| The narrow safety density window,shallow gas,and shallow flow are the challenges of deepwater operations.In the process of cementing with abnormal pressure formation in deep water,if the wellbore pressure is not controlled scientifically,it will lead to accidents such as loss of circulation and gas bolting,which will make it difficult to guarantee the quality of cementing and even lead to blowout disaster.The rheological properties of cement slurry are greatly affected by the wide range of alternating temperature fields in deepwater wellbore.In addition,the hydration reaction of cement in turn affects the wellbore temperature.Therefore,in order to accurately control the wellbore pressure during cementing displacement,it is necessary to conduct in-depth research on the rheological properties of cementing slurry downhole.Therefore,it is of great significance to the safety of drilling engineering to study the interaction between hydration heat and temperature of cement and the influence of temperature and hydration on the rheology of cement slurry in the process of cementing.This paper establishes a cementing transient temperature field calculation model under the influence of cement hydration,a wellbore transient pressure calculation model during cementing,a key parameter calculation model during the U-tube effect,and simulates and analyzes the wellbore flow during cementing.Based on the theoretical and experimental research of many researchers,the rheological parameter calculation model of cement slurry considering the influence of temperature and hydration time and the temperature and pressure coupling calculation model of cementing wellbore were established.The numerical solution method was given,and the friction under the condition of cementing was simulated numerically.Based on the above research,the software for calculating hydraulic parameters of deep-water cementing was independently developed,and combined with the principle of manage pressure cementing technology,the hydraulic design and optimization method of cementing for deepwater cementing operation was given.The main research conclusions are as follows:(1)In long cementing in the process of grouting displacement,bottom hole temperature falling fast at the beginning,and then under the action of the cementing cement hydration heat,and a small rise,this paper puts forward the consideration of well cementing cement hydration heat deepwater cementing wellbore temperature field model of the calculation results are basically identical with the experimental measurement results,the model prediction error within5%,can accurately reflect the cementing grouting for the downhole temperature condition.In addition,the U-pipe effect can lead to a spike in bottomhole pressure,so it is necessary to optimize the flow rate and fluid consumption during cementing to mitigate or avoid the U-pipe effect.(2)The rheological properties of cement slurry are most significantly affected by temperature and cement hydration time.The computational model of the rheological parameters(yield stress and plastic viscosity)proposed in this paper at different temperatures and times is in good agreement with the experimental data,and the error is less than 10%,which can well meet the needs of engineering calculation.(3)Based on the rheological calculation model of cement slurry,the temperature-pressure coupling calculation model proposed in this paper can more accurately calculate the cementing wellbore pressure.The comparative verification shows that the numerical calculation results of the model are in good agreement with the field measurement results.(4)Based on the self-developed deepwater cementing hydromechanics calculation software,a set of wellbore pressure optimization method combining density optimization and wellhead back pressure compensation is presented in this paper.Numerical simulation proves that this set of wellbore pressure optimization method can provide guarantee for safe cementing in deepwater area. |
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