Identification, Integration and Upscaling of Mudrock Types - A Pathway to Unlocking Shale Plays
- Joan M. Spaw (Marathon Oil Company)
- Document ID
- Society of Petroleum Engineers
- SPE/EAGE European Unconventional Resources Conference and Exhibition, 20-22 March, Vienna, Austria
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 5.1.4 Petrology, 5.1.3 Sedimentology, 5.5.2 Core Analysis, 5.5 Reservoir Simulation, 5.1.5 Geologic Modeling, 4.3.4 Scale, 5.1.1 Exploration, Development, Structural Geology, 1.6.9 Coring, Fishing, 5.4.2 Gas Injection Methods, 5.5.3 Scaling Methods, 5.8.2 Shale Gas, 1.2.3 Rock properties, 1.14 Casing and Cementing, 5.6.5 Tracers, 5.6.1 Open hole/cased hole log analysis, 5.1 Reservoir Characterisation
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A multidisciplinary approach to shale characterization in a variety of North American gas- and liquids-rich shale plays has lead to improved understanding of the bulk physical, chemical and mechanical properties of these deposits and their geologic history. This effort is leading to successful exploitation of these enigmatic resources. Microfacies analysis of mudrocks provides a platform for upscaling from the "nano?? to the regional scale, and results in comprehensive mudrock characterizations.
Microfacies analysis of mudrock types within a select stratigraphic interval in a basin leads to the recognition of mudrock lithofacies. Lithofacies identification allows for calibration of petrophysical models, documentation of basinspecific variations in mudrock composition and microfabrics, the distribution of organic-rich members of these intervals, definition of the mechanical stratigraphy for completion design, and provides the litho-stratigraphic building blocks for predictive sequence stratigraphic models.
Successful exploration and exploitation of mudrocks as resources can be advanced when the recognition of mudrock lithofacies provides a methodical means to tie together the geologic, chronostratigraphic, geochemical and petrophysical data from a diverse spectrum of physical scales and technical disciplines.
As mudrock resource exploitation continues to expand globally, it has become increasingly apparent that these rocks do not form homogeneous and featureless, widespread deposits nor can they be adequately characterized by a few bulk physical and chemical properties. Instead, mudrocks exhibit heterogeneity evidenced by multiple attributes that vary greatly both vertically and laterally within a basin (Schieber, 1989, 1994; Loucks and Ruppel, 2007; Jacobi, et al., 2008). The inherent nature of mudrocks makes the identification of characteristic types challenging. Many attributes of these rocks are obscured by their dark coloration. The situation is exacerbated by their very fine-grained constituents, finescaled sedimentary structures, and their nano-scale pore systems. The associated biota, predominantly microfossil assemblages, tends to be below the resolution of a hand lens. The fissility of some of these rocks makes physical measurements challenging. A further complication is the lack of a commonly used classification system for these rocks with over 80 classifications (K. Milliken, 2010) currently available in the literature.
Many of these challenges were previously viewed as insurmountable due to a lack of technology as well as a focus on mudrocks as seals or source rocks rather than commercially exploitable reservoir rocks. It is important to note that the complexity and value of understanding these rocks has been recognized since they were first examined under a petrographic microscope (Sorby, 1908), and a holistic approach to mudrock characterization has been championed for decades (Potter et al., 1980; Schieber, 1984).
A multidisciplinary approach to shale characterization that integrates compositional and textural petrologic data from core samples with petrophysical, geochemical and biostratigraphic data provides a platform for upscaling data from the nano- to regional-scales and results in a comprehensive characterization.
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