Well methods put control in drillers' hands

摘要

Dual gradient drilling methods have been proposed as a means to provide simpler, safer and more economic deepwater well designs. This research investigates riser gas lift as a potential means to implement a dual gradient system. The specific concerns addressed in this study were kick detection, cessation of formation feed in, removal of kick fluids, and re-establishing hydrostatic control with a constant bottomhole pressure method. These concerns were studied using a transient, multiphase simulator. Two alternatives for stopping formation flow were considered, a "load up" method of reducing the nitrogen rate versus closing a subsea BOP. BOP closure was shown to be more reliable for stopping flow and minimizing kick volume. Further, a relatively conventional approach of circulating up a gas-lifted choke line against a surface choke was compared with a dynamic approach based on reducing the nitrogen rate and to the use of a seafloor choke. It was concluded that methods using a choke were much simpler and more effective for controlling pressure than controlling the nitrogen rate.