Advanced Technologies for Monitoring CO Saturation … Library/Events/2012/Carbon Storage RD... ·...
Transcript of Advanced Technologies for Monitoring CO Saturation … Library/Events/2012/Carbon Storage RD... ·...
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Advanced Technologies for Monitoring CO2
Saturation and Pore Pressure in Geologic
Formations DE-FE0001159
Gary Mavko and Tiziana Vanorio
Rock Physics Project/Stanford University
U.S. Department of Energy
National Energy Technology Laboratory
Carbon Storage R&D Project Review Meeting
Developing the Technologies and Building the
Infrastructure for CO2 Storage
August 21-23, 2012
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Presentation Outline
• Benefit to the Program
• Project Overview
• Motivating technical challenge
• Approach
• Technical Status
– Laboratory results
– Theoretical modeling
• Summary
Mavko & Vanorio – Stanford University Rock Physics Project.
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Benefit to the Program • Program goals being addressed.
– Develop technologies that will support industries’ ability to
predict CO2 storage capacity in geologic formations.
– Develop technologies to demonstrate that 99% of injected
CO2 remains in injection zones.
• Project benefits statement.
– The project is developing CO2-optimized rock-fluid models
that will incorporate the seismic signatures of (1) saturation
scales and free vs. dissolved CO2, (2) pore pressure
changes, and (3) CO2-induced chemical changes to the
host rock. These models will be an integral part of
interpretation of seismic images of the subsurface at
injection sites. They address the program’s needs to predict
storage capacity and to ensure 99% containment of CO2.
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Project Overview: Goals and Objectives
• The goal of this project is to provide robust quantitative
schemes to reduce uncertainties in seismic interpretation for
saturation state and pore pressure in reservoirs saturated
with CO2-brine mixtures.
• Success criteria include
- Creation of laboratory dataset on changes in porosity,
permeability, and elastic properties associated with
injection of CO2-brine mixtures in four different lithologies.
- Improved theoretical models that predict the frequency-
dependent seismic velocity changes associated with
injection, including changes in pore pressure, saturation,
and dissolution or precipitation of minerals in the rock
frame.
Mavko & Vanorio – Stanford University Rock Physics Project.
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Technical Status
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The Challenge: Seismic Monitoring of CO2
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Map of Seismic Reflectivity
or Changes of Reflectivity
Rock/Fluid
Model
Interpreted Saturation
Interpreted Pressure
Workflow for monitoring changes in the subsurface
Mavko & Vanorio – Stanford University Rock Physics Project.
Changes in: • Seismic Vp
• Seismic Vs
• Density
• Attenuation ?
Changes in: • Saturation
• Stress/pressure
• Rock mineral frame
model
Interpreted Saturation
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Rock’s Seismic (Elastic) Response
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Mineralogy ✔ ✔
Porosity ✔ ✔
Microgeometry ✔ ✔
Stress/Pressure ✔ ✔
Fluids ✔
Affected by:
Bulk modulus: Shear modulus:
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Rock’s Seismic (Elastic) Response
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Mineralogy ✔ ✔
Porosity ✔ ✔
Microgeometry ✔ ✔
Stress/Pressure ✔ ✔
Fluids ✔
Mavko & Vanorio – Stanford University Rock Physics Project.
Affected by:
Bulk modulus: Shear modulus:
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Conventional Seismic-Fluid Model
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Mavko & Vanorio – Stanford University Rock Physics Project.
Current technology for seismic monitoring of injected CO2
saturation is based on the equations of Gassmann (1951):
bulk modulus
shear modulus
bulk density
These assume chemically inert processes; ie. constant
microgeometry, porosity, mineralogy, and frame stiffness.
They also require knowledge of the compressibility and density
of CO2-brine mixtures as a function of T, P, and salinity.
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The Problem
Multiphase CO2-rich fluid-rock systems can be
chemically reactive, altering the rock frame via
dissolution, precipitation, and mineral replacement.
Errors from ignoring the physicochemical factors during
CO2 injection can affect not only the magnitude, but also
the sign, of predicted seismic velocity changes, resulting
in seriously compromised estimates of saturation and
pressure of CO2-rich fluids
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Mavko & Vanorio – Stanford University Rock Physics Project.
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Approach: Tasks
1. Project Management, Planning, Reporting
2. Laboratory Measurements
• Sample selection (MVA working groups, ExxonMobil, Stanford)
• Rock characterization (porosity, perm, elastic velocities,
microstructure)
• Exposure to CO2-brine, while monitoring Vp, Vs
• Repeat characterization
• CO2-brine mixture characterization vs. T and P
3. Theoretical Modeling
• Empirical/theoretical expressions for CO2-brine properties
• Quantification of changes to pore microstructure
• Derive equations to describe velocity-vs.-saturation, accounting for
chemical changes to rock microstructure.
4. Validation
5. Collaboration with MVA Working Groups
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Mavko & Vanorio – Stanford University Rock Physics Project.
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Laboratory Work
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Experimental Design
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• Injection of CO2-rich brine into carbonates/sandstones dissolution
of Calcite and Chamosite
• Injections are performed under reservoir pressure conditions
Pc up to 15-55 MPa and Pf up to 15-28MPa
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Rock Samples
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Micritic Carbonates
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Rock Samples
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Micritic Carbonates
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Fe-rich Chlorite (Chamosite) Sandstones from the Tuscaloosa Formation, Cranfield, MS
Rock Samples
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Fe-rich Chlorite (Chamosite) Sandstones from the Tuscaloosa Formation, Cranfield, MS
Rock Samples
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Experimental Protocol
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Pre-Injection dry
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Monitoring Properties
• Chemical composition (pH, Cation concentration) of
the brine and the injected pore volumes
• Porosity and permeability as a result of dissolution
and mechanical compaction
• P- and S- wave velocities of the saturated sample
and of the dry frame
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Carbonate Rocks
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Velocity vs. Injected Volume and Pressure
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Velocities of the dry rock frame
after injection
V
P
V
P
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Velocity vs. Injected Volume and Pressure
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Time-Lapse SEM
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Mavko & Vanorio – Stanford University Rock Physics Project.
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Time-Lapse SEM
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Chamosite-Rich Sandstones
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Velocity vs. Injected Volume and Pressure
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Velocities of the dry rock frame
after injection
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Velocity & Fe Conc. vs. Inject. Volume and Pressure
27 – 27 Tiziana Vanorio.
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Time-Lapse SEM
Mavko & Vanorio – Stanford University Rock Physics Project.
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Time-Lapse SEM
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Time-Lapse SEM
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Time-Lapse SEM
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Rock Physics Models
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Modeling: Elastic Response to Saturation
Increasing CO2
f L2
VP
VP 0
Finite element and analytical
methods to simulate velocity vs.
frequency response of CO2
saturation. In the field, we expect
Sw heterogeneities to depend on
lithologic scales
Different scales of saturation
Data from Cadoret, 1993
1kHz
50kHz
500kHz
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Modeling: Elastic Response to Saturation
Increasing CO2
f L2
VP
VP 0
We have developed a simple,
differential scheme that allows
us to analytically superimpose
distributions of saturation scales
in the rock.
Data from Cadoret, 1993
1kHz
50kHz
500kHz
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Mavko & Vanorio – Stanford University Rock Physics Project.
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Modeling: Fluid-Solid Substitution
Classic Scenario: Rock with some initial pore fill. We have measured (e.g., from well logs):
• Initial elastic constants
• Porosity
• Mineral moduli
We want to predict the new elastic moduli of the same rock, when the pore space is filled with something else.
In our case, this could be brine, CO2, or solid
mineral.
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Modeling: Fluid-Solid Substitution
Predicting the new moduli after substitution of the
pore fill is (almost) never unique, without knowledge
of the pore space geometry.
But … we can predict bounds on the substituted moduli.
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Mavko & Vanorio – Stanford University Rock Physics Project.
Modeling: Fluid-Solid Substitution
– 37
Gassmann gives a unique prediction, only because we make a very strong assumption that the pore space is connected. If we don’t know much about the pore space, then Gassmann gives a lower bound. It is well known that disconnected pores, squirt, etc yield a different result. (Gibiansky and Torquato, 1998)
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Mavko & Vanorio – Stanford University Rock Physics Project.
Modeling: Fluid-Solid Substitution
– 38
So how do we model solid substitution?
… we need an exact continuum mechanics equation for the rock elasticity.
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Mavko & Vanorio – Stanford University Rock Physics Project.
Modeling: Fluid-Solid Substitution
– 39
Points on the HS bounds are physically realizable -- the
HS equations are the exact expressions for the effective
moduli of those materials.
Porosity
Bulk
Modulu
s
Quartz
Soft solid
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Mavko & Vanorio – Stanford University Rock Physics Project.
Modeling: Fluid-Solid Substitution
– 40
Fluid or solid substitution for a point on the HS bounds
is exact and unique.
Porosity
Bulk
Modulu
s
Quartz
Substitute
stiffer pore fill
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Mavko & Vanorio – Stanford University Rock Physics Project.
Modeling: Fluid-Solid Substitution
– 41
Off the bounds? We construct modified upper HS bound through
point X. Hence, MUHS is the exact expression for modulus of
material at X, which can be constructed from points P and Q,
which in turn are constructed from the end points.
“Embedded Bounds Method”
Porosity
Bulk
Modulu
s
K fl 1GPa; G fl 0.5GPa;
Initial pore fill – soft solid
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Mavko & Vanorio – Stanford University Rock Physics Project.
Modeling: Fluid-Solid Substitution
– 42
Fluid or solid substitution for point X can be computed
exactly...
Porosity
Bulk
Modulu
s
Porosity
Bulk
Modulu
s
K fl 1GPa; G fl 0.5GPa; K fl 3GPa; G fl 2GPa
Initial pore fill – soft solid New pore fill – stiffer solid
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Mavko & Vanorio – Stanford University Rock Physics Project.
Modeling: Fluid-Solid Substitution
– 43
… but not uniquely. We can construct an infinite number of
MUHS and an infinite number of MLHS bound through point X.
Each transforms to a different modulus at X’ after substitution.
Bulk
Modulu
s
Bulk
Modulu
s
Initial pore fill – soft solid New pore fill – stiffer solid
Porosity Porosity
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Accomplishments to Date
• Laboratory measurements completed on four lithologies (clean
sandstone, clay-bearing sandstone, calcite-cemented sandstone,
carbonates)
• Apparatus built and tested for measuring dynamic elastic moduli of CO2-
brine mixtures.
• Analytical method developed to model frequency- and saturation-
dependent elastic properties of CO2-bearing rock.
• Preliminary model developed for “solid-substitution.”
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Summary
• We have observed irreversible changes in porosity, permeability, and
elastic properties in carbonate and clay-bearing rocks when injected
with CO2-brine mixtures.
• These changes to the solid rock frame are not included in conventional
interpretation of seismic data.
• Preliminary observations suggest that dissolution moves elastic
properties along normal diagenetic trends, which gives strategies for
modeling the elastic response to dissolution or precipitation.
• We have developed a strategy for modeling “solid substitution in rocks,
based on embedded Hashin-Shtrikman bounds. We have shown that all
fluid or solid substitution is nonunique unless information on pore
microgeometry is available.
• Many rock models have an implicit geometry. Be cautious with
substitution. Even though it fits the original data exactly, its substituted
prediction might be wrong. 45
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Future Plans
• Complete measurements on the compressibility of CO2-brine mixtures.
• Complete theoretical modeling on effects of frequency, saturation,
pressure, and permanent changes to the rock frame.
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Appendix
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Organization Chart
• Mavko PI
• Dr. Tiziana Vanorio – Laboratory lead
• 1 Postdoc
• 2 Graduate Students
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49
Gantt Chart
= task completed