TIGHT GAS RESERVOIR CHARACTERIZATION IN MONTNEY FORMATION, NORTHEASTERN BRITISH COLUMBIA, WESTERN CANADA

Abstract

The Montney Formation is a primary focus of unconventional gas reservoir in northeastern British Columbia, Western Canada. This study presents the sedimentology and ichnology, Rock-Eval geochemistryand reservoir potential, C13 and O18 isotopic composition, and magnetostratigraphy correlation of the Montney Formation in the Fort St. John area (T86N, R23W and T74N, R13W), northeastern British Columbia. The Montney Formation consists of siltstone with subordinate interlaminated very fine-grained sandstone. Five lithofacies association were identified in the study interval: Lithofacies F-1 (organic rich, wavy to parallel laminated, black coloured siltstone); Lithofacies F-2 (very fine-grained sandstone interbedded with siltstone); Lithofacies F-3A (bioturbated silty-sandstone attributed to the Skolithos ichnofacies); Lithofacies F-3B (bioturbated siltstone attributed to Cruziana ichnofacies); Lithofacies F-4 (dolomitic, very fine-grained sandstone); and Lithofacies F-5 (massive siltstone). The depositional environments interpreted for the Montney Formation in the study area is lower shoreface through proximal offshore to distal offshore settings. Rock-Eval data (hydrogen Index and Oxygen Index) shows that Montney sediments contains mostly gas prone Type III/IV with subordinateType II kerogen, TOC ranges from 0.39 – 3.54 wt% with a rare spike of >10.9 wt% along the Montney / Doig boundary. The vitrinite reflectance data and Tmax shows that thermal maturity of the Montney Formation is in the realm of ‘peak gas’ generation window. Magnetostratiphy analyses from this study shows that the Montney Formation in the study area exhibits normal and reverse polarity intervals across the Upper Montney and Lower Doig formations boundary. The geomagnetic polarity correlation matched known intervals of the Triassic GPTS at 245 Ma. The results suggest that Lowermost Doig phosphatic zone (Montney / Doig boundary) occur within a single magnetostratigraphic interval characterized by a coplanar Trypanites – Glossifungites demarcated discontinuity surface, interpreted herein as a regionally correlatable surface.