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Evaluation of Down Hole Seal Plugs Used in Drilling & Well Operations
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As the demand for hydrocarbons increases, the oil companies are forced to start oil and gas exploration in complicated and remote fields. When drilling such environment, the requirement for safety, reliability and operational efficiency of down hole tools is vital. An evaluation of different drill pipe convoyed seal plugs is performed with respect to plug features, benefits,operational procedure and limitations. A comparison based on the different plug design and a review of applications for such plugs is made. Design requirements stated in ISO 14310:Petroleum and Natural Gas Industries, Downhole Equipment, Packers and Bridge Plugs, is presented and related challenges and technology gaps discussed. An investigation of plug failure and reason for failure between January 2009 and March 2010 is carried out. Normally, down hole seal plugs uses an elastomeric sealing element to provide the seal against the casing wall. The plugs are rated to different temperatures and pressures due to the variation in the design of the elastomeric sealing element. When operating with elastomers, proper material selection is important to construct a wide performance envelop of the seal,making the seal more flexible with respect to working area. A possible new technology for down hole sealing application is metal-to-metal sealing. Metal-to-metal sealing shows superior seal reliability compared conventional a resilient elastomer seal with respect to pressure and temperature rating. This technology may become the new solution to provide a seal with ahigh integrity level in extreme well environments. This technology is new, and does not meet the requirements stated in ISO 14310. V0 qualication is required for casing plugs acting as a secondary well barrier used by Statoil. The survey of application utilizing drill pipe convoyed seal plugs shows the most common application for casing suspensions plugs is to act as a secondary well barrier and to provide a gas tight seal for temporary abandonment of the wellbore when pulling the blow out preventer and the marine drilling riser. The present plugs used by Statoil shows good reliability and are efficient in use. However,limitations are seen when operating in extreme wells with difficult well trajectories. An improvement in design on plugs to be used in such wells is to make the plug able to be set and retrieved without rotation, making control of the applied forces on the plug more easily. The investigation of plug failure shows a decrease in failure trend after the implementation of ISO 14310 in 2005. In the time period investigated, a total of 350 plug runs where performed with a recorded failure rate of 9 %. The main reason of failure in this period is pressure test failure of the plug, making up 57 % of the reason of failure. Before the ISO 14310 become operative the main area of failure was when latching on the running/retrieving tool to the plug.