The Effect of Continuous Circulation on Pressure Oscillations Caused by Rig Heaving
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Drilling operations are preformed by several countries. Some countries are forced to drill offshore, whereas others to drill onshore. Offshore drilling operations are more challenging comparing to onshore operations. The sea waves disturbs the rig/drill ship continuously. Floaters such as drill ships and floating rigs are more affected by the waves than fixed construction. The result of the sea waves are horizontal and vertical movements of the floaters. However, the horizontal movements are eliminated with advanced positioning systems. Whilst the vertical movements are avoided with use of heave-compensators. Extension of the drill string is needed during drilling operations. The extension stage is called connections . During connections, the mud pump and the heave-compensators are disabled. Which causes the floaters to oscillate vertically due to the sea waves. Such vertical movements of the floaters causes the drill string to move vertically inside the well. Vertical movements of the drill string are unwanted, as they create pressure changes in the wellbore. Pressure alterations may cause huge damages to the well and the drill string. However, several control techniques have been developed in order to obtain constant pressure throughout a connection. Common for this techniques are the consideration of a deactivated mud pump and no mud circulations, as in reality. It is therefore interesting to activate the mud pump and investigate the effect of continuous circulation during connections. Furthermore, the possibility to control the circulation to attain constant pressure. This thesis presents simulations and results that indicates damped pressure oscillations during connections, using controlled circulation.