Gas-phase Mobility Research Articles

Analyzing Foam Injection Dynamics in Porous Media: A Combined Computational and Experimental Approach

The study of foam injection dynamics into porous media holds numerous applications, with its primary use being the optimization of the oil extraction process. Additionally, it finds utility in various other domains, including soil decontamination techniques. This study focuses on evaluating foam injection through low-cost experiments and computational models. The model integrates a classic two-phase immiscible fluid flow in a porous media framework, augmented by a mobility reduction factor to simulate foam’s impact on gas phase mobility. Simple experiments were conducted to assess water displacement using both gas and gas-foam injection methods. Results revealed that while gas injection tends to form preferential paths rapidly, leading to gas disruption, foam injection generates a more compact front, enhancing sweep efficiency by mitigating preferential path formation. The computational model successfully reproduced the experimental findings qualitatively. This research introduces a cost-effective experiment suitable for didactic purposes, illustrating complex concepts and underscoring the complementary nature of experimental and computational methodologies in advancing engineering techniques.

A comprehensive review direct methods to overcome the limitations of gas injection during the EOR process

Among the Enhanced Oil Recovery (EOR) methods, gas-based EOR methods are very popular all over the world. The gas injection has a high ability to increase microscopic sweep efficiency and can increase production efficiency well. However, it should be noted that in addition to all the advantages of these methods, they have disadvantages such as damage due to asphaltene deposition, unfavorable mobility ratio, and reduced efficiency of macroscopic displacement. In this paper, the gas injection process and its challenges were investigated. Then the overcoming methods of these challenges were investigated. To inhibit asphaltene deposition during gas injection, the use of nanoparticles was proposed, which were examined in two categories: liquid-soluble and gas-soluble, and the limitations of each were examined. Various methods were used to overcome the problem of unfavorable mobility ratio and their advantages and disadvantages were discussed. Gas-phase modification has the potential to reduce the challenges and limitations of direct gas injection and significantly increase recovery efficiency. In the first part, the introduction of gas injection and the enhanced oil recovery mechanisms during gas injection were mentioned. In the next part, the challenges of gas injection, which included unfavorable mobility ratio and asphaltene deposition, were investigated. In the third step, gas-phase mobility control methods investigate, emphasizing thickeners, thickening mechanisms, and field applications of mobility control methods. In the last part, to investigate the effect of nanoparticles on asphaltene deposition and reducing the minimum miscible pressure in two main subsets: 1- use of nanoparticles indirectly to prevent asphaltene deposition and reduce surface tension and 2- use of nanoparticles as a direct asphaltene inhibitor and Reduce MMP of the gas phase in crude oil was investigated.

Factors Influencing the Rheology of Methane Foam for Gas Mobility Control in High-Temperature, Proppant-Fractured Reservoirs

Gas-enhanced oil recovery (EOR) through huff-n-puff (HnP) is an important method of recovering oil from fracture-stimulated reservoirs. HnP productivity is hampered by fracture channeling, leading to early gas breakthroughs and gas losses. To mitigate these issues, foam-generating surfactants have been developed as a method of reducing injected gas phase mobility and increasing oil recovery. This work investigates foam generation and propagation by a proprietary surfactant blend in high-temperature, high-pressure, high-permeability, and high-shear conditions that simulate the environment of a proppant-packed fracture. Bulk foam tests confirmed the aqueous stability and foaming viability of the surfactant at the proposed conditions. Through several series of floods co-injecting methane gas and the surfactant solution through a proppant pack at residual oil saturation, the effects of several injection parameters on apparent foam viscosity were investigated. The foam exhibited an exceptionally high transition foam quality (>95%) and strong shear-thinning behavior. The foam viscosity also linearly decreased with increasing pressure. Another flood series conducted in an oil-free proppant pack showed that swelling of residual oil had no effect on the apparent foam viscosity and was not the reason for the inversely linear pressure dependency. An additional flood series with nitrogen as the injection gas was completed to see if the hydrophobic attraction between the methane and surfactant tail was responsible for the observed pressure trend, but the trend persisted even with nitrogen. In a previous study, the dependence of foam viscosity on pressure was found to be much weaker with a different foaming surfactant under similar conditions. Thus, a better understanding of this important phenomenon requires additional tests with a focus on the effect of pressure on interfacial surfactant adsorption.

Development of a high-throughput differential mobility separation–tandem mass spectrometry (DMS-MS/MS) method for clinical urine drug testing

IntroductionDifferential mobility separation (DMS) is an analytical technique used for rapid separation of ions and isomers based on gas phase mobility prior to entering a mass spectrometer for analysis. The entire DMS process is accomplished in fewer than 20 ms and can be used as a rapid alternative to chromatographic separation. ObjectiveThe primary objective was to evaluate the utility of DMS-tandem mass spectrometry (DMS-MS/MS) as a replacement for immunoassay-based clinical toxicology testing. MethodsA sensitive DMS-MS/MS method was developed and validated for simultaneous identification of 33 drugs and metabolites in human urine samples. After DMS optimization, the method was validated and used to screen 56 clinical urine samples. These results were compared to results obtained by immunoassay. ResultsThe DMS-MS/MS method achieved limits of detection ranging from 5 to 100 ng/mL. Moreover, the total analysis time was 2 min per sample. For the method performance evaluation, DMS-MS/MS results were compared with previously obtained urine toxicology immunoassay results. DMS-MS/MS showed higher sensitivity and identified 20% more drugs in urine, which were confirmed by LC-MS/MS. ConclusionThe DMS-MS/MS as applied in our lab demonstrated the capability for rapid drug screening and provided better analytical performance than immunoassay.

How Narrow Is the Gas Phase Mobility Distribution of Enveloped Viruses? The Case of the Φ6 Bacteriophage.

We use the Φ6 bacteriophage previously exploited as a BSL-1 surrogate of severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome (MERS) coronavirus to obtain the first high-resolution gas phase mobility spectra of an enveloped virus. The relative full width at half-maximum found for the viral mobility distribution (FWHMZ < 3.7%) is substantially narrower than that reported by prior mobility or microscopy studies with other enveloped viruses. It is nevertheless not as narrow as that recently found for several non-enveloped viruses (FWHMZ ≈ 2%), presumably due to particle to particle variability of enveloped viruses. This 3.7% is an upper bound to the actual width. Nevertheless, the well-defined mobility peaks obtained indicate that gas phase mobility analysis is a more discriminating methodology than that previously demonstrated for physically based non-genetic viral diagnostic of enveloped viruses. These results are obtained by analysis of the original cell culture medium containing the virus, purified only by passage through a 0.22 μm filter and by dialysis into a 10 mM aqueous ammonium acetate buffer. We confirmed that this buffer exchange preserves infectivity. Therefore, the 63.7 nm mobility diameter found, although smaller than the 75 nm previously inferred by microscopy, corresponds to the full particle including the envelope.

Cross-Linking/Mass Spectrometry Combined with Ion Mobility on a timsTOF Pro Instrument for Structural Proteomics.

The combination of cross-linking/mass spectrometry (XL-MS) and ion mobility is still underexplored for conducting protein conformational and protein-protein interaction studies. We present a method for analyzing cross-linking mixtures on a timsTOF Pro mass spectrometer that allows separating ions based on their gas-phase mobilities. Cross-linking was performed with three urea-based MS-cleavable cross-linkers that deliver distinct fragmentation patterns for cross-linked species upon collisional activation. The discrimination of cross-linked species from non-cross-linked peptides was readily performed based on their collisional cross sections. We demonstrate the general feasibility of our combined XL-MS/ion mobility approach for three protein systems of increasing complexity: (i) bovine serum albumin (BSA), (ii) Escherichia coli ribosome, and (iii) HEK293T cell nuclear lysates. We identified a total of 623 unique cross-linking sites for BSA, 670 for the E. coli ribosome, and 1623 unique cross-links for nuclear lysates, corresponding to 1088 intra- and 535 interprotein interactions and yielding 564 distinct protein-protein interactions. Our results underline the strength of combining XL-MS with ion mobility not only for deriving three-dimensional (3D) structures of single proteins but also for performing system-wide protein interaction studies.

Adeno-associated Virus Virus-like Particle Characterization via Orthogonal Methods: Nanoelectrospray Differential Mobility Analysis, Asymmetric Flow Field-Flow Fractionation, and Atomic Force Microscopy.

Adeno-associated virus (AAV)-based virus-like particles (VLPs) are thriving vectors of choice in the biopharmaceutical field of gene therapy. Here, a method to investigate purified AAV serotype 8 (AAV8) batches via a nanoelectrospray gas-phase mobility molecular analyzer (nES GEMMA), also known as an nES differential mobility analyzer, is presented. Indeed, due to AAV’s double-digit nanometer scale, nES GEMMA is an excellently suited technique to determine the surface-dry particle size termed electrophoretic mobility diameter of such VLPs in their native state at atmospheric pressure and with particle-number-based detection. Moreover, asymmetric flow field-flow fractionation (AF4, also known as AFFFF) and atomic force microscopy (AFM) techniques were employed as orthogonal techniques for VLP characterization. In addition, AF4 was implemented to size-separate as well as to enrich and collect fractions of AAV8 VLPs after inducing analyte aggregation in the liquid phase. Bionanoparticle aggregation was achieved by a combination of heat and shear stress. These fractions were later analyzed with nES GEMMA (in the gas phase) and AFM (on a solid surface). Both techniques confirm the presence of dimers, trimers, and putative VLP oligomers. Last, AFM reveals even larger AAV8 VLP aggregates, which were not detectable by nES GEMMA because their heterogeneity combined with low abundance was below the limit of detection of the instrument. Hence, the combination of the employed orthogonal sizing methods with the separation technique AF4 allow a comprehensive characterization of AAV8 VLPs applied as vectors.

Numerical Study of Immiscible Foam Propagation in Porous Media in the Presence of Oil Using an Implicit-Texture Foam Model

Gas injection is one of the established methods in enhanced oil recovery. Nevertheless, poor sweep efficiency and viscous instabilities result in early gas breakthrough. Lowering injected gas mobility through foaming is a potential solution to solve the forenamed challenges. Although foaming of the injected gas has been proposed in various stages of oil production, comparatively few studies are carried out about foam injection modeling in the presence of oil. In this study, we aimed to numerically investigate the immiscible foam propagation in a thick, heterogeneous, water-flooded sandstone reservoir with a primary goal to control the surge of the produced gas–oil ratio (GOR) and also the possible incremental oil production by foam. To this end, the implicit-texture local-equilibrium foam model was used to address that how a stable foam front could affect fluid saturation and their mobility in the presence of waterflood residual oil. We treated the reservoir model by considering a pair of horizontal injection/production well through the upper and lower parts of the reservoir to mimic the foam-assisted gravity drainage scheme. Foam generation was considered through alternating (SAG) and simultaneous injection of gas and surfactant solution, and its performance was compared with continuous gas injection and water alternating gas injection. Results showed that gas-phase mobility was reduced in the presence of foam, leading to delaying of gas breakthrough and thereby improvement of gas sweep efficiency. The latter caused a significant reduction in produced gas–oil ratio, enhanced the control of the front movement, and resulted in better oil sweeping. In comparison to the SAG method, occurrence of fingering phenomena in foam co-injection was less likely. In addition, foam front in co-injection method exhibited relatively slower movement compared to the SAG method. Also, with ignoring the prescribed pressure constraint in injection well, the stability and uniformity of the generated foam front decreased, leading to more occurrences of fingering and thus reduction in oil recovery.

Reevaluating the Role of Polarizability in Ion Mobility Spectrometry

With the expanding commercial availability of gas-phase separation systems that incorporate gas-phase mobility, there is a concurrent rise in efforts to cast the gas-phase mobility coefficient in terms of an ion-neutral collision cross-section (CCS). The motivating factors for this trend are varied, but many aim to complement experimental results with computationally generated CCS values from in silico structural approximations. Unfortunately, the current paradigm for relating experimental mobility results to computationally derived structures relies upon empirical approaches, including a myriad of variables that do not realistically bound the comparison. In this Critical Insight, we advocate for the development of a self-consistent experimental and computational framework that uses laboratory results to constrain the scope of the modeling effort. This paper aims to prompt discussion, challenge assumptions, and promote the development of more efficient, accurate computational techniques within the gas-phase ion measurement community. Specifically, we postulate whether experimental deviations from Langevin's polarization limit (Kpol) are suitable to estimate the relative contributions of hard-sphere collisions and long-range interactions within CCS values. Not surprisingly, different molecule classes exhibit different trends in the K/Kpol ratio when normalized for reduced mass, and the most common IMS calibrants (e.g., tune mix, polyalanine, tetraalkylammonium salts) follow different polarizability trends than many of the analytes probed in the literature. Succinctly, if gas-phase ion structure is largely invariant based upon the colliding neutral and newly developed experimental efforts can quantitatively capture ion polarizability, then modeling efforts describing a target analyte must be self-consistent as the collision neutral is changed in silico.

Travelling Wave Ion Mobility-Derived Collision Cross Section for Mycotoxins: Investigating Interlaboratory and Interplatform Reproducibility.

Parent and modified mycotoxin analysis remains a challenge because of their chemical diversity, the presence of isomeric forms, and the lack of analytical standards. The creation and application of a collision cross section (CCS) database for mycotoxins may bring new opportunities to overcome these analytical challenges. However, it is still an open question whether common CCS databases can be used independently from the instrument type and ion mobility mass spectrometry (IM-MS) technologies, which utilize different methodologies for determining the gas-phase mobility. Here, we demonstrated the reproducibility of CCS measurements for mycotoxins in an interlaboratory study (average RSD 0.14% ± 0.079) and across different traveling wave IM-MS (TWIMS) systems commercially available (ΔCCS% < 2). The separation in the drift time dimension of critical pairs of isomers for modified mycotoxins was also achieved. In addition, the comparison of measured and predicted CCS values, including regulated and emerging mycotoxins, was addressed.

Experimental study on the temperature effects of foamy oil flow in porous media

The foamy oil flow phenomena occur in the primary production period of heavy oil during the solution gas derive have been considered as the key factor that leading to unusual high recovery efficiency. Temperature, as a critical fundamental property, will largely affect foamy oil behavior. The temperature effect on foamy oil behavior has not yet been fully understood. There are controversial opinions upon the effect of temperature which requires further verification. Therefore, it is important to study the influence of temperature on foamy oil flow. In this study, the sand-pack pressure depletion tests under different temperatures are conducted to investigate the temperature effect on foamy oil behavior. The experimental study suggests the negative effect of temperature on the foamy oil flow. As the temperature increases from 20 °C to 50 °C, the foamy oil behavior is weakened due to the oil viscosity reduction. Lower oil viscosity causes less gas being trapped by the oil phase and increases the gas phase mobility. Consequently, the oil recovery factor reduces form 19.35% to 6.96% and both the gas recovery factor as well as cumulative gas-oil ratio increase. In addition, the second foamy oil flow region is observed during the experimental study, where foamy oil flow appears second time during the late stage of production after oil–gas two phase flow region. Gas is continuously released from the oil phase at the two-phase flow region and causes an increase of oil viscosity. As a result, the oil recovery is enhanced at the late stage of production.

Assessing the Impact of Drift Gas Polarizability in Polyatomic Ion Mobility Experiments.

Due to the core assumptions of kinetic theory and the drive toward realizing reproducible gas-phase measurements, ion mobility experiments are commonly conducted in the presence of an inert, neat buffer gas, usually nitrogen or helium. Mixing drift gases in defined, static ratios can provide useful information not only for optimizing the separation of analytes but also for defining the interaction between the ion and neutral particle. In a foundational effort, we seek to validate the role of the drift gas polarizability on the observed mobility of the ions by systematically mixing drift gases to discretely access a range of bulk gas polarizabilities not given by pure drift gases. Compared to historical efforts to probe the role of polarizability on the ion-neutral collisional cross section where a linear relationship was assumed, the data collected in the present effort clearly illustrate a quadratic dependency of the ion-neutral particle collision cross section and polarizability (R2 > 0.999). When translating these data into the mobility dimension, we illustrate that the gas-phase mobility of polyatomic ions conforms to Blanc's law. These observations combined with considerations related to Langevin's polarization limit provide an experimental mechanism to estimate to what degree an ion-neutral interaction conforms to either the hard-sphere or induced-dipole model. To support these observations, additional comparisons are made with the respective reduced masses, polarizabilities, and mobilities of ions in mixtures where different degrees of hard-sphere interactions are present.

Study on property evaluation and numerical simulation of air-foam flooding in low permeability reservoir

ABSTRACT Comprehensively considering the migration law of air and foam in porous media, various physical and chemical phenomena, and the change of gas phase mobility are researched, then mathematical models of air-foam flooding are established. Based on air-foam flooding experiments, the relevant parameters of empirical model for numerical simulation of air-foam flooding were obtained. Matching of parallel core displacement experiment and air foam test flooding in Wuliwan Oilfield is completed with total fitting degree of more than 90%, and the reliability of empirical model of numerical simulation for air-foam flooding is verified.

Virus Size Analysis by Gas-Phase Mobility Measurements: Resolution Limits.

Electrospraying (ES) dissolved viral particles, followed by charge reduction and size analysis with a differential mobility analyzer (DMA), offers a flexible size-analysis tool for small particles in solution. The technique relies on pioneering work by Kaufman and colleagues, commercialized by TSI, and often referred to as GEMMA. However, viral studies with TSI's GEMMA have suffered from limited resolving power, possibly because of imperfections in either the instrument (DMA or charge reduction) or the sample solution preparation. Here, we explore the limits of the resolution achievable by GEMMA, taking advantage of (i) cleaner charge reduction methods and (ii) DMAs of higher resolving power. Analysis of the literature provides indications that mobility peak widths (fwhm) of 2% or less may be achieved by combining careful sample preparation with improved instrumentation. Working with purified PP7 bacteriophage particles small enough to be classifiable by existing high-resolution DMAs, we confirm that fairly narrow viral mobility peaks may be obtained (relative full width at half-maximum fwhm <5%). Comparison of spectra of a given apian virus sample obtained with TSI's GEMMA and our improved instrumentation confirms that one critical limitation is the DMA. This is further verified by narrow peaks from murine parvovirus, norovirus, and encephalomyelitis virus samples, obtained in our improved GEMMA with little sample preparation, directly from infected cell cultures. Classification of purified large (60 nm) coliphage PR772 particles leads to broad peaks, due to both viral degradation and limited intrinsic resolution of the DMAs used to cover the range of such large particles. We conclude that improved DMAs suitable for high-resolution analysis of particles larger than 30 nm need to be developed to determine the intrinsic mobility width of viral particles.

Optimized Reconstruction Techniques for Multiplexed Dual-Gate Ion Mobility Mass Spectrometry Experiments.

When coupling drift-tube gas-phase ion mobility separations with ion trapping mass analyzers an integrative, stepped approach to spectral reconstruction is a logical, yet highly inefficient means to determine gas-phase mobility coefficients. This experimental mode is largely predicated on the respective time scales of the two techniques each requiring tens of milliseconds to complete under routine conditions. Multiplexing techniques, such as Fourier and Hadamard based techniques, are a potential solution but still require extended experimental times that are not fully compatible with modern front-end separation schemes. Using a basis pursuit denoising (BPDN) approach to deconvolute Fourier transform ion mobility mass spectrometry (FT-IMMS) drift time spectra, we demonstrate significant time savings while maintaining a high degree of spectral resolution and signal-to-noise ratio. Under ideal conditions, the FT-IMMS operates with increased ion transmission (up to 25%); however, the linear chirp that spans into the kHz range often leads to significant levels of ion gate depletion, which limit both resolving power and ion transmission. The method proposed in this manuscript demonstrates the potential to reduce IMS acquisition time while simultaneously maximizing spectral resolution at longer effective gate pulse widths compared to the traditional set of multiplexing and signal averaging experiments.

Ion mobility–mass spectrometry of supramolecular complexes and assemblies

Despite their structural and functional differences, synthetic supramolecular assemblies share many similarities with biological assemblies, especially enzymes. The assemblies can be on the same length scale, and their structures and guest binding are typically governed by non-covalent interactions. Thus, only relatively weak interactions define the shape of a synthetic supramolecule or the secondary and tertiary structure of a protein, such that the resulting dynamism makes structure elucidation challenging. For biomolecules such as peptides, proteins, glycans and lipids this has often been tackled using ion mobility–mass spectrometry (IM-MS), whereby analyte ions are separated according to their gas-phase mobility and their mass-to-charge ratio. IM-MS is an established method in omics, separation sciences and small-molecule structural chemistry, but has only recently grown in popularity for the study of synthetic supramolecular assemblies in the gas phase. This Review describes IM-MS techniques and how they can help us understand the structures of molecular self-assemblies, host–guest complexes and metallosupramolecular complexes. Ion mobility–mass spectrometry (IM-MS) is a gas-phase method for structural characterization — a tool prevalent in biology but only recently finding applications in supramolecular chemistry. This Perspective describes how IM-MS techniques give us information about the structures of molecular self-assemblies, host–guest complexes and metallosupramolecular systems.

Investigating Supercritical CO2 Foam Propagation Distance: Conversion from Strong Foam to Weak Foam vs. Gravity Segregation

This study investigates how to determine the optimal supercritical CO2 foam injection strategies, in terms of total injection rate (or injection pressure, equivalently) and injection foam quality, to place injected foams deep and far into the reservoir. Two different mechanisms that limit field foam propagation, such as “conversion from strong foam to weak foam” and “gravity segregation,” are examined separately, and the results are combined together. The first is performed by using a mechanistic foam model based on bubble population balance, while the second is conducted by an analytical model (called Stone and Jenkins model) and reservoir simulations with a commercial software (CMG-STARS). Note that the gas-phase mobility, required as a key input parameter for gravity segregation simulations, is calibrated by the mechanistic model, which is a significant advance in this study. The results from both mechanisms show in general that foam propagation distance increases with increasing injection pressure or rate (which is often limited by the formation fracturing pressure) and increases with decreasing foam quality down to a certain threshold foam quality below which the distance is not sensitive to foam quality any longer. It is found that the mobilization pressure gradient (i.e., the pressure gradient above which foam films are mobilized to create a population of bubbles) plays a key role to determine the distance. Therefore, the injection of supercritical CO2 foams with lower mobilization pressure gradient should be more favored in field applications. As a step prior to real-world reservoir applications, this study deals with a relatively ideal reservoir (i.e., large homogeneous cylindrical reservoir) focusing on the steady state after foam treatment in the absence of oil.

Differentiating Parallel and Antiparallel DNA Duplexes in the Gas Phase Using Trapped Ion Mobility Spectrometry.

Deoxyribonucleic acids can form a wide variety of structural motifs which differ greatly from the typical antiparallel duplex stabilized by Watson-Crick base pairing. Many of these structures are thought to occur in vivo and may have essential roles in the biology of the cell. Among these is the parallel-stranded duplex-a structural motif in which DNA strands associate in a head-to-head fashion with the 5' ends at the same end of the duplex-which is stabilized by reverse Watson-Crick base pairing. In this study, parallel- and antiparallel-stranded DNA duplexes formed from two different 12-mer oligonucleotides were studied using native electrospray ionization combined with trapped ion mobility spectrometry and mass spectrometry. The DNA duplex charge plays an important role in the gas-phase mobility profile, with a more compact form in negative mode than in positive mode (ΔΩ ≈ 100 Å2 between -4 and +4). Despite sequence mismatches, homo- and hetero-DNA duplexes were formed in solution and transfer to the gas phase, where a more compact structure was observed for the parallel compared to the antiparallel duplexes (ΔΩ ≈ 50 Å2), in good agreement with theoretical calculations. Theoretical studies suggest that a reduction (or compaction) along the helical axis of the parallel and antiparallel DNA duplexes is observed upon transfer to the gas phase.

Effect of Foam on Liquid Phase Mobility in Porous Media

We investigate the validity of the assumption that foam in porous media reduces the mobility of gas phase only and does not impact the liquid-phase mobility. The foam is generated by simultaneous injection of nitrogen gas and a surfactant solution into sandstone cores and its strength is varied by changing surfactant type and concentration. We find, indeed, that the effect of foam on liquid-phase mobility is not pronounced and can be ignored. Our new experimental results and analyses resolve apparent discrepancies in the literature. Previously, some researchers erroneously applied relative permeability relationships measured at small to moderate capillary numbers to foam floods at large capillary number. Our results indicate that the water relative permeability in the absence of surfactant should be measured with the capillary pressure ranging up to values reached during the foam floods. This requires conducting a steady-state gas/water core flood with capillary numbers similar to that of foam floods or measuring the water relative-permeability curve using a centrifuge.

Characterization of gas-oil flow in Cyclic Solvent Injection (CSI) for heavy oil recovery

Cyclic Solvent Injection (CSI) has emerged as an effective follow-up process to the primary cold production, namely, Cold Heavy Oil Production with Sand (CHOPS). In this recovery process, the solvent is designed to maintain a strong nature of gas at in-situ conditions. As a result, the porous medium is spatially divided into two zones with differing fluid properties, which are gas zone, also called solvent chamber, and heavy oil zone. The CSI process is governed by the gas-oil flow as the solvent chamber is predominated by free gas-oil flow and the heavy oil zone by dispersed gas-oil flow (i.e. foamy oil flow).The gas-oil flow in CSI considerably differs from that in heavy oil solution gas drive, and therefore, needs to be investigated separately. The differences mainly arise from the origin of free gas. In CSI, the free gas originates at the solvent chamber, whereas in heavy oil solution gas drive, it evolves from solution gas. The free gas, in accordance with where it originates, yields occurrence time and quantity that have different dependency on the pseudobubblepoint pressure of oil. Consequently, the gas-oil flow in CSI results in the characteristics far more susceptible to the quantity of free gas and the nonequilibrium nature of foamy oil than heavy oil solution gas drive.This study is aimed at characterizing the gas-oil flow in CSI under the effects of pressure depletion rate as well as the solvent chamber. To fulfill this objective, the gas-liquid relative permeability curves were inferred with the use of numerical simulations and modified fractional flow models. The numerical simulations were carried out to history-match seven lab-scale CSI tests performed at different pressure depletion rates. The modified fractional flow models were applied to describe the foamy oil flow. The distinct characteristics of the gas-oil flow were examined based on sensitivity analysis and comparison to the previous findings on heavy oil solution gas drive.The results suggest that, at low pressure depletion rates, the gas-oil flow in CSI yield the characteristics that have also been observed in heavy oil solution gas drive. At sufficiently high pressure depletion rates, however, the free gas that exists even when the dispersed gas bubbles are immobile results in the different behavior of critical gas saturation and gas phase mobility. The solvent chamber misleads the gas-liquid relative permeability curves if the critical gas saturation is too high to properly describe the simultaneous flow of free gas and foamy oil. The solvent injectivity is also affected by the pressure depletion rate due to the foamy oil that has remained as unproduced in the solvent chamber during a previous production period.