Hydraulic fracturing is a method used to enhance hydrocarbon recovery from tight geological formations by injecting viscous fluids to fracture the rock and deposit proppants. This research investigates the effects of long-term exposure of tight sandstone formations to remaining water-based cross-linked polymer fracturing fluid (FF) under extreme conditions. The objective is to minimize the need for immediate flow-back and cleanup operations. Core flooding experiments are conducted to evaluate the impact of fracturing fluids on core samples and to assess changes in fluid properties over time. This study used a standard industry fracturing fluid (FF) formulated with low-salinity water (TDS 819 ppm) containing CMHPG polymer, cross-linker, breaker, biocide, pH buffer, surfactant, and gel stabilizer. The FF was broken and filtered before use. Formation water (FW) used for saturation and permeability tests had a TDS of 36,600 ppm. Core samples from Scioto tight sandstone, with permeability ranging from 0.1 to 1.5 millidarcies, had porosity values of 15%-18% measured using gas. Permeability tests were performed at 145°C, 2500 psi confining pressure, and 970 psi back pressure. The cores were saturated with 100 cc of FW, and permeability was measured after FW saturation, FF saturation, and a second FW saturation. Core samples were aged in FF-filled cells at 145°C and 600 psi for extended periods, and permeability was remeasured. Simultaneously, the FF was aged under identical conditions, and different viscosity and characterization tests were applied to the fluid. The initial permeability measurements revealed a decrease following exposure to the fracturing fluid (FF). After the second saturation with formation water (FW), the permeability slightly improved but remained below the initial value. Long-term aging of the core samples for one and three months resulted in a minimal further reduction in permeability. This pattern was observed both immediately after aging with FF-saturated rock and after subsequent FW flooding. The fracturing fluid and its residue were characterized separately. Rheological properties of the fluid were evaluated before and after breaking and filtering (24 hours) and again after one month of aging. The fluid’s color noticeably changed after one month. Residues collected on the filter paper were dried and weighted. This study highlights the long-term impact of water-based cross-linked polymer fracturing fluids on tight sandstone formations. While permeability decreases initially, minimal further reductions occur after extended aging and repeated flooding. Changes in the fluid’s rheological properties and chemical composition over time provide valuable insights for optimizing fracturing fluid formulations, improving well cleanup, and enhancing well performance.
Othman et al. (Tue,) studied this question.