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ABSTRACT: Crossplots of Nuclear Logging Relationships Aid in Estimating Sizes and Shapes of Sands in Order to Improve Maps

ALLEN, ROB L. , Halliburton Energy Services

Much more detailed maps of clastic formations can be made by extracting large quantities of additional depositional information from commonly available well logs. Advances in quantitative analysis of log patterns can provide improved estimates of horizontal shapes of sandstone reservoirs and other sediments. Combinations of properties extracted from gamma ray, neutron, and density type logs have been used to make horizontal lithofacies patterns on cross-plots. Characteristics of plot patterns are related to specific shapes of sedimentary units such as channels, lacustrine sediments, marshes, beaches, and bars.

Changes in radioactivity tool responses often relate to depositional mechanisms and changes in water movements that deposited sediments. Instead of using conventional interpolation techniques, sedimentation patterns caused by waves and currents were more effectively modeled with wave and current laws. Lithology log calculated relative grain size distributions and depositional energies have been combined with log patterns analysis to make cross-plots. These partial derivative plots display distinctly different clusters, curved filaments, or long and relatively straight groups of points. Patterns on plots have closely resembled surface and deeply buried clastic geologic systems. Indications of the extents and distributions of sediments have significantly improved reservoir maps. Plots have been used to model reservoirs on several continents. However, land and offshore Gulf of Mexico examples will be provided for this conference.


AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas