System for Control of Downhole Pressure During Drill Pipe Connection - A Potential Method for Compensating of Pressure Variation in a Borehole
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The oil industry is currently experiencing a very rough period where the need for constant new inventions, technologies, and an increase in earning and profit is greater than ever. In addition to exploring increasingly more difficult and less accessible fields, there is a big focus on exploiting already discovered fields in a better way. By implementing Managed Pressure Drilling (MPD) technologies in a brand new way, valuable operational rig time increases while non-productive time reduces. Drilling operations are often performed on floating drilling rigs, meaning that the rigs will move according to waves and weather. During drilling operations, these movements are neutralized with heave-compensating systems in the derrick. However, when connecting new stands, the drill string is placed in slips on the drill floor, resulting in the drill string moving with the waves and the rig. Small clearances between the borehole and the drill string causes the drill string to act as a piston pump causing high pressure variations in the bottom hole pressures despite a relatively low wave amplitude. For a heave height of only 1½ m, the induced pressure may be approximately 18 bars. HeaveLock is an autonomous valve located in the drill string close to the drill bit, and its design is limiting the volume flow and fluid pressure in an efficient way. This thesis has mainly focused on new potential HeaveLock designs. A new design has been modeled, and simple simulations in a simulation program has been performed. This thesis has also evaluated the different valve designs based on the categories construction costs, complexity, maintainability, user-friendly assembling, force calculations, integrity requirements, as well as wear. The evaluation resulted in a valve design recommendation, i.e. a balanced electric valve. Research for mechanical HeaveLock components have also been conducted, but the thesis concludes that precisely which product to be used needs further investigationFurther work related to HeaveLock is to perform detailed fluid simulations with actual drilling parameters, determining components and control system, as well as constructing the physical valve. Ultimately, a full-scale testing of the valve is in place.