EXPLORING FOR PERMIAN TRAPS USING SEISMIC VOLUMES CONDITIONED WITH WELL DATA, NORTHWEST SHELF TEXAS

Geocellular models constructed from 3D seismic volumes and log data combined with sequence stratigraphy were used to discover new oil in areas previously condemned with dry holes. Normalized log data from seventy regional wells were used to build 3D models of porosity, lithology, and stratigraphy.

The seismic workflow included deriving an acoustic impedance inversion volume that was used to calculate seismically constrained porosity and gamma-ray reservoir models. They were combined with the log-based models using geostatistical collocated co-kriging method. This produced a predictive 3D model that combined data from both the wells and the seismic data. Velocity modeling and depth conversion further refined the structural model.

Sequence stratigraphy and mapping from the combined models identified an undrilled area of potential reservoir rock along a Permian shelf. This was a new fairway of potential reservoir along strike on the shelf. Gamma-ray data were used in the lithology model to distinguish between non-reservoir siltstones and productive dolomites. The gamma-ray cut-off was used to eliminate the siltstones resulting in more accurate reservoir maps. Several successful exploration wells were drilled offsetting a dry hole using this modeling method.

After the exploration phase, the area moved to the reservoir management team (RMT). Detailed variogram analysis was performed on both the well and seismic data to further refine the reservoir model to identify development locations. Information from sidewall cores was used to calculate a revised free water level. Capillary pressure information indicated that the free-water level could be deeper than previously estimated. This information was used to drill several additional successful development wells.

This project is an example of regional modeling applied to discover oil in areas with little recent exploration. Modeling enabled the identification of the play fairway, detailed mapping, and accurate prediction of anticipated reservoir quality. It is also an example of project management as after a series of successful exploration wells, the RMT performed further detailed reservoir modeling. This enabled the RMT to continue drilling wells and expand the geographic and stratigraphic extent of the Permian reservoir.