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An Updated Characterization of the Wafra First Eocene Dolomite Reservoir, Partitioned Zone (PZ), Saudi Arabia and Kuwait - Static and Dynamic Studies

Meddaugh, William *1; Aziz, Shamsul 1; Steve, Bachtel 1; Champenoy, Nicole 1; Dull, Dennis 1; Gumilar, Bambang 1; Heesackers, Vincent 1; Hruska, Marina 1; Montgomery, Paul 1; Osterloh, W. Terry 1; Patience, Richard 1; Pollitt, David 1; Playton, Meghan 1; Mark, Skalinski 1; Rowan, Dana 1; Rubin, Eugene 1; Saller, Art 1; Toomey, Niall 1
(1) Chevron, Houston, TX.

As part of on-going studies related to a potential steamflood project for the First Eocene reservoir a comprehensive reservoir characterization project was undertaken that included the following: (1) sequence stratigraphy augmented by bio-, chemo-, and magneto-stratigraphy; (2) diagenesis characterization based on core, thin section, and isotope analysis; fracture characterization using cores and FMI logs; (4) petrophysical studies focused on permeability heterogeneity; (5) oil and water sampling across the field and by perforation depths complemented by core organic geochemistry; and (6) dynamic data analysis. The results of these studies were used to constrain a new set of stochastic geological models using a very fine grid that have been built specifically to allow probabilistic forecasting using sector-based roll-up workflows and novel very large area-based forecasting workflow.

The reservoir consists of highly dolomitized, meter-scale depositional cycles comprised of basal peloid dolopackstones (subtidal) capped by peloid dolowackestones and dolomudstones. The meter-scale cycles are combined into sequences based on stacking patterns and evidence of subaerial exposure. The sequences are bundled into two composite sequences with transgressive (thicker, more subtidal facies) and highstand sequence sets (thinner, more intertidal facies). Chemo- and magneto-stratigraphic work confirms the core and well log based stratigraphy. The diagenetic history is complex with early dolomitization followed by dissolution of dolomite cores and precipitation of anhydrite cement and a final late-stage that includes anhydrite dissolution and calcite cementation. The reservoir contains some fractures (up to about 0.0035 fractures/foot in the southwest), but is not a “classic” fractured reservoir. Three main fracture sets were indentified; Set 1 (NE-SW) parallel to the NE SHmax direction, Set 2 (E-W), and Set 3 (NW-SE) which is parallel to the anticlinal structures in the field. Though limited, the available dynamic data also does not support the First Eocene as a fractured reservoir. There are significant variations of both water chemistry and oil quality in the reservoir. The north and west areas have generally higher gravity oil and water with lower TDS/salinity as compared to the southeastern area. Appropriate data were used to build fine-scaled stochastic models that are the basis for on-going probabilistic steamflood forecasting.


AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain