Investigating Sequestration Potential of Carbonate Rocks during Tertiary Recovery from a Billion Barrel Oil Field , Weyburn , Saskatchewan : the Geoscience Framework ( IEA Weyburn CO 2 Monitoring and Storage Project )
Introduction In Western Canada the application of CO2 injection for enhanced, ‘tertiary’ oil recovery is a relatively recent addition to the arsenal available to reservoir engineers. The first successful application of CO2 as a miscible fluid in Western Canada began in 1984 at Joffre Field, a Cretaceous marine siliciclastic reservoir in southern Alberta. A significant portion of the remaining proven conventional oil reserves in Western Canada, however, reside in large mature Paleozoic carbonate fields, such as the Mississippian Weyburn Field in SE Saskatchewan (Figure 1). In combination with economically dictated tertiary recovery schemes, these large fields could provide attractive geologic sites for future sequestration of greenhouse gases. An immediate challenge to geoscientists is to assess the ability of these geologic containers to store CO2 for geologically significant lengths of time.
Sedimentology, Ichnology, and Paleoecology of the Mississippian Midale Carbonates in the Williston Basin, Radville Area, Saskatchewan: Preliminary Interpretations
Abstract Abundant and diverse trace fossil suites are characteristic of fully marine, deeper subtidal, carbonate environments, yet relatively few studies have focused on the ichnology of carbonate depositional environments. Integration of ichnology, paleontology, and sedimentology can provide a powerful approach to paleoenvironmental reconstruction. The Midale carbonates in the Radville area consist of two facies associations: 1) a muddy facies association and 2) a bioclastic facies association. Vertical distribution and relative thicknesses of these facies associations and diversity of associated ichnofossil assemblages indicate deposition in a relatively deep subtidal, quiescent outer-to-inner shelf marine environment which was episodically influenced by storm activity. Thick bioturbated dolomitic mudstones are dominant components of the muddy facies association. Interbedded thinner coarse bioclastic units represent episodic higher-energy storm events which interrupted fairweather mudstone deposition. Trace fossils in this succession are typical of the Cruziana ichnofacies. Two assemblages were recognized: 1) a distal Cruziana ichnocoenose, and 2) a proximal Cruziana ichnocoenose. The distal Cruziana assemblage consists of Planolites, Chondrites, Rhizocorallium, Teichichnus, Thalassinoides, Asterosoma, Zoophycos, Helminthopsis, Subphyllochorda, Palaeophycus and locally, Siphonichnus. The proximal Cruziana assemblage includes predominant Planolites and Chondrites, few Rhizocorallium, Asterosoma, Teichichnus and Palaeophycus, as well as rare Anconichnus, Zoophycos and Phycodes. Also, rare escape traces (fugichnia) are associated with the bioclastic units. The vertical distribution of bioclastic facies associations show overall coarsening-upward and thickening-upward trends. At least six major coarsening-up units are recognized on the basis of depositional textures and trace fossil assemblages. These subtidal units show an overall shallowing-upward trend which culminate in restricted intertidal deposits near the top of the Midale carbonates.
VIRDEN ROSELEA AND NORTH VIRDEN FIELDS MANITOBA
ABSTRACT The Virden-Roselea and North Virden fields are located on the northeast flank of the Williston Basin. They were discovered in 1953 and development is still in progress. The reservoir rocks are largely stable shelf, clastic limestone members of the Mississippian Lodgepole formation. A combination of: (1) local structural warping and (2) permeability barriers, from secondary effects, have formed the trap. These secondary processes in order of occurrence are: (1) leaching of limestone at the post-Mississippian unconformity. (2) dolomitization of the leached limestone during initial evaporite deposition of Amaranth (Middle Jurassic) age, resulting in a major decrease in permeability and a minor decrease in porosity. (3) anhydrite infilling during later Amaranth deposition resulting in reduced porosity and locally in reduced permeability. Within any separate accumulation each individual permeable zone in the reservoir has its oil water interface which, once up dip from edge water, becomes the base of the permeable zone and thus follows the structure. It is probable that the main source of the oil is from the down dip shale and argillaceous limestone facies of the clastic limestone reservoir rock.