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The AAPG/Datapages Combined Publications Database

Four Corners Geological Society


Natural Fracture Systems in the Southern Rockies, 1999
Pages 133-134

Abstract: Horizontal Exploitation of Oil and Gas-Bearing Natural Fracture Systems in the Cane Creek Clastic Interval of the Pennsylvanian Paradox Formation, Grand and San Juan Counties, Utah

Kenneth W. Grove1, David M. Rawlins2

The Cane Creek Clastic Interval (Paradox Clastic #21) is a self-sourced reservoir consisting of abnormally over-pressured and fractured dolomitic siltstone and black organic-rich shale interlayered with thin beds of anhydrite. Within the “fairway” it is generally bounded above and below by pressure-sealing bedded halite. However, in isolated places, the lower halite has changed facies into anhydrite.

Pore fluid pressure gradients exceed 0.85 psi/ft, but only in the presence of open fractures. Fracture data from seven oriented horizontal Cane Creek cores suggests the presence of a regional northeast-southwest, near vertical, open extensional fracture system which appears to be little affected by the orientations of the localized second-order folds. This dominant fracture direction is consistent with the inferred regional stress regimes in the basin from the mid-Pennsylvanian through Cretaceous/early Tertiary. Multiple fracturing events probably occurred throughout this broad period of geologic time. Oil and gas generation and over-pressuring occurred during maximum burial (Late Cretaceous-early Tertiary) resulting in charging of newly-formed fractures and re-activated earlier sets with the migrating hydrocarbons. Salt seals prevented the escape of hydrocarbons and maintained over-pressured conditions.

Discrete fractures preserved in the cores vary from those which are totally open with no fracture-filling mineralization to fractures which are completely filled with halite, calcite, or anhydrite. Some of the halite-filled fractures exhibit fracture widths of 1 to 2 cm., indicating the potential for the presence of highly permeable fracture systems. Halite commonly occurs in two habits: as clear, coarsely crystalline, anhedral to euhedral masses, and as “fibrous”, needlelike crystalline coatings with the long axes of the prisms oriented normal to the fracture surfaces. The significance of these two different habits has not yet been determined. Calcite and anhydrite mineralization are generally restricted to the smaller aperture fractures. It is also common to see evidence of reactivated fractures, both on the megascopic and microscopic scales, supporting the concept of a relatively complex multi-phase fracture history.

The Cane Creek Interval is generally highly structured in areas of massive salt flowage. Second-order folds with amplitudes of 15 ft - 100 ft and apparent wavelengths of 300 ft - 1,000 ft have been encountered in the horizontal wells and provide challenges in landing and staying “in-zone”.

In 1991, Columbia Gas Development Corporation and its partners, Exxon and Enserch Exploration, completed the first medium-radius horizontal well in Utah as a Cane Creek producer. The Kane Springs Federal #27-1 had an initial production potential of 914 BOPD. Since that time, three additional high-volume producers have been completed and two wells have been temporarily abandoned. A seventh well was completed in a shallower Paradox clastic zone. Columbia’s horizontal success rate in the Cane Creek is 57%, a marked improvement over vertical exploration. Through October, 1996, the two best horizontal Cane Creek wells have yielded 355 MBO and 312 MBO respectively and continue to produce on-pump. Additional drilling and 3D seismic programs may offer clearer insights into the detailed structural setting and fracture distribution in this newly-developing horizontal play.

Acknowledgments and Associated Footnotes

1 Gustavson Associates, 5757 Central Ave., Suite D, Boulder, CO 80301

2 Marathon Oil Company, Midland, TX

Copyright © 2011 by the Four Corners Geological Society