Lower Bahariya Formation in the Khalda Field--Sedimentation, Diagenesis, and Reservoir Properties

A. M. Conway, K. A. Fahmy, R. McGarva

Khalda field is located in the northern portion of the Khalda west concession in the western desert of Egypt. Production is from the upper Cenomanian lower Bahariya Formation. The trap is established by a north-south-trending, oval, domal anticline dissected by east-west faulting. A major northeast-southwest-trending fault zone bounds the feature to the east. The lower Bahariya comprises a sequence of tidal flats at the base, which pass upward through mixed flats and terminate in mud-rich flats. These are overlain by shallow marine sands and capped by the marine shales and limestones of the upper Bahariya. The whole sequence represents the action of a progressive, yet punctuated, marine transgression across a tidal flat. Facies associations, recognized from core and wirel ne-log data include inner shelf and mud-rich tidal-flat claystones, tidal heterolithic deposits, rippled sand-sheet/shoal complexes, cross-bedded sands, bioturbated shoal/bar complexes, lag deposits, tidal and storm channel fills, and shallow marine-shelf sheet-sand deposits.

From facies correlations, an 11 zone reservoir modeling scheme has been defined. Reservoir quality, dependent on facies type, grain size, and distribution of authigenic cements, is best where rippled sand-sheet/shoal complexes and shallow-marine sheet-sands are abundant. Diagenetic modeling indicates that much of the observed porosity is secondary following carbonate dissolution and that quartz cement is the only major factor causing porosity reduction. Authigenic glauconite, found in large concentrations, together with fine laminations, controls effective permeability.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.