Offshore well costs and risks have proven the need for research in deep water drilling and well control. This paper presents the experimental research that is ongoing at the Dual Gradient Drilling Laboratory to understand the physics involved in gas migration.
A scaled prototype of an offshore well was built to mimic the Controlled Mud Level (CML) Drilling method. Instrumentation and cameras were used to monitor flow rate and gas liquid ratio. Set rates for the mud outflow and inflow were determined and tested at constant gas influx, by increasing the mud inflow in narrow increments.
The prototype was successfully tested and removed a large amount of gas from the system before the gas migrated into the voided section. The results of these tests show that using high mud inflow rates can eliminate the single bubble system, leading to a dispersed bubble system. With dispersed gas bubbles the removal of the gas is a process of determining an optimal outflow rate that would also accommodate the fluid level requirement. Also, it was observed that the geometry of the outflow line have a major effect on the gas flow behavior. With the reduced outlet diameter, a Bernoulli flow was observed which increased bubble dispersion.
This paper provides information regarding the research on gas behavior and migration in a scaled riser system during circulation. These experiments can be used to study the effects of flow rates on gas dispersion and elimination from the CML Drilling method.