Predicting Fracture Porosity Evolution in Sandstone

Stephen E. Laubach, Robert Lander and Linda Bonnell (Research Fellows, The University of Texas at Austin), Jon E. Olson (Department of Petroleum and Geosystems Engineering, The University of Texas at Austin), Julia F. W. Gale, Randall A. Marrett (Department of Geological Sciences, The University of Texas at Austin), co-principal investigators; Jon Holder (Department of Petroleum and Geosystems Engineering), Kitty L. Milliken (Department of Geological Sciences), Dick Larese (consultant), and Robert M. Reed; assisted by John N. Hooker, Leonel Gomez, and Meghan Ward

The continuity of fracture porosity is fundamental to how fractures conduct fluids. It is an increasingly central issue in recovering water and hydrocarbon supplies and geothermal energy, in predicting flow of pollutants underground, in engineering structures, and in understanding large-scale crustal behavior. Researchers at BEG, the Departments of Geological Sciences and Petroleum and Geosystems Engineering, and Geocosm L.L.C. are working to develop an understanding of how fracture growth and diagenetic alteration interact to systematically create and destroy fracture porosity. This cross-disciplinary research will fundamentally advance researchers' understanding of how diversity of natural fracture patterns evolves and enable better predictions of fracture-pattern attributes in the subsurface where sparse sampling is the rule.

As an essential step in a broad study of links between mechanical and chemical processes in opening fractures, researchers will test a new theory of cementation in fractures that predicts fracture-porosity evolution as a function of temperature, surface area, and opening history. The centerpiece of this effort is a study focused on the Piceance Basin of Colorado that combines fracture and diagenesis observations, mechanical and diagenetic modeling, and novel rock-property tests on specially prepared artificial rocks that have cement properties matching those of rocks at various positions along the modeled burial-history curve of a target formation in the basin. This study is supported by a grant from the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy. The research is divided into characterizing fractures and cements, constraining temperature and load conditions, modeling burial history and the diagenetic–fracture pathway, and quantitatively linking diagenesis model results to geomechanical model and scaling observations. Researchers also seek to demonstrate how chemical and mechanical interaction combine to produce aperture, length, and spacing patterns—essential ingredients in understanding the role of fractures in fluid flow in the Earth. In a separate study that has been proposed to the Jackson School, these results may be extended to enable estimation of fracture-opening rates, which will be a significant contribution to understanding crustal mechanics and a constraint on intraplate tectonic processes.

In addition to five published papers, research from this project has been recognized in an AAPG Distinguished Lecture tour (Bonnell), an SPE Distinguished Lecture tour (Laubach), and three invited keynote lectures at international symposia (two by Olson and one by Laubach/Milliken). In February 2004, project leaders organized an AAPG Hedberg Research Conference on the interaction of chemical and mechanical processes in the Earth that featured presentations on many aspects of the research program. The project also won the award for best university presentation at the U.S. Department of Energy Symposium "Flow and Transport: from Pore to Reservoir Scales." Geocosm's Rob Lander presented "Predicting Fracture Porosity in Sandstone," a talk co-authored by Larese, Bonnell, Laubach, Gale, Holder, and Olson. In July, results were also presented to the Fracture Research and Application Consortium, a group of companies that support our research on application of new insights into fractures to petroleum exploration and development.

 

For more information, please contact Steve Laubach, principal investigator. Telephone 512-471-6303; e-mail stephen.laubach@beg.utexas.edu.

July 2005