Numerical Simulation Of Cementing Efficiency In Expanding Well

During the drilling of deep and ultra-deep well and complicated geological conditions,due to the poor stability of the evaporite bed,mudstone and coal seams,the wellbore collapse was severe,resulting in the formation of large annulus,"ice-sugar gourds" wells and sawtooth wells,resulting in irregular diameters and inefficient replacement.As the fluids in the wells are affected by multiple mechanics and actual geometric flow fields in the process of contact and mutual displacement,it is easy to cause serious damage to the wells during the cementing process,such as the channeling,the incomplete displacement of the mud cake,and the lack of tight sealing.The poor cementation quality has brought many problems to downhole and resource development,and has affected post-operational measures such as fracturing and acidification,which are very unfavorable to the stable production of oil and gas.For the problem of the low efficiency of cementing annulus replacement caused by irregularities in the geometrical curve of the wellbore,the research at home and abroad is not comprehensive.Therefore,it is of great significance to study the influence of the irregularity of the diameter of the well on the replacement efficiency to control the quality of the wellbore in the field and it is of great significance to study the effect of rheological parameters on displacement efficiency under irregular calibers for controlling the rheological parameters of cementing construction.In this paper,modeling software CFD and computational fluidics software Fluent were used to study the effects of different geometry hole diameter curves and rheological parameters of ?? equation on the displacement efficiency of cement slurry.The results show that the more complex of the geometric curve of the well diameter,the lower of the displacement efficiency.When the geometric curve of well diameter changes,the displacement efficiency gradually decreases with the increasing of the diameter expansion rate.With the increase of the diameter of the single sag,the displacement efficiency gradually decreases.The length of the single sag has a great influence on the displacement efficiency.When the length is less than the critical value,the displacement efficiency in the sag is extremely low.When the length is greater than the critical value,the displacement is almost unchanged.As the number of sag increases gradually,the displacement efficiency decreases gradually,and the more the number,the slower the rate of decline.With the increase of the zigzag angle,the displacement efficiency decreases gradually.As the number of jags gradually increases,the displacement efficiency gradually decreases,but the decreasing range gradually decreases.Under different geometric curve of well diameter,the effect of wellbore conditions on displacement efficiency was studied.The results show that the greater the eccentricity,the lower the displacement efficiency.The larger the well angle,the lower the displacement efficiency.As replacement time increases,displacement efficiency increases first and then remains stable.The influence of the rheological properties of the working fluid on the displacement efficiency in the HB mode,the results show that:under different caliper curves,the flow regime shows the same rule for the displacement efficiency,the plug flow has the highest displacement efficiency,and the turbulent flow is the second,and the laminar flow is third;The static shear forces of cement slurry and drilling fluid show different effects on the displacement efficiency under different well diameter curves.As the static shear force of cement slurry increases,the displacement efficiency gradually increases.With the gradual increase of drilling fluid dynamics,the displacement efficiency gradually decreases.The consistency coefficients of cement paste and drilling fluid show different effects on the displacement efficiency under different well diameter curves.As the consistency coefficient of cement slurry increases,the displacement efficiency gradually increases.With the increasing of the consistency coefficient of drilling fluid,the displacement efficiency has been reduced;The fluidity index of cement slurry and drilling fluid shows almost the same effect on the displacement efficiency under different well diameter curves.With the increasing of the fluidity index,the displacement efficiency gradually increases.