HeaveLock - A New System For Reduced Surge And Swab Pressure For Floating Drilling Operations
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Managed pressure drilling is only carried out from fixed installation in harsh environments today. Rig heave is compensated with top drive compensation system under drilling or tripping of pipe. During connections the string is hung off in the rotary and moves up and down in the well as the rig heaves. Thereby is the formation exposed to uncontrollable surge and swab pressures for the duration of the connection. These pressure fluctuations are one of the main showstoppers for MPD on floaters. HeaveLock is a downhole BHA valve that compensates pipe movement induced surge and swab pressures during connection time through the adjustment of ECD by variable flow at bit. Pipe velocity and required choke opening are measured and controlled by a downwhole computing system. Energy and fluid volume are stored in the string as compressed fluid prior to HeaveLock activation to enable full compensation capacity when the string is detached from the top drive. An analysis of surface equipment and the operational constraints is based on the developed Excel spreadsheet, which has been developed in course of this Thesis. The spreadsheet uses a simplified surge and swab model to simulate downhole pressure induced by pumping and pipe movement. In this thesis the string is assumed to be rigid, and move in phase with the drilling rig to simplify the surge and swab calculations.First simulations with the simplified model indicated flow between 200 and 2280 lpm to reduce the pressure fluctuation from 20 to 5 bar. A more advanced ECD simulation program was included into the model and required flow reduced to a range of 550 1620 lpm. 40 m3 of common drilling fluids allow a compression of 800 1200 liter with 490 bar applied pressure, which is sufficient to store fluid for increasing flow at bit temporarily over the pumping rate. Further limitations and program outputs are presented and discussed. A recommended operational procedure is given to illustrate the working principle of HeaveLock. For more accurate flow range estimation however, a more dynamic surge and swab model is recommended.