BIOTURBATION INFLUENCE ON RESERVOIR QUALITY: A CASE STUDY FROM THE LOWER TRIASSIC MONTNEY FORMATION OF THE WESTERN CANADIAN SEDIMENTARY BASIN

The Lower Triassic Montney Formation is one of western Canada’s most lucrative unconventional hydrocarbon plays, but many geological aspects are poorly understood. Throughout many areas of the very fine-grained formation, alternating layers of bioturbated and unbioturbated facies are present. Bioturbation greatly influences the distribution of permeability and porosity by altering pore-throat distribution and concentrating cementation and dissolution processes during diagenesis. These small-scale features can significantly impact reservoir properties. To better understand how bioturbation impacts the vertical and horizontal permeability of the Upper Montney Formation, the Shell Groundbirch 16-2-78-22W6 was investigated. The core was logged and permeability was measured every 10 cm along the 182 meter core, using a Pressure Decay Permeameter. Trace fossil assemblages were identified and are dominated by Phycosiphon with subordinate Teichichnus and Cylindrichnus. Within each bioturbated zone, individual traces can be isolated to specific beds or extend to multiple bedsets, with bioturbation intensity reaching up to 100%. Biogenetically mediated siltstone possessed permeability ranging from 0.2 to 1.0 md, whereas non-bioturbated, planar laminated siltstone possessed permeability ranging from 0.01 to 0.08 md. Although this permeability is low, the order of magnitude difference between bioturbated and non-bioturbated zones suggests a dual-porosity flow media model. It is hypothesized that the bioturbated zones have higher permeability due to the facies being relatively more homogeneous as a result of bioturbators disrupting original grain alignment and sedimentary structures, that would act as flow barriers if left unaltered. Understanding the influence of bioturbation on permeability and porosity within the Montney Formation will help provide ichnological models for other unconventional, fine-grained reservoirs around the world.