Technical Paper: Field Test Results of a New Dielectric Dispersion Tool: Improving Production Prediction in the San Jorge Basin

Society: IBP
Paper Number: 3160_10
Presentation Date: 2010


The San Jorge Basin is a major oil producing area of Argentina. Volcanic activity and a continental environment created complex reservoirs with fresh formation waters that vary laterally and with depth. Identifying hydrocarbon producing layers becomes a real challenge. Interpreters have used many different evaluation methods, with disappointing results. This is the motivation behind testing a new approach: could a dielectric dispersion measurement improve the rate of success in producing hydrocarbons in these reservoirs?

Dielectric tools are able to measure water saturation independently from salinity, which is determined in the process. The tool is a new multi-frequency propagation device measuring dielectric dispersion. Although reading deeper than previous ones, it remains a shallow device and Patagonia wells are often deeply invaded. Dielectric water saturation becomes an upper limit of the true virgin zone saturation and salinity approximates the true formation water salinity. An efficient interpretation model becomes crucial to a successful interpretation of the measurement.

The approach chosen was to compare the water filled porosity from dielectric to a bound fluid volume from nuclear magnetic resonance and a total porosity from nuclear or other logs, to calculate the oil filled volume. Given the complex texture of the reservoir, quantifying the irreducible water is essential. This irreducible saturation is compared to the water saturation from dielectric, to assess if the layer will produce oil.

A statistical analysis of test results confirms that this approach is promising. Test results are available on three wells and show that production prediction with dielectric dispersion was correct 71% of the time. Oil bearing sands were correctly identified 77% of the time. In conclusion, knowing the amount of oil present in the invaded zone helps in the identification of producible oil zones.

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