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DOE OSTI2021

Tracer Testing to Characterize Hydraulic Stimulation Experiments at the Raft River EGS Demonstration Site

A series of three tracer tests was conducted over a 3.5-year period as part of the Raft River EGS Demonstration Project in order to characterize the evolution of fluid flow processes resulting from the hydraulic stimulation of the target injection well RRG-9. Injectivity increased very little in RRG-9 as the result of hydraulic stimulation experiments over a 300-day period but increased significantly as brine was injected continuously over the subsequent three years. Here, the tracer tests revealed that fluid flow patterns evolved over time along the injection/production pathway with tracer breaking through progressively earlier and to more wells over the duration of the testing.

EGS↗

DOE OSTI2014

Thermal drawdown and late‐stage seismic‐slip fault reactivation in enhanced geothermal reservoirs

Abstract Late‐stage seismic slip in geothermal reservoirs has been shown as a potential mechanism for inducing seismic events of magnitudes to ~2.6 as late as two decades into production. We investigate the propagation of fluid pressures and thermal stresses in a prototypical geothermal reservoir containing a centrally located critically stressed fault from a doublet injector and withdrawal well to define the likelihood, timing, and magnitude of events triggered by both fluid pressures and thermal stresses. We define two bounding modes of fluid production from the reservoir. For injection at a given temperature, these bounding modes relate to either low‐ or high‐relative flow rates. At low relative dimensionless flow rates the pressure pulse travels slowly, the pressure‐driven changes in effective stress are muted, but thermal drawdown propagates through the reservoir as a distinct front. This results in the lowest likelihood of pressure‐triggered events but the largest likelihood of late‐stage thermally triggered events. Conversely, at high relative non‐dimensional flow rates the propagating pressure pulse is larger and migrates more quickly through the reservoir but the thermal drawdown is uniform across the reservoir and without the presence of a distinct thermal front, and less capable of triggering late‐stage seismicity. We evaluate the uniformity of thermal drawdown as a function of a dimensionless flow rate Q D that scales with fracture spacing s ( m ), injection rate q ( kg/s ), and the distance between the injector and the target point L ∗ ( Q D ∝ qs 2 / L ∗ ). This parameter enables the reservoir characteristics to be connected with the thermal drawdown response around the fault and from that the corresponding magnitude and timing of seismicity to be determined. These results illustrate that the dimensionless temperature gradient adjacent to the fault dT D / dx D is exclusively controlled by the factor Q D . More significantly, this temperature gradient correlates directly with both the likelihood and severity of triggered events, enabling the direct scaling of likely magnitudes and timing to be determined a priori and directly related to the characteristics of the reservoir. This dimensionless scaling facilitates design for an optimum Q D value to yield both significant heat recovery and longevity of geothermal reservoirs while minimizing associated induced seismicity.

Gan, Quan↗

DOE OSTI2017

On the transcritical mixing of fuels at diesel engine conditions

Whilst the physics of both classical evaporation and supercritical fluid mixing are reasonably well characterized and understood in isolation, little is known about the transition from one to the other in the context of liquid fuel systems. The lack of experimental data for microscopic droplets at realistic operating conditions impedes the development of phenomenological and numerical models. To address this issue we performed systematic measurements using high-speed long-distance microscopy, for three single-component fuels (n-heptane, n-dodecane, n-hexadecane), into gas at elevated temperatures (700–1200 K) and pressures (2–11 MPa). We describe these high-speed visualizations and the time evolution of the transition from liquid droplet to fuel vapour at the microscopic level. The measurements show that the classical atomization and vaporisation processes do shift to one where surface tension forces diminish with increasing pressure and temperature, but the transition to diffusive mixing does not occur instantaneously when the fuel enters the chamber. Rather, subcritical liquid structures exhibit surface tension in the near-nozzle region and then, after time surrounded by the hot ambient gas and fuel vapour, undergo a transition to a dense miscible fluid. Although there was clear evidence of surface tension and primary atomization for n-dodecane and n-hexadecane for a period of time at all the above conditions, n-heptane appeared to produce a supercritical fluid from the nozzle outlet when injected at the most elevated conditions (1200 K, 10 MPa). This demonstrates that the time taken by a droplet to transition to diffusive mixing depends on the pressure and temperature of the gas surrounding the droplet as well as the fuel properties. We summarise our observations into a phenomenological model which describes the morphological evolution and transition of microscopic droplets from classical evaporation through a transitional mixing regime and towards diffusive mixing, as a function of operating conditions. We provide criteria for these regime transitions as reduced pressure–temperature correlations, revealing the conditions where transcritical mixing is important to diesel fuel spray mixing.

02 PETROLEUM↗

DOE OSTI2015

The microwave assisted synthesis of 1-alkyl-3-methylimidazolium bromide as potential corrosion inhibitor toward carbon steel in 1 M HCl solution saturated with carbon dioxide

Injection of corrosion inhibitor into the fluid current of oil and gas pipelines is an effective way to mitigate corrosion rate on the inner-surface parts of pipelines, especially carbon steel pipelines. In this research, two alkylimidazolium ionic liquids, 1-decyl-3-methylimidazolium bromide (IL1) and 1-dodecyl-3-methylimidazolium bromide (IL2) have been synthesized and studied as a potential corrosion inhibitor towards carbon steel in 1 M HCl solution saturated with carbon dioxide. IL1 and IL2 were synthesized using microwave assisted organic synthesis (MAOS) method. Mass Spectrometry analysis of IL1 and IL2 showed molecular mass [M-H+] peak at 223.2166 and 251.2484, respectively. The FTIR,{sup 1}H-NMR and {sup 13}C-NMR spectra confirmed that IL1 and IL2 were successfully synthesized. Corrosion inhibition activity of IL1 and IL2 were determined using weight loss method. The results showed that IL1 and IL2 have the potential as good corrosion inhibitors with corrosion inhibition efficiency of IL1 and IL2 are 96.00% at 100 ppm (343 K) and 95.60% at 50 ppm (343 K), respectively. The increase in the concentration of IL1 and IL2 tends to improve their corrosion inhibition activities. Analysis of the data obtained from the weight loss method shows that the adsorption of IL1 and IL2 on carbon steel is classified into chemisorption which obeys Langmuir’s adsorption isotherm.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Single-nanometer iron oxide nanoparticles as tissue-permeable MRI contrast agents

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99 GENERAL AND MISCELLANEOUS↗

DOE OSTI2018

Spray Combustion Cross-Cut Engine Research DOE VT Report

02 PETROLEUM↗

DOE OSTI2021

Fuel Spray Mixing and Wall Interaction

All future high-efficiency engines will have fuel directly sprayed into the engine cylinder. Engine developers agree that a major barrier to the rapid development and design of these high-efficiency, clean engines is the lack of accurate fuel spray computational fluid dynamics (CFD) models. The spray injection process largely determines the fuel–air mixture processes in the engine, which subsequently drive combustion and emissions in both direct-injection gasoline and diesel systems, particularly at cold-start conditions when aftertreatment is ineffective. Engines must be tolerant to a range of fuels, and there must be an understanding of how specific fuel properties affect the spray mixing and evaporation processes to intentionally create better fuels and better injectors. More predictive spray combustion models will enable rapid design and optimization of future high-efficiency engines, providing more affordable vehicles and saving fuel.

33 ADVANCED PROPULSION SYSTEMS↗

DOE OSTI2018

Exergy of air, CO 2 , and H 2 O for use as geothermal fluids

Geothermal energy refers to the thermal energy naturally stored in the hot rock formation buried deep beneath the Earth’s surface. To harvest this source of energy, a fluid is pumped down in a set of injection wells, circulates through the hot rock and then is collected via a set of production wells for heating or other purposes. Furthermore, the selection of this fluid is an important component of a geothermal system. In this work, we review, evaluate, and develop the fundamental equations that can reliably predict the thermodynamic and the transport properties of air, CO 2 , and H 2 O. Using these equations, we characterize and compare the heat extraction and exergy carried by these fluids as they circulate through a hot rock reservoir to determine which fluid offers better functionality for geothermal heat harvesting applications. The results indicate that, in terms of heat extraction and exergy, air is a better fluid compared to CO 2 and water.

15 GEOTHERMAL ENERGY↗

DOE OSTI2022

Leakage From Coexisting Geologic Forcing and Injection‐Induced Pressurization: A Semi‐Analytical Solution for Multilayered Aquifers With Multiple Wells

Abstract Abnormal fluid pressures (above or below hydrostatic pressure) can develop and persist in sedimentary basins. The common occurrence of abnormal pressures may cause challenges for project permitting of geological carbon sequestration (GCS), particularly in reservoirs with pre‐injection overpressure. The leaky wells that may exist in some sedimentary basins can provide flow paths between deep brine aquifers and shallower freshwater aquifers. Pre‐injection relative overpressures can cause brine leakage through leaky wells even before any injection occurs. The tendency for flow through leaky wells is coupled with the process of pressure dissipation that occurs through aquitards. Specifically, with non‐zero permeability, aquitards can dissipate pressure over large areal extents and thereby reduce leakage rates through leaky wells. This study presents development of a semi‐analytical solution for hydraulic head and brine leakage in multilayered aquifer–aquitard systems with geologic pressure forcing. The geologic forcing that causes abnormal pressures in the multilayered system can coexist with any number of injection, extraction, and leaky wells that also affect fluid pressure. The semi‐analytical model is applied to explore how leakage through leaky wells varies as functions of pressurization rate, along with aquitard and leaky well properties in an overpressured multilayered system. The results show that although injection‐induced pressures can dissipate rapidly through suitably permeable aquitards, coexisting geologic forcing may create sustained rates of brine leakage into freshwater aquifers through leaky wells. In GCS, a very low‐permeability aquitard with high capillary entry pressure to free‐phase CO 2 is desired to serve as the caprock to prevent leakage of CO 2 from the storage reservoir. Nevertheless, the results from this study show that the brine leakage impact to shallow freshwater aquifers through leaky wells might substantially decrease with increasing aquitard permeability values, as long as small aquitard permeability and high capillary entry pressure serve to prevent CO 2 leakage.

Cihan, A.↗

DOE OSTI2017

The Influence of Hydraulic Fracturing on Carbon Storage Performance: Hydraulic Fracturing in Carbon Storage

We report that conventional principles of the design and operation of geologic carbon storage (GCS) require injecting CO 2 below the caprock fracturing pressure to ensure the integrity of the storage complex. In nonideal storage reservoirs with relatively low permeability, pressure buildup can lead to hydraulic fracturing of the reservoir and caprock. While the GCS community has generally viewed hydraulic fractures as a key risk to storage integrity, a carefully designed stimulation treatment under appropriate geologic conditions could provide improved injectivity while maintaining overall seal integrity. A vertically contained hydraulic fracture, either in the reservoir rock or extending a limited height into the caprock, provides an effective means to access reservoir volume far from the injection well. Employing a fully coupled numerical model of hydraulic fracturing, solid deformation, and matrix fluid flow, we study the enabling conditions, processes, and mechanisms of hydraulic fracturing during CO 2 injection. A hydraulic fracture's pressure-limiting behavior dictates that the near-well fluid pressure is only slightly higher than the fracturing pressure of the rock and is insensitive to injection rate and mechanical properties of the formation. Although a fracture contained solely within the reservoir rock with no caprock penetration, would be an ideal scenario, poroelastic principles dictate that sustaining such a fracture could lead to continuously increasing pressure until the caprock fractures. We also investigate the propagation pattern and injection pressure responses of a hydraulic fracture propagating in a caprock subjected to heterogeneous in situ stress. In conclusion, the results have important implications for the use of hydraulic fracturing as a tool for managing storage performance.

58 GEOSCIENCES↗

DOE OSTI2021

A screening model for predicting injection well pressure buildup and plume extent in CO 2 geologic storage projects

We present a new screening model for predicting injection well pressure buildup and CO 2 plume migration for CO 2 geologic sequestration projects. The model requires only limited information and is quite accurate when compared to detailed simulation results. Such models can assist project developers during the early days of project planning (e.g., for 45Q related projects), and also help regulators perform simple checks against detailed numerical models. The screening model consists of two correlations: one for injectivity index in terms of the slope of the CO 2 fractional flow curve, and the second for total storage efficiency within the footprint of plume as a function of gravity number and slope of the CO 2 fractional flow curve. Using these two correlations, as well as a knowledge of some basic reservoir characteristics and estimates of fluid properties from standard correlations, the injection-well pressure buildup and CO 2 plume extent in the formation can be readily estimated. Finally, the new correlations show a good match with the results of the underlying simulations, and also provide good agreement with independent calculations for two example problems.

42 ENGINEERING↗

DOE OSTI2013

Assessment of Brine Management for Geologic Carbon Sequestration

Geologic carbon sequestration (GCS) is the injection of carbon dioxide (CO 2 ), typically captured from stationary emission sources, into deep geologic formations to prevent its entry into the atmosphere. Active pilot facilities run by regional United States (US) carbon sequestration partnerships inject on the order of one million metric tonnes (mt) CO 2 annually while the US electric power sector emits over 2000 million mt-CO 2 annually. GCS is likely to play an increasing role in US carbon mitigation initiatives, but scaling up GCS poses several challenges. Injecting CO 2 into sedimentary basins raises fluid pressure in the pore space, which is typically already occupied by naturally occurring, or native, brine. The resulting elevated pore pressures increase the likelihood of induced seismicity, of brine or CO 2 escaping into potable groundwater resources, and of CO 2 escaping into the atmosphere. Brine extraction is one method for pressure management, in which brine in the injection formation is brought to the surface through extraction wells. Removal of the brine makes room for the CO 2 and decreases pressurization. Although the technology required for brine extraction is mature, this form of pressure management will only be applicable if there are cost-effective and sustainable methods of disposing of the extracted brine. Brine extraction, treatment, and disposal may increase the already substantial capital, energy, and water demands of Carbon dioxide Capture and Sequestration (CCS). But, regionally specific brine management strategies may be able to treat the extracted water as a source of revenue, energy, and water to subsidize CCS costs, while minimizing environmental impacts. By this approach, value from the extracted water would be recovered before disposing of any resulting byproducts. Until a price is placed on carbon, we expect that utilities and other CO 2 sources will be reluctant to invest in capital intensive, high risk GCS projects; early technical, economic, and environmental assessments of brine management are extremely valuable for determining the potential role of GCS in the US. We performed a first order feasibility and economic assessment, at three different locations in the US, of twelve GCS extracted-water management options, including: geothermal energy extraction, desalination, salt and mineral harvesting, rare-earth element harvesting, aquaculture, algae biodiesel production, road de-icing, enhanced geothermal system (EGS) recharge, underground reinjection, landfill disposal, ocean disposal, and evaporation pond disposal. Three saline aquifers from different regions of the US were selected as hypothetical GCS project sites to encompass variation in parameters that are relevant to the feasibility and economics of brine disposal. The three aquifers are the southern Mt. Simon Sandstone Formation in the Illinois Basin, IL; the Vedder Formation in the southern San Joaquin Basin, CA; and the Jasper Interval in the eastern Texas Gulf Basin, TX. These aquifers are candidates for GCS due to their physical characteristics and their close proximity to large CO 2 emission sources. Feasibility and impacts were calculated using one mt-CO 2 injected as the functional unit of brine management. Scenarios were performed for typical 1000MW coal-fired power plants (CFPP) that incurred an assumed 24 percent carbon capture energy penalty (EP), injected 90 percent of CO 2 emissions (~9 million mt- CO 2 injected annually), and treated extracted water onsite. Net present value (NPV), land requirements, laws and regulations, and technological limits were determined for each stage of disposal, and used to estimate feasibility. The boundary of the assessment began once extracted water was brought to the surface, and ended once the water evaporated, was injected underground, or was discharged into surface water bodies. Results of the assessment were generated, stored, and analyzed using Microsoft Excel spreadsheets and ESRI Geographical Information System (GIS) maps. Conclusions about the relative benefits and impacts of alternative brine-management strategies were highly sensitive to local climate and weather, and aquifer water chemistry. The NPV of certain scenarios ranged from -$50/mt-CO 2 (a cost) to +$10/mt-CO 2 (revenue). The land footprint of the scenarios in this study ranged from <1 km 2 to 100 km 2 . Brine extraction as a pressure management tool for GCS has potential for improving the economics and for minimizing the environmental impacts of CCS. In order to maximize this potential, careful analysis of each saline aquifer and region must be conducted to determine a regionally appropriate brine use sequence (BUS) at the time of site selection. Models that use GIS will be essential tools in determining such sequences for individual CFPP. Future studies that perform risk and life cycle assessments (LCA) of BUS scenarios, incorporate additional impact metrics into the BUS model, and enhance the temporal sensitivity of the model would improve the robustness of this regional assessment method.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2025

Hydrogen Generation and Serpentinization of Olivine Under Flow Conditions

Serpentinization of olivine is often studied in the laboratory under batch conditions. Olivine conversion in situ with enhanced natural hydrogen production will likely be implemented via injection of aqueous solutions. Hence, transport is relevant to the extent of olivine reaction and, potentially, the morphology of precipitates formed. To test conditions for optimal H 2 generation and outcomes, serpentinization was induced by injecting pH = 12.5 brine at 0.015 cm 3 /min (0.5 pore volumes per day) into an olivine sand pack (250 to <355 μm grain size) at 245°C generating, at minimum 76 and 89 mol% H 2 at 35 and 57 d, respectively. Grain-coating serpentine with radiating needles cemented the reacted sand grains. Importantly, pore space was maintained between the dissolving grains and the serpentine precipitates. Hence, reactivity continued as a result of fluid access to mineral surfaces, the large grain size, and the continuous injection of undersaturated alkaline fluids.

08 HYDROGEN↗

DOE OSTI2017

A practical method to obtain kinetic data from $\mathrm{TGA}$ (thermogravimetric analysis) experiments to build an air injection model for enhanced oil recovery

To build an air injection model for enhanced oil recovery, it is necessary to obtain the kinetic data from thermal experiments. For TGA (thermogravimetry analysis) experiments, fitting the weight loss data using different forms of the Arrhenius Equation is practiced to obtain a single set of kinetic data which are used for the whole temperature range. The problem is that the kinetic data changes with the test temperature, oil composition, etc. Therefore, the obtained kinetic data do not represent the actual physics. Here this paper presents a detailed practical method to obtain kinetic data from TGA experiments to build an air injection model. The air injection model contains two parts. One part is to define fluid pseudo-components and their physical properties. The other part is to define oxidation reaction and the corresponding kinetic data. In order to validate the air injection model, both air purging TGA experiments and nitrogen purging TGA experiments are conducted. The fluid model (pseudo-components and their properties) is validated by matching model results with the nitrogen purging TGA experiments. Then, the kinetic data are obtained by matching the model results with the air purging TGA experiments. To verify the above approach to build an air injection model, TGA experiments using a pure hydrocarbon C20 and a Wolfcamp crude oil were conducted. The pure hydrocarbon C20 is used to verify the approach. Then seven oxidation reactions of seven pseudo components are utilized to define the air injection model for the Wolfcamp crude oil. The selection of the pseudo components was validated with the nitrogen purging TGA experiments and the oxidation reactions were validated with the air purging TGA experiments. The result shows that the combination of isomerization reactions and oxygen addition reactions can perfectly simulate a light oil air injection process in the low temperature region. This paper shows that an air injection model can be built using the kinetic data by analyzing TGA experiments.

42 ENGINEERING↗

DOE OSTI2016

Effect of post injections on mixture preparation and unburned hydrocarbon emissions in a heavy-duty diesel engine

This work explores the mechanisms by which a post injection can reduce unburned hydrocarbon (UHC) emissions in heavy-duty diesel engines operating at low-temperature combustion conditions. Post injections, small, close-coupled injections of fuel after the main injection, have been shown to reduce UHC in the authors’ previous work. In this work, we analyze optical data from laser-induced fluorescence of both CH 2 O and OH and use chemical reactor modeling to better understand the mechanism by which post injections reduce UHC emissions. The results indicate that post-injection efficacy, or the extent to which a post injection reduces UHC emissions, is a strong function of the cylinder pressure variation during the post injection. However, the data and analysis indicate that the pressure and temperature rise from the post injection combustion cannot solely explain the UHC reduction measured by both engine-out and optical diagnostics. In conclusion, the fluid-mechanic, thermal, and chemical interaction of the post injection with the main-injection mixture is a key part of UHC reduction; the starting action of the post jet and the subsequent entrainment of surrounding gases are likely both important processes in reducing UHC with a post injection.

33 ADVANCED PROPULSION SYSTEMS↗

DOE OSTI2015

Lattice Boltzmann simulation of immiscible fluid displacement in porous media: Homogeneous versus heterogeneous pore network

Injection of anthropogenic carbon dioxide (CO{sub 2}) into geological formations is a promising approach to reduce greenhouse gas emissions into the atmosphere. Predicting the amount of CO{sub 2} that can be captured and its long-term storage stability in subsurface requires a fundamental understanding of multiphase displacement phenomena at the pore scale. In this paper, the lattice Boltzmann method is employed to simulate the immiscible displacement of a wetting fluid by a non-wetting one in two microfluidic flow cells, one with a homogeneous pore network and the other with a randomly heterogeneous pore network. We have identified three different displacement patterns, namely, stable displacement, capillary fingering, and viscous fingering, all of which are strongly dependent upon the capillary number (Ca), viscosity ratio (M), and the media heterogeneity. The non-wetting fluid saturation (S{sub nw}) is found to increase nearly linearly with logCa for each constant M. Increasing M (viscosity ratio of non-wetting fluid to wetting fluid) or decreasing the media heterogeneity can enhance the stability of the displacement process, resulting in an increase in S{sub nw}. In either pore networks, the specific interfacial length is linearly proportional to S{sub nw} during drainage with equal proportionality constant for all cases excluding those revealing considerable viscous fingering. Our numerical results confirm the previous experimental finding that the steady state specific interfacial length exhibits a linear dependence on S{sub nw} for either favorable (M ≥ 1) or unfavorable (M < 1) displacement, and the slope is slightly higher for the unfavorable displacement.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2012

Integrated Reflection Seismic Monitoring and Reservoir Modeling for Geologic CO 2 Sequestration

The US DOE/NETL CCS MVA program funded a project with Fusion Petroleum Technologies Inc. (now SIGMA) to model the proof of concept of using sparse seismic data in the monitoring of CO 2 injected into saline aquifers. The goal of the project was to develop and demonstrate an active source reflection seismic imaging strategy based on deployment of spatially sparse surface seismic arrays. The primary objective was to test the feasibility of sparse seismic array systems to monitor the CO 2 plume migration injected into deep saline aquifers. The USDOE/RMOTC Teapot Dome (Wyoming) 3D seismic and reservoir data targeting the Crow Mountain formation was used as a realistic proxy to evaluate the feasibility of the proposed methodology. Though the RMOTC field has been well studied, the Crow Mountain as a saline aquifer has not been studied previously as a CO 2 sequestration (storage) candidate reservoir. A full reprocessing of the seismic data from field tapes that included prestack time migration (PSTM) followed by prestack depth migration (PSDM) was performed. A baseline reservoir model was generated from the new imaging results that characterized the faults and horizon surfaces of the Crow Mountain reservoir. The 3D interpretation was integrated with the petrophysical data from available wells and incorporated into a geocellular model. The reservoir structure used in the geocellular model was developed using advanced inversion technologies including Fusion's ThinMAN™ broadband spectral inversion. Seal failure risk was assessed using Fusion's proprietary GEOPRESS™ pore pressure and fracture pressure prediction technology. CO 2 injection was simulated into the Crow Mountain with a commercial reservoir simulator. Approximately 1.2MM tons of CO 2 was simulated to be injected into the Crow Mountain reservoir over 30 years and subsequently let 'soak' in the reservoir for 970 years. The relatively small plume developed from this injection was observed migrating due to gravity to the apexes of the double anticline in the Crow Mountain reservoir of the Teapot dome. Four models were generated from the reservoir simulation task of the project which included three saturation models representing snapshots at different times during and after simulated CO 2 injection and a fully saturated CO 2 fluid substitution model. The saturation models were used along with a Gassmann fluid substitution model for CO 2 to perform fluid volumetric substitution in the Crow Mountain formation. The fluid substitution resulted in a velocity and density model for the 3D volume at each saturation condition that was used to generate a synthetic seismic survey. FPTI's (Fusion Petroleum Technologies Inc.) proprietary SeisModelPRO™ full acoustic wave equation software was used to simulate acquisition of a 3D seismic survey on the four models over a subset of the field area. The simulated acquisition area included the injection wells and the majority of the simulated plume area.

02 PETROLEUM↗

DOE OSTI2019

Feasibility of using in situ deformation to monitor CO 2 storage

Deformation during CO 2 injection can lead to problems, like seismicity or fluid leaks, but small strains have the potential to be a useful signal for monitoring. The objective of this paper is to evaluate the possible evolution of the strain field during injection, and then assess existing and emerging techniques for measuring the strain field. Poroelastic analyses show that normal strains caused by injection into a reservoir are tensile in the vicinity of the well, but everywhere else at least one strain component is compressive. The vertical strain is compressive in the confining unit, and the radial strain decreases and changes sign from tensile to compressive with distance from the well. Tilting is away from the injection well at the ground surface, but it is towards the well overlying the reservoir. Methods for measuring in-situ strain include instruments that are grouted in the annulus between casing and wall rock (~ 0.1 microstrain resolution), portable strain sensors that are temporarily clamped to the borehole wall (~0.01 microstrain resolution), and strainmeters that are grouted in place (~0.001 microstrain resolution). Instruments for measuring in-situ normal strains at the magnitudes and rates expected during injection are emerging, but they have yet to be fully evaluated in applications related to CO 2 storage. Finally, in-situ strain data measured with emerging instruments promises to fill an important gap between the episodes of fast strain rates measured by seismic data, and the slow strains measured over relatively long periods of time by InSAR and GPS.

42 ENGINEERING↗