Introduction to September Focus: Prairie Provinces

Nothing has contributed more to the accelerated advancement of Canada over the past several decades, than the exploration and mining of primary resources. And beneath the rich soil of the Prairies Provinces lie some of the greatest natural resources of our country - vast mineral deposits and oil and gas fields. The region is of fundamental relevance for Canada, as Alberta and Saskatchewan contain the country’s largest petroleum resource - the Athabasca oilsands, Saskatchewan has the largest reserves of potash and high-grade uranium, and one of the largest diamond-bearing kimberlite fields in the world, and Manitoba is well known for its diverse world-class mineral deposits.

Most operations in the oil and gas exploration, development and production, and in the mineral exploration, extraction and processing, require interconnecting concepts from geoscience, engineering, mining and other disciplines. From the humble beginnings of our mining and petroleum industries in the mid-18th and mid-19th centuries, arose some of the strongest in the world, Canada being now one of the world’s leading mining and oil producing countries. The great diversity and complexity of the region’s geology, and types of hydrocarbons and minerals present, prove that this worldwide success is not born in a vacuum, but it is the result of interaction and expertise of many talented and dedicated professionals educated in Canada and abroad, researchers and students, their hunger for knowledge, their capacity to take risks, their combined effort for the progress of science and technology, and their determination to build something for the next generations.

This special section of the Recorder highlights several contributions and includes an overview of the exploration history in the Prairie provinces, and three articles that will give the readers an understanding of some of the current geophysical practices in subsurface characterization.

In the paper leading off the section, “Geoscience across Canada – resource exploration in the Prairie provinces”, Hayes provide a historical overview of the resource exploration in the Prairies during the 20th century, from the discovery and delineation of big hydrocarbon fields in the Plains, Foothills and Deep Basin regions, to findings of other big resources such as diamonds and potash and related salts in Saskatchewan. He presents exploration alternatives to the decline of the hydrocarbon and potash exploration at the beginning of the 21st century, such as exploration for water, lithium, helium and geothermal resources.

The next paper “Methods of fault detection with geophysical data and surface geology” by Schulte et al. explores various methods for fault detection using geophysical and geological data, and how they need to be integrated to obtain a more complete picture. In the first part, the authors focus on the application of seismic techniques for fault recognition, from seismic imaging of large-scale faults, to subtle faults identification using properties contrast obtained from seismic inversion, and automatic detection of discontinuities from geometric attributes such as coherency, curvature and flexure analysis. In the second part, we see how the gravity and magnetic methods respond to the lateral variations in the rock properties, and therefore can help in the detection of steep discontinuities. Examples of magnetic data showing subtle lineaments are presented from central and southern Alberta. The third section describes the use of topographic maps and surface geology to investigate surficial lineaments and their correlation with basement faults and fractures. The authors show how major joint sets observed throughout Western Canadian Sedimentary Basin are possibly controlled by tectonic stress fields affecting the basement.

In “Application of Full Zoeppritz AVO inversion for delineating porous sand geobodies over Aquistore seismic survey”, Gerami presents a quantitative interpretation workflow, showing the application of seismic inversion and lithology prediction over a deep saline CO₂ storage reservoir in Saskatchewan. Inversion results from the three-term Aki-Richards approximation and full Zoeppritz methods were compared in order to determine which method works best for strong contrast layers. The superior results from the full Zoeppritz method were used to generate the lithology and probability volumes for each litho-class, based on probability density functions using P-impedance and porosity logs, as well as the porosity within the sand units. Sand geobodies were extracted using the combined porosity and sand probability cubes.

In the section’s final paper, “What is the value of a VSP and why it should be modeled?”, Schweigert and Schulte show how vertical seismic profile (VSP) data can provide information about the rock properties such as velocity, attenuation, and anisotropy, and how can be used in advanced processing and interpretation such as elimination of multiples, improving the velocity model for time-to-depth conversion, evaluation of macro-scale anisotropy, understanding the AVO response and tuning effects, and high frequency 3D imaging around from borehole. For a particular geometry, modeling of the VSP aids in the determination of the coverage area, critical angle for maximum offset, incident angle range for AVO analysis, and azimuth range for anisotropy. The authors also discuss the potential use of distributed acoustic sensing VSP to provide imaging along the horizontal portion of the borehole, and of time-lapse VSP to enhance oil recovery by monitoring fluid changes, stress effects in reservoir and caprock, and hydraulic fractures geometry.

As these contributions demonstrate, technical challenges associated with understanding subsurface geologic structure and the properties of rocks are complex and diverse, and require a combination of new ideas, advanced algorithms, problem-dependent workflows and cross-disciplinary knowledge. We hope that these articles will be a useful reference for the geoscientists involved in regional or local exploration studies, or in detailed reservoir evaluation of existing fields.