Gas Drainage Research Articles

Case study of gas drainage well location optimization in abandoned coal mine based on reservoir simulation model

The development of abandoned coal mine gas has multiple advantages in terms of safety, economy, environment, and society. Due to previous excavations, the gas distribution is heterogeneous, thereby hindering well location optimization. In this study, considering the Shenbei abandoned coal mine as an example, the authors developed a workflow for well location optimization through simulation. The workflow includes: (1) the setup of an initial reservoir simulation model with the preliminary well location designed by experience; (2) the optimization of the well location based on the flowline distribution, and it is preferred that the well connect a large number of flowlines; (3) the simulation based on the optimized well location, and (4) repetition of the steps until the optimized well locations are determined. Moreover, the role of fracturing is also examined through simulation scenarios. The simulation results show that the locations of the two originally designed wells (1# and 4#) should be optimized due to the relatively low gas production without fracturing. The two wells are optimized according to the flow streamlines, demonstrating performance improvement. Moreover, the simulation results also show that there is no need to optimize the well 4# location if the fracturing technology is applied. An additional well is suggested based on the flow streamline analysis and gas production performance simulation. The main conclusions drawn from this study are as follows. (1) Five optimized well locations are determined for the Shenbei abandoned coal mine, and they should be located within the “O” ring, a high permeability region nearby the previous excavation zone; (2) Fracturing is an effective method for stimulating gas production; however, the extent of fracturing varies from well to well; (3) The workflow applied in this study is effective for the well location optimization in abandoned coal mines.

Research on the influence of radius test based on hydraulic fracturing measures

By analyzing the mechanism of hydraulic fracturing, and the special geological conditions of a certain mine, the relevant parameters of hydraulic fracturing and increasing permeability suitable for the mine are determined through on-site fracturing pump tests. After two sets of hydraulic fracturing tests in the test areas, and compared with the original drainage parameters, the average coal seam gas drainage concentration increased by an average of 3.55, 3.65 times, and the scalar drainage increased by 3.6, 3.1 times. The average water content of coal seams increased by 1.43 times and 1.65 times. Finally, after comprehensive analysis of the borehole gas drainage concentration, gas drainage scalar and coal seam water content measured in test area 1 and test area 2, it is concluded that the influence radius of fracturing and permeability is 25~30m. It provides an effective reference for the layout of hydraulic fracturing boreholes and increasing the effect of gas drainage.

A field application of methane drainage by surface vertical well fracturing in complicated geologic structure area: a case study

ABSTRACT The pre-drainage elimination outburst technology by the surface vertical well fracturing (PDEO) is a method to guarantee the safety of coal mining and promote the coalbed methane development, however, its application effect in complicated geologic structure area is ambiguous. Taking the field test in the Xinjing coal mine as an example, the effects of outburst elimination and gas production by PDEO are examined, the control effects of geological structure on the gas drainage are clarified. Results show that the hydraulic fracturing comprehensive curve can reflect the gas production effect, and the gas production of CBM wells with different fracturing curve types follows this sequence: stationary type > descending type > ascending type > fluctuating type. The cumulative gas production shows an S-shape evolution trend with time and can be described with the Logistic equation. The maximum gas content and gas desorption index of monitoring points in the drainage affected area are averagely reduced by 12.83% and 7.30% than those beyond the drainage affected area, confirming the effectiveness of PDEO technology. The CBM wells located near the closed reverse fault structural belt and the coal seam erosion zones have high gas production, while the gas production of CBM wells near the axis of the syncline with water accumulation decreases to a certain extent. It is difficult to obtain the ideal drainage effect for CBM wells near water-rich abnormal area. This study will provide the engineering experiencefor the surface CBM extraction and offer some references for the prevention and control of coal and gas outburst in complicated geologic structure area.

The Security of Energy Supply from Internal Combustion Engines Using Coal Mine Methane—Forecasting of the Electrical Energy Generation

Increasing emissions from mining areas and a high global warming potential of methane have caused gas management to become a vital challenge. At the same time, it provides the opportunity to obtain economic benefits. In addition, the use of combined heat and power (CHP) in the case of coalbed methane combustion enables much more efficient use of this fuel. The article analyses the possibility of electricity production using gas engines fueled with methane captured from the Budryk coal mine in Poland. The basic issue concerning the energy production from coalbed methane is the continuity of supply, which is to ensure the required amount and concentration of the gas mixture for combustion. Hence, the reliability of supply for electricity production is of key importance. The analysis included the basic characterization of both the daily and annual methane capture by the mine’s methane drainage system, as well as the development of predictive models to determine electricity production based on hourly capture and time parameters. To forecast electricity production, predictive models that are based on five parameters have been adopted. Models were prepared based on three time variables, i.e., month, day, hour, and two values from the gas drainage system-capture and concentration of the methane. For this purpose, artificial neural networks with different properties were tested. The developed models have a high value of correlation coefficient. but showed deviations concerning the very low values persisting for a short time. The study shows that electricity production forecasting is possible, but it requires data on many variables that directly affect the production capacity of the system.

Hydraulic Fracture Propagation and Permeability Evolution in the Composite Thin Coal Seam

Hydraulic fracturing can improve the permeability of composite thin coal seam. Recently, characterizing hydraulic fracture (HF) propagation inside the coal seam and evaluating the permeability enhancement with HF extension remain challenging and crucial. In this work, based on the geological characteristics of the coal seam in a coal mine of the southwest China, the RFPA2D-Flow software is employed to simulate the HF propagation and its permeability-increasing effect in the composite thin coal seam, and a couple of outcomes were obtained. (1) Continuous propagation of the hydraulic microcrack-band is the prominent characteristic of HF propagation. With the increment of the injection-water pressure, HF generation in the composite thin coal seam can be divided into three stages: stress accumulation, stable fracture propagation, and unstable fracture propagation. (2) The hydraulic microcrack-band propagates continuously driven by the fluid-injection pressure. The microcrack-band not only cracks the coal seam but also fractures the gangue sandwiched between the coal seams. (3) The permeability in the composite thin coal seam increases significantly with the propagation of hydraulic microcrack-band. The permeability increases by 1~2 magnitudes after hydraulic fracturing. This study provides references to the field applications of hydraulic fracturing in the composite thin coal seam, such as optimizing hydraulic fracturing parameters, improving gas drainage, and safe-efficient mining.

Prediction Model for Spontaneous Combustion of Coal around Boreholes Using Bedding Gas Drainage

To accurately and reliably predict the time of spontaneous combustion of fractured coal around a borehole induced by gas drainage along the seam, this study performed an orthogonal test taking the No. 10 Coal Mine of Pingdingshan as the research object, in terms of the suction negative pressure and coal seam buried depth. COMSOL Multiphysics was used to model the orthogonal test results, and a multielement statistical analysis of four factors and their relationships with the spontaneous combustion of coal around the borehole and a single-factor analysis in line with the site conditions were performed on the modeling results through multiple regression. The results showed a nonlinear regression relationship between the sealing hole length, sealing hole depth, negative pressure, and coal seam depth and the spontaneous combustion of the coal around the gas drainage borehole; the prediction regression model is significant. Taking the field gas drainage in the No. 10 Coal Mine of Pingdingshan as an example, the relationship between the time of spontaneous combustion of gas drainage and the drainage pressure follows a power of two. When the drainage negative pressure is less than 45 kPa, the coal around the borehole is more likely to undergo spontaneous combustion with increasing pressure, and the sealing hole length has a positive linear correlation with the time of spontaneous combustion of the coal around the borehole. When the sealing hole length is 23 m, the time of spontaneous combustion of the coal around the gas drainage hole is >500 days, and the coal around the borehole does not easily undergo spontaneous combustion. When the sealing depth is 15 m, the time of spontaneous combustion of the coal around the gas drainage hole is 76 days, which is most likely to cause spontaneous combustion.

Numerical analysis of multi-factors effects on the leakage and gas diffusion of gas drainage pipeline in underground coal mines

Gas drainage system is a critical technique to prevent gas outbursts in the underground coal mine. The leakage of gas drainage pipelines can pose serious threats to the safety production of underground mining. In this paper, a multi-factors gas drainage pipeline leakage and diffusion (GDPLD) model is proposed based on the OpenFOAM platform, which can analyze the leakage and diffusion characteristics inside the pipelines. With field measurement data in a coal mine, the GDPLD model is verified with good practicability. Furthermore, scenario analysis in the context of different leak sizes, locations, and pipeline diameters is presented to evaluate the specific characteristics of gas leakage and diffusion inside the pipeline with negative pressure. The results showed that the leakage accident close to the pump station with a large leak size and small pipeline diameter usually represents the worst case, and when gas sensors are installed downstream of the leakage location, it is helpful to realize effective detection of the leakage accident. This study can help to improve the understanding of the leakage and diffusion characteristics of gas drainage pipelines and provide technical supports for the monitoring system design of the gas drainage pipelines in underground coal mines.

Effect of low‐level roadway tunneling on gas drainage for underlying coal seam mining: Numerical analysis and field application

AbstractCoalbed methane (CBM), which is extremely rich in deep coal reserves in China, is not only the material cause of gas explosion and coal‐gas outburst disasters but also a clean and environmentally friendly energy source. Gas drainage must be carried out during deep coal mining to avoid gas accidents while obtaining clean energy. The low‐level roadway is an effective gas drainage measure for coal seams with high coal‐gas outburst risk and low‐permeability, and it can simultaneously realize the functions of gas drainage before and during mining. Roadway tunneling has a strong influence on the stress and permeability properties of the adjusted coal seams, and further determines the gas drainage efficiency and the layout of the air‐return roadway. Taking the Pingshu Coal Mine as an example, this paper analyzes the influence of the vertical distance between the low‐level roadway and the underlying coal seam, and the influence of the width and height of the low‐level roadway on the stress relief and deformation characteristics. The results indicate that the low‐level roadway tunneling results in a nonuniform stress disturbance of coal seam #15. And a reasonable layout and size parameters of the air‐return roadway in coal seam #15 were proposed based on which gas drainage practices were carried out with good effects in panel #15211. The research can effectively guide the elimination of coal and gas outburst in return air roadway, and achieve the purpose of safe and rapid tunneling coal roadway under the environment of highly‐gassy coal seam. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.

Variation law of roof stress and permeability enhancement effect of repeated hydraulic fracturing in low‐permeability coal seam

AbstractHydraulic fracturing experiments were conducted to study the change of initial fracture pressure and roof stress under repeated hydraulic fracturing in coal mines and to investigate the actual penetration enhancement effect on coal seams. The results show that as the fracturing is repeated, a lower initiation pressure is required. The roof stress changes consistently with water injection pressure. First, the stress in the area around the water injection hole gradually increases, and then stress transfers to the surroundings. With the re‐implementation of fracturing, the area of increased stress expands, and the scope of influence of hydraulic fracturing also becomes larger. When fracturing in a coal mine, for the same total fracturing time, the total water injection volume of repeated fracturing is 35% higher than that of single fracturing, and the affected area is increased by 31%. The concentration of repeated hydraulic fracturing is about 36% higher than that of a single hydraulic fracturing, and the pure flow of gas drainage is increased by about 1.3 times. The results of this study can guide the efficient implementation of hydraulic fracturing underground in coal mines, so as to achieve a larger impact range of coal seam hydraulic fracturing and better gas drainage effects.

Influences of Gas Drainage Pipe Positions on Spontaneous Coal Combustion in the Gob: A Case Study of Baode Coal Mine in China

ABSTRACT Gob buried pipe is a common technological means for gas extraction. This method can effectively address the transfinite gas problems on the working face. However, it may induce spontaneous coal combustion in the gob. In this study, the disturbance effect of the gob buried pipe’s entrance position on oxidation of residual coals in the gob is analyzed. A physical model with the same size as the 81307 fully mechanized caving face in the Baode Coal Mine in China is constructed. Then, the airflow leakage field and oxygen concentration field in the gob under different exploitation conditions are solved. Results demonstrate that extraction by buried pipe may change the airflow leakage field in the gob. Specifically, the gas penetration range into the gob is narrowed, which decreases the oxidation zone width in the gob to some extent. When the entrance is far from the working face, the return airway’s oxidation zone is small. With the increase in the distance from the entrance to the working face, the boundaries of the return airway’s oxidation zone also move backward, increasing risks. Combining with field practices, a gap of 100 m between the entrance and the working face can meet fire-resistance requirements of gob and decrease gas concentration at the corners of the return airway, achieving the best effect. The study could help to optimize gob buried pipe’s entrance position, prevent spontaneous coal combustion, so as to guarantee the safety of mining.

Numerical simulation of borehole wall remodel during gas drainage

Gas drainage bearing coal and rock mass can be simplified as isotropic homogeneous body with gas saturation. Numerical method was used to study the influence of borehole wall remodel-size, remodel-length and negative pressure on gas drainage effect which based on gas diffusion and seepage equation of pore fracture system and governing equation of coal and rock mass degeneration. The results showed that borehole wall remodel can maintain the support of coal skeleton in borehole and prevent blocking the gas flow channel, gas pressure drop in remodelled section is more obvious than that in the non-remodelled section, the longer the remodelled length of borehole wall the more smooth the gas flow channel between borehole and coal body around borehole, with the increase of negative pressure, the decrease range of gas pressure at the same depth increases, but the difference is small under different negative pressure. On the premise of preventing borehole creep instability, borehole wall remodel can provide high-quality gas flow channel for coal seam gas drainage, maintain the continuous influence of negative pressure on coal body along borehole depth to extend the life cycle of gas drainage and is not sensitive to borehole wall remodel size and negative pressure.

Research on quality inspection technology of gas drainage borehole sealing hole in Sihe Coal Mine

The quality of the hole sealing of coal seam gas drainage directly determines the efficiency of coal seam gas drainage. This paper uses the YFZ3 gas drainage borehole sealing quality tester to measure the gas drainage parameters at different locations in the borehole W33011 coal seam in Sihe Coal Mine. According to the change law of the measuring point data, it judges the quality of the sealing hole and determines the reasonable sealing depth. The research results show that Sihe Coal Mine should strengthen the training and supervision of underground plugging workers, and strictly control the details of the plugging process, such as the grouting pressure, water-cement ratio configuration and grouting volume during the plugging process. The detection borehole has a serious air leakage channel in the range of 12m~20m, and the sealing depth should be increased to 20m to increase the concentration of single-hole gas drainage.

Study on Gas Comprehensive Control Technology in Steep and Extra Thick Coal Seam

In order to improve the gas drainage amount and drainage rate of steeply inclined and extra thick coal seam and realize the safe and efficient mining of coal mine, the distribution and evolution law of surrounding rock stress field and fracture field of horizontal slicing mining face in steeply inclined coal seam were revealed by using numerical simulation method, and the gas flow process and law from lower pressure relief gas to slicing mining face were analyzed The comprehensive control measures of the combination of pressure relief gas interception and drainage and buried pipe drainage in the goaf of this layer have realized the effective gas control of the mining face in the mine production process. The research results play a typical demonstration role for the comprehensive control of rock burst and gas in steep and extra thick coal seam in Xinjiang and even in the whole country, and have promotion significance.

Effect of the proppant on fracture compressibility in coal seam

The paper discusses enhancement of gas drainage well productivity in coal seams using the hydraulic fracturing technology. Filling of a fracture with proppant provides a long-term increase in the gas drainage well performance. The results of the laboratory experiments to determine coal permeability under various stress conditions show that proppants significantly reduce fracture compressibility and the propped fracture becomes less sensitive to stress variations.

Research on screen pipe hole protection technology of large diameter directional long drilling hole

In order to solve the problems of serious hole collapse and poor gas drainage effect of large diameter directional long borehole in roof under complex geological conditions, based on the gas geological conditions of 32 coal seam in Zouzhuang coal mine, the research on hole protection technology of full hole under large diameter directional long borehole of roof under complex geological conditions was carried out. The construction efficiency was improved by 32%, the drilling hole forming effect was good, and the gas drainage effect reached the expectation.

Case analysis of in-situ stress coal and gas outburst and prevention countermeasures

The coal and gas dynamic disasters in Fengcheng mining area are serious. There are currently 6 pairs of coal and gas outburst mines. In view of the increase in the proportion of in-situ stress-oriented outbursts in the mining area as the mining depth increases, the establishment of classified disaster control measures is proposed. Stereo gas drainage system, and proposed to explore the use of deep hole pre-splitting blasting, roof strike long drilling, hydraulic reaming, hydraulic fracturing and other new technical measures. It is of great significance to safe and efficient production in mining areas.

Research on Classification Management Method of Xushen Gas Field

Xushen gas field not only exploits volcanic gas reservoir, but also develops glutenite reservoir. In the production process, there are great differences in gas well productivity, formation pressure and single good reserves. By establishing the fine management mode of four types of wells, the “one type, one method, one well, one policy” has been realized. It mainly forms the multi-factor comprehensive production allocation technology with “two optimizations and three control” as the means, improves the winter peak regulation mechanism of withdrawal, supplement and shortterm emergency peak shaving, determines the drainage gas production technology to meet the current development needs, explores the treatment method of easy freezing plugging well with “three-step” as the main method, and effectively governs Low-yield and low-efficiency wells.

Numerical simulation study on gas drainage by interval hydraulic flushing in coal seam working face

In order to solve the problem of difficult gas extraction in coal mine, a method of gas extraction from coal seam by interval hydraulic flushing is put forward. Based on the coal seam gas occurrence conditions of 7609 working face in Wuyang Coal Mine, the numerical simulation research on gas drainage by ordinary drilling and hydraulic flushing drilling was carried out by using COMSOL numerical simulation software. The results show that with the increase of hydraulic flushing coal quantity, the effective gas drainage radius also increases. The effective extraction radius of ordinary drilling is 0.5 m, and the effective extraction radius is 1.0 m, 1.2 m and 1.3 m respectively when the coal flushing quantity is 0.5t/m, 1.0t/m and 1.5t/m. As multiple boreholes are drained at the same time, the boreholes will affect each other, which will reduce the gas pressure and increase the effective drainage radius, the spacing between boreholes can be greater than twice the effective drainage radius of a single borehole when arranging boreholes. And the smaller the flushing interval, the more uniform the gas pressure reduction area. According to the numerical simulation results, the ordinary drilling and 1.0t/m interval hydraulic flushing test were carried out in the field. Through observation and analysis, the gas concentration of the interval hydraulic flushing drilling module was increased by 31.2% and the drainage purity was increased by 5.77 times compared with the ordinary drilling module. It shows that the interval hydraulic flushing drilling can effectively improve the gas drainage effect.

Permeability Enhancement Properties of High-Pressure Abrasive Water Jet Flushing and Its Application in a Soft Coal Seam

High-pressure abrasive water jet flushing (HPAWJF) is an effective method used to improve coal seam permeability. In this study, based on the theories of gas flow and coal deformation, a coupled gas-rock model is established to investigate realistic failure processes by introducing equations for the evolution of mesoscopic element damage along with coal mass deformation. Numerical simulation of the failure and pressure relief processes is carried out under different coal seam permeability and flushing length conditions. Distributions of the seepage and gas pressure fields of the realistic failure process are analyzed. The effects of flushing permeability enhancement in a soft coal seam on the gas drainage from boreholes are revealed by conducting a field experiment. Conclusions can be extracted that the gas pressure of the slotted soft coal seam is reduced and that the gas drainage volume is three times higher than that of a conventional borehole. Field tests demonstrate that the gas drainage effect of the soft coal seam is significantly improved and that tunneling speed is nearly doubled. The results obtained from this study can provide guidance to gas drainage in soft coal seams regarding the theory and practice application of the HPAWJF method.

Numerical modeling of gas flow in coal pores for methane drainage

The sudden explosion of methane during underground coal mining is a major dilemma. To mitigate its occurrence and reduce the extent of methane diffusion, gas drainage operations are carried out before mining. This paper investigates methane gas flow in a coal block in order to calculate the pressure of gas and its molecule velocity for methane gas drainage operation. A coal piece surrounded by cleats was used for geometrical modeling and numerical simulation. Movements of fluid and gas molecules in a porous medium were successfully simulated. The numerical solution is based on COMSOL Multiphysics software. The validity of the numerical simulation was assessed using an analytical model with satisfactory results.