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

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 pseudosteady 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. IntroductionThe use of hydraulic fracturing for well stimulation is widespread in the industry. This treatment is particularly prevalent in oil shales and gas shales and tight formations in general, where virtually all production can be attributed to the practice of fracturing. It is also used in the context of tight oil reservoirs; for example, in deepwater scenarios where the costs of drilling and completion are very high and well productivity, which is dictated by hydraulic fractures, is vital.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 usual reservoir dynamics.To overcome this problem, a multitude of modeling techniques and workarounds has been developed. These include use of dual-porosity models, enhancement of the productivity index of the fractured wells (Zhang et al. 2012), virtual well perforations to s...

CO2 Capture and Storage Performance Simulation in Depleted Shale Gas Reservoirs as Sustainable Carbon Resources

“…The numerical modeling and simulation of shale reservoirs exploited by MSFHWs is differed from nonhydraulically fractured reservoirs. Regarding some of the related works [14,28,29], defining a MSFHW in a numerical simulation model can be done using local grid refinement (LGR).…”

“…LGR, it is difficult to add or modify properties of different fractures segments through the simulation [28].…”

Simulation of shale gas transport and production with complex fractures using embedded discrete fracture model

“…However, the unstructured grids are still challenging to use efficiently in the field scale due to very complicated gridding issues and an expensive computational cost. Recently, a multisegment well approach has been developed to dynamically model hydraulic fractures. However, this approach is difficult to handle a large number of isolated natural fractures, which has no connection to primary hydraulic fractures and wellbore.…”