Gas Distribution Characteristics Research Articles

Numerical Simulation Study on Optimization of Development Parameters of Condensate Gas Reservoirs

Due to the retrograde condensation phenomenon in the development process, the fluid phase change is complex, and it becomes particularly difficult to accurately describe the fluid flow characteristics and residual oil and gas distribution characteristics during the development of condensate gas reservoirs. It is difficult to select the development program and subsequent dynamic adjustment for the efficient, reasonable, and sustainable development of condensate gas reservoirs. In this paper, the phase characteristics of condensate gas reservoirs are clarified; the basic fluid model is created by using computer modeling, using Win-Prop; and in view of the characteristics of the target condensate gas reservoirs, the CMG (Computer Modeling Group) numerical simulation method is applied to study the effects of six factors, the thickness of the reservoir, permeability, porosity, rock compression coefficient, the ratio of the vertical permeability to the horizontal permeability, and the injection of different media, on the development effect through the study of different development parameters of gas condensate reservoirs. The purpose of this study is to provide guidance for the rational development of condensate gas reservoirs in practical production.

Large-Scale Physical Simulation Experiment of Water Invasion Law for Multi-Well Development in Sandstone Gas Reservoirs with Strong Water Drive

In order to clarify the water invasion law and residual gas distribution characteristics in edge and bottom water gas reservoirs with multi-well development, a large-scale three-dimensional physical simulation model was developed and a physical simulation experiment method for the water invasion law of multi-well development in sandstone gas reservoirs with strong water drives was established. Water invasion physical simulation experiments of multi-well development under the conditions of different water body multiples and production systems were conducted. The results show the following: (1) Gas wells near fractures and high-permeability zones experience the earliest water breakthrough. The larger the water body multiple, the faster the rate of water invasion, the earlier the water breakthrough time of gas wells, the more severe the degree of water invasion in gas reservoirs, and the lower the ultimate recovery rate. (2) Shutting in low-position gas wells immediately after water breakthrough reduces the overall water production of the gas reservoir and extends the overall water-free gas production period. However, the ultimate recovery rate is lower than when the wells are not shut in. (3) The residual gas in the fracture model is mainly distributed around the fracture and the edge of the gas reservoir, with the ultimate recovery rate ranging from 38.5% to 58.2%. The residual gas in the fracture–high-permeability zone model is mainly distributed around the fracture–high-permeability zone and the edge of the gas reservoir, with the ultimate recovery rate ranging from 28.32% to 41.8%. The experimental results have important guiding significance for the economical and efficient development of similar gas reservoirs.

Research on Gas Control Technology in Goaf Based on the Influence of Mining Speed

To comprehensively understand the influence of mining speed on gas emissions in goaf during coal seam extraction, enhance gas extraction efficiency in goaf, manage gas emissions at the working face, and ensure safety in the mining production process. This study focuses on the No. 3 mining area of Wangjialing Mine, employing numerical simulations to analyze the evolution of mining-induced fractures and the characteristics of gas distribution in the overburden at varying mining speeds. Furthermore, by integrating actual gas emission and extraction data at the production face, this study examines the quantitative relationship between mining speed and gas emissions in the goaf, identifying optimal regions for high-position borehole layouts and conducting borehole optimization design and investigation. The results of this study indicate that the initial caving step distance of the goaf roof increases with the advancement speed of the working face. Conversely, the maximum height of through fractures in the overburden decreases as the mining speed increases, while delamination fractures are minimally affected by the advancement speed. By categorizing and averaging data on goaf mining speed, the impact of initial and periodic pressure on gas emissions can be effectively mitigated, revealing a linear correlation coefficient of 0.94 between goaf gas emissions and mining speed. At varying mining speeds of the working face, the efficient extraction layer and horizontal distance parameters of gas extraction boreholes in the goaf conform to the linear equation y = ax ± b. Based on the research findings, an optimization design for mining face speed and high-level borehole parameters in the goaf was implemented. The average gas extraction rate of high-level directional boreholes reached 68% throughout the extraction period. Gas emissions at the working face were effectively controlled below 10 m3/min, with the maximum gas concentration at the upper corners and return airflow kept below 0.8%. This effectively managed gas emissions at the working face, ensuring safe production in the mine, providing a theoretical basis for identifying gas-rich areas in the mining-induced overburden, and enhancing gas extraction efficiency at the working face.

Characterization of spatiotemporal distribution of gas in the goaf of W-type ventilated working face

In order to solve the problem of gas over limit near the return air trough of W-type ventilated working face, a method combining numerical simulation and on-site measurement was used to study the spatial and temporal distribution characteristics of gas in the goaf under the W-type ventilated mode, and the reliability of the model was verified. Delineate the gas-rich area and suitable pumping area in the goaf, by analyzing the pumping of the top plate high-level directional borehole in the area, optimize the best layout of the top plate high-level directional borehole. The results show: The gas concentration in the goaf gradually increases from shallow to deep in the direction, and increases rapidly in the range of 0–75 m; in the direction of inclination, it is approximately symmetrically distributed along the axis of the return air trough, and gradually decreases toward the air inlets on both sides. The gas concentration in the middle area of the working face is higher than 0.85%; in the vertical direction, the further away from the coal seam roof, the higher the gas concentration, but the growth rate decreases, and the range of high gas concentration gradually expands. The gas concentration of the goaf reflected by the changes in the concentration of the working face has gradually increased in the early stages of mining. and then changes periodically with the cycle of roof pressure in the later stage. There is a strong correlation between the amount of gas emission the goaf and the mining speed of the working face. The regularity of the simulation result is the same as the regularity of the measured results, and the absolute value of the relative error is within 10%, that the concentration of extraction from high-level directional borehole increases with the height of the arrangement, mixed and pure volume decreases with the height of the arrangement. Comparison of the average mixed volume, concentration, pure volume and total extraction volume of each high-level directional borehole, it can be seen that the average pure volume from 3#holes is 3.9 times higher than that from 1#holes, and the total extraction volume accounts for 29% of the total extraction volume from the drill site, it is obtained that the best layout of the high-level directional boreholes of the 3203 working face is between 25 and 35 m above the top board. During the high-level drilling period, the gas concentration in the return air trough was between 0.42% and 0.75%, which effectively prevented the occurrence of gas over limit accidents.

An Evaluation Method of Gas-Bearing Properties Based on Gaussian Bimodal Function Pore Structure Characterization: A Case Study of Tight Sandstone in the East China Sea Basin

The Xihu Sag in the East China Sea Basin is located at the edge of the eastern Chinese continent and has great exploration potential. In recent years, the development of low-permeability and tight sandstone gas has become an important area of exploration and development in the Huagang Formation (E3h) of the Xihu Sag. The tight sandstone reservoir in the Xihu Sag is characterized by serious heterogeneity, high water saturation, low resistivity, and a complex gas–water relationship. Because of these characteristics of tight sandstone reservoirs, it is difficult to perform an evaluation of them. In this work, a bimodal Gaussian density function was constructed using the data of high-pressure mercury intrusion (HPMI) and nuclear magnetic resonance (NMR); this approach was used to analyze the pore structure parameters. The reservoirs were divided into four types using the fitting parameter η, and the rock electric parameters that correspond to different pore structures were quite different. When combined with the log response equation of η with acoustic interval transit time (AC), density (DEN), and natural gamma (GR) logging curves, an evaluation method of gas-bearing properties that was based on the characteristics of the pore structure was established. Compared with the water saturation test of the sealing core, it was found that the water saturation calculated by the classification of the pore structure was more accurate than that obtained by the conventional method, and the error was less than 8.35%, which proves that this method is feasible and effective. The findings of this study can help provide a better understanding of the distribution characteristics of gas and water in tight sandstone and provide help for tight gas exploration and development.

Research on gas hazard prevention and control of a high-gas fully mechanized mining face based on ventilation system optimization.

The gas accumulation in the return corner of a high-gas fully mechanized mining face can easily cause the gas volume fraction to exceed the safety limit, threatening the safety of coal mines. In this study, the unit method was used to analyze the gas sources and emissions based on the actual case. The airflow and gas distribution characteristics of the two-inlet-one-outlet (TIOO) ventilation system and the one-inlet-two-outlet (OITO) ventilation system were studied using CFD numerical simulation. The results show that under the TIOO ventilation system, the "U"-type air leakage in the goaf leads deep gas into the return corner, which causes the gas volume fraction in the return corner to rise to 0.4-2.0%. After the mining face is optimized into the OITO ventilation system, the "J"-type air leakage of the goaf suppresses the high concentration of gas in the deep position of the goaf. Combined with the gas extraction measures, the gas volume fraction in the return corner, exhaust roadway's outlet, and retaining roadway's outlet is controlled at 0.28%, 0.34%, and 0.23%. This study will provide new ideas for solving the problem of gas accumulation in the return corner of a high-gas fully mechanized mining face.

Gas-bearing prediction of deep reservoir based on DNN embeddings

The extraction of gas-bearing information from the deeply underground reservoir is extremely difficult due to the weak seismic response and complicated gas distribution characteristics. To predict gas-bearing reservoirs efficiently, we developed a deep neural network (DNN) embedding-based gas-bearing prediction scheme. First, the cepstrum coefficient that is sensitive to hydrocarbons is computed using the raw seismic data. A DNN model inspired by the x-vector in speech recognition is designed, comprising the long short-term memory (LSTM) networks and two fully connected (FC) networks, stacked from the bottom to the top layer. Then, the cepstrum features are fed into the DNN for training and testing, and DNN embedding is extracted from the top layers after optimized network parameters are determined. Finally, the gas-bearing probability of the reservoir is predicted by calculating the cosine distance between pairs of DNN embeddings. When applied to synthetic seismic data, the proposed method offers greater than 90% accuracy at SNR > 3 dB. Besides, the predicted result applied in deep carbonate reservoirs in China’s Sichuan Basin is in basic agreement with the actual situation, demonstrating the certain feasibility of the proposed scheme.

Insight into proactive inertisation strategies for spontaneous combustion management during longwall mining of coal seams with various orientations

ABSTRACT Spontaneous combustion of coal occurs in the longwall (LW) goaf during mining cycles due to coal oxidation at low temperatures and air ingress. Coal seam orientations, dictated by the elevations of maingate (MG) and tailgate (TG) and the height of working face and starting-up line, significantly impact the gas distribution in the goaf. Despite this, there has been limited study on the effects of coal seam orientations on spontaneous heating management. To fill this knowledge gap, extensive computational fluid dynamics (CFD) modeling was conducted based on the actual conditions of an Australian underground coal mine and verified with onsite gas monitoring data, after which extensive parametric studies of how coal seam orientations influenced gas distribution were conducted. Simulation results indicate that coal seam orientations significantly impact spatial gas distribution in the LW goaf and the development of proactive goaf inertisation strategies. Regardless of coal seam orientations, nitrogen performs better than carbon dioxide in reducing the oxidation zone area. In addition, at least 1.5 m3/s of nitrogen is required to effectively prevent spontaneous heating, and the area ratio of oxidation zone to active goaf is approximately 10%, reducing by about 15% compared to scenarios without inertisation. The modeling results shed insight into the goaf gas distribution characteristics under various coal seam orientations and provide guidance on developing corresponding proactive inertisation strategies for managing spontaneous heating in the goaf, thus improving mining safety.

Physicochemical characteristics of three-phase products of low-rank coal by hydrothermal carbonization: experimental research and quantum chemical calculation

In this paper, the distribution characteristics of gas, liquid, and solid products of low-rank coal by hydrothermal carbonization (HTC) at different temperatures are studied. Advanced testing methods are used to explore changing rules of physicochemical characteristics. Reaction properties of different regions are explained based on the mechanism of quantum chemistry. Experimental results showed that as the temperature increases, the volatile content decreases, the fixed carbon content increases, and impurities are removed in the form of gas or ions. The coal aliphatic properties are reduced, whereas the aromatization degree is significantly enhanced. Meanwhile, the specific surface area after upgrading is reduced, but the average pore diameter is increased, and the pore structure density is enhanced. The content of carbon-containing groups increases but that of carbon-oxygen groups decreases, which corresponds to the O/C ratio. Theoretical calculation results demonstrate that the more negative and positive areas of the surface electrostatic potential (ESP), the smaller distribution proportion. The ESP value in the vicinity of oxygen-containing group is relatively negative, indicating that it is more reactive, which is a good proof of the experiment's conclusions. In summary, low-rank coal obtained after HTC meets the blast furnace injection requirements and can be used for injection.

Parameter Optimization and Application of Gas Extraction Technology by Buried Pipes in Goaf of Multi-roadway U-type Working Face

ABSTRACT The gas extraction method by buried pipes in closed connection roadways of goaf was proposed. It was intended to solve large gas emission quantity and over-limit gas concentration at the upper corner in the goaf of highly gassy mine. The study object was 81307 fully mechanized mining face in Baode Coal Mine. The gas distribution characteristics in the goaf during no extraction and those during gas extraction by buried pipes under different extraction parameters were numerically simulated via COMSOL Multiphysics, and the best layout parameters of buried pipes in the goaf were determined. A field optimization experiment was carried out for the extraction parameters. Results showed that the extraction measure by buried pipes could effectively solve the aforementioned over-limit gas concentration at the upper corner when the layout spacing of closed connection roadways was 100 m, extraction pressure was −32 kPa, diameter of extraction pipe was 800 mm, and extraction flow was 600 m3/min. During the experiment, the average gas concentration at the upper corner was 0.38% and that in the return airway was 0.29%. Both of which were lower than the national safety standard, thus reaching the goal of safety production.

Research on the influence of different obstacle structures on the energy distribution characteristics of pulse detonation gas

In order to improve the gas energy conversion efficiency at the outlet of the pulse detonation combustor, numerical calculation methods were used to study the influence of three different cross-section obstacle structures of square, circle and trapezoid on the distribution characteristics of gas pressure potential energy, kinetic energy and internal energy in a single cycle at the outlet of pulse detonation combustor. The results show that: the expansion of pulse detonation gas mainly includes three-stages: primary expansion, secondary expansion, and over-expansion. Gas pressure potential energy, kinetic energy, and internal energy increase during the primary and secondary expansion stages, and decrease during the over-expansion stage. Pulse detonation combustor with trapezoidal cross-section obstacle structure has the smallest proportion of gas energy at the outlet of the combustor during the over-expansion stage and the highest proportion during the secondary expansion stage. Compared with square and circle cross-section obstacle structures, the gas energy distribution at the outlet of the pulse detonation combustor with trapezoidal cross-section obstacle structure is the easiest for turbomachinery to convert the gas energy.

A method for identifying the fire status through ventilation systems using tracer gas for improved rescue effectiveness in roadway drivage of coal mines

When a coal mine fire occurs, the rescue of trapped mine workers is difficult, because some efficient fire-fighting measures (such as nitrogen injection) cannot be implemented. The development and severity of a fire is difficult to determine, and the integrity of the auxiliary ventilation system may be unknown. These situations pose additional challenges to the trapped mine workers and increase the difficulty level for the rescue team. A novel method using the tracer gas technique is developed to remotely gather information to determine the location and severity of the fire. Laboratory experiments were conducted to understand the tracer gas distribution characteristics when the fire causes damage to the ventilation duct. A mathematical model was developed that uses the tracer gas concentration curve to determine the location and severity of the fire. The model combines the Expectation Maximization (EM) algorithm with the Gaussian Mixture (GM) model. Validated using experimental data, it is demonstrated that the method can determine the fire location with low error. The information collected using this method reflects basic living environmental conditions of the trapped mine workers and provides important input for quickly formulating an effective fire rescue plan that saves lives.

Differentiated warning rule of power transformer health status based on big data mining

Accurate on-line monitoring of transformer operation status is essential to ensure the reliability of power system. The dissolved gas analysis (DGA) method, which compares the gas concentration to the pre-set threshold, is most widely used for transformer status warning. However, existing standards apply either single threshold value or rough classification to diversified transformers with different properties, which therefore affects the accuracy of status warning. This paper establishes a differentiated warning rule through big data analysis mining. The Fuzzy C -means method is applied to identify optimal transformer properties, which can reflect the individualized characteristics of transformer to the best extent. As verified by the probability plot, the full sets of dissolved gas data under the selected properties conform to the Weibull Model. Association analysis is then carried out between the dissolved gas distribution characteristics and defect/ fault rate, and the warning thresholds are accordingly calculated. Correlating the gas concentration and gas increase rates with established warning values, the transformer operation status can be identified. The verification test indicates that the differentiated warning rule shows better performance than conventional methods and demonstrates an accuracy as high as 98.21%.

Natural Gas Reservoir Characteristics and Non-Darcy Flow in Low-Permeability Sandstone Reservoir of Sulige Gas Field, Ordos Basin

In order to reveal the gas–water distribution and formation mechanism of the low-permeability sandstone gas reservoir, the gas reservoir distribution and the formation mechanism in a low-permeability sandstone gas reservoir are investigated using data obtained from a physical simulation experiment of gas percolation. The exploration and experimenting for petroleum in the upper Paleozoic gas pool of the Sulige gas field in the Ordos basin in this paper. Results showed that the gas reservoir is characterized by low gas saturation, a complex distribution relationship of gas–water, and weak gas–water gravity differentiation. The characteristics of gas distribution are closely related to permeability, gas flow, and migration force. The capillary pressure difference is the main driving force of gas accumulation. There exists a threshold pressure gradient as gas flows in low-permeability sandstone. The lower that permeability, the greater the threshold pressure gradient. When the driving force cannot overcome the threshold pressure (minimal resistance), the main means of gas migration is diffusion; when the driving force is between minimal and maximal resistance, gas migrates with non-Darcy flow; when the driving force is greater than maximal resistance, gas migrates with Darcy flow. The complex gas migration way leads to complicated gas- water distribution relationship. With the same driving force, gas saturation increases with the improvement of permeability, thus when permeability is greater than 0.15 × 10−3 µ m2, gas saturation could be greater than 50%.

The sloshing effects on distribution characteristics of gas–liquid mixture in spiral-wound heat exchanger

Spiral-wound heat exchanger (SWHE) is important equipment for industry, and it is suitable for floating production storage off-loading (FPSO). However, two-phase mixture maldistribution always restricts the heat transfer capacity of SWHE in FPSO. Few studies have focused on the maldistribution of SWHE. According to this, an experimental device was fabricated to evaluate the maldistribution of a novel distributor on the sloshing platform. The effects of vapor qualities and mass flow rates were analyzed at the range of 0.106–0.702 and 608.5–1491.6 kg h−1, respectively. The following conclusions are drawn: With the augmentation of vapor quality, the gas–liquid uniformity deteriorates after optimizing under steady and sloshing conditions. Heave condition improves gas and liquid flow uniformity by 2.9–11.0% and 1.7–3.7% separately, and pitch condition improves the gas flow uniformity by 0.5–3.7%, and roll condition lowers the liquid flow uniformity by 2.0–7.2% in the variation of vapor quality. It is also proved that the flow uniformity achieves better performance with the increasing mass flow rate under steady, heave and pitch conditions. Heave condition improves the distribution characteristic by 4.4–8.7% for the gas phase and 2.0–9.5% for the liquid phase, and pitch condition elevates the gas flow uniformity by 3.1–7.7%. Under the roll condition, the distribution performance of the experimental model changes worse after better and obtains the best performance at the mass flow rate of 1183.8 kg/h. At large mass flow rates, gas entering into liquid space under roll condition can bring the structural problem. Increasing the tube diameter and making the upper baffle tilt from shell to center barrel are beneficial to keep the distributor structure safe.

An 80 mW/8 K high-frequency pulse tube refrigerator driven by only one linear compressor

High-frequency pulse tube refrigerator (HPTR) has significant advantages in terms of compactness and high reliability, but it is difficult to obtain very low cooling temperatures. To obtain temperatures below 10 K, multi-stage structures driven by more than one compressor are currently used. This paper reports a two-stage gas-coupled HPTR driven by a single compressor that is extremely compact and even comparable to a single-stage structure. The pre-cooling temperature influences and gas distribution characteristics, which are two important issues in the research of gas-coupled structure refrigerator, were first numerically calculated and analyzed. Then the calculation results were verified by experiments and the cooling performance was tested. Before gas-coupling with the lower stage, the pre-cooling stage can obtain 4.3 W/40 K cooling capacity with 330 W electric input power, which belongs to a high-efficiency 40 K refrigerator that has been reported so far. With an electric power of 400 W, the gas-coupled HPTR taking the developed 40 K refrigerator as the pre-cooling stage achieves a no-load temperature as low as 5.7 K, which is the lowest record of the current two-stage gas-coupled structure in HPTCs. The developed two-stage HPTR can obtain a cooling capacity as high as 80 mW/8 K, and the two stages can also output the cooling capacity of 100 mW/9.3 K and 1000 mW/40 K simultaneously.

Gas distribution characteristics for heterogeneous flows in the slender particle-containing scrubbing–cooling chamber of an entrained-flow gasifier

Dual-tip conductivity probes and a high-speed camera were used to study the gas distribution characteristics in a cold model apparatus of the slender particle-containing scrubbing–cooling chamber. The three-dimension column was 200mm in internal diameter and 1353mm in height. The effects of superficial gas velocities, fiber volume fractions and fiber aspect ratios on global gas holdups were determined. The results showed that under the influence of reverse buoyancy and negative pressure gradients, plume gas flow went up along the outside of the downcomer in downcomer spout region. Local radial gas holdup which was closely related with the internals and flow patterns presented obviously proximate core peak distribution in bubble-breaking plate region. The foam region consisted of bubble coalescence and breakup as well as droplets formation and splashing. At higher gas velocities, the increasing rate of global gas holdup gradually reduced. With the increase of fiber volume fraction, global gas holdup slightly increased at low gas velocities due to suppressed bed turbulence and bubble loading, but decreased at high velocities for increased liquid viscosity and vortex-shedding. Due to suppressed small-scale velocity fluctuation, global gas holdup increased with increased fiber aspect ratio. A modified drift-flux model containing crowding factor and fiber number density for global gas holdup correlations was proposed and all of the data could be calculated with a relative deviation less than 10%.

Numerical Simulation of Several Parameters of Distribution Uniformity of Tracer Gas in Stope

Tracer gas technology is an effective way to evaluate underground coal mine ventilation system, especially in stope, air leakage from working face to gob can be quickly detected by this method. While tracer gas distribution characteristics may be different with the variation of ventilation parameters, therefore, ascertaining the uniform distributed location as sampling point is essential to improve the measuring accuracy of tracer gas technology. This study conducts simulations of tracer gas distribution in four ventilation models with different parameters, aiming to analyze the effects of gob and height difference between roadway and working face on tracer gas distribution uniformity. The result shows the porous characteristics of gob is not conductive to tracer gas uniform distribution, the height difference between roadway and working face increases the turbulence intensity of airflow and promotes the uniform distribution of tracer gas. In no height difference stope, tracer gas and airflow can be mixed uniformly at 5D of return roadway, but in height difference stope, only 1D is required. Finally, a practical case study is conducted to verify the validity of simulation.

Evaluations of oil and gas lateral migration across faults: A case study of Shigezhuang nose structure of Wen'an slope in Baxian sag, Jizhong depression, Bohai Bay Basin, East China

Abstract To study the possibility and location of lateral migration of oil and gas across faults, a quantitative evaluation method for lateral migration of oil and gas across faults was established using the Shuangjing Knipe graphic method to identify the juxtaposition site and juxtaposition patterns of sand and sand in the upper and lower walls of the reverse faults and the consequent faults, combined with the oil and gas limit method of fault lateral seal in the test oil area. The quantitative evaluation method was applied to the first and two members of the Paleogene Shahejie strata (referred to as Es1 and Es2) of Shigezhuang nose structure of Wen'an slope in Baxian sag, Jizhong depression, Bohai Bay Basin, to determine the juxtaposition site of sand and sand in the upper and lower walls of the fault, and the shale gouge ratio (SGR) lower values are 26% and 29% respectively in the strata Es1 and Es2. Thus, the location of lateral migration of oil and gas across faults was determined. Based on the oil and gas distribution characteristics of the strata Es1 and Es2, and variation trend of nitrogen compounds in 4 wells in the strata Es1, the results were consistent with the quantitative evaluation of the location of lateral migration of oil and gas across faults, the feasibility of the evaluation method was preliminarily verified.

Prediction of coal mine goaf self-heating with fluid dynamics in porous media

Coal mine goaf self-heating due to exothermic coal oxidation has been recognized as a major threat to coal mine safety. To evaluate the risk of the coal mine goaf self-heating hazard, both gas distribution characteristics in goaf and heat transfer mechanisms in porous media must be studied. However, due to the difficulty of determining goaf permeability and the complexity of the overlaying strata caving characteristics, it is a considerable challenge to determine the thermal-fluid field coupling. Based on the volumetric average method in porous media, this work develops three numerical models for solving fluid dynamics and heat transfer in both longwall face and goaf. The Brinkman-Forchheimer-extended Darcy model is introduced to describe inertia and frictional forces in fluid phase exerted by solid phase. Temperature profile is highly dependent on and affects coal oxidation rate; therefore, governing equations for energy and oxygen mass equilibrium must be coupled. A two-dimensional goaf permeability distribution model is established based on different caving conditions in goafs. Three scenarios are simulated and validated by field and experimental data, and it is observed that these models are capable of predicting gas flow pattern and temperature distribution.