Evaluation of Pumping Methods for Startup of Non-flowing Wells

Abstract

The high cost of starting a non-flowing well is the background for this project. This is a concern, mainly for offshore and subsea completed wells. Typically, coiled tubing (CT) is run into the production tubing to a depth approximately 1000 m below the wellhead. Nitrogen gas is then injected through the CT to dilute the wellfluid and reduce the hydrostatic pressure in order to bring the well on stream. This is a high cost operation due to the large intervention unit needed and the time required. In addition, HMS is a concern with gas lift operations due to the high pressure nitrogen gas used.This thesis has proposed a design based on using a wireline (WL) powered pump as an alternative to CT. The pump was designed using computer-aided design (CAD). Finite element method (FEM) analyzes of critical parts was performed to verify the structural integrity. The design is based on a using slightly modified conventional surface WL winch system In addition, known principle of downhole completion and pump components were used. The pump concept created may also be deployed using a riserless light well intervention (RLWI) vessel. The design proposed can be used for 7 inch and 5 ½ inch tubing. The length of the pump is 16 meters and fits with standard lubricator lengths of 20 meters. The design is based on the sucker rod pump principle.To further study the potential of the pump, dynamic simulations were performed. The intention was to simulate the pump cycle to analyze the performance of the system. Results from the simulations verified that the WL operated pump has an economical potential compared to CT. The time consumption to bring the well back on stream was 158 minutes for a 7 inch tubing and 92 minutes for a 5 ½ inch tubing. Compared with CT, the potential savings for a subsea completed well could be in the order of 2,5 MUSD.The overall conclusion is that a WL powered pump system can be used for startup of non-flowing wells.Further work will be needed for automation of the WL winch system. This is important for optimizing and better control of the pump system.