Study On Mechanical Deformation And Material Modification Of High Temperature Cementing Cement

The integrity of oil well cement sheath is the prerequisite for oil and gas producting normally and production increase,and it is the guarantee for prolonging the production life of oil and gas wells.In the process of oil and gas well construction and production,the cement sheath will bear various stress effects from the casing and the formation,requiring the cement sheath to have good mechanical deformation so that it will not be easily damaged.Once the integrity of the cement sheath is damaged,the oil and gas production efficiency will be affected,and construction accidents will be caused and the construction safety will be endangered.With the maturity of exploration and development technologies,more and more high-temperature and deep-wells are appearing in the exploration and exploitation tasks.Therefore,the research on mechanical deformation of cement under high temperature is significant both analyze or evaluate the ability to withstand stress of cement sheath and related construction parameters.At present,the mechanical properties of cement at high temperature are mainly concentrated on the compressive strength of cement.Generally,the uniaxial compressive strength of cement is taken as the main engineering criterion,and focus on testing and analysis to compressive strength.However,there are mainly two types of damage of the cement sheath under the action of the downhole load.The first is when the external load exceeds the ultimate strength that the cement stone can carry,the cement ring will produce strength damage;The second is the mechanical deformation ability of the cement sheath.As the cement sheath has poorer mechanical deformation ability than the casing material,so the cement sheath is easily deformed and destroyed under the deformation stress of the casing,causing the cement sheath to undergo radial failure in the low stress environment to generate radial cracks.In the high stress environment,the cement sheath is separated from the cementing surface of the bushing,resulting in a micro-annulus,and cement sheath sealing performance is damaged.Therefore,the bearing capacity of the cement sheath depends not only on the compressive strength of the cement sheath,but also on its mechanical deformation ability.Based on the theory of hydration and strength maturation of oil-well cement at high temperature,this paper studies the mechanical deformation of cement at high temperature.Firstly,three representative sets of cemengt slurry with the density of 1.90g/cm3,2.20g/cm3,and 2.40g/cm3 which commonly used in high temperature cementing were selected,and study on mechanical deformation of cement at high temperature curing with the temperature of 90℃,120℃,150℃,180℃ and 210℃.The uniaxial stress-strain and triaxial stress-strain test and SEM microscopic test have been used to obtain the mechanical deformation and mechanism analysis of cement.The results show that the structure and morphology of the hydration products are the main factors that affect the mechanical deformation of the cement.The modification of materials was studied for the characteristics of cementite with density of 1.90g/cm3,large elastic modulus,small Poisson’s ratio,and poor mechanical deformation.From the fiber materials,elastic particle materials and latex materials,XW fiber,XJF rubber powder and JR latex were selected respectively to study the modification of mechanical deformation materials,and the mechanical deformation was improved through uniaxial and triaxial tests.The results show that the three types of materials have different degrees of improvement effect on the mechanical deformation of cement,and the effect mechanism of the modified material is analyzed through SEM microscopic testing of cement.Finally,through the cement sheath integrity equipment testing device simulated high-stress environment and low stress environment,the cement sheath with modified material was evaluated for mechanical sealing integrity,to verify the effect of the modified material to improve the mechanical deformation of the cement sheath.The results show that the cement sheath meets mechanical integrity requirements after the addition of JR latex and XW fibers.