Geological characteristics and reservoir properties in the unconventional Montney Formation, southwestern Alberta, Canada

摘要

In order to understand the unconventional reservoir characteristics in the Montney Formation, the detailed geological examinations, such as core interpretation, petrographic analysis and the poro-perm measurement (including MICP), have been performed from the Kakwa well, drilled in southwestern Alberta, Canada. The studied Montney section, mostly comprised of fine to coarse siltstone, can be informally subdivided into three distinctive intervals, on the basis of a prominent log marker, inferred to represent a major regional falling and flooding surface. The core description and the log characters have confirmed that the entire section mostly comprises a series of multi-stacked, higher-order parasequences. They are characterized by the coarsening-upward succession, having homogeneous to pinstripe-laminated shale (Facies A), heterolithic siltstone (Facies B), and massive to faintly laminated coarse siltstone (Facies C). The succession is interpreted to be formed in response to a progradational shoreface setting, wherein trace fossils typically show a diminutive and low-diversity suite. The mineralogical analysis has revealed that the cored samples are composed mostly of detrital grains of quartz, feldspar and dolomite with the major cement materials of illite, chlorite and smectite, the ratio of which would be lithofacies-controlled, having a higher proportion of clay and TOC in the more distal facies. Clays, mostly authigenic in origin, commonly occlude primary pores, but disseminated organics contain the pervasive organic nanopores. Pore-throat size distribution shows modal radius (5 to 75 nm) that has a positive correlation with the grain-size variation, but has a negative correlation with respect to the TOC and clay contents. Likewise, the poro-perm system appears to be facies-dependant. The mineralogical and petrographic studies have led to the general conclusions that the poro-perm characteristics are strongly influenced by the pervasive presence of organics and authigenic clays that would fill and occlude the paleopore network. The study results tentatively suggest that the Middle Montney, coarsest and most porous (up to 7%), will have the highest potentiality with respect to the poro-perm system.