Field Examples of Ultrasonically Enhanced Density, Neutron-Porosity, and Caliper Logs Obtained While Drilling

Abstract

Summary Density, photoelectric factor (Pe), and neutron-porosity measurements made while drilling are extremely sensitive to the distance between the sensors and the borehole wall (standoff). To minimize these effects, an ultrasonic transducer is positioned collinearly with the nuclear sensors. Rapid pulsing of the transducer provides frequent measurements of the standoff. These measurements are used to average the nuclear data in a manner that emphasizes the smallest standoff data. This greatly improves the quality of the density, Pe, and neutron-porosity logs. Additionally, the standoff measurements are used to correct the neutron log for residual standoff effects. Measurements from the standoff transducer are also combined with those from two other ultrasonic transducers to obtain a high-resolution caliper log. Besides providing useful borehole information, the caliper readings are used to correct the nuclear measurements for hole-size effects. This new technology is illustrated with log examples from a variety of wells. One of the examples illustrates the effectiveness of an enhanced-vertical-resolution processing technique in identifying thin beds.