Since 2012, horizontal wells at the Saleski Pilot are operated with cyclic steam injection and production, recovering bitumen from the naturally fractured Grosmont carbonate reservoir. A recent geochemical characterization study indicates distinctive vertical variation in fluid compositions within the reservoir. The Grosmont is a highly fractured carbonate rock. Targeted production horizons in this reservoir are Grosmont C (20 m pay) and Grosmont D (30 m pay) units, which are separated by a laterally extensive, 1-2 m thick Marl. The Marl is partially oil saturated, interlaminated with green shale, and fractured. It is indistinguishable by core observation whether the Marl layer is a barrier or a baffle for fluid flow. The geochemical bitumen characterization provides indications to address this question.

For the Saleski Pilot project, a number of bitumen samples were extracted from vertical cores to determine the molecular composition of the bitumen in place and to identify biomarkers for production correlation. There is evidence that the oil in Grosmont C and D units originated from the same source rock. However, the observation of biomarker discontinuity between the two units, C and D, indicates the Marl was likely a barrier (no fluid communication) during the biodegradation process. The significant differences in degraded oil compositions above and below the Marl further suggest different conditions lead to independent biodegradation processes in each unit.

Continuous production samples were taken from Saleski Pilot wells (both in Grosmont C and D units) and analyzed to allocate production intervals. The results have shown evidence of mass communication between the two units, which suggests the Marl is being a baffle rather than barrier during thermal operation. This finding suggests that the oil was biodegraded in the formation prior to any fracturing.

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