Numerical Simulation on Characteristics of Hydraulic Fracture Initiation Induced by Circle Pumping Method

Abstract

ABSTRACT: Hydraulic fracturing is an important treatment for tight reservoirs, however, it may induce high initiation pressure of fracture or generate a hydraulic fracture with simple shape. In order to increase hydraulic fracture efficiency, recently, the fatigue hydraulic fracturing method is proposed by several scholars. Experimental data show that this method can generate complicated hydraulic fractures, reduce initiation pressure, reduce magnitude of seismicity and increase permeability. Using the circle pumping schedule is a method to generate the fatigue loading inside hydraulic fractures. In this paper, a flow-geomechanics coupled numerical simulation model is first built. This coupled model has two governing equations. The first governing equation is the transient flow model (TFM) which is used to describe the flow behavior of fluid inside hydraulic fractures. The second governing equation is the rock deformation equation which is used to calculate the stress solution of rocks. The maximum tensile criterion is used to judge whether the hydraulic fracture can be generated. Several factors affecting fluid flow and hydraulic fracture initiation are analyzed by this numerical simulation model. The results show that (1) The circle pumping schedule can initiate new fractures around the hydraulic fracture. This pumping schedule induces heterogeneous distribution of fracture pressure and further induces tensile stress in several locations. This tensile stress initiates new fracture. (2) input pressure amplitude, frequency, roughness and viscosity affect hydraulic fracture initiation. 1. INTRODUCTION The success of unconventional reservoir development is the benefits of hydraulic fracturing and horizontal wells (Rong et al.,2004; Karacan et al., 2011; Dong et al., 2019; Nguyen et al., 2020; Wang et al., 2020; Zhang et al., 2020;). The production rate of the unconventional reservoirs increases with stimulated reservoir volume (SRV) induced by hydraulic fracturing. In order to reduce initiation pressure and magnitude of seismicity but increase the SRV, the circle pumping hydraulic fracturing method (CPHFM) has been proposed and investigated. The HFST results show that the production rate of shale oil reservoir is increased by 10% when the CPHFM is used (Ciezobka et al., 2018). The borehole pressure generated by the CPHFM is higher than the one by ordinary method so the extra hydraulic fractures is initiated around perforations(Ciezobka et al., 2018).