When and Where Can a Fracture Be Initiated From a Horizontal Well in Staged Fracturing Shale Formation

摘要

Multiple hydraulic fractures are postulated to initiate in a horizontal well during staged fracturing in tight and shale gas formations with either an open hole or a perforated completion.This process is often evaluated based on a plane strain assumption and fracture initiation is predicted when a tangential stress near a wellbore or perforation exceeds the corresponding tensile strength.Results from a 3D finite element model developed indicate that critical fracturing locations may not be in the middle of the packed section normally assumed,but this critical stressing region can be located at the vicinity of packer area where a 3D analysis is required.This phenomenon can directly impair our evaluation on increased productivity or EUR over fracturing spacing and ultimate fracturing geometries.More over plastic yielding can initiate before a hydraulic fracture initiation,which either forces the fracture to initiate in an unexpected location and orientation or blocks a fracture from initiating.Two-dimensional poro-elastoplastic calculations are also used to analyze the stresses near a perforated holes.The critical stress and the corresponding wellbore pressure for fracturing or plasticity,which ever takes place first,are analyzed and selected as the corresponding mechanisms so that surface pressure responses can be interpreted accordingly.Fracturing initiation pressures from twenty-two(22)stages of a staged fractured horizontal well in a field from Pengshui,China are used for fracturing initiation interpretations.