Study On Nano-composite Cement-based Plugging And Protecting Material For Drilling In Frozen Soil

With the vigorous development of our country's economy,the construction of Western engineering and exploration and development of mineral resources have made further progress.There are a lot of permafrost in western China,and the condition of frozen soil stratum is complex.In the process of drilling,some of the structural development,soft and hard interbed,rock mass loose broken,strong sensitivity,especially the steep-dip fissure for the vicious leakage of the creation of conditions,resulting in the frozen soil drilling in the drill hole collapse,shrink diameter and slurry leakage and so on frequently.Drill hole plugging is a very serious problem in the frozen soil drilling,so it is urgent to carry out the research on plugging and protecting for frozen soil drilling.At present,there are some deficiencies in the use of drilling fluid wall plugging and protecting,it is urgent to explore new material of drill hole plugging and protecting to solve the problem of retaining plugging and protecting in the drilling process of natural gas hydrate in permafrost region.It is a traditional and important method to use cement-based material to plugging and protecting,which has some advantages in solving the leakage of drill hole in complex stratum,but it also has some defects.In the low temperature environment construction,single cement often can not be very good to meet the site construction requirements,resulting in poor wall plugging effect may not be able to reach the purpose of retaining wall plugging.Compounding can effectively improve the cement performance,the Portland cement and sulphoaluminate cement composite,with an unexpected"hydration synergy"effect.The characteristic of composite cement is very good for borehole plugging and protecting in frozen soil area,which is often occurred in the ground of hole collapse,which is based on this fine characteristic,and further solves the problem of coordination and unification between rheology,setting time and slurry strength.Based on the preliminary test,the research foundation of silicate-sulphoaluminate composite cement as the plugging material for retaining wall is established,and the requirement of drilling in permafrost area for plugging material property of retaining wall is taken as precondition,adding admixture to modify the composite cement to meet the construction requirement.The final selection of Nano-SiO₂,water-reducing agent JSS,early strength LC and antifreeze CC as admixture combination,and through the orthogonal test to determine the optimal dosage of each admixture,the development of nano-composite cement-based plugging and protecting material.The test results show that the properties of nano-composite cement have reached the requirements of the frozen soil drilling plugging and protecting by testing the characteristics of fluidity,setting time and compressive strength of the nano-composite cement-based plugging and protecting material.The shear stress of nano-composite cement slurries under different shear rates was tested under low temperature conditions.The linear regression method was used to analyze the obtained data,and it was found that the flow pattern conformed to the Herschel-Bulkley rheological model.The apparent viscosity,dynamic shear force,fluidity index,and consistency coefficient of the cement slurry were characterized to lay a good foundation for the establishment of a drill hole plugging and protecting diffusion model.In order to highlight the unique"hydration synergy"effect of nano-composite cement,the"right angle thickening"of nano-composite cement and the characteristics of very short initial and final coagulation time interval are explained by hydration heat test from thermodynamic angle.The hydration products of different curing ages were analyzed by X-ray diffraction?XRD?.The type and quantity of hydrated products were studied with the change of reaction time.The"hydration synergy"effect of the nano-composite cement was explained from the hydration products.The cement stone was observed by electron microscope?SEM?.The structure of cement stone with different curing age was analyzed and explained qualitatively and quantitatively,and the hydration and hardening process of nanocomposite cement was further explored from the micro structure angle,which would provide reference for the theoretical research of the composite cement system.