Determination of Critical Fracturing Spacing Affecting the Simultaneous Growth of Multiple Hydraulic Fractures from a Horizontal Wellbore

Abstract

ABSTRACT The multi-stage hydraulic fracturing and horizontal well have become the most important technologies in extracting oil and gas from unconventional reservoirs. However, the stress shadow effect often hinders the simultaneous growth of multiple fractures when design parameters such as fracture spacing and injection parameters are not set properly. Therefore, one of the key issues in a fracturing treatment is the determination of the fracture spacing within a fracturing stage under different combinations of geomechanical and injection parameters. This paper presents a numerical study by using the in-house code, DeepFrac, a fully coupled hydraulic fracturing simulator based on the dual boundary element method and finite volume method. The evolution of the optimal fracture spacing with the geomechanical and injection parameters is investigated. The results demonstrate the dependence of the optimal fracture spacing on the energy dissipation and in-situ stress contrast. A dimensional analysis is carried out, and two dimensionless groups are determined including the dimensionless toughness and dimensionless in-situ stress difference. A critical fracturing spacing is proposed based on the dimensionless groups, which can capture the combined role of different parameters in the fracture growth. The effectiveness of the proposed critical fracturing spacing determination criterion is verified by a few additional numerical experiments. INTRODUCTION The growth of multiple parallel hydraulic fractures (HFs) subjected to a single fluid source is commonly seen in various geological scenarios, such as dike swarms driven by magma supplied by mantle plume and artificial fractures created by fluid injection in the extraction of hydrocarbons. In order to promote the productivity of gas and oil, the hydraulic fracturing treatment is often designed in such a way that simultaneous growth of multiple fractures in each stage can be achieved (Nie et al. 2022). Although such multistage technique has effectively enabled cost savings, field practices have shown that a large portion of perforation clusters failed to initiate or contribute to production according to production logs in Miller et al. (2011). The reasons behind such phenomenon include nonuniformity of rock properties, in-situ stress, stress shadow effect, etc. The stress shadow effect refers to the suppression of some fractures exerted by the neighboring HFs (Peirce and Bunger 2015), which can lead to preferential growth of some HFs and eventually results in a nonuniform fracture pattern.