Identifying flow intervals by pore geometry and petrophysics: Middle Trinity aquifer (Lower Cretaceous limestone)
- Univ. of Texas, San Antonio (United States)
A core from the Lower Cretaceous middle Trinity aquifer of southern Kendall County, Texas, was analyzed to compare its petrographic and petrophysical properties to its hydraulic flow characteristics. The analyses helped determine flow intervals in the core. Flow intervals are defined as vertical zones having similar geologic (depositional and diagenetic) history, petrophysical properties, and hydraulic conductivity characteristics. The information gathered from the study of a single core may be integrated with similar data from other cores or well logs to define 'flow units.' Methodology involved visual and image analysis examination of thin sections and epoxy pore casts of samples to evaluate pore geometry (pore size, pore throat size, pore interconnectivity, and pore throat size heterogeneity). Samples were thus grouped into pore-type families. Representative samples from each pore-type family were tested for air and brine permeability, porosity, and mercury injection capillary pressure. Pore throat size distributions obtained from the capillary pressure analyses were compared to the data derived from the pore casts and thin sections. Pore geometry evaluated correlated well with mercury capillary pressure data for the most permeable zone of the core. Geologically, this flow interval consists of a porous, medium-grained peloid grainstone that is characterized by large pores connected by large pore throats. Wherever present, such pore throat to pore body size ratios enhance flow through the rock. Correlation between pore geometry and capillary pressure data deteriorate in packstones with increasing micrite mud content and wackestones with increasing dolomitization. These lower correlations are due to decreasing pore throat size and increasing pore throat size heterogeneity in these rocks.
- OSTI ID:
- 5618178
- Report Number(s):
- CONF-910403-; CODEN: AABUD
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 75:3; Conference: Annual meeting of the American Association of Petroleum Geologists (AAPG), Dallas, TX (United States), 7-10 Apr 1991; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
AQUIFERS
HYDRAULIC CONDUCTIVITY
POROSITY
FLUID FLOW
CALCULATION METHODS
GROUND WATER
CRETACEOUS PERIOD
FLOW MODELS
LIMESTONE
MICROSTRUCTURE
PETROGRAPHY
TEXAS
CARBONATE ROCKS
CRYSTAL STRUCTURE
DEVELOPED COUNTRIES
FEDERAL REGION VI
GEOLOGIC AGES
HYDROGEN COMPOUNDS
MATHEMATICAL MODELS
MESOZOIC ERA
NORTH AMERICA
OXYGEN COMPOUNDS
ROCKS
SEDIMENTARY ROCKS
USA
WATER
580000* - Geosciences