Patent attributes
Aspects of this invention include a downhole tool and method for making a physical caliper measurement of a subterranean borehole. The tool is configured to make the physical borehole caliper measurement only when the measured pressure in each of three or more outwardly extendable blades is greater than a predetermined threshold pressure. Blade positions are measured and the borehole caliper calculated only when the pressure in each of the blades exceeds the threshold. Exemplary embodiments of the invention enable physical caliper measurements to be made with increased accuracy with each of the blades making firm contact with the borehole wall. Methods in accordance with the invention are especially well suited for use in directional drilling applications in that they tend to enable accurate caliper measurements to be made without repositioning the steering tool in the borehole.