Supramolecular reinforced gel fracturing fluid applied in ultra-deep reservoirs: Mechanism research of sand-carrying under fracturing fluid lubrication

Abstract

Hydraulic fracturing plays a pivotal role in developing deep/ultra-deep oil and gas reservoirs. The high in-situ stress in deep/ultra-deep reservoirs results in narrow fracture apertures, which increases frictional resistance between proppants and fracture walls. This hinders proppant migration to the deeper regions of fractures for effective support, necessitating fracturing fluids with enhanced sand-carrying capabilities. In this study, two types of polymers capable of forming physically crosslinked networks through supramolecular interactions were synthesized. When crosslinked with organic zirconium, they form a supramolecular reinforced gel fracturing fluid. The fracturing fluid exhibits high strength, excellent shear recovery, and strong water-binding capacity, which allows the lubricating liquid film formed by the fracturing fluid on the fracture surface to maintain stability under ultra-high temperature conditions in ultra-deep reservoirs, thereby effectively reducing the frictional resistance between the proppant and the fracture walls. Data from the tribological experiment show that under the lubrication of the supramolecular reinforced gel fracturing fluid, the coefficient of friction (COF) of the proppant-fracture wall contacts is 0.48, which is 15.23 % lower than that of partially hydrolyzed polyacrylamide (HPAM) gel fracturing fluid. The relationship between the lubricating performance of the fracturing fluid and its sand-carrying ability was studied using the computational fluid dynamics-discrete element method (CFD-DEM) simulation approach. Under the lubrication effect of the fracturing fluid, the deep migration rate of the proppant (defined as the ratio of the number of proppants flowing out of the fracture to the total number of proppants) significantly increased from 7.16 % at a COF of 0.8–69.02 % at a COF of 0.05. This indicates that improved lubricating performance of the fracturing fluid enhances the proppant's ability to migrate into the deeper regions of the fracture.