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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 68 (1984)

Issue: 4. (April)

First Page: 482

Last Page: 482

Title: Deposition, Diagenesis, and Porosity Relationships in the Glorieta Formation, Keystone (Holt) Field, Winkler County, Texas: ABSTRACT

Author(s): Richard C. Haack, A. D. Jacka


Production of hydrocarbons from the Chevron 7C H. E. Lovett well, Keystone (Holt) field, is from the upper part of the Glorieta formation (Leonardian). The field is located near the western margin of the Central Basin platform (Permian basin) on a present-day structural high.

The 116-ft (35.4-m) core contains at least 7 cycles of deposition, which consist, upward from the base, of progradational subtidal, intertidal and supratidal deposits. Supratidal deposits predominantly consist of dolostones with fenestral cavities; sabkha deposits are not represented. Scattered nodules of nonevaporitic anhydrite have been emplaced within subtidally deposited carbonates after dolomitization. Intrabiopelgrapestone grainstones, oointrabiopelgrainstones, intrabiopelpackstones and wackestones, and intrapelpackstones and wackestones are the predominant lithofacies. Dolostone is the predominant lithology.

The cored interval was exposed subaerially several times, and episodes of freshwater diagenesis were interspersed with influxes of dolomitizing and anhydritizing fluids. Most dolostone intervals record the following five stages of diagenesis: (1) early dolomitization; (2) emplacement of nonevaporite anhydrite as cement, replacement or a combination of both; (3) dissolution of anhydrite; (4) precipitation of dolomite cement; and (5) emplacement of second generation anhydrite as cement and replacement. Some intervals contain additional stages of diagenesis including precipitation of the clay mineral dickite and calcite as cements.

The core contains many highly porous dolostone intervals, and 9 distinct pore types are preserved. These include primary intergranular, fenestral, and intrabiotic voids; secondary intercrystalline pores; hollow micrite envelopes; biomolds, oomolds and fractures; and tertiary anhydrite molds. The most abundantly represented pores are secondary intercrystalline and tertiary anhydrite molds.

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