AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Workflow from Seismic to Static Modeling Capturing Key Heterogeneities Impacting Production Performance in a Super-Giant Middle East Carbonate Field
(1) ADCO, Abu Dhabi, United Arab Emirates.
(2) Kelkar & Associates, Abu Dhabi, United Arab Emirates.
Building a full-field static model in a Super-giant oilfield with more than 700 wells and 47 years of production history is a challenging task, especially when the main reservoir spans three distinct sedimentological domains with their own complexities and production issues.
Oil is produced from an Aptian carbonate reservoir averaging 400ft thick with complex internal reservoir architecture. The lower reservoir units comprise continuous platform and ramp carbonate layers deposited during overall transgression. A platform dominated by stacked patchy rudist build-ups and inter build-up ponds developed in the south of the field during later aggradation. Rapid water advance along high-permeability layers led to irregular water fingering which must be captured in the static and dynamic models.
Facies architecture and property distributions are very different in the central highstand progradation and northern late highstand clinoform domains dominated by more steeply dipping reservoir units (1-3 degrees). Non-reservoir carbonate mudstones associated with transgression form local flow barriers confirmed by pressure and production data.
Different strategies were used in structural and property model building to account for heterogeneities across the field. The southern platform interior with rapid facies variations of non-reservoir ‘pond’ facies and stacked coral/rudist shoals was modeled using well data combined with seismic attributes. Production in the north is supported by peripheral water injection, WAG pattern and line-drive gas injection. Deterministic mapping of 3rd and 4th order clinoform sequences is critical for understanding fluid movement. A key modeling challenge was to accurately represent the clinoform geometries. With dips up to 3 degrees downlap of layers occurs within 1-2km, resulting in ambiguous well-based correlations. High-quality seismic data was used to map clinoform ‘corridors’ and constrain reservoir thickness. Stochastic methods (SGS) guided by a deterministic layering framework and controlled by a core/log-based lithofacies model were used to populate the petrophysical properties. The central area comprises a thick succession of good reservoir quality facies with ‘transparent’ seismic character. Recent seismic analysis has led to the recognition of clinoforms although they could not be mapped deterministically. An architecture was established using well correlation guided conceptually by the overall clinoform shape.