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Probability of encountering coalbed discontinuities during vertical and horizontal borehole drilling
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    "Probabilities of encountering coalbed discontinuities during vertical or horizontal drilling in a specific coalbed can be estimated based on analysis of mined-out areas of the coalbed where the size, shape, orientation, and distribution of discontinuities are known. The resultant probability estimates can be applied to cost-risk evaluations of drilling programs proposed for exploratory, developmental, or methane drainage purposes in undeveloped areas of that coalbed. Data compiled from mine maive hypothetical drilling programs--one for drilling vertical boreholes. Analysis based on a mined-out area of the Beckley coalbed indicated that vertical methane drainage boreholes spaced 1,000 feet apart in a square grid pattern would each have a 29-percent probability of encountering a discontinuity in a geologically unexplored area of the coalbed. It was also determined that exploratory vertical drilling could locate most of the discontinuities if a borehole spacing of 2,500 feet were used. For horizontal drainage boreholes in the Beckley coalbed, the analysis indicated a linear relationship between hole length and the probability of encountering a discontinuity." - NIOSHTIC-2

    NIOSHTIC no. 10002361

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