Research On Anti-pollution Of Cement Slurry In Changning-Weiyuan Shale Gas Cementing

Due to the serious eccentricity of the casing and the irregular diameter of the shale gas horizontal well,it is easy to cause the drilling fluid to be replaced with low efficiency,which leads to serious pollution of the oil-based drilling fluid and the cement slurry,which affects the cementing quality.In this paper,the cement-based cement slurry,oil-based drilling fluid and spacer fluid used in Changning-Weiyuan are used as research objects to determine the influence of oil-based drilling fluid on the key performance of cementing cement slurry,and analyze the oil-based drilling fluid and cement slurry.Insufficient anti-pollution performance of the spacer fluid during mixing,based on the contact pollution mechanism of cementing cement slurry,from the perspective of cementing cement slurry,guiding the screening of cementing slurry anti-pollution agent to improve the anti-pollution ability of cementing cement slurry The effective exploitation of shale gas provides protection.Through laboratory experiments,it is found that the lipophilic oil-based drilling fluid has great incompatibility with the hydrophilic cement slurry.When the oil-based drilling fluid is mixed with the cement slurry,the rheological properties of the cement slurry mixing will be deteriorated.The thickening time is shortened and the strength of the cement stone is reduced.Through the modern analysis methods such as XRD,ESEM,TG,Zeta potential and interfacial tension test,the mechanism of contact pollution of cementing cement slurry is proved:1 After the oil-based drilling fluid is mixed with the cement slurry,the interface is formed under the action of shearing force.Unstable oil-in-water cement slurry with high tension,emulsified and thickened,resulting in poor rheological properties of cement slurry mixing and shortened thickening time;2 non-curable oil-based drilling fluids ranging from "0.5-1mm" The spherical large particle size state is distributed in the cement stone,which destroys the integrity of the cement stone,resulting in a significant decrease in the strength of the cement stone.When the blending ratio of the oil-based drilling fluid is greater than the blending ratio of the spacer fluid,spacer fluid can not solve the rheological property of the cement slurry mixed with the separator liquid,and the thickening time is shortened;as long as the oil-based drilling fluid is mixed The strength of mixed and cemented cement stones is still greatly reduced.Based on the solution of the oil-based drilling fluid and cement slurry contact pollution,this paper guides the screening of surfactant FB2 and polypropylene fiber,which can significantly improve the anti-pollution ability of cement slurry without affecting the performance of cement slurry.After adding surfactant FB2 and polypropylene fiber to the cement slurry,FB2 can be adsorbed at the oil-water interface to reduce the oil-water interfacial tension,so that the oil-based drilling fluid can be stably distributed in the cement slurry in a spherical small particle size to form a stable Oil-in-water cement slurry to improve the rheological properties and thickening time of cement slurry;polypropylene fibers with good hydrophilicity and lipophilicity are randomly dispersed in the cement stone and connected to the non-curable oil.When the mixed cement stone is subjected to external force,the polypropylene fiber prevents the cement stone from being broken and greatly increases the strength of the cement stone.For example,the fluidity of cement slurry blended with 25%oil-based drilling fluid is improved from 9cm to 21.3 cm,the thickening time is changed from 37min to 318min,and the cement stone strength increase rate is over 40%.