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A numerical model was developed using CrunchFlow to simulate reactive transport and porosity and permeability changes of sandstone and carbonate rock samples taken from the Lower Tuscaloosa Formation and the Selma Chalk Formation, Jackson County, MS, USA. The model predicted a permeability decrease from 2190 mD to 2038 mD for the Lower Tuscaloosa Sandstone sample in a static batch reactor after 180 days of exposure to CO2-saturated brine, which is consistent with measured permeability results. The model predicted a negligible permeability change from 2.00 mD to 2.08 mD for the Selma Chalk carbonate sample after 180 days of exposure to CO2-saturated brine. Based on model prediction, key mineral dissolution and precipitation reactions in the Lower Tuscaloosa Sandstone sample include dissolution of quartz, chlorite, and feldspar, as well as precipitation of amorphous silica and kaolinite. For the Selma Chalk carbonate sample, key predicted reactions include dissolution of calcite, quartz and chlorite, and precipitation of kaolinite and amorphous silica. Initial porosity, initial feldspar content and the exponent n value (related to pore structure and tortuosity) used in permeability calculations were three important factors affecting permeability evolution of sandstone samples under CO2 sequestration conditions. The small permeability change predicted for both the Lower Tuscaloosa Sandstone and the Selma Chalk caprock after exposure to CO2-saturated brine suggests that poro-permeability changes during CO2 injection into the Lower Tuscaloosa Formation are not likely to significantly affect reservoir and seal quality. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.

Rare earth elements (REE) are of strategic importance because they find numerous applications in various sectors of the global economy. The concern about the REE supply challenge has led to increasing interest and research in the recovery of REE from end-of-life products and secondary sources such as coal and coal by-products. The work reported here was focused on examining the technical feasibility of physical separation techniques for the enrichment of REE from coal and coal by-products. Particle size, magnetic and density separations were performed on coal, coal ash, clay and shale samples. It was found that the samples responded to particle size separation differently. For all ash samples, higher REE concentrations were found in the finer fractions. For the clay and shale samples, however, the REE concentrations decrease as the particle size reduces possibly because RE minerals were not effectively released by grinding. Magnetic separation showed that REE are enriched in non-magnetic fractions for all ash samples. All samples responded similarly to density separation. Among the three methods, density separation showed the highest enrichment of REE. A combination of these methods is recommended. Finally, correlations between elements were demonstrated, which leads to the classification of three groups containing mainly Al/Si, Fe and Ca, respectively. REE are strongly associated with the Al/Si group.

Saline aquifers are the largest potential continental geologic CO2 sequestration resource. Understanding of potential geochemically induced changes to the porosity and permeability of host CO2 storage and sealing formation rock will improve our ability to predict CO2 plume dynamics, storage capacity, and long-term reservoir behavior. Experiments exploring geochemical interactions of CO2/brine/rock on saline formations under CO2 sequestration conditions were conducted in a static system. Chemical interactions in core samples from the Lower Tuscaloosa formation from Jackson County, Mississippi, with exposure to CO2-saturated brine under sequestration conditions were studied through six months of batch exposure. The experimental conditions to which the core samples of Lower Tuscaloosa sandstone and Selma chalk were exposed to a temperature of 85°C, CO2 pressure of 23.8 MPa (3500 psig), while immersed in a model brine representative of Tuscaloosa Basin. Computed tomography (CT), X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM), brine chemistry, and petrography analyses were performed before and after the exposure. Permeability measurements from the sandstone core sample before and after exposure showed a permeability reduction. No significant change of the permeability measurements was noticed for the core sample obtained from Selma chalk after it was exposed to CO2/brine for six months. These results have implications for performance of the storage interval, and the integrity of the seal in a CO2 storage setting. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd

A numerical model was developed to simulate reactive transport with porosity and permeability change of Mount Simon sandstone (samples from Knox County, IN, USA) after 180 days of exposure to CO2-saturated brine under CO2 sequestration conditions. The model predicted formation of a high-porosity zone adjacent to the surface of the sample in contact with bulk brine, and a lower porosity zone just beyond that high-porosity zone along the path from the sample/bulk brine interface to sample core. The formation of the high porosity zone was attributed to the dissolution of quartz and muscovite/illite, while the formation of the lower porosity zone adjacent to the high porosity zone was attributed to precipitation of kaolinite and feldspar. The model predicted a 40% permeability increase for the Knox sandstone sample after 180 days of exposure to CO2-saturated brine, which was consistent with laboratory-measured permeability results. Model-predicted solution chemistry results were also found to be consistent with laboratory-measured solution chemistry data. Initial porosity, initial feldspar content, and the exponent n value (determined by pore structure and tortuosity) used in permeability calculations were three important factors affecting permeability evolution of sandstone samples under CO2 sequestration conditions.

A numerical model was developed with the use of reactive transport code CrunchFlow to estimate porosity, permeability and mineral composition changes of Mount Simon sandstone under typical geological carbon sequestration conditions (P = 23.8 MPa and T = 85 °C). The model predicted a permeability decrease from 1.60 mD to 1.02 mD for the Mount Simon sandstone sample in a static batch reactor after 180 days of exposure to CO2-saturated brine, which is consistent with measured permeability results. Model-predicted solution chemistry results were also consistent with laboratory-measured solution chemistry data. SiO2 (am) was the primary mineral that causes permeability decrease, followed by kaolinite. Both SiO2 (am) formation and kaolinite formation were attributed to the dissolution of quartz and feldspar. This study shows that the formation of SiO2 (am) and kaolinite in the pore space of host rock is possible under typical CO2 sequestration conditions. SiO2 (am) and kaolinite precipitation at the CO2 plume extent could reduce the permeability of host rock and improve lateral containment of free-phase CO2, contributing to overall security of CO2 storage.

CO2 solubility data in the natural formation brine, synthetic formation brine, and synthetic NaCl+CaCl2 brine were collected at the pressures from 100 to 200 bar, temperatures from 323 to 423 K. Experimental results demonstrate that the CO2 solubility in the synthetic formation brines can be reliably represented by that in the synthetic NaCl+CaCl2 brines. We extended our previously developed model (PSUCO2) to calculate CO2 solubility in aqueous mixed-salt solution by using the additivity rule of the Setschenow coefficients of the individual ions (Na(+), Ca(2+), Mg(2+), K(+), Cl(-), and SO4(2-)). Comparisons with previously published models against the experimental data reveal a clear improvement of the proposed PSUCO2 model. Additionally, the path of the maximum gradient of the CO2 solubility contours divides the P-T diagram into two distinct regions: in Region I, the CO2 solubility in the aqueous phase decreases monotonically in response to increased temperature; in region II, the behavior of the CO2 solubility is the opposite of that in Region I as the temperature increases.

Deep saline aquifers are reported to have the largest estimated capacity for CO2 sequestration. Knowledge of possible geochemically-induced changes to the porosity and permeability of host CO2 storage sandstone and seal rock will enhance our capability to predict CO2 storage capacity and long-term reservoir behavior.An experimental study of the potential interaction of CO2/brine/rock on saline formations in a static system under CO2 sequestration conditions was conducted. Chemical interactions in the Mount Simon sandstone environment upon exposure to CO2 mixed with brine under sequestration conditions were studied. Samples were exposed to the estimated in-situ reaction conditions for six months. The experimental parameters used were two core samples of Mount Simon sandstone; Illinois Basin model brine; temperature of 85°C, pressure of 23.8 MPa (3,500 psig), and CO2. Micro-CT, CT, XRD, SEM, petrography, and brine, porosity, and permeability analyses were performed before and after the exposure. Preliminary permeability measurements obtained from the sandstone sample showed a significant change after it was exposed to CO2- saturated brine for six months. This observation suggests that mineral dissolution and mineral precipitation could occur in the host deposit altering its characteristics for CO2 storage over time.

In order to evaluate the extent of CO2–water–rock interactions in geological formations for C sequestration, three batch experiments were conducted on alkali feldspars–CO2–brine interactions at 150–200 °C and 300 bars. The elevated temperatures were necessary to accelerate the reactions to facilitate attainable laboratory measurements. Temporal evolution of fluid chemistry was monitored by major element analysis of in situ fluid samples. SEM, TEM and XRD analysis of reaction products showed extensive dissolution features (etch pits, channels, kinks and steps) on feldspars and precipitation of secondary minerals (boehmite, kaolinite, muscovite and paragonite) on feldspar surfaces. Therefore, these experiments have generated both solution chemistry and secondary mineral identity. The experimental results show that partial equilibrium was not attained between secondary minerals and aqueous solutions for the feldspar hydrolysis batch systems. Evidence came from both solution chemistry (supersaturation of the secondary minerals during the entire experimental duration) and metastable co-existence of secondary minerals. The slow precipitation of secondary minerals results in a negative feedback in the dissolution–precipitation loop, reducing the overall feldspar dissolution rates by orders of magnitude. Furthermore, the experimental data indicate the form of rate laws greatly influence the steady state rates under which feldspar dissolution took place. Negligence of both the mitigating effects of secondary mineral precipitation and the sigmoidal shape of rate–ΔGr relationship can overestimate the extent of feldspar dissolution during CO2 storage. Finally, the literature on feldspar dissolution in CO2-charged systems has been reviewed. The data available are insufficient and new experiments are urgently needed to establish a database on feldspar dissolution mechanism, rates and rate laws, as well as secondary mineral information at CO2 storage conditions.

Long term containment of stored CO 2 in deep geological reservoirs will depend on the performance of the caprock to prevent the buoyant CO 2 from escaping to shallow drinking water aquifers or the ground surface. Here we report new laboratory experiments on CO 2 –brine–caprock interactions and a review of the relevant literature. The Eau Claire Formation is the caprock overlying the Mount Simon sandstone formation, one of the target geological CO 2 storage reservoirs in the Midwest USA region. Batch experiments of Eau Claire shale dissolution in brine were conducted at 200 °C and 300 bars to test the extent of fluid-rock reactions. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis indicate minor dissolution of K-feldspar and anhydrite, and precipitation of pore-filling and pore-bridging illite and/or smectite, and siderite in the vicinity of pyrite. We also reviewed relevant reactivity experiments, modeling work, and field observations in the literature in an attempt to help define the framework for future studies on the geochemical systems of the caprock overlain on geological CO 2 storage formations. Reactivity of the caprock is generally shown to be low and limited to the vicinity of the CO 2 –caprock interface, and is related to the original caprock mineralogical and petrophysical properties. Stable isotope studies indicate that CO 2 exists in both free phase and dissolved phase within the caprock. Carbonate and feldspar dissolution is reported in most studies, along with clay and secondary carbonate precipitation. Currently, research is mainly focused on the micro-fracture scale geochemistry of the shaly caprock. More attention is required on the potential pore scale reactions that may become significant given the long time scale associated with geological carbon storage.

Development of in situ electromagnetic (EM) retorting technologies and design of specific EM well logging tools requires an understanding of various process parameters (applied frequency, mineral phases present, water content, organic content and temperature) on oil shale dielectric properties. In this literature review on oil shale dielectric properties, we found that at low temperatures ( 200 °C) and constant frequency, e′ generally increases with temperature regardless of grade while e″ fluctuates. At these temperatures, maximum values for both e′ and e″ differ based upon oil shale grade. Formation fluids, mineral-bound water, and oil shale varve geometry also affect measured dielectric properties. This review presents and synthesizes prior work on the influence of applied frequency, oil shale grade, water, and temperature on the dielectric properties of oil shales that can aid in the future development of frequency- and temperature-specific in situ retorting technologies and oil shale grade assay tools.

Heterostructures between montmorillonite and embedded alpha-Fe2O3 nanoparticles are explored to create new hybrid particles with high magnetic response and magnetic-field induced tunability. α-Fe2O3 nanoparticles are hybridized to montmorillonite clays by using an intercalation technique. Also, stable aqueous fluids consisting of the heterostructured particles are prepared and the rheology of the fluids under external magnetic field is examined. When α-Fe2O3 a nanoparticles are embedded in the interlayer space of montmorillonite clays, the magnetization per Fe atom increases at most 60 times. This unique combination of the magnetization and the coercivity is traced to the suppressed growth of embedded α-Fe2O3 nanoparticles by the aluminosilicate layers, leading to the size control, anisotropic magnetic interaction, and uniaxial stress of two-dimensionally distributed α-Fe2O3 nanoparticles. Furthermore, high magnetization of heterostructured particles leads to strong dependence of fluids' viscosity on the external magnetic field. The present study indicates that the new heterostructured particles have unique magnetic fielddependent properties that are not attainable in individual clay or iron oxide particles.

Exposure to 7 MPa of helium at room temperature alters the texture of Upper Freeport coal in a lump form. The differences in texture and porosity between coal powder and lumps may affect the transport and interaction of fluids and coal. In this work, the information about the coal texture and micro- and meso-porosity was obtained via the BET, BJH, and Dubinin–Astakhov analyses. We further investigated the free-fluid-phase volume (free-volume) effects due to helium interaction with the powder and the lumps. During the manometric experiment, helium penetration into the dry coal matrix resulted in slow relaxation of pressure. After exposure of coal to helium, there have been no significant changes of the macroscopic dimensions observed and the relaxation process can be attributed to microscopic ‘free-volume’ effects. Evolution of the sorption–desorption rates indicates that exposure to helium may change the texture and apparent (helium) density of dry coal.

The permeability of coal samples from Pittsburgh Seam was determined using carbon dioxide as the flowing fluid. The confining pressure was varied to cover a wide range of depths. The permeability was determined as a function of exposure time of carbon dioxide while the confining stress was kept constant. The porosities of the coal samples were found to be very low and most of the samples had porosities less than 1%. The permeability of these coal samples was very low—less than 1 μD. Since the objective of this study was to investigate the influence of CO2 exposure on coal permeability, it was necessary to increase the initial permeability of the coal samples by introducing a fracture. A longitudinal fracture was induced mechanically, and CT scans were taken to ensure that the fracture was present throughout the sample and that the sample was not damaged otherwise during the process. In this study, the permeability of coal was determined by using pressure transient methods. Two types of pressure pulses were used: A-spike and Sine-6 pressure transients. It was first established that the permeability of fractured coal samples did not change with exposure time when an inert gas (Argon) was used as the fluid medium in the experiments. However, the permeability of coal samples decreased significantly when carbon dioxide was used as the fluid medium. This reduction can be attributed to the coal swelling phenomenon. The results show that the permeability reduction in fractured coal samples can be over 90% of the original value, and the exposure time for such reductions can range from 1.5 days up to a week, typically about 2 days under laboratory conditions. The permeability decreased significantly with the increase in confining pressure. The higher confining pressure appears to close internal fractures causing a reduction in permeability.

Experiments were conducted to determine the solubility of CO2 in a natural brine solution of the Oriskany formation under elevated temperature and pressure conditions. These data were collected at temperatures of 22 and 75 degrees C and pressures between 100 and 450 bar. Experimentally determined data were compared with CO2 solubility predictions using a model developed by Duan and Sun (Chem. Geol. 2003, 193, 257-271). Model results compare well with Oriskany brine CO2 solubility data collected experimentally, suggesting that the Duan and Sun model is a reliable tool for estimating solution CO2 capacity in high salinity aquifers in the temperature and pressure range evaluated. The capacity for the Oriskany formation to sequester dissolved CO2 was calculated using results of the solubility models, estimation of the density of CO2 saturated brine, and available geographic information system (GIS) information on the formation depth and thickness. Results indicate that the Oriskany formation can hold approximately 0.36 gigatonnes of dissolved CO2 if the full basin is considered. When only the region where supercritical CO2 can exist (temperatures greaterthan 31 degrees C and pressures greaterthan 74 bar) is considered, the capacity of the Oriskany formation to sequester dissolved CO2 is 0.31 gigatonnes. The capacity estimate considering the potential to sequester free-phase supercritical CO2 if brine were displaced from formation pore space is 8.8 gigatonnes in the Oriskany formation.

Many types of materials e.g., rubber, polymer, coal, change their volume and structure after absorption of gaseous and liquid substances. Various kinds of volume changes affect the accuracy of absorption measurements by gravimetric and manometric methods, the two major techniques currently employed. The errors associated with the volumetric effects, specifically, the case of carbon dioxide sorption on coal, were investigated. It was demonstrated that the resulting error in the buoyancy correction in the gravimetric method is equivalent to the corresponding error in the assumed void volume in the manometric method. It is suggested that the integration of the two methods, combined with the binary gas mixture technique of in-situ volume measurement, will contribute to dramatically improve the accuracy of absorption measurements for plastic materials.

The ultimate capacity of saline formations to sequester carbon dioxide by solubility and mineral trapping must be determined by simulating sequestration with geochemical models. These models, however, are only as reliable as the data and reaction scheme on which they are based. Several models have been used to make estimates of carbon dioxide solubility and mineral formation as a function of pressure and fluid composition. Intercomparison of modeling results indicates that failure to adjust all equilibrium constants to account for elevated carbon dioxide pressures results in significant errors in both solubility and mineral formation estimates. Absence of experimental data at high carbon dioxide pressures and high salinities make verification of model results difficult. Results indicate standalone solubility models that do not take mineral reactions into account will underestimate the total capacity of aquifers to sequester carbon dioxide in the long term through enhanced solubility and mineral trapping mechanisms. Overall, it is difficult to confidently predict the ultimate sequestration capacity of deep saline aquifers using geochemical models.

The reaction of carbon dioxide (CO 2 ) with brine samples collected from the Oriskany Formation in Indiana County, PA, was investigated in an autoclave reactor under various conditions. A geochemical code, PHREEQC, was used as to simulate the reaction in the autoclave reactor. The combined experimental and modeling data suggests that pH (pH > 9) plays a key role in the formation of carbonate minerals. The effects of temperature and CO 2 pressure have a lesser impact on the formation of carbonate minerals.

An industrial fly ash sample was cleaned by three different processes, which were triboelectrostatic separation, ultrasonic column agglomeration, and column flotation. The unburned carbon concentrates were collected at purities ranging up to 62% at recoveries of 62%. In addition, optical microscopy studies were conducted on the final carbon concentrates to determine the carbon forms (inertinite, isotropic coke and anisotropic coke) collected from these various physical-cleaning processes. The effects of the various cleaning processes on the production of different carbon forms from high carbon fly ashes will be discussed.

Triboelectrostatic separation has been investigated as a method for separating unburned carbon from coal combustion fly ash. It was found that when a fly ash is exposed to moisture before it undergoes separation, the charging properties of the components of the fly ash change significantly. The mineral and carbon components of the fly ash appear to charge oppositely to how they were charged before exposure to moisture. A correlation was found between the degree of charge reversal and the relative amounts of leachable ions, especially calcium and sodium ions, present on the surface of the ash.

The dry beneficiation of three types of Slovakian brown coal, namely Ci'gel, Handlova', and Nova'ky coal was conducted via triboelectrostatic separation. Three different types of separators—parallel plate, cylindrical and louvered plate—were used for this study. It was found that a parallel plate separator could reduce the ash contents of Ci'gel and Handlova' coals. The poor quality of separation for the Nova'ky coal studied is probably due to the particle–particle interactions and surface oxidation states of the coal.

Dry triboelectrostatic separations of fly ash derived from both coal combustion and the combustion of coal mixed with 10 wt% biomass were conducted. Two different types of triboelectrostatic separators — parallel plate and louvered plate separators — were used for this study. It is found that the material of construction for the tribocharger in the louvered plate separator affects both the deposition pattern and the quantity of recovery of the separated products. The poor quality of separation for the biomass fly ash studied is probably due to the physical/chemical nature of the biomass fly ash which is significantly different from that of coal fly ash.

Powder and lumps of the Argonne Premium Upper Freeport coal were compared in a 9-month-long CO2 sorption−desorption study. On the basis of the slope analysis, CO2 induced the lumps swelling by 7%. The powder swelled by 8% and then rapidly shrank by 3% on desorption. This was verified by a “single point” injection of helium and the pressure-and-density technique, which was sufficiently sensitive. Low-pressure Langmuir-fit parameters suggest that the microporous textures of the powder and lumps are similar. The samples demonstrated greatly increased sticking coefficients and a slightly larger number of the “sorption ready” sites, after the CO2-induced swelling and structural rearrangement resulted in variable degrees of the matrix shrinkage. No permanent changes in the void volume and dry mass were detected after complete desorption. The observed hysteresis in sorption−desorption behavior of both samples upon the approach to the CO2 density fluctuation ridge is interpreted as a contribution of condensation ...

An ultrasonic technique was developed to measure the slurry concentration in an autoclave reactor. Preliminary measurements were conducted on slurries consisting of molten FT-200 wax, glass beads, and nitrogen bubbles at a typical Fischer–Tropsch (FT) synthesis temperature of 265 °C. The data show that the velocity and attenuation of the sound are well-defined functions of the solid and gas concentrations in the molten FT-200 wax. The results suggest possibilities for directly measuring solids concentration during operation of a three-phase slurry reactor under the reaction temperature and with molten FT-200 wax.

Local gas holdup, bubble diameter and bubble rise velocity in the nitrogen/Drakeol-10 oil system were measured at both laboratory (ambient temperature and pressure) and industrially relevant (high temperature and pressure) conditions using a dual conductivity probe in a slurry-bubble-column reactor. It was found that a constant superficial velocity, the Sauter mean bubble diameter decreases with increasing pressure and temperature. The bubble rise velocity significantly decreases as the pressure increases. Large bubbles rise faster than smaller bubbles. Akita and Yoshida's correlation [1] was utilized to compute the bubble size. Predicted values agree with the experimental data at high temperature.

Summary Parameters related to seismic and ultrasonic elastic waves traveling through a porous rock material with compliant pores, cracks and isometric pores are subject to variations which are dependent on the physical properties of the rock such as density, porosity, permeability, frame work moduli, fluid moduli, micro structural variation, and effective pressure. Our goal is to understand these variations through experiments completed using rhyolites, coal, and carbonate samples. Understanding these lithologies are relevant to enhanced oil recovery, enhanced geothermal, and CO2 storage activities. Working in the COREFLOW laboratory at the National Energy Technology Laboratory (NETL) of the United States Department of Energy (DOE) we performed several experiments on these rock types with various different pore filling fluids, effective pressures, and temperatures. We measured P, S1 and S2 ultrasonic velocities using a New England Research (NER) Autolab 1500 device and calculated the lame parameters (Bulk modulus (K), Young’s modulus (E), Lame’s first parameter (λ), Shear modulus (G), Poisson’s ratio (ν), P-wave modulus (M)). Using an aluminum reference core and the ultrasonic waveform data collected, we employed the spectral ratio method to estimate Q. This method uses the ratio of the amplitude-frequency spectrum (obtained via fast Fourier Transform and processed using Matlab) of the rock core compared with the amplitude-frequency spectrum of the aluminum reference core to calculate the quality factor (Q). The primary focus of these calculations was P waveform attenuation. The quality factor is a dimensionless value that represents the attenuation of a seismic wave as it travels through a rock. Seismic attenuation is dependent on wave velocity, the path length or time the wave is in the rock, and of course the physical properties of the rock through which the wave travels. Effective pressures used in our experiments varied between 0.01 MPa and 50 MPa and temperatures varied between 21o C to 80o C which allowed us to more accurately represent subsurface conditions. Pore-filling fluids consisted of deionized water, oil/water mix, gas, and supercritical CO2. Carbonate samples were tested dry (atmospheric gas as pore fluid) and with deionized water, oil, and CO2. By understanding how seismic waves attenuate we can better understand what collected seismic signals traveled through. This knowledge and understanding of seismic wave attenuation could prove to be a powerful tool for better subsurface imaging, tracking of sequestrated CO2, and energy exploration.

The application of the three-phase slurry reactor system for coal liquefaction processing and chemical industries has recently received considerable attention. To design and efficiently operate a three-phase slurry reactor, the degree of dispersion of the solid (catalyst) in the reactor must be understood and controlled. An ultrasonic technique was developed to measure the concentration of solids in an autoclave reactor. Preliminary measurements were conducted on slurries consisting of molten paraffin wax, glass beads, and nitrogen bubbles at 189 C. The data show that the velocity and attenuation of the sound are well-defined functions of the solid and gas concentrations in the molten wax. The results suggest possibilities for directly measuring solids concentration during operation of a three-phase slurry reactor.

An ultrasonic technique was developed to measure the concentration of solids in a three-phase slurry reactor. Preliminary measurements were taken on slurries consisting of water, glass beads, and nitrogen bubbles. The data show that the speed and attenuation of the sound are well defined functions of the solid and gas concentrations in the slurries. A simple model is proposed to correlate the concentration of solids with the measured characteristics of the ultrasonic signals.

For heterogeneous catalysis, ordinary differential equations in time can be used to interpret transient tracer data obtained in a continuous stirred tank reactor or gradientless reactor in which a steady-state reaction is occurring. The same procedure is often used for plug-flow reactor modeling. However, for transient tracing data obtained with a plug-flow reactor operating under differential conversion, it is necessary to use a set of partial differential equations involving distance through the reactor as well as time. In this paper, the authors present a case study of methanation on a nickel catalyst to illustrate the modeling procedure needed to estimate the desired parameters.

Summary In order to monitor a CO2 injection site with seismic surveying, the dynamic rock matrix must be thoroughly understood. To assist in this understanding, we present our approach to upscaling micro-scale rock matrix properties to reservoir scale and seismic velocity ranges based on theoretical rock wave propagation models and show the richness of useful data produced by micro computed tomography (µCT). We have acquired and processed µCT images of limestone samples to gain understanding of 3-D pore orientation, pore volume distribution and pore surface area geometry at a resolution of 1.3 to 3.9 microns. By comparing µCT scans from before and after timed CO2 exposures, rock density, and pore volume changes are quantified. In an 18.5% porosity limestone sample, our analysis identifies and describes over twelve thousand pores in a 26 cubic millimeter volume at 4X zoom (3.9 micron/pixel). By observing available reactive surface area of the porosity and mass change over a series of time increments and comparing results to chemical model predictions, we refine limestone-CO2 interaction models to predict how, over time, a carbonate reservoir will change due to storage of CO2. This porosity and density change model will be applied to a larger-scale reservoir model that detects the presence of CO2 density signatures. This application will be implemented to produce theoretical seismic volumes of uncompromised future reservoirs that can be compared to repeat surveys for leak detection.

Two different types of clay nanoparticle hybrid, iron oxide nanoparticle clay hybrid (ICH) and Al(2)O(3)-SiO(2) nanoparticle clay hybrid (ASCH), were synthesized and their effects on the rheological properties of aqueous bentonite fluids in steady state and dynamic state were explored. When ICH particles were added, bentonite particles in the fluid cross-link to form relatively well-oriented porous structure. This is attributed to the development of positively charged edge surfaces in ICH that leads to strengthening of the gel structure of the bentonite susensions. The role of ASCH particles on the interparticle association of the bentonite fluids is different from that of ICH and sensitive to pH. As pH of ASCH-added bentonite suspensions increased, the viscosity, yield stress, storage modulus, and flow stress decreased. In contrast, at low pH, the clay suspensions containing ASCH additives were coagulated and their rheological properties become close to those of ICH added bentonite fluids. A correlation between the net surface charge of the hybrid additives and the rheological properties of the fluids indicates that the embedded nanoparticles within the interlayer space control the variable charge of the edge surfaces of the platelets and determine the particles association behavior of the clay fluids.

The Scurry Area Canyon Reef Operators Committee (SACROC) field, located in the Permian Basin of West Texas is an enhanced oil recovery (EOR) site into which large volumes of CO2 have been injected. We acquired core samples and 3D seismic surveys from the site in order to better characterize the movement of the CO2 injection plumes. The samples of SACROC reef limestone were used for ultrasonic velocity measurements, detailed mineralogy and Scanning Electron Microscopy (SEM) characterization, Computed Tomography (CT) scanning, thin section studies, and porosity measurements. Using a NER AutoLab 1500 at the National Energy Technology Laboratory (NETL) Core Flow Lab we have measured P and S wave velocities, porosity, and permeability at varying pressures, temperatures, and fluid saturations that simulate reservoir conditions after successive floods. Measurements were also taken with supercritical CO2 at in situ pressures and temperatures. We also modeled the expected velocities for our samples using the standard Gassmann and other rock physics. We created a tool that groups grayscale ranges into three categories, cleans boundaries between groups, and produces a polygon map of the macropores, micropores, mineral grains, and matrix. In addition, the CT and SEM pore maps were analyzed to reveal pore shape statistics. Pore volume, area, and connectivity is essential for chemistry experiments that will emulate time exposure of CO2 to limestone. Further, this analysis technique allows us to obtain pore orientation information, which is important in understanding the anisotropic conditions that may affect seismic data. This multi-scale approach can help to characterize what is occurring inside of the reservoir. Fine scale measurements of how CO2 affects pore-space dissolution can help to inform us of any changes in overall reservoir storage capacity due to changing porosity. Core-scale velocity measurements under in situ conditions will allow us to predict changes in future well log or seismic surveys. Combining microscale, mesoscale, and macroscale information should lead to a better understanding of the various processes at work when CO2 is sequestered in a limestone reservoir.

The SACROC field, located in west Texas in the Permian Basin, is t he oldes t CO2 enhanced oil recovery site in the United States, with over 93 milli on tons of CO2 injected as of 2007. Recently, t he Na tional Energy Technology Labora tory (NETL) of the United Sta tes Department of Energy has begun to support an enhanced oil recovery project at the SACROC field in north central Texas, working in close collaboration with the Bureau of Economic Geology in Austin, Texas. The project requires the injection of CO2 at a depth of approximately 2040 meters into a reef structure. This project involves both repeat reflection seismic surveys and rock physics based analysis of core material. In the SACROC field, hydrocarbons were flooded out using water, and will be flooded w ith liquid CO2 during the summer of 2008. An experiment is planned whereby we first image fluid floods through reservoir rock using a CT scanner at NETL in order to see what the residual saturations of the previous fluids are. We th en plan to conduct velocity measurements in this order, so that we can obtain a good estimate of conditions in different parts of the reservoir. W e will then measure the P and S wave velo cities, porosity, and permeability at varying pressures and temperatures that simulate reservoir conditions after each successive flood. In addition to velocity ulus, Poisson’s ratio, and stress and strain measuremen ts, we will measure porosity, permeability, Young’s Mod measuremen t under simulate d in situ reservoir conditions. Preliminary P and S wave velocity measurements were made in dry Berea sandstone samples in order to have a base r eference material to compare our results to. Our Berea measurements were 2402 m/s for V p , 1688 m/s for V s , and 0.703 for V s / V p for an unstressed sample, which agrees well with the literature. The measured ve locities, the P and S waveforms, the velocity vs. confining pressure will be used to calibrate our acoustical measurements both in dry and saturated samples of the carbonate SACROC reservoir rock using oil, gas, water, and CO2. We then plan on doing the first of several seismic surveys in the SACROC field in west Texas. The first survey will be comple ted during the summer of 2008, and presented at this meeting. Using our velocity measurement s, we hope to be able to discern the difference between areas of the reservo ir rock that are saturated with different pore - filling phases. With repeated surveys over the next few years, we hope to be able to observe the area of extent of various floods of CO2 that are scheduled to be injected into several wells in the area using the laboratory me asurements we collected.