Other than drill rate and directional information; Gamma Ray is often the only MWD/LWD data gathered during the drilling of a horizontal well that can be used as an indicator of geology. While the tool and the telemetry system are simple; there are many parts that must work together in order for the geologist to have usable data to properly land and steer a well. While the Gamma Ray tool is simple in design; it's value is often misunderstood or overestimated by those that use it. Elementary techniques of log/data evaluation are often overlooked because of trust in technology. Understanding the technology, breaking down the parts of the system and a review of available data can often help identify problem data or noise gathered during the drilling of a horizontal well. Simply remembering that the data must fit within the bounds of the offset data character and range is paramount to successful interpretation of the GR data. This step is often overlooked because of the expense of gathering the data; and thereby the high intrinsic value placed upon it. Spurious GR values have convinced even the most experienced geologist and mudloggers to misinterpreted drill samples. Proper interpretation of GR data can reduce costly and unnecessary adjustments to the directional path of a well. Understanding the operation of the telemetry system and the limits of the data can reduce the overall well cost by reducing trips to replace working tools or sidetracks to stay in zone.
AAPG Datapages/Search and Discovery Article #90193 © 2014 Rocky Mountain Section AAPG Annual Meeting, Denver, Colorado, July 20-22, 2014