Change laws of pressure transferring efficiency over time in the setting stage of cement slurry in deep wells
With the development of oil and gas wells to deep and ultra-deep strata,the geological conditions get more and more complicated,and the production gets more and more difficult.Particularly,the strata with high temperature,high pressure and narrow pressure window are the prominent difficulty in cementing engineering.In the process of cementing in deep and ultra-deep strata with pressure sensitivity,the accurate control of slurry column pressure is the key to ensure the cementing safety and the interlayer isolation quality of cement sheath.To explore the pressure loss laws and pressure transferring capacity of cement slurry in the setting stage,this paper establishes a hydrostatic column pressure evaluation device and a pressure transferring efficiency evaluation method for cement slurry.Then,the hydration rate and static gel strength of the cement slurry with different thicknesses in the process of slurry hydration are tested by using microcalorimeter and ultrasonic static gel strength tester.Finally,the change laws of slurry pressure loss and pressure transferring efficiency over time are analyzed.And the following research results are obtained.First,according to the hydration process,the pressure loss in the setting stage of the slurry system with good settlement stability can be divided into two stages,i.e.,the stable stage of hydration induction and the rapid reduction stage of hydration acceleration.Second,in the hydration induction period,the static gel strength of the cement slurry with suspension-dispersion structure develops slowly,and its pressure loss rate increases with the decrease of thickness,following the theory of gel suspension.In this period,the liquid slurry can transfer the top pressure efficiently and quickly with pressure transferring rate exceeding 95％.Third,in the hydration acceleration period,the microstructure of the slurry changes into the gel-grid structure,and the formation of hydration products enhances the strength of the gel grid and its bonding strength with external interface to transfer the solid gravity and the upper additional pressure to the external interface,reducing the hydrostatic column pressure and pressure transferring efficiency of the cement slurry,and eventually making the slurry free of pressure transferring ability.In conclusion,the research results can provide experimental and theoretical support for the efficient implementation of pressure holding and waiting in the cementing process in pressure-sensitive strata,and lay a solid foundation for the efficient development of deep and ultra-deep reservoirs.
CementingPressure holding and waiting on cementPressure lossPressure transferringEarly hydrationMicrostructure
万方数据
维普
