Electrical Logging Systems and Results of Unconsolidated Marine Sediments
Authors: Bouma Arnold H. , Ferebee Thomas W. , Chmelik Frank B. , Huebner George H. 
Published: October 2008

The application of electrical logging technology to the study of unconsolidated marine sediments is still in its early stages. Progress in instrumentation development and the results from sea trials indicate the potential for marine logging techniques. Existing electrical logging analytical techniques cannot be extrapolated readily to produce reliable parametric values in unconsolidated marine sediments.

Electrical resistance and spontaneous potential measurements made on extruded cores appear to be relatable directly to various geological and geotechnical parameters. These core scanner data also have been checked by absolute resistivity measurements made on small cylindrical samples taken from the same cores.

Horizontal correlation of sediment strata over long distances can be conducted rapidly with an in situ electrical logging probe. For-Calibration purposes, measurements should be done on cores via the core scanner. Although a certain comparison with the high resolution seismic profiles exists, the base for the logging parameters differs and is more refined than the acoustical impedance characteristics.

The towed array records parametric variations often mastered in complimentary high resolution acoustical subbottom profiling. The measurements are independent of vertical density changes. Additionally, the towed array can be used in water normally too shallow for other techniques. The ability of the towed array to "see" the bottom of oyster reefs makes it possible to estimate the volume of such reefs. Soft, gas-containing, shallow water muds off the Mississippi Delta reveal variations undetectable by seismic means. A survey of Heald Bank showed both major and minor variations in lithology that were in direct agreement with extensive core analyses previously done from that area.

INTRODUCTION

Within the geological section of the Department of Oceanography of Texas A&M University, emphasis has been placed on the use of electrical resistance(resistivity) and S.P. (spontaneous potential) measurements in unconsolidated marine sediments. Both parameters are measured by electrical scans of extruded cores with an in situ probe and by a towed array that is towed over the bottom behind a vessel.

The top few tens of feet of the sea bottom, especially of the continental shelf have been very important to the offshore industry. Offshore structure anchoring, pipelines, and cables depend heavily on the properties of these upper sediments, while incorporation of waste material on the marine mining of minerals primarily deal with the upper parts of the deposits.

The large marine industries concerned with cables, offshore installations, dredging or pollution, all require accurate and detailed information on the properties, structures and distribution of the upper sediments. No one technique can provide answers to all these questions and thus a combination type of approach is required. The high costs of marine work warrant continuous research to develop additional systems that either replace existing techniques or are complimentary to these techniques. The aim is always directed to better and more information and at the same time a reduction in costs. Time-reducing systems, such as the "Hi-Resolve System" therefore should receive proper attention (Chmelik et al., 1972; Huebner et al., 1973).