About This Item
- Full TextFull Text(subscription required)
- Pay-Per-View PurchasePay-Per-View
Purchase Options Explain
Share This Item
The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
David
D. Pollard,3 and Mark D. Zoback
1Manuscript received August 20, 1996; revised manuscript
received September 2, 1997; final acceptance February 25, 1998.
2Department of Geological and Environmental Sciences, Stanford
University, Stanford, California 94305-2115. Present address: Amoco Exploration
and Production Company, 501 Westlake Park Boulevard, Houston, Texas 77079.
3Department of Geological and Environmental Sciences, Stanford
University, Stanford, California 94305-2115.
4Department of Geophysics, Stanford University, Stanford,
California 94305-2551.
This work is supported by Chevron USA, the Department of Energy contract
DE-PS22-94BC1114973, the Stanford Rock Fracture Project, the Stanford Borehole
Geophysics Laboratory, and the Phillips Fellowship. We thank Bruce Bilodeau
of Chevron Production Company for subsurface data, discussion, and review
critical for this study. We especially thank Alden Carpenter for an introduction
in the field to the Monterey exposures along the coast and at Chico Martinez
Creek. We thank Jim Eacmen, Tony Murer, Dalton Lockman, Scott Hornafius,
and Steve Graham for showing us additional exposures and discussion. Thanks
to Jeannie Barnett and Scott Johnson for data, discussion, and photographs.
Colleen Barton at Stanford University, and Michael Ponek at Texaco Inc.,
assisted with borehole microresistivity image processing and image interpretation.
Review by Steve Graham and discussion with Juliet Crider, Michele Cooke,
Lisa Koenig, and Caroline Isaacs significantly improved the manuscript.
We thank Carlos Fonseca-Rivera for his expertise in siliceous sediments
in the field, Carl Twisselman for access to the Chico Martinez Creek field
area, and A. J. Field and F. Campbell for their hospitality during field
work in the coastal areas. We thank Rich Herrmann, formerly at Chevron
and now at GeoGraphix Inc., for initiating, organizing, and supplying data
at the start of this study, and Steve Smith for a smooth transition. We
also wish to thank our fellow colleagues in the structural geology, active
tectonics and geomechanics, and the borehole geophysical research groups
for insightful discussion and support. Special thanks to David
Campagna,
Visiting Scholar at Stanford, for his helpful review of the manuscript
and assistance with manuscript preparation. AAPG reviewers A. Brown, M.
Clark, and B. Higgs provided insightful comments to improve the manuscript.
ABSTRACT
Petroleum-filled breccia zones are exposed in the Antelope Shale at
Chico Martinez Creek on the northeastern flank of the Temblor Range near
McKittrick, California. Breccia zones are found predominantly parallel
to bedding in porcelanite units (4-10 cm thick) and are bounded above and
below by siliceous shale beds (2-20 cm thick). Spacing between breccia
zones is a function of lithology and diagenesis. This section of the Antelope
Shale exposure originated as alternating layers of pure and terrigenous-rich
diatomaceous sediment, in which these compositional variations influence
the postdiagenetic material properties. Terrigenous-rich diatomite diagenetically
alters to an incompetent siliceous shale (opal CT), whereas the cleaner
sediments alter to a more brittle porcelanite (opal CT). Secondary fractures,
or splay cracks, localize in the more brittle porcelanite in response to
shearing along both bed-parallel lithologic discontinuities and bed-parallel
fractures. With increased shearing, the fractured porcelanite subsequently
evolves into brecciated fault zones. In the Chico Martinez Creek outcrop,
individual breccia zones combine to make a petroleum-filled compound breccia
zone approximately 10 m thick in which the original zones are partially
obliterated by subsequent deformation.
This outcrop-based conceptual model for the development of hydrocarbon
pathways in the Monterey Formation is applied to the subsurface using formation
microscanner (FMS) data and core. Bed-parallel breccia zones are identified
in the Antelope Shale at Buena Vista Hills oil field. In the borehole image,
the brecciated fault zone appears as unorganized patches of high and low
resistivity with hints of bedding. At least one breccia zone identified
in the borehole image correlates directly to hydrocarbon production as
indicated by spinner flow-meter data. Although core recovery from fractured
or brecciated zones is typically poor, there appears to be an association
between fractures related to shearing processes and hydrocarbon occurrence
in cores examined for this study. Oil-stained and brecciated fracture zones
associated
End page 1551----------------
with slip exist in Buena Vista Hills and other nearby fields producing
from the Antelope Shale.
Our multidisciplinary study, involving both geologic field data and
borehole geophysical data, on the Monterey Formation reveals a critical
relationship in which brittle fault zones provide permeable conduits for
hydrocarbon transport and production.
Field studies of low-permeability siliceous shale units of the Monterey
Formation in the southern San Joaquin Valley and coastal California show
evidence for fault control on hydrocarbon transport important for both
migration and production. Shearing along preexisting discontinuities, such
as bedding planes and joints, locally increases permeability in the sheared
zone and surrounding fractured rock. As the rock is subjected to shear,
it begins to systematically fragment and subsequently to brecciate, thereby
creating interconnected voids for hydrocarbon transport.
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 |
AAPG Member?
Please login with your Member username and password.
Members of AAPG receive access to the full AAPG Bulletin Archives as part of their membership. For more information, contact the AAPG Membership Department at [email protected].