CO2 Replacement Research Articles

Adiabatic laminar burning velocities of C3H8-O2-CO2 and C3H8-O2-N2 mixtures at ambient conditions-PART II: Mechanistic interpretation

The effect of diluents on the laminar burning velocity of the premixed C3H8-O2-N2 and C3H8-O2-CO2 mixtures was numerically studied. Global flame parameters including adiabatic flame temperature (Tad), overall reaction order (n), activation energy (Ea), Zeldovich number (Ze) and Lewis number (Le) were calculated. Results show that the N2/CO2 alters all flame parameters. Based on asymptotic analysis for one-step overall reaction, these parameters correlates the laminar burning velocity. The change of Arrhenius effect, combination of thermal and chemical effect is the dominant factor, compared to the change of transport effect. Sensitivity analysis revealed that thermal effect is the dominant factor in Arrhenius effect. The correctness of one-step model was validated with experimental and numerical results. Detailed mechanism model analysis illustrates the linear correlations between laminar burning velocity and maximum (H + OH + O) concentration. The chemical effect of CO2 replacement of N2 in oxidizer is smaller than the thermal effect but much bigger than the transport effect in the calculation domain. The chemical effect of CO2 changes drastically with equivalence ratios and oxygen fractions.

An Experimental Study on Improved Production Performance by Depressurization Combined with CO2-Enriched Air Injection

Efficiently and safely producing natural gas stored as gas hydrates remains an urgent and, as yet, unsolved challenge. The CO2 replacement method is attractive for combining methane production and ...

Influence of Carbon Dioxide on the Adsorption of Methane by Coal Using Low-Field Nuclear Magnetic Resonance

The adsorption capacity of coal with respect to carbon dioxide (CO2) is greater than that of methane (CH4). Studying the CO2 replacement of CH4 in coal is essential to understanding the mechanism behind CO2-enhanced coalbed methane. In this paper, scanning electron microscopy was used to qualitatively study the influence of CO2 injection pressure on the fracture characteristics of coal. The time effect of the CH4/CO2 adsorption and the effect of the CO2 injection on the CH4 adsorption were quantitatively studied using low-field nuclear magnetic resonance. The results suggest three different CH4 states in the coal samples: CH4 adsorbed on the pore surface, free CH4 in the pore center, and free CH4 between the coal particles. Indeed, the greater the CO2 injection pressure, the more developed the fracturing and network, which, in turn, increases connectivity. As the adsorption time of CH4/CO2 increases, the adsorption rate of CO2/CH4 gradually decreases. In essence, CO2 preferentially replaces the CH4 of the minipores. As the CO2 injection pressure increases, the difference between the CO2 equilibrium pressure and the initial injection pressure increases. Moreover, the CH4 production rate increases, the transverse relaxation time (T2) spectrum of the adsorption-state area decreases, the T2 spectrum of the free-state area increases, and the number of adsorption holes gradually decreases, whereas the number of seepage holes increases.

Study of biosurfactant effects on methane recovery from gas hydrate by CO2 replacement and depressurization

The application of gas hydrate as a significant source of energy, which substantially contains methane, has recently attracted the consideration of many researchers. One of the essential methods of methane recovery from hydrate deposits is to inject carbon dioxide and its replacement in the hydrate structure of methane. Due to the low efficiency of this method, it is required to improve and provide other solutions to enhance the rate of replacement. In this study, depressurized and injection of rhamnolipid by carbon dioxide were investigated in porous media. Accordingly, a set of experiments was conducted to capture the effect of rhamnolipid on the kinetics of the hydrate formation growth. Further, rhamnolipid was compared to the well-known chemical surfactant, sodium dodecyl sulfate (SDS). The results of this comparison revealed that rhamnolipid was able to reduce the induction time and the total time of the process by 99% and 84% compared to SDS, respectively. In addition, it increased the amount of gas consumed by 20%, with the hydrate kinetic growth rate enhanced by seven times higher than the SDS. Generally, as this surfactant is bio-comparable and offers excellent results on the kinetics of hydrate formation, it can be promising as an eco-friendly promoter and play a valuable role in the future of methane recovery industry. The results revealed that the injection of rhamnolipid could enhance the rate of replacement process by 72.6% and the amount of carbon dioxide storage by 10% compared to the initial experiment performed without biosurfactant.

Time-dependent observation of a cage-specific guest exchange in sI hydrates for CH4 recovery and CO2 sequestration

CH4–CO2 replacement in naturally occurring gas hydrates has been considered a promising method for both energy recovery and CO2 sequestration. In this study, the time-dependent guest exchange behaviors and guest distributions during CH4–CO2 replacement were closely examined at two different CO2 injecting pressures (2.2 and 3.5 MPa) using nuclear magnetic resonance (NMR), in-situ Raman spectroscopy, powder X-ray diffraction (PXRD), and gas chromatography. The 13C NMR spectra confirmed that the cage occupancy ratio of the CH4 molecules in the large 51262 and small 512 cages (θL/θS,CH4) after the replacement was significantly smaller than that before the replacement because of the preferential occupation of CO2 in the large 51262 cages. The time-dependent Raman spectra revealed that the rate of CO2 inclusion and the resultant CH4 depletion in the hydrate phase during the replacement was faster at a higher CO2 injecting pressure. The Rietveld refinement of the PXRD patterns offered a quantitative cage occupancy of CH4 and CO2 molecules before and after the replacement. The time-dependent cage occupancy values of CH4 and CO2 during the replacement obtained from a multi-methodological approach, which is a combination of PXRD analysis and in-situ Raman measurement, demonstrated that a significant guest exchange in the large 51262 cages had a greater effect on the extent of replacement and that the kinetics of the CH4–CO2 replacement was accelerated at a higher CO2 injecting pressure. The results provide a better understanding of the kinetics and mechanism of the cage-specific CH4–CO2 replacement occurring in the sI hydrates for CH4 recovery and CO2 sequestration.

Comparative analysis of the consolidation and shear behaviors of CH4 and CO2 hydrate-bearing silty sediments

The successful production trial in Ignik Sikumi located in Alaska North Slope showed the significant potential of applying the CH4–CO2 replacement method to natural hydrate production. The comparison on the mechanical behaviors of CH4 and CO2 hydrate-bearing sediments is the key factor in assessing the geomechanical stability of hydrate reservoirs before and after the CH4–CO2 replacement. Large amount of hydrates have been discovered in silty reservoirs. However, studies focusing on the mechanical behaviors of CH4 and CO2 hydrate-bearing silty sediments are rare to date. This paper reports the results of a comparative analysis of the mechanical behaviors, including the isotropic consolidation behaviors and stress-strain relationships of CH4 and CO2 hydrate-bearing silty sediments. The results show that the CH4 and CO2 hydrate-bearing silty sediments present similar compression and swelling indexes. Various hydrate saturation shows differential effects on the strength and stiffness of CH4 and CO2 hydrate-bearing silty sediments. In addition, CO2 hydrate-bearing silty sediments displays weaker contraction behaviors than that of CH4 hydrate-bearing silty sediments.

Microsecond simulation study on the replacement of methane in methane hydrate by carbon dioxide, nitrogen, and carbon dioxide–nitrogen mixtures

Replacement of methane (CH4) in CH4 hydrate by carbon dioxide (CO2) can enable recovery of CH4, which is a potential future energy resource, while sequestering CO2 to mitigate the effects of global warming. However, little work has been done to address the effects of impurities on CO2 replacement, and the detailed mechanisms. Here, microsecond molecular dynamics simulations were performed to understand the influence of nitrogen (N2) gas on the process of replacing CH4 in CH4 hydrate with CO2 at 280 K and 6 MPa. The results show that CO2 molecules can penetrate more deeply into CH4 hydrate phase when it is mixed with N2. This is mainly because N2 can favor the decomposition of CH4 hydrate and expand the replacement area of CH4 by guest molecules. We confirm that the replacement of CH4 by CO2 and N2 preferably occurs in large and small cages, respectively. In most cases, a mixture hydrate reforms at the outmost layer of the hydrate surface. The CO2/N2 mixture shows an overall higher replacement efficiency than pure CO2 case. Our work demonstrates that CH4 recovery by CO2 injection in CH4 hydrate can be facilitated by N2. The penetration depth of replacement is sensitive to the ratio of N2 to CO2. The knowledge obtained in this study will be helpful for the effective utilization of CO2/N2 mixtures to maximize the recovery percentage of CH4 from hydrate.

Hydrate Stability and Methane Recovery from Gas Hydrate through CH4–CO2 Replacement in Different Mass Transfer Scenarios

CH4–CO2 replacement is a carbon-negative, safer gas production technique to produce methane gas from natural gas hydrate reservoirs by injecting pure CO2 or other gas mixtures containing CO2. Laboratory-scale experiments show that this technique produces low methane volume and has a slow replacement rate due to the mass transfer barrier created due to impermeable CO2 hydrate layer formation, thus making the process commercially unattractive. This mass-transfer barrier can be reduced through pressure reduction techniques and chemical techniques; however, very few studies have focused on depressurization-assisted and chemical-assisted CH4–CO2 replacement to lower mass-transfer barriers and there are many unknowns. In this work, we qualitatively and quantitatively investigated the effect of the pressure reduction and presence of a hydrate promoter on mixed hydrate stability, CH4 recovery, and risk of water production during CH4–CO2 exchange. Exchange experiments were carried out using the 500 ppm sodium dodecyl sulfate (SDS) solution inside a high-pressure stirred reactor. Our results indicated that mixed hydrate stability and methane recovery depends on the degree of pressure reduction, type, and composition of injected gas. Final selection between CO2 and CO2 + N2 gas depends on the tradeoff between mixed hydrate stability pressure and methane recovery. Hydrate morphology studies suggest that production of water during the CH4–CO2 exchange is a stochastic phenomenon that is dependent on many parameters.

CO2/N2 injection into CH4 + C3H8 hydrates for gas recovery and CO2 sequestration

CO2 injection into CH4 hydrate (sI) is a promising method for simultaneous energy production and global warming mitigation. In fact, the natural abundance of sII hydrates have been also confirmed. The gas exchange kinetics in sII hydrates were significantly different from those in CH4 hydrate. In this work, the injection of CO2 with or without N2 into CH4-C3H8 hydrate-bearing sediments was experimentally investigated to explore gas recovery and CO2 sequestration during the replacement. The results indicated that the CH4-CO2 exchange in large cages was always controlled by gas diffusion through newly-formed mixed hydrate layer. Differently, the CH4-N2 exchange in small cages changed from gas exchange-controlled to gas diffusion-controlled with the increase of N2 partial pressure. It was found that the recovery of CH4 was much more continuous than that of C3H8 in gaseous CO2/N2 replacement while CH4 and C3H8 were released synchronously in liquid CO2 replacement. CH4-C3H8 hydrate particles soaked in liquid CO2 may undergo almost complete structural transitions from sII to sI hydrate rich in CO2. The analysis of heterogeneous compositions of the replaced hydrates indicated that the presence of N2 may have inhibition effects on the structural transition of CH4-C3H8 hydrates. With the injection of gaseous CO2/N2, there was only a surface structure-transition followed by an iso-structural conversion in the deeper layers of hydrate particles. The structural transition played an important role in the replacement of sII hydrate, which made sII gas hydrate reservoirs to be promising target regions for efficient gas production and CO2 sequestration.

Experimental and numerical investigation of vitiation effects on the auto-ignition of n-heptane at high temperatures

Abstract The ground test in wind-tunnel with high temperatures plays an important role in the scramjet design and refinement. To simulate supersonic flight conditions, combustion-heated approach in ground tests introduces carbon dioxide and water vapor in the test flow. Understanding of vitiation effects is crucial for extrapolating the ground test results to the actual flight conditions. The primary goal of this work is to investigate the vitiation effects of CO2 and H2O on auto-ignition of n-heptane. With 20% CO2 or H2O replacement of N2 in air, ignition delay times of n-heptane/air were investigated behind reflected shock waves at temperatures of 1050–1400 K, pressures of 2 and 10 atm, and with equivalence ratios of 1.0 and 0.5. The addition of CO2 shows slightly inhibiting effect, whereas H2O shows a promoting effect on the ignition of n-heptane. Further numerical simulations of kinetic mechanism were performed to investigate the thermal, chemical and third-body collision effects of CO2 and H2O separately. Results indicated that the thermal effect of CO2 is the dominant factor for the inhibiting effect on n-heptane ignition, and the third-body collision of H2O is the major factor promoting the ignition of n-heptane.

Experimental study on natural gas hydrate exploitation: Optimization of methane recovery, carbon dioxide storage and deposit structure preservation

Abstract Aim of this work is locating how CO2 replacement into methane hydrate deposits may be performed, in order to increase both methane recovered and carbon dioxide stored quantities. The experimental section deals with the study of natural gas hydrate formation process and replacement of methane, contained into water cages, with carbon dioxide. In particular, the formation of methane hydrate is analyzed to understand the parameters that most influence the replacement process. A total of 10 tests were carried out in a laboratory scale reactor. Test 1–8 were performed adopting thermal stimulation as replacement technique, while in Test 9 and Test 10 depressurization was used. Results obtained have led to the conclusion that the rate of methane hydrate formation positively influences the percentage of CO2 stored, while the initial saturation of the sand pores has a negative effect. The presence of hydrate agglomerates hinders the gas transition preventing the replacement process. Finally, a greater quantity of CO2 hydrate, both via replacement process and via new hydrate formation, is related to a higher deposit structure preservation. As emerges from the experimental tests, the adopted replacement strategy influences the experimental relationships.

Gas hydrate exploitation using CO2/H2 mixture gas by semi-continuous injection-production mode

The CO2 replacement technique is considered as a promising approach for both gas hydrate recovery and CO2 sequestration. Based on this technique, the continuous CO2/H2 injection-production mode had been studied in our previous work. However, there are limitations on this continuous mode, such as lower CH4 recovery and CO2 sequestration ratios, lower CH4 concentration in produced gas and higher injection-production ratio caused by the fast breakthrough of injected gas. Here we proposed a so called semi-continuous injection-production mode, in which continuous injection-production process is interrupted periodically by stopping injection and production operations for letting injected gas diffuse sufficiently, delaying its breakthrough and increasing its effective sweep region. A series of experimental simulations were performed with respect to this mode in a three-dimensional simulator with a volume of 10.6 L. The results indicated that for the injected gas with low CO2 concentration, the CH4 recovery and concentration in the produced gas could be enhanced dramatically by the semi-continuous gas injection method. Additionally, the fast decomposition stage of CH4 hydrate could be retained separately in the replacement process, thereby effectively improving production efficiency. However, the corresponding CH4 concentration in the produced gas decreased and the injection production ratio increased. Notably, the process combining the CH4 steam reforming with cyclic injection-production was first simulated. The results showed an excellent CO2 storage capability and CH4 hydrate recovery ratio, which was mainly controlled by the gas composition of the re-injected gas. Through systematically comparing and analyzing the CH4 concentration, recovery ratio, production efficiency and injection-production ratio, it is demonstrated that the semi-continuous injection-production mode is superior to the continuous one. The results obtained in this work are of significance for guiding future NGHs exploitation.

Natural gas hydrates: Comparison between two different applications of thermal stimulation for performing CO2 replacement

Natural gas hydrates represent a valid opportunity for the permanent storage of CO2. In this work thermal stimulation technique has been deepened for replacing CH4 with CO2. Using a lab-scale reactor, eight experimental tests were carried out, characterized by two phases. The first one consists in the methane hydrates formation and is the same for all experiments. The second one consists in the replacement process and has been conducted with two different methods. In the first four tests CO2 was first introduced to reach a solid phase of methane hydrates and a gaseous phase composed of both CH4 and CO2; subsequently the temperature was increased. In the other four tests, the first step consisted in increasing temperature and then introducing CO2. In this case, the temperature required to move the thermodynamic conditions from a region suitable for the formation of both CH4 and CO2 hydrate to a region where the formation process can only involve CO2, was achieved without additional thermal energy; in fact, when the CO2 hydrates began to form, an immediate and massive release of heat took place. The results show that the methane yield and the amount of CO2 that can be stored do not differ between the two types of tests, but the thermal energy required to complete the process is much lower in the tests conducted with the second method.

Research progress in hydrate-based technologies and processes in China: A review

Natural gas hydrate (NGH) is considered as an alternative energy resource in the future as it is proven to contain about 2 times carbon resources of those contained in the fossil energy on Earth. Gas hydrate technology is a new technology which can be extensively used in methane production from NGH, gas separation and purification, gas transportation, sea–water desalination, pipeline safety and phase change energy storage, etc. Since the 1980s, the gas hydrate technology has become a research hotspot worldwide because of its relatively economic and environmental friendly characteristics. China is a big energy consuming country with coal as a dominant energy. With the development of the society, energy shortage and environmental pollution are becoming great obstacles to the progress of the country. Therefore, in order to ensure the sustainable development of the society, it is of great significance to develop and utilize NGH and vigorously develop the gas hydrate technology. In this paper, the research advances in hydrate-based processes in China are comprehensively reviewed from different aspects, mainly including gas separation and purification, hydrate formation inhibition, sea–water desalination and methane exploitation from NGH by CH4–CO2 replacement. We are trying to show the relevant research in China, and at the same time, summarize the characteristics of the research and put forward the corresponding problems in a technical way.

A review: Enhanced recovery of natural gas hydrate reservoirs

Natural gas hydrate (NGH) is a highly efficient and clean energy, with huge reserves and widespread distribution in permafrost and marine areas. Researches all over the world are committed to developing an effective exploring technology for NGH reservoirs. In this paper, four conventional in-situ hydrate production methods, such as depressurization, thermal stimulation, inhibitor injection and CO2 replacement, are briefly introduced. Due to the limitations of each method, there has been no significantly breakthrough in hydrate exploring technology. Inspired by the development of unconventional oil and gas fields, researchers have put forward some new hydrate production methods. We summarize the enhanced hydrate exploiting methods, such as CO2/N2–CH4 replacement, CO2/H2–CH4 replacement, hydraulic fracturing treatment, and solid exploration; and potential hydrate mining techniques, such as self-generating heat fluid injection, geothermal stimulation, the well pattern optimization of hydrate exploring. The importance of reservoir stimulation technology for hydrate exploitation is emphasized, and it is believed that hydrate reservoir modification technology is a key to open hydrate resources exploitation, and the major challenges in the process of hydrate exploitation are pointed out. The combination of multiple hydrate exploring technologies and their complementary advantages will be the development trend in the future so as to promote the process of hydrate industrialization.

Experimental investigation of the behavior of methane gas hydrates during depressurization-assisted CO2 replacement

CO2 replacement with depressurization assistance is a crossover concept that has been proposed in recent years for natural gas hydrate development. It combines the merits of two traditional methods to improve production and reduce risks. To verify the feasibility of this new method and evaluate the corresponding efficiency, experimental apparatus has been designed to simulate the horizontal interface between a CO2 injection well and a CH4 production well based on the independent extraction mechanism and well structure design. To prepare natural gas hydrate-bearing samples under conditions that conform to actual field conditions, silica sand is packed into a core-holding tube with methane gas and distilled water at appropriate pressures and temperatures. Then a horizontal extraction process with an injection well and a production well are simulated, and the parameters influencing the pressure system, such as inlet pressure (pressure of injection well), outlet pressure (pressure of production well), and confining pressure (pressure of the overburden layer), are controlled as variables and analyzed. The ratio of generated methane and injected CO2 is used to evaluate the corresponding utilization efficiency (UE) in this work. Results indicate that all these pressure parameters have certain effects on CO2 replacement behavior. Generally, the fluid flow driven by pressure differences, and the special phase equilibria properties are the essence of their influence. The feasibility of enhancing CO2 utilization efficiency with depressurization assistance is verified based on experimental data. In consideration of time and cost, the relative pressure parameters should be optimized comprehensively to maximize commercial efficiency before field application.

Experimental investigation into gas recovery from CH4-C2H6-C3H8 hydrates by CO2 replacement

The replacement of CH4-C2H6-C3H8 ternary hydrates in sandy sediments by gaseous and liquid CO2 was studied to explore the gas recovery from structure II (sII) gas hydrate reservoirs. It was found that the swapping pattern in sII mixed hydrates is significantly different from that in the pure methane hydrate, which is a structure I (sI) hydrate. CH4, C2H6 and C3H8 can be recovered heterogeneously from the mixed hydrates by CO2 replacement. The results showed CH4 was the easiest to replace in all of the experimental runs. In addition, there was a preferential release of C3H8 over C2H6 with higher mole ratio of CO2 to initial hydrate. The guest-to-cavity size ratio was used to qualitatively study the gas exchange kinetics in the mixed hydrates. It was proposed that the isostructural conversion and structural transition coexisted in the mixed hydrates replacement. The spatial distribution of multiple components in the replaced hydrate particles was obtained by coupling gas production measurements with compositional analysis of the hydrate dissociation. It was found that further hydrate structure-transition from sII to sI occurred in deeper layers of the hydrate particles in replacement with higher mole ratio of CO2 to initial hydrate. A power function relation was found to exist between the replacement efficiency and mole ratio of CO2 to hydrate. These results are of significance for guiding successful sII hydrate recovery and CO2 sequestration.

Natural gas recovery from hydrate compounds using CO2 replacement strategies: experimental study on thermal stimulation.

CH4 hydrates could represent a sustainable energy source by coupling their extraction to a CO2 replacement process. This permits a permanent CO2 storage in a solid phase and the reduction of the seabed modification due to the CH4 extraction. Promising methodologies for CO2 replacement are depressurization, thermal stimulation (or a combination of both), or the use of chemical inhibitors. We have taken into account thermal stimulation. The CH4 hydrates were formed with a pore saturation of 10%, whereas different concentration of gaseous CO2 were fluxed inside the reactor. In a first set of experiments, the CO2 concentration was fixed at values never higher than 15%, while in a second set the gaseous CO2/CH4 ratio was inverted. Two tests for each condition were performed. In all tests, the temperature was increased at the end, to improve the replacement process. Results demonstrated that the CO2 fluxed leads to hydrates formation and, at the same time, hinder the CH4 hydrates dissociation. Two parameters were evaluated: i) the ratio between the stored CO2 and the amount of CO2 injected (ηcapture), ii) the ratio between both CO2 and CH4 hydrates moles after the replacement process, and the CH4 hydrates moles before the replacement (ηentrapped). The assumed ηcapture value are 0.42 and 0.44 in the first conditions, and 0.27 and 0.28 in the second one. By contrast, the second parameter shows an opposite behavior, being the two values 0.13 for the first conditions and 0.27 and 0.74 respectively for the second ones. This could be explained by the fact that injection of higher quantity of CO2 produces a greater thickness of CO2 hydrates in the external parts of pores, which prevent the CH4 to flowing

Structural transition induced by cage-dependent guest exchange in CH4 + C3H8 hydrates with CO2 injection for energy recovery and CO2 sequestration

This study investigated a structural transition induced by cage-dependent guest exchange in the CH4 + C3H8 hydrate with CO2 injection for CH4 recovery and CO2 sequestration. The influence of the CO2 replacement on the crystalline structure of initial CH4 + C3H8 hydrates and the cage-dependent distribution of guest molecules were quantitatively investigated using powder X-ray diffraction, 13C nuclear magnetic resonance spectroscopy, and gas chromatography. The quantitative analyses demonstrated that the CO2 occupation caused the depletion of C3H8 molecules in the large 51264 cages of structure II hydrates, thereby resulting in the subsequent transformation into CO2-rich sI hydrates and the coexistence of structure I and structure II hydrates after the replacement. The guest-exchange behavior observed from time-dependent Raman spectra indicated that the replacement rate was increased with an increase in pressure of injected CO2 and that the extent of the replacement was enhanced at higher pressure of injected CO2. Overall experimental evidence of the partial structural-transition replacement suggests that CO2 molecules first occupied structure II hydrates predominantly with the rapid guest exchange at the surface and that the initial structure II hydrates were subsequently converted to the CO2-rich structure I hydrates from the surface to the inner side. Precise identification of the mechanism responsible for the partial structural transition occurring in the CH4 + C3H8 - CO2 replacement will be very helpful in developing a strategy for actual CO2 injection into structure II gas hydrate reservoirs for energy recovery and CO2 sequestration.

Natural gas hydrate exploitation by CO2/H2 continuous Injection-Production mode

CO2 replacement is considered as a promising method for the simultaneous development of natural gas hydrate and CO2 sequestration. The addition of small molecular gases, such as N2 and H2, into the injected gas can increase the gas recovery ratio and prevent CO2 liquefaction. Based on previous studies, this work presents methane hydrate exploitation using the CO2/H2 continuous injection-production mode. The mechanism combines gas sweep with CH4/CO2 replacement. A series of experiments were carried out to optimize the injected gas composition and flow rate, which have a significant effect on the rate of CH4 hydrate decomposition, amount of CO2 sequestration, and cost. The compositions of the injected gases had little effect on the recovery rate when a relatively higher flow rate was employed. A balance between CH4 production and CO2 sequestration was established when the CO2 mole fraction was slightly <74%, and the temperature of the reservoir did not decline throughout the whole process. The injection rate affected both the displacement efficiency and the production cost. Moreover, through these experiments, we discovered a more economically feasible and productive measure for regulating the injection rate.