The Denver-Julesburg basin, with approximately 1,000 Lower Cretaceous fields and over 30,000 wells, presents a unique opportunity for statistical analyses of its exploration history. Comparison of an analysis of the current activities in the basin with a similar analysis made 20 years ago by J. J. Arps provides an interesting perspective of the known distribution of field sizes, as well as speculations on the basin’s exploration future.
Five years ago 12,200 exploratory wells had been drilled in this basin and resulted in the discovery of 820 fields. As a result of the known field-size distribution in the basin at that time, the average size of an undiscovered field was predicted to be on the order of 1 million bbl of recoverable resources. Since then, more than 5,000 additional exploratory wells have been drilled, and the average size of the 125 new fields discovered is in the predicted range. Exploration statistics indicate that the rate of oil discovery has declined in the past 5 years, even though the frequency of wildcat drilling has accelerated. Newly discovered fields are generally located in the heavily drilled areas as opposed to the sparsely drilled or “under developed” areas of exploration.