Based On The Research On The Cement Slurry System For Preventing Gas Channeling In High Temperature And High Pressure Gas Wells In Shunnan Area

The buried depth of the natural gas in Shunnan block is approximately 6500?7700m,and the bottom temperature is up to 140?200 degree,which brings the oil gas pressure to around 70?100 MPa.With high formation temperature and high pressure,reservoir structure in this area are complex and active,and oil gas pressure window is narrow.From so far,the high pressure gas liner cementing quality rate is not high,and the main problem is the gas channeling,to solve this problem,the key is research of anti gas channeling slurry system.To solving gas channeling problem during waiting on cement phase and curing stage,three kinds of functional materials were used with high temperature retarder and filtrate reducer admixtures according to the gas channeling prevention mechanism,which combined into three types of cement slurry system.Functional materials had no adverse effect on the performance of foundation engineering and the properties of these slurries are as followed:the fluid loss was within 40mL,and the transition time is within 5min,in addition,compressive strength of 24 hours is more than 22MPa.We put forward some new methods named breakthrough pressure and continuous breakthrough speed separately that can directly reflect the ability of preventing gas channeling for different stages of cement slurry system.Furthermore,we corelate the anti gas channeling ability of each functional cement slurry system with cementitious structural strength and cementation of cement stone strength which identified the key influence on the performance of gas channeling prevention.The experimental results indicated that adding functional material will improve the cement slurry cementing structure strength and increase fluid channeling resistance;the suitable dosage of thixtropic agent activated ultrafine SiO2 are 1.0?2.0%(BWOC),the amount of elastic particles should be controlled within 1.6?2.0%,the dosage of toughness fiber are 0.35?0.45%.The Three Axial Stress experimental results illustrated the elastic modulus of both elastic cement slurry and toughness cement slurry are reduced more than 40%compared with ordinary cement slurry,what's more,the residual strain of both slurry are small,which shows that the addition of fiber and particles improved the mechanical properties of cement stone;SEM research results shows that the addition of the active ultrafine SiO2 creates different types of crystal in the early hydration offered the high early strength of cement stone;fiber could embedding and anchoring in cement and improve the integrity of the cement stone through the stress dispersion and brings higher anti gas channeling ability in solid phase.We designed a multifunctional collaborative cement slurry system namely thixotropic elastic toughness cement slurry system,which could be applied to high temperature and high pressure gas well cementing in Shunnan block,the slurry loss is 26 mL;compared with the conventional cement slurry,the system's gel structure strength recovery rate in liquid phase is increased by 306.25%and up to 0.0585Pa·s-1,the breakthrough pressure is increased by 108%and up to 509.6Pa;the interfacial bonding strength of bonding interface is 1.812MPa,the breakthrough pressure increased by 240%which ends to 0.085MPa compared with conventional system,gas channeling prevention perfomanced well;the compressive strength of cement stone with 48 hours is as high as 35.8 MPa,the elastic modulus is reduced by 48.9%and ended as 5110MPa.To sum up,the thixtropic elastic toughness slurry system we manufactured has the characteristic of highly anti gas channeling ability and well performance of long-term integrity of cement stone,which has important practical significance to solve the problem of gas channeling in Shunnan block.