Thermal Stimulation Method Research Articles

AI-based composition model for energy utilization efficiency optimization of gas hydrate recovery by combined method of depressurization and thermal stimulation

The combination of depressurization and thermal stimulation is one of the most promising techniques for producing gas from natural gas hydrate reservoirs. The energy utilization efficiency is the core factor that determines whether the technology can be better applied to engineering practice. In contrast to previous works, this paper proposes an AI-based composition model, which realizes the dynamic optimization of the energy utilization efficiency based on the learning and evaluation of different thermal stimulation policies. As shown by the optimization results, the proposed model achieved good performance in both the hydrate recovery target and the economic target coordination by adjusting the coefficients of the optimization control policy function. Based on a systematic assessment of the energy utilization efficiency of different thermal stimulation policies, the model increased the energy production-injection ratio by 4.5 times in Scenario I, and the CH4 recovery efficiency was increased by 1.6 times in Scenario II. The learning results of the AI model also showed that the reactor scale hydrate recovery had a size effect, such that the later the thermal energy injection was, the higher the energy efficiency that could be obtained. Moreover, through the model learning, the quantitative relationship between each thermal stimulation policy and its developmentally changing energy utilization efficiency was established. The results showed that in the initial hydrate recovery period, thermal stimulation policies with a high injection temperature and low injection rate achieved greater energy utilization efficiency. As recovery progressed, gradually lowering the injection temperature and increasing the injection rate gave the policy a higher energy utilization efficiency. The proposed methodology provides a feasible approach for dynamic thermal stimulation parameter optimization and improves the hydrate recovery economy.

THE NEW STIMULATING METHOD IN THE SPEECH THERAPY WORKOUT SYSTEM FOR THE RESTORATION OF THE SWALLOWING FUNCTION IN SEVERE BRAIN INJURIES

Background. The significance of this study becomes more relevant due to the higher incidence and complication of dysphagia in patients with severe brain damage as a result of stroke, traumatic brain injury, and other diseases and injuries. Purpose The study aimed to assess the effectiveness of the new stimulating method - "passive-active logopedic cryomassage" for restoring impaired swallowing function (dysphagia) in patients with severe brain injury, used in the system of speech therapy measures at the early stage of rehabilitation in the neurointensive care unit. Methods. The study involved 96 patients with dysphagia caused by severe brain damage, who received speech therapy assistance aimed at restoring the impaired swallowing function in a system of early rehabilitation measures carried out in a neurorehabilitation department. The severity of dysphagia was evaluated using an integrative assessment of swallowing function scale. Results. The practice of using the new method developed in combination with thermal and tactile stimulation: "passive-active logopedic cryomassage" indicated its higher efficiency in comparison with the traditionally used methods of speech therapy stimulation. In the course of this study, there were three categories of patients: patients with a rapid positive effect, patients with a delayed effect, and patients with no apparent positive effects. There was an analysis of all possible causes of different therapeutic effects. Conclusion. This new method of combined thermal and tactile stimulation - "passive-active logopedic cryomassage" can be recommended with all its indications and contraindications for widespread use in the clinical practice assisting speech therapists in the restoration of impaired swallowing function in patients with severe brain injury

Experimental investigation of using combined CH4/CO2 replacement and thermal stimulation methods for methane production from gas hydrate in the presence of SiO2 and ZnO nanoparticles

A combination of thermal stimulation and CH4/CO2 replacement methods in the presence of nanoparticles was employed to enhance CH4 recovery and CO2 storage for a previously formed CH4 hydrate in a reactor. To this end, first, the effects of different CO2 injection pressures and CO2 hydrate formation temperatures were examined on the replacement process, and the optimum condition was obtained among the studied P-T conditions. In the second stage, silica and zinc oxide nanoparticles were added to the system to explore the influence of the nanomaterials on CH4 recovery and CO2 storage under the optimum conditions. The results indicated that the optimum methane recovery condition was 45 bar and 8 °C. Further, the efficiency of the combined method was enhanced significantly in the presence of nanoparticles. According to the results, the methane recoveries of 37.7% and 51.9% plus the CO2 storages of 54.6% and 68.4% were obtained in the presence of silica and zinc oxide nanoparticles, respectively. This study could be helpful to introduce a new approach for enhancing CH4 recovery from hydrate resources.

New insights into phosphorescence properties of LuAGG: Long afterglow phosphor-in-glass for optical data storage

Newly long afterglow phosphor-in-glass (PiG) plays pivotal roles in the region of optical data storage. By using solid-phase reactions and unique spectrum modulation methods, a color-tunable PiG with decent persistent phosphorescence which can be tuned from green to blue has been fabricated. Lu3Al2Ga3O12: Ce3+, Cr3+ (LuAGG: Ce3+, Cr3+) based on TBZNA glass could emit bright green light signal located at 350 and 420 nm ascribed to the 5d1/5d2-4f transitions when corresponding optical data was being loadout. The doping of Cr3+ increases the density of the trap and provides additional traps between the shallow trap and the deep trap to capture more electrons, further improving afterglow decay time. And the storage time and cyclic reading times are derived by the method of thermal stimulation. Thereinto, tunable emission color has been obtained via changing the concentration of Ga3+, using UV excitation. Moreover, the influence of the Cr3+/Ga3+ on luminescence properties of long-afterglow-PiG materials have been described in detail. Achieved results confirm that it makes LuAGG-PiG as a long afterglow PiG matrix, demonstrating its promising application in optical data storage.

Enhanced Methane Production Efficiency with In Situ Intermittent Heating Assisted CO2 Replacement of Hydrates

Natural gas hydrates attract worldwide attention for extensive reserve. Current exploitation methods of thermal stimulation, depressurization and inhibitor injection consume much energy, inducing f...

Experimental investigation on gas hydrate recovery using temperature separation mechanism of vortex tube

As a type of clean energy, natural gas hydrate production is currently receiving great attention. The main disadvantage of conventional thermal stimulation method is great heat loss during delivering of hot fluid. A novel hydrate recovery technique using the vortex tube temperature separation effect is proposed in this paper. The compressed gas is tangentially injected into the vortex tube to generate hot stream to decompose solid hydrate in site. Experiments were carried out in a large-scale lab reactor (100 L) and the decomposition behavior of both sandy and sand free deposits are investigated. Experimental results show that the temperature near the hot end of vortex tube increase and the resistivity decrease gradually due to hydrate dissolve under the effect of hot tube of the vortex tube. For the sandy reservoir, the production time is 407 min and 415 L gas is recovered. As to the sand free reservoir, the recovery time is 2220 min and 238 L gas is obtained. The self-preservation behavior is observed during the decomposition process of sandy deposit. Compared with conventional heating injection techniques, the present method has the merits of no chemical injection, no moving parts, low heat loss and little maintenance.

Distribution and reformation characteristics of gas hydrate during hydrate dissociation by thermal stimulation and depressurization methods

Pore-scale distribution and reformation characteristics of gas hydrate in porous sediments can provide invaluable information on macroscale production behaviors. In this work, the X-ray computed tomography (X-ray -CT) has been conducted to detect distribution characteristics of the hydrate-bearing sample during hydrate formation and dissociation. Experimental results indicate that, during hydrate formation, mass and heat transfer can lead to the transformation of grain-attaching (grain-cementing and grain-contacting) hydrate to pore-filling hydrate, as well as the heterogeneous distribution of gas hydrate in pores. During hydrate dissociation, whether the thermal stimulation stage or the depressurization stage, the hydrate decomposition initiates from the ablation of the hydrate-gas interface, and the grain-cementing hydrate remains intact until the hydrate cracks into particles and collapses. In addition, during the thermal stimulation stage, the migration of “memory water” under the equilibrium hydrate formation condition leads to the hydrate reformation, and the hydrate reformation promotes the homogeneous distribution of gas hydrate in pores. During the depressurization stage, gas hydrate is reformed below the hydrate “dissociation front” because of the endothermic process of hydrate dissociation and the pressure-driven fluid flow. The reformed grain-cementing hydrate provides fluid flow channels instead of plugging the pores and throats. However, the shut-in time after the depressurization-induced gas production should not be too long to prevent the pore plugging by the further growth of the reformed hydrate. Additionally, the depressurization process finally leads to the grain migration and may reduce the sediment strength under the loose grain filling condition.

A self-similarity transport model of gas desorption inside high maturity shale under thermal enhanced conditions

Thermal stimulation methods have been investigated to enhance gas extraction from the high maturity shale recently. In this paper, a Longmaxi shale core sample, with vitrinite reflectance = 2.8%, was selected for canister tests to investigate the gas desorption process first at 55 °C and then switched to 110 °C. A mathematical model (self-similarity) was proposed to mimic the gas decaying process in nano-sized pore system. Gas adsorption/desorption incorporated advection and Knudsen flow were considered in this model. For high Knudsen number flow, the effective diffusion coefficient of the gas in the model was assumed to be a power law of density gradient. From the experiment, when heating temperature was raised from 55 °C to 110 °C, more adsorbed gas started desorbing to the porous media. It was found that the gas production rate increased significantly (20 times) and the cumulative gas production also raised considerably (11 times). By selecting an appropriate exponent m for effective diffusion coefficient, the gas production rate decayed as 1t at 55 °C and declined as 1t2 at 110 °C, which fit well with experimental data. The scaling results indicated that Knudsen flow was the dominant source of the gas flow in the whole heating process. In conclusion, Knudsen flow is the dominant gas transport form during the heating process. Thermal stimulation can significantly promote gas production rate. Moreover, the developed mathematical model can well predict the gas production rate in the heating process.

Investigation of gas hydrate production with salinity via depressurization and thermal stimulation methods

Natural gas resources trapped in hydrate reserves worldwide are a new substitute for conventional energy. To safely and efficiently extract natural gas from hydrates, fields test and laboratory investigations were systematically conducted. Salinity is a significant factor impacting the exploitation of the marine hydrates. In this study, a two-dimensional cylindrical model was developed to determine the influences of salinity on gas recovery induced by depressurization and thermal stimulation. The results indicated that, with the same exploitation method, higher salinity accelerated the pressure-drop propagation rate and temperature increment spread, thereby promoting the hydrate dissociation rate and shortening the gas production process. Furthermore, thermal stimulation improved the average gas generation rate by almost five times that with depressurization at the same salinity.

Stability and exchange of guest molecules in gas hydrates under the influence of CH4, CO2, N2 and CO2+N2 gases at low-pressures

Gas recovery from the natural gas hydrate (NGH) deposits is a current topic of interest. Apart from the conventional thermal stimulation, depressurisation and chemical injection methods, the guest molecular replacement method in hydrates offers dual advantage such as retention of their structural stability, and as a sink for carbon dioxide (CO2). However, the molecular exchangeability shows significant variance and the mechanism is also incomprehensible. This study is aimed at probing the stability of gas (CH4 & CO2) hydrates in the presence of CO2/CH4, N2 and their mixtures at low-pressure (~1.0 MPa) conditions. The selected experimental conditions help gain insight into the guest-guest exchange. Evaluation of gas pressure during the dissociation process indicates the presence of mixed hydrates. The micro-Raman investigations elucidate the occurrence of mixed hydrate seed crystals, encasing both CH4/CO2 molecules of initial hydrates, and also the molecules from the injected gas. The characteristic signatures of CH4 & CO2 molecules in hydrate systems broadly agree with the literature data, while that of N2 pointedly closer to the gas phase signature, indicating its role as a help-gas to promote replacement/rearrangement of guests in hydrate lattice.

Experiments on the thermally enhanced permeability of tight rocks: A potential thermal stimulation method for Enhanced Geothermal Systems

ABSTRACT Creating a good fracture network in hot dry rocks is the key to the success of an Enhanced Geothermal Systems project. Instead of creating large-scale fractures, the proposed thermal stimulation method has clear advantages by generating small-scale cracks, increasing crack density, and forming fracture networks in tight rocks. Granite samples from a tight formation in Lijin County in China were thermally treated at various temperatures to evaluate the permeability enhancement and the feasibility of thermal stimulation. Scanning electron microscope (SEM) method was also used to investigate the changes in interior structure in granite rocks. The experiments show that the threshold temperature of Lijin granites is around 300°C, the permeability can improve approximately 2 orders and the porosity can increase more than 5 times when heating over 600°C. Both crack length and width increase about 10 folds under the experiment conditions, and the original mineral disappearance and new mineral generation were observed. Thermal cracking under high temperatures plays a key role in permeability and porosity enhancement. Numerical simulation results show that the heated zone is very limited if only heating in a borehole. To expand the affected zone and improve energy recovery, a new thermal stimulation method combining microwave excitation with proppants to heat inside hydraulic fractures is proposed and discussed.

A novel natural gas hydrate recovery approach by delivering geothermal energy through dumpflooding

Conventional thermal stimulation methods require a tremendous investment on in surface heating facilities and a sustained investment in continuous heat injection. Using a heat exchange well to deliver geothermal energy via carbon dioxide or water provides a way to greatly reduce the heat injection cost. However, hydrate bearing layers are often found in harsh natural environments (offshore or continental permafrost), where access to and transportation of heat-delivery media are extremely challenging. Therefore, this paper proposes to boost hydrate recovery with geothermal energy delivered through dumpflooding and a coupled numerical model is built to evaluate the performance of the new method. The results indicate that the hydrate dissociation and gas production are greatly enhanced due to the high temperature of the water flowing from the geothermal reservoir to the hydrate bearing layer; therefore, the feasibility of utilizing the dumpflooding method to exploit hydrate bearing layers is proved. Analyses of influential factors suggest that the pore volumes of hydrothermal reservoirs affect both the rate and temperature of water flowing from the hydrothermal reservoir to the hydrate bearing layer. Higher hydrothermal reservoir temperatures and pressures are favorable for hydrate recovery. Nevertheless, energy efficiency drops as the pore volumes, temperature and pressure of hydrothermal reservoirs increase. The pressure loss caused by friction is negligible compared with that caused by gravity and therefore has nearly no influence on performance.

Gas-Liquid-Solid Migration Characteristics of Gas Hydrate Sediments in Depressurization Combined with Thermal Stimulation Dissociation.

The exploitation of natural gas hydrate is always hindered by the migration of water and sands due to gas production. Depressurization combined with thermal stimulation is an effective method for hydrate dissociation. This paper reported the influence of gas–liquid–solid migration on morphological change of hydrate sediments in natural gas production using visualization method. Different backpressures combined with thermal stimulation methods were applied to simulate natural gas hydrate exploitation. Pressure compensation was first employed to study sediment recovery features. The expansion rate of a porous medium layer under combined dissociation and different backpressure (4.5, 3.5, 2.5, 1.5, and 0.1 MPa) was discussed. A 176% hydrate sediment expansion rate was found after the combined dissociation at 0.1 MPa. In addition, it was observed that the height of the water layer above the porous media after pressure compensation was gradually reduced with a decrease in backpressure and eventually disappeared at 0.1 MPa. It was also found that the disappearing water layer caused an anomalous memory effect phenomenon. Expansion and subsidence of sediments provide a better reference for hydrate exploitation and geological safety.

The dynamic behavior of gas hydrate dissociation by heating in tight sandy reservoirs: A molecular dynamics simulation study

Knowledge on the kinetics of gas hydrate dissociation in microporous sediments is very important for developing safe and efficient approaches to gas recovery from natural gas hydrate (NGH) deposits. Herein, molecular dynamics (MD) simulations are used to study the dissociation kinetics in microporous sediments. The hydrate phase occupies a confined sandy nanopore formed by two hydroxylated silica surfaces with a buffering water layer between the hydrate and silica phase, meanwhile, this system is in contact with the bulk phase outside the pore. The hydrates in this sediment system dissociate layer-by-layer in a shrinking core manner. The released methane molecules aggregate and eventually evolve into nanobubbles, most of which are spherical cap-shaped on the hydroxylated silica surfaces. At high initial temperatures, a faster decomposition of the hydrate phase is observed, however, fewer methane molecules migrate to the bulk phase from the pore phase. These phenomena may occur because more methane molecules are released from the hydrate phase and facilitate the formation of nanobubbles with large heat injection; these nanobubbles can stably adsorb on the surface of silica and capture the surrounding methane molecules, thereby decreasing the number of methane molecules in the water phase. In addition, the injection speed of heat flow should be significantly increased at high dissociation temperatures when using the thermal stimulation method to extract gas from hydrates in tight sediments. This study provides molecular level insight into the kinetic mechanism of hydrate dissociation and theoretical guidance for gas production by thermal injection from sediments with low permeabilities.

Non-destructive testing of light armours of CFRP after ballistic impacts by IR thermography methods

Multi-layered composites are frequently used in many military applications as constructional materials and light armours protecting personnel and armament against fragments and bullets. One of the many methods used in non-destructive testing of composites is active infrared thermography. In active thermography it is necessary to deliver energy to the examined sample in order to obtain significant temperature differences indicating the presence of subsurface anomalies. To detect possible defects in composite materials different methods of thermal stimulation can be applied to the tested material, these include heating lamps, lasers, eddy currents, microwaves or ultrasounds. The use of a suitable source of thermal stimulation on the test material can have a decisive influence on the detection or failure to detect defects. Non-destructive testing was carried out using the following sources of thermal stimulation, heating lamp, flash lamp, ultrasound and eddy currents. The paper presents the possibility of applying IR thermography methods for detecting defects in ballistic covers made of carbon fiber reinforced composites used in the construction of military vehicles.

Effect of temperature on safety and stability of gas hydrate during coal mine gas storage and transportation

Knowledge of the dissociation kinetics of gas hydrate is essential for evaluate the risk of coal mine gas (CMG) during CMG hydrate storage and transportation. In this study, the hydrate dissociation experiment is conducted by using visual hydrate formation and dissociation experimental device for two kinds of CMG samples under four different temperatures. The thermal stimulation method (above the equilibrium temperature) is applied for hydrate dissociation. Based on the experimental data, it is found that the pressure curve during gas hydrate dissociation is mainly composed of three stages, including rapid dissociation, slow dissociation, and stable stages. Temperature has a significant effect on the average dissociation rate for the gas system, where a higher temperature is related to greater average dissociation rate. The maximum average dissociation rate is determined to be 4.34 ∙ 10−3 mol/min (System II-4). The mole number of methane increases obviously with the increase of temperature, while nitrogen and oxygen change slightly. It demonstrates that methane hydrate has higher risk in storage and transportation.

Numerical simulation of simultaneous exploitation of geothermal energy and natural gas hydrates by water injection into a geothermal heat exchange well

A new geothermal energy-assisted natural gas hydrate recovery method (GEAN) that can simultaneously exploit geothermal energy and natural gas hydrates (NGHs) by injecting water into a geothermal heat exchange well was proposed in this paper. GEAN involves no hydraulic fracturing in the geothermal reservoir and, thus, avoids the fracturing cost and decreases the damage to the geothermal reservoir. Moreover, compared with conventional thermal stimulation methods, no surface fluid heating is required. Thus, GEAN produces less carbon emissions and is more environmentally friendly. A numerical simulation model was then built to investigate the heat mining rate, the along-well water temperature, and the development performance of the hydrate-bearing layer (HBL). Finally, factors that affect the heat exchange performance were analyzed. With a geothermal reservoir temperature of 135 °C and an 1800-m-long horizontal wellbore through the geothermal reservoir, it was found that the injected water, which originally had an ambient temperature of 20 °C, returns to the HBL with a temperature of up to 89.4 °C after being heated by the geothermal heat exchange well. Moreover, the heat mining rate is over 0.3 MW throughout the production process. Therefore, the feasibility of using geothermal energy to recover NGHs by the GEAN method was proven. Compared with the depressurization method, GEAN achieved an increment cumulative gas production of 63.9%. The HBL candidate with a higher geothermal gradient is preferred due to the corresponding higher temperature of the geothermal reservoir and better heat exchange performance. The optimal water injection rate and horizontal wellbore length in the geothermal reservoir are 150 m3/d and 1800 m, respectively. Performances of the heat exchange well and HBLs could be more effectively improved by properly raising the insulation level.

Dissociation characteristics of methane hydrate using depressurization combined with thermal stimulation

Methane hydrate is considered as a potential energy source in the future due to its abundant reserves and high energy density. To investigate the influence of initial hydrate saturation, production pressure, and the temperature of thermal stimulation on gas production rate and cumulative gas production percentage, we conducted the methane hydrate dissociation experiments using depressurization, thermal stimulation and a combination of two methods in this study. It is found that when the gas production pressures are the same, the higher the hydrate initial saturation, the greater change in hydrate reservoir temperature. Therefore, it is easier to appear the phenomenon of icing and hydrate reformation when the hydrate saturation is higher. For example, the reservoir temperature dropped to below zero in depressurization process when the hydrate saturation was about 37%. However, the same phenomenon didn't appear as the saturation was about 12%. This may be due to more free gas in the reservoir with hydrate saturated of 37%. We also find that the temperature variation of reservoir can be reduced effectively by combination of depressurization and thermal stimulation method. And the average gas production rate is highest with combined method in the experiments. When the pressure of gas production is 2 MPa, compared with depressurization, the average of gas production can increase 54% when the combined method is used. The efficiency of gas production is very low when thermal stimulation was used alone. When the temperature of thermal stimulation is 11 °C, the average rate of gas production in the experiment of thermal stimulation is less than 1/3 of that in the experiment of the combined method.

Overview of Gas Hydrates as a Future Energy Source and Their Physical/Chemical Properties

This paper reviews the structures, physical and chemical properties, origins and global distribution, amount of energy resources, production technologies, and environmental impacts of gas hydrates to understand the gas hydrates as future energy sources. Hydrate structures should be studied to clarify the fundamentals of natural gas hydrates, hydrate distributions, and amount of energy sources in hydrates. Phase equilibria, dissociation enthalpy, thermal conductivity, specific heat, thermal diffusivity, and fluid permeability of gas hydrate systems are important parameters for the the efficient recovery of natural gas from hydrate reservoirs. Depressurization, thermal stimulation, inhibitor injection, and chemical exchange methods can be considered as future technologies to recover the energy sources from natural gas hydrates, but so far depressurization is the only method to have been applied in test productions of both onshore and offshore hydrates. Finally, we discuss the hypotheses of environmental impacts of gas hydrates and their contribution to global warming due to hydrate dissociation.

Investigation on the Benefits of Steam Adsorption and Distribution during Cyclic Steam Injection to Improve Oil Recovery - FNE Case Study, Sudan

One of the main types of Enhanced Oil Recovery (EOR) methods is thermal stimulation method which is an increasingly common method of extracting heavy oil. there are different forms of the technology of thermal method Cyclic steam stimulation, Steam flooding and In-situ combustion “Fire flooding” are commonly applied to oil reservoirs, which are relatively shallow very viscous oil at the reservoir temperature, the most widely used steam injection methods for heavy oil recovery is Cyclic Steam Stimulation “steam soak or huff and puff” method. Most of commingle thermal wells has a problem in steam intensity distribution among the layers, which will lead to inconsistency in steam adsorption and some layers would adsorb more than double of the designed steam injected volume. This phenomenon will lead to low productivity and negatively impact the distribution of water cut in the different layers. Steam adsorption and distribution represent one of the main challenges of heavy oil production from Sudanese oil fields, very limited studies have been conducted in this field in Sudan oil fields, and this study is focused on addressing this challenge to maximize recover factor from each well and each field. In this paper the challenge facing Bentiu reservoir in Fula North East (FNE) located in heavy oil zone with target of production around 85% of the total reserves will be highlighted. The field has shallow depth ranging between 520m and 700m and low pressure gradient 1.09 psi/m, and with reservoir temperature around 44 o C. The study covers an investigation on the benefits of steam adsorption to enhance the oil recovery focusing on the distribution of the steam inside the layers, also cover the analyzing and reviewing the actual steam intensity distribution among each layer in the two wells that are later compared with the designed ones. In a later stage, we designed a pilot model that has been designed using advanced thermal EOR Simulator to understand the effect of commingle injection and production (Steam adsorption and distribution) using data from single layers. An optimum steam injection protocol that will maximize the recovery factor from these oil zones has been designed and the results show that the injection rate has significant effect in steam distribution. Keywords: Cyclic Steam Stimulation, Enhanced Oil Recovery (EOR), Steam-Assisted Gravity Drainage (SAGD), Hot water flooding and In situ combustion,