In-situ gas contents of a multi-section coal seam in Sydney basin for coal and gas outburst management

The gas content is crucial for evaluating coal and gas outburst potential in underground coal mining. This study focuses on investigating the in-situ coal seam gas content and gas sorption capacity in a representative coal seam with multiple sections (A1, A2, and A3) in the Sydney basin, where the CO_(2) composition exceeds 90%. The fast direct desorption method and associated devices were described in detail and employed to measure the in-situ gas components (Q_(1), Q_(2), and Q_(3)) of the coal seam. The results show that in-situ total gas content (Q_(T)) ranges from 9.48 m^(3)/t for the A2 section to 14.80 m^(3)/t for the A3 section, surpassing the Level 2 outburst threshold limit value, thereby necessitating gas drainage measures. Among the gas components, Q_(2) demonstrates the highest contribution to Q_(T), ranging between 55% and 70%. Furthermore, high-pressure isothermal gas sorption experiments were conducted on coal samples from each seam section to explore their gas sorption capacity. The Langmuir model accurately characterizes CO_(2) sorption behavior, with ft coefcients (R^(2)) greater than 0.99. Strong positive correlations are observed between in-situ gas content and Langmuir volume, as well as between residual gas content (Q_(3)) and sorption hysteresis. Notably, the A3 seam section is proved to have a higher outburst propensity due to its higher Q_(1) and Q_(2) gas contents, lower sorption hysteresis, and reduced coal toughness f value. The insights derived from the study can contribute to the development of efective gas management strategies and enhance the safety and efciency of coal mining operations.

Influence of Ground Stress on Coal Seam Gas Pressure and Gas Content

The influence of ground stress was quantitatively analyzed on coal seam gas pressure and gas content in this paper.Mining activities in coal mine can result in stress concentration in the coal(rock)body around the mining space,but porosity of the coal seam would not change too much.Therefore,gas pressure and gas content in the coal seam are slightly affected.Studies showed that the free gas was gradually transformed into adsorbed gas,and the gas adsorption volume was small,and then gas pressure increases roughly linearly when the porosity decreased because of stress influence.Additionaly,when porosity of coal seam reduced to 40%,the amount of adsorbed gas accounted for no more than 10%of coal seam gas content,and the increase of gas pressure did not exceed 15%of the original gas pressure.

Calculation of gas content in coal seam influenced by in-situ stress grads and ground temperature

On the basis of the analysis of coal bed gas pressure in deep mine, and the coal bed permeability ( k ) and the characteristic of adsorption parameter ( b ) changing with temperature, the author puts forward a new calculating method of gas content in coal seam influenced by in situ stress grads and ground temperature. At the same time, the contrast of the measuring results of coal bed gas pressure with the computing results of coal bed gas pressure and gas content in coal seam in theory indicate that the computing method can well reflect the authenticity of gas content in coal seam,and will further perfect the computing method of gas content in coal seam in theory,and have important value in theory on analyzing gas content in coal seam and forecasting distribution law of gas content in coal seam in deep mine.

A rapid and accurate direct measurement method of underground coal seam gas content based on dynamic diffusion theory

Coal seam gas content is frequently measured in quantity during underground coal mining operation and coalbed methane(CBM)exploration as a significant basic parameter.Due to the calculation error of lost gas and residual gas in the direct method,the efficiency and accuracy of the current methods are not inadequate to the large area multi-point measurement of coal seam gas content.This paper firstly deduces a simplified theoretical dynamic model for calculating lost gas based on gas dynamic diffusion theory.Secondly,the effects of various factors on gas dynamic diffusion from coal particle are experimentally studied.And sampling procedure of representative coal particle is improved.Thirdly,a new estimation method of residual gas content based on excess adsorption and competitive adsorption theory is proposed.The results showed that the maximum error of calculating the losing gas content by using the new simplified model is only 4%.Considering the influence of particle size on gas diffusion law,the particle size of the collected coal sample is below 0.25 mm,which improves the measurement speed and reflects the safety representativeness of the sample.The determination time of gas content reduced from 36 to 3 h/piece.Moreover,the absolute error is 0.15–0.50 m^3/t,and the relative error is within 5%.A new engineering method for determining the coal seam gas content is developed according to the above research.

Discussion of the indexes of nonoutburst coal seam upgrade and its corresponding critical values

In view of the measurement difficulties of indexes recommended by the 50Items Experience of Coal Mine Gas Prevention in the process of the nonoutburst coalseam upgrade, this paper took the No.8 coal seam of Huainan Mining Group as research object. Discussed the suitability of indexes and corresponding critical values, putforward method in determining the indexes and its critical values by analysis and investigation of the gas geological condition and the-spot tracking near position where anoutburst occurred combined with laboratory experiment, and established the indexesand its critical values of nonoutburst coal seam upgrade in No.8 coal seam of HuainanMining Group. The results show that it is suitable to take gas content and tectonic softcoal thickness easily to gain in routine production as primary upgrade indexes that itscritical values are 7.5 m^3/t and 0.8 m, respectively. In addition, takefvalue and Ap valueas auxiliary indexes.

STUDY ON THE THRESHOLD GAS PRESSURE IN COAL AND GAS OUTBURST

Based on the statistical data of 26 outburst prone coal seams in China, this paper presents the relationship among the threshold gas pressure in coal and gas outburst and the volatile content and hardness of coal by mathematical statistics. The threshold value of gas pressure for outburst pmin in MPa may be calculated by formula Pmin =5(0. 1+0. 07Kf), where / is the hardness and V the volatile content (%) of a soft bed. In China, the value of Pmin of some outburst prone coal seams ranges from 0. 57 to 0. 1 MPa.

多元回归分析在煤层瓦斯含量预测中的应用

根据某矿影响煤层瓦斯含量的大量参数值,运用多元回归分析的数学模型,建立了煤层瓦斯含量预测的多元回归方程,并对方程及其系数的显著性作了检验,进行了学生化残差分析。通过此数学模型能够直观地反映煤层埋深、煤层厚度、地质构造、煤的顶底板岩性及煤的变质程度对煤层瓦斯含量的影响关系。结果证明预测的准确性较高,此方法可为矿井预测瓦斯含量提供一种有效途径。

软、硬煤层残余瓦斯含量区域效果检验临界值研究

针对软、硬煤层瓦斯含量区域突出危险性效检指标临界值存在较大差异这一工程实际。建立软、硬煤样相关参数关系模型,对基于残余瓦斯含量的区域防突措施效果检验指标临界值进行研究。结果表明:同一煤质软煤和硬煤瓦斯吸附量差别不大,但随着煤的变质程度降低,软、硬煤瓦斯吸附量差值先减小后增大。对存在软、硬分层的煤层,建议采用0.74MPa时软、硬煤瓦斯含量测值的小值(取整)作为煤层残余瓦斯量指标的临界值。此研究因地制宜地确定符合矿井实际的突出预测指标临界值和区域措施效果检验指标临界值,对降低防突成本具有重要意义。

冯营矿区段突出煤层瓦斯预抽及效果评价

从煤层预抽瓦斯方法、钻孔布置等方面介绍了冯营矿研究区段煤层瓦斯抽采情况。通过现场实测煤层残存瓦斯含量、残存瓦斯压力,并结合相关实验参数计算煤层瓦斯抽采率,对研究区段煤层预抽瓦斯效果进行整体评价,认为该区段煤层预抽瓦斯效果达标,但仍存在一些问题。对存在问题进行分析,并提出了一些建议。

松软煤层水力冲孔与二氧化碳爆破联合增透技术

为有效解决松软煤层瓦斯透气性低、瓦斯抽采效果差的问题,提出一种水力冲孔与二氧化碳致裂爆破联合增透方法,即在水力冲孔基础上引入二氧化碳致裂爆破措施,加快松软煤体向孔洞移动的速度,进一步提高煤层透气性,延长高瓦斯流量抽采时间。在贵州高山煤矿9号煤层进行对比试验,抽采30d后,联合增透技术抽采钻孔瓦斯抽采量比单独使用水力冲孔措施提高45%;抽采60d后,联合增透技术采区域平均残余瓦斯含量比单独使用水力冲孔增透措施时降低了22%,为其他矿区松软煤层瓦斯抽采提供参考。

关于“煤层残存瓦斯含量”的几个问题探讨

对现有的行业规程、规范及技术标准中关于"煤层残存瓦斯含量"的定义、测定与计算方法存在的歧义与不统一、不规范的问题进行了分析,指出随着矿井煤炭的开采与瓦斯的抽采,煤层残存瓦斯含量是一个动态的概念,应该按照实际条件将煤层瓦斯残存量分为瓦斯残留量与瓦斯残存量两个基本类型,并分别对其进行了定义及描述,以更好地满足测定、计算与应用的需要。

煤层预抽后残余瓦斯含量分布影响控因研究

针对煤层预抽影响因素多、无法准确预测残余瓦斯含量分布的难题,基于煤岩体力学理论分析残余瓦斯含量分布的影响因素,并以平庆煤矿117802回采工作面为研究对象,对不同因素影响下的残余瓦斯含量分布规律和控制机理进行研究。结果表明:117802回采工作面残余瓦斯含量呈离散型和高含量集中分布,主要受控于采掘活动与地质构造的复合应力作用和预抽时间;残余瓦斯含量呈现明显的复合应力作用区域特征,由集中应力往卸压作用区域规律性递减,依次为窄煤柱集中应力、宽煤柱集中应力、采空区—煤柱区—断层带共同影响、采空区卸压和采空区—断层带共同卸压;残余瓦斯含量与预抽时间呈现负相关关系,预抽2~6月后平均值大于8m^3/t,预抽7~10月后平均值均小于8m^3/t。

综采面顺层钻孔瓦斯抽放消突技术研究

成庄矿为了消除煤层的突出危险性,安全有效地开采井下3号煤层4311综采面,采用顺层钻孔预抽该综采面回采区域煤层瓦斯。成庄矿4311综采面作为试验区进行了消突措施、消突效果技术研究,在该综采面预抽煤层瓦斯过程中以及抽放结束后,进行煤层残余瓦斯含量测定,并对该综采面煤层区域进行预抽煤层瓦斯抽采效果达标和消突效果达标评判。上述措施确保了该矿综采面4311的高产高效安全生产,取得了良好的经济效益。

寺河矿区西二盘区煤层气井抽采效果评价

为解决寺河矿区生产期间瓦斯浓度高的潜在安全问题,对寺河矿区西二盘区进行煤层气井排采,在石炭系太原组和二叠系山西组的3~#煤层、15~#煤层的煤炭地质、煤层气地质等资料的基础上,对相应煤层的含气特性进行了综合分析。数据研究表明,寺河矿区西二盘区主煤层在一定排采时间内,瓦斯浓度有降低的趋势,同时得到含气量实际降低的结果,通过生产数据拟合、参数修正预测了煤层气产能及未来含气量随时间抽采变化的规律。

近距离上保护层开采卸压保护效果研究

为了研究近距离上保护层开采对被保护层的卸压保护效果,对被保护层的残存瓦斯参数、煤层透气性系数等指标进行测定。结果表明,保护层开采后被保护层的残存瓦斯压力和瓦斯含量都远低于原始数值,工作面突出危险性指标都小于临界值。

基于临界残余瓦斯含量的抽采半径确定方法

对上社煤矿15#煤层进行了抽采半径考察,得出了不同预抽时间对应的抽采半径。根据上社煤矿5.4m的煤层厚度,选择2.7m的抽采半径布置抽采钻孔,经过248d抽采后,瓦斯含量降至8m3/t以下,回采期间突出危险性预测指标K1值降至0.5mL/(g·min0.5)以下。实践证明,瓦斯含量降低法确定钻孔抽采半径方法简单、可靠,有效解决了区域防突问题,实现了矿井安全生产。

由残存瓦斯量确定煤层瓦斯压力及含量的方法

系统研究了突出煤样的破碎粒度、瓦斯压力对突出煤层残存瓦斯含量的影响.实验结果表明,煤的破碎粒度对残存瓦斯含量有显著影响,粒径越大,残存瓦斯量越大,当煤样粒径较大或较小时,煤样的残存瓦斯含量均趋于恒定.利用相同暴露时间下同一粒径煤样得出残存瓦斯含量与煤层瓦斯压力和瓦斯含量均存在幂函数关系.依据此规律,可在测定煤层的残存瓦斯量后,结合已确定的煤样残存瓦斯量与瓦斯压力和瓦斯含量关系推算出煤层的瓦斯压力及瓦斯含量.该方法的提出为煤层瓦斯压力和瓦斯含量的确定特别是对突出煤层提出了一种新的可靠便捷方法,并在祁南煤矿现场得到了验证.