Study On The Effect Of Volume Shrinkage Of Cement Slurry On Ring Air Enthalpy

It has always been a technical problem that the annulus with pressure after cementing and most of the natural gas wells will face this problem. A major cause of leading with the problem that annulus with pressure is gas channeling, there are a lot of causes will lead to gas channeling, gas channeling prevention performance of cement slurry has an important influence on the gas channeling. The volume shrinkage of the cement slurry is one of the important indexes of gas channeling prevention performance of cement slurry. Therefore, to explore the effect of volume shrinkage of cement slurry on gas channeling has important guidance value for the design of gas channeling prevention performance of cement slurry.Research was carried out to explore the effect of volume shrinkage at different stages on gas channeling on the basis of existing studies from the volume shrinkage and its influencing factors. Based on the hydration reaction and hydration process combined with the volume shrinkage curve, the hydration heat curve and the TGA curve, the cause of the volume shrinkage and the shrinkage process were analyzed,finally found that in the process of cement hydration the more free water converted into bind water and chemical combination water, the greater the volume shrinkage. The volume shrinkage of different cement slurry system was analyzed by the OWC-1102 type high temperature and high pressure volume shrinkage apparatus and the length measuring instrument,and then the influence factors and the mechanism of the volume shrinkage are analyzed, finally found that at 90?, the water cement ratio from 0.3 increased to 0.6, the volume shrinkage rate increased by 0.24% at the beginning of the coagulation time., the volume shrinkage rate increased by 1.2% in the final setting time;At 90?, comparing with the basic formula with 35% silica fume and the formula without silica fume, the volume shrinkage rate decreased by 0.38% at the beginning of the coagulation time, the volume shrinkage rate decreased by 0.69% in the final setting time; comparing with the basic formula with 15% slag and the formula without slag, the volume shrinkage rate decreased by 0.17% at the beginning of the coagulation time, the volume shrinkage rate decreased by 0.46% in the final setting time.Reasonable experimental methods were used to test the change of pore pressure in different stages, the change of pore pressure during the coagulation process, and the change of interfacial bond strength, combined with gas channeling, the effects of the volume shrinkage at the beginning of the coagulation time and the volume shrinkage after condensation are analyzed,experimental data analysis showed that the volume shrinkage rate of the initial condensation decreased from 0.81% to 0.39%. and the pore pressure of the initial setting time decreased from 0.9MPa to 0.3MPa, the cementation strength of the one or two interface gradually decreases with the increase of the volume shrinkage rate. The effect of volume shrinkage on interfacial bond strength is greater when drilling fluid filter cake exists; Through the calculation of the growth rate of cement strength, the influence of the appearance volume shrinkage on the bond strength is compared with the existing condition of the drilling fluid filter cake. The measures to improve the volume shrinkage of the cement slurry are put forward from the aspect of optimizing the formula of the cement slurry, laboratory experiment results show that the optimum performance of the conventional cement slurry system is good, the volume shrinkage performance has been alleviated.Due to the limitation of the experimental conditions, the influence of the volume shrinkage rate on the gas channeling between the initial and final setting of the cement slurry has not made an in-depth study. It is suggested that the content of this part is further studied in the future.