Development of a method for adjusting rock compaction parameters and aquifer size from production data and its application to Nam-Su fractured basement reservoir of Vietnam

The Nam-Su is a major naturally fractured basement reservoir (FBR), offshore Vietnam. To date, simulation models of Nam-Su FBR have failed to give an adequate history match without invoking the presence of large aquifers. In a previous study (Son et al., 2007), the authors investigated several possible alternatives to achieve a satisfactory history match. They modeled porosity reduction by compaction along with the change of aquifer size and produced an improved history match that is consistent with the geological nature of the system. The key to such modeling is reservoir rock compressibility. Estimating the values of rock compressibility from cores is a challenge in FBR's due to the failure of coring from a naturally fractured interval, and thus reliable values are not available. We developed a computer-assisted history matching method to resolve these two problems together and save significant time compared to the manual trial-and-error methods used to adjust these parameters generally used in Vietnam. The methodology developed has been applied successfully to determine rock compaction coefficients and adjust aquifers' sizes of the Nam-Su FBR. Comparisons between our adjusted model and the existing model show considerable improvement between computed and measured values. Simulators can always be adjusted to obtain a history match even with geologically unrealistic values. The approach outlined here is more physically realistic than existing approaches and hence should provide/provides better production and other forecasts.

Automated summary

The simulation models of Nam-Su FBR have struggled to achieve a satisfactory history match without invoking large aquifers, but researchers have improved the match by modeling porosity reduction through compaction and aquifer size changes. The key lies in reservoir rock compressibility, which is challenging to estimate in FBRs due to difficulties in coring naturally fractured intervals. A new computer-assisted history matching method has been successfully applied to determine rock compaction coefficients and adjust aquifer sizes, providing better production forecasts compared to manual trial-and-error methods commonly used in Vietnam.