Article
Predicting rock strength variability across stratigraphic interfaces in caprock lithologies at depth: Correlation between outcrop and subsurface
Environmental Geosciencess
(2012)
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 interfaces vary with changing
interface type. Dynamic elastic moduli, calculated from wirelinelog
data, show that Young’s modulus ranges by as much as 40 GPa
(5,801,510 psi) across depositional interfaces 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 conditions associated with increased
fluid pressures and will allowfor better site screening and subsurface
fluid management.
Keywords
- rock strength,
- borehole,
- logging,
- fractures,
- faults
Disciplines
Publication Date
Winter December, 2012
DOI
10.1306/eg.06011212001
Citation Information
Elizabeth S Petrie, Tamara N. Jeppson and James P. Evans. "Predicting rock strength variability across stratigraphic interfaces in caprock lithologies at depth: Correlation between outcrop and subsurface" Environmental Geosciencess Vol. 19 Iss. 4 (2012) p. 125 - 142 Available at: http://works.bepress.com/james_evans/114/
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