CO2 Residual Trapping Research Articles

Temperature sensitivity of reactive ester tracers for measuring CO2 residual trapping capacity

An understanding of the fundamental properties of chemical tracers (e.g. partitioning and sorption) is critical for assessing their subsurface behavior and to accurately model and interpret field tracer data. Carbon dioxide–water (CO2/H2O) partition coefficients have been previously determined for the reactive ester tracers, propylene glycol diacetate, triacetin and tripropionin, suggesting their suitability for assessing the residual trapping capacity of a geological formation for CO2 in a single well chemical tracer test. Understanding the temperature dependent behavior of chemical tracers significantly enhances their utility in field trials leading to a more accurate estimate of reservoir properties. However, very little information is known on the relationship between temperature and the partitioning process for these chemical tracers. In this paper, the temperature dependence of the partitioning process has been determined for temperatures ranging from 60 to 120°C. The variations in the partition coefficient with temperature were shown to correlate reasonably well with the van't Hoff equation for all tracers. The enthalpy associated with the partitioning process was determined by a regression fit to this equation and was shown to be the smallest for propylene glycol diacetate and the largest for tripropionin. It was found that the estimated enthalpy is approximately linearly correlated with the number of carbon atoms in the organic ester. Furthermore, we have shown that the temperature dependence of the tracer partition coefficient causes significant variation in the estimate of residual saturation.

Process‐dependent residual trapping of CO2 in sandstone

AbstractThis paper demonstrates that the nature and extent of residual CO2 trapping depend on the process by which the CO2 phase is introduced into the rock. We compare residual trapping of CO2 in Berea Sandstone by imbibing water into a core containing either exsolved CO2 or CO2 introduced by drainage. X‐ray computed tomography measurements are used to map the spatial distribution of CO2 preimbibition and postimbibition. Unlike during drainage where the CO2 distribution is strongly influenced by the heterogeneity of the rock, the distribution of exsolved CO2 is comparatively uniform. Postimbibition, the CO2 distribution retained the essential features for both the exsolved and drainage cases, but twice as much residual trapping is observed for exsolved CO2 even with similar preimbibition gas saturations. Residually trapped exsolved gas also disproportionately reduced water relative permeability. Development of process‐dependent parameterization will help better manage subsurface flow processes and unlock benefits from gas exsolution.

Review and implications of relative permeability of CO2/brine systems and residual trapping of CO2

The adoption of carbon capture and storage (CCS) as a method of mitigating anthropogenic CO2 emissions will depend on the ability of initial geological storage projects to demonstrate secure containment of injected CO2. Potential leakage pathways, such as faults or degraded wells, increase the uncertainty of geological storage security. CCS as an industry is still in its infancy and until we have experience of industrial scale, long term CO2 storage projects, quantifying leakage event probabilities will be problematic. Laboratory measurements of residual saturation trapping, the immobilisation of isolated micro-bubbles of CO2 in reservoir pores, provides an evidence base to determine the fraction of injected CO2 that will remain trapped in the reservoir, even if a leakage event were to occur. Experimental results for sandstone, the most common target lithology for storage projects, demonstrate that 13–92% of injected CO2 can be residually trapped. Mineralisation, the only other geological trapping mechanism which guarantees permanent trapping of CO2, immobilises CO2 over hundreds to thousands of years. In comparison, residual trapping occurs over years to decades, a timescale which is more relevant to CCS projects during their operational phase and to any financial security mechanisms they require to secure storage permits.

Interfacial Tension Effect on Cluster Size Distributions for Residual Trapping of CO2 in Sandstones

Abstract The residual trapping of CO2 could ensure long-term carbon geological storage. The understanding of the characteristic of the residual phase including saturation, size distribution is essential. The residual phase distribution is a complex function of pore morphology, interfacial tension (IFT) and wettability. Here, we numerically study IFT effect on the residual saturation and sizes distribution by using a highly efficient GPU (Graphic Processing Unit) based multi-phase lattice Boltzmann method. The results of direct simulation on real reservoir rocks imply that there is less trapping of CO2, but with a greater surface area for dissolution in low IFT condition.

Ranking Importance of Uncertainties for the Assessment of Residual and Dissolution Trapping of CO2 on a Large-scale Storage Site

Abstract We propose an approach to assess the importance ranking of uncertainty sources, with regards to the behavior of the mobile CO 2 during the post-injection period: a variance-based global sensitivity analysis is performed on three output parameters characterizing the location and the quantity of mobile CO 2 , considering residual and dissolution trapping. The use of advanced meta-modeling techniques of ACOSSO-type allows circumventing two major difficulties: 1. The large number of computationally intensive reservoir-scale flow simulations; 2. The different nature of uncertainties whether linked to parameters (continuous variables) or to modeling assumptions (scenario-like variables). The feasibility of the approach is demonstrated using a potential site for CO 2 storage in the Paris basin (France), for which the amount, nature and quality of the data available at disposal and the associated uncertainties can be seen as representative to those of a storage project at the post-screening stage. A special attention has been paid to confront the results of the sensitivity analysis with the physical interpretation of the processes.

Design of a two-well field test to determine in situ residual and dissolution trapping of CO2 applied to the Heletz CO2 injection site

Field testing is a critical step to improve our knowledge on in situ-trapping mechanisms of CO2 injected in geological formations and their relative importance. In this study, we present a two-well test sequence aimed at quantifying field values of both residual and dissolution trapping of CO2. Then, we apply it to the Heletz experimental CO2 injection site, using numerical modelling. The sequence includes a hydraulic test to measure residual scCO2 saturation and a novel tracer technique, together with measurements of abstracted fluid compositions for quantification of the rate of CO2 dissolution in the reservoir. The proposed tracer technique uses a tracer with negligible aqueous solubility, which is injected with the scCO2 and enriched in the scCO2 phase as CO2 dissolves. We show that this tracer can provide direct information about the dissolution of mobile scCO2. We also show that the rate of abstracted dissolved CO2 can be used to predict the total rate of CO2 dissolution, provided that the amount of dissolved CO2 in the formation stabilizes, and that this can be achieved with the proposed abstraction scheme. We conclude that the combination of these measurements is a promising tool for detailed field-scale characterization of residual and dissolution trapping processes.

Determining Residual CO2 Saturation Through a Dissolution Test-results from the CO2CRC Otway Project

Residual CO2 trapping (Sgr-CO2) is a key mechanism for geological CO2 storage. The CO2CRC undertook a sequence of field tests with the aim of comparing different ways of determining Sgr-CO2 including a dissolution test. Dissolution test results show an unexpectedly early breakthrough and low maximum CO2 concentrations in the back- produced water making the data inconclusive when using traditional data interpretation. Here, we consider two conditions to explain the observations: Firstly, residual CO2 is vertically unevenly distributed and, secondly, the fluid and residual CO2 are not in equilibrium. Furthermore, we postulate localised flow channels have formed during the 3- month test period caused by advective flow of CO2-saturated, low pH water leading to transport-controlled mineral dissolution.

Experimental and Numerical Study of Residual CO2 Trapping in Porous Sandstone

To understand the structural and residual CO2 trapping mechanism, we conducted laboratory experiments and 2-D fluid flow simulations. The results of elastic wave velocity measurements indicate that there are strong effects of injected CO2 volume on elastic wave velocities. We calculated CO2 saturation from changes of Vs and estimated the irreducible water saturation and residual CO2 saturation. We also discovered the strong effect of small-scale heterogeneity of pore structure on fluid behavior by 2-D fluid flow simulation. The simulation results indicated that the laminae restricted fluid flow and stored CO2 as the residual trapped CO2. These results indicate that the small- scale heterogeneity is important to forming residual trapped CO2.

Influence of Methane in CO2 Transport and Storage for CCS Technology

CO(2) Capture and Storage (CCS) is a good strategy to mitigate levels of atmospheric greenhouse gases. The type and quantity of impurities influence the properties and behavior of the anthropogenic CO(2), and so must be considered in the design and operation of CCS technology facilities. Their study is necessary for CO(2) transport and storage, and to develop theoretical models for specific engineering applications to CCS technology. In this work we determined the influence of CH(4), an important impurity of anthropogenic CO(2), within different steps of CCS technology: transport, injection, and geological storage. For this, we obtained new pressure-density-temperature (PρT) and vapor-liquid equilibrium (VLE) experimental data for six CO(2) + CH(4) mixtures at compositions which represent emissions from the main sources in the European Union and United States. The P and T ranges studied are within those estimated for CO(2) pipelines and geological storage sites. From these data we evaluated the minimal pressures for transport, regarding the density and pipeline's capacity requirements, and values for the solubility parameter of the mixtures, a factor which governs the solubility of substances present in the reservoir before injection. We concluded that the presence of CH(4) reduces the storage capacity and increases the buoyancy of the CO(2) plume, which diminishes the efficiency of solubility and residual trapping of CO(2), and reduces the injectivity into geological formations.

Sensitivity Study of Simulation Parameters Controlling CO2 Trapping Mechanisms in Saline Formations

The primary purpose of this study is to understand quantitative characteristics of mobile, residual, and dissolved CO2 trapping mechanisms within ranges of systematic variations in different geologic and hydrologic parameters. For this purpose, we conducted an extensive suite of numerical simulations to evaluate the sensitivities included in these parameters. We generated two-dimensional numerical models representing subsurface porous media with various permutations of vertical and horizontal permeability (kv and kh), porosity (\({\phi}\)), maximum residual CO2 saturation (\({S_{\rm gr}^{\max}}\)), and brine density (ρbr). Simulation results indicate that residual CO2 trapping increases proportionally to \({k_{\rm v}, k_{\rm h}, S_{\rm gr}^{\max}}\) and ρbr but is inversely proportional to \({\phi.}\) In addition, the amount of dissolution-trapped CO2 increases with kv and kh, but does not vary with \({\phi }\) , and decreases with \({S_{\rm gr}^{\max}}\) and ρbr. Additionally, the distance of buoyancy-driven CO2 migration increases proportionally to kv and ρbr only and is inversely proportional to \({k_{\rm h}, \phi }\) , and \({S_{\rm gr}^{\max}}\) . These complex behaviors occur because the chosen sensitivity parameters perturb the distances of vertical and horizontal CO2 plume migration, pore volume size, and fraction of trapped CO2 in both pores and formation fluids. Finally, in an effort to characterize complex relationships among residual CO2 trapping and buoyancy-driven CO2 migration, we quantified three characteristic zones. Zone I, expressing the variations of \({S_{\rm gr}^{\max}}\) and kh, represents the optimized conditions for geologic CO2 sequestration. Zone II, showing the variation of \({\phi}\) , would be preferred for secure CO2 sequestration since CO2 has less potential to escape from the target formation. In zone III, both residual CO2 trapping and buoyancy-driven migration distance increase with kv and ρbr.

Two-phase gravity currents in porous media

We develop a model describing the buoyancy-driven propagation of two-phase gravity currents, motivated by problems in groundwater hydrology and geological storage of carbon dioxide (CO2). In these settings, fluid invades a porous medium saturated with an immiscible second fluid of different density and viscosity. The action of capillary forces in the porous medium results in spatial variations of the saturation of the two fluids. Here, we consider the propagation of fluid in a semi-infinite porous medium across a horizontal, impermeable boundary. In such systems, once the aspect ratio is large, fluid flow is mainly horizontal and the local saturation is determined by the vertical balance between capillary and gravitational forces. Gradients in the hydrostatic pressure along the current drive fluid flow in proportion to the saturation-dependent relative permeabilities, thus determining the shape and dynamics of two-phase currents. The resulting two-phase gravity current model is attractive because the formalism captures the essential macroscopic physics of multiphase flow in porous media. Residual trapping of CO2 by capillary forces is one of the key mechanisms that can permanently immobilize CO2 in the societally important example of geological CO2 sequestration. The magnitude of residual trapping is set by the areal extent and saturation distribution within the current, both of which are predicted by the two-phase gravity current model. Hence the magnitude of residual trapping during the post-injection buoyant rise of CO2 can be estimated quantitatively. We show that residual trapping increases in the presence of a capillary fringe, despite the decrease in average saturation.

Two-phase gravity currents in porous media

We develop a model describing the buoyancy-driven propagation of two-phase gravity currents, motivated by problems in groundwater hydrology and geological storage of carbon dioxide (CO2). In these settings, fluid invades a porous medium saturated with an immiscible second fluid of different density and viscosity. The action of capillary forces in the porous medium results in spatial variations of the saturation of the two fluids. Here, we consider the propagation of fluid in a semi-infinite porous medium across a horizontal, impermeable boundary. In such systems, once the aspect ratio is large, fluid flow is mainly horizontal and the local saturation is determined by the vertical balance between capillary and gravitational forces. Gradients in the hydrostatic pressure along the current drive fluid flow in proportion to the saturation-dependent relative permeabilities, thus determining the shape and dynamics of two-phase currents. The resulting two-phase gravity current model is attractive because the formalism captures the essential macroscopic physics of multiphase flow in porous media. Residual trapping of CO2 by capillary forces is one of the key mechanisms that can permanently immobilize CO2 in the societally important example of geological CO2 sequestration. The magnitude of residual trapping is set by the areal extent and saturation distribution within the current, both of which are predicted by the two-phase gravity current model. Hence the magnitude of residual trapping during the post-injection buoyant rise of CO2 can be estimated quantitatively. We show that residual trapping increases in the presence of a capillary fringe, despite the decrease in average saturation.

Determining CO2 /brine relative permeability and capillary threshold pressures for reservoir rocks and caprocks: Recommendations for development of standard laboratory protocols

Important parameters for the determination of fluid transport in reservoir rocks are capillary pressures and relative permeabilities for the CO2/brine system. These factors influence the plume migration, residual CO2 trapping and CO2 dissolution in the reservoir brines. CO2-brine relative permeabilities for different rock types are rare in public literature and usually adapted from mathematical relations or from more recent experimental data. The experimental data vary greatly in saturation and relative permeability endpoints, between 10 and 100%. It is necessary to reduce the uncertainty in the data range, since these parameters are sensitive and indispensable for the numerical simulation of the evolution of a CO2 plume in the subsurface. The petrophysical properties of caprocks are the limiting factor to the amount of CO2 stored in potential storage sites. The caprock sealing capacity is determined by the capillary pressure (or column height) at which the trapped fluid starts leaking through a caprock. These rocks have high capillary threshold pressures, which, combined with wettability and interfacial tension (IFT), determine the final column height that a seal can hold. Those three factors - capillary pressure, wettability and IFT - play an important role in the geological storage of CO2 in controlling the potential of CO2 moving through the seal. The capillary threshold pressures need to be determined accurately toestimate brine displacement in caprocks and hence the onset of viscous flow or leakage to the surface. Within the framework of the Carbon Capture Project (CCP3), we plan to establish standard experimental protocols with academic and/or commercial laboratories.

Estimating CO2 residual trapping from a single-well test: Experimental design calculations

Abstract Residual trapping is one of the four trapping mechanisms that have been identified for geological CO2 storage, a means to reduce atmospheric emissions and the related impacts as a result of continued use of fossil fuels. The objective of this research is to design a single-well injection-withdrawal test to estimate residual CO2 trapping (Sgr) in brine aquifers. Due to the high cost associated with drilling to depths of potential CO2 storage site, single-well test can cost-effectively provide data sets to assess reservoir properties and reduce uncertainties in the appraisal phase for finding commercial scale storage sites. The main challenges in the design are the following: (1) It is difficult to quantify the amount that is trapped using a mass balance approach; (2) correlations among various parameters leads to a highly uncertain or non-unique Sgr estimate; and (3) the Sgr estimate could be biased due to heterogeneity of the geological medium. We have proposed our design to address each of these challenges by (1) use a detailed reservoir model to simulate the relevant physical processes in the tests; (2) perform a test sequence that yields multiple types of complementary data to constrain the estimate of Sgr; (3) remove or reduce the bias caused by the heterogeneity of the storage formation by repeating the same test under different saturation conditions. The design will be applied to a practical field test that will be carried out as part of the CO2CRC Otway Project, at Victoria Australia.

Concept and experimental study for a new enhanced mineral trapping system by means of microbially mediated processes

The effectiveness of CO2 geological storage depends on a combination of physical and geochemical trapping mechanisms. Over time, the physical process of residual CO2 trapping and geochemical processes of solubility trapping and mineral trapping increase. According to the IPCC special report, mineral trapping is believed to be comparatively slow, potentially taking a thousand years or longer. This paper proposes a concept of enhanced mineral trapping system of CO2 geological storage by means of microbially mediated processes and describes some results of related preliminary microbial experiments. Environmental microorganisms have influences on groundwater chemistry and mineral precipitation and dissolution, and even accelerate mineral precipitation processes. The research objective is to accelerate mineral trapping by microbial activities. Especially, biomineralization of carbonate minerals acts an important role for the enhanced mineral trapping system. It is expected to reduce the time scale of mineral trapping from several thousand years to several decades (human life time). It is also expected to play a role for sealing capability. The goal of the research project is to extract optimum bacteria to form carbonate-forming habitats and to evaluate the possibility of bacteria-enhanced CO2 geological storage using numerical model. To develop the system, we plan to carry out the following four procedures; (1) looking for various kinds of carbonate-forming bacteria from natural samples, (2) extraction of bacteria for the condition of the system and further extraction of the bacteria with optimum performance of carbonate precipitation by laboratory experiments, (3) measurement the microbial kinetic parameters, such as specific growth rate of the bacteria by some laboratory experiments (4) performance assessment by hydro-bio-geochemical modeling using experimental data including microbial kinetic parameters. According to the research plan, we carried out literature investigation to make an inventory and preliminary laboratory experiments as the first step of looking for the optimum bacteria. Our target is biomineralization by moderately halophilic carbonate-forming bacteria, which few researchers have studied yet. Screenings of bacteria consists mainly of three steps as follows: 1) purchase of moderately halophilic bacteria, some of which are known carbonate-forming species, 2) selection of carbonate-formers from the isolated halophiles, and 3) selection of practically applicable carbonate-formers with higher performances. Preliminary batch culture experiments were performed with purchased different 6 species of moderately halophilic bacteria; Chromohalobacter marismortui, Halobacillus trueperi, Halomonas halophila, Marinobacter hydrocarbonoclasticus, Marinococcus halophilus, and Virgibacillus salexigens. Initial concentration of Ca2+ was set between 2.60 g/l and 2.75 g/l in the liquid cultures. Gradual decrease in Ca2+ concentration was observed for all microbial samples. After 98 days, Ca2+ concentration in the liquid culture of Mb. hydrocarbonoclasticus was 0.440 g/l. Ca2+ concentration of C. marismortui was 0.448 g/l after 189 days. Decrease in Ca2+ concentration was also observed for other 4 microbial species, although its degree and decreasing rate varied among species. Meanwhile, decrease in Ca2+ concentration was not observed in abiotic liquid culture. Chemical analysis by EPMA was also carried out for some microbes after the incubation, and higher peak of calcium, oxygen, carbon and minor magnesium were detected. These results indicate that the decrease in Ca2+ concentration was caused by microbial carbonate precipitation.

Ｘ線ＣＴ法による多孔質岩石内ＣＯ２残留ガストラップ現象の分析

CCS (Carbon dioxide Capture & Storage) is expected as one of most efficient methods in order to reduce the amount of exhausted CO2 into the air. In the projects, the estimation of storage volume and the assessment of CO2 trapping effect in the reservoir are necessary. The objective of this paper is to analyze the residual CO2 trapping in the porous media after the storage of CO2 in the aquifer by means of X-ray CT. The CO2 injection and successive water injection test were conducted, and the replacement and trapping process of water — CO2 was analyzed by X-ray CT method. Here, the amount of CO2 replaced in the pore during CO2 injection tests was estimated. The amount of residual CO2 trapped in the rock pore during successive water injection tests was also estimated, and relations between the replaced/trapped CO2 and the porosity distribution of rock were discussed. It was found that more CO2 was stored at the relatively high porosity region, and that the residual ratio at the high porosity region easily decreased during the water injection process. However, it was also found that the approximately 10 % of injected CO2 was still remained after the six to ten times pore volume of water was injected into the rock sample.

Role of correlation structures of permeability field on residual trapping mechanisms and buoyancy-driven CO2 migration

Previous research suggests that for many geological CO2 sequestration reservoirs, up to 60% of the injected CO2 will be trapped by capillary forces (irreducible saturation), a mechanism termed residual CO2 trapping. More specifically, our recent models of ongoing field tests of geological sequestration suggest that residual CO2 trapping can be maximized if the CO2 plume rises a greater distance due to buoyancy (i.e., injection at the deepest part of a thick reservoir) and sweeps a larger area before coming in contact with low permeability caprock. Although this strategy maximizes the residual CO2 trapping in theory because CO2 plume contacts more pore spaces, it also increases the probability that upwelling- CO2 may come into contact with faults or other leakage pathways. Geological heterogeneity seems to play greater role with respect to residual CO2 trapping potential. To help clarify what processes and properties will maximize residual CO2 trapping and minimize CO2-buoyant flow, we conducted a systematic analysis of permeability (k) fields and its correlation structures. The k fields served as primary parameterization of a numerical model describing CO2 migration during a 100-year simulation period. We compared various permutations of two-dimensional conceptual models, including homogeneous, random, homogenous with low-k lens, and anisotropically-correlated k fields. Using a Sequential Gaussian Simulation method, for most of models, we generated 10 realizations in each model permutation. In each simulation, the amount of mobile-, residual-, and aqueous-trapped CO2 was calculated and the spatial distribution of the CO2 plume was quantified using the first and second spatial moments. Both homogeneous and random simulation results suggest that the amount of residual trapped CO2 increases as the effective k increases. These results imply that the overall velocity distribution, which governs the sweeping area of the CO2 plume, is a critical factor for residual CO2 trapping. However, as overall velocity (or k field) increases, we observed that the CO2 plume reaches the caprock more quickly. In simulations of anisotropically correlated k fields with specific correlation length ratios of 25 m×10 m,50 m×10 m, and 100 m×10 m in x (horizontal) and z (vertical) directions, respectively, the CO2 migration distance due to buoyancy force is shorter as the horizontal correlation length becomes greater. In addition, as the horizontal correlation length becomes greater, residual trapping increases because the CO2 plume spreads farther laterally, sweeping a larger area. In sum, results of this analysis suggest that heterogeneous k fields with greater anisotropic correlation ratios tend to maximize residual trapping and minimize buoyancy-driven CO2 migration. Our findings also suggest that k correlation structures, especially anisotropic media with specific ratios of correlation lengths, can strongly impact CO2 trapping mechanisms by controlling velocity and tortuosity, which in turn determines the sweeping area of CO2 plumes.