Computational Fluid Dynamics Applied to Investigate Development and Optimization of Highly Conductive Channels within the Fracture Geometry

Abstract

AbstractA conventional proppant pack may lose up to 99% of its conductivity due to gel damage, fines migration, multiphase flow, and non-Darcy flow. Therefore, pillar fracturing was developed to generate highly conductive paths for hydrocarbon to flow. This paper describes experimental results and numerical models of a new method of generating stable proppant pillars The proposed treatment method depends on fingering phenomena observed when a less viscous fluid, that does not carry proppant, is injected to displace a more viscous one that carries proppant. The low-viscosity fluid will channel through the high-viscosity fluid and create isolated proppant pillars. This method promises to reduce proppant costs, pumping horsepower, and gel damage compared to conventional treatments.Large-scale experiments (Slot tests: 2-ft height and 16-ft length) were performed to evaluate the development and stability of the created channels. In additional, a computational fluid dynamics (CFD) model was constructed using commercial CFD software, to simulate the experiment and to scale it up into full fracture dimensions. The study focused on effects of surface injection rate (1 to 120 bpm) and viscosity ratio (from 2 to 200) between the two injected fluids.Experimental results and numerical modeling confirmed that viscous fingering phenomena can be used to create a pillar fracture with conductive and stable channels. The numerical CFD model was able to accurately predict the experimental results. Increasing the injection rate reduces the main channel width while increasing the channel branching. Full piston displacement behavior was achieved after 60% of the fracture height, when a high-viscosity fluid displaced a low-viscosity fluid and their viscosity ratio was greater than 5. By reducing the viscosity ratio between the two fluids, the created channel shape converts from cylindrical (where the beginning and end of the channel have the same width) into conical behavior (where the beginning of the channel is wider than the end). This explains why the length of the channel decreases with the viscosity ratio between the two fluids. The distance between proppant pillars tends to be reduced with increasing distance from the wellbore, or with reduced pulse stage volume, time, or rate. A full description of the created channel (distance between proppant pillars) characteristics (size, width and length) will be presented in this paper.