An Analytical Method for Predicting the Growth of New Fractures in the Shadows of Existing Hydraulic Fractures in Shale Gas Formations

摘要

Hydraulically fracturing shale gas reservoirs has been a major area of concern since critical development in the past few years.Horizontal well with multi-stage hydraulic fracturing is the key to enhance well productivity and achieve successful well completion.Fracture geometry is the major source of oil and gas production in a shale reservoir.Several models were derived to expose the feasibility of fracture spacing in order to achieve successfully-developed hydraulic fractures in horizontal well.In past studies, propagation of hydraulic fractures alongside the maximum horizontal stress direction during the initiation processing was assumed.But in reality,this phenomenon is far more complex.The initial crack created before treatment fluid injection cannot be exactly perpendicular to the horizontal well,the inclination angle between initial crack and in-situ principle stress direction concentrated in a narrow range.During the propagation of a fracture,the stress field gradually affects and forces the fracture to extend along the maximum stress direction.Based on the in-situ stress field re-oriented by the propped fracture and the effect of well completion situation on the fracture propagation trajectory,authors derived a new analytical model to quickly inform the geometry of new a fracture near the shadows of existing hydraulic fractures. Various states of anisotropic stress have been applied to the simulated models with assigning criteria for fracture initiation and propagation.One of the factors that need to be addressed is the trajectory of a fracture in the presence of varying stress fields.The injection of treatment fluid in the initial crack exerts pressure from inside and the stress field around the fracture tip controls fracture extension direction.The new analytical model presented in this paper is used to quickly predict hydraulic fracture propagation trajectory based on completion situation.The fracture geometry obtained by this model is a reliable resource for designing the multi-stage hydraulic fracture spacing in shale gas formation and evaluating hydraulic fracturing horizontal well completion.