Heterogeneity in Carbonates - The Effect of Data Density from Reservoir Modeling of the Wafra First Eocene Reservoir, Partitioned Neutral Zone (PNZ), Saudi Arabia and Kuwait

William Meddaugh, Niall Toomey, Kera Gautreau, and Stewart Griest
Chevron Energy Technology Company, Houston, TX

The giant heavy oil First Eocene reservoir at Wafra Field has been on primary production since 1954. The field has produced about 300 million barrels to date from dolomitized packstones deposited in shallow water on a gently dipping, low energy inner shelf or ramp under arid to semi-arid conditions. The estimated original oil in place is 9-12 billion barrels. The reservoir average porosity is 35% and the average permeability is 250 mD.

Geostatistical models for the First Eocene reservoir have been generated since 2002 to support reservoir management decisions. A full field model was generated in 2002 using data from about 250 primary development wells drilled on 500 m spacing. Geostatistical analysis of the full field wells yielded semivariogram models with an average XY range of 1490 m (range 1170-2150 m).

Reservoir models were generated in 2005-2007 to support a small scale steamflood test (SST) consisting of a single, 1.25-acre inverted 5-spot and an observation well in the Wafra Main Area. Geostatistical analysis of the SST and surrounding wells yielded semivariogram models with an average XY range of 305 m (range 175-490 m).

Reservoir models were generated in 2007-2008 for a large scale steamflood pilot (LSP) consisting of 16, inverted 5-spot patterns covering 40-acres in the Wafra West Area. The LSP project includes a total of 60 wells (including five cored wells), 56 of which were drilled in 2007-2008. The well based data is supplemented by a recently acquired high resolution 3D seismic volume and detailed sequence stratigraphic interpretation. Geostatistical analysis of the LSP and surrounding wells yielded semivariogram models with an average XY range of 290 m (range 135-480 m). Work is in progress to determine the best approach to integrate the results obtained from the SST and LSP to the update the full field model.

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