Study On Offshore Reverse Circulation MPD Technology Using Dual Concentric Strings

Due to shortage of oil and gas resources and cutbacks of many maturing oil-fields, the supply of crude oil and gas can't meet the demands of national economy development. Oil and gas exploration and development will focus on offshore. However, offshore drilling is a daunting task. The precise downhole pressure control to keep the wellbore safe, exerting hydraulic weight on bit in extended reach drilling, the high day-rate of the floating rig, so a advanced offshore drilling method is needed to answer these challenges of offshore drilling.A new drilling method called "Deep-water Reverse Circulation MPD" is introdued which uses dual concentric strings. The closed circulation system can makes the pressure control more precisely. The piston attached on drilling string can exert sufficient hydraulic WOB. The expansion liner drilling and the well cleaning devices can extend the ERD's range.The technique features and the advantages of this drilling method are summarized. On this basis, the structure of some relevant key equipments are designed, which include the top injecter, the flow switcher, the automatic non-return valve and the manul controll non-return valve.The well temperature field model and wellbore pressure field model are established based on the the principle of energy and momentum conversation. The method to calculate the parameters of pressure loss and temperature is summarized, The circulation rate selection of this method is based on the hole cleaning and stabilization of wellbore.By analyzing the pressure control methods, it is found that to adjust the back pressure first, and change the circulation rate next.