35 Sediments, Carbonates (Posters)

Sunday, 31 October 2010
8:00 AM - 6:00 PM
Hall D

STRATIGRAPHIC FACIES AND POROSITY DISTRIBUTION OF THE EOCENE CARBONATES IN NW OFFSHORE LIBYA, BOURI OIL FIELD

Paper number: 35-16
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

The carbonates of Jirani Dolomite Member and Eocene Nummulites deposits (Jdeir Formation) along the southern Tethys margin constitute an important hydrocarbon reservoir. The best reservoir quality is recognized within dolostone of back-bank and Numulithoclast facies, which are interpreted as high-energy foreshore deposits. Reservoir quality decreases in the transgressive facies and in the muddier foreshoal facies but clearly increases in regressive facies. The best reservoir quality and highest porosity are found also on a palaeohigh characterized by relatively large Nummulites, with high intraskeletal porosity, forming an ideal hydrocarbon reservoir.

The Dolostones facies characterize the back-bank environment of the Jirani carbonate ramp of NW Libya. These deposits may represent the Late Highstand Systems Tract (HST) of the 'Third-Order' Early-Middle Eocene depositional sequences. Dolostones facies shows intercrystalline porosity and some vuggy porosity. The dolotones with idiotopic texture at the base of the investigated sections have high porosities (12-30 %). Dolo-wackestones and dolo-mudstones with xenotopic texture at the top of the Jirani Member section have lower porosities (10-16 %). The reservoir characteristics with lateral continuity of porous zones at the base of the section and less porous zones at the top again reflect the stacking pattern of shallowing-upward cycles within the overall shallowing-upward trend of the HST. Primary facies, biofabric, and dolomitization processes thus control the distribution of porosity and permeability.