Abstract

This work presents results from an ongoing laboratory study investigating pore network characteristics and matrix permeability of selected intervals within the Montney Formation (Western Canada). The primary objectives are to: 1) compare different laboratory-based methodologies for determination of porosity and matrix permeability; 2) characterize the pore network attributes (porosity, pore size distribution (PSD), dominant pore throat size, specific surface area) and matrix permeability of the selected target intervals; and 3) analyse the effects of different controlling factors (anisotropy, effective stress, bitumen saturation) on matrix permeability. Eight selected pairs of core plugs, drilled vertically and horizontally, are analysed in this study. These core plugs are obtained from a vertical interval of 15 m within the fine-grained intervals of the Upper Montney Formation in British Columbia (Canada). The experimental techniques used for characterization include: bitumen reflectance (BR_o); Rock-Eval pyrolysis; helium pycnometry; Archimedes, caliper and 3D laser scanner analyses; low-pressure gas (N₂) adsorption; pulse-decay; and crushed-rock gas (N₂, He) permeability measurements.

Excluding one of the samples (a laminated vertical core plug): 1) the slip-corrected pulse-decay gas (N₂) permeability values (measured at effective stress of 15.8 MPa) and apparent crushed-rock gas (He) permeability values generally increase with increasing porosity (4.2–8.1%), ranging from 1.4 · 10⁻⁵ to 8.6·10⁻⁴ mD: and 2) the slip-corrected pulse-decay (N₂) permeability values (1.2·10⁻⁴–8.6·10⁻⁴ mD) are consistently higher than apparent crushed-rock (He) permeability values (1.4·10⁻⁵–1·10⁻⁴ mD). Pulse-decay (N₂) permeability values measured parallel to bedding (horizontal core plugs) are consistently between 10% and 25 times higher than those measured perpendicular to bedding (vertical core plugs). Based on a single pair of laminated core plugs analysed in this study, the degree of permeability anisotropy (ratio between parallel and perpendicular permeability values) appears to be significantly higher for the laminated core plugs (up to 25 times) than bioturbated core plugs (up to 3.5 times). Compared to pulse-decay (N₂) permeability values, there is a minimal discrepancy (considering the maximum experimental error margin) between the crushed-rock gas permeability values that were measured on pairs of horizontal/vertical core plugs after crushing/sieving. In a gross sense, slip-corrected pulse-decay (N₂) permeability values decrease with increasing bitumen saturation.

Applying multiple analysis techniques on a selected suite of core plugs and crushed-rock materials derived from them, this study provides: 1) valuable insight into the causes of observed variations in porosity/permeability values obtained from laboratory-based techniques; and 2) an integrated description of pore network characteristics and matrix permeability for selected fine-grained intervals within the Montney Formation.