Thru Tubing Capillary Dead String System, Decreased Critical Velocity System (DCV)
Mark Embrey
BJ Services
Abstract
Gas wells often begin their liquid loading in the casing. A partial solution to this problem has been to install a dead string through the perforated interval. The dead string reduces the flow area through the casing which in turn increases gas velocity allowing liquids to be lifted into the production tubing. In some wells a dead string may be all that is required to unload a well. However, many wells may require extra assistance to lift their liquids.
Wells with dead strings have not been candidates for through tubing capillary installations due the plug that resides in the dead string below the perforated sub. The only method of injecting chemical down hole was a capillary banded to the outside of the production tubing. This method can present problems. A workover rig is required to pull the production tubing should the capillary become plugged or damaged.
A new simple solution allows for a through tubing capillary installation, with the injection point being below the plug, in wells with dead strings. A plug, that is designed to seal off in a mechanical seat nipple, is attached to the capillary. The plug is then lowered in the hole with capillary hung above and below and landed in the seat nipple. This plug seals off the dead string while still allowing continuous chemical injection to the bottom of the well. The completion consists of (from bottom to top): dead string, seating nipple, perforated sub, and production tubing.
This system has been installed in a liquid loading gas well in East Texas. The well had previously been in an intermittent, slug flow state. After the dead string and capillary installation, the well is now effectively carrying it’s liquids to surface in steady state flow. Ten more installations are planned by the end of the year. These case studies will be discussed in the presentation.