In the strata of the Oligocene clay basins of Devonshire, wireline increases penetration rate by a factor of at least 3. It eases the casing problem and, in conjunction with mud flush, often obviates casing. Efficient bit design improves core recovery and cuts down costs. The wireline system, efficient bit design and mud flush have reduced costs on all cored footage, including the cost of grouting and the restoration of the disturbance to agricultural land, to £4·72 per metre, or £1·55 per foot.

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