Deep porosity preservation in the Norphlet Formation, Mobil Bay, Alabama

Conference · Fri Mar 01 00:00:00 EST 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:5788118

Ajdukiewicz, J M; Paxton, S T; Szabvo, J O ^[1]

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1. Exxon Production Research Co., Houston, TX (United States)

Compaction and pressure solution have commonly been assumed to destroy primary intergranular porosity in deeply buried sandstones. However, primary porosities of up to 20% are preserved at depths greater than 20,000 feet in the Norphlet Formation of Mobile Bay. Previous workers have called upon a number of mechanisms to preserve these high porosities in the Norphlet, specifically chlorite rim cements, gas emplacement, overpressuring, and decementation. In contrast, our study of data from 23 Norphlet wells, including 450 thin sections, indicates that these suggested mechanisms are not the primary cause of porosity preservation in the Norphlet. The authors propose an alternative interpretation: that in the Norphlet, as in other well-sorted, ductile-grain-poor sandstones, porosity loss from compaction did not go to completion under reservoir (premetamorphic) conditions, but stabilized at depths of about 5,000-8,000 feet and porosity values of about 26%. Porosity loss below these values is due to cementation. For cementation to occur, both an adequate source of cement and geochemical conditions favoring cement precipitation must be present. Computer simulations of Norphlet burial history, including post-depositional fluid-flow patterns, suggest that conditions favorable to quartz cementation never occurred in the bulk of the Norphlet because of the formation's stratigraphic position and isolation from a basinward source of silica-saturated fluids.

• OSTI ID: 5788118
• 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

Related Subjects

02 PETROLEUM
03 NATURAL GAS
ALABAMA
NATURAL GAS DEPOSITS
PETROLEUM DEPOSITS
RESERVOIR ROCK
GEOLOGIC HISTORY
POROSITY
CEMENTS
COMPUTERIZED SIMULATION
DIAGENESIS
GEOLOGIC FORMATIONS
GEOLOGIC MODELS
SANDSTONES
BUILDING MATERIALS
DEVELOPED COUNTRIES
GEOLOGIC DEPOSITS
MATERIALS
MINERAL RESOURCES
NORTH AMERICA
RESOURCES
ROCKS
SEDIMENTARY ROCKS
SIMULATION
USA
020200* - Petroleum- Reserves
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& Exploration
030200 - Natural Gas- Reserves
Geology
& Exploration