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.
Subtle Seals and Fluid-flow Barriers in Carbonate Rocks
~~ Carbonate rocks that contain microporosity or unconnected molds or vugs can act as “subtle seals” (porous barriers to hydrocarbon migration). Subtle seals may contain mobile water, and may have porosities exceeding those in the reservoir. The common denominator of such seals is small pore-throat size and consequent high breakthrough pressure, i.e., the hydrocarbon-phase pressure required to allow secondary migration. Chalks, diatomites, and finely sucrosic dolomites are some rocks that can act as subtle seals. These rocks are composed of well sorted, mud-sized particles, and thus have the requisite high porosity and small pore throats. Weyburn Field in Saskatchewan is an example of a field sealed by such rocks. Other possible subtle seals include rocks that have been “chalkified” by exposure to freshwater phreatic and vadose diagenesis. Wackestones or mudstones with small pore throats and unconnected molds or vugs may not only serve as high-porosity seals, but may also have high resistivities and appear to be pay from log-calculated water saturations. Cement-filled fractures also can act as barriers to fluid flow, while not much reducing porosity on the scale of cores or well logs. Subaerial cementation, teepee structures, and sheet cracks create low permeability interbeds in otherwise permeable formations at Cottonwood Creek Field, Wyoming. These interbeds have dramatic effects on fluid flow in the Permian Phosphoria reservoir in this field.
Geological, mineralogical and chemical characterization of Devonian kaolinite-bearing sediments for further applications in the ceramic (tiles) industry in La Paz, Bolivia
Clay minerals are widely distributed in Bolivia; among them, illitic clays are most common in the Altiplano where they are mined for use in the ceramic industry that has been growing in the last few years. In addition to illitic sediments, kaolinitic sediments have been recently discovered in sedimentary units in the Bolivian Altiplano. Residual ball clay occurrences in Devonian sedimentary units were studied as part of this work. Geological mapping and geophysical studies (ERT and GPR) were done for better understanding the origin of the deposits and were part of a preliminary study of the mineral potential to define the relationship with the host rock. Chemical and mineralogical techniques such as X-Ray Diffraction, Scanning Electron Microscopy and Inductively Coupled Plasma analyses were performed in samples from the studied area to verify the presence of kaolinite. Atterberg limits and behaviour of the raw material in ceramic specimens supported by chemical analyses show that this material is suitable for manufacturing tile ceramics. This study provides fundamental knowledge for deposit exploitation and future generation of an alternative source of employment for the inhabitants of Micaya.