Challenge: Preserving Sector Model Integrity in Downscaling from the Full Field Earth Model for Steam Flood Forecasts in a Carbonate Reservoir: 1st Eocene Reservoir, Wafra Field, Partitioned Zone, Kuwait and Saudi Arabia

Dull, Dennis W.; Osterloh, Terry; Shook, Michael; Rubin, Eugene

The challenge in rescaling an earth model is to preserve the integrity of the original model whether coarsening or fining the grid. This entails capturing the statistical, spatial, and dynamic flow characteristics of the original model. A key consideration is a quantitative description of the two models to demonstrate the heterogeneity is preserved.

The 1st Eocene is a large carbonate reservoir deposited on a shallow carbonate ramp that has been dolomitized and has an average porosity of 35 percent and average permeability of 250 md. The core porosity commonly exceeds 50 percent and has measured core permeability of over 6000 md.

Saudi Arabian Chevron is in the process of developing a full field plan for the expansion of the steam flood from the existing Large Scale Pilot (LSP). The Wafra 1st Eocene fine scale full field model (FFM) covers an area of several hundred km2 with 25 m x 25 m areal grid cells and 607 layers with a total of 257 million cells. Due to the size of the earth model, the facies and property modeling was done separately for each of the 16 high frequency sequences that compose the 1st Eocene reservoir. The 257 million cell FFM was too large for history matching and was subsequently upscaled to 100 m x 100 m and 137 layers. The history matched model (HMM) contains 3.6 million cells.

Based on the HMM, eight 1 km2 sector models were selected to represent the full range of reservoir diversity of the 1st Eocene reservoir. For the steam flood a fine gridded model of 5 m x 5 m was required for each sector location. A workflow was developed to not only preserve the statistical and spatial continuity of the coarse sector model in the finely gridded model but to quickly evaluate and compare the dynamic flow characteristics or heterogeneity of each model to insure model integrity. We describe the workflows and show their application using Wafra 1st Eocene as an example.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013