Research On The Separating And Injecting Device And The Distribution Law Of Wellbore Temperature And Pressure In The Multi-gradient Drilling

More and more drilling operations are going to the deep waters when the focus of exploration and development of petroleum have shifted to the ocean around the global in recent years.In deep waters,the pore pressure is higher than that in land drilling because of the higher density of the seawater,and the compaction of the strata blow the mud line is low,which leads to the low formation fracture pressure and high caving pressure.Therefore,the problem of narrow density window widely exists in deepwater drilling,and the deeper the water is,the more serious the problem is.The dual gradient drilling technology(DGD)solves this problems to a certain degree through injecting the low density light medium into the bottom of the riser to form a double density gradient in the annulus.However,with the increasing of the depth of the deepwater drilling,the DGD can not completely solve problem of the narrow density windows very well in deepwater drilling operations.Therefore,it is necessary to study the multi-gradient drilling technology(MGD)with the better ability to adapt to the narrow density window.The MGD can control the wellbore pressure more accurately,making the wellbore pressure better matched to the narrow density windows through using separating and injecting device.Based on the existing design,this paper optimize the design of separating and injecting device which is the key equipment of MGD,improving its main structure,and design the diversion tube and venturi,improving its separating efficiency.Through the numerical simulation,the separation effect is analyzed,and then the size of the separating and injecting device is also optimized,which lays the foundation for the equipment manufacturing and laboratory test in the near future.Through combining the drilling fluid circulation pressure profile and the pressure window of the formation,figure out the critical point where the wellbore pressure is higher than the fracture pressure,providing a theoretical basis for scientifically positioning the separating and injecting device.The calculation model of wellbore temperature and pressure is established,and the distribution law of wellbore pressure and temperature was analyzed.In this paper,the research results of the separating and injecting device and MGD calculation model of temperature and pressure is of positive significance for the development of MGD in the future.