Trap Saturation Research Articles

Investigating thermoluminescence signal saturation in quartz and feldspar using emission spectrometry

Luminescence-based thermometry and dating often requires determination of the saturation level for specific signals and the corresponding dose. However, previous studies found non-monotonic dose responses for some monochromatic thermoluminescence (TL) and optically stimulated luminescence (OSL) signals from quartz as well as spectral overlap of emission bands, substantially complicating data interpretation. Therefore, the present study examines (1) the variability in the TL emission spectrum of quartz and feldspar from bedrock and sediment of different provenances and, (2) the saturation characteristics of the blue emission band for both quartz and feldspar in the dose range from 0.25 kGy to 50 kGy. The experimental results confirm differences in the spectra which appear to be characteristic of their geological origin and chemical composition. Spectral analysis shows that in the temperature range 175–220 °C the blue emission band at ∼2.5 eV dominates over other bands for all quartz samples studied. A broad UV-blue TL signal peaking at ∼2.5−3.0 eV and composed of probably three overlapping, individual bands is characteristic for K-feldspar, while one Na-feldspar exhibits an additional band at ∼2.2 eV.In the studied dose range, the emissions at ∼2.5 eV and ∼2.6 eV increase as a function of dose up to 6 kGy for both quartz and feldspar. A difference in dose response was observed for high doses (>6 kGy) where feldspar samples reached a stable saturation level while for quartz the blue emission band intensity decays until 50 kGy after having attained a maximum. Our results suggest the suitability of feldspar TL for palaeothermometry and thermochronometry from the perspective of signal saturation characteristics. However, the spectral overlap of several bands in the UV-blue emission requires careful optical filter selection to isolate the signal of interest. The non-monotonic dose response of the ∼2.5 eV emission of quartz around 200 °C glow curve temperature probably precludes its use for temperature sensing based on relative trap saturation levels.

Enhancing Hydrogen Recovery from Saline Aquifers: Quantifying Wettability and Hysteresis Influence and Minimizing Losses with a Cushion Gas

This study aims to numerically assess the impact of wettability and relative permeability hysteresis on hydrogen losses during underground hydrogen storage (UHS) and explore strategies to minimize them by using an appropriate cushion gas. The research utilizes the Carlson model to calculate the saturation of trapped gas and the Killough model to account for water hysteresis. By incorporating the Land coefficient based on laboratory-measured data for a hydrogen/brine system, our findings demonstrate a significant influence of gas hysteresis on the hydrogen recovery factor when H2 is used as a cushion gas. The base model, which neglects the hysteresis effect, indicates a recovery factor of 78% by the fourth cycle, which can be improved. In contrast, the modified model, which considers hysteresis and results in a trapped gas saturation of approximately 17%, shows a hydrogen recovery factor of 45% by the fourth cycle. Additionally, gas hysteresis has a notable impact on water production, with an observed 12.5% increase in volume in the model that incorporates gas hysteresis. Furthermore, optimization of the recovery process was conducted by evaluating different cushion gases such as CO2, N2, and CH4, with the latter proving to be the optimal choice. These findings enhance the accuracy of estimating the H2 recovery factor, which is crucial for assessing the feasibility of storage projects.

The Effect of Multiple Cycles of Surfactant-Alternating-Gas Process on Foam Transient Flow and Propagation in a Homogeneous Sandstone

Summary Years of laboratory studies and field tests show that there is still uncertainty about the ability of foam to propagate deep into a reservoir. Many factors have been identified as potential causes of nonpropagation, the most concerning being the lack of sufficient pressure gradient required to propagate foam at locations far from the point of injection. Most researchers that investigated foam propagation did so by coinjecting surfactant and gas. Coinjection offers limited information about transient foam processes due to limitations in the experimental methods needed to measure foam dynamics during transient flow. Foam injection by surfactant-alternating-gas (SAG) has proven to be more effective and common in field application. Repeated drainage and imbibition cycle offer a more favorable condition for the quick generation of foam. Foam can also be propagated at a lower pressure gradient in SAG mode. The objective of this study is to experimentally investigate how transient foam dynamics (trapping, mobilization, and bubble texture) change with multiple cycles of SAG and also with distance from the point of injection. A pair of X-ray source and receiver, differential pressure transducers, and electrical resistance sensors were placed along a 27-cm long, homogeneous, and high-permeability (KL = 70 md) Berea sandstone core. Foam was then generated in situ by SAG injection and allowed to propagate through the core sample under a capillary displacement by brine (brine injection rate = 0.5 cm3/min, Nca = 3×10-7). By use of a novel analytical method on coreflood data obtained from axial pressure and saturation sensors, we obtained trapped foam saturation, in-situ foam flow rates, apparent viscosities, and inferred qualitative foam texture at different core sections. We then observed the following: (i) Maximum trapped foam is uniform across the core sections, with saturation ranging from 47% to 52%. At the vicinity of foam injection, foam apparent viscosity is dominantly caused by gas trapping. At locations farther away, foam apparent viscosity is dominated by both gas trapping and refinement of foam texture. (ii) Cyclic injection of foam further enhances the refinement of foam texture. (iii) Textural refinement increases foam apparent viscosity as it propagates away from the point of injection. (iv) As the foam strength increases, the average gas flow rate in the core sample decreases from 0.5 cm3/min to 0.06 cm3/min. (v) There is no stagnation of foam as remobilization of trapped gas occurs during each cycle at an average flow rate of 0.002 cm3/min.

Residual trapping of CO2, N2, and a CO2-N2 mixture in Indiana limestone using robust NMR coreflooding: Implications for CO2 geological storage

Carbon capture and sequestration (CCS) in geological formations is a prominent solution for reducing anthropogenic carbon emissions and mitigating climate change. The capillary trapping of CO2 is a primary trapping mechanism governed by the pressure difference between the wetting and nonwetting phases in a porous rock, making the latter a key input parameter for dynamic simulation models. During the CCS operational process, however, the CO2 is prone to contamination by impurities from various sources such as surfaces (e.g., pipelines and tanks) and the subsurface (e.g., existing natural gas). Such contamination can strongly influence the overall CO2 wettability, storage capacity, and containment security. Hence, the present study uses the nuclear magnetic resonance (NMR) core flooding technique to investigate and compare the residual saturations of pure CO2, pure N2, and a 50:50 CO2/N2 mixture in an Indiana limestone. The longitudinal and transverse relaxation times (T1 and T2) are measured to examine the displacement process of the pore network, and the trapping mechanism is evaluated at the pore scale as a determinant of the field-scale flow behavior. The NMR T1-T2 and 2D maps are used to observe the fluid configurations in the pore network, and the T1/T2 ratios are used to evaluate the microscopic wettability of the limestone grains by the pore-space fluids following each drainage/imbibition process step. The results indicate substantial residual gas trapping in the rock for the CO2-brine, N2-brine, and CO2/N2-brine systems, corresponding to gas saturations of 25%, 27%, and 26%, respectively. In the CO2-brine system, the intermolecular interplay between the CO2-enriched brine and limestone grains results in a higher T1/T2 ratio and significantly reduces the hydrophilicity of the limestone. Furthermore, the NMR T2 distribution reveals the occurrence of preferential water displacement into the large pores (r > 1 µm) and from the intermediate pores (0.03 µm < r < 1 µm), whereas water remains immobile in the smaller pores (r < 0.03 µm). The insignificant difference in residual trapping saturation between pure CO2 and the CO2-N2 mixture indicates the potential to allow for impurities in the CO2 phase in CCS without reducing the residual trapping capacity. Thus, the present work provides comprehensive information on the impact of gas injection on residual gas trapping in subsurface geological formations at the pore scale, thereby aiding in the development of CCS and other potential applications in enhanced oil recovery (EOR).

Hydrogen uptake and diffusion kinetics in a quenched and tempered low carbon steel: experimental and numerical study

To better understand hydrogen uptake kinetics, electrochemical permeation tests have been performed in a quenched and tempered low-alloy steel. Hydrogen uptake and transport has been studied with three different surface roughness, in four different solutions (1 M H2SO4, 1 M H2SO4+As2O3, 0.1 M NaOH and 3.5% NaCl) and two different hydrogen charging current densities (1 and 5 mA/cm2). A strong effect of the charging solution, current density and surface roughness has been demonstrated. In 1 M H2SO4 + As2O3 solution and 5 mA/cm2, hydrogen recombination on the surface of the samples is strongly reduced and interstitial diffusion prevails due to the trap saturation (DL≈Dapp). However, in 1 M H2SO4, 0.1 M NaOH and 3.5% NaCl, hydrogen transport is dominated by trapping and detrapping processes (DL>Dapp). Permeation transients are numerically reproduced through Finite Element simulations and compared to the experimental results. The relationship between hydrogen diffusion kinetics at the microstructural level and surface effects is clearly established by a mapping strategy obtained from the wide range of experimental results, combined with a numerical approach.

The Impact of Relative Permeability Hysteresis on CO2 Sequestration in Saline Aquifer

This work analyzed the amount of capillary-trapped CO2 for maximum residual gas saturation due to relative permeability hysteresis. Upward migration of CO2 is unwanted because it increases the risk of CO2 migration from storage sites to the surface. One way to mitigate CO2 leakage risk is to reduce the vertical CO2 migration to improved storage capacity and containment security. A compositional simulator (CMG-GEM) was used to simulate the flow of two components (CO2 and H2 O). A fluid model was built with the PR 78 EOS using WINPROP. A base case model without relative permeability hysteresis was simulated and compared with the case with relative permeability hysteresis. The amount of CO2 trapped, and CO2 saturation distribution were analyzed for maximum trapped gas saturation of 0.3, 0.4 and 0.5. Results shows an increase in the amount of CO2 trapped as the maximum residual gas saturation was increased from 0.3 to 0.4 and 0.5 with a value of 16560128mol for the base case study, 49041744mol, 59502924mol and 67286728mol respectively for maximum residual gas saturation due to relative permeability hysteresis of 0.3, 0.4 and 0.5 respectively. Very little accumulation of CO2 occurs when the maximum trapped gas saturation due to relative permeability hysteresis was set at 0.5. Result reveals that after 200 years, almost all the CO2 was trapped in the formation. Therefore, the imbibition cycle at the trailing end of the CO2 plume should be considered as accounting for hysteresis effects has led to a spread-out distrib

Effects of pore size and pore connectivity on trapped gas saturation

Abstract Trapped or residual air (or gas) is known to affect the multiphase hydraulic properties of both soils and rocks. Trapped air is known to impact many vadose zone hydrologic applications such as infiltration and flow in the capillary fringe, but is also a major issue affecting recoverable oil reserves. Although many studies have focused on the relationship between porosity and trapped gas saturation (S gt ) in sandstones, far fewer studies have been carried out for carbonate rocks. This work aims to analyze the influence of porous media properties on trapped gas saturation in carbonate rocks. For this we used thirteen Indiana Limestone and Silurian dolomite rock samples from the USA, and several coquinas from the Morro do Chaves formation in Brazil. Pore size distributions were obtained for all samples using Nuclear Magnetic Resonance (NMR), and Mercury Injection Capillary Pressure (MICP) data from three of the samples to determine their pore throat size distributions. Additionally, 3D microtomography (microCT) images were used to quantify macropore profiles and pore connectivities. Results indicate a lower capacity of gas trapping in carbonate rocks in which micro- and mesopores predominate. Results also indicate that in carbonate rocks, pore size exerts a greater influence on the ability of gas trapping compared to pore connectivity, so that rocks with a predominance of macropores have greater capacity for gas trapping, even when the macropores are well interconnected. These findings show that pore characteristics very much affect the processes governing gas trapping in carbonate rocks, and indirectly the multiphase hydraulic properties and recoverable oil reserves of carbonate rock reservoirs.

Development of a pheromone monitoring system for the goosefoot groundling moth, Scrobipalpa atriplicella (von Röslerstamm) in quinoa, Chenopodium quinoa (Willdenow)

The goosefoot groundling moth, Scrobipalpa atriplicella, (Lepidoptera: Gelechiidae) is a serious pest of quinoa, Chenopodium quinoa, in North America and Europe. Previous studies found male S. atriplicella were attracted to a generic pheromone lure containing (Z)-5-dodecenyl acetate. Here, we identified further candidate sex pheromone components from female pheromone glands using gas chromatography-electroantennographic detection. We confirmed (Z)-5-dodecenyl acetate to be an antennally active compound, and identified a previously unidentified minor component, (E)-5-dodecenyl acetate. Field tests confirmed males were most attracted to a two-component blend in a 95:5 ratio of (Z)-5-dodecenyl acetate to (E)-5-dodecenyl acetate. We found that the 95:5 major to minor ratio captured more S. atriplicella moths and the lowest number of non-target noctuid moths compared to other ratios tested. The number of S. atriplicella captured varied with trap type, but not the two heights tested (0.5 and 1 m), however, we recommend pheromone-baited wing traps deployed at either at 0.5 or 1 m heights to reduce the possibility of trap saturation with sticky traps with smaller surface areas. These findings allow for future development of a pheromone-based monitoring program for this significant pest of quinoa in Canada.

Preliminary assessment of tritium permeation and retention in the European Water Cooled Lithium Lead Test Blanket Module with TESSIM-X

• T inventory in the ITER EU Water-Cooled Lithium-Lead Test Blanket Module investigated. • T from vacuum vessel (gas, neutrals) and solute T in PbLi included in modeling. • Effect of neutron damaging on trap concentrations included in models. • T retention in the range of 0.75 g is expected over plasma operation period. • Comparison with the TMAP7 code performed. Tritium self-sufficiency is a key requirement for future fusion power plants. Therefore, it will be necessary to minimize tritium losses to the surrounding systems, such as the tritium breeding modules, plasma-facing components, cooling system, etc. These components and systems will act also as a tritium sink, as tritium will be retained in the metal walls in traps produced during manufacturing or induced by neutron irradiation. The design of the tritium breeding systems and plasma-facing components will therefore have a direct impact on the performance, operational safety and cost of any future power plant. Consequently, accurate modeling of tritium transport and retention in these systems is needed for future engineering designs of the tritium breeding systems and supporting safety requirements. In this work, tritium permeation and retention was modeled with the diffusion-transport code TESSIM-X for the current European WCLL (Water Cooled Lithium Lead) Test Blanket Module (TBM) for the ITER TBM Programme, with the inclusion of neutron-induced traps. Trap saturation is considered for dpa values of 0.25 and above, leading to an increase in trap concentrations relative to undamaged material of roughly a factor 3. The code was also benchmarked against the well-established TMAP7 code.

Noninvasive sampling of mountain lion hair using modified foothold traps

AbstractAlthough genetic analysis is an increasingly affordable option for wildlife studies, obtaining high‐quality samples from cryptic carnivores remains difficult. To address this, we modified and tested 20.3‐cm (8‐inch) foot snares in unbaited trail sets for noninvasive collection of hair samples from mountain lions (Puma concolor). We deployed 22 hair traps in the Black Range in southern New Mexico from May to November 2017, monitored by remote cameras, at 66 locations for 1,618 trap nights ( = 24.5 nights, SD = 7.2 nights). Photos indicated 20 instances of mountain lions passing within 2 m of a hair trap and we collected 7 mountain lion hair samples, which averaged &gt;20 hairs/sample. All samples contained hair with visible roots and were identifiable to species; 6 of the 7 (85.7%) yielded sufficient DNA for individual identification. We attributed failure to obtain samples to 3 primary causes: individual trap saturation (2 instances), trap failure (2 instances), and non‐trigger events (9 instances). Black bears (Ursus americanus) and heavy rains were the primary sources of disturbance to hair trap sets, contributing to individual trap saturation and trap failure. We speculate that low trigger rates were associated with pan tension having been set too high in the first month of the study, as well as disturbance of hair traps or leading foot placements by nontarget species. We discuss strategies to increase hair sample collection rates, including seasonal use of hair traps, more selective placement on the landscape, and altering physical attributes of the hair traps. The quality of hair samples we collected and subsequent amplification rates indicated that, along with proper deployment strategies, hair traps are a viable tool for noninvasively collecting genetic material for individual identification of mountain lions and other elusive species.

Laboratory Investigation of Impact of Slickwater Composition on Multiphase Permeability Evolution in Tight Sandstones

Summary Fracturing fluid filtrate that leaks off during injection is imbibed by strong capillary forces present in low-permeability sandstones and may severely reduce the effective gas permeability during cleanup and post-fracture production. This work aims to investigate the role fracturing fluid filtrate from slickwater has on rock-fluid and fluid-fluid interactions and to quantify the resulting multiphase permeability evolution during imbibition and drainage of the filtrate by means of specialized core laboratory techniques. Three suites of experiments were conducted. In the first suite of experiments, a fluid leakoff test was conducted on selected core samples to determine the extent of polymer invasion and leakoff characteristics. In the second suite, multigas relative permeability measurements were conducted on sandstone plugs saturated with fracturing fluid filtrate. A combination of controlled fluid evaporation and pulse decay permeability technique was used to measure liquid and gas effective permeabilities for both drainage and imbibition cycles. These experiments aim to capture dynamic permeability evolution during invasion and cleanup of fracturing fluid (slickwater). The final suite of experiments consists of adsorption flow tests to investigate, identify, and quantify possible mechanisms for adsorption of the polymeric molecules of friction reducers present in the fluid filtrate to the pore walls of the rock sample. Imbibition tests and observations of contact angles were conducted to validate possible wettability changes. Results from multiphase permeability flow tests show an irreversible reduction in endpoint brine permeability and relative permeability with increasing concentration of friction reducer. Our results also show that effective gas permeability during drainage/cleanup of the imbibed slickwater fluid is controlled to a large degree by trapped gas saturation than by changes in interfacial tension. Adsorption flow tests identified adsorption of polymeric molecules of the friction reducer present in the fluid to the pore walls of the rock. The adsorption friction reducer increases the wettability of the rock surface and results in the reduction of liquid relative permeability. The originality of this work is to diagnose formation damage mechanisms from laboratory experiments that adequately capture multiphase permeability evolution specific to a slickwater fluid system, during imbibition and cleanup. This will be useful in optimizing fracturing fluid selection.

Microdosimetric modeling of the relative efficiency of Al2O3:C (Luxel, blue emission) optically stimulated luminescent detectors exposed to ions from 1H to 132Xe

Passive radiation detectors based on the optically stimulated luminescence of anion-defective aluminum-oxide doped with carbon (Al2O3:C) are commonly used for personal, environment and medical dosimetry. However, their luminescence efficiency in measuring a certain type of radiation is strongly affected by the pattern of energy deposition at the nanoscale and the corresponding possible saturation of trapping, luminescent or competitive centers within the detector. To better understand the results of the measurements and to further exploit their use in complex radiation environments, including space and clinical particle beams, the efficiency of the detectors should be known for a wide variety of particles and particle energies.In this work, radiation transport simulations using the Monte Carlo code PHITS are coupled with the Microdosimetric d(z) Model to calculate the efficiency of the blue emission (F centers) of Al2O3:C (Luxel) optically stimulated luminescent detectors in case of exposures to ions from 1H to 132Xe. The model was initially developed to describe the response of differently doped thermoluminescent detectors based on lithium fluoride. This study represents the first application of the Microdosimetric d(z) Model to a different material (aluminum oxide) and a different phenomenon (optically stimulated luminescence). The results of the theoretical calculations were compared to experimentally determined efficiency data and good agreement (average relative deviation ∼ 6%) was found in case of simulations performed using radiation sensitive targets with a diameter of approximately 100 nm. Furthermore, the possibility of determining the optimal target size by using only a subset of the available data was proven successful.

Generalised model for simulation of two- and three-phase cycle-dependent hysteresis in sandstones

Many Enhanced Oil Recovery (EOR) processes involve injecting multiple slugs to improve the volumetric sweep efficiency in the reservoir, such as Water-Alternating-Gas (WAG), polymer flood, surfactant flood, and steam injection. Precise estimations of hysteresis phenomenon in relative permeability (kr) and capillary pressure (Pc) plays a crucial role in conducting accurate prognosis of oil production, reliable decision making, and feasibility assessment of EOR plans. Over the years, abundant high-quality experimental data revealed limitations of existing hysteresis models in the literature and highlighted the necessity of introducing a reliable hysteresis model.This paper presents a new hysteresis model for accurate estimation of ultimate oil recovery and pressure drop in coreflood experiments. In contrast to the existing models, all required parameters are directly calculated from experimental data, eliminating the tuning procedure, and reducing the associated uncertainties. This study also includes a detailed discussion of estimating trapped gas saturation and application of Land’s trapping model in cyclic systems, considering their importance in CO2 sequestration and non-aqueous contaminant flow in soil. The presented model also benefits from a new procedure for estimating final saturations during a WAG experiment based on common observations of WAG experiments. A comprehensive set of cyclic two- and three-phase experiments performed on a homogenous sandstone over a wide range of injection scenarios, fluid, and rock properties were successfully used to validate the model. The detailed analysis and comparison of various cyclic experiments herein provide an excellent benchmark for future validation and development of hysteresis models.

Broadband Nonlinear Photoresponse and Ultrafast Carrier Dynamics of 2D PdSe2

AbstractPalladium diselenide (PdSe2) exhibits considerable potential for application in broadband optoelectronic devices. In this work, the broadband nonlinear optical performance and ultrafast carrier dynamics from ultraviolet to near‐infrared of a trilayer PdSe2 are systematically studied. PdSe2 is found to achieve a giant saturable absorption performance. The modulation depth is 22.47% at 520 nm, whereas the nonsaturable loss and saturation intensity are only 3.83% and 15.47 GW cm−2, respectively, which are better than those of many 2D semiconductors. Based on these findings, a PdSe2‐based visible light thresholder is proposed, its function is to extract an undetectable pulse signal drowned in strong stochastic noise and thereby improve the signal‐to‐noise ratio. Pump–probe technique, along with first‐principles calculation and transient absorption spectra, reveals the intrinsic recombination mechanism, including Auger scattering and trap saturation. This work is expected to establish the foundation for the development of next‐generation PdSe2‐based devices in optoelectronics and visible light communication.

Reappraisal of Peak Shape Method Based on Average Geometrical Symmetry Factor and Its Application to Thermoluminescence Glow Curves

A new set of peak shape formulas at different fractional intensities is proposed to extract the activation energy from a thermoluminescence (TL) glow curve. The peak shape coefficients are formulated on the basis of the average geometrical symmetry factor which is estimated considering its dependence on the relevant TL parameters. An empirical dependence of the geometrical symmetry factor on order of kinetics and other parameters is also reported. The present method is used on TL peaks generated in general order kinetics (GOK) approximation and in one trap one recombination center (OTOR) model using a wide range of TL parameters. During the course of TL peak simulation, an alternative analytical approach to evaluate the “temperature integral” is developed. The present method seems to be useful to evaluate the activation energy for all peaks except for the heavy retrapping cases when the initial trap saturation is considerably high. A probable reason behind this limitation is also explored by examining the correspondence between the temperature average of order of kinetics and the retrapping‐to‐recombination probability. Finally, the new peak shape formulas are tried on isolated single peaks deconvoluted from composite experimental TL curves reported in the literature and the results are quite satisfactory.

Foam Flow in Different Pore Systems—Part 1: The Roles of Pore Attributes and Their Variation on Trapping and Apparent Viscosity of Foam

Summary Lateral propagation of foam in heterogeneous reservoirs, where pore geometries vary laterally, depends on the roles of pore geometries on the foam properties. In this paper, the pore attributes of 12 different rock samples were characterized in terms of porosity, permeability, pore shape, pore size, throat size, aspect ratio, coordination number, and log mean of surface relaxation times (T2LM). These were measured from gas porosimeter and permeameter, X-ray microcomputed tomography (CT)-based pore-network models, thin-section photomicrographs, and nuclear magnetic resonance (NMR) surface relaxometry. The samples have a wide range of porosity: 12 to 29%; permeability: 1 to 5,000 md; average pore size: 3.7 to 9 µm; average throat size: 2.4 to 8 µm; average aspect ratio: 1 to 1.7; average coordination number: 2.6 to 5.2; and T2LM: 9.4 to 740 ms. Nitrogen foam flow experiments (without oil) were then conducted on each rock sample using a specialized coreflood apparatus. A graphical analysis of the coreflood data was used to estimate the total saturation of trapped foam (10 to 66%), flowing foam (3 to 14%), and apparent viscosity of foam (3.2 to 73 cp). Trapped foam saturation and apparent viscosity values were then correlated with each of the measured pore attributes. The results revealed that all pore attributes, except aspect ratio, have positive correlations with foam trapping and apparent viscosity. The best correlation with trapped foam saturation was obtained when the most influential pore attributes (pore size, throat size, aspect ratio, and coordination number) were combined into a single mathematical function. Foam apparent viscosity also appears to be mostly influenced by trapped foam saturation, permeability, and coordination number of pore systems. Trapping is also likely enhanced by the presence of fenestral or channel pores. Furthermore, the shape and angularity of pores seem to facilitate snap-off and trapping of foam, because rock samples with angular pores trapped the highest foam saturation compared with other samples with rounded and subrounded pores. It was also shown that the correlation between trapped foam saturation (and foam apparent viscosity) and the absolute permeability of porous media may reverse at some high-permeability values (greater than several darcies), when one or both of the following conditions exist: (1) The aspect ratio of a lower-permeability porous medium is lower than that of a higher-permeability porous medium, and (2) the coordination number of a lower-permeability porous medium is higher than that of a higher-permeability porous medium. Finally, T2LM showed a good correlation with foam trapping, making NMR logging a prospective tool for pre-evaluating foam performance in targeted reservoir sections.

Relative Permeability Hysteresis and Capillary Trapping during CO2 EOR and Sequestration

Residual or capillary trapping is an important mechanism of CO2 trapping in underground porous media. Recent experimental investigation has shown that relative permeability and capillary pressure are function of saturation changing direction or hysteresis phenomenon in addition to the saturation and hysteresis leads to irreversible change in relative permeability and capillary pressure curve. In this paper, an extended review was performed on the relative permeability hysteresis models. Moreover, an experimental investigation was conducted during CO2 injection as the non–wetting phase in carbonate rocks at pressure and temperature of 10.3 MPa and 60 ℃. In this study, the effects of absolute permeability of carbonate rock samples and CO2 injection strategy on hysteresis phenomenon in the CO2 residual trapping process were investigated. During first part of experiments, CO2 relative permeability was examined during CO2 injection and brine injection at constant rate of 0.2 cc/min as drainage and imbibition process for different absolute permeability of rock samples. During second part of experiments, CO2 trapping saturation was calculated during the continuous CO2 injection and CO2 Water Alternative Gas (WAG) injection. Results of first part of experiments showed that increasing of the absolute permeability leads to increasing initial and residual CO2 saturation at the end of drainage and imbibition process, respectively. Moreover, it was concluded that increasing rock permeability results in increasing of the hysteresis effect on the CO2 relative permeability. In the second part of experiments, results revealed that CO2 WAG injection strategy has higher CO2 residual saturation in compared to CO2 continuous injection at equal pore volume of injected CO2. The findings of this paper can be applied for investigating of CO2 sequestration projects in aquifers for improvements of CO2 residual trapping and studying the performance of capillary trapping as one of the main mechanisms of CO2 trapping.

Subpore‐Scale Trapping Mechanisms Following Imbibition: A Microfluidics Investigation of Surface Roughness Effects

AbstractSurface roughness is ubiquitous in subsurface formations due to weathering and diagenesis. Yet micromodel studies of porous media have not sufficiently addressed the impact of pore‐wall roughness on multiphase fluid displacement. We investigate the influence of pore‐wall roughness on capillary trapping by implementing surface roughness into glass micromodels and conducting imbibition experiments. Time‐lapse fluorescence microscopy, micromolding in capillaries, and scanning electron microscopy are used to examine flow behavior during spontaneous and forced imbibition experiments with capillary numbers between 10−6 and 10−4. It is found that surface roughness causes interface pinning and irregular displacement fronts within a single pore, promotes latent pore filling following imbibition, enhances snap‐offs, and contributes to interface relaxation. Furthermore, we verify a cooperative effect between corner flow and surface roughness that causes pore filling to occur at over 10 times the channel width ahead of the main bulk front. Consequently, a significant increase in trapped air saturation of up to 60% is observed, especially at lower capillary numbers and narrower pores. Effects of surface roughness also decrease the rate of spontaneous imbibition, which is slower than the prediction from Washburn's equation. Our results emphasize the importance of surface roughness in building conceptual models for capillary trapping when the ratio of surface roughness‐to‐pore size reaches a critical value of about 0.1. Above this critical threshold value, subpore‐scale trapping mechanisms contribute significantly to capillary trapping, which theoretical and numerical models should consider for accurate quantification of fluid‐transport processes.

MICRODOSIMETRIC UNDERSTANDING OF DOSE RESPONSE AND RELATIVE EFFICIENCY OF THERMOLUMINESCENCE DETECTORS.

LiF:Mg,Ti detectors show relative efficiency η for heavy charged particles significantly lower than one. It was for a long time not recognised that η varies also for electron energies and, as a consequence for photons. For LiF:Mg,Cu,P detectors measured photon energy response was named ‘anomalous’ because it differed significantly from the ratio of photon absorption coefficients. The decrease of η was explained as a microdosimetric effect due to local saturation of trapping centres around the electron track. For TLD-100 it was noticed by Horowitz that the measured photon energy response disagrees with the ratio of absorption coefficient by about 10%. It was demonstrated that a fraction of the TL signal in LiF:Mg,Ti is generated in the supralinear dose–response range, due to the high local doses generated by photon-induced tracks. Prediction of TL efficiency is particularly important in space dosimetry and in dosimetry of therapeutic beams like protons or carbon ions.

Experimental analyses of the mechanisms leading to American lobster (Homarus americanus) ventless trap saturation

Experimental analyses of the mechanisms leading to American lobster (Homarus americanus) ventless trap saturation