Deposition and diagenesis of a Pettet reservoir at Lisbon field, Claiborne Parish, Louisiana
Rocks of the Pettet zone at Lisbon field consist of three shoaling-upward oolite cycles that were deposited over a paleotopographic high as dip-trending, lenticular sand bodies. The lower 5 ft of the ooid shoals consists of superficial ooid packstones and grainstones, which are succeeded vertically by regular ooid packstones and grainstones. Adjacent to the shoals are marine rocks consisting of intraclast, ooid, bivalve packstones, and oyster wackestones and packstones. The open-marine shelf downdip from the shoals and the marine lagoon updip from the shoals were blanketed by skeletal mudstones and wackestones. Shoal deposition probably started during periods of relative rise in sea level. The basal two oolites are capped with unconformities that marked sea level retreats. During these retreats, the topographically high shoals were partly exposed as islands, and silty shales were deposited as laterally equivalent facies in a quiescent marine environment. Diagenetic alteration began in the marine environment and continued into the subsurface. Marine diagenesis includes mainly micritization of grains in the oolites. Later, vadose and freshwater diagenesis occurred during the periods of exposure. Aragonitic allochems were selectively dissolved, and magnesian calcites were altered to low-magnesium calcite. Lime mud underwent aggradational neomorphism, and columnar to blocky calcite rim cements were precipitated in the lower parts of the leached sand buildups. Selective dissolution of aragonite produced abundant moldic porosity in the superficial ooid packstones and grainstones where most of the ooid nuclei were composed of mollusk fragments. In contrast, many ooid cortices around the moldic voids were preserved, suggesting that the cortices were of a different mineralogy - probably magnesium calcite.
- Research Organization:
- Texas A and M Univ., College Station
- OSTI ID:
- 6987921
- Report Number(s):
- CONF-8610199-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 70:9; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
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