--> Geological Controls on Sweet Spots Within a Laterally Extensive Shoreface Sandstones, Albian Wilrich Member, Spirit River Formation, West-Central Alberta

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Geological Controls on Sweet Spots Within a Laterally Extensive Shoreface Sandstones, Albian Wilrich Member, Spirit River Formation, West-Central Alberta

Abstract

Progradational, wave dominated shoreline sandstones forming extensive, laterally continuous sandstone reservoirs often have sweet spots that is not revealed by net sandstone maps and cross sections. Within the sandstone sheet, as it was deposited at different times, mineral composition and depositional processes likely varied slightly resulting in subtle lateral changes in porosity, pore types and thereby permeability of the sandstones. The studied Wilrich Member is a wave dominated, mainly progradational and very slightly aggradational, shallow marine shoreface that prograded northward along the axis of the foreland basin following a maximum transgression of the Moosebar Sea. The subsurface study area (T46 to 57 and R14 to 22 W5) is located within the Alberta Deep Basin in west-central Alberta. The Wilrich is an emerging highly economic liquids rich tight sandstone play hosting a continuous hydrocarbon accumulation. Lateral changes in composition, sedimentary processes and trace fossil assemblages were documented in cores examined within the study area, together with identification of key sequence stratigraphic surfaces. Using the cored wells, sedimentary facies and stratigraphic surfaces were picked and correlated between wells based on the petrophysical well log response, showing subtle variations in facies thicknesses, which together with the identification of sequence stratigraphic surfaces allows for the subdivision of the Wilrich shoreface sandstone sheet into several parasequences. The sandstone sheet formed as laterally northward accreting shorefaces, regressive surfaces of marine erosion and transgressive surfaces separate the shoreface sandstone sheet into several parasequences. Within the northern and youngest portion of the sandstone sheet there is a greater content of chert granules and pebbles likely reflecting a change in mineralogy and to higher permeability. This study shows how the identification of shorefaces facies and their variation with key sequence stratigraphic surfaces can unravel the internal stratigraphy of a laterally continuous sandstone sheet in order to characterize the different parasequences by the variation in mineral composition and sedimentary processes and thereby identify sweet spots within a tight sandstone reservoir.