Safety assessment on twin-packer string of HTHP well

After HTHP (high temperature and high pressure) oil and gas wells are put into production, the fluid medium in the closed space of twin packer of completion string is thermally expanded due to the effect of high temperature reservoir fluids, and leads to confined pressure building.As a result, the tubing may be collapsed and the production casing may be damaged, doing serious harm to string service life and wellbore integrity.To deal with the safe production problems caused by the increasing of pressure in closed space, the coupling mechanism between borehole and strata under the effect of temperature load was analyzed by using the theories of elasticity and thermal conduction.Then, the relationships of string displacement deformation at free tubing and cemented production casing vs.temperature and pressure were investigated.Finally, a pressure prediction model for the closed space of twin packer was established.Meanwhile, the safety performance of packer string in different working conditions was checked and analyzed.It is indicated in the stage of flowing production, the annulus pressure increases with the spacing of twin packer and the safety of strings is not impacted.Inthe stage of completion fluid circulation, the annulus pressure decreases with the increasing of twin packer spacing if the extreme working condition is taken into consideration, but it is always higher than the internal pressure strength of production casing.Therefore, the packer shall not be set at once and its setting shall be performed after a while so as to ensure the safety of strings.