed on oil and gas wells in low-permeability reservoirs. However, simulating fractured wells is still challenging and impractical using local grid refinement in full-field models with a large number of wells each with multiple fractures. This paper describes a novel modeling technique by which hydraulic fractures are represented as part of the well model, rather than 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. The main advantages are: 1) the fracture mesh is made independent of the simulation grid and thus model building is simpler; 2) fractures can be added and altered at any simulation time; 3) fractures can intersect the reservoir grid lines at any angle; 4) fracture geometry and properties can be fully honored. This technique is designed to model long-term pseudo-steady state fracture flows and uses Darcy flow equations in the lateral well branches that represent the fracture. The accuracy, stability, and practicality of this new technique have been investigated using a suite of simulation models ranging from a single well in a homogeneous reservoir to a real field sector model with numerous wells, each with multiple fractures. Where possible, the behavior of a reference model—built using traditional grid-refinement techniques—is compared against the multilateral, multisegment well model equivalent. The results of these experiments presented in this paper show a close agreement between the reference gridded fractures and the well model fractures when the system reaches a pseudo-steady state. They also show that the new approach suffers from a lesser degree of numerical instability when modeling extremely thin and highly conductive fractures. Finally, the results confirm the practicality and flexibility of this approach.