IEA GHG Weyburn CO 2 monitoring and storage project C. Preston a , M. Monea b , W. Jazrawi b , K. Brown T ,c , S. Whittaker d , D. White e , D. Law f , R. Chalaturnyk g , B. Rostron h a Natural Resources Canada, 1 Oil Patch Drive, Devon, Alberta, Canada T9G 1A8 b Petroleum Technology Research Centre, 6 Research Drive, Regina, Saskatchewan, Canada S4S 7J7 c Geological Storage Consulting, Inc., 17 Royal Oak Crescent, Calgary, Alberta, Canada T3G 4X8 d Saskatchewan Industry and Resources, 201 Dewdney Avenue, Regina, Saskatchewan, Canada S4N 4G3 e Natural Resources Canada, 615 Booth Street, Ottawa, Ontario, Canada K1A 0E9 f Alberta Research Council, 250 Karl Clark Road, Edmonton, Alberta, Canada T6N 1E4 g University of Alberta, Civil and Environmental Engineering, 220 Civil Building, Edmonton, Alberta, Canada T6G 2G7 h University of Alberta, Earth and Atmospheric Sciences, 3-19D Earth Science Building, Edmonton, Alberta, Canada T6G 2E3 Abstract This paper presents an integrated overview of the results from over 50 individual technical research projects conducted under the auspices of the International Energy Agency Greenhouse Gas R&D Programme [1] [International Energy Agency Greenhouse Gas R&D Programme, http:// www.ieagreen.org.uk]. The overall project, called the IEA GHG Weyburn CO 2 Monitoring and Storage Project [2] [IEA GHG Weyburn CO 2 Monitoring and Storage Project, http://www.ieagreen.org.uk], was created to predict and verify the ability of an oil reservoir to securely and economically store CO 2 . Research activities in the project were divided into four bthemesQ that applied leading-edge science and engineering in geophysics, geomechanics, geochemistry, geology, reservoir engineering, risk assessment, and economics. D 2005 Elsevier B.V. All rights reserved. Keywords: IEA GHG (International Energy Agency Greenhouse Gas R&D Programme); PTRC (Petroleum Technology Research Centre); Weyburn; CO 2 (carbon dioxide); Storage; Monitoring 0378-3820/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fuproc.2005.01.019 T Corresponding author. Tel.: +1 403 208 5577. E-mail address: [email protected] (K. Brown). Fuel Processing Technology 86 (2005) 1547– 1568 www.elsevier.com/locate/fuproc
Transcript
Fuel Processing Technology 86 (2005) 1547–1568
www.elsevier.com/locate/fuproc
IEA GHG Weyburn CO2 monitoring
and storage project
C. Prestona, M. Moneab, W. Jazrawib, K. BrownT,c, S. Whittakerd,
D. Whitee, D. Lawf, R. Chalaturnykg, B. Rostronh
aNatural Resources Canada, 1 Oil Patch Drive, Devon, Alberta, Canada T9G 1A8bPetroleum Technology Research Centre, 6 Research Drive, Regina, Saskatchewan, Canada S4S 7J7cGeological Storage Consulting, Inc., 17 Royal Oak Crescent, Calgary, Alberta, Canada T3G 4X8
fAlberta Research Council, 250 Karl Clark Road, Edmonton, Alberta, Canada T6N 1E4gUniversity of Alberta, Civil and Environmental Engineering, 220 Civil Building,
Edmonton, Alberta, Canada T6G 2G7hUniversity of Alberta, Earth and Atmospheric Sciences, 3-19D Earth Science Building, Edmonton, Alberta,
Canada T6G 2E3
Abstract
This paper presents an integrated overview of the results from over 50 individual technical
research projects conducted under the auspices of the International Energy Agency Greenhouse Gas
R&D Programme [1] [International Energy Agency Greenhouse Gas R&D Programme, http://
www.ieagreen.org.uk].
The overall project, called the IEA GHG Weyburn CO2 Monitoring and Storage Project [2] [IEA
GHG Weyburn CO2 Monitoring and Storage Project, http://www.ieagreen.org.uk], was created to
predict and verify the ability of an oil reservoir to securely and economically store CO2. Research
activities in the project were divided into four bthemesQ that applied leading-edge science and
engineering in geophysics, geomechanics, geochemistry, geology, reservoir engineering, risk
assessment, and economics.
D 2005 Elsevier B.V. All rights reserved.
Keywords: IEA GHG (International Energy Agency Greenhouse Gas R&D Programme); PTRC (Petroleum
Technology Research Centre); Weyburn; CO2 (carbon dioxide); Storage; Monitoring
T Corresponding author. Tel.: +1 403 208 5577.
0378-3820/$ -
doi:10.1016/j.
E-mail add
see front matter D 2005 Elsevier B.V. All rights reserved.
Fig. 4. Weyburn initial EOR area Actual production.
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–1568 1551
A secondary objective was the application of economic realities to such an
undertaking by predicting the point at which a CO2 storage project reaches its economic
limit. The application of customized economic models to the various storage cases
helped in assessing not only cases of CO2 storage in conjunction with EOR operations
but also of CO2 storage in non-EOR situations such as saline aquifers, which have a
significantly larger CO2 storage potential compared to depleting oil pools [7].
The ultimate deliverable from the IEA GHG Weyburn Project was a credible
assessment of the permanent containment of injected CO2 through formal risk analysis
techniques including long-term predictive reservoir simulations not only in the
Williston Basin but also at other sedimentary basins where CO2 storage may be
contemplated.
3. Results and discussion
The IEA GHG Weyburn Project was completed in June 2004. Results show strong
support for both the feasibility and safety of geological CO2 storage [11]. Clearly, CO2
storage can safely take place without impacting EOR operations [12]. In fact,
economic studies demonstrated that implementation of incentives used to motivate
additional CO2 storage, beyond that associated with EOR, could also ultimately result
in additional oil recovery [13]. A Phase 2 of the IEA GHG Weyburn Project began in
mid-2004.
The following has been organized into four main bthemes,Q which were chosen to
group over 50 research subtasks in a manner corresponding to the main objectives of
the project.
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–15681552
3.1. Geological characterization of the geosphere and biosphere
3.1.1. Purpose
The principal aim of geological characterization was to assess the integrity of the
geological bcontainerQ encompassing the Weyburn Unit for effective long-term storage of
CO2 [11]. Data obtained during this assessment were used to develop a three-dimensional
system model that includes features and properties of an area extending 10 km beyond the
CO2 flood extent to provide the geological framework for the risk assessment of the long-
term fate of CO2 injected into the subsurface at Weyburn (see Fig. 5).
3.1.2. Technical approach
The Weyburn Oil Pool is a giant oilfield containing about 1.4 billion barrels of oil in
place in limestones and dolostones (Midale Beds) of Mississippian age. Carbonates of the
Midale reservoir occur at about 1.5 km depth in the northeastern portion of the Williston
Basin, a sedimentary basin broadly similar to the Illinois and Michigan basins of North
America and numerous intracratonic basins that occur elsewhere around the world.
Characterization of the Weyburn geological system for CO2 storage targeted the
delineation of primary and secondary trapping mechanisms and the identification of any
potential pathways of preferential CO2 migration [11]. To place these components within a
regional or basinal context, the geological framework was constructed for a region
Williston BasinRegional Study
(200 x 200 km)
System Model
(10 km beyond EOR)
Manitoba
Saskatchewan
Alberta
North Dakota
South Dakota
Montana
Wyoming
Fig. 5. Geoscience framework.
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–1568 1553
extending 200�200 km around the Weyburn Field that includes portions of Saskatchewan,
North Dakota, and Montana [17]. Large-scale studies such as this more effectively reveal
basin hydrogeological flow characteristics and the underlying tectonic framework that can
greatly influence depositional patterns of sedimentary packages and fracture development.
Increased detail was focused within an area extending 10 km beyond the limits of the CO2
flood that forms the basis for the system model used in risk assessment.
The development of a comprehensive geological model for use in risk assessment
required a focused and highly integrated multidisciplinary approach. Lithostratigraphic
mapping identified over 140 individual surfaces from the Precambrian basement to
ground surface. The lithostratigraphic units were used to define larger flow packages, or
hydrostratigraphic units, that were mapped and characterized using extensive data
analysis to provide fundamental information on fluid behavior within the basin as
required by performance assessment [14]. Much of the 2000 km of 2D seismic data
processed to refine the characterization of subsurface features and basement tectonics was
integrated with high-resolution aeromagnetic data to augment fracture and regional fault
delineation [15]. Detailed geological studies performed on primary seals (those in contact
with the reservoir) and secondary seals (barriers to flow higher in the stratigraphic
column) included core descriptions, petrography, isotope geochemistry, and fluid
inclusion studies [18]. Shallow hydrogeological surveys defined the distribution and
continuity of potable aquifers in near-surface sediments of the study region. Remotely
sensed imagery analysis was used to determine whether structural elements observed in
the deep subsurface are related to linear surface features identified through air photo and
satellite imagery. Soil gas surveys, designed to transect some of the linear surface
features, were performed regularly around the Weyburn Unit to monitor for changes in
CO2 fluxes in soils that may be due to potential anthropogenic CO2 migration. Other
specialized studies undertaken included obtaining cores from selected strata above the
reservoir for petrophysical measurements, till sampling for soil gas characterization,
shallow aquifer demarcation, and natural analog comparisons. Integration of these diverse
data provided a coherent and representative geological model that can be tailored for use
in risk assessment.
3.1.3. Results and conclusions
A good geological description of the reservoir and a large surrounding region was
developed from both existing and newly generated geological, geophysical, and
hydrogeological information. A robust system model of the geosphere and the biosphere
was constructed to serve as the platform for the long-term risk assessments of the Weyburn
CO2 storage site [16]. The main conclusion of the work was that the geological setting at
the Weyburn field appears to be highly suitable for long-term geological storage of CO2
[11].
One of the most important results from this work was the development of a
tremendous geoscience dataset pertinent to understanding the geological storage of CO2
in the Williston Basin and other sedimentary basins. A great deal of information was
accumulated within a relatively short time span so there remains an additional
opportunity for more advanced interpretation and integration of this world-class
database.
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–15681554
3.2. Prediction, monitoring, and verification of CO2 movements
3.2.1. Purpose
An underlying goal of the IEA GHG Weyburn Project was to optimize effective
management of the reservoir for enhanced oil recovery and storage of CO2. To
accomplish this, an improved understanding of the reservoir properties and the nature of
how the injected CO2 spreads and interacts with the rock matrix and reservoir fluids was
required. The specific objectives of this work were to test and improve conventional
geological-based simulator predictions of how the CO2 flood will progress, and to assess
the chemical reactions and mechanisms for long-term storage of CO2 within the
reservoir. Monitoring entailed observing the physical and chemical effects of CO2
injection on the state of the reservoir system with a focus on tracking the spread of CO2
within and potentially outside the reservoir. Verification was defined as the
substantiation of the interpreted monitoring results to allow reliable estimation of the
volume and distribution of CO2 in the subsurface.
3.2.2. Technical approach
Initial predictions of how the CO2 flood would progress were based on flow
simulations using an existing reservoir model that was constructed with the well-bore
geology from the dense network of wells in the Weyburn field (see Fig. 6) [13]. A variety
of seismic and geochemical sampling methods were subsequently used to monitor the CO2
injection process and characterize the reservoir between boreholes. Seismic imaging of the
CO2 in the subsurface was accomplished primarily by time-lapse 3D multi-component
surface seismic reflection imaging complemented by time-lapse and static borehole (VSP
and crosswell) seismic surveys and passive seismic monitoring (see Table 1 for a detailed
list). Rock/fluid property measurements, combined with reservoir simulation and
production history matching including seismic constraints, were used to calibrate the
seismic observations to known CO2 injection volumes and to update the reservoir
simulation model [15].
The geochemistry of produced oil, gas, and brine was regularly monitored and analyzed
for a broad range of chemical and isotopic parameters to infer injection-related chemical
processes within the reservoir and to track the path of injected CO2. This analytical work
was supported by model calculations and laboratory studies on geochemical reactions. Soil
gas sampling was designed to detect injected CO2 that may have escaped from the
reservoir and migrated to the surface [14].
3.2.3. Results and conclusions
Seismic surveys were highly successful and were used in bground-truthingQ reservoirmodeling. The seismic surveys clearly demonstrated an ability to detect anomalies in the
reservoir induced by CO2 invasion (see Fig. 7) [15]. Geochemical fluid sampling gave
good insights into the movement of CO2 within the reservoir and gave strong indication
of incipient CO2 breakthrough at wells (see Fig. 8) [14]. Tracer surveys were not as
successful due to a variety of technical and operational problems. Geochemical modeling
to determine the long-term CO2 material capture in various sequestration forms (trapping
mechanisms) was reasonably concluded. However, further efforts in reactive transport
Fig. 6. Fence diagram of predicted CO2 saturation distribution after 26 months of CO2 injection using the geological-based reservoir simulation model.
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Table 1
Data acquisition schedule
Schedule of geochemical and seismic monitoring activities within the Phase 1A CO2 injection area. 3D multi-
component surface seismic surveys (CSM=Colorado School of Mines; EnCana) were supplemented by borehole
crosswell seismic survey; CO2=injected volume of CO2; fluid/gas=production fluid sampling.
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–15681556
modeling to complete the geochemical picture will be made in Phase 2. There was no
evidence from either the time-lapse seismic or the soil gas sampling to indicate
migration of measurable amounts of CO2 into the overburden or seepage to the surface
[14,15].
3.3. CO2 storage capacity and distribution predictions and the application of economic
limits
3.3.1. Purpose
There were several objectives within this theme: to estimate the maximum CO2 storage
capacity achievable both physically and economically at a geological storage site, to
predict the CO2 distribution and trapping mechanisms within the storage site, and to
determine if the CO2 storage performance can be improved through the application of
conformance control treatments.
3.3.2. Technical approach
A multi-phase, multi-component compositional reservoir simulation model was
used to predict the CO2 storage capacity in the Weyburn Unit reservoir [13]. The
approach taken in modeling the size and complexity of 75 EOR patterns was to start
with fine-grid single-pattern simulations and end with a coarse-grid 75-pattern
simulation. The process involved three levels of upscaling: (1) from a detailed
geological model of the Weyburn reservoir to a fine-grid reservoir simulation model;
(2) from three fine-grid single-pattern models to coarse-grid models of the same
4D-3C Time-Lapse Seismic Surveys vs. Baseline survey (Sept. 2000)
2001-2000 2002-2000
Marly Zone
Courtesy: EnCana Corporation
Fig. 7. Time-lapse seismic surveys vs. baseline survey (September 2000).
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–1568 1557
patterns; and (3) from three coarse-grid single-pattern models to a 75-pattern model
using the same grid resolution.
Laboratory measurements of oil properties and CO2–oil phase equilibrium behaviour
using oil samples collected periodically from different wells provided information to
tune the equation-of-state parameters in the PVT model used in the reservoir
simulation. The reservoir simulation model was validated by both laboratory-scale
and field-scale simulations. In the laboratory-scale simulation, CO2 coreflood experi-
ments conducted with different oil samples were history-matched, while in the field-
scale simulation, field production histories in three different patterns with different
CO2 injection strategies (i.e., bsimultaneous but separate water and gas injectionQ(SSWG), bVuggy water-alternating gasQ (VWAG), and bMarly, Vuggy water-alternating
gasQ (MVWAG)) were history-matched. Then, the reservoir simulation model was used
to predict the CO2 storage performance during the EOR period, first in the three single
patterns and then in the entire 75 EOR patterns. EnCana’s operating strategies were
followed as closely as possible. This was labeled the base case. Alternative CO2
storage cases after EOR were also investigated with a focus on promoting additional
CO2 storage.
Using the predicted CO2 distribution in the reservoir at the end of EOR, a geochemical
model was used to provide a preliminary assessment of the amount of CO2 that will be
stored in the reservoir through different trapping mechanisms (solubility, ionic, and
mineralogical trappings) [14]. The geochemical modeling also used formation and
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–15681558
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–1568 1559
injection fluid compositions, detailed mineralogical assessment of each of the major flow
units in the reservoir, and evaluation of mineral kinetic data.
The performance of both CO2 storage and EOR depends on achieving maximum
sweep efficiencies (conformance). These sweep efficiencies can be improved through
conformance control techniques [19]. The Weyburn reservoir pay zone is a fractured
carbonate with large permeability contrasts, which allows the injected CO2 to finger
and bypass a significant fraction of the recoverable oil. Laboratory evaluation of
commercially available technologies for conformance control such as CO2–foam, gel,
and gel–foam processes was conducted to select the most suitable options for the
Weyburn reservoir. Well production histories provided by EnCana were analyzed to
select candidate wells with high production gas-to-oil ratios for future conformance
control field trials. The analysis included reservoir simulation modeling using existing
fine-grid single-pattern simulations to design the field trial and predict the field trial
performance.
With the prediction of CO2 storage capacities and EOR performance, an economic
model was used to apply economic constraints to the CO2 storage cases [13]. This storage
economic model has the capability to calculate CO2 capture, transportation, and storage
costs, in addition to the conventional economic evaluation of an EOR process. The model
can be run either for stand-alone CO2 storage options (e.g., depleted oil or gas reservoirs,
saline aquifers, etc.) or storage in conjunction with CO2 EOR projects. The objective of the
storage economics model was to guide geological storage decisions where not only
estimates of the maximum amount of CO2 that can be physically stored can be determined,
but also how much of that CO2 is actually economically stored under different gas credits
assumptions.
3.3.3. Results and conclusions
Modeling started with fine-grid, individual well patterns and gradually upscaled to a
coarser, 75-pattern grid. Good history match was achieved with actual production data (see
Fig. 9). Also, predictions of total CO2 injected matched reasonably well EnCana’s internal
estimates [21]. Other CO2 storage cases were also investigated including continuing with
CO2 injection past the termination of the commercial EOR project (approximately year
2033), while continuing to produce incremental oil from wells still operating under a
certain gas-to-oil ratio limit and disposing of produced water elsewhere to make room for
additional CO2 injected [13].
Conformance control treatments developed in this project predicted a substantial
improvement in volumetric sweep efficiency from the application of specially formulated
gel treatments to the best candidate wells. If successfully applied, conformance control
may contribute another 10% additional recovery of the total EOR oil from the wells
treated. This in turn could accommodate another 1.8 million tons of additional CO2
Fig. 8. Geochemical fluids in the reservoir. Contour maps of total alkalinity, [Ca], and d13CHCO3across the initial
injection area (outlined in blue). Pre-injection (baseline) contoured measurements are shown on the far left while
post-CO2 injection values (after 10, 21, and 31 months of continuous injection) are contoured to the right. Dots
represent well locations sampled during each trip. CO2 dissolution is evident by 10 months, and carbonate
dissolution is evident by 21 months, as can be seen in the d13CHCO3values (becoming more negative and more
positive, respectively).
Fig. 9. Oil production rate history match (figure shows one of the initial patterns).
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–15681560
stored, assuming a case where 20% of the EOR patterns received a gel treatment
[19].
Detailed mineralogy of the Weyburn reservoir was determined from microscopic
examination, X-ray diffraction (XRD) results, and LPNORM analysis of approximately
100 samples that established the presence and abundances of minerals for each of
EnCana’s reservoir flow units. Results show that even in a carbonate reservoir such as
Weyburn, silicate minerals are present in sufficient quantity to react with CO2-charged
fluid and enable mineral fixation of CO2. Using estimates of the porosity and the volume
of each of the flow units and the reactions determined through the geochemical modeling,
the maximum potential amount of trapping in each flow unit was estimated (see Table 2).
After 5000 years, it was determined that a free supercritical CO2 gas phase will no longer
exist, having been effectively trapped [14].
A storage economic model was successfully developed. Alternate economic scenarios
were tested (e.g., the above case predicated on continued CO2 injection in the Weyburn
Unit past the economic limit of the EOR operation). The EOR phase allowed 23 MT of
CO2 to be physically and economically stored. The post-EOR phase allows for up to an
additional 31 MT of CO2 to be physically stored. However, the portion of the 31 MT that
can be economically stored would depend on the amount of the CO2 credits received and
the desired rate of return for the operation.
Table 2
Geochemical modeling results
Geochemical modeling results summary
Maximum potential CO2 trapping in the Midale reservoir
22.5 million tons of solubility trapping of CO2
0.257 million tons of trapping of CO2
22.3 million tons of mineral trapping of CO2
Up to 49% of the injected CO2 can be trapped in bnewQ carbonate minerals
Summary
45 million tons of CO2 potential trapping
20 million tons of CO2 planned injection
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–1568 1561
3.4. Long-term risk assessments of the storage site
3.4.1. Purpose
The risk assessment was done to identify and evaluate the risks associated with
geological storage of CO2 within the Weyburn reservoir and assess the reservoir’s ability
to securely store CO2.
3.4.2. Technical approach
Risk assessment embodies the overall process of risk analysis and risk evaluation.
Risk analysis involves the systematic use of project information to identify sources of
potential CO2 leakage and to estimate their probability and magnitude. Risk evaluation
examines the acceptability of these risks considering the needs, issues, and concerns of
stakeholders. Geological storage of CO2 is a developing technology and, as such, does
not have a sufficient knowledge base from which to extract historical data on all
leakage risks. Consequently, the risk analyses conducted in the IEA GHG Weyburn
Project focused on assessing storage system performance or behavior to increase our
understanding of crucial processes. These processes will form a critical component of
the final risk assessment in Phase 2. This risk assessment process will ultimately
mature into a framework that considers social, economic, and political factors
associated with geological storage; evaluates the risks associated with a geological
storage reservoir; and assesses the effectiveness of remedial actions that can be taken
to minimize both near-term and long-term probabilities and consequences arising from
CO2 leakage. Equally important, this process will provide the basis for communication
about the existence, nature, form, magnitude, and acceptability of risks associated with
the geological storage of CO2.
As with many engineered or natural systems, the Weyburn bSystem,Q which was
comprised of the geology of the reservoir and overlying and underlying layers, varying
well types, groundwater flow regimes, fluid characteristics, and so on, is very complex.
This complexity was managed through application of a rigorous and formal systems
analysis approach, firstly to identify and define the system and, secondly, to define base
and alternative scenarios for the long-term fate of CO2 within the system. Scenarios are
the plausible and credible ways in which the Weyburn System might evolve over
decades to thousands of years. Integration of the performance assessment with the
major research themes of the project remains an essential element in its success.
Geological characterization research led to a detailed three-dimensional System Model
description. Embedded within the System Model is the entire 75 EOR pattern area
planned for CO2 flood rollout and used to predict the CO2 storage capacity in the
Weyburn reservoir. These large-scale simulation results provided the necessary fluid
phase and pressure distributions at the end of EOR for the long-term risk assessment
out to 5000 years.
From an assessment perspective, the two main elements of the System Model are
the geosphere and biosphere. The geosphere, which includes the reservoir, incorporates
all geological, hydrogeological, and petrophysical information assimilated for the
System Model. The biosphere extends to a depth of about 300 m below ground
surface and includes soil, surface water, and the atmosphere, and flora and fauna
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–15681562
found within these areas. To assist in identifying the processes that could be relevant
to the evolution or performance of the system, a list of features, events, and processes
(FEPs) was developed (see Fig. 10). Features are physical characteristics of the system
(e.g., permeability), events are discrete occurrences influencing the system (e.g.,
earthquakes), and processes identify the physics of change within the system (e.g.,
diffusion). Fig. 11 provides a small sample of the FEPs list defined for this project.
An evaluation of these FEPs, including their interactions, was used to describe how
the system will evolve over the timeframe of the risk assessment and form the
foundation for the development of a scenario that describes how the system is
expected to evolve (called the base scenario) in the far future, and other scenarios that
describe alternative but feasible futures.
Based on reviews of the FEPs by project researchers and stakeholders, a base
scenario was developed and is summarized in Table 3 and Fig. 12. As part of
Category WEYBURN FEP TITLE Category WEYBURN FEP TITLESYSTEM FEPs SYSTEM FEPs (continued)Rock properties Other gas
Mechanical properties of rock (including stress field) Gas pressure (bulk gas)Mineralogy Release and transport of other gasesOrganic matter (solid)Presence and nature (properties) of faults / lineaments GeologyPresence and nature (properties) of fractures Seismicity (local)Cap-rock integrity Temperature / thermal field
Uplift and subsidence (local)Hydrogeological properties
Cross-formation flow Abandoned WellsFluid characteristics of rock Annular space (quality / integrity)Geometry and driving force of groundwater flow system Boreholes - unsealed (extreme case)Groundwater flow (including rate and direction) Corrosion of metal casing (abandoned wells)Hydraulic pressure Expansion of corrosion products (abandoned well metal casing)Hydrogeological properties of rock Incomplete borehole sealing / Early seal failurePore blockage Incomplete records of abandonment / sealingSaline (or fresh) groundwater intrusionTransport pathways NON-SYSTEM FEPs
EFEPsChemical/Geochemical Artificial CO2 mobility controls
Carbonation Climate changeColloid generation Cross-formation flow (fast pathways)Degradation of borehole seal (cement / concrete) Depth of future wells drilledDissolution of minerals/precipitates/organic matter EarthquakesDissolution / exsolution of CO2 EOR-induced seismicityDissolved organic material Exreme erosionGroundwater chemistry (basic properties) Fault activationMethanogenesis Future drilling activitiesMicrobial activity GlaciationMineral surface processes (including sorption/desorption) Hazardous nature of other gasesPrecipitation/Coprecipitation/Mineralisation Hydraulic fracturing (EFEP?)Reactive gaseous contaminants Hydrothermal activityRedox environment / heterogeneities Igneous activitySalinity gradient Major rock movement
Metamorphic processesCO2 Properties and Transport Mining and other underground activities
Advective flow of CO2 Monitoring (future)Colloid transport Regional uplift and subsidence (e.g. orogenic, isostatic)Diffusion of CO2 Rock properties - undetected featuresDispersion of CO2 (e.g. faults, fracture networks, shear zone, etc.)Gas flow Sea-level changeSource term (CO2 distribution) Seismic pumpingThermodynamic state of CO2 Seismicity (EXTERNAL)Transport of CO2 (including multiphase flow)
Fig. 10. Features, events, and processes relevant to the Weyburn CO2 storage system.
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–1568 1563
the systems analysis approach, alternative scenarios (modifications to the base
scenario) were also developed (see Table 4). Storage system performance
simulations in the IEA GHG Weyburn Project were performed primarily on the base
scenario.
3.4.3. Results and conclusions
This was the most challenging theme in the project.
A comprehensive deterministic risk assessment (DRA) numerical simulation approach
was employed in simulating the potential of CO2 migration away from the Weyburn Unit
and into the geosphere and the biosphere over a period of up to 5000 years following the
conclusion of the commercial EOR project. Augmenting the deterministic assessment
was a smaller, stochastic (probabilistic risk assessment or PRA) simulation of the same
systems model but using a compartment model and analytical methods. A benchmarking
exercise was also undertaken to ensure that the two PRA/DRA approaches gave similar
results on a simple, idealized test case. The benchmarking proved reasonably successful,
illustrating both the challenges and value in comparing deterministic and stochastic
simulation approaches and highlighting the limitations inherent in both approaches.
Initial numerical simulation results on a single pattern indicated that an estimated 2.7%
of the initial CO2 in place may migrate out of the 75 patterns, 5000 years after the end of
EOR, most of it igrating laterally into the unconfined eastern areas of the Midale
reservoir. The migration is carried out by diffusion through the oil and water phases,
pushed along by the action of slow-moving aquifers. However, no CO2 appears to ever
reach or penetrate the Watrous formation, a regionally extensive and thick aquitard above
the main anhydrite cap rock, which forms the primary seal for the Midale reservoir [20].
Table 3
Base scenario
! System model domain: the Weyburn 75-well patterns and a 10-km zone surrounding it.
! Time frame: inception of EOR using injected CO2 and with an nominal end time taken as the earlier of 5000
years or the time at which there is 50% loss (to the biosphere) of CO2 that was in place within the geosphere at
the end of EOR.
! The caprock may have natural fractures or discontinuities but all are isolated or sealed such that caprock
integrity is not impaired.
! There is a series of aquifer/aquitards above and below the reservoir horizon. These media may contain fractures
and fissures.
! Will consider physical trapping features, which have naturally contained the oil/gas within the reservoir.
! Will consider geochemical effects (formation of carbonate minerals and CO2 removal by solubility and ionic
trapping) in the aqueous phase of all aquifers.
! The biosphere starts from the deepest possible potable aquifer and technically includes all of the glacial till and
surficial deposits (i.e., it extends to a depth of about 300 m below ground surface). It includes soil, surface
water, atmosphere, flora, and fauna.
! Includes the presence of all wells found within the system model domain.
! All wells assumed to have been abandoned following current field abandonment procedures applicable at the
time of abandonment. Note that this includes wells that may have been sealed in earlier years according to
different abandonment procedures and regulations.
! Well seals may degrade after abandonment. Well seals are primarily the cement used to fill the annulus between
the casing and borehole, cement and metallic plugs used to fill the casing bore, and the cap welded onto the
casing approximately 4 m below ground surface. Consideration should also be given to degradation of the
casing itself within the reservoir and all aquifers and aquitards penetrated by the casing.
! The base scenario includes consideration of FEPs that could affect the storage and movement of CO2. These
include, but are limited to, processes such as hydrodynamics, geochemistry, buoyancy and density-driven flow,
dissolution of CO2 in water and residual oil, and pressure–temperature changes occurring within the geologic
formations.
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–15681564
Early simulations confirmed that wells and their integrity strongly influence
leakage from the storage reservoir [18], that the Marly permeability controls CO2
leakage rates through boreholes, and that storage within the geosphere is greatly
• Defined as the “expected evolution of the Weyburn CO2 storage system”
– CO2 migration pathways will be a combination of natural and man-made pathways– Wellbore casing seals will be assumed not to leak at time zero– CO2 -rock -water interactions may occur (long-term geochemical modeling)
Fig. 12. Weyburn base scenario.
Table 4
Description of the alternative scenarios
Alternative scenario name Unique characteristics
Engineering options for EOR:
(a) maximize CO2 storage;
(b) water flush at the end
of EOR
Option (a) involves larger reservoir pressures; overpressurisation and
caprock fractures are possible problems. Option (b) would result in
changes to CO2 distributions in the reservoir and could also decrease
CO2 storage
Well abandonment options Emphasis on improved long-term sealing capabilities
Leaking wells Involves extreme failures only as the base scenario has dnormalT leakageFault movement of reactivation,
including undetected faults
Could represent a new and fast CO2 transport pathway; could affect
several formations
Tectonic activity Low probability but possible
Deliberate and accidental
human intrusion: (a)
destruction of surface
casing; (b) resource
extraction
Likely scenario involves intrusion into the reservoir in search for CO2 or
petroleum. Option (a) could affect the uppermost seal in one or more wells.
Option (b) likely involves extraction of some shallower resource, but could
lead to CO2 blowout from CO2 trapped in formations above the reservoir
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–1568 1565
enhanced where there is groundwater flow above about 1 m/year in any upper aquifer
zones.
Synthesis of all available well information within the initial EOR area of the project
provided the performance assessment studies with ranges of well types and their
associated transport properties. Cement degradation models incorporating sulphate
attack, mechanical fatigue, carbonation, and leaching have provided wellbore cement
hydraulic conductivities in the range of 1�10�16 m2 for most well types (see Fig. 13).
For historical injection and production pressures within aging wellbores, modeling
predicted minimal impact on the sealing capability of the wellbores over the life of the
EOR project.
Performance assessment studies to date show clear support for the conclusion
reached within the geological characterization studies—the geological setting at the
Weyburn Field is highly suitable for long-term subsurface storage of CO2. These
studies highlighted the significant capacity of the geosphere region surrounding
the reservoir to effectively sequester CO2 and prevent its migration to the
biosphere. The performance assessment studies also clearly identified wellbores
as a potential primary CO2 leakage pathway to the biosphere in the Weyburn Field
[20].
4. Conclusions
4.1. General conclusions
Very encouraging results have been achieved to date. The information and datasets
have added significantly to all the technical disciplines that are represented within the
project.
Fig. 13. Bounding seal.
C. Preston et al. / Fuel Processing Technology 86 (2005) 1547–15681566
The IEA GHG Weyburn Project has developed a suite of leading-edge monitoring and
verification technologies. The technologies are applicable to many sites around the
world—not just CO2-EOR projects.
The established technical reputation of the research providers was important to the
credibility of the project and the results. There was great cooperation and support among
the sponsors and the research providers.
4.2. Major challenges in completing the IEA GHG Weyburn Project
Integration of all the elements of the project within and between technical disciplines
required a significant effort. Effective integration was critical to the understanding of the
overall system and process that is required for CO2 storage Projects.
