Constraining Uplift in the Piceance Basin Using Diagenetic Modelling of Quartz Cementation in Late Cretaceous Williams Fork Sandstones, Colorado

Burial history controls thermal exposure and influences pressure history, which in turn influence the timing and amount of gas generation, overpressuring, quartz cementation, natural fracture formation, and ultimately, reservoir quality. Studies based on apatite fission-track and thermal maturation suggest that maximum burial in the Piceance Basin occurred between 45 and 20 Ma, and that post-Laramide uplift began at approximately 10 Ma as the Colorado River system eroded large quantities of sediment. However, there is debate about the magnitude and pattern of this uplift. For tight gas reservoirs of the Late Cretaceous Williams Fork sandstones estimates of eroded section using stratigraphy, vitrinite reflectance extrapolation, and basin modeling vary from 3800 ft to 6100 ft for the MWX well, from 3700 ft to 9167 ft for the MF31-19G well, and 4400 ft near the Last Dance 43C-3-792 well.

Because quartz cementation is sensitive to thermal exposure, diagenetic modeling (TouchstoneTM) of quartz cement abundance can be used to better constrain both the amount and timing of uplift. In our study, we tested multiple burial history scenarios for these three well locations. The burial scenarios that led to the closest match between petrographically measured and predicted quartz cement abundances suggest that the maximum burial depth and removed overburden at the base of the Williams Fork are 13,575 ft and 5,147 ft for the MWX well, 15,163 ft and 3,157 ft for the MF31-19G well, and 13,067 ft and 5,068 ft for the Last Dance 43C-3-792 well respectively. We used the same approach for the Rifle Gap outcrop locality (Grand Hogback). The scenario that gave the best match of model results with present-day quartz cement abundance from point-count analyses indicates that the base of Williams Fork reached its deepest burial (~7,000 ft) about 50 Ma ago and uplift started around 35 Ma (~3000 ft of uplift).

Using quartz cement, which is sensitive to temperatures reached and time spent in those temperature ranges, as a paleothermometer provides an independent estimate of amount of erosion. However, because finite pore space is available for quartz cementation; once porosity is entirely occluded this gauge is insensitive to further thermal exposure unless other pore space becomes available (secondary pores, fractures).

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California