Theory and Implementation of a Borehole Caliper Measurement Made While Drilling

Like comparable wireline measurements, measurement-while-drilling (MWD) formation-evaluation tools are dependent on the borehole condition. Because of this dependency, the borehole size must be known for appropriate borehole corrections to be made to porosity measurements. This paper describes caliper measurements that can compute the effective diameter of a uniform of nonuniform borehole with nonmechanical means. The basis for the caliper measurement is a gamma/gama density sensor that uses asymmetric detector placement to define the borehole size. The derivation of the caliper is presented with field log comparisons