The initial tests performed in the Downhole Simulation Cell (DSC) on a Pierre Shale core indicated that Gilsonite could plug off the core pore spaces and microfractures and deposit a thin film on the surface which would not allow any filtrate invasion . Tests showed no softening of the shale, no cation exchange, and no erosion of the borehole. A similar core sample was run using the same mud system without the Gilsonite and indicated a 45% washout and filtrate invasion. Using this success, the study was continued looking at the temperature limitations of low and high softening point Gilsonites, and evaluating various surfactants, and additives to permit easy of mixing in fluid systems.
A field trial of this invention, Bore-Plate, was run on an offshore well in the Gulf of Mexico. The field trial was very successful with the well reaching its total depth of 8400 feet with no problems. After surface casing was set at 4500 feet, the mud system was broken over to a lignite/polymer mud containing 2 ppg of the Bore-Plate additive. No mixing or coalescing problems were observed while adding the mixture to the system. Additional concentrations were maintained at a level of 2.5-3.0 ppb. Mud weights ranged from 9.7 to 10.7 ppg. Hole angle averaged 21 degrees. In this directional well, compared to surrounding wells, no excessive torque or drag were experienced.
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