ABSTRACT

Wireline log interpretation and analysis techniques were developed by the petroleum industry to identify and quantify pore fluids in petroleum reservoirs, to characterize the properties of reservoirs, to identify lithology, and to facilitate geologic interpretation. In subsurface environmental investigations the information required is almost identical. Such investigations must identify and quantify pore fluids in contaminated media, quantify contaminant concentrations in ground water, determine the hydrologic properties of aquifers, and characterize subsurface geology. Given the great similarity of information required, classical petroleum log interpretation and analysis principles should have direct and useful application to environmental questions. However, attempts to apply these principles have often produced disappointing results that can many times be attributed to differences in the physical environments, primarily hole and formation conditions, in which logging data are acquired by the two disciplines.

Classical wireline logging theory is based on central assumptions regarding the physical environment in which tools are operated. Environmental logging may occur both above and below the water table, in formations that contain air and/or fresh water, in holes that may be filled with air, water, or mud, and where the salinity of the formation and borehole fluids may be similar. In these cases those central assumptions are commonly not valid.

Geologists and log analysts must be aware of these differences and how they affect the various types of wireline logs. Some of these problems may be resolved by further research, rethinking of existing theory, and the development of new analytical techniques.