Experimental Evaluation of the Rheological Properties and Influencing Factors of Gel Fracturing Fluid Mixed with CO2 for Shale Gas Reservoir Stimulation

Abstract

Foam gel fracturing fluid has the characteristics of low formation damage, strong flowback ability, low fluid loss, high fluid efficiency, proper viscosity, and strong sand-carrying capacity, and it occupies a very important position in fracturing fluid systems. The rheological properties of gel fracturing fluid with different foam qualities of CO2, under different experimental temperatures and pressures, have not been thoroughly investigated, and their influence on it was studied. To simulate the performance of CO2 foam gel fracturing fluid under field operation conditions, the formula of the gel fracturing fluid was obtained through experimental optimization in this paper, and the experimental results show that the viscosity of gel fracturing fluid is 2.5 mPa·s (after gel breaking at a shear rate of 500 s−1), the residue content is 1.3 mg/L, the surface tension is 25.1 mN/m, and the interfacial tension is 1.6 mN/m. The sand-carrying fluid has no settlement in 3 h with a 40% sand ratio of 40–70-mesh quartz sand. The core damage rate of foam gel fracturing fluid is less than 19%, the shear time is 90 min at 170 s−1 and 90 °C, the viscosity of fracturing fluid is >50 mPa·s, and the temperature resistance and shear resistance are excellent. The gel fracturing fluid that was optimized was selected as the base fluid, which was mixed with liquid CO2 to form the CO2 foam fracturing fluid. This paper studied the rheological properties of CO2 foam gel fracturing fluid with different CO2 foam qualities under high temperature (65 °C) and high pressure (30 MPa) and two states of supercooled liquid (unfoamed) and supercritical state (foamed) through indoor pipe flow experiments. The effects of temperature, pressure, shear rate, foam quality, and other factors on the rheological properties of CO2 foam gel fracturing fluid were considered, and it was confirmed that among all the factors, foam quality and temperature are the main influencing factors, which is of great significance for us to better understand and evaluate the flow characteristics of CO2 foam gel fracturing fluid and the design of shale gas reservoir fracturing operations.

A Review of Weak Gel Fracturing Fluids for Deep Shale Gas Reservoirs

“…The fracturing fluid still has good sand-carrying performance under high temperature conditions [30][31][32]. Crosslinked gel fracturing fluids have excellent temperature and shear resistance and an effective sand-carrying capacity [33]; they are mainly composed of a gel formed by the combination of a thickener and a crosslinking agent [34].…”

Development and Gelation Mechanism of Ultra-High-Temperature-Resistant Polymer Gel

“…Clean fracturing fluids, devoid of residues after gel breaking and causing minimal reservoir damage, face challenges due to their elevated costs and limited temperature endurance [ 17 ]. In contrast, gel fracturing fluids showcase notable capabilities in temperature and shear resistance, along with effective sand-carrying properties [ 18 , 19 ]. These traits align well with the specific requirements of deep and ultradeep reservoirs, thus positioning gel fracturing fluids as a highly promising solution for practical implementation.…”

Optimization of Carbon Dioxide Foam Fracturing Technology for Shale Gas Reservoir

“…Fu and Liu simulated and studied the rheology and stability of CO 2 foam under high-temperature and high-pressure experimental conditions [33]. Wang et al [34] optimized the formula of CO 2 gel fracturing fluid for shale gas reservoir with experiments and studied the rheological characteristics of CO 2 foam gel fracturing fluid with different CO 2 foam qualities under two conditions of high temperature (65 °C) and high pressure (30 MPa), as well as nonfoaming and foaming through indoor pipe flow. Cai et al [35] studied the fracture initiation and extension behavior during supercritical carbon dioxide injection fracturing, established an induced strain model, and systematically studied the influencing factors of fracture initiation.…”