Optimizing Fracture Spacing to Induce Complex Fractures in a Hydraulically Fractured Horizontal Wellbore

Abstract As conventional hydrocarbon reservoirs are depleted and new sources sought for economic and security reasons, unconventional reservoirs attract the oil and gas industry's attention. Among the unconventional options, shale gas reservoirs have become prominent. After many years of working to effectively recover hydrocarbons from the shale gas reservoirs, it has been accepted that creating complex fracture networks by hydraulic fracturing is one of the most efficient ways to produce gas from these reservoirs. Although several factors affect development of the complex fracture networks, the in-situ stress anisotropy (i.e. the maximum in-situ horizontal stress – the minimum in-situ horizontal stress) is the most significant factor. Low in-situ stress anisotropy increases the chance of creating complex fracture networks with hydraulic fracturing. In order to compensate for the in-situ stress anisotropy, M.Y. Soliman suggested arranging a sequence of fracturing stages to make use of the induced stress caused by the net fracturing pressure (Soliman et al. 2008; East et al. 2011). This method is so called Texas Two Step method (TTSM). This research analyzes the effectiveness of TTSM by utilizing the boundary element method (BEM). In addition, the research analyzes and models fracture geometries caused by interaction among multiple hydraulic fractures to determine the optimal fracture spacing for multistage fracturing operations. From the results, this research concludes that curved fractures can enhance or vitiate the stress contrasts induced by the net fracturing pressure, depending on the shape of the curved fractures. It further calculates optimal fracture spacing for operations using the Texas Two Step method.