The case history presented here describes an investigation of the Northwest shelf of the Delaware basin carried out in 1979 for estimating the potential of finding new reserves and a follow-up study to measure predictions against results.

A total of 191 new-field wildcats had been drilled during 1974-1979 in the study area. An analysis of target zones and success ratios showed that the best chances of drilling a successful test were in the San Andres (Permian) and Silurian-Devonian. However, cumulative frequency plots of existing fields in these two intervals showed that the chance of finding a field larger than 1 million bbl (159,000 m³) in either of these zones was relatively low.

As a result of the 1979 analysis, three prospective areas representing 8% of the total study area were high graded, or rated as having a higher potential than other parts of the study area. The 1980-1983 drilling results show that the original high-graded areas contain 52% of the 21 successful San Andres tests and the only discovery in the Silurian-Devonian. However, as predicted by the analysis, all of these discoveries appear to be small.