Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Sequence Stratigraphy of the First Eocene Reservoir (Paleocene-Eocene) at Wafra Field, Partitioned Zone, Kuwait and Saudi Arabia: The Use of Stacking Patterns to Define the Stratigraphic Framework of a Low-Angle Carbonate Ramp
(1) Chevron Energy Technology Company, Chevron, Houston, TX.
The Paleocene-Eocene aged First Eocene reservoir of the Wafra Field illustrates the use of stacking patterns to define lower-order sequence stratigraphic packages to be used in reservoir modeling both for framework generation and reservoir property distribution. The definition of these packages provides genetic units that allow a more geologically robust interpretation to guide reservoir distribution in the giant multi-billion barrel heavy oil field.
Stacking patterns are defined as systematic vertical changes in cycle thickness or facies proportions. A thinning upward set of cycles (with higher proportions of shallow water facies) is interpreted as a decrease in accommodation (early to late highstand) on the platform and thickening upward cycles are interpreted as increasing accommodation (transgression to early highstand).
Detailed core descriptions from 9 wells reveal a large number of small-scale (<1 - 5m), shallowing-upward “depositional cycles” or “parasequences” that represent the highest order of stratigraphic packaging observed. The cycle boundaries are recognized by surfaces of exposure (on tidal flat sediments) or eroded surfaces (+/- exposure) on top of subtidal strata. Two main cycle types have been identified to date; 1) supratidal to intratidal capped cycles (SIC), and 2) subtidal dominant cycles (SDC). The SIC are relatively thin and contain a higher percentage of shallow water facies including peloidal dolomudstone and dolopackstone, algal boundstone and bedded anhydrite. The SDC are relatively thick and dominated by thick homogeneous burrowed peloidal dolopackstone with variable amounts of nodular anhydrite. An upward increase in successive composite sequences of algal boundstone and anhydrite facies may be caused by restriction resulting from accommodation loss or the onset of the Paleocene-Eocene Thermal Maximum.
The observed “depositional cycles” are interpreted as a series of 16 “sequences” based on the interpreted stacking of cycles. The First Eocene sequences were grouped into 2 “cycle sets” or “systems tracts” within 2 composite sequences that define the First Eocene reservoir. Cycle sets that contain a higher percentage of SICs (highstand cycle sets) show an overall lower permeability and potentially vertical barriers to flow due to more abundant lower permeability tidal flat facies. The identification and distribution of these vertical barriers is critical to the development of the full field steam flood.