In trying economic times when exploration budgets are cut, a partially explored basin can experience a slowdown in activity, leaving us questioning whether sufficient reserves remain to justify further exploration.

In such situations a clear idea of the basin's potential is necessary in order to continue drilling new wells. A series of studies was undertaken and probability plotting was used to analyze the Black Warrior basin of Mississippi for the number and size distribution of undiscovered natural gas reserves.

Part of the study was the use of decline curve analysis to predict ultimate gas reserves from 256 active wells in the basin. A recovery factor as a function of depth for the Warrior gas fields was developed. Original gas in place figures were calculated using the recovery factors and the predictions of ultimate reserves. It was found that the ultimate reserves by field in the Black Warrior basin are log-normally distributed.

By using probability plots in any partially explored basin, one can foresee the economic justification for further exploratory drilling. This method is the most thorough and informative technique that can be applied to a basin which has a proven potential of future discoveries. As exploration becomes more selective, this technique could become a valuable tool to many exploration programs.

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