Study On Formation Pressure Prediction Method Under Uncontrolled Blowout Conditions Caused By Gas Kick

With the decrease of onshore oil and gas resources,offshore oil and gas production has become an important growth pole to ensure national energy security.However,due to the formation uncompacted due to the existence of the sea water section,the safety density window of drilling fluid is narrow during the drilling and completion of offshore deep-water formations,which makes it difficult to precisely control the wellbore pressure,and it is easy to have a gas kick and lost circulation.If it is not handled properly,it is easy to develop into a blowout accident.The blowout explosion accident of the Deepwater Horizon drilling platform in the Gulf of Mexico in 2010 resulted in a large amount of oil leakage,which led to the "most serious oil leakage accident" in the history of the United States.It took more than three months to complete the rescue,causing serious harm to the surrounding environment.Therefore,carrying out theoretical research on wellbore gas-liquid two-phase flow model and predicting the annular multiphase flow law during gas kick can provide theoretical basis and engineering application guidance for safe and efficient drilling.With the continuous development of deep-water oil and gas exploration and development technology,the requirements for well control means and formation pressure prediction methods are getting higher.However,when the blowout is out of control and the well cannot be shut in,the conventional method to determine the formation pressure by reading the casing pressure and riser pressure after shut in cannot be used.Therefore,establishing a set of formation pressure prediction methods under the condition that the blowout is out of control and the well cannot be shut in can provide reliable well killing parameters and theoretical guidance for well killing rescue or rescue well construction.The research object of this study is the annular multiphase flow law in the process of gas kick and the prediction of formation pressure under the condition of out of control blowout.Based on the wellbore gas-liquid two-phase flow model,the research methods such as theoretical analysis,experimental research and numerical simulation are used to establish the research system of formation pressure prediction under the condition that the well cannot be shut in due to out of control blowout,and reveal the gas-liquid two-phase flow law after gas invasion into the wellbore,The jet flow characteristics of out of control blowout fluid are studied.The research results of this paper are expected to provide theoretical guidance for the development of the transient flow of gas-liquid two-phase in the wellbore during the gas invasion process,as well as for the effective prediction of formation pressure when the well cannot be shut in due to out of control blowout,which is of great practical significance for ensuring drilling safety,improving drilling efficiency,reducing drilling costs,and timely taking reasonable well killing design and construction after out of control blowout.The main research contents of this paper are as follows:(1)According to the characteristics of gas-liquid two-phase flow in wellbore during gas kick,the governing equations of drift flow model for gas-liquid two-phase transient flow are established.Based on the finite volume method,Roe scheme is used for numerical calculation.Combined with the simulation example,the development law of gas invasion volume,mud pit increment,bottom hole pressure,section gas content and section gas phase velocity along the well depth after gas invasion is analyzed.The research results lay a theoretical foundation for the prediction of annular multiphase flow law and formation pressure in the subsequent gas invasion process.(2)The multiphase flow law in the annulus during the gas invasion process and after the well is shut in is studied,mainly investigating the influence of drilling fluid density,drilling fluid viscosity,drilling fluid displacement,initial wellhead back pressure and formation pressure on the multiphase flow law in the annulus.At the same time,gas kick simulation experiments were carried out on the full scale experimental wells in the Well Control Training Center of Daqing Drilling Engineering Company,and the prediction accuracy of the gas-liquid two-phase drift flow model based on the finite volume method was verified through experiments.The research results can provide theoretical guidance for the subsequent prediction of formation pressure.(3)The relationship between the characteristic parameters of fluid jet out of control and the wellhead jet velocity is established.Firstly,an image recognition method for the height of blowout liquid column is proposed,and experiments on the height of blowout liquid column are carried out.The effects of fluid density,fluid viscosity,gas content,wellbore hydraulic diameter and other parameters are investigated,and a prediction model for jet height is established according to the π theorem.At the same time,experiments on jet height are carried out in full-size experimental wells.By means of computational fluid dynamics(CFD),the numerical simulation of underwater wellhead oil spill diffusion was carried out,and the effects of jet velocity,fluid density,fluid viscosity and ocean current velocity on the oil spill diffusion were investigated.Based on the simulation results and π theorem,the relationship between oil spill diffusion time and wellhead jet velocity was established.(4)The formation pressure prediction method based on blowout fluid jet characteristic parameters/long short-term memory(LSTM)is established.The formation pressure prediction method based on blowout fluid jet characteristic parameters is to calculate wellhead parameters based on gas-liquid two-phase drift flow model after a certain formation pressure value is given,and forward modeling the fluid jet characteristic parameters after out of control blowout.The formation pressure prediction method based on LSTM is based on the gas-liquid two-phase drift flow model.By constantly adjusting the formation parameters,the time series evolution characteristic data set of the mud pit increment is obtained,and the complex nonlinear mapping relationship between the formation pressure and the mud pit increment is established.Combined with the measured time series of the mud pit increment,the inversion of the formation pressure is realized when the blowout is out of control and the well cannot be shut in.The good prediction results of the model are verified by the measured data of full-scale experimental wells.