Permeability Distribution Research Articles

In situ coal permeability and favorable development methods for coalbed methane (CBM) extraction in China: From real data

Permeability plays a significant role in the economic viability of coalbed methane (CBM) development. In China, in situ permeability obtained from injection fall-off tests range from 0.0001 to 41 mD at depths of 130–1728 m, with the majority (78%) falling between 0.01 and 1 mD. Coal reservoirs with high rank, common cleat mineralization, and depth-dependent high stress may result in extremely low permeability. Low-rank coal and cataclastic coal exhibit more favorable permeability conditions at shallow depths. Heterogeneity in coal rank, coal texture, and stress magnitude results in a discrete distribution of permeability both regionally and vertically. Most deep seams are highly compressed with extremely low permeability (<0.1 mD) as high stress levels. Multilateral horizontal wells work best with high permeability seams, while vertical wells with conventional hydraulic fracturing demonstrate limited adaptability to deep and low-permeability seams due to insufficient proppant-supported fractures. With increasing depth, both vertical and horizontal wells should employ larger fracturing scales to create effectively supported zones with higher fracture conductivity and reduced stress sensitivity to enhance CBM productivity. Horizontal wells with large-scale volume fracturing demonstrate superior performance compared to vertical wells in extracting CBM from deep, low-permeability, and high gas saturation reservoirs.

Automatic History Matching for Adjusting Permeability Field of Fractured Basement Reservoir Simulation Model Using Seismic, Well Log, and Production Data

Developing automatic history matching (AHM) methods to replace the traditional manual history matching (MHM) approach in adjusting the permeability distribution of the reservoir simulation model has been studied by many authors. Because permeability values need to be evaluated at hundreds of thousands of grid cells in a typical reservoir simulation model, it is necessary to apply a reparameterization technique to allow the optimization algorithms to be implemented with fewer variables. In basic reparameterization techniques including zonation and pilot point methods, the calibrations are usually based solely on the production data with no systematic link to the geological and geophysical data, and therefore, the obtained permeability distribution may be not geologically consistent. Several other reparameterization techniques have attempted to preserve geological consistency by incorporating 4D seismic data; however, these techniques cannot be applied to our fractured basement reservoirs (FBRs) as they do not have 4D seismic data. Taking into account these challenges, in this study, an AHM methodology and workflow have been developed using a new reparameterization technique. This approach attempts to minimize the potential for geological nonconsistency of the calibrated results by linking the permeability to geophysical data. The proposed methodology can be applied to fields with only traditional geophysical data (3D seismic and conventional well logs). In the proposed workflow, the spatial distributions of seismic attributes and geomechanical properties were calculated and estimated from 3D seismic data and well logs, respectively. After that, a feed-forward artificial neural network (ANN) model trained by the back-propagation algorithm of the relationship between initial permeability with seismic attributes and geomechanical properties of their grid cell values is developed. Then, the calibration of the permeability distribution is performed by adjustment of the ANN model. Modification of the ANN model is performed using the simultaneous perturbation stochastic approximation (SPSA) algorithm to calibrate transmission coefficients in the ANN model to minimize the discrepancy between the simulated results and observed data. The developed methodology is applied to calibrate the permeability distribution of a simulation model of Bach Ho FBR in Vietnam. The effectiveness of the methodology is evident by comparing the historical matches with an available manually history-matched simulation model. The application shows that the proposed methodology could be considered as a suitable practical approach for adjusting the permeability distribution for FBR reservoir simulation models.

Stochastic lithofacies and petrophysical property modeling for fast history matching in heterogeneous clastic reservoir applications

For complex and multi-layered clastic oil reservoir formations, modeling lithofacies and petrophysical parameters is essential for reservoir characterization, history matching, and uncertainty quantification. This study introduces a real oilfield case study that conducted high-resolution geostatistical modeling of 3D lithofacies and petrophysical properties for rapid and reliable history matching of the Luhais oil reservoir in southern Iraq. For capturing the reservoir's tidal depositional setting using data collected from 47 wells, the lithofacies distribution (sand, shaly sand, and shale) of a 3D geomodel was constructed using sequential indicator simulation (SISIM). Based on the lithofacies modeling results, 50 sets of porosity and permeability distributions were generated using sequential Gaussian simulation (SGSIM) to provide insight into the spatial geological uncertainty and stochastic history matching. For each rock type, distinct variograms were created in the 0° azimuth direction, representing the shoreface line. The standard deviation between every pair of spatial realizations justified the number of variograms employed. An upscaled version of the geomodel, incorporating the lithofacies, permeability, and porosity, was used to construct a reservoir-flow model capable of providing rapid, accurate, and reliable production history matching, including well and field production rates.

Optimal metabolite transport in hollow fibre membrane bioreactors

Hollow fibre membrane bioreactors provide a fast and efficient method for engineering functional tissue for use in medical treatments. Flow is utilised to overcome mass transport limitations by perfusing a nutrient-rich culture medium through the fibre lumen, which can then transport along the fibre lumen or across the porous membrane wall. Cells seeded at the outer membrane wall consume the nutrient and subsequently produce waste metabolites, which are transported away through an external extra-capillary space (ECS) along with excess nutrient. We present and investigate a two-dimensional axisymmetric model for fluid flow and solute transport through a single-fibre bioreactor configuration, with cells seeded to the external fibre wall. Fluid flow is modelled by steady lubrication and Darcy equations, which are coupled to the solute transport problem modelled by a system of advection–diffusion equations, supplemented with a reaction term to model the cell layer. Our model analysis reveals how spatially varying wall permeability distributions can be utilised to provide uniform nutrient delivery to a spatially uniform, homogeneous cell population. We also reveal how maximising the transmural pressure drop across the membrane wall is the dominant mechanism for waste removal rather than traditional experimental methods of flushing the ECS.

The Dependence of Water and Gas Breakthrough on the Choice of Model Parameters in Naturally Fractured Reservoirs Using Sector and Full Reservoir Models

Assessing fractures in carbonate reservoirs is crucial due to their substantial impact on reservoir permeability. Understanding the characteristics of these fractures is vital for optimizing oil production. Additionally, extremely heterogeneous and anisotropic permeability distribution within the natural fractured reservoir is often caused by the complexity of a fracture network. Therefore, accurate reservoir modelling and simulation must be conducted in order to achieve ultimate recovery. In this paper, a sector model has been developed based on the studied example field, and its results are compared with the full reservoir model to find out the degree of resemblance between their outputs. The study area has four natural fracture compartments, with an average reservoir height of 95m and WOC and GOC depths of 685 m and 590 m, respectively. A dual-porosity and single-permeability modelling system was used to simulate the properties of the reservoir rock. This model was derived from the Petrel layercake model. A sensitivity analysis was also carried out to look into the relationships between field performance and the well. The outcomes of both models demonstrated that matrix permeability and fracture dimension had a significant impact on the early breakthrough of water and gas to comparable, huge extents. Other factors, such as aquifer size and WOC, show a moderate impact on water and gas breakthrough as well as final recovery.

Advanced Geostatistical Techniques for Building 3D Geological Modeling: A Case Study from Cretaceous Reservoir in Bai Hassan Oil Field

A 3D Geological model was generated using an advanced geostatistical method for the Cretaceous reservoir in the Bai Hassan oil field. In this study, a 3D geological model was built based on data from four wells for the petrophysical property distribution of permeability, porosity, water saturation, and NTG by using Petrel 2021 software. The geological model was divided into a structural model and a property model. The geological structures of the cretaceous reservoir in the Bai Hassan oil field represent elongated anticline folds with two faults, which had been clarified in the 3D Structural model. Thirteen formations represent the Cretaceous reservoir which includes (Shiranish, Mashurah, U.kometan, Kometan Shale, L. Kometan, Gulneni, Dokan, Mauddud, Jawan/Mud, Batiwah, Shuaiba, Garagu, L.Sarmord). According to the property model, the model for each petrophysical property was constructed based on core data and CPI. By using the geostatistical method, the property model was constructed. The Mauddud Formation is considered one of the most promising hydrocarbon reservoirs in the Bai Hassan oil field based on the results of the property model, where the ratio of water saturation is around 30%, the porosity value is reaching up to 31%, and the net to gross ratio is averaging at 70%.

Vacuum consolidation theory of dredged slurry considering nonlinear clogging behaviors

Clogging in the prefabricated vertical drains (PVDs) and soils is an inherent feature associated with vacuum treatment of slurry ground. The clogging column is characterized by nonlinear growth of volume over time and nonlinear permeability distribution along the radial direction. This study aims to develop a drain-well consolidation model for vacuum treatment of dredged slurry, with specific considerations of the nonlinear behaviors of the clogging column and PVD drainage capacity. The constitutive compression and permeation behaviors of the dredged slurry are described by extended power functions, which avoids the singularities associated with the conventional logarithmic constitutive equations when the effective consolidation stress approaches zero. Parametric studies were conducted to explore the consolidation effects while considering different combinations of parameters that govern the nonlinear behaviors of the clogging column and PVD-drainage capacity. The significance of considering the abovementioned nonlinear behaviors was demonstrated by comparing the field test results on a dredged slurry ground. Results indicate that clogging primarily affects consolidation by causing a nonlinear permeability distribution along the radial direction of the clogging column and nonlinear attenuation of PVD-drainage capacity.

Woven filter media used in wet filtration processes: investigation of pore size distribution, air and water permeability and finding correlations between them

Currently, methods for evaluating the performance of woven filter media used for filtration processes are mainly reduced to air permeability and filtration resistance. However, filtration processes are not limited to dry filtration only. Moreover, critical performance-related factors such as the pore size distribution and liquid permeability are studied but often omitted and ignored in the characterization process. The present study aims to investigate and analyze three characteristics, namely air and liquid permeability and pore size distribution, and to examine correlations between the studied characteristics. The results of the present study show that correlations between the studied characteristics do exist. Polynomial and exponential functions could describe the correlation between the mean flow pore diameter and permeability. At the same time, the dependency between air and water permeability is characterized by a logarithmic function. Consequently, the characterization and selection of filter cloths should be done by analyzing several different parameters simultaneously. These correlations could become the basis of a system of media indexing in the future.

Simulation of thermo-hydro-mechanical coupled heat extraction process of geothermal reservoir under varied geological conditions with CO2 as working fluid

The use of supercritical CO2 as a working fluid instead of H2O in an enhanced geothermal system (EGS) for extracting heat from hot dry rock geothermal resources has garnered significant attention. The objective of this study is to investigate how different geological conditions affect the heat extraction behavior of supercritical CO2 and to reveal the efficiency differences between supercritical CO2 and H2O as working fluids in each geological scenario, providing deeper insight into reservoir management. A series of 3D coupled thermo-hydro-mechanical models were established. Besides, the impact of initial temperature, pressure, porosity, permeability, and stress field on the heat extraction of EGS with different working fluids are also analyzed and compared. Results indicate that, at the same circulating volumetric flow rate, CO2-EGS generally exhibits an earlier thermal breakthrough time, lower net energy production, and reduced heat extraction rate compared to H2O-EGS. Taking into account the extended reservoir lifespan and the relatively small pressure difference between injector and producer in CO2-EGS, CO2 is a more suitable working fluid than H2O. Furthermore, the performance of CO2-EGS is primarily affected by the initial temperature, porosity, and permeability distribution pattern, rather than the initial pressure. On the one hand, a reservoir with low initial temperature, porosity and homogeneous permeability were found to be more conducive to enhancing the average net energy production. On the other hand, reservoir vertical permeability anisotropy can have a more profound impact on CO2-EGS efficiency compared to horizontal y permeability anisotropy. Additionally, this study also examined the impact of in situ stress field. It was found that, compared to H2O-EGS, both isotropic and anisotropic in situ stress fields have a weak effect on the performance of CO2-EGS, which can be attributed to the similarity of the channelization degree of the flow field under different stress conditions.

Implementing pore size distribution into saturation height function modelling of reservoir rock types: A case study on a carbonate gas reservoir

The accurate determination of saturation-height functions for modeling multiphase fluid flow in porous media is critical for applications, such as hydrocarbon recovery and subsurface CO2/H2 storage. The challenges associated with water saturation distribution in carbonate reservoirs arise from their inherent heterogeneity and complex pore systems. Addressing such challenges, this study aims to introduce a robust saturation-height function model that considers a non-linear relationship between capillary pressure and saturation, leading to more reliable estimates of fluid saturations. To achieve this, modifications were performed on a saturation height model based on the relationship between porosity, permeability, and pore size distribution (PSD). First of all, the capillary pressure model implemented in the previously introduced PSD-based approach was replaced by a model suitable for heterogeneous reservoirs, fitting the available mercury injection capillary pressure (MICP) data with higher accuracy. Additionally, the derivation of the relations between the optimum pore throat radius and matching parameters of the capillary pressure model was conducted by finding the best correlation among all the available data in the previous approach. For the first time in this study, considering the resemblance in rock properties like capillary pressure and PSD within each rock type, individual correlations among these parameters were established for each reservoir rock type. The predicted saturation height model was cross-checked against the log and core-derived saturation heights, demonstrating a high level of consistency, particularly along the gas-saturated regions. The obtained results were also compared with the conventional saturation height models, including the Leverett J-Function, Johnson's method, and Cuddy's approach. The significance of the modifications was underscored through a comparison of results with those achieved by the previous approach in which the rock typing was ignored. Although the PSD method, which ignored rock types, exhibited high consistency with log data, our modifications yielded far better predictions by improving the coefficient of determination from 0.68 to 0.84.

Effect of scale and matrix porosity on the relationship between permeability and resistivity in fracture-matrix system

Monitoring site permeability distribution by resistivity is an effective method to characterize fracture-matrix system. In this study, a link between permeability and resistivity in a fracture-matrix system was established. Fluid flow and electrical current processes in a random fracture-matrix system were numerical simulated. The fracture-matrix system was generated based on field data from the Three Gorges Project in China. The fracture-matrix system with six scales (5 m, 10 m, 15 m, 30 m, 45 m, and 60 m) and three matrix porosities (0.1, 0.01, and 0.004) were created using a Monte Carlo approach. The effects of scale and matrix porosity on the relationship between permeability (k) and resistivity (ρ) were examined. The results showed that a functional relation was established to describe the k-ρ relationship. The k-ρ relationship is influenced by scale and matrix porosity. When the matrix porosity is 0.004, k-ρ relationship is scale-independent, while the relationship is scale-dependent when the matrix porosity is greater than 0.01. The scale-dependent is more obvious with the increase of porosity. When the scale reaches the representative elementary volume (REV) value, the k-ρ relationship is matrix-dominated below the critical fracture aperture and fracture-dominated above the critical fracture aperture. The results provide a basis for using resistivity characterize fracture permeability variations and will be helpful to evaluate risks of underground engineering.

Investigation on Three-Dimensional Void Mesostructures and Geometries in Porous Asphalt Mixture Based on Computed Tomography (CT) Images and Avizo

To investigate the void mesostructure in porous asphalt mixtures (PA), computed tomography (CT) and Avizo were utilized to scan and reconstruct the three-dimensional (3D) void model of PA-16 specimens. The void mesostructure of the specimen was quantitatively characterized through the anisotropy evaluation index. The equivalent pore network model (PNM) was extracted using the medial axis method. Based on the PNM model, the topological structure of the specimen and the morphological characteristics of the connected pores were analyzed. The results showed that the void anisotropy evaluation method can reflect the microscopic morphology of voids in porous asphalt mixtures. The cross-sectional porosity of representative elementary volume (REV) is mainly distributed between 20% and 25%, and about 90% of the macropores have a diameter between 0.5 mm and 3 mm. The distribution of cross-sectional porosity is uneven along the REV height direction. As the smallest cross-section of the seepage path, the equivalent radius of the throat is mainly between 0.1 mm and 1.5 mm, which is much smaller than the equivalent radius of the pore. The topological structure of pores is quite different, and their coordination numbers are mainly concentrated within 18. The pores with coordination numbers 1 to 10 constitute the main body of the pores inside REV, accounting for over 98% of the total number of pores. In addition, the permeability calculation results show that there is a significant difference in the permeability of each axis of REV compared to the total permeability of the superpave gyratory compactor (SGC) specimen, which illustrates that the permeability distribution presents an obvious spatial anisotropy. This study effectively reveals the heterogeneity of the 3D void morphology of porous asphalt mixtures, and it provides a reference for a better understanding of the void flow rules in drainage pavements.

Seepage Model of Heterogeneous Municipal Solid Waste Landfill and Application under Process of Waste Accumulation

The distribution of leachate directly impacts the safety and stability of the landfill, so it is important to research the distribution of seepage characteristics and migration patterns of leachate. The study aims to investigate the impact of heterogeneous permeability distribution and clogging of the drainage layer on leachate transportation in landfills. To achieve this, a heterogeneous transient seepage model was developed. Results showed that when considering the heterogeneous permeability of the waste in the buried depth direction, the maximum perched water level was higher, which is not conducive to the safety and stability of the landfill. Taking Xi’an Jiangcungou Landfill as a research object, the maximum perched water level of each waste layer was higher compared to the homogeneous condition when considering the landfill process and heterogeneous permeability. The differential value ranged from 0.08 m to 1.88 m. Furthermore, the calculation results obtained from the heterogeneous seepage model were found to be in good agreement with both actual field data and referenced survey data, thus confirming the reliability of the model. These research findings not only offer technical support but also provide a solid theoretical foundation for leachate level control and safety and stability assessments.

Performance evaluation of surrogate models for simulating multiphase NAPL transport in heterogeneous aquifers

Abstract A better understanding of the distribution of nonaqueous phase liquid (NAPL) plumes is of great importance to groundwater pollution remediation and control. However, the efficiency of surrogate models in simulating the transport is still not well addressed. Selecting a leakage problem as an example, 50 sets of random permeability distributions are generated using the Monte Carlo method, and a numerical model is used to obtain benchmark data of NAPL transport. Four machine learning methods are employed to simulate dense NAPL transport under point leakage sources across spatiotemporal scales. The validation of the models demonstrate that the random forest model can also effectively capture the spatial-temporal distribution of the plume in heterogeneous aquifers, with a maximum mean absolute error and root mean square error smaller than 5.55 × 10−4 and 5.88 × 10−5, respectively. Meanwhile, the multiple phase outcome from the random forest model fits well with the numerical results under the scenarios of linear leakage sources and light NAPL transport. The total time consumed in the computation is reduced by over 150 times after using the surrogate models. The results suggest that surrogate models can provide a promising way to understand NAPL transport in heterogeneous aquifers.

An improved magnetic dipole model for MFL testing based on non-uniform magnetic charge distribution

ABSTRACT Magnetic flux leakage (MFL) signal prediction is important in ferromagnetic defect evaluation and reconstruction. At present, the magnetic dipole model (MDM) is the most widely applied method because of its high efficiency. However, it has low accuracy when applied to analysing complex defects (complex in profile and magnetic permeability) due to the original setting of uniform magnetic charge distribution. To solve the issue, this paper proposes an improved MDM method for MFL inspection of ferromagnetic materials by calculating the non-uniform magnetic charge distribution. It partly applies the finite volume method (FVM) to derive the magnetic charge distribution on the defect surface, which makes it able to take into account the defect’s profile and magnetic permeability distribution. The new magnetic charge distribution can increase the MDM’s accuracy for complex defect MFL field prediction with little extra cost. Experimental results show that, when compared with traditional MDM, the proposed one can achieve a maximum 69% decrease in root mean squared error when analysing complex defects. Compared with the numerical method, the computation time could reach a great reduction.

Target-based sedimentary diagenesis simulation and three-dimensional diagenesis evolution modeling

Deposition and diagenesis are important factors affecting the quality of oil and gas reservoirs. Previously reported diagenesis studies mainly involve qualitative analysis, such as the determination of diagenetic events and diagenetic evolution sequences and modeling of two-dimensional diagenetic evolution, with less effort devoted to quantitative numerical simulation and three-dimensional diagenetic evolution models. This study proposes a new method for target-based diagenesis simulation by integrating the discrete element method, the quartet structure generation set method, and morphological algorithms. This new hybrid method can quantitatively simulate the effects of mineral grain deposition, compaction, cementation, dissolution, and replacement. Since specific minerals can undergo specific diagenetic alterations through mineral labeling, the sequence and path of diagenesis can be predefined in this method. Taking the sandstone reservoir of Lower Member 3 of the Shahejie Formation in Linnan Sag, Huimin Depression, Bohai Bay Basin, East China as an example, the new simulation method used the constructed diagenetic evolution sequence based on thin section identification and geochemical analysis to systematically simulate deposition and diagenesis in the study area and to construct a three-dimensional diagenetic evolution model. The predicted porosity, permeability, and pore size distribution of the simulated digital rocks are in good agreement with the experimental values, which validates the high accuracy of the simulation method. Based on these three-dimensional multi-mineral evolution models, the evolution trends of porosity and permeability during the sedimentation and diagenesis process were elucidated, revealing the variation in reservoir quality in the studied area and indicating reservoir sweet spots. The constructed 3D diagenesis evolution models are widely applicable and can be used not only for permeability simulation but also for the study of electrical, acoustic, and mechanical properties of reservoirs.

CFD modelling of longwall goaf atmosphere under vertical boreholes gas drainage

To effectively control and utilise large amounts of gas emissions from underground coal mining, Australia and many other countries rely heavily on a series of vertical boreholes to capture the gas during mining. This gas capture not only reduces the greenhouse gas impact but also recovers a significant amount of energy. Vacuum pumps are connected to surface boreholes to drive gas flow from the goaf and overlying fractured strata. However, applying high suction pressure to the boreholes may cause more oxygen to enter the goaf from the longwall working face. This influx of oxygen can potentially react with residual coal in the goaf, accelerating coal self-heating and possibly resulting in endogenous fires. By analysing extensive goaf gas drainage data collected from Australian longwalls, researchers have established the normal trend of goaf gas concentration and flow rate as a result of intensive goaf gas drainage. This paper further developed goaf gas flow CFD models with the operating vertical boreholes, which were then calibrated using field borehole production data under certain operating conditions. The CFD model simulated the distribution of O2 and CH4 as well as the gas flow pathways in the goaf, considering the complication of goaf gas drainage. This study found that the O2 concentration is higher on the goaf tailgate side under the influence of tailgate side boreholes compared to the maingate side. Furthermore, for the well-compacted goaf, a significant proportion of the ventilation air travels through ‘high permeability flow channels’ provided by the goaf edge on tailgate side, and then circulates back into the goaf boreholes. These CFD modelling results not only enable ventilation engineers to visualize the goaf gas flow patterns under the impact of multiple operating boreholes, but also to understand the impact on goaf atmosphere through sensitivity analysis of natural goaf characteristics, such as goaf permeability distributions and gas emission rates.

On-Demand 3D Spatial Distribution of Magnetic Permeability Based on Fe3 O4 Nanoparticle Liquid Toward Micro-Cavity Detectors.

The change of 3D spatial distribution of magnetic permeability can lead to the generation of introduced electrical signals. However, present studies can only achieve rough regulation by simple shape deformation of magnetic elastomers such as compression, bending, or stretching. Accurate control of the 3D spatial distribution of magnetic permeability is still an open question. In this study, an on-demand 3D spatial distribution of magnetic permeability by controlled flowing of Fe3 O4 nanoparticle liquid (FNL) is demonstrated. The flowing routes of FNL are tuned by a 3D-printed cage with pre-designed hollow structure, thus changing the 3D spatial distribution of magnetic permeability. Then, eight symmetrically distributed coils under cage are used to receive characteristic induction voltage signals. Maxwell numerical simulation reveals the working mechanism of signal generation. Notably, those eight coils can detect FNL flowing status in eight directions, allowing recognition of up to 255 different FNL flowing combinations. By introducing machine learning, the micro-cavity detector based on FNL can distinguish nine kinds of micro-cavity structures with an accuracy of 98.77%. This work provides a new strategy for the adjustment of the 3D spatial distribution of the magnetic permeability and expands the application of FNL in the field of space exploration.

Model of a post-caldera volcano-hosted and vapor-dominated system through a numerical simulation study of the Bedugul geothermal field, Bali Island, Indonesia

To significantly increase the use of geothermal resources, describing geothermal systems in post-calderas is essential because this type of system is infrequent and has not yet been thoroughly researched. The Bedugul geothermal field (BGF), Bali Island, Indonesia, is a representative system with a complex structure composed of a vapor-dominated zone formed above a deep liquid reservoir. This study examines the BGF system and updates a conceptual model, particularly the fluid flow and heat transfer in the reservoir. A dual-porosity model and TOUGH2 EOS1 equation of state for water and steam module are used to simulate natural state conditions, including calderas with a domain area of 148.8 km2 and a thickness of 3.3 km. The BGF model was calibrated using the available geosciences data, temperature core holes and deep explorations wells and then evaluated statistically. A reliable natural state model with decent accuracy was obtained by optimizing the parameter calibration of the physical and structural properties of the reservoir model; the anisotropic and heterogeneous fracture permeability distribution and specific boundary conditions are crucial to the calculation accuracy. The BGF model reveals hot hydrostatic liquid, vapor-dominated, and transition zones and an overpressured liquid domain that is specific to a vapor-dominated geothermal system overlying a liquid reservoir. Occurrence of counterflow is also a noted feature in the vapor-dominated zone. Because of the high pressure in the steam zone, around 47 bar at a near-saturation temperature of 260 °C, the BGF is characterized as a premature field of a vapor-dominated system.

Broadband and precise reconfiguration of megahertz electromagnetic metamaterials for wireless power transfer

It is a significant challenge to construct reconfigurable electromagnetic metamaterials that can precisely manipulate broadband megahertz electromagnetic waves. Herein, we report a reconfigurable electromagnetic metamaterial (REMM) composed of a two-dimensional periodic array of spiral copper-clad unit cells, each paralleled with a micro-tunable capacitor, which has nearly linear voltage-controlled properties. Moreover, the on-board integrated sample-and-hold modules, linked to all the REMM unit cells, are activated sequentially to perform precise voltage regulation of micro-tunable capacitors for controlling the electromagnetic properties of each unit cell. The experiment results demonstrate that the REMM sample has a maximum frequency adjustment range of 2.1 MHz, ranging from 8.7 MHz to 10.9 MHz with less than 0.1 MHz adjustment step. Furthermore, in a wireless power transfer system, the proposed REMM can achieve the desirable magnetic-field manipulation by precisely adjusting the permeability distribution compared with the traditional metamaterial slab merely capable of full-negative permeability. As a result, the power transfer efficiency (PTE) can be increased from 9.53% to 11.51% (1.69% for the case without the metamaterial slab), and approximately 3.5-fold improvement (from 0.28% to 0.98%) can be achieved when coils are misaligned. This work lays the foundation for the control of electromagnetic waves through using broadband and precise reconfiguration of megahertz electromagnetic metamaterials.