| In order to solve the problems of deep water drilling,such as narrow safety density window and difficult wellbore pressure control,foreign scholars put forward CML DGD technology.At present,it has been applied to the North Sea,Mexico and other sea areas,but the relevant research is still lacking in China.This technology control the wellbore pressure profile by accurately adjusting the riser level through the underwater system.Compared with conventional manage pressure drilling technology,the wellbore fluid flow of CML DGD is more complex,and the wellbore pressure control method is different.So,the conventional wellbore flow model and pressure control parameter design method of conventional drilling cannot be directly applied to CML drilling.Therefore,it is necessary to study the wellbore pressure prediction model and control parameter optimization method of CML drilling.In order to improve the prediction accuracy of wellbore pressure in CML drilling,a wellbore pressure calibrate model was established.The model takes the measured bottom hole pressure as the input parameter and inverts the annulus friction calibrate coefficient by the untraced Kalman filter algorithm,so as to improve the prediction accuracy of wellbore pressure.Numerical simulation analysis is carried out on the wellbore pressure calibration model.The results show that the model can accurately predict the wellbore pressure profile at any time,which makes up for the deficiency that the downhole measurement tool can only measure at a single point.In addition,wellbore pressure calibration model can adjust the calculation results in time according to downhole conditions,and has good adaptability to complex downhole conditions.Aiming at the design problem of wellbore pressure control parameters in CML drilling,an optimization model of wellbore pressure control parameters was established.The optimization objectives of the model are drillable depth and bottom hole pressure difference.The optimized parameters of the model were riser level,mud density and pump rate.The stochastic direction method is used to solve the model.The results show that the drilling depth can be significantly increased and the well structure can be optimized by optimizing the riser liquid level,mud displacement and density.In addition,the dynamic optimization of riser level and mud displacement during drilling can significantly reduce the bottom pressure differential,which is beneficial to protect the reservoir and improve the ROP. |
