Wang, Yuhong (2003-05). Determination of uncertainty in reserves estimate from analysis of production decline data. Master's Thesis. Thesis uri icon


  • Analysts increasingly have used probabilistic approaches to evaluate the uncertainty in
    reserves estimates based on a decline curve analysis. This is because the results represent
    statistical analysis of historical data that usually possess significant amounts of noise.
    Probabilistic approaches usually provide a distribution of reserves estimates with three
    confidence levels (P10, P50 and P90) and a corresponding 80% confidence interval. The
    question arises: how reliable is this 80% confidence interval? In other words, in a large
    set of analyses, is the true value of reserves contained within this interval 80% of the
    time? Our investigation indicates that it is common in practice for true values of reserves
    to lie outside the 80% confidence interval much more than 20% of the time using
    traditional statistical analyses. This indicates that uncertainty is being underestimated,
    often significantly. Thus, the challenge in probabilistic reserves estimation using a
    decline curve analysis is not only how to appropriately characterize probabilistic
    properties of complex production data sets, but also how to determine and then improve
    the reliability of the uncertainty quantifications.
    This thesis presents an improved methodology for probabilistic quantification of reserves
    estimates using a decline curve analysis and practical application of the methodology to
    actual individual well decline curves. The application of our proposed new method to 100
    oil and gas wells demonstrates that it provides much wider 80% confidence intervals,
    which contain the true values approximately 80% of the time. In addition, the method
    yields more accurate P50 values than previously published methods. Thus, the new methodology provides more reliable probabilistic reserves estimation, which has
    important impacts on economic risk analysis and reservoir management.

ETD Chair

publication date

  • May 2003