Lock Down Verification System for Tubing Hanger

This master thesis is a product development project, carried out in cooperation with Aker Subsea, which is a part of Aker Solutions. The goal of the master thesis was to develop concepts for a new verification system, which can confirm landing and locking during installation of Tubing Hanger. Tubing Hanger (TH) is installed and locked into Xmas Tree`s spool body, after the Xmas Tree (XT) is landed and locked onto the wellhead. Production stream from well flows through the TH. Thus it is of high importance that TH is properly locked before production of oil or gas is started, in order to prevent the possibility of leakage to the environment. Today`s verification methods do not provide any information about TH`s position relative to the XT, before it is locked. Therefore a new verification system needs to be developed, which can verify that: 1) TH has landed in the right position. 2) TH is sufficiently locked to the XT spool. In order to come up with new verification methods I started off with an extensive analysis phase. I did a general study of subsea production systems (appendix A). In addition a more detailed study was carried out to get to know lock down sequence related to TH installation, and today`s verification methods (chapter 4). As part of the analysis phase reported incidents were studied (appendix B) and a hazard identification study was carried out (appendix C). Before starting to develop the actual verification concepts, I carried out a technology analysis (appendix D). For the concept development work I chose to only focus on landing and locking of TH, and have not taken into account what kind of verification is needed for retrieval of TH. Retrieval of TH is needed for product maintenance, and when production system is disassembled. In order to come up with as many verification concepts as possible, I started off with a creative concept phase, where “everything is possible“. Further on positive and negative concept characteristics were evaluated in order to narrow down number of relevant concepts. The final concept selection process was an expert test carried out by employees at Aker Solutions. The result of the concept development work are two verification concepts. Here is a short description of each solution: • A proximity switch with two sensors is positioned in XT spool, and two target magnets with opposite poles (north/south) are positioned in TH`s activation sleeve. When TH lands in right position the north poled magnet will activate one of the sensors, and when TH is locked properly to the spool, the south poled magnet will activate the other sensor. Verification signal is sent through a wireless communication system to a ROV (Remotely Operated Vehicle) and then up to rig and operator. • One proximity switch is positioned in XT spool to verify correct landing of TH, and another switch is positioned in Tubing Hanger Running Tool (THRT) to verify lock down. Land verification switch uses wireless communication and lock verification switch is connected to topside with an electric wire. Either of these two concepts can be supplemented with additional verification methods in order to increase system safety. I have managed to reach the goals that were set up for the project. I also learned a great amount about subsea engineering and got many new experiences. It has been an exciting project, and it has been very giving to have the opportunity to work with a project with focus on improving safety of the oil and gas production system. Lock down verification system for TH is a crucial part of the subsea system that can prevent damage of product components, project delays, huge extra costs and leakage to the environment.