海石湾井田CO2成藏演化机制及防治技术研究

以窑街海石湾井田为研究背景,以海石湾井田煤二层中CO2为主要研究对象,运用地球化学、岩石学、构造地质学、表面物理化学、岩石力学、采矿工程、渗流力学、数值模拟等多学科理论,采用理论分析、实验室实验与现场工程实践的研究方法,系统地开展了井田CO2成因、CO2成藏规律、CO2的赋存状态、海石湾煤对CO2的吸附解吸特性、孔隙压力对煤层卸压作用机制以及工程实践等多方面的研究,并取得了一定的创新成果,主要研究结论如下:(1)根据对海石湾井田煤二层中CO2的碳同位素与氦同位素测定结果,实测海石湾井田主要测点的CO2含量均大于60%,实测δ13CCO2变化范围主要为+1.00‰～-5‰,3He/4He测定值均为10-8数量级,R/Ra为0.004 2～0.185 0,分析认为海石湾煤田中CO2为无机地壳来源。并根据F19断裂构造岩性质、多期运动性以及实验分析,提出了海石湾井田CO2为F19韧-脆性剪切带的动力变质成因;且F19断裂在井田CO2成藏过程中起到了成气断裂、输气断裂和封气断裂的多重作用。(2)建立了修正的D-A模型,该模型对现有的高压吸附实验数据具有较高的拟合精度,并对海石湾煤对超临界CO2吸附等温线进行了分析,引入了聚合物的自由体积理论对异常吸附等温线进行了理论分析,并得到了解吸曲线的初步验证。(3)海石湾井田煤二层埋深600～1 000 m时,地温为31.72～43.88°C,实测最大瓦斯压力为7.3 MPa,井田东部CO2浓度超过90%,计算海石湾井田东部区域的混合瓦斯含量达到50～60 m3/t,现场测定、实验测定以及理论计算结果表明,海石湾井田煤二层中赋存超临界CO2。(4)数值模拟结果表明,随着保护层工作面推进,下伏煤岩体的采动卸压范围及煤二层的膨胀变形量均随着孔隙压力的升高而增大,最大绝对变形量为328 mm,最大相对变形量可达0.5%,随着保护层推进与孔隙压力的增大,被保护层发生塑性破坏并随之增大,并进行了理论分析,结果表明孔隙压力在增强被保护层卸压中起着重要作用。(5)远距离上保护层开采及卸压瓦斯抽采实践验证了高孔隙压力在煤层卸压中的作用,抽采单孔流量达到2 m3/min以上,煤层透气性增大878倍,煤层瓦斯含量由53 m3/t降至12 m3/t,消除了煤二层的突出危险性,同时工程实践也验证了相关结论。

Mechanism of CO_2 pools formation and CO_2 control technology of Haishiwan coalfield

This paper took Haishiwan coalfield as the background and CO2 in the No.2 coal seam of Haishiwan mine area as the main study object,systematically carrying out study of various aspects on the causes of CO2,CO2 enrichment regularity,CO2 occurrence in coal seam of Yaojie coalfield,adsorption and desorption of CO2 in coal,numerical simulation and engineering practice applied to eliminate the risk of coal and CO2 outburst regionally,making some innovations.During the researches,the authors adopted all kinds of research methods that multi-disciplinary theory includes geochemistry,petrology,structural geology,surface chemistry,rock mechanics,mining engineering,mechanics,numerical simulation,theoretical analysis,laboratory experiments and field engineering practice.The main research content and conclusions are as follows:(1) The CO2 concentration range in the eastern coalfield is 18.79% to 96.6%.The δ13CCO2 values are mainly in the range of-5.0‰ to +1.0‰(PDB),suggesting an inorganic origin of CO2.The 3He/4He ratios are(0.6~25.9)×108,and the R/Ra is 0.004 2~0.185 0,which is a characteristic of crust-derived CO2 gas.The dynamic-thermal metamorphism of the F19 ductile-brittle shear zone is believed to result in the release of CO2 from basement marble formations,which shows an inorganic source of CO2 in the Haishiwan coalfield.The regional geological evolution and multi-periodical F19 fault movement control the formation,migration,and accumulation of CO2.The F19 fault plays multiple roles in the generation,transport,and sequestration of gas during the CO2 formation.(2) The studies on the characteristics of coal absorbing CO2 or CO2 and CH4 mixed gas are carried out under low pressure.The D-A model can fit the adsorption isotherms of CO2 well under low pressure.At the same time,the authors establish the modified D-A,which fit the present high-pressure adsorption data well.The modified model is applied to analyze the supercritical CO2 adsorption isotherms of Haishiwan coal field and abnormal adsorption isotherms introducing free volume theory of polymer.The result is preliminarily verified by desorption curve.(3) The mining depth of the Haishiwan mine coal is 600 to 1 000 m,where the coal reservoir temperature is in the range of 31.72 to 43.88 °C.The measured mixture gas pressure is not less than 7.3 MPa;the CO2 concentration range in the eastern coalfield exceeded 90%;statistical gas content is in the range of 50 to 60 m3/t.Supercritical CO2 is likely to exist in the No.2 coal seam of the Haishiwan coalfield according to in situ measurement,experimental determination and theoretical analysis.(4) The numerical simulation results indicate that the range of pressure-relief and dilatational strain of lower coal-rock mass increases along with the pore pressure increases,the maximum absolute and the maximum relative amount of deformity reach 328 mm and 0.5% under pore pressure of 9 MPa respectively.At the same time,the plastic area also increases along with pore pressure enlargement.It is indicated that the pore pressure plays strengthen role in the protected coal seam pressure relief according to plate theory.(5) High pore pressure acts on pressure relief of coal seam,which has been verified in practice of remote protective coal seam mining and pressure-relief gas drainage.The singe gas drainage flow reaches more than 2 m3/min.The coal seam permeability increases by 878 times.The gas content decreases from 53 m3/t to 12 m3/t.The risk of outburst has been eliminated with regard to the No.2 coal seam.