About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

Environmental Geosciences (DEG)

Abstract

DOI:10.1306/eg06011212001

Predicting rock strength variability across stratigraphic Previous HitinterfacesNext Hit in caprock lithologies at depth: Correlation between outcrop and subsurface

Elizabeth S. Petrie,1 Tamara N. Jeppson,2 James P. Evans3

1Department of Geology, Utah State University, Logan, Utah; [email protected]
2Department of Geology, Utah State University, Logan, Utah; present address: Department of Geoscience, University of Wisconsin-Madison, 220 Weeks Hall, Madison, Wisconsin; [email protected]
3Department of Geology, Utah State University, Logan, Utah; [email protected]

AUTHORS

Elizabeth Petrie is a Ph.D. candidate at Utah State University. Her research focuses on structural geology, rock mechanics, and fluid flow. She received her B.S. degrees in geology and biology from the University of New Mexico (2000) and an M.S. degree in geology from Utah State University (2003). Before returning for a Ph.D., she worked as a geologist in the petroleum industry.

Tamara Jeppson received her B.S. degrees in geology and physics at Utah State University in 2009 and is currently working on her M.S. degree at the University of Wisconsin-Madison. Her current research uses ultrasonic velocity measurements to derive the elastic properties of fault zone material. Her research interests are fault zone properties, earthquake mechanics, and petrophysics.

James P. Evans is a professor of structural geology. He received his B.S. degrees in geology and engineering from the University of Michigan, and his M.S. degree and Ph.D. in geology from Texas AampM University in 1983 and 1987, respectively. He is a fellow of the Geological Society of America and leads a research group in rock deformation, fluid flow, and structural analyses.

ACKNOWLEDGEMENTS

This research was supported by grants from the GDL Foundation Fellowship to Elizabeth Petrie and Department of Energy grant number DE-FC26-0xNT4 FE0001786. Software and software support came from the Seismic Micro-Technology Kingdom and Sirovision softwares, both granted by the Utah State University. We thank fellow researchers within the Utah State University Department of Geology structure group for their feedback and discussions, Doug Sprinkel and Thomas Chidsey from the Utah Geologic Survey for their stratigraphic insights, as well as Alvar Braathan for use of the TinyPerm II. We also thank the reviewers for their insightful comments on the original submission.

ABSTRACT

Open faults and fractures act as a major control of fluid flow in the subsurface, especially in fine-grained, low-permeability lithologies. These discontinuities commonly form a part of seal bypass systems, which can lead to the failure of hydrocarbon traps, CO2 geosequestration sites, and waste and injected fluid repositories. We evaluate mesoscale variability in fracture density, morphology and the variability in elastic moduli in the Jurassic Carmel Formation, a proposed seal to the underlying Navajo Sandstone for CO2 geosequestration. By combining mechanostratigraphic outcrop observations with elastic moduli derived from wireline-log data, we characterize the variability in fracture pattern and morphology with the observed variability in rock strength within this heterolithic top seal.

Outcrop inventories of discontinuities show that fracture densities decrease as bed thickness increases and that fracture propagation morphology across lithologic Previous HitinterfacesNext Hit vary with changing interface type. Dynamic elastic moduli, calculated from wireline-log data, show that Young's modulus ranges by as much as 40 GPa (5,801,510 psi) across depositional Previous HitinterfacesNext Hit and by an average of 3 GPa (435,113 psi) across the reservoir-seal interface. We expect that the mesoscale changes in rock strength will affect the distributions of localized stress and thereby influence fracture propagation and fluid flow behavior within the seal. These data provide a means to closely tie outcrop observations to those derived from subsurface data and estimates of subsurface rock strength. The characterization of rock strength variability is especially important for modeling the response of caprocks to changing stress Previous HitconditionsTop associated with increased fluid pressures and will allow for better site screening and subsurface fluid management.

Pay-Per-View Purchase Options

The article is available through a document delivery service. Explain these Purchase Options.

Watermarked PDF Document: $14
Open PDF Document: $24