Hydraulic Fracturing to Investigate Impact of Fracturing Medium, Bedding Angle and Perforation Length on Fracture Growth in Low and High Brittle Shale

Abstract

Advancements in the technique for early estimation of the hydraulic fracturing potential of fracturing fluid in different shale formations are needed to successfully stimulate reservoir volume and recover the trap hydrocarbons. The determination of fracture initiation and propagation in shale remains unclear, particularly with regard to the choice of type of fracturing fluid during fracturing operation at high confinement. Hydraulic fracturing with supercritical carbon dioxide (SC CO2) and SC CO2 foam are an encouraging technique to overcome significant use of water in shale gas production. Our study was carried out to explore the fracture propagation and fracture initiation pressure under high confinement stress. The hydraulic fracturing experiments are performed to study fracture propagation in the black shale of three different fields to generalize the scope of work using low, medium and high brittle shale: Eagle Ford, Wolfcamp and Mancos. Three different fracturing fluids were selected for fracturing tests: SC CO2, SC CO2 foam and slick water to investigate the impact of low, medium and high viscous fluids. We evaluated the fracture pressure curve, breakdown pressure (fracture initiation pressure), fracture network variation and the impact of bedding angle, perforation length, injection mediums and formation variations on fracture morphology. During hydraulic fracturing with slick water a consistent rise in the injection pressure is recorded whereas sudden fluctuations are recoded with the injection of SC CO2. With the injection of SC CO2 foam, a sudden decrease in injection pressure appears due to imbibition of SC CO2 foam in the pores matrix. Moreover, fracture initiation pressures in shale rocks varied by changing bedding angle and perforation length. Fracture initiation pressure increases with bedding angles. An appreciable difference in fracture initiation pressure with SC CO2, SC CO2 foam and slick water are 5023psi, 6456psi and 6168psi, respectively at high conferment pressure (3500psi). Comparison of hydraulic fracturing of Eagle Ford, Wolfcamp and Mancos shale with different injection medium shows that SC CO2 foam produced complex fracture networks with high aperture and length for parallel, inclined and perpendicular perforations along the bedding. With all types of shale, SC CO2 foam injection has produced dense fracture network. Thus, fracturing with SC CO2 foam can potentially enhance the stimulated reservoir volume.