This work describes the development of a fully coupled geomechanics and multiphase flow formulation to model dynamic propagation of injection-induced fractures, in a three dimensional poro-thermo-elastic reservoir domain. A dynamic filtration model for permeability reduction is employed on the fracture to incorporate effects of internal damage and external filter cake build-up due to suspended solids injection. The formulation for arbitrary fracture propagation is based on a finite volume implementation of the cohesive zone model, which is coupled with multiphase flow in the reservoir domain with multiple injection wells and fractures. This is the first instance where a finite volume formulation of multiphase flow in the reservoir has been coupled with induced fracture propagation by plugging of suspended solid particles, in a poro-thermo-elastic domain.
Water Injection is a common oil field activity for pressure maintenance, enhanced oil recovery, and produced water reinjection or disposal. Field studies and experimental work have established that poroelastic and thermoelastic effects, coupled with injectivity decline due to plugging and filtration caused by suspended particles in injection water, lead to permeability reduction, fracture initiation and propagation in water injectors (Sharma et al., 2000). Injection induced fracture propagation and stress reorientation is a combination of several near wellbore and field scale phenomena, which are briefly discussed below.
Particle plugging and filtration in injection induced fractures
Particle plugging occurs in two stages, internal and external filtration. After the formation is plugged internally, a filter cake starts building up on the surface of the fracture. A transition time was defined by Pang & Sharma, 1997 after which the injected particles can no longer plug the formation internally and an external filter cake deposition commences. Wennberg and Sharma, 1997 proposed the concept of filtration coefficient, and their implementation improved the predictions of the rate of internal filtration and transition time to external filtration. The permeability reduction model proposed by Sharma et al., 1997 predicted the permeability profiles by the particle plugging on the fracture face.