More than 3500 wells producing from the sandstones belonging to the Morrow Group (Pennsylvanian) and underlying Springer Group (Mississippian-Pennsylvanian) were the subject of detailed 'reservoir analysis within portions of the Anadarko Basin (USA). Within the study area, these reservoirs will ultimately produce more than 8 TCF gas, with individual completions >25 BCF gas. Because the area has been drilled by many companies, a large variation in the drilling and completion techniques has been observed, consequently, large variation in the results exists. Detailed stratigraphic correlation resulted in accurate reservoir nomenclature throughout the study area which allowed the examination by specific reservoir and within subsets of wells with similar parameters.
The results were unexpected and should have significant impact
on the decision making processes in both exploration and development
efforts. For example, mud balance influences how much invasion
into a zone. When it is combined with pH of the water, the mud
pH demonstrates the more impact on ultimate recovery than any
single drilling of completion factor examined. Interestingly,
mud water loss (typically below 8 ml) did not appear to have much
impact upon this observation. Another observation suggests that
the practice of perforating selected intervals of a revservoir
has a direct relationship to ultimate recovery - usually not favorable.
Extensive stratigraphic correlations, detailed geologic analysis,
and the findings presented demonstrate that changes in the decision
making process should result in opportunities for significant
infield development, trend extensions, and the further exploration
in what may be considered a "drilled out" play.