Rocky Mountain Carbonate Reservoirs: A Core Workshop

This core workshop was organized to give geologists from across the country and around the world the opportunity to see a wide variety of carbonate reservoirs as well as some carbonate source rocks from the Rocky Mountain region. Cores displayed at the workshop range in age from Cambrian to Cretaceous and come from a number of the major oil-producing basins in the Rocky Mountains. Depositional facies represented in the cores range from sabkhas and tidal flats through algal and coral buildups to relatively deep water chalks. Dolomite and evaporite minerals are important in approximately half the cores described; the others are dominantly limestone. Porosity of many different types is discussed. Diagenesis, or lack of it, has played a major role in forming virtually all the reservoirs. Thus, the workshop offers the chance to observe and study a wide variety of depositional and diagenetic textures in a number of economically important rock units.
Sedimentology of a Carbonate Source Rock: The Duvernay Formation of Alberta, Canada Available to Purchase
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Published:January 01, 1985
Abstract
The Duvernay Formation is an organic-rich basinal carbonate succession that has provided most of the petroleum presently found in Leduc-age reefs of east central Alberta. It accumulated under deep-water anoxic bottom conditions that favoured the preferential preservation of organic material. This, together with slow sedimentation rates resulted in a rich (up to 17 wt. percent TOO source rock. Rich source intervals occur as dark black laminites interbedded on a fine scale with leaner bioturbated lime mudstones. Intervals sampled had very low amounts of insolubles, rendering them true carbonate source rocks.
Comparison of reservoir oil Level of Organic Metamorphism (LOM) and source rock LOM suggests that long distance secondary migration has taken place within the basin with distances on the order of 100 kms (60 miles) being indicated. Migration took place through a dolomitized aquifer underlying the Leduc reefs, with the amount of petroleum entering each reef being dependant on the nature of vertical permeability barriers separating the two. A portion of the reef-platform system conforms to a classical example of spill-point updip displacement of petroleum, but other portions do not, and an understanding of the mode of migration into these buildups is important. Furthermore, it seems conceivable that the Duvernay Formation could have contributed significantly to hydrocarbons presently found in the giant Athabasca and associated tar sands. The multidisciplinary approach embodied in this study has resulted in a better understanding of carbonate source rocks in general, as well as the apprection of a more fully integrated exploration model.