Horizontal Shale Gas Well Fracturing Cause Damage Sets Analysis And Prevention Measures

In order to accelerate the development of shale gas business of China National Petroleum Corporation.Southwest Oil and Gas Field Company conducted science and technology researches and field testes actively.By the end of year 2013,three horizontal wells of shale gas have been drilled,and the stage fracturing technical was adopted in the three wells,but there was casing damage in all the three horizontal wells.The reservoir missing induced by casing damage of fractured shale gas well reduces the single well production and results in considerable economic loss.The paper are mainly aimed at the research of casing damage issues.By reading a lot of research literatures and analyzing the data of Oil Field,it can conclude that the casing damages in shale reservoirs have several following characters:(1)all the casing damages are after one stage of hydraulic fracturing;(2)there is a certain distance between the location of casing damage and the previous stage of hydraulic fracturing;(3)the more the number of stages of hydraulic fracturing,the more extent of casing deformation is.By comparing the characters of casing damages in North America shale gas reservoir and Sichuan tight oil reservoir,it can conclude that it is the shear casing damage in the study area.By analyzing the single well data of casing damage,the mechanisms of casing damage induced by shale reservoirs fracturing concluded as the following three categories:fault activity,lithologic interface and the casing collar failure,and the corresponding geological model is also established;Many mechanical properties of shale reservoirs are obtained by conducting a large number of experiment tests;The shear mechanics model of casing damage is built by analyzing of single well data of casing damage and in-situ stress characteristics,and the critical injection pressure of causing formation slide is also obtained by adopting the model.Through the above comprehensive analysis of casing damage,several prevention strategies for casing damage of shale reservoirs are put forward:1)prevent the slippage of formation and fault by controlling injection pressure.2)adjust the well track and reduce the wellbore shear stress:by overall considering wellbore shear stress and fracturing volume,it is suggested that the intersection angle between wellbore direction and minimum principal stress direction should be from 30 degree to 45 degree.3)protect casing collars and avoid to perforate at the location of casing collars.