Producing Oil Sands Thin Sections for Reservoir Characterization

Summary Reservoir quality of oil sands can be observed directly in thin sections. Direct observation of important geological factors that control reservoir quality include: texture, grain size and sorting; grain orientation and packing; and any cementation if present. Additional observations include silts and clays, clay infilling of pore spaces, and size and shape of voids. Thin sections provide a means of detecting secondary physical/chemical processes that have altered the primary depositional texture which affects the final geometry of the pore structure. Geologic factors are known to directly impact reservoir porosity and permeability. As part of a large 2D to 3D case study, thin section analysis was carried out on the pore to grain scale of Upper McMurray Formation oil sands. Samples used were obtained from a non-industry outcrop and non-industry cores with no industry funding in order to ensure fair practice. Oil sands, as observed under the microscope, exhibit a 2D fabric which is the result of the components including: primary grains; fines such as silt and clay; bitumen; and voids along with their spatial relationship. Going from 2D to 3D, the fit of oil sands fabric determines flow through the reservoir during recovery. The routine method of producing thin sections in unconsolidated material was employed for the oil sands samples with few modifications applied in order to identify an approach that would least alter the bitumen contained in the samples. Due to the unconsolidated nature of oil sands reservoirs, application of conventional thin section methods must be modified and tailored for the unique nature of the oil sands. This short methods paper discusses producing thin sections from non-frozen samples and common artefacts which can occur during production.