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New Insights for Energy Exploration
Developing Better Ways to Visualize Basin Evolution
With the support of a grant from the American Chemical Society's Petroleum Research Fund, Lyal Harris, professor at Quebec's Institut National de la Recherche Scientifique (National Institute of Scientific Research), is leading a team that is developing more effective ways to study the formation and subsequent deformation of sedimentary basins and underlying metamorphic basement rocks. In the process, he's taking the capabilities of existing geological research to the next level, developing improvements that may enable companies that explore for hydrocarbons and minerals to be more efficient.
Learning from models
Over time, geologists have developed increasingly sophisticated methods for understanding the formation of geological formations with complex structural geometries. Analog simulations under controlled laboratory conditions, such as sandbox modeling, offer relatively inexpensive, concise techniques that aid explorationists and researchers' interpretation of brittle structures in sedimentary basins and fold and thrust belts.
The majority of analog modeling research done to date has relied on sandbox techniques, Harris explains. Simulations using a high-acceleration centrifuge, however, offer better ways to study some dynamic geological systems. Examples include the studies of basin formation and inversion where the focus is on understanding body forces resulting from density differences (e.g., where shale or salt undergo ductile deformation and migrate due to density differences with overlying rock layers). Other examples include situation in which contrasts in the mechanical properties of different layers in a sedimentary package control the development of folds, or where ductile deformation of underlying metamorphic basement affects folding of overlying sedimentary strata.
Cross-section of a centrifuge model simulating upright to hinterland-verging folds in a layered sedimentary sequence (blue modeling clay and pink silicone putty microlaminates) during channel flow of ductile basal layers (yellow, red and green lower viscosity silicone putties). Some layers are doped for better imaging on CT scans. Model by Chris Yakymchuk (Queens University), a summer student in the INRS-ETE laboratory.
Scanning the possiblities
Traditionally, the analysis and study of both sandbox and centrifuge models consists of manually sectioning vertical slices for two-dimensional (2-D) structural interpretation. This only allows the final geometry of sandbox models to be studied and cutting centrifuge models may affect the development of subsequent structures. X-ray computed tomography (CT scanning) is used in the analysis of sandbox models. Harris and his team are, however, exploring new ways to use this technology to deliver more useful analyses of centrifuge models. "CT scanning has not been commonly used to analyze centrifuge analog models," he observes, "largely due to problems in imaging thinly layered 'microlaminates' of modeling clays and silicones used to simulate layered sedimentary rocks."
The group has been working to improve the science of creating and analyzing analog models in a number of ways. For example, his team is developing a range of modeling materials with diverse rheological properties. "In previous modeling," the researcher notes, "especially in centrifuge testing, researchers only used a limited range of materials, and we've been able to extend range that to include new materials to simulate a range of different rock types."
Harris' team, which includes graduate and undergraduate students, a postdoctoral fellow and a summer research fellow, is also optimizing CT-scanning and visualization procedures to image the evolution of fine structural details in the models through time, in both 2-D and 3-D; meanwhile, other team members are creating software to enable semi-automated layer extraction from models.
Seismic shifts in insight
The group's results to date have been highly encouraging, says Harris. "Centrifuge modeling using the new materials and techniques we have developed in this project," he explains, "has proven to be a powerful technique for studying the '4D' evolution of numerous structures in sedimentary basins and fold-thrust belts. Furthermore, the new techniques and processes allow the study of such factors as isostatic adjustments during erosion and post-orogenic extension, including the effects of channel flow in underlying ductile metamorphic basement, the interaction between diapirs and mobile shales with faults, and effects of basement heterogeneities on the geometry of structures in overlying strata, etc."
"This project has enabled more information to be extracted from analog models to assist in field and seismic interpretation in petroleum exploration," Harris notes. "Our results also have applications for mineral exploration and general structural geology research."
In the process of scaling geologic structures to a size that can be researched in a laboratory, Harris observes, "we clearly can't recreate all the complexities and factors that exist in nature. By simplifying these structures and analyzing them, we're able to reexamine long-held assumptions, and to develop new ideas about what we can expect to find and how to interpret structures in the field." Harris is currently seeking new research contracts using the INRS-ETE physical modeling and CT-scanning facilities.
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