Abstract
Reservoir cooling during waterflooding or waste-water injection can significantly alter the reservoir stress field by thermo-poro-elastic effects. Colloidal particles in the injected water decrease the matrix permeability and buildup the injection pressure. Fractures may initiate and propagate from injectors. These fractures are of great concern for both environmental reasons and strong influence on reservoir sweep and oil recovery. This paper introduces methods to fully couple reservoir simulation with wellbore flow models in fractured injection wells.
A method to fully couple reservoir-fracture-wellbore models was developed. Fluid flow, solid mechanics, energy balance, fracture propagation, and particle filtration are modelled in the reservoir, fracture and wellbore domains. Effective stress in the reservoir domain is altered by thermo-poro-elastic effects during cold water injection. Fracture initiation and propagation induced by thermal and filtration effects is modelled in the fracture domain. Particle filtration on the borehole and fracture surfaces is modelled by matrix permeability reduction and filter cake build-up. Leakoff through the borehole and fracture surface is balanced dynamically. The coupled nonlinear system of equations is solved implicitly using Newton-Raphson method.
We validate our model with existing analytical solutions for simple cases. We show how the poro-elasticity effect, thermo-elasticity effect, water quality, and wellbore open/cased conditions influence well injectivity, induced fracture propagation and flow distribution. Simulation results show that water quality and thermal effects control fluid leak-off and fracture growth. While it is difficult to predict the exact location of fracture initiation due to reservoir heterogeneity, we proposed a reasonable method to handle fracture initiation without predefined fracture location in the water injection applications. In open-hole completions, this may lead to "thief" fractures propagating deep into the reservoir. Thermal stress changes in the injection zone are shown to be significant because of the combined effect of forced convection, heat conduction and poroelasticity. The accurate predictions of thermal stress in different reservoir layers allow us to study fracture height growth and containment numerically for the first time. We show that controlling the temperature and the injection water quality is also found to be an effective way to ensure fracture containment.
Water Injection Fracture Pressure and Fracture Propagation Investigating in Poorly Consolidated Sandstone