Seismic Petrophysics in Tight Gas Sands - a Piceance Basin, Mesa Verde Example

Darrell Hoyer¹ and Roger Young^2
1Hoyer Petrophysics Inc., Fort Collins, CO
²eSeis Inc., Houston, TX

Recent advances in seismic AVO analysis are applied to seismic data over the Rulison Gas Field in the Piceance Basin of Colorado. Pre-stack migrated gathers are analyzed for amplitude changes with offset and a cross-plot technique is used to evaluate reservoir properties of the low porosity Williams Fork Sands of the Mesa Verde. Seismic Lithology (LithSeisTM) is correlated to clay volume from open hole log analysis, AVO type is used to identify coal seams and porosity determined from seismic data is normalized to the open hole log porosity.

A reservoir summation sensitivity study compares the results of seismic analysis to log analysis. The reservoir summation results indicate that the reservoir volume (Porosity*Net Sand) from seismic analysis has a good fit to open hole results. The seismic summation results demonstrate that the AVO type cutoff eliminates the high porosity coal seams and that seismic porosity is sensitive to a 6 or 8% cutoff. The seismic reservoir summation run over the completed/hydraulically fractured, Williams Fork Sand interval also has a good correlation to production results and EUR estimates from the wells included in this study.

The result of pore pressure prediction from seismic frequency decay (QxTM) is also presented. In addition to drilling applications, pore pressure from seismic data adds to the potential understanding of the roll that faulting and natural fractures seem to have on the gas reservoir in the Rulison Field.

AAPG Search and Discovery Article #90092©2009 AAPG Rocky Mountain Section, July 9-11, 2008, Denver, Colorado