Condensate-gas ratio and deep-cut yield in liquid-rich unconventional plays are primarily controlled by thermal maturity and hydrocarbon migration pathways. While regional maturity trends have long been recognized in basin analysis studies, predicting fluid compositional variations at sub-regional to local scales remains challenging, due to stratigraphic and structural complexity. The present study aims at demonstrating geological controls on hydrocarbon compositional variations in the Montney resource play of Western Canada through the integration a large gas analysis dataset within a well-defined stratigraphic framework.
Predicting spatial variations of well productivity and liquid/gas ratio in unconventional plays requires an understanding of the mechanisms and geological heterogeneity that control the present-day distribution of in situ fluids. Gas wetness, iC4/nC4 ratio and other compositional attributes give indirect indications of hydrocarbon thermal maturity, migration and mixing. Based on production data and gas analyses from over 1,500 wells, compositional variations were mapped within individual stratigraphic units over an area of about 3,500 square kilometers. Compositional trends mapped in this study suggest that stratigraphic and structural discontinuities influence fluids distribution in the Montney Formation. Third-order sequence boundaries and internal clinoform architecture, provide the framework controlling facies belts and hydraulic units. Fluids composition produced from different stratigraphic intervals show distinct spatial trends, stressing the need for mapping compositional variations within a well-defined stratigraphic framework. Within individual stratigraphic units, both gas wetness and iC4/nC4 ratios show local departure from the regional maturity trend and the influence of linear discontinuities interpreted as faults. Furthermore, gas-enriched elongated areas consistent with regional gas migration pathways are also observed. The huge amount of well data released by operators in recent years, combined with an improved understanding of the high-resolution stratigraphic architecture of the Montney Formation, allows for an unprecedented review of the geological controls on fluids distribution in an unconventional hybrid play. This knowledge can be used by Montney operators to better predict and target liquid-rich sweet spots at sub-regional and local scales and as a conceptual analogue for other unconventional hybrid plays.