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Integrated Fracture Analysis: An Important Tool for Deciphering Complex Fracture Patterns*
Eric Erslev1
Search and Discovery Article #40456 (2009)
Posted October 15, 2009
*Adapted from oral presentation at AAPG Convention, Denver, Colorado, June 7-10, 2009
1Department of Geosciences, Colorado State University, Ft. Collins, CO (mailto: [email protected])
Understanding fracture timing and genesis is critical to efficient hydrocarbon exploration and production. Current hypotheses for fracture formation in the Rocky Mountains include regional tectonic compression and extension during pre-, syn- and post-Laramide times as well as more localized deformation due to folding and gravitational collapse of contractile structures.
The
integrated analysis of both shear (minor faults) and extensional (joints)
fractures in rocks of a variety of ages provides a key tool for differentiating
fracture 
mechanisms
. Kinematic data from conjugate minor faults (n = 21,129)
within pre-Laramide units give similar average slip (N67E-01) and compressive
stress (N67E-02) directions for the Laramide Orogeny. Average Laramide fold
(N24W) and arch (N23W) axes are consistently perpendicular to these directions,
indicating genesis by thrust-related folding. The largely unimodal shortening
and compression directions vary slightly in space, with more E-W directions in
the southern and eastern Rockies and more NE-SW directions in the Colorado
Plateau.
Whereas
some open, potentially hydrocarbon-transmitting joints strike ENE and are thus
consistent with syn-Laramide formation; many are highly oblique, commonly with
NW-SE strikes. In some areas, hypotheses invoking pre-Laramide jointing can be
falsified by the fact that these joints cut Paleogene rocks. Locally,
NW-SE-striking joints also cut Miocene strata, making them post-Laramide in
age. Multiple mechanisms for post-Laramide joint formation make generalizations
inadvisable, with evidence at different localities for fracturing during (1)
regional Rio Grande extension, (2) localized gravity detachment into basin
lows, and (3) localized back-sliding on Laramide thrust faults. These
mechanisms predict very different fracture and hydrocarbon production patterns,
indicating the value of integrated fracture analyses.
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Bergbauer, S. and D.D. Pollard, 2004, A new conceptual fold-fracture model including prefolding joints, based on the Emigrant Gap Anticline, Wyoming: GSA Bulletin, v. 116/3-4, p. 294-307.
Brown, A.R., 1983, Structural Interpretation from Horizontal Seismic Sections: AAPG Bulletin, v. 67/3, p. 430.
Erslev, E.A. and N.V. Koenig, 2009, Three-dimensional kinematics of Laramide basement-involved Rocky Mountain deformation, USA: Insights from minor faults and GIS-enhanced structure maps, in Kay, S.M., V.A. Ramos, and W.R. Dickinson, W.R. eds., Backbone of the Americas: Shallow Subduction, Plateau Uplift, and Ridge and Terrane Collision: The Geological Society (London) Memoir 204, p. 125-150, DOI: 10.1130/2009.1204(06).
Erslev, E.A., and S.M. Larson, 2006, Testing Laramide hypothesis for the Colorado Front Range arch using minor faults, in Raynolds, R. and E. Sterne, eds., Special Issue on the Colorado Front Range: Mountain Geologist, v. 43, p. 45-64.
Haws, G.W., and N.F.
Hurley, 1992, Applications of pressure-interference data in
Ruf, J.C., 2000, Origin of Laramide to Holocene fractures in the northern San Juan Basin, Colorado and New Mexico: Colorado State University, Colorado, Master’s thesis, 167 p.
Stanton, H.I. and E.A. Erslev, 2004, Sheep Mountain: Backlimb tightening and sequential deformation in the Bighorn Basin, Wyoming, in 53rd Field Conference Guidebook: Casper, Wyoming Geological Association, p. 75-87.
Whitehead, N.H. III, 1997, Fractures at the surface, San Juan Basin, New Mexico and Colorado, in T.E. Hoak, A.L. Klawitter and P.K. Blomquist, editors, Fractured reservoirs; characterization and modeling: Rocky Mountain Association of Geologists, Denver, Colorado, p. 27-42.
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