The 95/8-in. reamer shoe has PDC cutters on the gauge to help clear debris and cavings from the well and a drillable aluminum nose (Fig. 1).A REAMER SHOE WITH POLYCRYSTALLINE DIamond compact (PDC) cutters on the outer body helped run a 95/8-in. casing string through unstable formations.
BP Exploration had encountered difficulty in running casing through the unstable Haisborough formation in the West Sole area of the North Sea. The Haisborough group contains unstable shales that are fractured due to upward movement of an underlying salt dome.
These shales cave in as the well is drilled, leading to overgauge hole, packing off, and ledging in interbedded salt, mudstone, dolomite, and anhydrite sections.
On the recent Hoton well, attempts to cure the hole caving by adding gilsonite (a variety of natural asphalt) to the mud were unsuccessful.
Trips in and out of the hole to 2,500 m can take more than 24 hr. Thus, it is critical to solve hole problems to ensure the casing can be run in one trip. A 95/8-in. reamer shoe was picked up to help run the casing to bottom.
The reamer shoe, developed by Brit Bit Ltd. and Enterprise Oil plc, is a stabilized casing shoe with PDC cutters built onto the outer body (Fig. 1). The nose is eccentric to give a mule shoe profile so that it can be rotated off ledges and is made of aluminum so that it can be drilled out with a PDC bit. The reamer shoe has three 2-in., directed-flow ports in the nose.
The reamer shoes are designed to overcome various difficulties encountered in running casing. The exact nature of the problem determines which style of shoe is most appropriate, and similarly the choice of cutting structure depends on the type of obstruction likely to be encountered. The reamer shoes are able to cut formation as well.
In the Hoton well, where the formation was difficult to drill, a shoe fitted with PDC cutters was run because of the shale cavings.
With the reamer shoe attached, it took 61 hr to run the 95/8-in. casing on well 48/7b-12 (14 hr were spent retrieving the mudline hanger to surface and running the backup because the hanger failed). The casing had to be washed all the way down through open hole. Initially, a Lafleur circulating tool was used to wash the casing down. When no additional progress could be made by washing, a water bushing was made up to allow the casing to be rotated at 40 rpm while circulating. The casing was then cemented as programmed.
The reamer shoe was drilled out using a BB1290 PDC bit (9 mm and 13 mm cutters) on a steerable motor. The shoe track was drilled out in 2.5 hr, and there were no problems drilling the shoe.
On the last West Sole well where the 95/8-in. casing was run under similar conditions, it took three attempts to get the casing to bottom using conventional shoe equipment.
Copyright 1997 Oil & Gas Journal. All Rights Reserved.
