Role of petrographic analysis in wireline log interpretations
- Litton/Core Lab., Dallas, TX (USA)
Wireline logs typically affected by rock characteristics include the spontaneous potential (SP), gamma-ray density, acoustic, and neutron logs. Petrographic studies reveal textural, mineralogic, and porosity data, which are then compared to wireline log signatures. Although the SP log responds to the permeability characteristics of a formation, the SP response may be suppressed by a decrease in grain size, addition of detrital and/or authigenic clays, and introduction of carbonate cements. The gamma-ray log records the natural radioactivity of a formation. This log is commonly used to establish depositional environments and shale volume corrections for density and sonic porosity calculations. Many clay minerals do not contain radioactive elements, whereas many nonclay minerals do contain radioactive elements. Therefore, interpreted clay mineral content based on gamma-ray log responses may be misleading. However, porosity can be calculated from density and acoustic logs by establishing matrix density and traveltime values, respectively. To measure porosity accurately, these values must account for all minerals in the formation. Neutron logs respond to the total amount of hydrogen in a formation, irrespective of the element's distribution. Due to potentially high amounts of irreducible water, neutron logs measure the total porosity of a formation, but at least part of this total porosity will be ineffective porosity in terms of fluid-flow characteristics.
- OSTI ID:
- 5429660
- Report Number(s):
- CONF-8703189--
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (USA), Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Vol. 71:2; ISSN 0149-1423; ISSN AABUD
- Country of Publication:
- United States
- Language:
- English
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