Study On Mechanical Properties Of Cement Sheath In Shale Gas Well Under Fracturing Condition

With the development of oil and gas field development technology,people are paying more and more attention to wellbore integrity issues.Wellbore integrity issues are not only related to the safe operation during drilling,but also directly affect the long-term stable production of oil and gas wells in the later period.The destruction of wellbore integrity often causes problem such as sustained annular pressure,affecting the safe development of oil and gas wells.In this paper,firstly,the fracturing mechanics model of shale gas horizontal wells is established according to the external loading of the wellbore.Then the temperature field distribution and temperature stress of the wellbore during the fracturing process are calculated using the numerical calculation method.Horizontal well fracturing mechanics model was used to evaluate cement sheath integrity according to Von Mise conditions.Next,based on the mechanical model,the effect of the cement sheath thickness,elastic modulus and Poisson’s ratio on its own stress situation was analyzed.It was found that the appropriate thickness,small elastic modulus and Poisson’s ratio should be selected for the cement sheath integrity.Finally,the influence of perforation parameters on the stress state of cement sheath was investigated using ANSYS.It was considered that the pore diameter and shot density of perforation should be small,which is beneficial to the integrity of cement sheath.The perforation should be chosen in the direction of the minimum equivalent stress of cement sheath inner boundary.During the perforating,the phase angle should be carefully selected to avoid perforating in the direction of the maximum equivalent stress of cement sheath inner boundary.