Study On Washing Mechanism Of Mud Cake And Optimization Of Injection Parameters

Deep ultra-deep oil and gas resources have become the focus of today’s exploration of proven oil and gas reserves,and their high temperature and high pressure environment puts forward new requirements for cementing quality.However,the virtual mud cake generated by the cementing process is attached to the well wall,resulting in low cement-ing quality,and subsequent oil test production may cause the risk of channeling.Therefore,how to efficiently deal with the virtual mud cake on the well wall in the cementing process has become a key means to improve the quality of high temperature and high pressure cementing.In this paper,the flushing efficiency of the rinsing fluid inside the wellbore is studied as the research object,and the flushing efficiency of the mud cake of the well wall during the cementing process is studied,and the optimization of the construction parameters by this law is studied.Firstly,based on the experimental device,the physical model of the mud cake flushing device is constructed,the internal flow characteristics of the device are analyzed,the distribution law of the internal phase parting,velocity and other param-eters of the flow field is obtained,and the experimental scheme for the evaluation of flushing efficiency is determined.Secondly,the experimental test was carried out through the evaluation of small-size rinsing efficiency in the laboratory,and the rinsing efficiency of mud cake under high temperature conditions was quantitatively analyzed,and verified with digital models.Finally,a full-size mud cake flushing numerical model is constructed,and the influence of important parameters such as different flushing displacement,flush-ing time and rinsing speed on the rinsing efficiency of mud cake is obtained by integrating on-site construction parameters,and important construction parameters such as flushing displacement,flushing fluid type,and rinsing time are jointly optimized according to the test law and digital model law.The research contents and conclusions of this paper are as follows:（1）The mathematical model of the mud cake flushing device was constructed,the flow characteristics inside the mud cake flushing efficiency evaluation device were com-pared and analyzed by hydrodynamic method,the distribution law of the internal phase parting,velocity,flow direction and other parameters of the flow field was obtained,and the experimental scheme and digital model method suitable for the research of the wash-ing efficiency were determined.（2）A quantitative analysis of the mud cake cleaning efficiency under high tempera-ture conditions was conducted using an indoor rotating shear-mud cake washing device,and the influence of washing time,washing flow rate,and washing speed on the cleaning efficiency was obtained.The experimental results showed that the cleaning efficiency inside the wellbore increased with the increase of experimental temperature.The relation-ship curve between cleaning efficiency and washing time had a peak value and was pos-itively correlated with washing speed.With the increase of temperature,the rheological properties of the washing fluid improved,and the turbulent diffusion increased,leading to an increase in cleaning efficiency.（3）Based on ICEM CFD software,a full-scale wellbore mud cake washing device geometry model was constructed,and numerical calculations were performed using Flu-ent software.The calculation results were analyzed using CFD-POST software to obtain the influence of different parameter conditions on the concentration distribution of mud cake inside the wellbore.The results show that the washing fluid entering the wellbore has a shearing effect on the mud cake.With an increase in rotational speed,the washing fluid produces turbulent diffusion.As the mud cake thickness and compaction increase,the washing efficiency will be significantly reduced.（4）Based on the results of the flushing efficiency test and numerical simulation,the impact of flushing parameters on the efficiency of mud cake flushing was analyzed com-prehensively,and the parameters were optimized to meet the complex working conditions on site.The results showed that the flushing displacement was the main factor affecting the flushing efficiency,and the greater the flushing displacement,the greater the variation in flushing efficiency.According to the principle of shear rate,the flushing efficiency can be increased to over 95%when the flushing displacement is more than 0.32 m³·min^-1 and the flushing time is more than 25 min,which provides guidance for the optimization of field injection and replacement parameters.