Evaluation of Clay Mineral Distribution Within the Bute Inlet Turbidity System, British Columbia, Canada

Abstract

Reservoir quality is defined by its hydrocarbon storage capacity and deliverability which, are fundamentally controlled by porosity and permeability, respectively. These important parameters determine the economic value and development plans for oil and gas fields. These pore-scale attributes are initially controlled by depositional and diagenetic processes that commonly act together to determine final reservoir qualities. Although there are a significant number of individual studies regarding pore-scale reservoir quality controls of particular fields and formations, only a few of these studies attempt to predict reservoir quality by way of linking depositional processes to early diagenetic pathways.

This case study will be the first to investigate the overall distribution of detrital clay content within an active turbidity system in an attempt to understand initial depositional and early diagenetic processes and controls for prediction of reservoir quality. The Bute Inlet is an 80km long and 4km wide fjord system along the southwestern coast of B.C, Canada in water depths of up to 660m. The depositional system is dominated by a single sinuous channel 45km long that can be up to 90m deep and shaped by quasi-monthly turbidity currents. Repeat multi-beam mapping, acoustic Doppler current profiler moorings and bed sediment cores were collected across the fjord. The Bute Inlet submarine channel is the first where sedimentation and flow properties of turbidity currents have been measured and analysed from their initiation at a delta front to their dissipation across the terminal lobe.

The deposits were sampled by way of box cores (20), piston cores (3) and sediment surface grabs (19) throughout the Bute Inlet in an attempt to characterise general sediment type, clays, flow properties, and overall distribution. The turbidity system is sourced from Precambrian metamorphics (orthogneiss), Triassic volcanics and Cretaceous quartz granodiorites. Results indicate that the overall mineralogy is of texturally immature sands composed of plagioclase, amphibole, chlorite, illite/biotite and locally, vermiculite, all consistent with source rock compositions. Further studies include clay fraction investigations and treated XRD runs. This is followed by a discussion of the possible implications of detrital clay distribution on early diagenesis and evolution of pore-scale attributes of the deposits.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018