A new LWD sensor is introduced for measuring a high-resolution borehole image in large boreholes and both in light and heavy oil base mud. The new sensor uses advanced radar technology, and in addition to caliper (time-of-flight) image, delivers an electrical image to help geoscientists visualize and understand the stratigraphy and fractures.

A pulse radar operating in the multi-gigahertz range is implemented within the bottom hole assembly. As the BHA rotates, the radar measurements scan the borehole surface. The time of flight is converted to a distance to the borehole wall. The amplitude of the reflected signal correlates with the micro-resistivity/permittivity of the formation in the immediate vicinity of the borehole.

Up until recently, sensors capable of performing these caliper measurements while drilling have been limited to smaller size boreholes and lighter muds. A new technology, based on a downhole radar rotating with the bottom hole assembly extends the application to boreholes of 18 inches and more in oil base mud. The same technology yields a micro-resistivity/permittivity image that is prized by the geoscientists for recognizing key geological features, including layered formations, fractures, faults, and unconformities. Here again the new technology is the first to our knowledge to obtain such information while drilling in large holes and light and heavy oil base mud.

A new technology, namely the downhole pulsed GHz radar brings a new solution to well-known problems. High resolution calipers and micro-resistivity images while drilling have been made available to the industry in recent years, however they are restricted to smaller than 12 ¼" boreholes and water base mud. The article below explains how and how well the new technology has significantly increased the range of applicability to oil base mud for large hole sizes, like 12 ¼" and 17-1/2".

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