Innovative way of 1.25" CT Clean Out Job Beyond the Norm

Abstract

Debris cleanout in well is a common coiled tubing operations worldwide with the simple objective to clear a flow path in the tubing for either production fluid to surface, injection fluid. This paper documents a distinctive approach to executing a coiled tubing (CT) sand clean out operation without establishing any fluid or gas return to surface, by methodical and calculated procedure of hard penetration into Holdup Depth (HUD). The subject is Well H, which was completed with 2-3/8" 4.6 ppf dual completions tubing and of which production from both strings is flowing with sand. The short string and long string have both been set with the Thru-Tubing Sand Screen (TTSS) at the X-Nipple profile. Tubing Clearance Check (TCC) run conducted by wireline confirmed the HUD. The high sand interval column above the TTSS is deemed as beyond the effective capability of slickline sand bailing. Instead, coiled tubing was proposed to execute the clean out of well until End of Tubing (EOT) with a 1.25" OD coil, allowing for replacement of the TTSS downhole. Initially, coil run in hole (RIH) and tagged the sand HUD. At this depth, bottoms up of Treated Fresh Water (TFW) was pumped into well to circulate the sand particles out of tubing, but no solid return of fluid was observed at surface. Nitrogen gas was introduced into well with TFW to improve lifting efficiency of cleanout fluid. Sand return was not observed at surface with this attempt, but nitrogen return was. Risk assessment was conducted at this point due to the acknowledgement that the absence of solid fluid or sand return at surface runs the risk of coil being stuck downhole under accumulation of sand debris that did not successfully circulate out of well during cleanout operation. Decision was then made to continue clean out based on a precautious regiment of pumping nitrified TFW while hard biting or penetrating HUD at 50 ft interval. Adopting this precautious method to conduct sand cleanout, the job was safely executed and coiled tubing was able to tag onto the TTSS. The well was handed over to wireline to retrieve the TTSS assembly, comprising of XN-lock mandrel and 10 ft Sand Screen. Sand cleanout allows for wireline access to retrieve the old TTSS and install a newer TTSS downhole. The success of this novel approach is the ability to deliver the coiled tubing sand clean out job beyond the normal sand clean out practices, but still within the safe working envelope and without jeopardizing technical safety.