Fractures in Carbonates: From Digital Outcrops to Mechanical Models
Published:January 01, 2011
Paul Gillespie, Erik Monsen, Laurent Maerten, David Hunt, John Thurmond, Dean Tuck, 2011. "Fractures in Carbonates: From Digital Outcrops to Mechanical Models", Outcrops Revitalized: Tools, Techniques and Applications, Ole J. Martinsen, Andrew J. Pulham, Peter D.W. Haughton, Morgan D. Sullivan
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Prediction of fractures in carbonate reservoirs represents a very significant challenge. We describe the use of a digital outcrop analogue from faulted and jointed Lower Jurassic rocks from Somerset, U.K., that provides exceptional exposure of fractured carbonates. The aims were to gather high-resolution and exact information about the fracture systems and to understand the mechanics of the fracture development. A 2.5 km section of coastline was digitally captured and built into a high-resolution photorealistic model. Faults were hand interpreted in an immersive virtual reality environment. A line sample of the faults in the photorealistic model compares well with a similar line sample taken in the field.
The photorealistic data also include large bedding-plane exposures of joint systems. The joints were extracted semi-automatically using a combination of image curvature and ant tracking; ground-truthing of the resulting joint map confirms the validity of the interpretation. By using this semi-automatic technique it is possible to digitize far more joints than would be possible for a human interpreter.
The detailed fracture data provide a rich source of data for modelling of fracture systems. However, in order to be predictive in the subsurface, it is not sufficient to have a purely statistical fracture description and so we turn to mechanical modelling. On the assumption that the joint system formed in the perturbed stress system around pre-existing faults, we performed boundary element modelling and were able to match to the joint system in the photorealistic model using an extensional stress regime and fluid-pressure perturbations along the fault plane.
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Outcrops Revitalized: Tools, Techniques and Applications
Outcrops are fundamental to everything we hope to achieve in geological understanding. They are gateways to geological processes, earth history and they help ground-truth remote sensing applications. With increasing resolution of subsurface tools and techniques, one could be forgiven in believing that outcrops have had their day and their utility is less than in the past great eras of field mapping and the development of facies models. This premise is far from the truth and this new SEPM volume illustrates how new analytical techniques are revitalizing outcrops and in the process creating a wealth of new data and fresh geological understandings. In this book you will find a compilation of the growing arsenal of outcrop tools and techniques and a consideration of future developments. This collection of papers, delivered at a SEPM Research Conference on the West coast of Ireland in the summer of 2008, is a smorgasbord of case studies, workflows, modeling, and applications which spans clastic and carbonate settings. Whatever your interest in outcrop geology and its application there is something in this volume for you. If you are seeking guidance for using new outcrop tools, looking for efficiencies in data collection or desiring new insights for old and favorite outcrops, this volume is a must have. This volume also makes an excellent reference or textbook for any group of professionals or students working or studying the new technologies that have allowed new insights from outcrops. We also consider this a superbly timed publication because many new outcrop tools are now becoming mainstream via reduced purchase and operating costs. Once you read this volume, and there are reduced prices for SEPM members and students, please share your new experiences with the authors and editors and help continue the revitalization of our shared and continually surprising outcrop library of the earth.