A Three-Dimensional Reservoir, Wellbore, and Hydraulic Fracturing Simulator that is Compositional and Thermal, Tracks Proppant and Water Solute Transport, Includes Non-Darcy and Non-Newtonian Flow, and Handles Fracture Closure

Abstract

Abstract We present a three-dimensional reservoir, wellbore, and hydraulic fracturing simulator with the following capabilities: (1) compositional fluid model, (2) multiphase flow, (3) thermal, (4) proppant transport with gravitational settling, bulk slurry gravitational convection, hindered settling, clustered settling, and the effect of proppant concentration on slurry viscosity, (5) solute transport, (6) non-Newtonian fluid rheology with the modified power law (capable of representing the low shear rate viscosity plateau), (7) non-Darcy flow in the fractures, and (8) the ability to handle fracture closure. The simulator is still a work-in-progress; additional features are planned in future work. The simulator is a practical tool for designing hydraulic fracturing treatments and predicting future production. The combination of reservoir and fracturing simulation enables: (1) comparison of proposed frac designs on the basis of predicted production, (2) more realistic simulation of pressure drawdown in the fracture during production by using flow equations designed for fracture flow, (3) description of processes involving tight coupling of production and stimulation, such as refracturing, and (4) avoidance of tedious handoffs between separate fracturing and reservoir simulation codes. We develop general-purpose constitutive equations for fracture transport that are realistic for mechanically open or closed fractures and for all values of proppant mass per fracture area. In limiting cases, the equations reduce to well-known constitutive equations, such as Darcy's law, the cubic law, and Forchheimer's law. Between limiting cases, the equations smoothly transition between governing regimes. The current model is applicable for hydraulic fracturing in formations that do not exhibit strong fracture network "complexity" during stimulation. Modeling stimulation of secondary fractures requires special considerations that are not implemented in the current version of the code. We demonstrate the model capabilities with a generic simulation of a single-stage frac job from a vertical well, followed by production. After the injection of a pad, water is injected with 60 mesh proppant. This is followed by lower rate injection of water gelled with guar and 20 mesh proppant. The fracturing treatment generates a large, well-propped fracture. The fracture propagates below the water-hydrocarbon contact, resulting in significant watercut during production.