Conditioned Forward Stratigraphic Modeling in Large Carbonate Fields: A Dionisos Model of Karachaganak

Miriam S. Andres¹, Phil Bassant², and Paul M. Harris^1
1ETC, Chevron, San Ramon, CA, USA
²International E&P, Chevron, Jakarta, Indonesia

Karachaganak is a large Devonian to Permian age isolated carbonate 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. Flow-unit orientation is critical as it strongly influences vertical reservoir connectivity. 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 sealevel 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 the seismic cube disagree and in areas of poor seismic quality such as subs-salt environments. Furthermore the model offered alternative scenarios to existing seismic interpretations.

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