Depositional environments and diagenesis of lower Pennsylvanian Caddo Formation, Stephens County, Texas

Conference · Sun Feb 01 00:00:00 EST 1987 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:5406046

Guzan, M; Humphrey, J ^[1]

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1. Sun Exploration and Production Co., Abilene, TX (USA)

Since its discovery in 1916, the Lower Pennsylvanian Caddo limestone has been one of the most prolific producing intervals in the central Texas region. Favorable reservoir characteristics, with porosities from 9 to 24% and permeabilities from 0.1 to 1,000 md in the pay interval, have enabled many oil companies to initiate successful secondary recovery waterflood projects. Since its discovery, more than 200 million bbl of oil has been recovered from this formation in Stephens County alone. The Caddo reef trend developed during the Early Pennsylvanian, generally along the axis of the Bend flexure. Close examination of whole core and thin sections reveals the formation to be a series of small reef mounds characterized by wackestones. The wackestones consist of green algae, brachiopods, and some rugose corals, which are found on the leeward side (back reef). This sequence is commonly found in the top segment of the Caddo. Deeper into the formation the sequence grades into a packstone/wackestone, characteristic of an oceanward margin (fore reef), and is distinguished by red algae, foraminifera (fusulinids and miliolids), and crinoid hash. The basal sequence is a series of alternating lime mudstones and shales that are heavily silicified. Diagenesis is the key to reservoir rock quality. Moldic porosity was created through dissolution of organisms composed of low magnesium calcite (brachiopods) and aragonite (corals) during periods of subaerial exposure of the back reef. During this period of low sea level, fore-reef sediments were partly cemented by CaCO{sub 3} and were not subaerially exposed. Therefore, moldic porosity was not created in the fore-reef sediments. Porosity in the fore reef was later created in places by dissolution of this cement. Secondary dolomite was later precipitated along pore walls, and in places it occluded porosity in the pore spaces.

• OSTI ID: 5406046
• Report Number(s): CONF-8703189-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 71:2; Conference: American Association of Petroleum Geologists Southwest Section convention, Dallas, TX (USA), 22-24 Mar 1987; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
PETROLEUM DEPOSITS
RESERVOIR ROCK
DEPOSITION
TEXAS
CALCITE
DIAGENESIS
ENHANCED RECOVERY
GEOLOGIC FORMATIONS
LIMESTONE
PENNSYLVANIAN PERIOD
PETROLEUM
POROSITY
REEFS
ALKALINE EARTH METAL COMPOUNDS
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATE ROCKS
CARBONATES
ENERGY SOURCES
FEDERAL REGION VI
FOSSIL FUELS
FUELS
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
MINERAL RESOURCES
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
RECOVERY
RESOURCES
ROCKS
SEDIMENTARY ROCKS
USA
020200* - Petroleum- Reserves
Geology
& Exploration
020300 - Petroleum- Drilling & Production