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Abstract: Five Things Geophysicists Should Know About Shale Plays

Five Things Geophysicists Should Know About Shale Plays

The Shale Revolution caught geophysicists off guard. Shales had been studied for a variety of reasons (e.g., relationships between velocity, compaction and pore pressure) but not as low-porosity reservoirs that show vertical heterogeneity at all possible scales. Consequently, many geophysicists have framed shale-play imaging problems using inappropriate tools and paradigms. In this presentation, I present five characteristics of shale plays that should enable improved geophysical analyses.

The term “shale play” has become meaningless. Originally intended to describe gas production from fine-grained source rocks (“source-rock reservoirs”), the term is now applied almost indiscriminately to production from many types of low-permeability rock (e.g., shaly sandstones, carbonates).
Source-rock reservoirs aren’t clay dominated. Hydraulic fracturing is needed to establish commercial production from these rocks. Clays make the rocks ductile and harder to fracture. As such, the clay content of shale plays is generally less than 50%. The remainder of the rock is usually composed of fine-grained calcite and/or quartz, organic matter and other minerals.
Links between VTI anisotropy and clay or organic content are not straightforward in source-rock reservoirs. Scanning electron microscopy often reveals textures that are incompatible with the conceptual models used to develop mathematical models of shales.
HTI anisotropy is complicated by natural fracture geometries. Aligned natural fractures generally combine with bedding to produce systems that are best described as orthorhombic. In some cases, multiple fracture orientations produce systems that are effectively isotropic.
Integration of geophysical and geological data and concepts is needed to significantly advance geophysical research on shale reservoirs. This effort will allow geophysicists to define, for a specific shale, which assumptions are reasonable, which analogs are appropriate, what appropriate ranges of properties are, etc.

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Distinguished Lecturer

Bruce Hart

AAPG-SEG Distinguished Lecturer

Research Scientist

Equinor, Austin

Video Presentation

Abstracts

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Ice Age and the Giant Bakken Oil Accumulation