REFINING THERMAL MATURITY TRENDS WITHIN THE UTELAND BUTTE MEMBER OF THE GREEN RIVER FORMATION, UINTA BASIN, UTAH

Lacustrine source rocks of the Eocene Green River Formation are a key source for hydrocarbons produced from numerous conventional and unconventional accumulations within Uinta Basin. One of the most prolific Uinta Basin source rocks is the informal Uteland Butte member, which represents an early freshwater lacustrine interval of the Green River Formation. Advances in unconventional drilling and completion practices have resulted in extensive horizontal development of the Uteland Butte oil play, with industry leading well results.

Thermal maturity is a key factor in petroleum systems. Maturity is particularly important in Uinta Basin due to the waxy, high pour point oils being produced. Understanding the relationships between source rock maturity, oil properties, and present-day temperature gradients are critical to ensuring these oils will flow to the surface. Programmed-temperature pyrolysis (PTP) has proven to be a useful tool for mapping thermal maturity trends. When used properly, parameters derived from PTP measurements, such as Tmax, can provide reliable thermal maturity information. However, it has been observed that Tmax values for Uteland Butte source rocks can yield inconsistent results. This is primarily due to the presence of low-temperature shoulders on the S2 peak from which Tmax is obtained.

One approach to addressing the peak shoulder problem is to apply chemometric analysis techniques like multivariate curve resolution (MCR). When applied to PTP data, MCR analysis generates end-member components and weights for each sample, effectively separating overlapping peaks. The MCR model can then be used to reconstruct “true S2” peaks representing residual kerogen and excluding unexpelled oil, making it possible to obtain Tmax values that more reliably relate to thermal maturity. In this study, we have used MCR to obtain Tmax estimates for Uteland Butte samples with the goal of better defining thermal maturity trends in the basin. Numerous studies have documented lower present-day thermal gradients along the northern basin margin relative to other areas. Refined thermal maturity estimates relate well to present-day thermal gradients and provide insights into heat flow variability. These results will inform continuing development of resources in Uinta Basin.