PORE-PRESSURE PREDICTION IN SEDIMENTARY ROCKS USING SEISMIC DATA ACQUIRED AT THE ROCK SPRINGS UPLIFT (RSU) IN SOUTHWESTERN WYOMING

Evaluating formation pore pressure is a critical component for implementing safe drilling strategies and effective field development. Given seismic velocities and using empirical velocity-pressure transformation methods (e.g., Eaton, Bowers) the pore pressure can be estimated with sufficient accuracy in young sedimentary basins. This study evaluated the accuracy of formation pore pressure analysis using geophysical data from a stratigraphic test well at the Rock Springs Uplift, Wyoming- a geologically older, Laramide- age basin.

Pore pressure predictions are basin-specific and related to numerous variables such as the age of basin, burial, and temperature effects. None of the empirical correlations in literature are theoretically correct one hundred percent of the time, and which correlation to use is dependent on the data and geologic description available. Eaton’s velocity to pore pressure transformation was used.

Pore pressure estimations were only reliable within one geologic interval (Baxter Shale). This was due to the establishment of a reliable, linear normal compaction trend in that interval due to its constant lithology. Deeper intervals are prone to increased uncertainty and decreased resolution due to reflection seismic limitations. Although the normal compaction trend line cannot be verified past the Baxter Shale interval, overpressure is apparent due to the abrupt change that was seen in the density log.

Since seismic if often the only source of data available before a well is drilled, it is imperative it is used to extract as much detail of the subsurface that is possible.