Gas Layer Research Articles

Reservoir Fluid Identification Based on Bayesian-Optimized SVM Model

Tight sandstone reservoirs are characterized by fine-grained rock particles, a high clay content, and a complex interplay between the electrical properties and gas content. These factors contribute to low-contrast reservoirs, where the logging responses of the gas and water layers are similar, resulting in traditional logging interpretation charts exhibiting a low accuracy in the fluid-type classification. This inadequacy fails to meet the fluid identification needs of the study area’s reservoirs and severely restricts the exploration and development of unconventional oil and gas resources. To address this challenge, this study proposes a fluid identification method based on Bayesian-optimized Support Vector Machine (SVM) to enhance the accuracy and efficiency of the fluid identification in low-contrast reservoirs. Firstly, through a sensitivity analysis of the logging responses, sensitive logging parameters such as the natural gamma, compensated density, compensated neutron, and compensated sonic logs are selected as input data for the model. Subsequently, Bayesian optimization is employed to automatically search for the optimal combination of hyperparameters for the SVM model. Finally, an SVM model is established using the optimized hyperparameters to classify and identify the following four fluid types: water layers, gas layers, gas–water layers, and dry layers. The proposed method is applied to fluid identification in the study area, and comparative experiments are conducted with the K-Nearest Neighbor (KNN), Random Forest (RF), and AdaBoost models. The classification performance of each model is systematically evaluated using metrics such as the accuracy, recall, and F1-score. The experimental results indicate that the SVM model outperforms the other models in fluid identification, achieving an average accuracy of 91.41%. This represents improvements of 16.94%, 4.39%, and 8.30% over the KNN, RF, and AdaBoost models, respectively. These findings validate the superiority of the SVM model for fluid identification in the study area and provide an efficient and feasible solution for fluid identification in tight sandstone reservoirs.

Enrichment Mechanism of Helium in the Jiaoshiba Shale Gas Field, Sichuan Basin, SW China

ABSTRACTIn Sichuan Basin, uranium (U) and thorium (Th) are more abundant in organic‐rich shale than in granitic rocks, suggesting that organic‐rich shale is a significant source rock for helium (He). However, the He generation potential of organic‐rich shale and He enrichment mechanisms in shale gas fields remain limited in understanding. Based on the He, U and Th concentration tests, fluid inclusion analysis in the Jiaoshiba shale gas field, it was found that the He concentrations in shale gas is 340–730 ppm. The helium‐rich shale gas (≥ 500 ppm) was primarily found in synclinal units. The biggest helium abundance area (0.27 m3/m2) is located at the core of the Jiaoshiba anticline. The He is not solely derived from Wufeng–Longmaxi shale itself, for the current helium abundance (0.15–0.27 m3/m2) exceeds its historical He generation intensity (0.063–0.104 m3/m2) calculated by the U and Th concentration of the shale. Low‐angle deep faults are more favourable for He capture than high‐angle deep faults. The generation intensity of hydrocarbon is 21,851–29,224 times greater than He, which indicates that the dilution of hydrocarbon to He in organic‐rich shale is more significantly than in common source rocks (3000 times). The He enrichment model in the study area includes three stages: continuous burial, fold‐dominated, and fault‐dominated stages. In the anticline zone, He is continuously accumulated as carrier gas migration. In the syncline zone, He is mainly accumulated as the migration of carrier gas along faults and the water flows the aquifer, at the fault‐dominated stage. He‐rich gas is preferentially accumulated in shallow gas reservoirs associated with deep faults, and the shale gas layers in synclinal zones adjacent to low‐angle deep faults.

Quantifying the Volume of Residual Air in Commercial Intravenous Fluids and Assessing the Stability of Airless Intravenous Fluid Containers.

Commercial off-the-shelf (COTS) intravenous fluid (IVF) containers contain residual air, introducing the risk of venous air embolism (VAE). Venous air embolism occurs when air displaces blood flow in vasculature. The danger from residual air is often negligible in terrestrial settings, where gravitational forces generate buoyancy, pushing residual air to the top of the IVF container. However, in microgravity there is no buoyancy to separate liquid and gas layers. We performed experiments to quantify the amount of air in COTS IVF containers (Experiment 1) and identify the variables that affect the stability of sterilely produced airless containers (Experiment 2). Experiment 1: Residual air was quantified across varying volumes (100, 250, 500, and 1,000 mL), container design, and manufacturer (B. Braun, Baxter, ICU Medical, and Grifols) of 0.9% NaCl COTS IVFs. Each container was assessed for absolute volumes of air, as well as air:fluid ratios normalized to 1,000 mL. Experiment 2: 1,000 mL IVF containers from 3 manufacturers were filled with either (1) 100% saline or (2) 95% saline and 5% air by volume. Containers were stored for 168 days at 25°C or 40 °C. The containers were optically imaged to quantify the accumulation of air within each IVF container. Experiment 1: There was a trend toward larger container sizes and greater absolute volumes of residual air (R2 = 0.964). However, the smallest air:volume ratio occurred in the Baxter 500 mL VIAFLO Container (18.9 ± 3.8 mL air; 2.3% air by volume), whereas the largest ratio occurred in the B. Braun 250 mL EXCEL Container (55.0 ± 9.3 mL; 22.0% air by volume). Experiment 2: By day 168, 6 experimental containers had ruptured and 100% of the surviving containers (30/36) had an increase in air as compared to baseline. Containers placed at 40 °C had a larger increase in air (27.7 ± 6.6 mL) compared to containers stored at 25 °C (7.5 ± 4.1 mL; P < .0001). Residual air has a wide variety of volumes in COTS IVFs. The average amount of residual air is high enough to contribute to clinically significant VAEs, although unlikely to be fatal. If airless IVF containers are produced for exploration missions, a progressive increase in the amount of residual air should be expected. Extremes of temperatures and humidity will increase the reaccumulation of residual air and decrease the shelf-life of airless IVFs.

Gas layer charge influence law study of underwater explosion bubble pulsation

Abstract To discuss the influence of the gas layer on underwater explosion load, the influence of gas layer thickness on bubble pulsation period maximum radius, pressure peak value, and specific impulse during underwater explosion was first discussed. A simulation model of underwater explosion with gas layer charge is established by numerical simulation method, and the influence law of gas layer on the pulsation of underwater explosion bubble is calculated and analyzed. The results show that the pulsation period and maximum radius of the underwater explosion bubble increase with the increase of gas layer thickness. The peak value of bubble pulsation pressure decreases, while the specific impulse increases first and then decreases. The research conclusion shows that in a certain gas layer, the damage risk of protective structure may be increased due to the increase of pulsating pressure ratio impulse or the resonance between pulsating frequency and structure.

Numerical simulation of underwater explosive shock wave with gas layer charge

Abstract To investigate the effect of the gas layer on the explosive’s underwater explosion shock wave load, based on AUTUODYN kinetic analysis software, we establish a one-dimensional underwater explosion numerical simulation model with a gas layer charge and study underwater explosion with a gas layer charge on the impact of the peak pressure and specific impulse of the shock wave underwater explosion. The results show that the gas’s low impedance and the continuous reciprocal reflection of the shock wave in the layer of the shock wave in the water led to a lower pressure Peak pressure of the shock wave in the water and its post-wave oscillatory decay waveform. With the increase of the uncoupling coefficient, the peak pressure of the shock wave in the water decreases, and the specific impulse increases and then decreases, through the range of 5∼1, 000 kg of TNT spherical charge underwater explosion calculations, to verify the reliability of the conclusions. The study’s conclusion shows that applying an underwater blast protection project with a gas layer charge should be reasonably designed for gas layer thickness to avoid the enhancement of the impulse but increase the harm of the shock wave.

ENSURING THE SEALING OF GAS WELLS EQUIPPED WITH LINER

The current problem of fountain safety, which affects the further well operation, namely the problem of their sealing, is considered. Traditional and modern technologies used to ensure the sealing of gas wells (including offshore wells), equipped with liners that simultaneously cover gas and water layers, are analysed. The issue of mandatory testing of casing strings in two ways is considered in more detail: pressing after lowering and cementing of the liner; lowering the level of the working fluid in the wellbore. These tests are intended to detect the fact of the well sealing and its suitability for further operation, or to detect the sealing fact and at the same time collect data for the analysis of the further action plan to overcome the consequences of such sealing. The sequence of testing casing strings using vaporizer-type coiled tubing installation that consumes liquefied nitrogen is considered. Schemes of well tying during tests of the production casing are presented. The peculiarities of the pressing process when nitrogen is injected into the annular space and into the tubing are noted. As a result of calculating of nitrogen injection pressure (the permissible value of which was 80 % of the testing pressure of the production casing) and the permissible pressure in the casing pipes, a comparative graph was constructed. The analysis of the received data confirmed the feasibility of pressing using a coiled tubing unit when pumping liquid into the tubing, as a result of exceeding the permissible pressure value at a depth of 3500 m. The need to use an operational packer, which was installed in the pipeline at the level between the head of the liner and the productive horizon, was determined. The necessity of perforating the liner through the inner space of the tubing using a hydraulic sandblasting perforator was confirmed.

High-Resolution 3D Geological Modeling of Three-Phase Zone Coexisting Hydrate, Gas, and Brine

Three-dimensional geological modeling is essential for simulating natural gas hydrate (NGH) productivity and formulating development strategies. Current approaches primarily concentrate on the single-phase modeling of either hydrate or free gas layers. However, an increasing number of instances suggest that the three-phase coexistence zone, which includes hydrate, gas, and water, is common and has become a focal point of international research, as this type of reservoir may present the most viable opportunities for exploitation. At present, there exists a significant gap in the research regarding modeling techniques for such reservoirs. This study undertakes a comprehensive modeling investigation of the three-phase zone reservoir situated in the sand layer of the Qiongdongnan Basin. By employing deterministic complex geological modeling techniques and integrating existing seismic and logging data, we have developed a three-phase coexistence zone model that precisely characterizes the interactions between geological structures and utilizes them as auxiliary constraints. This approach effectively mitigates the potential impact of complex geological conditions on model accuracy. Through a comprehensive analysis of 105 seismic profiles, we enhanced the model’s accuracy, resulting in the creation of a three-phase coexistence zone model comprising 350,000 grids. A comparison between the modeling results and well data indicates a relatively small error margin, offering valuable insights for future development efforts. Furthermore, this method serves as a reference for modeling hydrates in marine environments characterized by three-phase coexistence on a global scale.

Investigation of enclosure fire dynamics with inclined ceilings

Inclined ceilings are common in heritage and modern buildings, but little is known about their influence on compartment fire dynamics, and the relationships between inclined angle and fire dynamics parameters have not yet been clarified. A total of 24 bench-scale experiments were conducted in compartments with eight different kinds of ceilings, namely, flat ceiling (0°), single-slope ceilings of 15°, 30°, and 45° and double-slope ceilings of 15°, 30°, 45°, and 60°. The time to flashover, mass loss rate, heat release rate, gas temperature, and radiation heat flux to the floor were measured and analysed. It was found that for both single and double slopes, the time to flashover increased with increasing angle and is proportional to the reciprocal of the opening factor; the heat release rate and radiation heat flux at the floor decreased as the inclined angle increased, while the gas temperature at the same height during the fully-developed stage first increased and then decreased with increasing slope angle; and the influence of the inclined angle on these parameter changes was greater on single-slope than on double-slope. In addition, selecting the hot gas layer as the control volume, the theoretical differential calculation equations for thickness and temperature of the hot gas layer were established based on the mass balance and energy balance of hot gas, respectively. Furthermore, the dimensionless fitting equations were further proposed to facilitate the estimation of the thickness and temperature of the hot gas layer. Moreover, a theoretical model of the radiation heat flux q̇f" was developed based on the theoretical thickness and temperature of hot gas, which could well predict the radiation heat flux at the floor in compartments with different inclined ceiling angles. Finally, CFD (Computational Fluid Dynamics) simulations were performed to explore the temperature and velocity distributions in compartments with different inclined angles of the ceiling. The experimental and simulation results obtained, and the theoretical models proposed provided an essential basis to quantify the variation of the fire parameters with inclined angle and visualize the flow field of inclined ceiling compartments.

Controlled Surface Polarity and Crystallinity of Gallium Nitride on Si (111) Using Atomic Layer Deposition for Selective Wet-Etch and STEM Analysis

Gallium nitride (GaN) has gained interest as photoelectronic materials and a buffer layer for other III-V deposition with applications in power electronics operated at high voltage and high temperature. The crystallinity and polarity of III-V semiconductors have a key role for the passivation layers on microLED, the formation of 2D electron gasses in high electron mobility transistors, and for templating growth of piezoelectric materials. The atomic layer annealing (ALA) was reported to improve the crystallinity of the III-V compounds (aluminum nitride) at low temperatures as compared to the conventional thermal ALD. In ALA, a pulse of ion bombardment is added to each ALD cycle to ensure polycrystalline film formation at low temperature. Polycrystalline GaN has been deposited by ALA at low temperatures even on amorphous substrates, but the polarity was not reported. The selective wet-etch process has several advantages for the III-V semiconductor device integration since the conventional plasma ion etching process is expensive, complicated, and leads to the surface damage by reactive plasma ion. The GaN surface polarity (N-polar or metal-polar) on sapphire was selectively etched by aqueous KOH solution. However, electrochemical etching study on the polarity of GaN ALD films has not yet been studied as types of ALD process. Figure 1a and 1b show the process parameter switching diagram for the GaN thermal ALD and GaN ALA processes, respectively. The chemical compositions of ALA and ALD GaN on Si were estimated by in-situ AES as shown in Figure 1c. Lower O content (below 3.3 at. %) and higher N/Ga atomic ratio were observed in the ALA GaN on Si (111) as compared to the thermal ALD GaN film (4.6 at. %). Figure 1d shows that the intensity of GaN (002) XRD pattern in thermal ALD GaN on Si was greatly improved in the GaN stacks (GaN thermal ALD/ALA/Si) with an ALA GaN buffer layer. The electrochemical behavior of the GaN ALD films was studied to elucidate the impact of surface polarity on selective KOH wet-etch. The linear sweep voltammograms of GaN thermal ALD and GaN ALA films in 1 M KOH solution were shown in Figure 1e. The applied potential was swept from zero (vs. Normal Hydrogen Electrode) to positive 3.7 V. The peak of current density at ~1.7 V was observed in the voltammogram of the GaN ALA film (N-polar), suggesting the occurrence of etching reaction by the dissolution and formation via the equations in Figure 1f. On the other hand, the absence of current density peak in the GaN thermal ALD film (Ga-polar) could suggest the unfavorable etching reaction as compared to the GaN ALA film. Figure 2a and 2b shows the HAADF-STEM images of ALD GaN on Si demonstrate highly ordered 3 nm x 5 nm ALD GaN layers with bright and dark regions. The circles of bright regions and the center of dark regions represent Ga atoms and tunnel points (empty element), respectively. The GaN polarity could be determined by drawing triangles connecting adjacent three tunnel points without the interruption of Ga. Using this method, upward triangles were obtained in the HAADF-STEM image (Figure 2a), suggesting the formation of N-polar GaN layers during the ALA GaN process on Si. Conversely, downward triangles from the STEM image of thermal ALD GaN /ALA GaN /Si (Figure 2b) suggested Ga-polar GaN during GaN thermal ALD process. The inset figures show the top-view SEM image of selectively wet-etched (30 min, 20 wt.% KOH (aq)) GaN films. The etched surface on the ALA GaN layers (inset of Figure 2a) indicated N-polar GaN surface. The inset SEM image in Figure 2b shows a nearly unchanged GaN surface in thermal ALD GaN /ALA GaN / Si is consistent with the Ga-polar GaN surface. These observations are in good agreement with the HAADF-STEM images.The data is consistent with being able to control the polarity of GaN by switching between thermal ALD and ALA. The ion bombardment in ALA promotes N-polar GaN while thermal ALD promotes metal polar GaN. This allows the facile formation of both electron and hole gas layers between ALA and ALD GaN. Figure 1

A three-phase dispersion profile model for stratified pipe flow: Effects of gas bubbles on the distribution of oil and water droplets

A three-phase dispersion profile model for stratified gas/oil/water pipe flow was developed. The main goal was to incorporate the effects of gas bubbles on the cross-sectional distribution of oil and water droplets in the continuous liquids. Gas bubbles entrain from the gas layer above the oil/water layers and modify the oil and water dispersion profiles in several different ways. Increased hindered settling due to gas bubbles, reduction of the effective background mixing density that affects buoyancy, turbulence suppression due to droplets and bubbles and finally reduction of oil and water droplet entrainment rate due to area blocking by gas bubbles at the oil/water interface. All three dispersion profiles were modelled consistently with respect to their mutual coupling. The tuned model qualitatively reproduced the shapes and magnitude of the volume fraction profile data obtained from X-ray measurements. Several areas were identified where more fundamental experimental research would be needed.

Feasibility analysis and parameter optimization of ultrasonic assisted electrolytic plasma polishing of small modulus gears

Precision polishing of small modulus gears is a difficult task due to the complexity of their geometry. Electrolytic plasma polishing technology as a green and efficient processing method, it can effectively decrease the friction between parts and improve the service life. However, considering the uneven distribution of gas layers on the surface of workpieces in electrolytic plasma polishing, which affects the precision of workpiece shapes after polishing, this study proposed the use of ultrasonic vibrations to generate pressure waves to improve the fluid characteristics. Comparative experiments on small modulus gear electrolytic plasma polishing with and without ultrasonic vibration were conducted. A high-speed camera was utilized to monitor the distribution of gas layers around the workpiece during the polishing process in real-time. The optical measurement methods were used to evaluate the gear precision. The results indicate that ultrasonic assistance is beneficial in improving the uniformity of the gas layers surrounding the workpiece, achieving higher gear precision, and obtaining a lower surface roughness after polishing. Through orthogonal experiments, this study analyzed the effects of various process parameters on the surface roughness of gear profiles and the uniformity of material removal after polishing. These parameters included power voltage, polishing time, workpiece immersion depth, ultrasonic frequency, and workpiece posture angle. An optimal combination of process parameters was identified. The results show that the best surface roughness and gear precision were achieved with a power voltage of 300 V, a polishing time of 4 min, a workpiece immersion depth of about 10 mm, an ultrasonic frequency of 40 kHz, and a workpiece tilt angle of 45°.

Application of nuclear magnetic resonance core logging technology in oil and gas exploration of deep/ultra deep low porosity and low permeability reservoirs

Abstract In order to improve the efficiency of deep/ultra deep oil and gas exploration decision-making and release production capacity, and to address the difficulties in implementing the physical and fluid properties of complex deep/ultra deep reservoirs, nuclear magnetic resonance logging technology is used to establish a permeability calculation method and a glutenite reservoir pore structure evaluation method so that the liquid production capacity of the reservoir is classified. Combing nuclear magnetic resonance logging with gas logging technology, an comprehensive hydrocarbon evaluation index SI is established to evaluate complex fluid properties. The results show that: (1) The permeability calculated by T2gm using nuclear magnetic resonance logging spectra is highly consistent with laboratory measurement results. (2) By combining the nuclear magnetic porosity and permeability of the test layer with the pore structure parameters calculated by nuclear magnetic, a classification standard for low porosity and low permeability glutenite reservoirs can be established, which can provide a preliminary evaluation of the reservoir’s liquid production capacity. (3) The comprehensive evaluation chart of nuclear magnetic resonance logging combining with gas logging can effectively distinguish oil layers, gas layers, and water layers, thereby distinguishing complex fluid properties. This research achievement is of great value for implementing the physical and fluid properties of deep/ultra deep complex reservoirs in Bohai Oilfield, and guiding efficient exploration and development operations.

Rock cutting image recognition based on color and texture feature fusion

Abstract In the realm of oil exploration, there is an increasing demand for precise lithological analysis, particularly in the rapid and accurate identification of fine rock cutting images. Therefore, a novel rock cutting image recognition method based on the fusion of color and texture features is proposed. This method utilizes the color histogram and grayscale co-occurrence matrix techniques to extract color and texture features from target images, respectively. Compared with the traditional single-feature recognition methods, this integrated feature method can greatly improve the accuracy of fragment recognition and ensure more accurate fragment classification by designing the feature fusion structure of the fragment image feature set. The model is established by using the support vector machine (SVM) classifier to realize the automatic classification and recognition of cuttings images. This not only reduces the time and labor intensity of manual operation, but also improves the efficiency and speed of cuttings analysis, which meets the needs of modern efficient drilling operations. More detailed and accurate stratigraphic data can be provided by high precision rock chip identification and lithology analysis. These data have important reference value for geologists to analyze stratigraphic structure and distribution, determine the location and distribution of underground oil and gas layers, and optimize drilling decisions and operation plans. Experimental results show that the method achieves an overall recognition accuracy of more than 90% in the task of detecting 126 rock chip images for conglomerate, 153 for mudstone, and 150 for sandstone, and up to 94% for mudstone and sandstone. It is proved that the recognition method proposed in this paper can better classify sandstone, mudstone and conglomerate in rock chips with high recognition accuracy.

Directional enhancement of underwater impact and bubble loads in neighbor two-phase fluid domains charge

The loading characteristics of underwater explosions and the dynamic behavior of bubbles are directly related to the charge structure. This study proposes a unique charge structure in a gas–liquid two-phase fluid domain. Numerical methods are used to investigate the effects of fluid layer thickness and gas–liquid ratio on underwater explosion shock wave load, bubble dynamics, and bubble pulsation load. The results show that the two-phase fluid layer significantly enhances the directional release of shock wave energy and bubble pulsation load. During the shock wave phase, a lagging wave effect appears in the liquid layer direction, causing a secondary high-energy shock, significantly increasing the specific impulse. The gas layer direction may form a pressure relief channel effect, enhancing the shock wave peak pressure. For the bubble motion phase, differences in the physical properties of the fluid layer medium lead to irregular bubble boundary movements, promoting bubble tearing and rupture. The gaseous medium converts the accumulated shock wave energy into the internal energy of the bubble, increasing its volume potential. Although this characteristic reduces the pulsation frequency, it significantly increases the specific impulse. Altering the fluid layer medium can control explosion loads and bubble movement, offering new insights for ocean engineering applications.

Evolution of linear internal waves over large bottom topography in three-layer stratified fluids

Evolutions of internal waves of different modes, particularly mode 1 and mode 2, passing over variable bathymetry are investigated based on a new numerical scheme. The problem is idealized as interfacial waves propagating on two interfaces of a three-layer density stratified fluid system with large-amplitude bottom topography. The Dirichlet-to-Neumann operators are introduced to reduce the spatial dimension by one and to adapt the three-layer system and significant topographic effects. However, for simplicity, nonlinear interactions between interfaces are neglected. Numerical techniques such as the Galerkin approximation, proven effective in previous works, are applied to save computational costs. Shoaling of linear waves on an uneven bottom is first studied to validate the proposed formulation and the corresponding numerical scheme. Then, for two-dimensional numerical experiments, mode transition phenomena excited by locally confined bottom obstacles and quickly varying topographies, including the Bragg resonance, mode-2 excitation, wave homogenization, etc., are investigated. In three-dimensional simulations, internal wave refraction by a Luneberg lens is considered, and good agreement is found in comparison with the ray theory. Finally, in the limiting case, when the top layer can be negligible (for example, a gas layer of extremely small density), the problem is reduced to a two-and-a-half-layer fluid system, where an interface and a surface are unknown free boundaries. In this situation, the surface signature of an internal wave is simulated and verified by introducing the realistic bathymetry of the Strait of Gibraltar and qualitatively compared with the satellite image.

New Parameter for Benchmarking Plasmonic Gas Sensors Demonstrated with Densely Packed Au Nanoparticle Layers.

Localized surface plasmon resonance (LSPR) gas sensitivity is introduced as a new parameter to evaluate the performance of plasmonic gas sensors. A model is proposed to consider the plasmonic sensors' surface sensitivity and plasmon decay length and correlate the LSPR response, measured upon gas exchange, with an equivalent refractive index change consistent with adsorbed gas layers. To demonstrate the applicability of this new parameter, ellipsoidal gold nanoparticles (NPs) arranged in densely packed hexagonal lattices were fabricated. The main advantages of these sensors are the small and tunable interparticle gaps (18-29 nm) between nanoparticles (diameters: 72-88 nm), with their robust and scalable fabrication technology that allows the well-ordered arrangement to be maintained on a large (cm2 range) area. The LSPR response of the sensors was tested using an LSPR sensing system by switching the gas atmosphere between inorganic gases, namely He/Ar and Ar/CO2, at constant pressure and room temperature. It was shown that this newly proposed parameter can be generally used for benchmarking plasmonic gas sensors and is independent of the type and pressure of the tested gases for a sensor structure. Furthermore, it resolves the apparent disagreement when comparing the response of plasmonic sensors tested in liquids and gases.

The impact of fire source location on hot gas layer temperature in multi-compartment pre-flashover fires: Analysis and semi-empirical model development

A numerical study of a two-room structure (multi-compartment) subjected to fire in the inner room was carried out, employing the CFD (Computational Fluid Dynamics) software called FDS (Fire Dynamics Simulator), to (i) analyze the influence of the fire source position on the hot gas layer temperature, Tu, and its behavior in a multi-compartment fire, and (ii) develop a semi-empirical engineering calculation model to predict Tu in the adjacent room to a pre-flashover well-ventilated fire room, taking into account the fire source position. The results showed that when the fire origin occurs close to walls or elevated above the floor level, a reduced air entrainment is observed in the fire plume and flame, causing an increase in the Tu and a reduction of the smoke production in the fire room. This reduction in the smoke production led to a lower increase in the Tu of the adjacent room in relation to the case when the fire source was at the center of the fire room. It was also observed that the Tu in both rooms was inversely proportional to the ventilation factor (A.H0.5), with a significant increase observed as the ventilation factor decreases, depending on the fire source position. Furthermore, a semi-empirical engineering calculation model was developed to predict the Tu in the adjacent room, considering different fire source locations at ground level and elevated. The model was validated against experimental data from the literature, showing a good agreement (deviation of ≈20 %), thus demonstrating its applicability to other cases.

Mechanism Research and Identification Method of Low Resistivity Gas Layers in the M block of Algeria

Abstract The M block in Algeria is located in the southern Sahara platform, with oil and gas reservoirs mainly composed of river-glacial marine facies, fluvial and shallow marine fine sandstones. The pore structure is complex, and the difference in resistivity logging between gas layers and water layers is not significant, resulting in difficulties in identifying and evaluating hydrocarbon zone and the occurrence of reservoir omission. Based on geological, mud logging, core experimental data, logging, formation water analysis and testing data together, the formation mechanism of low resistivity hydrocarbon zone and the response characteristics of logging curves were generalised. The research suggests that the main factors causing low resistivity in this area are strong heterogeneity, high formation water salinity, high shale content, etc. On this basis, in response to the difficulty of identifying low resistivity gas layers, three methods of assessment were constructed: resistivity reduction rate factor method, porosity curve differentiation technique method and double porosity overlap method, which can quickly identify low resistivity gas layers. The oil testing results have verified that this method significantly improves the interpretation accuracy, with a 17.2% increase in accuracy and good results. The test results show that the method can greatly improve the interpretation accuracy with current accuracy 89.1% and the method turns out to be effective. Based on the above methods, the distribution law of low resistivity oil and gas layers in the study area has been clarified, and favorable zones have been discovered, providing strong technical support for increasing reserves and production in the area.

Method—Multi-Cell Testing with Active Driven Gas Layer Concept: Advantages and Limitations

This study validates a novel method for simultaneous durability testing of multiple symmetrical cells with Ni/ceria fuel electrodes. The investigation demonstrates that gas diffusion losses in the multi-cell test setup utilizing the active driven gas layer concept have a smaller impact on cell performance compared to the single-cell setup. This method proves effective for testing multiple identical cells, offering a time and cost-efficient approach. However, testing symmetrical cells with different fuel electrodes reveals an unexpected pseudo-inductive loop in the impedance spectra, observable only in the multi-cell setup. Analysis of impedance spectra and relaxation times indicates that differences in electrode polarization resistance result in varying gas compositions at the two electrodes of a cell, disrupting symmetry and superimposing an additional Nernst voltage term. To understand this, an electrical equivalent circuit model with the Nernst voltage term was developed to reproduce the observed behavior. Comparison of experimental and simulation results substantiates the model and elucidates the mechanisms. The findings indicate that testing multiple cells with the active driven gas layer concept is applicable only for identical cells and not for those with different electrodes.

Research on Production Behavior of A Fractured Well in Gas Hydrate Reservoirs Considering Multilayer

Abstract Natural gas hydrates are internationally recognized as a new clean energy source with high prospects for commercial development. However, the vast majority of hydrates are hosted in oceanic clayey silty sediments, which are inefficient to exploit due to the extremely low effective permeability. In this paper, a novel development mode, that is, multilayer commingled production with a hydraulically fractured well, is proposed for the multilayered reservoir where hydrate and free gas coexist, to enhance productivity. Especially, the co-production behavior was numerically investigated, with the multilayered reservoir containing a hydrate-bearing layer, a three-phase layer, and a free gas layer located in the Shenhu Area as the geological background. The results indicated that the fracture provided flow channels for gas production in the multilayer, as well as greatly increasing the pressure drop spreading zone and changing the hydrate decomposition mode from around the wellbore to along the fracture surface. Compared with improving the fracture conductivity, increasing the fracture length is more effective for improving hydrate decomposition efficiency and co-production capacity. Specifically, when the fracture half-length was 30 m and the fracture conductivity was 100 D·cm, the cumulative gas production reached 949×104 m3 at 3600 days, which was 3.28 times that of the unfractured scenario. Additionally, fracturing the free gas layer hardly affects productivity as the free gas can be well-recovered by the wellbore. Overall, the proposed mode is promising for multilayered gas hydrate reservoirs, provides references for the co-production plan design, and contributes to the scale mining of hydrates.