Conditioned Forward Stratigraphic Modeling in Large Carbonate Fields: A Dionisos Model of Karachaganak*
Miriam Andres, Phil Bassant, and Mitch Harris
Search and Discovery Article #40352 (2008)
Posted November 20, 2008
*Adapted from oral presentation at AAPG International Conference and Exhibition, Cape Town, South Africa, October 26-29, 2008.
Click to view list of articles adapted from presentations by P.M. (Mitch) Harris or by his co-workers and him at AAPG meetings from 2000 to 2008.
Karachaganak is a large Devonian to Permian age isolated carbonate retrograde gas-condensate field in Northern Kazakhstan. Here, conspicuous steep (20-30 degrees) high-rise (<400 m) clinoforms are observed yet un-mapped due to poor seismic expression, and thus not integrated into the conventional geocellular model used for flow simulations. Although sufficiently simulating field-scale behavior and long-term production, this approach inadequately addresses individual well-performance as proportional bedding used in the conventional model construction cross-cuts steeply dipping flow units. Flow-unit orientation is critical as it strongly influences vertical reservoir connectivity, affecting produced-fluid composition which varies vertically in the reservoir. Steeply dipping flow units can also decrease horizontal transmissibility (flow across multiple flow units), leading to lateral variations in pressure which are merely the result of stratigraphy.
To address the above-mentioned challenges, we build a model using ‘Dionisos, a diffusion-based forward stratigraphic modeling package. Vertical thicknesses are conditioned by stretching the final model to mapped seismic surfaces. Facies are conditioned manually to interpreted facies maps by interval. Equally, geomorphologic elements of platform-top and slope are conditioned to seismic observations. Boundary input parameters, such as model age, eustatic sea level, as well as sediment production rates and depths, correspond to the respective geologic age of the reservoir. The resulting S-grid is populated with depositional facies and captures the non-stationary facies patterns currently difficult to achieve with conventional geostatistical simulations. 3D co-rendering of the Dionisos model and seismic cube has provided a powerful instrument used extensively to re-evaluate the seismic interpretation. We gained valuable insights in particular where model prediction and seismic cube disagree and in areas of poor seismic quality, such as sub-salt environments. Furthermore the model offered alternative scenarios to existing seismic interpretations.
DIONISOS —Diffusive Orientated Normal and Inverse Simulation of Sedimentation (by IFP -- Granjeon, 1997; Granjeon and Joseph, 1999)
Established workflow for ‘conditioned’simulation
Common visualization and communication tool.
Bassant, Phillip, and Paul M. (Mitch) Harris, 2008, Modeling Reservoir Architecture of Isolated Carbonate Platforms: Search and Discovery Article #40294 (http://searchanddiscovery.com/documents/2008/08070bassant/index.htm).
Bassant, Phillip, and Paul M. (Mitch) Harris, 2008, Analyzing Reservoir Architecture of Isolated Carbonate Platforms: Search and Discovery Article #40295 (2008) (http://searchanddiscovery.com/documents/2008/08071bassant/index.htm).
Granjeon, D., 1997. Modelisation stratigraphique deterministe - conception et applications d'un modele diffusif 3D multilithologique: Memoires Geosciences Rennes, Ph. D. Dissertation, Geosciences Rennes, Rennes, France, 189 p.
Granjeon, D., and Joseph P., 1999, Concepts and applications of a 3D multiple lithology, diffusive model in stratigraphic modeling, in J.W. Harbaugh et al., eds., Numerical Experiments in Stratigraphy: SEPM Special Publication 62, p. 197-210.