Recent investigations of the successful Cretaceous-Jurassic trend from northwest Florida into northeast Texas have identified certain high-pressure formations. These abnormal pressures have also been observed during actual drilling operations.

The authors, members of the Oilfield Products Division of Dresser Industries, Products Division of Dresser Industries, Inc., have studied these pressure zones in Mississippi and have developed a method of predicting them by interpreting lithologic predicting them by interpreting lithologic values from conductivity and interval transit time logs. The procedure and the interpretation and correction of terms are described in the paper.

Once a proper interpretation is established and plotted, formation pore pressures can be determined by formula or direct overlay. From these values, formation fracture gradients are obtained.

The relationship of formation pressure, fracture gradient and annular friction loss can be a valuable tool in setting up an economical, accurate and safe casing program for a well. Accurate interpretation of these values can also be the basis for well-control before, during and after drilling operations.


The purpose of this article is to show how the relationship of shale lithologic properties indicated by logs can be properties indicated by logs can be correlated to indicate pressure within the earth's formations. Fig. 1 shows the limits of the area investigated by the authors, the Cretaceous-Jurassic trend extending from northwest Florida across Mississippi and Louisiana and into northeast Texas. Wells to 22,000 ft have been evaluated to date. At present, the accuracy limits when using resistivity or interval transit time methods appear to be plus or minus 1/2 lb/gal mud-weight equivalent. The method employed has been to plot the shale lithologic properties on semi-log graph paper, then to use either an overlay or an empirical graph solution to derive formation pressure.

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