Doctor of Philosophy
Burns A. Cheadle
University of Western Ontario
The Second White Specks is an unconventional shale play in the Western Canada Foreland Basin, endowed with over 450 billion barrels of light oil in place. Inconsistent production performance, however, has hindered its economic viability as a resource play. One potential explanation for erratic production behavior, on local and regional scales, is heterogeneous distribution of retained oil charge in the source rock. This study focuses on the analysis of geochemical properties and thermal history of the organic matter to assess lateral variability in generated hydrocarbon in the Second White Specks.
The methodology comprised characterization of the organic matter integrating organic geochemistry and basin modeling. Rock-Eval and organic petrography determined thermal maturity, paleoenvironmental conditions, kerogen type and hydrocarbon generation. Because exhumation magnitude is a critical input in the basin models, and previous results are disparate and uncertain, exhumation magnitudes were estimated across the study area, using a robust and reproducible compaction method. Finally, 1-D and 2-D basin models integrated borehole temperature, thermal maturity, kerogen data and exhumation estimates.
Geochemical analysis reveals the Second White Specks is rich in organic matter with high generation potential. The kerogen is type II, dominated by liptinite macerals with secondary vitrinite and inertinite components. Altered bituminite indicates intense bacterial degradation. The organic matter richness decreases with thermal maturity because of hydrocarbon generation, although enrichment in the center of the basin suggests local enhanced preservation. The source interval in most wells in the regional “oil window” fairway is thermally mature, and modeling shows generation started in the Paleocene. Two wells, however, exhibit anomalous characteristics that provide insights into local charge variability. In one case, the organic matter is inexplicably immature despite close proximity to a thermally mature well. In the other case, variability in heat flow delayed the onset of hydrocarbon generation, resulting in anomalously low charge.
The estimated exhumation exhibits the expected general trend of increase toward the deformation front. The high lateral resolution provided by this study, however, revealed an unexpected local pattern suggesting possible control by basement structures.
Summary for Lay Audience
The Second White Specks is a shale play in the Western Canada Foreland Basin. Shale plays are petroleum source rocks, from which unexpelled hydrocarbons can be extracted with the use of hydraulic stimulation. The Second White Specks has not been significantly developed because of inconsistencies in the hydrocarbon production. The volume of produced hydrocarbons can vary by several orders of magnitude in adjacent wells, and the causes are not understood.
This work focuses on the study of the organic matter in these rocks, with the purpose to determine if there are geochemical variations that affect the hydrocarbon generation, resulting in production performance inconsistencies. The methodology consisted of the characterization of the organic matter from samples taken in petroleum wells to determine paleoenvironmental conditions, organic matter type, thermal maturity, and hydrocarbon generation. One novel aspect of this work involved creating a robust and consistent model of uplift and erosion of the overlying strata that occurred following the development of the Rocky Mountains adjacent to the study area. These exhumation estimates, along with data related to the temperature history of the Second White Specks, were integrated into basin models that portray the burial and thermal history.
This study found two anomalies that may contribute to the unpredictable production performance. There is one well that shows evidence that the organic matter has not generated hydrocarbons, located close to another well that has generated hydrocarbons. The potential reasons for this anomaly are discussed, but further investigation is required. Furthermore, variability in the heat flow resulted in an area where hydrocarbon generation began later than other wells in the area. Because of the late generation and the lower temperature, the hydrocarbon generation in this zone is significantly less than the surrounding area. These findings contribute to the understanding of the spatial variability of maturity and consequently may assist to better predict the production performance.
Aviles, Mailyng Angelica, "Organic geochemistry, organic petrography and basin modelling of the Upper Cretaceous Second White Specks and Upper Belle Fourche alloformations in the Western Canada Foreland Basin" (2021). Electronic Thesis and Dissertation Repository. 7903.