Automatic Mud Mixing
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At the time when easily extractable petroleum is explored, the role of automation technologies becomes more and more important since exploration moves into more challenging environment with higher risks and other work standards involved. Narrow drilling margins between pore pressure and fracture pressure, encountered in challenging areas, add requirements to a proper well control, therefore increasing the significance of drilling fluid used. To make the preparation of drilling fluid safer and cheaper with increased work quality, the process should be improved in a way of automation. The current thesis describes the automation of drilling fluid mixing, which is the continuation of the work done during the fall 2010. To get more realistic results the mud circulation model is improved with emphasis on downhole and mud mixing systems. The well is divided into control volumes to imitate the moving of the drilling fluid inside the drillstring and the annulus and to include disturbances such as production of shale cuttings and mud losses to the formation. The possibility of monitoring the downhole pressure is included as well. Mud mixing system is improved by introducing the mud dilution property with the help of water addition, which is controlled by a PID controller. To compensate for changing mud properties during circulation, the control of the density and viscosity at the point, where mud flows out of the well is designed. The performance of the model is tested in simulations, first in open-loop and then in closed-loop. Obtained results show the expected behavior of all variables and the possibility of automatic control. Additionally, necessary improvements are detected to include in the further work.