Determination of uncertainty in reserves estimate from analysis of production decline data

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Title: Determination of uncertainty in reserves estimate from analysis of production decline data
Author: Wang, Yuhong
Abstract: 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 .
URI: http : / /hdl .handle .net /1969 .1 /5902
Date: 2007-09-17

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Determination of uncertainty in reserves estimate from analysis of production decline data. Available electronically from http : / /hdl .handle .net /1969 .1 /5902 .

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