A new wireline coring device has recently become available. It saws a 60 inch long triangular sample of the formation with a pair of cutters which move along the borehole wall parallel to the axis of the tool. The formation sample retrieved is undisturbed by the cutting operation and retains the mud cake in place on the surface adjacent the borehole. Cores may be taken in boreholes of 7-7/8 inch diameter or larger. This device makes it possible to retrieve continuous cores in selected zones for quantitative determination of rock properties and for qualitative examination of strata characteristics such as dip and fracturing. Correlation and comparison of these triangular cores with logging measurements provides a new means for studying the effects of mud cake and invasion. Results of field tests are discussed and the characteristics of retrieved rock samples and mud cakes are described.

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