Abstract

Pore throat size distribution (PSD) is a fundamental characteristic that influences the large-scale petrophysical properties and reservoir quality of tight rocks in unconventional plays. Here, we use PSD data obtained from mercury intrusion capillary pressure (MICP) and nuclear magnetic resonance (NMR) measurements of Montney tight-gas siltstones to investigate the relationship of pore throat size to several other petrophysical attributes including porosity, permeability and total organic carbon (TOC) content. We find that pore size correlates positively with porosity but negatively with TOC. Additionally, we evaluate methods to estimate absolute permeability and gas relative permeability from MICP data and compare the modeled results with measured data. Estimates of absolute permeability using peak pore throat diameter in the bundle of tortuous tubes model are found to closely match measured permeability values when a tortuosity factor of 3 is applied. Estimates of relative permeability using MICP data in a modified Purcell approach are found to be comparable to measured values only if gas is considered as the wetting phase rather than the non-wetting phase. Hydrocarbon-wet reservoir conditions and the negative correlation of porosity with TOC are both consistent with the presence of solid bitumen/pyrobitumen as a pervasive pore-filling phase (Wood et al., 2018, this issue).