Drilling-mud logging through the years has primarily been a tool of the explorationist for formation evaluation. However, continuous well-site analysis of the mud and cutting returns has also become an important tool in drilling control.
The amount of the gas content in the mud system while drilling shales can be indicative of abnormal formation pressures. However, experience indicates that depending on the geological environment and the drilling technique applied such mud logging methods may or may not be directly related to downhole, in-situ pressure profiles.
Modern drilling technology is based on three main concepts, namely: well planning, well control, and optimization of drilling operations.
Often there is only a fine line between minimum over-balance of the drilling mud and the possibility of a well kick. This in turn makes well control a must, and the ability to immediately recognize and evaluate abnormal, downhole pressure conditions is critical. Many pressure detection methods are available or have been proposed and numerous technical papers have been written on the subject.
The best approach for identification and evaluation still is the study of a combination of several surface measured parameters verified by the interpretation of open hole logging data.
The amount of the gas content in the mud system while drilling shales can be indicative of abnormal formation pressures. However, since the gas cut can be a function of the geological environment penetrated, the drilling technique applied, and the downhole penetrated, the drilling technique applied, and the downhole thermodynamic conditions prevailing, this gas parameter may not have any direct relation to in-situ pressure profiles.