Study On Wall Stability Of Deep Shale Gas Well Considering Ageing Characteristics

Shale gas resource is a key point of national energy development in recent years.Because of its abundant storage and huge development value,shale gas exploitation and utilization have set off a high tide at home and abroad in recent years.With the quicker development of shale gas and frequent occurrence of safety accidents,such as shale gas well wall collapse,the study on the stability of shale gas wells is becoming more and more important.It is found in engineering practice that the physical and mechanical properties of shale wellbore are important factors affecting the stability of shale gas wells,and the action of water is an important inducement to weaken the mechanical properties of rock.In addition,rock failure often has a typical time effect.In order to solve these problems,a comprehensive analysis method,which combines laboratory test,theoretical analysis and numerical simulation,is adopted in this paper from the point of view of rock mechanics.The mechanical properties of shale and shale stability of wellbore are systematically analyzed and deeply studied.The main contents and achievements of the thesis are as follows:(1)The shale rock samples of Longmaxi formation were taken and processed into standard samples.The laboratory triaxial compression tests and triaxial compression tests with water pressure were carried out by using TFD-2000 microcomputer servo controlled triaxial rheological testing machine,and the basic mechanical properties of shale were analyzed.(2)Considering the aging characteristics of shale,laboratory tests of shale mechanical properties are carried out,including triaxial creep tests of solid samples and borehole shale samples,and on this basis,triaxial compression tests and triaxial creep tests were carried out under high stress and high water pressure.The creep characteristics of rocks and the creep failure mechanism of shale were studied by using the theory of rock creep.(3)According to the creep characteristics of shale,based on Burgers model,considering the plasticity of rock,the Mohr-Coulomb criterion is introduced,a new Cvisc model is formed.The parameters of creep model are identified by using the 1stOpt software of quasi-Newtonian BFGs algorithm.The results show that the Cvisc model can well reflect the creep characteristics of shale.(4)Taking a well in Jiaoshiba gas field as an example,the long-term stability of shale gas well is studied by using FLAC3 D numerical simulation software,considering time effect and Cvisc constitutive model.