Uncertainty Analysis: A Probability Approach to Development of a Large Carbonate Oil Reservoir in Persian Gulf

This paper describes a development strategy with peripheral water flood for S-reservoir, a large oil bearing carbonate part of the Persian golf oil reservoirs. The heterogeneity, discontinuity, size and different rock type characteristics of this reservoir lead to a decisional divergence between development options. In this paper it is explained how the sensitivity assessment and risk analysis can be used to identify the most dominating risk component(s) with respect to the field productivity and capability of meeting the oil production target. Once these dominating risk components become known, we could: a) further optimize the field development by properly formulating the drilling and completion strategy, b) re-prioritize the data acquisition and reservoir characterization program to lessen the uncertainties and further minimize the risks. In this study we have used the Experimental Design Methodology to shorten the number of simulation runs required for sensitivity assessment and risk analysis. The probability analyses identify and rank the most sensitive parameters that help in field development: maximize the exposure to the reservoir components that bring positive impact and minimize those that have the negative impact on field recovery and economics. The sensitivity analysis and risk assessment running concurrently with reservoir simulation to develop a Pareto Chart for different reservoir parameters such as Kv/Kh ratio, vertical transmissibility, horizontal transmissibility, residual oil saturation, aquifer radius, aquifer permeability, skin factor and the location of the producers. The most sensitive parameters with respect to oil recovery are identified for reassessment and further improvement and optimization of the development plan. Data acquisition program, reservoir performance evaluation and production injection strategies are conducted with these sensitivities in mind. They are executed with the highest priorities given to the most sensitive parameters. Monte Carlo simulations again are run on periodic basis with actual field data input to further optimize the development.

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Senior Reservoir Engineer , Schlumberger Information Solutions