Calibration of Brittleness To Elastic Rock Properties Via Mineralogy Logs in Unconventional Reservoirs
Calibration of Brittleness To Elastic Rock Properties Via Mineralogy Logs in Unconventional Reservoirs
Calibration of Brittleness To Elastic Rock Properties Via Mineralogy Logs in Unconventional Reservoirs
*Adapted from oral presentation given at AAPG International Conference and Exhibition, Cartagena, Colombia, September 8-11, 2013
**AAPG 2013 Serial rights given by author. For all other rights contact author directly.
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University of Oklahoma, Norman, Oklahoma (roderickperezaltamar@gmail.com)
Abstract
To optimally stimulate an unconventional reservoir hydraulically, it is important to identify brittle regions based on knowledge of the geology,
petrophysics, mineralogy, and rock mechanics of the area of study. This research reconciles some of the brittleness terminology in the literature
and classifies the Barnett Shale in terms of its geomechanical properties, defining the more-brittle regions in Young's modulus and Poisson's
ratio crossplots and - space. These geomechanical properties were defined, calibrated, and computed using specialized logging tools such
as: mineralogy, density, and P- and S-wave sonic logs, and calibrated to previous core descriptions and laboratory measurements. With proper
calibration these measurements provide a means to geomechanically characterize a reservoir.
In the Barnett Shale, the combination of high concentrations of quartz and calcite gives rise to more brittle rocks, while ductility is controlled
primarily by clay content. Contrary to the commonly held understanding, in the Barnett increased kerogen (TOC) does not make the rock more
ductile. Further, microseismic event locations from a 3D seismic survey acquired after more than 400 wells have been drilled and hydraulically
fractured in the area agree to the predicted brittle regions in the - crossplot, suggesting that hydraulically induced fractures preferentially
populate brittle regions and consequently, produce more gas. Thus, these results are useful to calibrate 3D seismic attribute brittleness
estimation.
References Cited
Alzate Buitrago, J.H., 2012, Integration of surface seismic, microseismic, and production logs for shale gas characterization: methodology and
field application: M.S. Thesis, The University of Oklahoma, Norman, Oklahoma, 121 p.
Browning, D.B., 2006, Investigating corrections between microseismic event data, seismic curvature, velocity anisotropy, and well production
in the Barnett Shale, Fort Worth Basin, Texas: M.S. Thesis, University of Oklahoma, Norman, Oklahoma, 105 p.
Goodway, B., J. Varsek, and C. Abaco, 2007, Isotropic AVO methods to detect fracture prone zones in tight gas resource plays: CSPG, CSEG,
CWLS Conference, p. 585-589.
Goodway, B., J. Varsek, C. Abaco, 2007, Anistropic 3D amplitude variation with azimuth (AVAZ) methods to detect fracture prone zones in
tight gas resource plays: CSPG, CSEG, CWLS Conference, p. 590-596.
Singh, P., 2008, Lithofacies and sequence stratigraphic framework of the Barnett Shale: Ph.D. Dissertation, The University of Oklahoma,
Norman, Oklahoma, 181 p.
Thompson, A., 2010, Induced fracture detection in the Barnett Shale, Ft. Worth Basin, Texas: M.S. Thesis, The University of Oklahoma,
Norman, Oklahoma, 69 p.
Zhang, K., 2010, Seismic attribute analysis of unconventional reservoirs and stratigraphic patterns: Ph.D. Dissertation, The University of
Oklahoma, Norman, Oklahoma, 147 p.
CALIBRATION OF BRITTLENESS TO
ELASTIC ROCK PROPERTIES VIA
MINERALOGY LOGS IN
UNCONVENTIONAL RESERVOIRS
Roderick Perez, Ph.D.
The University of Oklahoma
Reservoir
Source
Reservoir
Reservoir
Seal
The proliferation of the exploration activity into new shale plays has
increased the shale gas resources in the U.S. from 1 from 2006 to 336 TCF
BARNETT SHALE: in August 2011. In this dissertation we will focus on the Barnett Shale,
Low permeability* (<0.1 mD) located in the Fort Worth Basin (Texas).
Due to the low permeability, it is necessary apply enhanced recovery techniques, such
as hydraulic fracture stimulation or steam injection to extract the gas molecules from
the rock matrix and achieve gas production.
Finding areas in the shale play that are brittle is important in the
development of a fracture fairway large enough to connect the
highest amount of rock volume during the hydraulic
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fracturing process.
OUTLINE
Introduction
Objectives
Conclusions
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OUTLINE
Introduction
Objectives
Conclusions
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OBJECTIVES
Previous work (Thompson, 2010; Zhang, 2010) has
shown that seismic impedance, curvature, and other
attributes visually correlate with reservoir performance
Relative EUR value co-rendered with most positive Anisotropy intensity with polygons of microseismic events from six experiments.
curvature (Thompson, 2010) Notice the micro-seismic events appear in areas of low anisotropy intensity.
(Zhang, 2010)
Objectives
Conclusions
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WHAT IS BRITTLENESS???
BRITTLE DUCTILE
BRITTLENESS is the
measurement of stored
energy before failure, and is
function of:
Rock strength
lithology
texture
effective stress
temperature
fluid type
diagenesis
TOC Higher the magnitude of the
BRITTLENESS INDEX (BI) is BI, the more brittle the rock
the most widely used is
parameter for the quantification
of rock brittleness. If the rock has a large region of elastic behavior but
only a small region of ductile behavior the rock is
considered brittle. In contrast, If the material under
stress has a small region of elastic behavior and a
large region of ductile behavior, absorbing much
energy before failure, it is considered ductile
(opposite of brittle).
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BRITTLENESS
How do to quantify brittleness
1) Mineralogy??
2) Elastic parameters??
GEOLOGY GEOMECHANICAL
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BRITTLENESS INDEX
(Mineralogy)
Gamma ray (GR) vs. brittleness index (BI) corresponding to Well A (using Wang and Gales (2009) equation color-coded by total organic
carbon (TOC) content, and Singh (2008) Barnett Shale lithofacies definition ranked in relation to interpreted relative bottom oxygenation and
organic richness. Brittle (red), less brittle (orange), less ductile (yellow), and ductile (green) classification proposed (classification results are
shown in track 11 on previous slice.
11
BRITTLENESS AVERAGE
(Elastic parameters)
a) Set of elastic logs corresponding to Well A, b) Poissons ratio vs. Youngs modulus crossplot indicating empirically defined ductile-brittle regions, and the
expected fracture pathway geometry (modified from Grieser and Bray, 2007), (c) the Poissons ratio vs. Youngs modulus values corresponding to formations in
Well A overplotted by Grieser and Brays (2007) ductile (green)-brittle (red) regions color-coded with brittleness index from ECS mineralogy analysis.
Classification results are shown in track 13.
CALIBRATION OF BRITTLENESS TO ELASTIC
ROCK PROPERTIES VIA MINERALOGY LOGS
Poissons ratio vs. Youngs modulus crossplot (a) corresponding to each formation in the study area. (b) Poissons ratio vs. Youngs
modulus crossplot corresponding to Upper and Lower Barnett Shale color-coded by brittleness index (BI), overlapped by a
proposed brittle/ductile classification, and (c) the proposed classification.
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CALIBRATION OF BRITTLENESS TO ELASTIC
ROCK PROPERTIES VIA MINERALOGY LOGS
Youngs
Poissons ratio
Modulus
P-wave S-wave
Velocity Velocity
P-wave Modulus
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CALIBRATION OF BRITTLENESS TO ELASTIC
ROCK PROPERTIES VIA MINERALOGY LOGS
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OUTLINE
Introduction
Objectives
Conclusions
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SURFACE SEISMIC ESTIMATION OF
HYDRAULICALLY FRACTURED ROCK
Angle Gathers
RP reflectivity RS reflectivity
ZP impedance ZS impedance
vs. crossplot
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Goodway (2007)
SURFACE SEISMIC ESTIMATION OF
HYDRAULICALLY FRACTURED ROCK
Vertical slices A - A through (a) and (b) seismic volumes and their corresponding histograms. Notice that the shale formations
exhibit lower values of and (red and yellow) than the limestone formations (cyan and blue). Location of the line is shown in slice
22. (c) - crossplot color-coded by gamma ray from logs indicating that shale formations exhibit low and low . (d) Gamma ray
vs. brittleness index indicating that in the Barnett Shale high gamma ray values represent high brittleness and TOC, confirming the
core analysis by Singh (2008).
SURFACE SEISMIC ESTIMATION OF
HYDRAULICALLY FRACTURED ROCK
Vertical slices B - B through (a) and (b) seismic volumes and (c) through the crossplotted vs. volumes using a (d) 2D colorbar (location of line B - B is
shown in next slice). The range of the 2D colorbar enhances the differences between quartz- (yellow and red), clay (green), and limestone (magenta, blue, and
purple) -rich formations, providing an estimate of lithology and geomechanical behavior.
SURFACE SEISMIC ESTIMATION OF
HYDRAULICALLY FRACTURED ROCK
Stratal slices through vs. crossplot volumes corresponding to (a) Marble Falls, (b) Upper Barnett Shale, (c) Forestburg Limestone, (d) upper
Lower Barnett Shale, (e) lower Lower Barnett Shale, and (f) Viola Limestone using the 2D colorbar. Limestones appear as magenta, blue, and
purple, while quartz-rich shales appear as yellow and red, and clay-rich shales appear as green.
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SURFACE SEISMIC ESTIMATION OF
HYDRAULICALLY FRACTURED ROCK
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Microseismic events trend towards quartz rich areas, avoiding clay rich zones (green).
PRODUCTION LOGGING COMBINED WITH 3D SURFACE
SEISMIC
IN UNCONVENTIONAL PLAYS CHARACTERIZATION
Crossplot in gray of - of falling voxels within boxes shown in slide 24 for the Lower Barnett Shale.
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PRODUCTION LOGGING COMBINED WITH 3D SURFACE
SEISMIC
IN UNCONVENTIONAL PLAYS CHARACTERIZATION
Map view of microseismic event locations corresponding to (a) Well C and (b) Well D the orientation of the fracture lineaments formed by the microseismic events align with the current maximum
horizontal stress direction in the Fort Worth Basin (NE-SW). (c) Horizon slice along the top Viola Limestone through the most positive curvature seismic attribute volume. The majority of the
microseismic event locations fall into the areas with negative curvature values (bowl shapes). Red vectors indicate velocity anisotropy where the length of the vector is proportional of the degree of
anisotropy while the direction indicates the azimuth of maximum anisotropy (modified from Thompson, 2010). The seismic data were acquired after 400 wells stimulated, such that the velocity
anisotropy represents the post-frack stress regime.
Microseismic events trend towards negative curvature values (green) avoiding the most positive
curvature zones (orange) and follow the velocity anisotropy trend, previously described by26
Thompson (2010) and Browning (2006).
PRODUCTION LOGGING COMBINED WITH 3D SURFACE
SEISMIC
IN UNCONVENTIONAL PLAYS CHARACTERIZATION
The majority of the microseismic events are located in zone of low anisotropy strength, suggesting
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that the rock relax after being fractured.
OUTLINE
Introduction
Objectives
Conclusions
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CONCLUSIONS
Well calibration is key to have a accurate interpretation of
the rock brittleness.
2D color-bars are very useful to visualize cross-plot
volumes.
Microseismic is an indirect method to evaluate the
hydraulic stimulation in the reservoir.
Microseismic events
trend towards quartz rich areas, avoiding clay rich
zones.
trend towards negative curvature values (green)
avoiding the most positive curvature zones (orange)
and follow the velocity anisotropy trend.
are located in zone of low anisotropy strength,
suggesting that the rock relax after being fractured. 29
ACKNOWLEDGEMENTS
Devon Energy for providing the data for this research
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