Research On Improving Cement Injection Displacement Efficiency In Horizontal Sections Of Horizontal Wells In Block LX

At present,the development of unconventional oil and gas resources in the LX block has entered an accelerated stage,and more and more horizontal wells are being deployed and constructed in the target block.The level of cement replacement efficiency in horizontal wells directly affects the cement bonding quality and cement stone sealing effect,and indirectly affects the life of oil and gas wells and the safety of later production and construction.The special wellbore structure of horizontal wells leads to the widespread occurrence of casing misalignment in horizontal well sections.At the same time,the density and rheology of cement slurry will also affect the efficiency of cement injection displacement in horizontal wells.Therefore,the research on improving the efficiency of cement injection displacement in the horizontal well section of the LX block is of great significance to the safe and efficient development of oil and gas resources in the target block.By investigating the mechanism,experiment and numerical simulation of cement injection displacement,combined with the actual situation of the target gas block,it is determined that the main factors affecting the cement injection efficiency of the horizontal section of the horizontal well in the LX block are casing centering,cement slurry density,Displacement flow rate(displacement)and rheology of cement slurry.Based on the study of displacement flow in eccentric annulus,the calculation model of casing limit eccentricity is determined,and the analysis shows that the limit eccentricity of casing increases with the increase of inclination angle and dynamic shear force of drilling fluid.The difference between force and fluid density increases and decreases;the casing string is analyzed from the mechanical point of view,and a calculation model for the spacing and centering of casing centralizers is established.In this paper,a three-parameter H-B model is selected to describe the rheological characteristics of drilling fluid and cement slurry.The calculation model of cement displacement efficiency in different flow patterns is derived from the non-Newtonian fluid flat flow model.The analysis shows that the density difference of displacement fluid and the displacement flow rate are increased.As well as the consistency coefficient and popularity index of cement slurry can improve the efficiency of cement replacement.With the help of commercial CFD software FLUENT,a three-dimensional model of the horizontal well section annulus flow channel was established and meshed.Using fluid mechanics methods and principles,the casing centering,displacement flow rate,fluid density difference,and cement slurry rheology were measured during cement injection displacement.The relationship between parameters and displacement efficiency is numerically simulated and the numerical solution of the displacement efficiency calculation model is sought.The simulation results show that,under the simulation conditions of this paper,the cement injection displacement efficiency of horizontal well sections increases first and then decreases with the increase of casing centering degree.The centering degree is within a reasonable range(80%).The displacement efficiency is the highest;with the displacement flow rate increasing,the flow pattern develops from slug flow to turbulent flow.The displacement effect of turbulent flow is better than slug flow than laminar flow;the displacement efficiency first increases and then decreases with the increase of fluid density difference,and there is the greatest difference in fluid density.Optimal range(700kg/m~3 under the conditions of this study),the displacement efficiency is the highest;the displacement efficiency of cement injection is not sensitive to changes in the rheological parameters of the cement slurry,and the consistency coefficient,dynamic shear and fluidity index of the cement slurry should be appropriately increased.Increase the replacement efficiency,but the increase is not large.Comparing the simulation results and conclusions with previous indoor experiments,the replacement interface changes are similar and the conclusions are the same,which verifies the rationality and accuracy of this study.Finally,the research results are applied to two horizontal wells in the target block,combined with the actual conditions of the target wells,the horizontal well section casing centralizer placement spacing,displacement and rheological parameters of cement slurry are designed,and finally cementing quality is tested.The test results show that the displacement efficiency of the horizontal well sections of the two wells is relatively high,the cementing quality qualification rate is 100%and 96%,the quality rate is 70%and77%,and the cementing quality is high.