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Geomechanical analysis of microseismicity in an organic shale; a West Virginia Marcellus Shale example

Erich Zorn, Abhash Kumar, William Harbert and Richard Hammack
Geomechanical analysis of microseismicity in an organic shale; a West Virginia Marcellus Shale example
Interpretation (Tulsa) (February 2019) 7 (1): T231-T239

Abstract

Using an innovative workflow incorporating microseismic attributes and geomechanical well logs, we have defined major geomechanical drivers of microseismic expression to understand reservoir stimulation response in an engineering/geologic context. We sampled microseismic data from two hydraulically fractured Marcellus wells in the Appalachian Basin, West Virginia, vertically through the event cloud, crossing shale, limestone, sandstone, and chert. We focused our analysis on the Devonian organic shale and created pseudologs of moment magnitude Mw, b-value, and event count. The vertical moving-average sampling of microseismic data was completed such that the sample interval matched that of the geophysical well log. This technique creates robust, high-resolution microseismic logs that indicate subtle changes in microseismic properties and allow direct crossplotting of microseismic versus geophysical logs. We chose five geomechanical properties to form the framework against which to interrogate the microseismic data: Young's modulus (YM), Poisson's ratio (PR), brittleness, lambda-rho, and mu-rho. In addition, we included gamma as a useful measure of organic content. Having defined this microseismic-geomechanical crossplot space, we derived insights into the response of these units during hydraulic fracturing. Observations include (1) larger magnitude microseismicity occurs in high PR, high YM rocks; high event counts are found in low PR rocks, (2) low b-value (high in situ stress) is consistent with the occurrence of larger magnitude events and low event counts, and (3) YM and PR act as bounding conditions, creating "sweet spots" for high and low Mw, event count, and stress. In our crossplot space, there is a meaningful link between microseismicity and the elastic properties of the host rock. In light of this dependence of stimulation potential on elastic properties, the calculation of microseismic pseudologs at stimulation sites and application of our crossplot framework for microseismic-geomechanical analysis in unconventional shale will inform operators in planning and forecasting stimulation and production, respectively.


ISSN: 2324-8858
EISSN: 2324-8866
Serial Title: Interpretation (Tulsa)
Serial Volume: 7
Serial Issue: 1
Title: Geomechanical analysis of microseismicity in an organic shale; a West Virginia Marcellus Shale example
Affiliation: U. S. Department of Energy, Oak Ridge Institute for Science and Education, Pittsburgh, PA, United States
Pages: T231-T239
Published: 201902
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 20
Accession Number: 2019-034011
Categories: Economic geology, geology of energy sourcesSeismology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Technical papers
Illustration Description: illus. incl. sketch maps
N39°25'00" - N39°43'00", W80°25'00" - W79°46'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 2019
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