EFFECT OF BIOTURBATION ON OIL SAND FABRICS AND IMPLICATIONS FOR RESERVOIR QUALITY

Relict biogenic activities in unconsolidated reservoirs, more specifically oil sands, results in modification of inherit sedimentary fabric and textures of the host material increasing reservoir heterogeneities; importantly bioturbation create heterogeneities that alter the host material reservoir qualities including porosity and permeability. Understanding modifications as a consequence of bioturbation and subsequent heterogeneities in oil sand reservoirs is important for the economic success of bitumen recovery through in-situ recovery processes. Standard thin sections were prepared from oil sand samples with bioturbation features and those without obvious sedimentary structures and features. Fabric analysis included both compositional confirming sedimentary structures and features such as bioturbation and vectorial analysis by undertaking detailed petrographic image analysis (PIA). Petrographic image analysis involved 6000 point counts and revealed variations in the relative abundance of oil sand components in the host and bioturbated sections. Importantly, the point count dataset identified the activities of biogenic organism to increase the void component in the oil sand. Variations from bioturbation appeared as alterations in the host oil sand fabric; more specifically, modification in the nature of the skeletal coarse grain components. Sorting was determined from the use of visual comparators of the grain sizes digitized while porosity was determined using binary images of selected region of interest in the host and bioturbated section. Permeability was estimated using the empirical VanBaaren model. Biogenic activities in the study area has resulted in the alteration of the host material in terms of flow and storage capacity increasing porosity and permeability in bioturbated samples. This study is important in that it shows that petrographic image analysis is an excellent technique for rapid characterization of features and textures allowing for heterogeneities as a consequent of bioturbation which would be essential in unconventional play development as can aid in locating sweet spots for injector-producer SAGD well placement and optimizing recovery.