Research On Pressure Drilling Technology Of Mud Cap

Due to the complexity of handling full loss of return accident, it not only would prolong drilling cycle and increasing drilling costs, but also can cause a series of drilling accidents and complex conditions,such as well collapse and blowout, even lead to wellbore scrapped. Therefore, domestic and foreign experts and scholars have been working on how to prevent and deal with full loss of return accidents since the development of drilling engineering technology. Currently, it is necessary to take a specific drilling technology of managing pressure with mud cap for big loss formation and thoes wells that can not build circulation.Foreign Service Corporations have been in the forefront of research and application on drilling technology of managing pressure with mud cap, they have successfully applied to high pressure leakage reservoir by combining this technology with Early kick detection technology(EKD) in2003’s case.However, domestic technology development is just on the starting stage and only few conventional drilling technology of managing pressure with mud cap been used, so National Petroleum Science and technology key project21subject6(contract number:2011ZX05021-006) carries out research on how to establish complex downhole accident treatments. This paper obtained mud cap managed pressure drilling technology theory, process and equipment, design method for optimizing flow rate of sacrificing liquid is put forward and solve injection rate of annular mud cap problem through research on home and abroad development of mud cap managed pressure drilling technology,which can provide a reference for design and construction of mud cap managed pressure drilling technology, and help to promote mud cap managed pressure drilling technology and its safe application.This paper put forward the flow rate optimising design method and sacrificing fluid performance of mud managed pressure drilling technology.To a certain change of sacrificing fluid perormance,the minimum flow rate required to carry cuttings and satisfy the hydraulic design would vary with the change of Rheology for a well depth. As a result, the optimising of flow rate and the corresponding performance for sacrificing fluid can be obtained by comParatively analyzing in a well depth.Furthermore, this paper put forward design method for injection rate of mud cap.Then height of invasion gas in annular wellbore, mud cap volume at polluted area and time of gas invasion can be obtained through calculation of two-phase flow theory when the back pressure reach its limit value,considering the volume of mud cap polluted.In addtition, the total volume of mud cap required in the process of drilling can be obtained according to calculating injection rate by drilling speed conversion. Based on the theory research, a set of engineering design software for mud managed pressure drilling has been developed through using Visual Studio2010platform and SQL SERVER technology.This software aimes at sloving thoes problems encountered by mud cap managed pressure drilling,such as flow rate optimising of sacrificing fluid and injection rate of annular wellbore, moreover, it can manage wells’data,calculation leakage position, pressure, annular height of mud cap and injection volume of cleaning fluid.Finally, mud cap managed pressure drilling have been designed with AA and BB wells in the north of Sichuan province,which can help to guide construction operation.