External Vibration-Assisted Carbon Dioxide Sequestration in Heavy Oil Reservoirs: The Influences of Frequency and Cavity Distribution

Abstract

This study investigates the effect of external vibration stimulation on CO₂ dissolution behavior in heavy oil reservoirs, focusing on the influence of vibration frequency and cavity distribution within porous media. Experiments reveal that 5 Hz vibration significantly enhances CO₂ dissolution, while higher frequencies (10 Hz and 20 Hz) hinder the process. A more homogeneous and extensive distribution of oil-depleted cavities further improves dissolution rates, particularly in post-gas flooding scenarios. The dissolution process, observed under constant pressure conditions, is categorized into three stages: cavity filling, fast dissolution, and slow dissolution. Vibration stimulation effectively enhances the fast dissolution stage but has a minimal impact on the slow dissolution stage. Intermittent vibration shows mixed effects, improving dissolution at 100% oil saturation but reducing rates at 90% saturation due to cavity-induced flow disruptions. These findings demonstrate the potential of vibration-stimulated CO₂ dissolution (VS-CO₂ dissolution) as a novel technique for enhancing CO₂ storage and heavy oil recovery in reservoirs. This study provides critical insights for optimizing vibration frequency and cavity distribution, paving the way for improved field applications of this innovative technology.

1. Introduction

With the increasing global energy demand and the need to mitigate greenhouse gas emissions, the extraction of remaining heavy oil resources and the utilization of the abundant pore space in depleted reservoirs for CO₂ storage have garnered significant attention. Injecting CO₂ into these reservoirs simultaneously increases oil production while sequestering the gas underground as an integral part of carbon utilization measures. Despite the potential of CO₂ for enhancing oil recovery, its dissolution into heavy oil, particularly in porous media, often occurs at suboptimal rates due to inherent fluid properties and reservoir conditions. The literature indicates that CO₂ can dissolve in heavy oil through various mass transfer mechanisms, leading to numerous studies on CO₂ diffusivity in heavy oil under reservoir conditions [1,2,3,4,5]. Specifically, Yang and Gu [6] investigated interfacial interactions between crude oil and CO₂, revealing that only partial miscibility is achievable under typical reservoir conditions, which can influence long-term CO₂ sequestration and oil recovery. Wang [3] conducted experimental studies demonstrating that the molecular diffusivity of CO₂ is consistently lower in porous media compared to the bulk phase. The dissolution of CO₂ is route-dependent, with constant pressure and constant volume diffusion processes yielding different results. Liu et al. [4] investigated CO₂ diffusion in heavy oil porous media and found that the contact area between heavy oil and CO₂ significantly affects the total diffusion and the distribution of CO₂ concentration. However, few of these pioneering studies have examined the influence of external excitation on CO₂ dissolution in both the presence and absence of porous media, nor have they described the changes in oil volume under such external forces.

The diffusion of CO₂ in heavy oil has been extensively studied through experimental and mathematical modeling approaches, both in bulk phase and porous media. For instance, Zhou et al. [7] developed a novel experimental set-up to replicate real reservoir conditions and employed a mathematical model for history matching, accurately determining diffusion coefficients of 5.778 × 10⁻⁹ m²/s in the bulk phase and 3.222 × 10⁻⁹ m²/s in porous media. These findings provide critical insights into the mass transfer mechanisms of CO₂ in heavy oil, which are essential for optimizing CO₂-based enhanced oil recovery (EOR) processes. Furthermore, recent advancements in CO₂ injection techniques, such as particle jet technology [8], have demonstrated the potential to enhance injection efficiency by enlarging the bottom hole diameter, improving both oil recovery and storage safety. Collectively, these studies underscore the importance of understanding and optimizing CO₂ diffusion and injection processes to maximize EOR efficiency and carbon storage potential.

Gao et al. [9] conducted CO₂ injection experiments using oil-saturated cores in a wide temperature range to investigate the factors influencing CO₂ diffusivity. The results demonstrated that CO₂ diffusivity is highly sensitive to both tortuosity and temperature, while showing minimal dependence on initial pressure under high-pressure conditions. Increased tortuosity in the porous medium was found to significantly limit CO₂ solubility in oil, as evidenced by the pressure decay data. Based on the experimental observations, a mathematical model was developed to calculate the CO₂ diffusion coefficient, offering insights into the transport behavior of CO₂ in complex reservoir conditions.

Ma and Gu [10] studied the combination of CO₂-cyclic solvent injection (CO₂-CSI) with gas flooding (GF) and found that this approach enhances oil recovery more effectively than CO₂-CSI alone. This improvement is attributed to the extended foamy oil flow during the combined process, which increases the recovery factor. However, careful management of the CO₂ injection rate is essential to avoid adverse effects from strong free-gas flow in the later cycles.

Dai and Zhang [11] conducted an experimental study on the combined effects of external pressure and low-frequency vibratory excitations on oil slug mobilization and flow in a capillary model, focusing on two-phase flow in porous media. Building on the previous work of Cheng and Dai [12], this research analyzes flow phenomena and variations in pressure drop during and after oil slug mobilization, as well as the travel distance of the oil slug under different conditions. The results indicate that vibratory excitation positively influences oil mobilization by altering the contact angle between the oil slug and the tube wall, reducing required pressure, and increasing the oil travel distance. These findings enhance the understanding of two-phase flow dynamics in porous media and offer valuable insights into enhanced oil recovery through water flooding and vibratory stimulation techniques.

Alhosani et al. [13] employed high-resolution X-ray imaging to investigate CO₂, oil, and water distribution in oil-wet rocks under subsurface conditions. Their findings reveal that, contrary to conventional assumptions, CO₂ tends to occupy smaller pores or corner layers rather than the largest pores, which significantly restricts its mobility and enhances storage security. This behavior, observed in heterogeneous calcite formations, suggests that near-miscible conditions and the wettability order of oil–gas–water are favorable for both CO₂ recovery and secure storage in oil-wet or mixed-wet reservoirs. Building on this understanding, Behnoud et al. [14] numerically analyzed CO₂–oil displacement under near-miscible conditions at the pore scale, showing that reduced interfacial tension enables CO₂ to displace bypassed oil effectively in both large and small pores. By coupling phase-field modeling and mass transfer simulations, they demonstrated that near-miscible conditions can approach miscible recovery efficiencies while accommodating more realistic reservoir pressures, making them highly practical for field application.

Recent studies have highlighted the crucial role of complex mixed-wettability in governing CO₂ displacement efficiency within porous media. Liu et al. [15] constructed a multiscale model to simulate mixed-wettability by assigning different contact angles to distinct pore surfaces, revealing that such heterogeneity significantly affects imbibition and flow behavior. Building upon this, Sun et al. [16] demonstrated that phase transitions of CO₂ from gas to supercritical states alter its wetting characteristics, transitioning from a non-wetting to a wetting phase. This shift, combined with pore wall wettability variations, leads to different flow patterns and displacement behaviors. The comparative analysis further showed that mixed wettability can enhance displacement under certain conditions, although oversimplified assumptions of uniform wettability may lead to overestimations in CO₂ recovery performance.

The application of external vibration excitation to support multiphase fluid flow and oil recovery has been implemented for years; however, this technique remains in its preliminary exploration stage and faces numerous operational challenges. A comprehensive understanding of the fundamental mechanisms involved in vibration-assisted subsurface resource production is necessary to prevent improper operations that could damage oil well production. Previous research has focused on low-frequency and supersonic wave tests, primarily targeting light oil reservoirs. The previous study demonstrated that implementing vibration excitation in the CO₂-EOR process could enhance CO₂ dissolution in heavy oil with the same amount of CO₂ injected, even when reservoir pressure decreases [17]. This study uniquely investigates the impact of a low-frequency vibration stimulation on CO₂ dissolution rates in heavy oil under controlled reservoir conditions, addressing a significant gap in the existing literature. While previous research has focused on CO₂ diffusion and dissolution in bulk and porous media, few studies have explored the potential of vibration stimulation to enhance these processes [3,4]. The findings of Du et al. [18] and Kavousi et al. [19] suggest that external factors such as pressure, temperature, and fluid interactions play a critical role in CO₂ dissolution, providing a foundation for investigating the effects of vibration. By systematically analyzing the influence of vibration frequency and cavity distribution, this research aims to bridge the gap in understanding how external excitation can optimize CO₂ dissolution in heavy oil reservoirs. By systematically varying the vibration frequency and measuring the dissolution rates across three distinct reservoir conditions, this research aims to elucidate the mechanisms driving enhanced CO₂ solubility. The findings contribute valuable data to the field of enhanced oil recovery and inform optimized CO₂-EOR strategies, ultimately supporting global efforts in carbon management.

This study builds on the foundational work of Yang and Gu [6] and Wang and Zhao [8], who explored CO₂ injection efficiency and interfacial interactions, respectively. By integrating insights from these studies, this research aims to provide a comprehensive understanding of how vibration stimulation can enhance CO₂ dissolution in heavy oil reservoirs, contributing to the development of more efficient CCUS strategies.

2. Materials and Methods

2.1. Materials

The heavy oil sample used for this study was taken from Lloydminster, Saskatchewan Province, Canada. The heavy oil has a measured viscosity (µ_o) of 8940 cP using a viscometer (DV-II, Brookfield, Middleboro, MA, USA) at ambient pressure and a temperature of 21 °C. The measured density of oil was 0.9801 g/cm³ at ambient pressure and 21 °C by using a densitometer (DMA 512P, Anton Paar, Ashland, VA, USA). The injected CO₂ has a purity of 99.8 mol.% (Linde, Regina, SK, Canada).

2.2. Experiment Set-Up

The experimental set-up consists of a physical sandpack model, an oil and solvent injection system, and a vibration unit. A stainless steel cylindrical sandpack model, measuring 40 cm in length and 4 cm in diameter, was employed to house the fluids and the porous medium, which consisted of crystallized silica sand. Figure 1 provides a schematic diagram of the experimental set-up for the vibration-stimulated CO₂ dissolution (VS-CO₂ dissolution) study, and Figure 2 depicts the vibration unit used to oscillate the sandpack model. The sandpack model features an injection port on the right-hand side, where vibration is also applied, and a production port on the left-hand side.

The oil and solvent injection system, connected to the injection port of the sandpack model, comprises two cylinders containing crude oil and solvent samples, along with a two-stage gas regulator. The solvent is injected at a constant pressure using a syringe pump (500D, Teledyne, Lincoln, NE, USA). Horizontal vibration of the sandpack is generated using a vibration exciter (JZK-50, Sinocera, Suzhou, Jiangsu, China). The sandpack model is mounted on a sliding rail to ensure smooth movement, with the sliding assembly connected to the exciter shaft. The frequency of the shaker shaft is regulated by a signal generator (Model 3560c, Bruel & Kjær, Nærum, Denmark) and a power amplifier (Model YE5874A, Sinocera, Suzhou, Jiangsu, China), with the vibration power held constant throughout the experiments.

To evaluate the impact of vibrational excitation on CO₂ dissolution under different oil-depletion conditions, experiments were performed at 100% and 90% crude oil saturation, as depicted in Figure 3 and Figure 4. Experiments at 100% oil saturation represent the reservoir at its initial discovery stage, whereas those at 90% oil saturation simulate a depleted reservoir following primary and secondary recovery methods, such as Cyclic Solvent Injection (CSI) or gas flooding (GF). For all 90% oil saturation cases, meticulous preparation ensured that the cavity volume in the sandpack model was maintained at 10 ± 0.3% of the total pore volume, reflecting the production of 10% of the original oil.

The first 90% oil saturation scenario replicates the depleted reservoir condition following CSI, where 10% of the Original Oil In Place (OOIP) is recovered. In this scenario, a predetermined volume of CO₂ is injected into the sandpack model via the injection port. Following a specified soaking period, oil is produced from the same injection port. This injection–soaking–production cycle is repeated multiple times until 10% of the original oil is recovered. The cavity volume is localized in the near-wellbore region since both injection and production are conducted through the same port. This depleted oil scenario is referred to as “post-Cyclic Solvent Injection” (post-CSI). Subsequently, the VS-CO₂ dissolution experiment is performed to enhance oil recovery from the 90% oil-depleted reservoir while concurrently storing CO₂. The VS-CO₂ dissolution process is deemed complete when CO₂ breakthrough occurs at the production port of the sandpack. Additionally, crude oil is injected through the production port to re-establish 90% oil saturation and commence a new experimental run.

The second 90% oil saturation scenario simulates the depleted reservoir condition after gas flooding, where 10% of the OOIP is recovered, resulting in a more uniformly distributed cavity volume across the formation. To achieve this cavity distribution, gas is injected at 700 kPa through the injection port while oil is simultaneously produced from the production port. The flooding process terminates once 10% of the oil is recovered. This depleted oil scenario is designated as “post-gas flooding” (post-GF). Subsequently, the VS-CO₂ dissolution experiment is conducted to recover additional oil from the 90% oil-depleted reservoir while concurrently storing CO₂. The VS-CO₂ dissolution process is considered complete when CO₂ breakthrough occurs at the production port of the sandpack. Additionally, crude oil is injected through the injection port to restore 100% oil saturation, preparing the system for the next experimental run. The schematic diagrams of seismic vibration application for CO₂ dissolution under different reservoir conditions are illustrated in Figure 5.

As described earlier, the cavity distributions resulting from post-CSI and post-GF differ significantly. Furthermore, the oil restoration methods for the two scenarios vary: In post-CSI, oil is restored through the production port, whereas in post-GF, oil is fully restored via the injection port, with new cavities simultaneously generated through gas flooding.

2.3. Experimental Preparation

Prior to the experiments, the porosity and permeability of the sandpack model were measured. Crude Lloydminster oil was subsequently injected into the sandpack model at a low flow rate using a syringe pump. The experiments were performed under two distinct porosity and permeability conditions: Tests #1–6 were conducted with a porosity of 40.2% and a permeability of 11.4 Darcy, while Tests #7–25 were carried out with a porosity of 36.8% and a permeability of 8.4 Darcy.

2.4. Experimental Procedure

A total of 25 sandpack tests were conducted in this study. Initially, six experiments were performed, including vibration-free tests and VS-CO₂ dissolution tests at frequencies of 2 Hz and 5 Hz under 100% crude oil saturation. Subsequently, 19 additional experiments were carried out, involving vibration-free and VS-CO₂ dissolution tests at frequencies of 2 Hz, 5 Hz, 10 Hz, and 20 Hz, with either 100% or 90% crude oil saturation to replicate various reservoir conditions. In the latter phase, tests conducted at 100% oil saturation employed sandpack with lower porosity and permeability values compared to those used in the initial 100% oil saturation tests.

The detailed experimental set-up and conditions are illustrated in Table 1.

All experiments involved continuous CO₂ injection for three hours at a constant pressure of 3.5 MPa and room temperature. The CO₂ injection and dissolution rates were recorded by monitoring the volume change in the pump during the injection period. This study investigated both constant volume and constant pressure injection methods to assess CO₂ dissolution. Given that dissolution is predominantly influenced by pressure and significant pressure fluctuations have a greater impact on the dissolution rate than other factors, the constant pressure method was considered more reliable for this research.

In the constant volume approach, the reservoir pressure exhibited a rapid decline during the first 20 min, followed by a slower decrease from 20 to 50 min, and nearly stabilized after 50 min, with the pressure change falling below the detection range of the pressure gauge. Owing to these limitations, the constant volume method is not further discussed in this study.

Upon completing each experiment, CO₂ injection was immediately stopped, and the valve was opened for 20 h to release pressure, ensuring a consistent starting point for subsequent tests. Following this, crude oil was injected, and the weights of the models were measured and calibrated before beginning the next experiment. Unlike the conventional approach of refilling sand for each experiment, this method helps isolate the influence of variables such as porosity and permeability distributions on CO₂ dissolution. All VS-CO₂ dissolution tests were performed at the same vibration power output level to maintain consistency. The specific vibration parameters are provided in Table 2.

3. Results and Discussion

3.1. The Effect of External Vibration on CO₂ Dissolution

In Phase 1 of the study, six experiments were conducted under 100% crude oil saturation and a porosity of 40.2%. Test #1 was a CO₂ dissolution test performed without vibration. Test #2 employed intermittent vibration, alternating between a 90 min no-vibration period and a 90-min period with 2 Hz vibration. Tests #3 and #4 were dedicated to 2 Hz VS-CO₂ dissolution, while Tests #5 and #6 focused on 5 Hz VS-CO₂ dissolution.

As shown in Figure 6, under 100% crude oil saturation, the CO₂ dissolution rate is lowest in the no-vibration test. The highest dissolution rate is achieved with 5 Hz vibration excitation, followed by 2 Hz vibration excitation and then the no-vibration test. Further analysis reveals that after 160 min, the no-vibration test (Test #1) displayed a distinct marginal effect, marked by a sudden drop in the dissolution rate—a phenomenon absent in both the 2 Hz and 5 Hz experiments. This indicates that vibrational excitation may mitigate or delay the sudden decline in the dissolution rate. Although a decrease in dissolution rate also appears in the 2 Hz tests (Tests #3 and #4), it occurs earlier and progresses more gradually, with the rate stabilizing after the drop. In contrast, the no-vibration test shows a sharper and more substantial decline, indicating a clear difference in the dissolution behavior between the cases.

To investigate the relationship between vibrationally enhanced CO₂ dissolution rates and porosity, Phase 2 experiments employed a denser sandpack model with a reduced porosity of 36.8%, compared to 40.2% in Phase 1. Figure 7 presents the results of experiments conducted at 100% crude oil saturation in Phase 2, including some replicate tests from Phase 1. Similar to Phase 1, the Phase 2 experiments were conducted at an injection pressure of 3.5 MPa and room temperature.

The results from Phase 2 align with the conclusions derived from Phase 1. However, although the trends in CO₂ dissolution rates are comparable between the two phases, the dissolution rates at each frequency in Phase 2 are lower than those in Phase 1, attributable to the reduced porosity. This consistency across both sets confirms that while porosity influences the absolute dissolution rate, it does not alter the overall response pattern to vibration stimulation. Therefore, the observed discrepancies in rate magnitude are purely due to physical differences in pore structure.

3.2. The Effect of Vibration Frequency on CO₂ Dissolution

As outlined in the previous section, a vibration frequency of 5 Hz significantly enhances the CO₂ dissolution rate, while 2 Hz demonstrates a moderate improvement compared to no vibration. This initially suggests that higher frequencies generally result in higher dissolution rates. However, the results from Tests #10–13 contradict this trend. These experiments, which examined CO₂ dissolution rates under 10 Hz and 20 Hz vibrations, reveal that the dissolution rates at these frequencies are not only lower than those at 5 Hz but also significantly lower than those in the no-vibration tests.

These findings suggest the existence of an optimal vibration frequency for maximizing dissolution rates. Inappropriate vibrational excitation may impede gas diffusion, leading to a reduction in the dissolution rate. Thus, a vibration frequency of 5 Hz is identified as the most effective for enhancing CO₂ dissolution under the current experimental conditions. Additionally, it is hypothesized that vibrational excitation at this optimal frequency could further enhance CO₂ diffusion in crude oil within porous media.

3.3. The Effect of Pore Cavity Distribution on CO₂ Dissolution

This section examines the influence of pore cavity distribution on CO₂ dissolution under 90% crude oil saturation. Figure 8 and Figure 9 depict the CO₂ injection profiles for non-vibration and 2 Hz vibration conditions across varying cavity geometries at this saturation level.

In Tests #14 and #17, 10% of the oil was produced from the production side, creating cavities after gas flooding (post-GF) that were uniformly distributed from the injector to the producer. In contrast, in Tests #15 and #16, 10% of the oil was produced through cyclic CO₂ injection (post-CSI), resulting in cavities concentrated near the wellbore region. These two oil production methods generate distinct cavity geometries and distributions within the sandpack model.

As shown in Figure 8, the dissolution profiles of Tests #14 and #17 are significantly higher than those of Tests #15 and #16. The gas flooding process creates more uniformly distributed cavities in the reservoir compared to CSI production, leading to a larger contact area between CO₂ and crude oil. This expanded contact area significantly enhances the CO₂ dissolution rate.

Figure 9 replicates the experiment shown in Figure 8 but incorporates 2 Hz vibrational excitation. Tests #19 and #20, which employed gas flooding to generate a more extensive distribution of cavities within the porous medium, exhibit a significant improvement in CO₂ dissolution compared to Test #18, where CSI production created localized cavities near the wellbore. Although the 2 Hz vibration slightly increased the dissolution rate for both cavity distributions, the cavity distribution remains the primary factor influencing CO₂ dissolution. These results indicate that while vibrational excitation can enhance the dissolution rate, it cannot entirely offset the reduction in dissolution caused by unfavorable cavity geometries and distributions.

Figure 10 shows the CO₂ dissolution rates for different vibration frequencies during VS-CO₂ dissolution tests at 90% crude oil saturation following gas flooding production. The results are consistent with earlier findings, demonstrating that both 10 Hz and 20 Hz vibrations negatively affect dissolution, with 20 Hz exhibiting a more significant detrimental impact than 10 Hz. When comparing the no-vibration, 2 Hz, and 5 Hz conditions, vibrational excitation remains effective in enhancing CO₂ dissolution, though the overall improvement is limited.

Figure 11 illustrates the differences in CO₂ dissolution rates under non-vibration, 2 Hz, and 5 Hz conditions during VS-CO₂ dissolution tests at 90% crude oil saturation following gas flooding production. The results indicate that the dissolution rate at 5 Hz is higher than that at 2 Hz and without vibration; however, the improvement is marginal and short-lived. The dissolution process can be categorized into three stages: the initial cavity-filling stage, the intermediate fast dissolution stage, and the final slow dissolution stage. In the initial stage, all experiments produce similar results, while the effects of vibrational excitation are primarily observed during the intermediate fast dissolution stage. For the 90% crude oil saturation cases, the dissolution improvements from 2 Hz and 5 Hz compared to no vibration are less pronounced than those observed at 100% oil saturation. Notably, the detrimental effects of 10 Hz and 20 Hz on dissolution remain consistent and significant.

Mirjordavi et al. [20] identified the same three stages of CO₂ dissolution in both porous media and bulk phases, establishing a foundational framework for understanding the process. Expanding on this work, the current study investigates the effects of vibration stimulation using a constant pressure method to track changes in injection volume, in contrast to Mirjordavi’s pressure decay analysis during the injection period. This innovative approach highlights the unique contribution of this research in elucidating the influence of vibrations on CO₂ dissolution in porous media. While vibrations at 2 Hz and 5 Hz provide modest, short-term enhancements in dissolution rates, higher frequencies such as 10 Hz and 20 Hz exhibit a significant detrimental effect on the process.

3.4. The Effect of Intermittent Vibrations on CO₂ Dissolution

Test #2 employed intermittent vibration, alternating between 90 min of no vibration and 90 min of 2 Hz vibration excitation. As illustrated in Figure 6, at 100% crude oil saturation, this intermittent vibration slightly mitigated the decline in the dissolution curve and increased the dissolution rate in the later stages, although it did not significantly improve the overall rate. However, as depicted in Figure 12, at 90% crude oil saturation, intermittent 5 Hz vibration significantly reduced the dissolution rate. This indicates that, in the presence of cavities, intermittent vibration during the later stages can adversely affect CO₂ injection and dissolution. Similar detrimental effects were observed with 10 Hz and 20 Hz frequencies.

The findings align with Mirjordavi [20], who also identified three distinct stages of CO₂ dissolution. However, while Mirjordavi focused on pressure decay analysis, this study introduces vibration stimulation as a novel enhancement mechanism. Furthermore, these results contrast with those of Dai and Zhang, who reported minimal frequency-dependent effects in bulk phase experiments, suggesting that porous media play a critical role in vibrational enhancement [12]. The dissolution rates at 5 Hz were significantly higher than those at 2 Hz and no vibration, as confirmed by a one-way ANOVA, indicating a statistically significant (p < 0.0001) effect of vibration frequency on CO₂ dissolution. A one-way ANOVA was performed to evaluate the influence of vibration frequency on the total CO₂ dissolution rate. The analysis revealed a statistically significant effect of vibration frequency (F = 34.39, p = 0.000), confirming that the frequency level strongly influences dissolution behavior. The model showed a good fit, with an R² of 95.1% and a standard error (S) of 0.68. This statistical analysis underscores the effectiveness of 5 Hz vibration in enhancing CO₂ dissolution.

4. Conclusions

This study introduces vibration-stimulated CO₂ dissolution (VS-CO₂ dissolution) as a novel method to enhance CO₂ uptake in heavy oil reservoirs. The experimental results show that vibration stimulation significantly improves dissolution rates, with 5 Hz emerging as the optimal frequency under both full and partial oil saturation. Conversely, higher frequencies such as 10 Hz and 20 Hz were found to hinder the process, highlighting the importance of frequency tuning.

The dissolution process consistently followed three stages—cavity-filling, fast dissolution, and slow dissolution—across all tests, affirming the systematic behavior of CO₂ transport in oil-saturated porous media. Lower saturation (90%) combined with broader cavity distributions enhanced the contact between CO₂ and oil, further boosting dissolution. However, intermittent vibration, particularly at 5 Hz, led to flow disruption and decreased performance under certain cavity conditions, signaling the need for cautious field application.

These findings align with the foundational work of Mirjordavi on CO₂ dissolution stages but expand the framework by incorporating the effects of external vibration [19]. The complex interactions observed between vibration, cavity distribution, and saturation suggest that optimization must be context specific.

The practical implication is clear: Deploying 5 Hz vibration via downhole tools could improve CO₂ storage and heavy oil recovery in depleted reservoirs like those in Lloydminster and Cold Lake. This dual benefit positions VS-CO₂ dissolution as a promising, field-applicable enhancement technique. Future work should validate these laboratory results through numerical modeling and field-scale testing, especially to refine vibration strategies under varying geological and fluid conditions.

Author Contributions

Conceptualization, N.J. and S.L.; methodology, N.J, L.D. and S.L.; software, S.L.; data curation, S.L.; writing—original draft preparation, S.L. and Z.Z.; writing—review and editing, N.J., S.L., L.D. and Z.Z.; visualization, S.L.; supervision, N.J. and L.D.; project administration, N.J. and L.D.; funding acquisition, N.J. and L.D. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Acknowledgments

The authors thank Mitacs Canada for their financial support and appreciate the support from the Energy Systems Engineering and Industrial Systems Engineering programs at the Faculty of Engineering of Applied Science of the University of Regina.

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

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Figures and Tables

Figure 1 Schematic diagram of the experimental set-up for CCUS and VS-CCUS tests.

Figure 2 Schematic diagram of the vibration unit with the fixed sandpack.

Figure 3 Schematic diagrams of the vibration-stimulated CO₂ dissolution (VS-CO₂ dissolution) test with 100% oil saturation: (a) CO₂ injection with vibration, and (b) oil production.

Figure 4 Schematic diagrams of the 90% Saturated vibration-stimulated CO₂ Dissolution (VS-CO₂ dissolution) test process: (a) CO₂ injection, (b) the oil production with the CSI method, (c) the oil production with the gas flooding method, (d) CO₂ injection with vibration, and (e) crude oil refill from different sides to simulate varying reservoir conditions.

Figure 5 Schematic diagram of seismic vibration application for CO₂ dissolution into the reservoir with various conditions.

Figure 6 Tests # 1–6, CO₂ injection rate for non-VS-CO₂ and VS-CO₂ dissolution tests with 100% oil saturation (Phase 1 tests).

Figure 7 Tests # 7–13, CO₂ injection rate for non-VS-CO₂ and VS-CO₂ dissolution tests with 100% crude oil saturation (Phase 2 tests).

Figure 8 Tests # 14–17, CO₂ injection rate for VS-CO₂ dissolution tests with 90% crude oil saturation and different pore cavity shapes/distribution (Phase 2).

Figure 9 Tests # 18–20, CO₂ injection rate for 2 Hz VS-CO₂ dissolution tests with 90% crude oil saturation and different pore cavity shapes/distribution (Phase 2).

Figure 10 A comparison of CO₂ dissolution rates for 90% crude oil saturation tests, with 2 Hz, 5 Hz and no vibration during the transition stage in Phase 2.

Figure 11 CO₂ injection rate for 90% crude oil saturation tests with and without vibration excitation conducted in Phase 2.

Figure 12 A comparison of CO₂ dissolution rates at 90% crude oil saturation under three conditions: no vibration, constant 5 Hz vibration, and intermittent vibration (non-vibration alternating 5 Hz vibration) in Phase 2.

Table 1

Test schedule of VS-CO₂ dissolution experiments.

	Phase 1	Phase 2
Frequency	100% Crude oil Saturation	100% Crude oil Saturation	90% Crude oil Saturation
Porosity (%)	40.2	36.8
Permeability (mD)	11.4	8.4
No-vibration	Test # 1	Test # 7	Tests # 14–17
2 Hz	Tests # 3–4	Test # 8	Tests # 18–20
5 Hz	Tests # 5–6	Test # 9	Test # 21
10 Hz		Tests # 10–11	Test # 22
20 Hz		Tests # 12–13	Test # 23
Intermittent 2 Hz vibration	Test # 2
Intermittent 5 Hz vibration			Tests # 24–25

Table 2

Vibration characteristics for VS-CO₂ dissolution tests.

Power (W)	Frequency (Hz)	Amplitude (mm)	Acceleration (m/s2)	Velocity(m/s)
0.27	2	8.350	1.312	0.105
0.27	5	2.104	2.076	0.066
0.29	10	0.770	3.042	0.048
0.26	20	0.255	4.028	0.032

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