--> --> Abstract: Fit-for-Purpose Stochastic Evaluation of OOIP and Recoveries, Negage Field, Block 14 Deepwater Angola, by Kathleen Mabe, Pat Burdett, Yan Chen, Masroor M. Chaudhri, and Jay Byers; #90082 (2008)

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Fit-for-Purpose Stochastic Evaluation of OOIP and Recoveries, Negage Field, Block 14 Deepwater Angola

Kathleen Mabe1, Pat Burdett2, Yan Chen1, Masroor M. Chaudhri1, and Jay Byers1
1South Africa Business Unit, Chevron, Houston, TX
2Decision Strategies, Houston, TX

A fit-for-purpose method was developed to capture the probabilistic range in OOIP volumes and recoveries at Negage field in Angola Block 14. A systematic approach involving expert interviews, sensitivity analysis, analogue databases, and Crystalball Monte Carlo techniques were used to capture the uncertainty ranges for:
- Net to Gross
- Depth
- Porosity and water saturation
- Fluids
- Fault seal
- Vertical and Areal Baffles
- Permeability
- Kv/Kh
- Relative permeability
Uncertainties associated with seismic rock properties, thin-bed analysis, layering, depth variation, and faulting were incorporated into models. The OOIP and recovery distribution was determined by Monte Carlo simulations using key reservoir characteristics, recovery ranges by zone, zonal dependencies, property correlations, and risk values.

Negage reservoirs consist of high-quality deepwater turbidite channel sands of Miocene age. Discovered in October 2002, Negage field is located in 4,500 feet of water. The Congo River Canyon separates the Negage field from other Block 14 infrastructure, including the BBLT and Tombua-Landana developments. Negage is a challenged asset where understanding subsurface uncertainties is a crucial for economic evaluation and decision analysis modeling. Preliminary probabilistic OOIP and recoveries were used to prioritize development options for a major capital project in deepwater.

This fit-for-purpose recovery estimation method was applied before running the more rigorous Design of Experiments. The probabilistic results from both techniques will be compared to determine if the more simplistic approach is recommended for prioritizing development options of deepwater facilities. Benefits are realized by identifying areas where additional technical work is needed to better capture specific variables like permeability, fault seal, and reservoir connectivity.

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