The primary goal of a hydraulic fracturing treatment is to create a highly conductive flow path from the formation to the wellbore to increase well production. Engineering a fracture with high conductivity and half-length has been a source of continuous effort and challenge over the years. Because proppant-pack retained permeability is often a small fraction of the maximum expected value, techniques have been developed to create networks of open channels inside the fracture. An in-situ channelization (ISC) process generates heterogeneous proppant placement that leads to highly conductive channels.
ISC is unique to fiber-based composite fluids, by which channels spontaneously form in a fracture before fracture closure. The ISC process involves pumping a composite fluid that segregates into proppant pillars. This type of heterogeneous proppant placement is facilitated by the presence of fibers that hinder proppant settling and anchor the proppant pillars in place. One benefit of such process is the resulting high conductivity due to the channels, which are maintained open by pillars made of fibers and proppants. ISC has been observed and studied in laboratory conditions. It occurs with linear gels and crosslinked fluids within a well-defined range of parameters (fiber loading, proppant loading, fracture width, and rheology). With crosslinked fluids, ISC can be triggered by breaking the carrier fluid shortly before the fracture closure. With linear gels, ISC forms spontaneously after the placement of the composite fluid in the fracture. Experimental evidence also supports that pillars formed by ISC do not spread under closure pressure, but remain contained and competent.
The study of ISC required unique experimental setups of sufficiently large scale to capture the dimensions of a real fracture. The experimental evidence enabled identification of the mechanisms of ISC formation, the factors that favor the formation of channels, and the impact of ISC on fracture properties.
See more of this Group/Topical: Topical 9: 4th International Conference on Upstream Engineering and Flow Assurance