Abstract

Three-dimensional (3-D) seismic data has been used extensively over the past several years in many exploration and development applications throughout the Permian Basin. Many 3-D shoots are designed to identify reservoir fairways, but are often not supported in advance by detailed geologic study. Many times, large areas are shot and then individual prospects are high-graded from the resultant data, leaving large areas of data that have limited or no potential. Some of the targets for which the 3-D shoots are designed express themselves more subtly in the rock record than previously thought, or may be masked by complex tectonic overprints that may not be readily recognized in the interpretation stage. These pitfalls are particularly critical with shoots designed for large-scale exploration programs in less maturely developed areas.

Geologic modeling prior to design of a 3-D shoot is essential for stratigraphic correlation of geophysical data, in order to take full advantage of 3-D’s benefits. But it is also critical to identifying such features as abrupt changes in thickness or lithologic attributes of the section that are caused by unconformities, glacioeustatic sea level changes, or other reactivation surfaces. New geologic concepts of the Permian Basin developed over the past several years could have profound influences on geophysical evaluations and should be incorporated not only in the interpretative phase but also in the design phase of a 3-D program. This paper examines several case studies of selected zones throughout the Permian Basin where reservoir characteristics are often mis-interpreted by evaluation of 3-D seismic data. Examples from karsted Siluro-Devonian carbonates, Atoka fluvial sandstones, and Cisco-Canyon algal mounds are presented and are used to show how geologic modeling should be used to (1) establish the local depositional attributes of a target reservoir, and (2) narrow the focus of a 3-D shoot in order to provide data useful to more efficient design of a shoot area.