Deepwater Drilling: Return Flow Through Hose
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As the petroleum industry enhances their efforts to locate and produce fields in more and more challenged areas, bigger and deeper boreholes are required. The hydraulics of the borehole suddenly becomes the major power consumer of the drilling process. The proposed system where circulation occurs through hoses is a response to these increased hydraulic power requirements. A drilling system where mud circulation occurs in hoses instead of through the annulus is under development. Testing has been performed 3 times. The 2 first was drilled in 1990-92 and the third in 2009. The ones drilled during the 90s experienced no problems due to an anchorage system. The anchorage kept the upper part of the BHA stationary, absorbing the present mechanical lift. The anchorage did not have the ability to measure the resulting lift. The third attempt had no such anchorage. It was believed an anchorage was unnecessary due to a new refraction method. This new method was expected to not need excessive weight on bit. However, the third attempt was unsuccessful. An excel spreadsheet program have been modeled to calculate the lift forces. The program is built to be user friendly, where the user can input key parameters to simulate lift forces at different scenarios. An estimate of the present lift forces at a given scenarios can thus be calculated. The largest lift contributors to the system are the stagnation force and the frictional force in the return hose. Frictional forces can be reduced by increased return hose diameter, or lower flow rate. The stagnation force decreases with increased nozzle angle, and increases with decreased nozzle outlet area. Lift will occur in the range of 6 to 80 tons depending on the scenario. A slight change in parameters can increase the lift by 10 to 30 tons. This program gives a good estimate of the lift forces, and design of the system should be based on a preliminary analysis.