Abnormal formation pressures and their detection by pulsed neutron capture logs

Abstract

The present paper highlights the importance of abnormal formation pressure environments in oilfield operations. The detection and quantitative evaluation of overpressured formations is critical to exploration, drilling, and production operations involving hydrocarbon resources. As a result, an interdisciplinary technical team approach is required to optimize the safety, engineering, and financial aspects of operating in such hostile subsurface environments. Pulsed neutron capture (PNC) logging devices can be used for detection and quantitative evaluation of overpressure environments through the drillpipe and to monitor pressure depletion behind casing. Field observations clearly indicate that the Σ-values in shale formations decrease in a regular fashion with depth in normally compacted clastic sequences. Abnormal formation pressures are, however, flagged by divergence from this normal Σ-trend. Several field examples are presented to illustrate applications of PNC logging devices.