Gas Injection Experiments Research Articles

MHD simulations of cold bubble formation from 2/1 tearing mode during massive gas injection in a tokamak

Massive gas injection (MGI) experiments have been carried out in many tokamaks to study disruption dynamics and mitigation schemes. Two events often observed in those experiments are the excitation of the m = 2, n = 1 magnetohydrodynamic mode, and the formation of cold bubble structure in the temperature distribution before the thermal quench (TQ). Here m is the poloidal mode number, n the toroidal mode number. The physics mechanisms underlying those phenomena, however, have not been entirely clear. In this work, our recent NIMROD simulations of the MGI process in a tokamak have reproduced the main features of both events, which has allowed us to examine and establish the causal relation between them. In these simulations, the 3/1 and 2/1 islands are found to form successively after the arrival of impurity ion cold front at the corresponding q = 3 and q = 2 rational surfaces. At the interface between impurity and plasma, a local thin current sheet forms due to an enhanced local pressure gradient and moves inward following the gas cold front, this may contribute to the formation of a dominant 2/1 mode. Following the growth of the 2/1 tearing mode, the impurity penetration into the core region inside the q = 2 surface gives rise to the formation of the cold bubble temperature structure and initiates the final TQ. A subdominant 1/1 mode developed earlier near the q = 1 surface alone does not cause such a cold bubble formation, however, the exact manner of the preceding impurity penetration depends on the nature of the 1/1 mode: kink-tearing or quasi-interchange.

Relative permeability measurement of coal microchannels using advanced microchip technology

The gas–water flow in coal cleats is an important factor affecting coalbed methane production. However, difficulties are often encountered in the prediction of gas production. Limited understanding of two-phase flow behaviour in microchannels reduces prediction accuracy, often leading to overestimation. In this study, based on micro-computed tomography, advanced microchip technology is used to predict the optimal coal cleat in the polydimethylsiloxane chip. Gas and liquid injection experiments are carried out on the microchannels through the syringe pumps, as the two-phase flow morphology in the system can obtain flow information that cannot be provided by conventional laboratory measurements. The flow capacities of single-phase gas, water, and wetting liquid in the microchannels are compared, alongside determining the flow laws under different wettability and flow rates. The results show that in the single-phase fluid injection experiment, gas is more sensitive to the microchannel size effect than the liquid phase, and hydrophilic liquids flow readily. The gas–water relative permeability value in this study is significantly smaller than that obtained from conventional experiments, based on the steady-state method. This is a result of the gas–water forming a discontinuous plug flow in the microchannel, which produces higher resistance and reduces flow capacity. The occurrence of discontinuous flow regimes challenges the laminar flow assumption adopted in the steady-state method and suggests that conventional laboratory measurements of relative permeability measurements may misrepresent the physics of fluid flows in microchannels. The results also reveal that a hydrophilic environment and a suitable flow rate can increase the two-phase relative permeability. The results of this study enhance our understanding of and approach to core flooding measurement, with the differences in the relative permeability curves indicating that data uncertainty associated with the steady-state method is worthy of further research.

Non‐isothermal gas‐assisted displacement of viscous Newtonian fluids at high capillary number in gas‐assisted injection molding

AbstractGas‐assisted injection molding is a polymer processing technology in which a penetrating gas bubble hollows out a plastic part as it cools and solidifies within a mold. In this study, non‐isothermal gas injection experiments at high capillary number illustrate the effects of delay time in gas injection, tube diameter, capillary number, and temperature‐sensitive fluid viscosity and flow activation energy on coating thickness. Experiments with polybutene H‐300 and Dow Corning silicon oil (DC‐200) in stainless steel tubing (1.27 and 0.635 cm) demonstrated fractional coverage increasing from 0.6 to a maximum in the range of 0.63–0.83 at short delay times, then decaying toward 0.6 at long delay times upon approaching the cooled isothermal state. Further analysis is drawn from simulations based on a simple theoretical model incorporating one‐dimensional heat transfer with convection at the outer surface of the mold, non‐isothermal behavior of the viscous fluid, and radial velocity profiles in the one‐phase fluid flow region. Quantitative agreement is found between experimental and simulated results. Two‐dimensional modeling and simulation methods extend the prior results to illustrate transient axial and radial heat transfer as well as flow behavior with respect to the penetrating gas bubble within the fluid flow region.

Effects of gas injection combined with wettability alteration on boundary water inrush

The inrush of boundary water can aggravate water blockage during the middle-late-aquifer influx period, which is frequently encountered in various gas reservoirs. This study attempts to use gas injection combined with wettability alteration to address this problem. Gas injection experiments were conducted using a visual flow cell with and without wettability alteration, considering both continuous and temporary gas injection. Intercepting the boundary water, as a core characteristic of gas injection, was investigated. The results showed that the relative hydraulic conductivity was reduced to approximately 0.1 by combining continuous gas injection with wettability alteration to gas-wet, indicating that this method can potentially be applied in gas reservoirs with large hydraulic gradients. In addition, the flow path of the gas is smoother and shorter in the porous medium with wettability alteration, and the desaturated zone presents a conical development at different gas flow rates. After temporary gas injection in a porous medium with wettability alteration, the relative hydraulic conductivity can be reduced to less than 0.4 due to the internal trapped gas. Hence, temporary gas injection combined with wettability alteration can be applied when the hydraulic gradient is small. It is hoped that these results can provide new insights for addressing the boundary water inrush.

Experimental investigation of CO2 in continuous and water alternating gas injection

CO2 injection and water-alternating-gas injection are EOR methods for improving oil recovery. This paper shows Water alternating gas (WAG) and continuous gas injection experiments with CO2 in secondary recovery. Experiments were performed in sand-packed-model. The continuous gas injection experiments were conducted at 3800, 4200, 4600 and 5000 psi, then two WAG experiments was completed at 3800 psi. Also temperature was 190 °F (the reservoir temperature) in all experiments. Six tests were conducted to investigate continuous CO2 and WAG injection under the reservoir condition. In the first test, 1.2 PV (pore volume) of CO2 was injected into sand-packed-model at pressure of 3800 psi and temperature of 190 °F. Amount 1.2 PV of CO2 was injected into sand-packed-model at 4200 psi in the test 2. In third one, 1.2 PV of CO2 was injected at 4600 psi and 1.2 of PV CO2 was injected at 5000 psi in forth one. Water alternating gas injection experiments with CO2 were including two tests. In the first one, 0.3 PV of CO2 and 0.9 PV of brine were injected consecutively into model. In the second one, 0.3 PV of CO2 and 0.3 PV of brine were injected respectively into model and this test was completed in two cycles. The results indicate that increase of injection pressure enhances oil recovery in continuous CO2 injection and increase of injected CO2 increases oil recovery in WAG process. Also WAG injection increases oil recovery more than CO2 continuous injection.

Enhanced Oil Recovery in the Wolfcamp Shale by Carbon Dioxide or Nitrogen Injection: An Experimental Investigation

SummaryWe present a comprehensive investigation of gas injection for enhanced oil recovery (EOR) in organic-rich shale using 11 coreflooding experiments in sidewall core plugs from the Wolfcamp Shale, and three additional coreflooding experiments using Berea Sandstone. Our work studies the effect of pressure, minimum miscibility pressure (MMP), soak time, injection-gas composition, and rock-transport properties on oil-recovery factor. The injection gases were carbon dioxide (CO2) and nitrogen. The core plugs were resaturated with crude oil in the laboratory, and the experiments were performed at reservoir pressure and temperature using a design that closely replicates gas injection through a hydraulic fracture, minimizes convective flow, and exaggerates the fracture to the reservoir-rock ratio. We accomplished this by surrounding the Wolfcamp reservoir-rock matrix with glass beads. Computed-tomography (CT) scanning enabled the visualization of the compositional changes with time and space during the gas-injection experiments and gas chromatography provided the overall change in composition between the crude oil injected and the oil recovered.As gas surrounds the oil-saturated sample, a peripheral, slow-kinetics vaporization/condensation process is the main production mechanism. Gas flows preferentially through the proppant because of its high permeability, avoiding the formation and displacement of a miscible front along the rock matrix to mobilize the oil. Instead, the gas surrounding the reservoir-core sample vaporizes the light and intermediate components from the crude oil, making recovery a function of the fraction of oil that can be vaporized into the volume of gas in the fracture at the prevailing thermodynamic conditions. The mass transfer between the injected gas and the crude oil is sufficiently fast to result in significant oil production during the first 24 hours, but slow enough to cause the formation of a compositional gradient within the matrix that exists even 6 days after injection has started. The peripheral and the slow-kinetics aspects of the recovery mechanism are a consequence of the low fluid-transport capacity associated with the organic-rich shale that is saturated with liquid hydrocarbons.Our results show CO2 overperforms nitrogen as an EOR injection gas in organic-rich shale, and higher injection pressure leads to higher oil recovery, even beyond the MMP. The gas-injection scheme should allow enough time for the mass transfer to occur between the injected gas and the crude oil; we achieved this in the laboratory with a huff ’n’ puff scheme. Our results advance the understanding of gas injection for EOR in organic-rich shale in a laboratory scale, but additional work is required to rigorously scale up these observations to better design field applications.

Flume Experiment Evaluation of Resistivity Probes as a New Tool for Monitoring Gas Migration in Multilayered Sediments

Gas leakage can cause serious safety risks to offshore engineering facilities and offshore engineering projects. Monitoring the migration of gas in sediments is of great significance to the safety of marine engineering. In this study, we analysed the ability of ring-electrode resistivity probes (REPs) and circular point-electrode resistivity probes (CPEPs) to monitor the migration, accumulation, and release of gas in multilayered sediments (when the particle size of the overlying soil is smaller) using two groups of gas injection experiments with different gas injection pressures. In addition, the ability of REPs to monitor lateral gas migration was analysed by numerical simulations. The experimental results show that the two probes have different monitoring capabilities for different gas migration stages in multilayered sediments. REPs can effectively reflect the different stages of gas migration within the monitoring range according to the variation characteristics of the monitoring results, and they can effectively monitor the pattern, direction, and rate of gas migration. CPEPs are more sensitive, that is, the range of their monitoring results is about 10 times that of the REPs. They can accurately estimate the changes in the gas saturation of the soil around the probe.

Disruption mitigation efficiency and scaling with thermal energy fraction on ASDEX Upgrade

Disruption mitigation remains a critical and unresolved issue for ITER. Measurement uncertainties preventing quantification of a system’s efficacy remains a significant hurdle in producing and validating a viable disruption mitigation system. This study addresses this issue through the creation of a dataset on the ASDEX Upgrade tokamak targeted at developing analysis techniques to quantify mitigation that are applicable irrespective of the disruption mitigation system being studied. These experiments used a range of thermal energy fractions to address concerns for ITER from JET massive gas injection (MGI) experiments showing a decrease in efficacy with increasing thermal energy fraction. The dataset produced in this study used MGI valves in two toroidal locations. The high resolution foil bolometers and AXUV diode arrays were used to infer radiation emission profiles at varying toroidal distances from the injection location. The fueling efficiency of the two systems was found to be comparable and toroidal asymmetries over the entire disruption were found to be negligible. The AXUV diodes were cross-calibrated with the foil bolometers and used to estimate the thermal energy radiated and magnetic energy coupled to the vessel structure and coils. It was estimated that 75–95% of the thermal energy was radiated and an almost constant 60% of the total magnetic energy was coupled. Radiated energy fractions of 0.8–1.0 were calculated and no decrease as a function of thermal energy fraction was found. A ± 20% variation in the coupled magnetic energy was explored and it did not alter this trend.

CFD simulation of ozone gas flow for controlling Sitophilus zeamais in rice grains

Ozone gas (O3) is a prominent alternative for the integrated pest management of stored products. The present study fitted a computational fluid dynamics (CFD) model to elucidate the ozone gas flow dynamics in an aeration system, at a lethal concentration for Sitophilus zeamais Mots in rice grains. First, an experiment was carried out to understand the flow of ozone gas (2.2 mg L−1; 2 L min−1) in a cylindrical PVC column filled with 4 kg of rice grains. The ozone gas concentration was monitored every 12 h, at a point immediately above the grains. The gas flow was modeled using the CFD technique. The parameters used to feed the model and adjust it to the experimental data were the mass transfer coefficient and ozone-rice grain reaction constant. Then, a simulation of ozone gas injection in a silo with a static capacity of 69.6 tons of rice was performed. In the ozone gas injection experiment, 100% of insect mortality was observed on the sixth day, when the O3 concentration reached 0.1 mg L−1. In this case, the mass transfer coefficient was 0.55 m s−1, and the reaction constant was 0.78 s−1. At the concentration of 0.8 mg L−1, it is possible to treat 69.6 tons of rice grains within 9 days.

Quantitative characterisation of gas loss and numerical simulations of underground gas storage based on gas displacement experiments performed with systems of small-core devices connected in series

In this study, an experimental system in which small core devices with different configurations are connected in series was designed, and high-intensity gas injection and production experiments (3 groups, 28 times) were conducted to quantify the per-cycle gas loss (difference between the amounts of injected and produced gas). These experiments reveal that the lost gas fraction is positively correlated with the porosity and permeability of sandstone but negatively related to the number of injection-production cycles. Based on the experimental results, a three-dimensional gas–water two-phase numerical simulation model for high-intensity injection and production of underground gas was established, and a numerical simulation study (10 injection-production cycles) was performed to clarify the macroscopic migration law of gas and water during injection-production. The simulation results show that the gas could cross the gas–water contact (GWC) into the lower water area at approximately 350 m in the injection phase, while the water intrudes into the gas area at approximately 150 m along the high-permeability channel in the production process. Owing to the complex interaction between the gas and water, a large amount of the lost gas that cannot be produced accumulates in the transition zone generated by the reciprocating motion of the gas and water. A certain amount of the lost gas is produced in every cycle; however, the lost gas fraction will decrease with an increasing number of injection and production cycles (a single cycle yields a reduction of more than 10%) and eventually stabilise at approximately 5%. Finally, based on our results, some suggestions were provided for avoiding gas loss while building underground gas storage systems.

An Experimental Study on Bubble Growth in Laponite RD as Thixotropic Yield Material.

The growth and release of the leading major bubble at the tip of a needle in the thixotropic yield material Laponite RD was different from subsequent minor bubbles. The gas injection experiments combined with high-speed camera were conducted. The results showed that the shape of the major bubbles transformed from an inverted carrot shape to an inverted teardrop shape, while the shape of the minor bubbles tended to be elliptical. In addition, the pressure of bubble emergence consisted of hydrostatic pressure, capillary pressure, and cracking pressure. The major and minor bubbles differed only in the cracking pressure. The pressure when the minor bubble detached could be estimated from the lateral hydrostatic pressure. It can be deduced from dimensionless numbers that buoyancy and viscous forces were, respectively, the main driving force and resistance of bubble growth. The yield stress of Laponite RD and inertial force at the initial moment resulted in distinctive behavior of the major bubble. In addition to the viscosity resistance, surface tension, and hydrostatic pressure had a non-negligible influence on minor bubbles and still accounted for 10–20% of the total resistance in the later stage but less than 5% in major bubble growth.

Laboratory investigation of cyclic gas injection using CO2/N2 mixture to enhance heavy oil recovery in a pressure-depleted reservoir

CO2 has strong abilities of oil swelling and viscosity reduction for heavy oil extraction, N2 is a preferable gas media for pressure maintenance, and their mixture is then considered as an alternative method for enhanced oil recovery (EOR) in a pressure-depleted heavy oil reservoir. PVT analysis and cyclic gas injection experiments are conducted to reveal EOR mechanisms for CO2/N2 mixture, and five different CO2/N2 molar ratios (1:0 (pure CO2), 4:1, 7:3, 1:1, and 0:1 (pure N2)) are designed in this paper. PVT analysis shows that the changes of oil properties including saturation pressure, volume factor, and viscosity are highly related to CO2/N2 ratio of the mixture, and a higher CO2/N2 ratio can always lead to better gas/oil interactions. When CO2/N2 ratio is higher than 7:3, the viscosity can reduce to less than 60% of the initial oil viscosity. Gas injection experimental results show that 4:1 mixture can achieve an oil recovery of 17.31%, which is close to the recovery obtained by pure CO2. For the pressure-depleted oil reservoir, simultaneous CO2/N2 injection or N2 followed by CO2 injection is suitable injection mode for the mixture. With such a design of CO2/N2 mixture, an optimized EOR effect can be achieved with gas/oil interactions dominated by CO2 coupled with energy supplement provided by N2. A pilot test of CO2/N2 mixture injection is successfully conducted in a test well, and an oil increment of 337 t is obtained after 40,000 m3 of N2 injection followed by 80,000 m3 of CO2 injection.

Signal processing method based on energy ratio for detecting leakage of SG using EVFM

In the sodium-cooled fast reactor, the steam generator is a heat exchange device between sodium and water, which may cause leakage, resulting in a sodium-water reaction accident, which in turn affects the safe operation of the entire nuclear reactor. To this end, the electromagnetic vortex flowmeter is used to detect leakage of the steam generator and its signal processing method is studied in this paper. The hydraulic experiment was carried out by using water instead of liquid sodium, and the sensor output signal of the electromagnetic vortex flowmeter under different gas injection volumes was collected. The bubble noise signal is reflected by the base line of the sensor output signal. According to the relationship between the proportion of the bubble noise signal in the sensor output signal and the gas injection volume, a signal processing method based on the energy ratio calculation is proposed to detect whether the water contains bubbles. The gas injection experiment of liquid sodium was conducted to verify the effectiveness of the signal processing method in the detection of bubbles in sodium, and the minimum detectable leak rate of water in the steam generator was detected to be 0.2 g/s.

Non-linear magnetohydrodynamic simulations of pellet triggered edge-localized modes in JET

Non-linear magnetohydrodynamic simulations of pellet-triggered edge-localized modes (ELMs) in JET plasma have been carried out with the JOREK code. The pellet particle fuelling efficiency and the power flux at the divertor target during the pellet-triggered ELM have been studied. The pellet injection in unstable plasma delivers the particle fuelling but the pellet fuelling rate is smaller than the rate of particle loss during the pellet triggered ELM. The JOREK simulations estimate the power flux at the divertor target and found good agreement with the experimental observation. The energy deposition of the pellet triggered ELM shows a toroidally asymmetric profile. However, and due to this toroidal asymmetry, this effect cannot be captured by the existing layout of the divertor infra-red (IR) cameras available in JET. This work highlights the benefit of having a larger number of IR cameras to analyse the heat flux for the experiments which are assumed to be toroidally asymmetric, such as the pellet and/or gas injection experiments.

A Model Experiment of Fracture Induced Long‐Period Events: Injection of Pressurized Gas Into a Viscoelastic Rock Analog

AbstractLow‐frequency events observed in volcanic areas preceding phreatic or phreatomagmatic eruptions may be excited by the injection of pressurized gas into damaged/heated rocks or solidifying magmas. To simulate this process, we conducted a series of gas injection experiments in gels as an analog of such soft rocks. When we inject the pressurized air into a quasi‐Maxwell fluid with higher and lower shear moduli, cracks or a slug appears, respectively. The crack propagation velocity consists of the shear wave velocity of the gel. At the beginning of the crack generation, multiple cracks emerge, causing pulse‐like low‐frequency signals. In contrast, the slug grows faster than the shear wave velocity and excites high‐frequency oscillation. These results show the possibility that the low‐frequency seismicity observed in volcanic regions is the result of not only the resonance of a crack but also the crack propagation in soft rocks.

Floor noise based bubble detection method in sodium using EVFM

The steam generator is a heat exchange device between sodium coolant and water in the sodium-cooled fast reactors. Its transfer tubes are prone to leakage to result in sodium-water reaction, which will affect the operational safety of the entire nuclear reactor. To this end, a signal processing method is studied to detect the steam generator leakage using electromagnetic vortex flowmeter (EVFM). An EVFM is designed for measuring water flow to perform hydraulic experiments to collect the output signals of EVFM sensor under different gas injection volumes. The characteristics of the collected signals are analyzed in the frequency domain, and the floor noise based signal processing method is proposed and realized with a DSP-based hardware system in real time. The gas injection experiments in sodium are conducted to verify the effectiveness of the proposed signal processing method and developed system. The experimental results show that the EVFM with the floor noise based signal processing method can detect the minimum water leak rate in the steam generator as low as 0.1 g/s.

Study on Characteristics of Airflow Spatial Distribution in Abandoned Mine Gob and Its Application in Methane Drainage

At present, there are many known sources of methane resources in abandoned mine gobs. Therefore, investigations into the characteristics of airflow spatial distributions in abandoned mine gobs will be helpful in future methane drainage processes. In this study, a physical simulation experiment was first adopted to simulate the formation processes of abandoned gobs based on the geological conditions of the abandoned Yongan Mine in China. Gas injection experiments were then conducted to study the gas concentration distributions and variations in a simulated gob based on the measured gas concentrations at certain sampling points. The results indicate that the abandoned gob comprises a gas enrichment zone (GEZ), gas diversion zone (GDZ), and gas isolation zone (GIZ) from the bottom to the top in the incline edges of the abandoned gob, respectively. However, only the GEZ and GIZ exist in the incline center of the abandoned gob. The gas concentration in the GEZ is observed to be the highest, although the concentration is also found to be relatively high in the GDZ. Moreover, a shielding is found to exist between the boundaries of the GEZ and GDZ, which results in a dramatic decline in concentration in the latter due to its extremely low permeability. The study results were verified by using the methane drainage data from the surface vertical wells in the abandoned Yongan Mine. The field application indicated that the methane extraction flow rate could potentially increase by 1.5 times when the well bottom traversed the GDZ and entered the GEZ, compared to the flow rate when the well bottom was located in the GDZ.

Peak-to-peak standard deviation based bubble detection method in sodium flow with electromagnetic vortex flowmeter.

The steam generator (SG) is a heat exchange device between a sodium coolant and water in sodium-cooled fast reactors. Its transfer tubes are prone to leakage to result in sodium-water reaction, which will affect the operational safety of the entire nuclear reactor. To this end, a signal processing method is studied to detect the SG leakage using an electromagnetic vortex flowmeter (EVFM). Water flow is firstly used to replace liquid sodium for conducting the hydraulic experiments, and the output signal of the sensor of the EVFM (abbreviated as EVFM sensor output signal) is collected under different gas injection volumes. The characteristics of the signal are analyzed in the time domain, and the collected signals are modeled. A signal processing method of bubble detection in liquid sodium is proposed based on the peak-to-peak standard deviation, which is realized in real time on the hardware system based on a digital signal processor. The gas injection experiments in liquid sodium are conducted to verify the effectiveness of the signal processing method and system developed in this paper. The minimum amount leakage of water can be detected as 0.1 g/s.

Experimental Study on EOR Performance of Natural Gas Injection in Tight Oil Reservoirs

Gas injection is an effective enhanced oil recovery method in tight oil reservoirs. In the case of tight oil fields with sufficient natural gas supply, natural gas injection can significantly reduce the cost of operation, leading economic benefit. Natural gas flooding might be a promising EOR method for tight oil development. Based on the material and reservoir condition of a tight formation in Changqing Oilfield, this study conducted a series of natural gas injection experiments to evaluate the feasibility of natural gas injection after water flooding and analysed the influence of gas injection rate to EOR performance. Experiment results shows that natural gas injection can recover 20.8% more oil after water flooding. Sensitivity analyses indicates that natural gas injection had a higher oil recovery with low injection rate.

Experimental and numerical simulation of gas bubbles motion in liquid metal

Motion and heat transfer of bubbles with liquid metal have been investigated in the present paper. Theoretical studies have been provided with help of modern numerical approaches and the HYDRA-IBRAE/LM code to simulate two-phase flows. Two-fluid model has been used in the presented code to calculate thermal hydraulic processes into two-phase liquid metal coolant. To close two-fluid model, the system of constitutive relation has been used. The brief description some of the constitutive relations has been presented in the current paper. For example, some features of the wall friction coefficient calculation have been discussed. Gas injection experiments and experimental investigations of the bubbles motion and heat transfer have been provided on a liquid metal test facility. Obtained results can help to receive new information about two-phase liquid metal flows. On the base of this information a validation of numerical codes, which are already have an industrial application, can be carried out.