Experimental and Numerical Investigation of Proppant Placement in Hydraulic Fractures

摘要

In hydraulic fracturing treatments, a fracture is initiated by rupturing the formation at high pressure by means of a fracturing fluid. Slurry, composed of propping material carrieby the fracturing fluid, is pumped into the induced fracture channel to prevent fracture closure when fluid pressure is released. Productivity improvement is mainly determined by the propped dimension of the fracture, which is controlled by proppant transport and proper proppant placement. Settling and convection (Density driven flow) are the controlling mechanisms of proppant placement. In this study, proppant transport and placement efficiency of four non-Newtonian fluids with controlled density differences was experimentally investigated and numerically simulated. Small glass model was used to simulate hydraulic fracture and parameters such as slurry volumetric injection rate, proppant concentration, and polymer type (rheological properties) were investigated. It has been observed that small glass models easily and inexpensively simulated flow patterns in hydraulic fractures and the flow patterns observed are strikingly similar to those obtained by very large flow models used by previous investigators. Convection was observed to be significant flow mechanism even with small density contrast. As viscous to gravity ratio increases, due to increasing slurry injection rate or decreasing proppant concentration, convection settling decreases and proppant placement efficiency increases. Increasing non-Newtonian flow behaviour index (n) by using different types of polymers shows more gravity under-running and less proppant placement efficiency. Therefore, larger slurry volumes are needed to be injected in order to prop the entire fracture height. Experiments conducted were simulated and some of the simulated experiments were presented. The simulator quantitatively replicates the experimentally observed proppant placement and the match between the experimental and simulated results improves with the quality of fluids rheological data used in the simulation.