Natural fractures in the Barnett Shale and their importance for hydraulic fracture treatments

Julia F.W. Gale, Robert M. Reed, Jon Holder

    Research output: Contribution to journalArticle

    • 624 Citations

    Abstract

    Gas production from the Barnett Shale relies on hydraulic fracture stimulation. Natural opening-mode fractures reactivate during stimulation and enhance efficiency by widening the treatment zone. Knowledge of both the present-day maximum horizontal stress, which controls the direction of hydraulic fracture propagation, and the geometry of the natural fracture system, which we discuss here, is therefore necessary for effective hydraulic fracture treatment design. We characterized natural fractures in four Barnett Shale cores in terms of orientation, size, and sealing properties. We measured a mechanical rock property, the subcritical crack index, which governs fracture pattern development. Natural fractures are common, narrow (<0.05 mm; <0.002 in.), sealed with calcite, and present in en echelon arrays. Individual fractures have high length/width aspect ratios (> 1000:1). They are steep (>75°), and the dominant trend is west-northwest. Other sets trend north-south. The narrow fractures are sealed and cannot contribute to reservoir storage or enhance permeability, but the population may follow a power-law size distribution where the largest fractures are open. The subcritical crack index for the Barnett Shale is high, indicating fracture clustering, and we suggest that large open fractures exist in clusters spaced several hundred feet apart. These fracture clusters may enhance permeability locally, but they may be problematic for hydraulic fracture treatments. The smaller sealed fractures act as planes of weakness and reactivate during hydraulic fracture treatments. Because the maximum horizontal stress trends northeast-southwest and is nearly normal to the dominant natural fractures, reactivation widens the treatment zone along multiple strands.

    LanguageEnglish (US)
    Pages603-622
    Number of pages20
    JournalAAPG Bulletin
    Volume91
    Issue number4
    DOIs
    StatePublished - Apr 1 2007

    Fingerprint

    Shale
    shale
    Hydraulics
    hydraulic fracturing
    crack
    permeability
    fracture propagation
    rock property
    Multiple zones
    sealing
    gas production
    reactivation
    Cracks
    power law
    geometry

    ASJC Scopus subject areas

    • Fuel Technology
    • Energy Engineering and Power Technology
    • Geology
    • Geochemistry and Petrology
    • Earth and Planetary Sciences (miscellaneous)

    Cite this

    Natural fractures in the Barnett Shale and their importance for hydraulic fracture treatments. / Gale, Julia F.W.; Reed, Robert M.; Holder, Jon.

    In: AAPG Bulletin, Vol. 91, No. 4, 01.04.2007, p. 603-622.

    Research output: Contribution to journalArticle

    Gale, Julia F.W. ; Reed, Robert M. ; Holder, Jon. / Natural fractures in the Barnett Shale and their importance for hydraulic fracture treatments. In: AAPG Bulletin. 2007 ; Vol. 91, No. 4. pp. 603-622.
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