High Resolution Sequence Stratigraphy in the First Eocene Carbonate Reservoir from Wafra Field, Partitioned Neutral Zone (PNZ), Saudi Arabia and Kuwait

Niall Toomey, Scott W. Meddaugh, Kera Gautreau, and Stewart Griest
Chevron Energy Technology Company, Houston, TX

Development of a large scale steamflood pilot (LSP) in the heavy oil First Eocene reservoir at Wafra Field will test the feasibility of enhanced thermal recovery in the reservoir. The LSP project also provides a unique opportunity to develop a detailed sequence stratigraphic model. A total of 60 wells (including 5 cores) were drilled on an inverted 16 spot pattern covering a total of 40 acres. This high density data set provides a unrivaled view of the subtle stratigraphic changes across the project area.

The sediments of the First Eocene reservoir at Wafra Field were deposited in arid to semi-arid conditions on a shallow, low to moderate energy inner shelf or ramp. Facies types are dolomitized peloidal wackestone and packstone, with localized foram-rich grainstone, algal boundstone, and argillaceous mudstone. The abundance of evaporites, primarily gypsum and anhydrite as isolated nodules, coalesced nodules, and laterally extensive beds suggests restriction was sufficient for the development of salinas and sabkhas. Facies maps constructed for each stratigraphic surface within the reservoir interval indicate that facies belts are generally oriented in a northwest to southeast trend, parallel to the paleo-shoreline. These depositional facies maps reveal that facies bodies have geometries ranging from arcuate to elongate.

Numerous shallowing upward cycles are recognized from the cores in the First Eocene reservoir. A typical cycle consists of subtidal packstone to wackestone overlain by intertidal mudstones and wackestones. Cycles are capped by algal tidal flat mudstones or bedded to nodular evaporites. Hardgrounds or exposure surfaces are associated with the cycle tops. These cycle tops provide a framework for correlating core facies to log signature. The cycle tops are correlative with gamma rays highs which can be correlated across the entire field.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas