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1-D Measuring Rock Properties
Measuring Rock Properties
Maurice Dusseault
©MBDCI
The Optimization Loop
1-D Measuring Rock Properties
In situ state -p,σ,T
Better physics
Science studies
Better models
DESIGN
This
ongoing
process
requires
Behavioral laws
Predictions
measuring material parameters
Simulations
Other applications
Experience
New processes
RISK MANAGEMENT
& OPTIMIZATION
MONITOR
Process Control
PRODUCE
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Common Symbols in RM
E, n:
Young’s modulus, Poisson’s ratio
 f:
Porosity (e.g. 0.25, or 25%)
 c′, f′,To: Cohesion, friction , tensile strength
 T, p, po: Temperature, pressure, initial pres.
 sv, sh:
Vertical and horizontal stress
 shmin, sHMAX: Smallest, largest horizontal σ
 s1,s2,s3:Major, intermediate, minor stress
 r, g:
Density, unit weight (g = r × g)
 K, C:
Bulk modulus, compressibility
These are the most common symbols we use
1-D Measuring Rock Properties

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Stress and Pressure


1-D Measuring Rock Properties



Petroleum geomechanics
deals with stress & pressure
Effective stress: “solid stress”
Pressure is in the fluid phase
To assess the effects of Δσ',
Δp, ΔT, ΔC…
Rock properties are needed
 Deformation
properties…
 Fluid transport properties…
 Thermal properties…
sa – axial
stress
pore
pressure
A
po
sr – radial
stress

Fa
sa 
A
©MBDCI
Obtaining Rock Properties…
Properties data bank
Depth
Fric.
Coh.
XXX
YYY
ZZZ
Reflected
and direct
paths
REG. TIPO
1-D Measuring Rock Properties
Borehole
seismic
Rock
Properties
(E, ν, f, c′,
C, k,…)
3-D Seismic
SVS-337
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1-D Measuring Rock Properties
The Geology… (Lithostratigraphy)
How many rock types
must I define and test
for a reasonable,
useful Geomechanics
Analysis?
Source: University of Texas Bureau of Economic Geology
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This is a Challenging Problem…


1-D Measuring Rock Properties







How can I determine field rock behavior from
limited quantity, questionable quality core?
How do I cope with massive heterogeneity?
What about anisotropy (e.g.: shales)?
Can I test shale realistically in the laboratory?
Are laboratory results representative?
How many tests do I need?
I have no core (or bad core)! What do I do?
How many rock types to test (see diagram)?
And so on and so forth…
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Geological Models: Logs vs. Rocks
REG. TIPO
ER-EO
ER-EO
C-4
C-5
ER-EO
ER-EO
REG. TIPO
B-SUP
B-SUP
B-SUP
B-6/9
C-3
B-6/9
C-6
1-D Measuring Rock Properties
C-4
C-5
C-7
B-6/9
B-6/9
SMI
C-1
C-6
C-7
GUAS
C-2
C-6
C-7
GUASARE
C-3
C-4
C-5
C-6
C-7
GUASARE
FALLA ICOTEA GUASARE
SVS-337
SVS-30
Fault Structure, Center of Lago de Maracaibo (Venezuela)
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What is a GMU?



1-D Measuring Rock Properties



Geo-Mechanics Unit
Nature is too complex to
“fully” model
Simplification needed
A GMU is a “single
unit” for design and
modelling purposes
1 GMU = 1 set of
mechanical properties
GMU selected from
logs, cores, judgment
Log data
Core data
GMU 1
GMU 2
GMU 3
GMU 4
GMU 5
GMU 6
GMU 7
GMU 8
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GMU’s and Rock Mechanics


Rocks are heterogeneous, anisotropic, etc…
For analysis, we divide systems into GMU’s…
 Includes
1-D Measuring Rock Properties

Too many subdivisions are pointless
 Can’t

critical strata, overburden, underburden…
afford to test all of them
Too few subdivisions is risky
TOO FEW?
TOO MANY?
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Correlations for Properties


An adequate data base must exist
The GMU* is properly matched to the data
base, for example, using the following:
1-D Measuring Rock Properties
 Similar
lithology
 Similar depth of burial and geological age
 Similar granulometry and porosity
 Estimate of anisotropy (eg: shales and laminates)
 Correlations based on geophysical properties
Use of a matched analog is advised in cases
where core cannot be obtained economically
*GMU = geomechanical unit
©MBDCI
…UNCERTAINTY…
1-D Measuring Rock Properties
Reservoirs are heterogeneous & anisotropic at all scales (microns to kilometers)
70amgreat
of Athabasca
Even sandstone reservoirs show
variability,Oilsands,
especially
f = 30%,
So distances
= 0.8,  > as
1,000,000
vertically, and properties can change
over
small ascP
a
North of
Fort
McMurray,
Alta
few millimeters. Clearly, simplifications
are
needed
for analysis.
©MBDCI
1-D Measuring Rock Properties
Scale of Specimens to Test…
Is a 35 mm core representative of a
conglomerate with 20 mm pebbles?
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Plugging a Larger Diameter Core…
1-D Measuring Rock Properties
25 mm specimens plugged from a 125 mm core
Issues of scale and
representativeness
always arise in
Petroleum Geomechanics testing
1-D Measuring Rock Properties
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Scale and Heterogenity
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How Do We “Test” This Rock Mass?


1-D Measuring Rock Properties



Joints and fractures can
be at scales of mm to
several meters
Large f core: 115 mm
Core plugs: 20-35 mm
If joints dominate,
small-scale core tests
are “indicators” only
This issue of “scale”
enters into all Petroleum
Geomechanics analyses
A large core specimen
A core “plug”
1m
Machu Picchu, Peru, Inca Stonecraft
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Scale of Discontinuities
Laboratory specimen (“intact”)
70-200 mm
A tunnel in a rock mass
Rock vs Rock mass
1-D Measuring Rock Properties
--Intact rock
--Single discontinuities
--Two discontinuities
--Several disc.
--Rockmass
20-30 m
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Discontinuities & Rocks

1-D Measuring Rock Properties

Rocks are heterogeneous at all
scales (microns to kilometers)
In granular media, macroscopic
stresses are transmitted through
grain contact forces (fn, fs)
fs = shear force
fn = normal force
©MBDCI
Difficult Materials to Get and Test


1-D Measuring Rock Properties


Very high porosity materials (e.g.: diatomite)
Materials containing viscous oil with gas in
solution (expansion – e.g.: oil sands)
Highly fractured materials such as fractured
quartz-illite shales
Highly heterogeneous layered material from
great depth (core breaks apart at each layer,
referred to as “disking”…)
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Unusual Materials (Diatomite)…
Increasing stress on diatomite (through
pressure depletion) causes material
compaction and eventually pore collapse
SPE75230, Barenblatt et al, 2002
cylindrical
specimen
Source: Bruno and Bovberg, 1992
εh = 0
εh = 0
1-D Measuring Rock Properties
Δσ′v
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Oil Sand Core Expansion…
Radially
Axially
Schematic Diagram of Expansion of an 89 mm Core
1-D Measuring Rock Properties
90-91 mm
Corrugated surface
characteristic of thinlybedded and laminated
fine-grained sands of
variable oil saturation
Oil-poor to oilfree silty sands,
expansion much
less than other
material
95 mm
Oil-rich sample
expands to
completely fill
the liner
Core has expanded from 120.7mm to
127mm diameter and is now acting
like a piston in a cylinder
89 mm
Ironstone
band, no
expansion
PVC
liner
Cores separate readily along cracks which form
between zones of differing expansion potential
127 mm
Oil sand
Gas pressure inside liner
Observed Expansions of 89mm Core:

Ironstone
89 mm

Basal clays, clayey silts
89-91 mm

Oil-poor to oil-free silty sands
90-93 mm

Fine-grained oil-rich sand
91-95 mm

Coarse-grained oil-rich sand
94-95 mm
ref. Dusseault (1980) Fig. 5 & 6
©MBDCI
1-D Measuring Rock Properties
Quality Control – Oil Sand Cores
CT-Scan Evidence of Damage in Heavy Oil Cores
Courtesy of Glen Brook, Nexen and Apostolos Kantzas, U of Calgary
©MBDCI
1-D Measuring Rock Properties
Venezuelan Core Damage
Oil sands core from the Faja del Orinoco, depth of about
900 m. Massive core expansion from gas exsolution.
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Core – General Statement
1-D Measuring Rock Properties
Is this
coreisuseful
Geomechanics
tests?
ANY
CORE
better for
than
no core. However,
with poor core condition, all we can realistically
expect is a qualitative assessment, grain size,
clay mineralogy, fluids…, perhaps some rough
index tests of strength and deformability.
However, dry shale core – no strength tests
Best is high-quality intact core collected just for
geomechanics tests. Obtain, preserve and
transport the core carefully. Test it soon, test it
appropriately, but be aware that there is always
some damage…
©MBDCI
Use of Time-Lapse Seismics…
1-D Measuring Rock Properties
Seismic Attributes Relative Change Matrix
T
σ
po
Sg
D
…as T goes up,
Qp drops…
…as σ goes up, Qp
increases…
etc.
Modified from Doug
Schmitt, UofA, 2004
©MBDCI
MS & Integrated Monitoring…
1-D Measuring Rock Properties
Microseismic data can be collected and used to
update a Whole Earth Rock Properties Model (Mechanical Earth Model - MEM) based on combined lab, log,
geological and seismic data. This is an example of
microseismic sources located in a cyclic steam
Shell
Oil,
stimulation process in Peace River, Alberta (Shell
Oil).
Peace River
In geomechanics, because of massive uncertainly and
scale issues, we exploit whatever data sources we can.
We try to regularly update our MEM’s with new logs, new
core, new seismic data, better geological models, and
other information. Also, remember that the properties
can change, especially with large Δσ′, Δp, or ΔT.
©MBDCI
1-D Measuring Rock Properties
Testing Heterogeneous Materials?
These materials respond radically different to stress: one flows,
the other fractures. How might we incorporate such behavior in
our testing and modeling for a natural gas storage cavern?
Original specimen - Post-test appearance
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Inherent Anisotropy

Different directional stiffness is common!
1-D Measuring Rock Properties
 Bedding
planes
 Oriented minerals (clays usually)
 Oriented microcracks, joints, fissures…
 Close alternation of thin beds of different inherent
stiffness (laminated or schistose)
 Imbricated grains
 Different stresses = anisotropic response
 Anisotropic grain contact fabric, etc.
stiffer
less stiff
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Stiffness Anisotropy
1-D Measuring Rock Properties
Apparent axial
stiffness - M
M  s 
0°
L
30°
60°
90°
Vertical
core



0°
Δσ′a
L
L
30°
60°
e.g.: shales, laminated strata
90°
Bedding
inclination
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Cracks and Grain Contacts
E1
E2
Microflaws can
close, open, or
slip as s changes
E1
1-D Measuring Rock Properties
E3
Flaws govern
rock stiffness
The nature of the grain-to-grain
contacts and the overall porosity
govern the stiffness of porous SS
©MBDCI
Issues to Remember…


1-D Measuring Rock Properties






Natural lithological heterogeneity
Wide range of properties (e.g.: compressibility
or Chalk vs. low-f limestone)
Scatter of experimental data
Log data – lab test correlations (variance)
Core damage and quality control
Issues of scale (especially in fractured rocks)
Representativeness and GMU delineation
We must cope with all of these sources of
uncertainty…