Outburst Coal Seam Research Articles

An integrated drilling, protection and sealing technology for improving the gas drainage effect in soft coal seams

There are many problems within drilling in soft and broken coal seams, such as borehole collapse, borehole air leakage, CO Toxic gas generated during borehole construction, coal dust pollution to the working environment and other hazards. The efficiency of coal seam gas drainage can be seriously affected by the above problems. To solve these problems, an integrated drilling, protection and sealing (IDPS) technology is proposed for borehole construction. Four major technologies are integrated: the high-purity nitrogen as slag discharge medium is used for the long-distance drilling; the integrated screen pipe inserting technology is adopted to achieve the purpose of borehole protection in the whole drilling process; the new airbag grouting technology guarantees high-quality borehole sealing; and the dust collection device is utilized to realize safe and clean operation environment. The new technology proposed in this study have the following five advantages in such as: long-distance drilling in soft coal seams, borehole protection in the whole drilling process, high-quality borehole sealing, a dust-free and safe operation environment, and efficient gas drainage. The application of IDPS technology in Hudi Coal Mine shows that the problems such as difficult borehole formation, poor gas drainage effect and coal seam outburst risk in soft and broken outburst coal seam can be effectively solved. Meanwhile, the IDPS technology proposed in this study provides scientific guidance for gas drainage in soft and broken coal seam.

Study on application of high speed cross belt auger drilling machine in fragmentized coal seam

In order to extract gas efficiently in soft outburst coal seam with belt haulage roadway, a ZDY2800LG full hydraulic drilling rig with high drilling rate, cross-belt construction ability and strong adaptability of technology was developed. The whole process of industrial test of drilling machine is introduced in detail through three stages of formation groping, breakthrough seeking and efficient drilling.

Research on hydraulic permeability enhancement technology of high, medium and low pressure coal seam with deep well and high ground stress

Aiming at the problem of poor gas extraction, long outburst time and low pre-drainage efficiency in the drilling zone of the floor tunnel through the drilling, the problem of mining excavation replacement is severely restricted. Dingji Coal Mine has carried out ultra-high pressure, medium pressure, and low pressure hydraulic cutting coal seam enhanced permeability gas extraction technology tests. Through continuous exploration and summary, it has achieved remarkable results, maximized extraction, and accumulated rich hydraulic coal Through experience. The results show that: the high-pressure hydraulic coal seam anti-reflection pre-draining unit has a maximum extraction pure volume of 3.1m3/min, the single-hole average extraction pure volume is 0.008m3/min; the medium-pressure hydraulic coal seam anti-reflection pre-extraction unit has a maximum extraction pure volume of 2.2 m3/min, single-hole average extraction pure volume is 0.005m3/min; low-pressure hydraulic coal seam permeability enhancement unit extraction pure volume is maximum 1.3m3/min, single-hole average extraction pure volume is 0.002m3/min. 1351(1)Yunshun’s gas pre-drainage rate reached 65.2% after adopting high-pressure hydraulic coal seam penetration enhancement measures. Through statistical analysis of the anti-burst prediction index during coal tunnel footage, the sensitive index is relatively small, and the effect of pre-draining outburst is better. The lane enters 200m per month. The permeability enhancement technology of hydraulic coal seam has a significant effect on the pre-drainage of gas in high ground pressure outburst coal seam. It provides an effective method for improving the gas pre-drainage and outburst work, which is worthy of in-depth promotion and application.

Discussion on some problems of risk identification of coal seam outburst

The identification of coal and gas outburst is a complex work. In order to strengthen and standardize the identification of coal outburst risk, the state has issued a series of regulations and requirements. Combined with various problems encountered in outburst identification work, this paper studies and discusses the selection of identification indexes, the situation that adjacent mines are identified as outburst, the situation that they do not have identification conditions, the relationship between measurement points and identification scope, and the location of geological structure areas, etc., and puts forward suggestions for relevant regulations, which will be helpful for future outburst coal seam identification work and revision of national regulations.

A safe mining approach for deep outburst coal seam groups with hard‐thick sandstone roof: Stepwise risk control based on gas diversion and extraction

AbstractProtective seam mining is the preferred method for gas control and safe mining in high‐outburst coal seam groups. However, a hard‐thick sandstone roof (HTSR) triggers new gas problems when it covers directly above the first‐mined protective coal seam. To solve these problems, a typical case study in No. 12 Coal Mine was conducted. The simulation results indicate that the HTSR greatly prevents the plastic deformation of the upper roof formations without affecting the expansive deformation in the underlying protected seams. The pressure‐relief gas in protected seams will flow into the protective seam without continuing to migrate to roof strata, thereby turning the protective seam into a new high‐risk area. Therefore, roof presplitting (RPS) technology was proposed to effectively break the HTSR, create roof fracture passages, and divert the gob gas of the protective seam upward. Meanwhile, gob‐side entry construction (GSEC) was conducted to enhance gas discharge in the protective seam by adopting rapid filling, roof cutting, and active supporting technologies. Through the upper protective seam mining, RPS, and GSEC, gas migration passages were constructed step‐by‐step to divert the gas from high‐risk areas to low‐risk areas. As a key first step, gas diversion not only optimized the distribution of gas sources but also significantly reduced gas hazards. Source‐by‐source extraction was then performed to effectively control the high‐concentration gas in the newly formed gas source, further eliminating the mining risk. By applying the stepwise risk control method combined with gas diversion and extraction, the safe production was successfully achieved with excellent outburst prevention effects, and the gas extraction rate was significantly improved to more than 66%. This practice could be used for deep high‐gassy or high‐outburst coal seam group mining.

Experimental Study on Adsorption Pore Structure and Gas Migration of Coal Reservoir Using Low‐Field Nuclear Magnetic Resonance

For the quantitative recognition and characterization of the flow characteristics of polymorphism coalbed gas in tectonic coal, experiments on pore morphology, pore diameter distribution, and methane adsorption law in outburst tectonic coal were carried out by field emission scanning electron microscopy and low‐field nuclear magnetic resonance. The results revealed abundant round and dense “pyrolysis pores” in outburst tectonic coals, most of which were adsorption and seepage pores, with micropores accounting for 78.2%. Most pores were independent and formed the network pore space for gas enrichment and migration in outburst tectonic coal. The transverse relaxation time (T2) of methane adsorption in tectonic coal and crushed outburst tectonic coals presented three peaks, namely, adsorption, drifting, and free peaks. The isolation of nanopores and micropores revealed lower adsorption capacity of outburst tectonic coal than that of crushed outburst tectonic coal. The gas staged adsorption of raw coal with outburst tectonic low‐permeability was observed. Under low gas pressure, the T2 spectral peak area of methane adsorption increased remarkably, whereas that of desorbed methane increased slightly. As gas pressure was increased to a certain numerical value, the increment of methane adsorption decreased and tended to reach equilibrium. This finding reflected that methane adsorption tended to be saturated after gas pressure reached a certain value, but desorbed methane in isolated micropores increased quickly. The quantitative recognition and characterization of pore structure and gas adsorption in tectonic low‐permeability outburst coal seams based on low‐field magnetic resonance imaging provide an experimental method for gas exploitation in coal seams and the study and control of coal and gas outburst mechanism.

突出煤层保护层开采保护范围数值模拟研究

突出煤层保护层开采保护范围数值模拟研究

Spectral-acoustic method for outburst danger prediction considering in-situ gas pressure

The option of spectral-acoustic method for coal seam outburst danger prediction based on the influence of outburst danger basic factors on the amplitude-frequency characteristic of acoustic vibration median formed when breaking the rock massif by the operating mining equipment is justified. Basic outburst danger factors are: rock pressure, in-situ gas pressure, coal strength.

Research on Gas Outburst Coal Seam Mining Technology Based on the Theory of Gob-Side Entry Retaining

Under the condition of traditional mining technology of gas outburst coal seam, the continuous mining of working face is tense, the waste of resources is serious, the amount of roadway excavation is large, and the stress of surrounding rock is large, which results in frequent occurrence of gas outburst, large deformation of surrounding rock, and serious damage to the benefit of coal mine. In this study, a technical method system of gob-side entry retaining, layer-by-layer drainage and pumping roadway without digging rock is put forward. The technology of roof-cutting pressure relief and gob-side entry retaining is adopted to relieve the tension of continuously mining in working face, and to ensure the stability of surrounding rock while improving the recovery rate of resources, so as to provide sufficient time and space for gas drainage along layers in the next section. Gas control roadway instead of rock bottom roadway is used to optimize the layout of mining area and greatly reduce the pressure of roadway working end. Finally, by analyzing the effect of retaining roadway and drainage effect, it is concluded that the average displacement of roof and floor of roadway is 304 mm, the average displacement of two sides is 254 mm, the maximum resistance of support is 44.1 MPa, and the effect of retaining roadway is ideal; the effect of gas drainage is 1.88 times of the original scheme, and 14,989,000 m3 has been drained, and the outburst prevention effect is ideal.

Method and application of rapid detection of local outburst prevention effect of coal uncovering in crosscut and shaft

Before uncovering an outburst coal seam in crosscut and shaft, it is necessary to detect the effect of outburst prevention measure applied to the seam, which is a key step and the last link for ensuring the safety of coal miners. However, in the working face where outburst prevention measures have been taken, the large number of densely arranged discharge boreholes, as well as the difficulty in sealing pressure-measuring boreholes, makes it extremely hard to accurately detect the effect of the measure. In order to solve this problem, this paper studied the relationship between the initial rate of gas emission from the borehole (IRGEB) and the outburst danger through carrying out experiments on a self-designed oblong simulation device of outburst coal seam and a detection device of IRGEB. In addition, it proposed a method of testing the prevention effect using the initial volume of gas emission from the borehole (IVGEB) per unit length which actually refers to the time integral of IRGEB per meter. The experimental results show that IVGEB grows with the increase of outburst danger, but its critical value varies with the types of coal seams and gasses. As a result, it may take over 20 days to get the critical value of outburst detection of a specific coal seam. For this reason, this paper presented a simplified method of determining the critical value of IVGEB per unit length. When this method is applied, the total time taken up can be enormously reduced to shorter than 4 h just by drilling another borehole for measuring the IVGEB. The field application results indicate that the method can quickly detect whether outburst danger has been locally eliminated. Hence, it can be regarded as a very applicable method for the rapid detection of outburst prevention effect before coal uncovering in crosscut and shaft.

Permeability improvements of an outburst‐prone coal seam by means of presplitting and blasting with multiple deep boreholes

AbstractCoalbed methane, which is a significant potential unconventional source of energy, exhibits considerable challenges in the implementation of the exploration and production process, especially the degasification in low permeability of coal seams with high gas concentrations. Due to the difficulties in gas extraction, long mining period and low extraction concentration in soft and outburst coal seams, the permeability improvement method using presplitting and blasting technology with multiple boreholes has been proposed and applied to improve the permeability of soft coal seam, which is achieved by optimizing the inseam distribution of generated fractures through multiple control boreholes. Research results showed that the permeability improved by presplitting and blasting with deep boreholes is 2.5 times higher than that of the original coal seam. Within 6 days of extraction, the average extraction concentration and pure volume of the extraction borehole were 40.13% and 0.113 m3/min, respectively, which are 2.9 times and 4.1 times higher than the original data, respectively. Likewise, the average extraction concentration and purity of the extraction hole were 21.75% and 0.063 m3/min after being extracted within 14 days, which is twice and three times higher than that of the original average extraction concentration and purity volume, respectively. Besides, proposed technology has a little influence on the methane concentration of the coal seam 70 m ahead of the heading face. The research results promote the prevention and control of coal‐gas outburst in low permeability and high gas concentration coal seams.

Experimental study of the influence of water content on energy conversion of coal and gas outburst

In order to obtain the weakening influence of coal seam water injection on coal and gas outburst, taking the 1100 m outburst coal seam in Sunjiawan Coal Mine in Fuxin of China as the research object, coal and gas outburst energy conversion model was established. The influence of water content on coal and gas outburst test was studied by using a self-developed simulation experimental system. The relationships between water content and critical gas pressure, outburst strength and energy conversion rate were analyzed. The results show that gas pressure is the main power source of coal and gas outburst, and the relationship between water content and critical gas pressure increases exponentially. When the water content increases from 0% to 3% and 6%, the relative strength of outburst decreases by 9.6% and 1.2%, respectively. With the increase in water content, the relative outburst strength and absolute outburst strength will gradually decrease. Gas internal energy is the key factor affecting coal and gas outburst energy which is closely related to the outburst-forming and the outburst-triggering process. As the water content increases, the outburst-forming energy and the outburst-triggering energy increase linearly. However, the energy conversion ratio decreases linearly and the less prone to coal and gas outburst.

Risk assessment of dynamic disasters induced by gas injection displacement in coal seams

Gas injection displacement technology not only helps to increase gas production, but also serves to store greenhouse gases by reducing CO2 emissions. However, coal seam dynamic disasters caused by gas (CO2) injection displacement are rarely reported. In order to explore the change in coal seam outburst risk after gas injection, the indexes (ΔP) of initial velocity of gas diffusion and the isothermal adsorption curves of coal with different metamorphic degrees were experimentally measured under different concentration ratios of CO2/CH4 mixed gas, and the experimental process of gas injection displacement and the change in pore structure were also investigated. The experiment results indicate that the ΔP of CO2 is nearly three times of that of CH4. Therefore, the accuracy of safety situation judgment of a coal seam would be reduced if outburst risk of the coal seam is only assessed through the ΔP in the pure CH4 environment. The results of isothermal adsorption experiment show that the gas adsorption capacity of three kinds of coal increases with the rise of the CO2 concentration in the mixed gas. The results of gas injection displacement experiment reveal that CO2 plays a significant role in replacing CH4, but a large amount of CO2 has been adsorbed into the coal seam before CH4 can be completely desorbed, which in turn raises outburst risk of the coal seam. After the displacement, the internal pore structures of the three kinds of coal samples become tinier and tinier. Finally, a new comprehensive index K′=αBET×ΔP/f was established to assess the risk of dynamic disasters in a coal seam. Compared with the single index ΔP, the new comprehensive index K′ can more accurately grasp the possibility of outburst danger in a coal seam subjected to gas injection displacement.

Desorption characterization of soft and hard coal and its influence on outburst prediction index

ABSTRACT The zoning of the coal seam gas is zonal, which has a significant impact on the prominent prediction indicators, resulting in different prediction results for the same prominent prediction indicators in the same coal seam soft and hard coal. In this paper, the hard coal and soft coal in the coal seam are highlighted. The adsorption and desorption rules of the soft coal and hard coal in the outburst coal seam and its influence on the sensitivity of the outstanding prediction index are studied. The results show that: (1) the initial desorption of soft coal is larger than that of hard coal; (2) the outstanding prediction index has an exponential function relationship with gas pressure; (3) the sensitivity of prediction indicators is different. And concluded that: (1) the initial desorption rate of soft coal is faster than that of hard coal; (2) the outburst prediction index K1 and Δh2 increase with the increase of gas adsorption equilibrium pressure; (3) outburst prediction index K1 is more reliable than Δh2.

Application of Acoustic Emission Technique to the Evaluation of Coal Seam Hydraulic Flushing Effect

Hydraulic flushing has the advantages of reducing coal stress and improving coal seam permeability, so it is widely used in high gas outburst coal seams in China. However, the effect evaluation of stress relief and permeability enhancement will be necessary before coal mining. In this paper, an acoustic emission (AE) experiment system of coal seam hydraulic flushing was established, and the AE characteristics of coal during hydraulic flushing were studied. The results show that the changes in AE signals are basically consistent with those in load and water pressure. In addition, the quantitative relationship between the signals and the damage of coal around the borehole is revealed by the theory of damage mechanics. The in-situ AE test of hydraulic flushing was performed in the Liangbei Coal Mine, by measuring gas flow and coal stress simultaneously. The variation of AE activities and the effect evaluation of hydraulic flushing were analyzed. The results reveal that the changes in coal seam stress are basically consistent with those of AE signals. After the flushing has been completed for 1–3 h, the coal seam stress decreases rapidly, and the AE counts and intensity reach the peak. Therefore, this study proposes a new method for evaluating the effect of coal seam hydraulic flushing by AE, which has a very important practical significance.

Correlation between coal and gas outburst risk and adsorption properties of coal seams

AbstractBased on the Langmuir adsorption model, the adsorption constants of eighteen coal samples from the same coal mine with outburst risk, weak outburst risk, and non‐outburst risk were tested by high‐pressure capacity method under different temperature conditions. The results show that the adsorption constants a and b monotonically decrease with the increase in temperature. The relationship between a and temperature shows three stages: accelerated decreasing stage, decelerated decreasing stage, and stable stage. The b decreases with the increase in temperature also shows three stages, namely relative stability, slow decrease, and accelerated decrease. The a × b for the outburst coal seam decreases with increasing temperature, which is similar to b. The a × b for the weak and non‐outburst coal seams decreases with increasing temperature, which is similar to a. Furthermore, the a of the outburst coal seam decreases with the increase in temperature, and the decrease of b is the largest. The a of the weak and non‐outburst coal seams decreases with the increase in temperature, and the magnitude is relatively large. The b decreases slightly, with a smaller magnitude. The a × b of weak outburst seam is smaller than that of non‐outburst seam and is larger than that of outburst seam. The achievements can provide guiding significance for coal and gas outburst prevention and control.

Method and equipment for the safe development of preparatory workings in the gas-bearing coal seams

The article describes a method and equipment for the safe development of preparatory working on a gas-bearing, outburst hazardous coal seam by a heading machine. The described method significantly prevents the gas emission during mining operations. Determination of the amount of degassing and relief wells is performed according to the given in article mathematical formulas. This ensures a significant increase in the level of safety processing the preparatory roadway on a gas-bearing, prone to outbursts coal seam by a heading machine. Due to this, the speed of conducting excavation increases and the cost of mining is reduced. The proportionality coefficients of the mathematical models were determined. Mathematical models are used to calculate the number of relief and degassing wells, which are drilled during the impulse hydraulic loosing of the nearby part of the coal seam. Also the duration of liquid injection into a coal seam is also determined. Mathematical models for calculating the number of injection, unloading and degassing boreholes can be used in development of the passports for conducting preparatory workings on a gas-bearing, prone to outburst coal seam by a heading machine with a preliminary impulse hydraulic loosing of the nearby part of a coal seam.

A Sequential Approach for Integrated Coal and Gas Mining of Closely-Spaced Outburst Coal Seams: Results from a Case Study Including Mine Safety Improvements and Greenhouse Gas Reductions

Closely-spaced outburst coal seams (COCS) is the main condition of coal seams in southwest China, and gas disasters are one of the major problems affecting coal mine safety. Mining a protective seam and pre gas extraction are the most safety way to improve the efficiency of mining under these conditions. However, low pre-mining gas extraction efficiency coupled with the close proximity of adjacent working faces is a problem. When mining at an old working face has been completed but the new working face is not yet ready to be mined, coal-bed gasses can flow into the new working face from adjacent seams and this commonly causes methane monitoring instruments to sound an alarm. These gas extraction difficulties lead to a conflict between mine safety and profit. To solve these problems, a sequential approach for integrated coal and gas mining of closely-spaced outburst coal seams is introduced in this paper. Two fundamental principles are proposed: (1) Fully coordinating the spatiotemporal relationships between gas extraction, roadway development, and coal mining to maximize both mine safety and coal and gas production; (2) Defining a mining sequence for outburst coal seams and choosing the coal seam with the weakest outburst risk as the protective seam. A system for comprehensive gas extraction in underground coal mines is divided into four stages for gas extraction: gas extraction before coal roadway tunneling, gas extraction before coal mining, gas extraction during coal mining, and gas extraction from the goaf after coal mining. The Songzao mining area, China, is used as a case study to demonstrate the effectiveness of this model, and it brings three major benefits: it improves underground coal mine safety with physical gas accidents decreased by 66.8%, it makes underground coal-bed methane (CBM) extraction more efficient with the average gas extraction rate were respectively 45.13 m3/t and 62.4%, the highest in China, and it reduces greenhouse gas emissions equivalent to 3.5 million tonnes of carbon dioxide. This study could be used as a valuable example for other coal deposits being mined under similar geological conditions.

Permeability enhancements of borehole outburst cavitation in outburst-prone coal seams

Borehole outbursts eject coal power, create cavities and relieve in-situ stress while drilling cross-measure boreholes into outburst coal seams for pre-drainage. This paper highlights the borehole outburst cavitation to enhance the permeability of coal for the first time. Borehole outburst is a mechanical behavior, and the outburst trigger and development depend on the status of gas pressure gradient near the opening coal wall. It was testified that the high-pressure water, with 10–15 MPa in pressure and 20–30 m3/h in flow, was feasible to remove the failure coal near the opening wall and stimulate a new set of outbursts, thus creating bigger cavities and better permeability enhancement. Furthermore, an outburst control system was designed for borehole outburst cavitation. The system contains an outburst stimulation subsystem, a gas drainage subsystem and a separation subsystem, thus ensuring the flow and the separation of outburst ejections within a relatively closed environment. The outburst cavity reconstitutes the in-situ stress and permeability of the surrounding coal mass, leading to a failure zone, a plastic zone and a visco-elastic zone. The failure zone and the plastic zone due to borehole outburst cavitation are both effective in permeability enhancement. Finally, a field test in the No. 10 coal seam at the Luling mine proved that the sufficient permeability enhancement scope is approximately twelve times of the cavity radius. The permeability enhancement promotes the increase of borehole distance from 5 m to 12 m, thus reducing 78.7% of boreholes in number for the pre-drainage of the No. 10 coal seam.

Research on optimization of drill hole gas pre-drainage process in low permeability outburst coal seam

To study the drill hole gas pre-drainage technology in low-permeability outburst coal seam, this paper selects the 1031 working face of the first coal seam in the Songhe Coal Mine as the research and test area, adopts Ansys numerical simulation software for the simulated calculation of different drill hole spacing and different drainage time, different drainage effects are obtained, and the test results show that: when the hole spacing is 2.0 m, the drainage result is the best, the residual gas content in the coal seam of the working face drops to less than 5.92 m3/t, and the residual gas pressure drops to less than 0.58 MPa, the gas drainage rate is increased to 61.48%, and the outburst risk is also reduced. This optimization method has a guiding significance for the gas drainage and utilization of other low-permeability outburst coal seams.