Outlining of shale masses by geophysical methods

Shale masses are defined as large bodies of shale several hundred feet in thickness, formed either by diapirism or by deposition. Compared to the normal section, shale masses exhibit low velocities, low resistivities, and high fluid pressures, all of which seem to be due to the high porosity and low permeability. These physical properties allow the outlining of a shale mass by one or more of the following ways: gravity surveys, to outline the low-density material; reflection surveys, to outline the lack of reflection contrast and in some cases map velocity configuration; refraction surveys, to indicate the velocity of the anomalous mass and thus differentiate between shale and salt.