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Marcellus Shale - Geologic Controls from Production

Wrightstone, Gregory R.1
1 Exploration, Texas Keystone, Inc., Pittsburgh, PA.

The Middle Devonian Marcellus Shale is areally the largest of all the resource shale plays in North America, with the potentially productive area exceeding 30,000,000 acres. The “core area” of economically productive Marcellus, as defined by the various geologic factors, may be more than 15,000,000 acres.

The organic rich black shales of the Marcellus were deposited during Ettensohn’s second tectophase of the Acadian Orogeny. This deposition occurred in a foreland basin that roughly parallels the present day structural front. Factors affecting and controlling production include reservoir pressure, thickness of pay, porosity, permeability, geologic hazards, natural fracturing, and thermal maturation. One of the most important and least understood of these factors may be reservoir pressure, as production from the Marcellus is seriously impacted by low reservoir pressure. The herein named Big Sandy Low Pressure Sink and the associated Transitional Pressure Area cover an area of more than 8,000,000 acres where production is negatively impacted by abnormally low pressure gradients ranging from .1 to .35 psi/foot. Geologic hazards to be avoided include structurally complex areas with deep seated faulting and the lack of upper or lower frac boundaries.

More than 3,500 Marcellus wells have either been permitted or drilled in six states throughout the Appalachian Basin during the modern era of development. While the play is still in its infancy, early reported production rates and reserves compare favorably to other established shale plays.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009