Effect of Alternate Fracturing on Rock Porosity and Permeability Near Hydraulic Fractures

Abstract

ABSTRACT Stimulated Reservoir Volume (SRV) fracturing of horizontal wells significantly increases oil and gas production by generating a large amount of high-permeability main and branch fractures. This study attempts to explores the effect of fracturing sequences on smaller-scale fractures (micro-fractures, pore scales). We carried out multi-stage sequential and alternate hydraulic fracturing experiments, respectively. The effect of fracturing sequence on porosity and permeability characteristics was quantitatively analyzed from the microscopic perspective through Nuclear Magnetic Resonance (NMR) technology. The results show that: (1) the fracture deflection angle of alternating fracturing is about 50% of that of sequential fracturing, and alternate fracturing can reduce inter-fracture interference and effectively control crack propagation morphology; (2) alternate fracturing can reduce horizontal stress difference, which is more conducive to the formation of complex microcracks than sequential fracturing; (3) compared with sequential fracturing, the porosity and permeability near the fracture of alternate fracturing increased by 14.2% and 126.7%, respectively. In conclusion, alternate fracturing has more advantages in increasing the production performance of horizontal wells than sequential fracturing. INTRODUCTION The volume fracture formed by multi-stage fracturing of horizontal wells has significantly increased oil and gas production. It is one of the key technologies for the efficient development of unconventional oil and gas reservoirs (Shelley et al., 2012; Shelley et al., 2010). The stimulated reservoir volume (SRV) fracturing system is generally considered to be formed by main fractures and branch fractures. Multiple hydraulic fractures formed by multi-stage fracturing of horizontal wells will interact with each other. The hydraulic pressure in the formed hydraulic fractures will change the stress field distribution around the hydraulic fractures, thus affecting the initiation, extension, and development of new hydraulic fractures formed around them, thus affecting the recovery and fracturing efficiency of horizontal wells. This phenomenon is usually called the "stress shadow effect" (Bunger et al., 2012; Daneshy et al., 2012; El Rabaa, 1989; Nagel and Sanchez-Nagel, 2011).