Migration Of Carbon Dioxide Research Articles

Modeling pore-scale CO2 plume migration with a hypergravity model

Understanding site-scale carbon dioxide migration in saline aquifers is crucial for storage safety. High time and economic costs make establishing a full-scale model of this long-term and large-scale process difficult. Hypergravity model shortens the length and time scale, which has been applied to physical modeling of two-phase immiscible displacement. To evaluate the feasibility of hypergravity modeling two-phase displacement in porous media at pore scale, CO2 migration in saline aquifer is a suitable and classic problem. We used the phase field method to simulate the vertical displacement of brine by carbon dioxide due to buoyancy and pressure at the pore scale. The pore-scale phenomena of the two-phase displacement process were obtained by assessing different flow rates with or without gravity. We systematically analyzed the feasibility of the hypergravity model to evaluate CO2 migration in the geological domain by evaluating the hypergravity effect and using dimensionless analysis. We provide suggestions for performing the hypergravity model to evaluate and predict immiscible displacement in two-phase system.

Analysis of the Migration of Carbon Dioxide in Deep Saline Fractured Aquifer

In order to control greenhouse gases and protect the environment, carbon dioxide emission reduction has become a global research hotspot. Fractures in the deep saline aquifer enhance the heterogeneity of the aquifer, and have an important effect on CO2 migration, thus the detailed description and characterization of fractures in geological structure are very important. Existing research on the impact of fractures on CO2 migration, however, ignores the role that the fractures' characteristics play in this process. This work aims at addressing this gap. Based on the embedded discrete fractured model (EDFM), we quantified the role of the fractures in the mechanism of CO2 migration and studied the length, aperture, and orientation of the fractures. It is found that the CO2 plume takes the fracture as its preferred channel and changes the migration direction. The longer the fracture length and wider the fracture aperture, the faster the CO2 migration rate is. The change in fracture orientation mainly affects the migration direction of the CO2 plume. Due to the different angles of the plume entering the fracture, the influences on the CO2 migration rate are also different. When the orientation is 45°, the CO2 migration rate is the fastest, while it is the slowest at 135°. When there is a complex fracture network in the aquifer, the heterogeneity of the aquifer is enhanced. Compared with the non-fractured aquifer, the direction and rate of CO2 migration are greatly changed, and the instability of CO2 sequestration is increased.

Migration of carbon dioxide in sandstone under various pressure/temperature conditions: From experiment to simulation

AbstractThe pressure and temperature of a target CO2 storage reservoir can significantly affect the migration and relative permeability characteristics which can ultimately determine the carbon storage capacity and storage integrity of target formations. To understand these impacts, a CO2 core‐flooding experiment was conducted on a brine‐saturated sandstone containing a single clay interlayer perpendicular to the flow direction at a temperature of 313 K and a pressure of 8 MPa and the fluid distribution was monitored by a high‐resolution X‐ray computed tomography (X‐CT) scanner. Further, a one‐dimensional model was established to reproduce the CO2 flow behavior inside the sample under the same experimental condition and then the model was extended to different temperatures (313 and 350 K) and pressures (6, 8, 12, and 17.4 MPa). The experimental results show that the CO2 preferentially created high‐CO2‐saturation flow pathways which then expanded until they were large enough to transport the CO2 at the prescribed flow rate. The sub‐core scale heterogeneity also had significant effects on the CO2 migration, forming a barrier to downstream flow. The simulation results show that at a given temperature, the CO2 front migration velocity decreased with increasing reservoir pressure while the CO2 saturation along the pathways increased. Comparing simulations when the reservoir pressure was the same, the front‐migration velocity increased with increasing temperature, and the CO2 saturation along the pathways decreased. Meanwhile, the influence of temperature and pressure on CO2 saturation distribution was more evident in the parts of the core with high residual brine saturation. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Characterization Method and Application of Heterogeneous Reservoir Based on Different Data Quantity

Abstract Deep saline aquifers have strong heterogeneity under natural conditions, which affects the migration of carbon dioxide (CO2) injection into the reservoir. How to characterize the heterogeneity of rock mass is of great significance to research the CO2 migration law during CO2 storage. A method is proposed to construct different heterogeneous models from the point of view of whether the amount of data is sufficient or not, the wholly heterogeneous model with sufficient data, the deterministic multifacies heterogeneous model which is simplified by lithofacies classification, and the random multifacies heterogeneous model which is derived from known formation based on transfer probability theory are established, respectively. Numerical simulation is carried out to study the migration law of CO2 injected into the above three heterogeneous models. The results show that the migration of CO2 in heterogeneous deep saline aquifers shows a significant fingering flow phenomenon and reflect the physical process in CO2 storage; the migration law of CO2 in the deterministic multifacies heterogeneous model is similar to that in the wholly heterogeneous model and indicates that the numerical simulation of simplifying the wholly heterogeneous structure to the lithofacies classification structure is suitable for simulating the CO2 storage process. The random multifacies heterogeneous model based on the transfer probability theory accords with the development law of sedimentary formation and can be used to evaluate the CO2 migration law in unknown heterogeneous formations. On the other hand, by comparing the dry-out effect of CO2 in different heterogeneous models, it is pointed out that the multifacies characterization method will weaken the influence due to the local homogenization of the model in small-scale research; it is necessary to refine the grid and subdivide the lithofacies of the local key area elements to eliminate the research error. The research results provide feasible references and suggestions for the heterogeneous modeling of the missing data area and the simplification of large-scale heterogeneous models.

Predicting CO2 Plume Migration in Heterogeneous Formations Using Conditional Deep Convolutional Generative Adversarial Network

AbstractNumerical simulation of flow and transport in heterogeneous formations has long been studied, especially for uncertainty quantification and risk assessment. The high computational cost associated with running large‐scale numerical simulations in a Monte Carlo sense has motivated the development of surrogate models, which aim to capture the important input‐output relations of physics‐based models but require only a fraction of the cost of full model runs. In this work, we formulate a conditional deep convolutional generative adversarial network (cDC‐GAN) surrogate model to learn the dynamic functional mappings in multiphase models. The cDC‐GAN belongs to a class of semisupervised learning methods that can be used to learn the data generation processes. Like the original GAN, a main strength of the cDC‐GAN is that it includes a self‐training scheme for improving the quality of generative modeling in a game theoretic framework, without requiring extensive statistical knowledge and assumptions on input data distributions. In particular, our cDC‐GAN model is designed to learn cross‐domain mappings between high‐dimensional input (e.g., permeability) and output (e.g., phase saturations) pairs, with the ability to incorporate conditioning information (e.g., prediction time). As a use case, we demonstrate the performance of cDC‐GAN for predicting the migration of carbon dioxide (CO2) plume in heterogeneous carbon storage reservoirs, which has both numerical and practical significance because of the safe storage requirements now mandated in many countries. Results show that cDC‐GAN achieves high accuracy in predicting the spatial and temporal evolution patterns of the injected CO2 plume, as compared to the original results obtained using a compositional reservoir simulator. The performance of cDC‐GAN models, trained using the same number of training samples, stays relatively robust when the level of spatial heterogeneity is increased. Our cDC‐GAN is pattern based and is not limited by the underlying physics. Thus, it provides a general framework for developing surrogate models, and for conducting uncertainty analyses for a wide range of physics‐based models used in both groundwater and subsurface energy exploration applications.

Characteristics of Carbon Dioxide Emissions from a Seismically Active Fault

ABSTRACT Seismically active faults are key features of the earth, and earthquake-induced carbon dioxide released from natural faults has been detected. But the link between active fault deformation and amounts of carbon dioxide emission remains poorly understood. In this paper we monitor progressive carbon dioxide levels and strain signals from the boreholes in a seismically active fault, and show that the carbon dioxide variations are sensitive to the fault deformation over the same time scale of the observations. Therefore, we preliminarily propose a mass-wave propagation model (e.g., interaction of shock waves with advection-diffusion of mass, namely the gas hammer effect) to physically interpret carbon dioxide variations due to dilation or compaction of fluid paths in the natural fault. Of particular interest is that the penetration of shock waves into the natural fault mechanically influences carbon dioxide migration.

Fiber Bragg grating‐based experimental and numerical investigations of CO2 migration front in saturated sandstone under subcritical and supercritical conditions

AbstractCarbon dioxide (CO2) can be at risk of leakage during its storage in deep saline aquifers due to stress field changes in the reservoir. The aim of this study was to investigate the effects of CO2 injection pressure on dynamic strain response of the reservoir and the CO2 migration process. A series of core flooding experiments was performed with the‐state‐of‐art fiber Bragg grating sensors. The results show that the surface strain response was linearly correlated with CO2 injection pressure. Carbon dioxide migration velocity can be estimated from the strain response time differences among three gratings. The migration velocity of supercritical CO2 is higher than that of liquid CO2 but lower than gaseous CO2. Finally, numerical simulation was applied to model the CO2 migration process and the simulated values were compatible with those of experiments. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.

Evidence of methane and carbon dioxide migration to the near surface zone in the area of the abandoned coal mines in Wałbrzych District (Lower Silesian Coal Basin, SW Poland) based on periodical changes of molecular and isotopic compositions

The objective of this paper is to determine the reasons, origin and character of periodical changes of methane and carbon dioxide concentrations in the near-surface zone as well as emission of these gases to atmosphere after closing bituminous coal and anthracite mines in the former Wałbrzych Coal District (SW Poland). The measurements were performed during the period including the active impact of “water piston effect” on the migration of a coal-bearing gases as well as the period of stabilization of water table of the Pennsylvanian aquifer. In the years 1997–2005, 20 sampling sessions were completed during which 3210 soil gas samples were collected at a depth of about 1.2m and along 4 measurement lines located in the Gorce and the Sobięcin depressions. Maximum methane and carbon dioxide concentrations measured in soil gas samples reached 32.4 and 15.7vol%, respectively. Isotopic study shows that coal-bed gases, recent microbial methane, and multigenetic carbon dioxide from degassing of ground-waters of the Upper Pennsylvanian aquifer occur within the near-surface zone of the Wałbrzych Coal District. Within the Serpukhovian Wałbrzych and Upper Bashkirian-Moscovian Žacleř coal-bearing formations three genetic types of coal-bed gases occur: Variscan thermogenic (methane, higher gaseous hydrocarbons and carbon dioxide), endogenic (abiogenic) carbon dioxide and “late” (Late Cretaceous) and recent microbial methane and carbon dioxide. Changes of mean concentrations of methane and carbon dioxide in the near-surface zone recorded during years of studies demonstrated the influence of “water piston effect”, which drives migration of coalbed gases towards the earth surface. In both the Gorce and the Sobięcin depressions, gas migrates with various intensity. Generally, the lower methane emission measured in the years 2004–2005, and compared with the period 1999–2000, resulted from the stabilization of groundwater table whereas higher carbon dioxide emission confirms the degassing of shallow groundwaters. Anomalous concentrations of methane and carbon dioxide were related to numerous faults and fracture systems cutting the steeply dipping Upper Mississippian and Pennsylvanian coal-bearing formations, and to the outcrops of these rocks. However, in the near-surface zone, multiproportional mixing of coal-bed gases, recent microbial methane and carbon dioxide is observed. Periodical changes of stable carbon isotope composition of methane and carbon dioxide of near-surface zone in particular sessions are caused by the time-related change of location of water table of Pennsylvanian aquifer in the complicated structure of the Gorce and Sobięcin depressions. Persistently anomalous concentrations of methane and carbon dioxide in the near surface zone, still observed after several-years-long stabilization of groundwater table, seem to indicate a continuous supply of coalbed gases to the near-surface zone through pervious dislocations. Such an interpretation is confirmed by the extreme value of methane emission detected at a particular sampling site after the cessation of the “water piston” effect. It was presumably caused by the secondary intensification of gas flux from deep sources, triggered by neotectonic movements in the study area.

Framework for the assessment of interaction between CO2 geological storage and other sedimentary basin resources.

Sedimentary basins around the world considered suitable for carbon storage usually contain other natural resources such as petroleum, coal, geothermal energy and groundwater. Storing carbon dioxide in geological formations in the basins adds to the competition for access to the subsurface and the use of pore space where other resource-based industries also operate. Managing potential impacts that industrial-scale injection of carbon dioxide may have on other resource development must be focused to prevent potential conflicts and enhance synergies where possible. Such a sustainable coexistence of various resource developments can be accomplished by implementing a Framework for Basin Resource Management strategy (FBRM). The FBRM strategy utilizes the concept of an Area of Review (AOR) for guiding development and regulation of CO2 geological storage projects and for assessing their potential impact on other resources. The AOR is determined by the expected physical distribution of the CO2 plume in the subsurface and the modelled extent of reservoir pressure increase resulting from the injection of the CO2. This information is used to define the region to be characterised and monitored for a CO2 injection project. The geological characterisation and risk- and performance-based monitoring will be most comprehensive within the region of the reservoir containing the carbon dioxide plume and should consider geological features and wells continuously above the plume through to its surface projection; this region defines where increases in reservoir pressure will be greatest and where potential for unplanned migration of carbon dioxide is highest. Beyond the expanse of the carbon dioxide plume, geological characterisation and monitoring should focus only on identified features that could be a potential migration conduit for either formation water or carbon dioxide.

Experimental investigation of sandstone properties under CO2–NaCl solution-rock interactions

Carbon dioxide injection in saline aquifer disposal leads to geochemical alteration and geomechanical deformation of the host formations, both in the short- and long-terms. We performed triaxial compression and seepage-creep experiments on quartz–feldspar–detrital sandstone (as a typical storage reservoir material) as well as microscopy. Experimental results provided insight into the deformation of porous sandstone under a water-chemical environment (NaCl solution and CO2–NaCl solution), in both short- and long-terms: the long-term evolution of mechanical deformation and permeability during the migration of carbon dioxide and carbon fixation was thus analysed. Our aim was to study the influence of CO2–NaCl solution on the compressive strength and deformation of quartz–feldspar–detrital sandstone, as well as the impact of CO2–NaCl solution flow-through processes on the mechanical, hydraulic, and chemical properties of reservoir sandstone in terms of its time-dependent deformation, permeability, porosity, and mineral components. Comparison and analysis of short-term experimental results showed that the addition of CO2 enhanced the partial-mineral dissolution and the compressibility for sandstone, as well as helping the brittle–ductile transition in its stress–strain curves. The CO2 dissolved in the pore fluid reduced the compressive strength of sandstone to 7–15% of the compressive strength without CO2. For long-term mechanical and hydraulic properties of sandstone, the corresponding results showed that the threshold stress of shear dilatancy for the sandstone with the CO2–NaCl solution flow-through was reduced to about 17% of the threshold stress without CO2; its hydraulic conductivity was reduced to more than 50% at beginning and fell an order of magnitude at the axial deviatoric stress of 33MPa. In addition, the increment of time-dependent deformation in long-term test with CO2–NaCl solution flow-through was not obvious at the beginning creep but conspicuous as the increasing stress level, which up to about 20% of the strain without CO2 at the axial deviatoric stress of 33MPa. With the application of scanning electron microscopy and mercury intrusion porosimetry, the mechanism of the influence of CO2–NaCl solution on sandstone mechanical and hydraulic properties was further investigated at the micro-scale. Besides, the results of this microscopy described the effect of CO2–NaCl solution-sandstone interaction on the sandstone mineral components, shape, and structure; these reflect the sequestration capacity of CO2 in quartz-feldspar-detritus sandstone by carbon fixation.

Effects of capillary pressure – fluid saturation – relative permeability relationships on predicting carbon dioxide migration during injection into saline aquifers

Abstract Mathematical modeling and numerical simulations on carbon dioxide plume migration in confined saline aquifers have become important approaches to evaluate storage capacity and efficiency for carbon dioxide sequestration and to predict potential risks of leakage during and after carbon dioxide injection into subsurface formations. The effects of the characteristic functions relating capillary pressures and relative permeabilities to fluid saturations are critical in predicting carbon dioxide plume migration in saline aquifers. In this paper, four well known models, i.e. Brooks-Corey-Burdine model (BCB), Brooks-Corey- Mualem model (BCM), Van Genuchten-Burdine model (VGB), and Van Genuchten-Mualem model (VGM), were incorporated with an immiscible displacement process model to simulate carbon dioxide injection into saline aquifers. Parametric analysis was conducted to identify the influences of parameters in the Brooks-Corey based model on the predictions of carbon dioxide plume migration in a confined saline aquifer. A comprehensive comparison was carried out to reveal the different performances of the models with respect to the evolutions and patterns of carbon dioxide plume in the confined saline aquifer. The simulation results indicate that the saturation distributions of carbon dioxide are drastically sensitive to the capillary entry pressure. However, the parameters and in the Brooks-Corey based model, which are related to pore size distribution and tortuosity ratio of a porous medium, respectively, have little effects on predicting carbon dioxide plume migration in the saline aquifer. Moreover, different models may cause extensive influences on the carbon dioxide distributions at the region that is close to the injection well and at the leading edges of carbon dioxide plume in the saline aquifer. Hence, the results indicate that for the evaluation of the storage capacity and efficiency of a saline aquifer to trap carbon dioxide, the storage capacity of the saline aquifer could be over- estimated by using the BCB model, whereas it could be underestimated by using the VGM model. On the other hand, for evaluations of potential leakage of carbon dioxide in saline aquifers, where the movement of the leading edge of carbon dioxide plume is monitored, the VGM model is a safe choice in simulations. These results have potentially significant implications for estimation of carbon dioxide storage capacity of saline aquifers and assessments on potential risks of leakage.

Numerical simulation of carbon dioxide migration in a sandstone aquifer considering the fluid–solid coupling

Very limited investigations have been done on the numerical simulation of carbon dioxide (CO2) migration in sandstone aquifers taking consideration of the interactions between fluid flow and rock stress. Based on the poroelasticity theory and multiphase flow theory, this study establishes a mathematical model to describe CO2 migration, coupling the flow and stress fields. Both finite difference method (FDM) and finite element method (FEM) were used to discretize the mathematical model and generate a numerical model. A case study was carried out using the numerical model on the Jiangling sandstone aquifer in the Jianghan basin, China. The rock mechanics parameters of reservoir and overlying strata of Jiangling depression were obtained by triaxial tests. A two-dimensional model was then built to simulate carbon dioxide migration in the sandstone aquifer. The numerical simulation analyzes the carbon dioxide migration distribution rule with and without considering capillary pressure. Time-dependent migration of CO2 in the sandstone aquifer was analyzed, and the result from the coupled model was compared with that from a traditional non-coupled model. The calculation result indicates a good consistency between the coupled model and the non-coupled model. At the injection point, the CO2 saturation given by the coupled model is 15.39 % higher than that given by the non-coupled model; while the pore pressure given by the coupled model is 4.8 % lower than that given by the non-coupled model. Therefore, it is necessary to consider the coupling of flow and stress fields while simulating CO2 migration for CO2 disposal in sandstone aquifers. The result from the coupled model was also sensitized to several parameters including reservoir permeability, porosity, and CO2 injection rate. Sensitivity analyses show that CO2 saturation is increased non-linearly with CO2 injection rate and decreased non-linearly with reservoir porosity. Pore pressure is decreased non-linearly with reservoir porosity and permeability, and increased non-linearly with CO2 injection rate. When the capillary pressure was considered, the computed gas saturation of carbon dioxide was increased by 10.75 % and the pore pressure was reduced by 0.615 %.

Coupled Flow and Deformation Modeling of Carbon Dioxide Migration in the Presence of a Caprock Fracture during Injection

Understanding the transport of carbon dioxide (CO2) during long-term CO2 injection into a typical geologic reservoir, such as a saline aquifer, could be complicated because of changes in geochemical, hydrogeological, and hydromechanical behavior. While the caprock layer overlying the target aquifer is intended to provide a tight, impermeable seal in securing injected CO2, the presence of geologic uncertainties, such as a caprock fracture or fault, may provide a channel for CO2 leakage. There could also be a possibility of the activation of a new or existing dormant fault or fracture, which could act as a leakage pathway. Such a leakage event during CO2 injection may lead to a different pressure and ground response over a period of time. In the present study, multiphase fluid flow simulations in porous media coupled with geomechanics were used to investigate the overburden geologic response and plume behavior during CO2 injection in the presence of a hypothetical permeable fractured zone in a caprock, exis...

Densities and Excess Volumes of CO2 + Decane Solution from 12 to 18 MPa and 313.15 to 343.15 K

It has been widely considered that the global warming was induced by the increasing atmospheric concentrations of carbon dioxide, which has a significant impact on the sustainable development of the human society. Injecting carbon dioxide into depleted oil/gas reservoir has been developed to reduce carbon dioxide emission by the sequestration of CO2 underground, which is also considered as one promising approach to enhance oil recovery simultaneously. The evaluating of CO2 sequestration in oil reservoir needs highly accurate experimental data and models about the thermodynamic characters of CO2 + oil mixture. Density is one of key physical characters for simulating the diffusion and migration of carbon dioxide under the oil/gas reservoir. Research on volumetric behaviour is helpful to understand the expansion of the liquid phases in CO2 + oil mixture.In this paper, decane is investigated instead of petroleum because of the similar thermal physical property. The measurements have been performed at pressures from 12MPa to 18MPa and temperatures from 313.15K to 343.15K at four compositions x1 (x1 is the mole fraction of carbon dioxide) = 0.8690, 0.9135, 0.9430 and 0.9818 by a magnetic suspension balance (MSB). The accuracy of the experimental quantities presented in this work are T/K = ± 0.01, m/g = ± 10-5 respectively. One circulation pump (AKICO, Japan) is equipped to accelerate the dissolution of CO2 in decane. Some conclusions can be obtained from the experiment as follow: (1) the dissolution of CO2 increases the density of decane, the density of CO2 + decane solution increases with increasing pressure and decreases with increasing temperature. (2) the slope of density with respect to pressure increases with increasing CO2 mole fractions while the slope with respect to temperature decreases with increasing CO2 mole fractions. (3) the crossover phenomenon appears at different compositions and the crossover pressure increases with temperature. (4) the excess molar volumes of this binary mixture are negative and show negative increasing with temperature for the data reported in this work. The GERG - 2008 model is used to predict density of CO2 + decane solution, which takes temperature, pressure, and CO2 concentration into account. An empirical equation is also used to predict the density of this binary mixture. The predictions show that the empirical equation is in good agreement with the experimental data over the experimental range. The measurement and the model used in this work supplies the basic experimental data and theoretical analysis to CO2 sequestration and enhance oil recovery.

Developing a robust geochemical and reactive transport model to evaluate possible sources of arsenic at the CO2 sequestration natural analog site in Chimayo, New Mexico

Migration of carbon dioxide (CO2) from deep storage formations into shallow drinking water aquifers is a possible system failure related to geologic CO2 sequestration. A CO2 leak may cause mineral precipitation/dissolution reactions, changes in aqueous speciation, and alteration of pH and redox conditions leading to potential increases of trace metal concentrations above EPA National Primary Drinking Water Standards. In this study, the Chimayo site (NM) was examined for site-specific impacts of shallow groundwater interacting with CO2 from deep storage formations. Major ion and trace element chemistry for the site have been previously studied. This work focuses on arsenic (As), which is regulated by the EPA under the Safe Drinking Water Act and for which some wells in the Chimayo area have concentrations higher than the maximum contaminant level (MCL). Statistical analysis of the existing Chimayo groundwater data indicates that As is strongly correlated with trace metals U and Pb indicating that their source may be from the same deep subsurface water. Batch experiments and materials characterization, such as: X-ray diffraction (XRD), scanning electron microscopy (SEM), and synchrotron micro X-ray fluorescence (μ-XRF), were used to identify As association with Fe-rich phases, such as clays or oxides, in the Chimayo sediments as the major factor controlling As fate in the subsurface. Batch laboratory experiments with Chimayo sediments and groundwater show that pH decreases as CO2 is introduced into the system and buffered by calcite. The introduction of CO2 causes an immediate increase in As solution concentration, which then decreases over time. A geochemical model was developed to simulate these batch experiments and successfully predicted the pH drop once CO2 was introduced into the experiment. In the model, sorption of As to illite, kaolinite and smectite through surface complexation proved to be the key reactions in simulating the drop in As concentration as a function of time in the batch experiments. Based on modeling, kaolinite precipitation is anticipated to occur during the experiment, which allows for additional sorption sites to form with time resulting in the slow decrease in As concentration. This mechanism can be viewed as trace metal “scavenging” due to sorption caused secondary mineral precipitation. Since deep geologic transport of these trace metals to the shallow subsurface by brine or CO2 intrusion is critical to assessing environmental impacts, the effective retardation of trace metal transport is an important parameter to estimate and it is dependent on multiple coupled reactions. At the field scale, As mobility is retarded due to the influence of sorption reactions, which can affect environmental performance assessment studies of a sequestration site.

Heterogeneous saline formations for carbon dioxide disposal: Impact of varying heterogeneity on containment and trapping

Natural gas fields often contain carbon dioxide in their reservoir fluids. Exploitation of these resources requires the removal of carbon dioxide from produced fluids to meet quality standards for sale into a domestic market or for the processing of the gas into LNG. To limit the atmospheric emissions of carbon dioxide, a major greenhouse gas, it has been proposed that one method of abatement could be to inject the CO 2 into deep saline formations. This study shows that the selection process for identifying appropriate saline formations should not only consider their size and permeability but should also consider their degree of heterogeneity. To this end, notional yet realistic geological marine sand models were constructed, on an areal scale of 50 km 2, to examine the effects of reservoir heterogeneity on the migration and storage of a 50 million tonne plume over a time scale of 1000 yrs. The models were identical in geometry and in their distribution of porosity and permeability but were individually populated with facies realisations for different net-to-gross ratios. Standard geostatistical techniques were used to generate the various distributions. With regard to the shale content, the ratio of sand to shale was varied from 100:0 (i.e. homogeneous) to 40:60. A radial shale variogram, with a length of 300 m, was used. The models were up-scaled, using flow-based methods, to make the computation feasible. A set of metrics were developed and used to compare plume migration (both vertically and laterally) and containment (through dissolution and residual phase trapping) between the various scenarios. The study showed that heterogeneity had a significant impact on the subsurface behaviour of the carbon dioxide. Increasing the shale content, corresponding to a gradual decrease in reservoir quality, progressively inhibited vertical flow of the plume whilst promoting its lateral flow. This increase in the tortuosity of the carbon dioxide migration pathways resulted in a reduction in the rate of residual gas trapping through hysteresis effects. Ultimately, however, less carbon dioxide is likely to collect under the seal, thereby reducing the risk of seepage to overlying formations. It is evident that for the time scales of containment being considered here simulation periods of the order of tens of thousands of years, or even longer, will be required to demonstrate the onset of an equilibrium state.

Groundwater transport of tritium and krypton 85 from a nuclear detonation cavity

Underground nuclear detonations at the Nevada Test Site provide a unique opportunity to study the hydrologic transport of radionuclides in the field. At the Cambric experiment a pumped well 91 m from the detonation cavity was sampled regularly over 16 years and recovered 94% of the tritium but only 42% of the expected 85Kr, both following decay correction. In addition, the elution curves were different for these two ideal tracers of groundwater movement. Modeling is used to determine the fate of the missing 85Kr based on the phenomenology of underground nuclear detonations and the specific hydrogeology of the Cambric site. At Cambric, large amounts of carbon dioxide created by the detonation caused the upward migration of 85Kr through the collapsing chimney and into the unsaturated zone. A numerical model simulated tritium and 85Kr transport to the pumped well using tritium data to determine regional anisotropy in hydraulic conductivity and reduced hydraulic conductivity in the cavity region. The calibrated model reproduces the 85Kr breakthrough data when emplacement of 85Kr by the upward migration of carbon dioxide is included. Nuclear detonations provide long‐term tracer tests in the subsurface, but knowledge of the spatial distribution of sources at this specific site is essential in understanding the transport of these two radionuclide tracers.

Certain aspects of origin and migration of carbon dioxide in mercury deposits, as in the Nikitovka, Donbass

Certain aspects of origin and migration of carbon dioxide in mercury deposits, as in the Nikitovka, Donbass