フリージングによりアイソレーションした坑井における改修作業の紹介

抄録

At a Steam Assisted Gravity Drainage （SAGD） project on Japan Canada Oil Sands Limited （JACOS）, CANADA, steam leakage from a wellhead of a steam injector was discovered. The steam injection was ceased to eliminate the effects on the environment. Some damages on the wellhead were suspected as the cause of the leakage. In order to inspect an inside of the wellhead due to steam leakage, a “Freeze Application （Ice Plug）” without killing the steam injector was safely applied to remove the wellhead. The integrity of the ice plugs was confirmed by pressure tests, and then steam leakage points at the wellhead were safely remedied with minimal fluid loss to the formation. A typical “Freeze Application” process is shown as below. 1） An area is displaced with a “plug” of uncontaminated bentonite gel mixed to thick slurry. 2） The gel plug is frozen in place by use of dry ice （solid form of carbon dioxide） contained in a cribbing and tamped manually to keep in contact with the area to be frozen at all the times. 3） Pressure testing is always conducted to one and a half times the surface pressure of the well, or to the maximum wellhead pressure rating. In this paper, it consists of background of the steam leakage from the objective steam injector, investigation of remedial action, and then selection and introduction of “Freeze Application”.