Stable Isotopes of Clay Minerals from Autoclave Tests of Oil Sands: Implications for Clay Formation during Steaming of Alberta Clearwater Oil Sands

Authors

Shaoneng He, Nanyang Technological University, Singapore
Fred J. Longstaffe, Western UniversityFollow
Zhihong Zhou, Alberta Innovates

Document Type

Article

Publication Date

2019

Volume

104

Journal

Applied Geochemistry

First Page

202

URL with Digital Object Identifier

https://doi.org/10.1016/j.apgeochem.2019.04.001

Last Page

209

Abstract

In an effort to evaluate mineral-water isotopic exchange during cyclic steam stimulation (CSS), solutions and<2 μm berthierine-dominated solids from the Clearwater Formation oil sands of Alberta, Canada were analyzed for stable isotope compositions before and after reaction in autoclaves for 1008 h at 250 °C. There was no significant change in solution δ¹⁸O and δ²H, which is consistent with the high water/mineral ratio used in the experiments. The solids showed a marked decrease in both δ¹⁸O and δ²H following the experiments. Pre-run solids have δ¹⁸O of +9.5 to +12.9‰and δ²H of −114 to −113‰, whereas post-run solids have δ¹⁸O of −4.7 to +2.1‰ and δ²H of −147 to −128‰. Neither oxygen- nor hydrogen-isotope equilibrium was established between the solids and the solutions. Calculation suggests that oxygen-isotope exchange (44–58%) was greater between the solids and the solutions than was the case for hydrogen isotopes (23–50%). We propose that this behaviour resulted from partial inheritance of the pre-run berthierine structure during formation of the post-run smectite, chlorite-smectite and chlorite. This process confounds the use of clay mineral stable isotope compositions as a temperature indicator of in situ steam/steam condensate interaction with oil-sands reservoirs. The results also suggest an additional mechanism by which new clay minerals can be formed during CSS-related, artificial diagenesis.