REGIONAL-SCALE POROSITY AND PERMEABILITY VARIATIONS, PEACE RIVER ARCHAREA, ALBERTA, CANADA

This study examines the large-scale variability of porosity and permea bility of the sedimentary rocks in the Phanerozoic succession in the A lberta part of the Peace River arch-area of the Western Canada sedimen tary basin. The study is based on about 450,000 core analyses at appro ximately 22,000 wells in an area of more than 165,000 km2. Plug-scale porosity and permeability values are scaled up to the well scale by hy drostratigraphic unit, resulting in two sets of about 16,000 values ea ch for porosity and permeability, unevenly distributed both areally an d with depth. The permeability frequency distributions are lognormal f or most of the units or parts of the units. The regional-scale variabi lity of porosity and permeability is quite high, between 1 and 38% for porosity, and 0.001 md and 3 d for permeability. The clastic units of the foreland basin exhibit a relatively high correlation between perm eability and porosity. Several areal trends and patterns are identifie d for groups of hydrostratigraphic units, patterns that change gradual ly from one group to another. It is hypothesized that the observed var iability is caused by the dominance of the Peace River arch, carbonate deposition, or compaction at various times throughout the evolution o f the basin. Based on the predominant controlling factor, the geologic al history can be divided into four periods: arch influence during the Early to Middle Devonian, reefal carbonate-deposition influence durin g the Middle to Late Devonian, passive margin influence during the Lat e Devonian to Middle Jurassic, and orogenic influence since the Middle Jurassic.