Computer-assisted interpretation of geophysical well logs in a coal-depositional environment, Illinois Basin, Kentucky. Geological survey bulletin 1509

Journal Article · Tue Jan 01 04:00:00 EST 1980 · Geol. Surv. Bull. (U.S.); (United States)

OSTI ID:6565706

Daniels, J J; Scott, J H

Physical properties detected by well-logging probes include density, porosity, water content, resistivity, electrical polarizability, and natural gamma-ray radiation. Well-logging probes respond primarily to physical properties of the rock surrounding the drill hole, but are also affected by the properties of the fluid in the hole and by irregularities of the hole surface. A particular lithology may be characterized by physical properties that are measured by one type of geophysical well-logging device and not by another. Therefore, the geologic section near a borehole must be interpreted by using more than one type of well log to selectively determine individual lithologies. Interpretations of lithologies from borehole geophysical measurements are based on the fact that different rock types exhibit characteristic physical properties that can be measured by the probes. Interpretation of lithologies in a shallow sedimentary coal environment can be facilitated by using products and ratios of well logs. Coal is characterized by a low density, a low natural gamma-ray responses of black shale are slightly higher than those of coal. Limestone conglomerate and sandstone both have high resistivity and neutron response is higher for limestone conglomerate than for sandstone. The approximate amount of shale in shaly sandstone can be determined by the product of the resistivity and neutron well logs. In shale that contains only clay, the induced polarization well log can be used to distinguish the clays with a high cation-exchange capacity from those with a low cation-exchange capacity. After the geologic section has been interpreted using product and ratio well logs, the stratigraphic features in an area can be determined by comparing composite interpretations from drill hole to drill hole.

• OSTI ID: 6565706
• Journal Information: Geol. Surv. Bull. (U.S.); (United States), Journal Name: Geol. Surv. Bull. (U.S.); (United States); ISSN XDIGA
• Country of Publication: United States
• Language: English

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