Injection Flux Partitioning between Wellbore and Waterflood-Induced Fracture

Abstract

Waterflood-induced fractures, also known as self-induced fractures, are spontaneously created at injection wells during waterflooding. They propagate for sufficiently large distances in rock and transfer injected fluids far away from a well, both along the flooding layer and outside it. Essentially, the mechanics of waterflood-induced fracture propagation is similar to that for hydraulic fractures intentionally created for reservoir stimulation. However, there are several peculiarities that differ self-induced fractures from hydraulic fractures. Initiation of a waterflood-induced fracture is not an instant process and can take a lot of time. Depending on parameters of a formation, well orientation and injection rate, a fracture can either initiate quickly or not initiate at all. The part of the fluid that flows into the initialized fracture is also a question. As initial aperture of the waterflood-induced fracture is very small, it cannot take all the injected fluid, so part of it still filtrates into the formation through wellbore. In this work, we consider the process of initiation and fluid flow in waterflood-induced fractures. We develop an analytical model that can predict time of fracture initiation, taking clogging effects in account. Also, we present a semi-analytical model for injection fluid sharing between a fracture and a reservoir. The fracture is described by PKN analytical model. Finally, we collect initiation, flux partitioning and geometry data of self-induced fractures and compare them with hydraulic fractures. The present work investigates the differences between hydraulic and waterflood-induced fractures and is important for accurate modeling of the latter.