不同含水及负压条件下煤层气等温吸附解吸规律
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摘要
为了探究水分含量和负压对煤层气等温吸附、解吸特征的影响,采用大样量煤层气吸附/解吸仿真试验设备对鄂尔多斯盆地东缘北部煤矿煤样进行煤层气常规等温吸附解吸过程和负压解吸过程的实验室模拟,通过将煤样进行处理得到干燥煤样、平衡水煤样、饱和水煤样3种不同含水饱和度煤样,分别对其进行等温吸附测试、常规等温解吸测试和负压解吸测试,得到了煤样在不同含水饱和度、不同负压条件下的压力与吸附量实测数据,并采用不同的吸附/解吸方程式进行拟合。通过对比分析,研究了水分对等温吸附过程、解吸过程以及负压对解吸过程的影响,并从分子间作用力的角度解释了水分对等温吸附解吸过程的影响。结果表明:煤样解吸过程与吸附过程不可逆,存在解吸滞后;由于水分子与煤分子间的作用力大于甲烷分子与煤分子间的作用力,水分在与甲烷的竞争吸附中具有优势,煤样含水率越高,其吸附甲烷的能力越低;煤样含水率较低时,含水对煤岩降压解吸影响不明显;当煤样含水率高于某一值时,外来水分抑制煤层气降压解吸,分析认为这可能与煤样的物质组成和煤分子结构有关;由于水分对甲烷的置换解吸作用,若水力压裂过程中压裂液滤失严重,将降低煤层吸附气量,延长排水降压阶段,减少累计产气量,因此应严格控制压裂液滤失;负压解吸阶段,单位压降引起的解吸量更大,说明负压排采增产措施具有潜力。
This paper presents results of an experimental study on the influence of water saturation and negative pressure on isothermal adsorption and desorption of coalbed methane. The conventional isothermal adsorption and desorption processes and isothermal desorption process under negative pressure were simulated using large quantity coalbed methane adsorption/desorption simulation equipment.The coal samples used in the simulation were collected from the northeastern Ordos Basin.Using different treatment technique,three coal samples which have different water saturation were obtained,namely dry coal sample,balanced water coal sample,and saturated water coal sample.The pressure and adsorption volume under different water saturation and different negative pressure were measured and then studied by regression analysis.The influence of water on isothermal adsorption process was analyzed and interpreted from the perspective of intermolecular forces.The results show that the desorption process and adsorption process of coal sample are irreversible,with desorption hysteresis.Water has advantage in competitive adsorption of water and methane because the interaction between water molecules and coal molecules is greater than that between methane molecules and coal molecules.It is also found that higher water saturation of coal sample is associated with lower methane adsorbing ability.Within a certain range,the effect of water on depressurized desorption process is not significant.However,above a certain level of water saturation,the external water inhibits the depressurized desorption process.The inhabitation might be related to compositions of coal samples and molecular structure of coal.When fracture fluid loss is severe,gas content of the coal seam decreases due to desorption of methane replaced by water,resulting in longer drainage time and reduced cumulative gas production.The result demonstrates that the fracture fluid loss should be controlled strictly.Desorption volume caused by the unit pressure drop is larger in negative pressure desorption stage,which indicates that the negative pressure drainage and production measures has potential to enhance CBM recovery.
This paper presents results of an experimental study on the influence of water saturation and negative pressure on isothermal adsorption and desorption of coalbed methane. The conventional isothermal adsorption and desorption processes and isothermal desorption process under negative pressure were simulated using large quantity coalbed methane adsorption/desorption simulation equipment.The coal samples used in the simulation were collected from the northeastern Ordos Basin.Using different treatment technique,three coal samples which have different water saturation were obtained,namely dry coal sample,balanced water coal sample,and saturated water coal sample.The pressure and adsorption volume under different water saturation and different negative pressure were measured and then studied by regression analysis.The influence of water on isothermal adsorption process was analyzed and interpreted from the perspective of intermolecular forces.The results show that the desorption process and adsorption process of coal sample are irreversible,with desorption hysteresis.Water has advantage in competitive adsorption of water and methane because the interaction between water molecules and coal molecules is greater than that between methane molecules and coal molecules.It is also found that higher water saturation of coal sample is associated with lower methane adsorbing ability.Within a certain range,the effect of water on depressurized desorption process is not significant.However,above a certain level of water saturation,the external water inhibits the depressurized desorption process.The inhabitation might be related to compositions of coal samples and molecular structure of coal.When fracture fluid loss is severe,gas content of the coal seam decreases due to desorption of methane replaced by water,resulting in longer drainage time and reduced cumulative gas production.The result demonstrates that the fracture fluid loss should be controlled strictly.Desorption volume caused by the unit pressure drop is larger in negative pressure desorption stage,which indicates that the negative pressure drainage and production measures has potential to enhance CBM recovery.
引文
[1]张遂安,叶建平,唐书恒,等.煤对甲烷气体吸附-解吸机理的可逆性实验研究[J].天然气工业,2005,25(1):44-46.ZHANG Sui’an,YE Jianping,TANG Shuheng,et al.Theoretical analysis of coal-methane adsorption/desorption mechanism and its reversibility experimental study[J].Natural Gas Industry,2005,25(1):44-46.
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[3]亓宪寅,杨典森,陈卫忠.煤层气解吸滞后定量分析模型[J].煤炭学报,2016,41(S2):475-481.QI Xianyin,YANG Diansen,CHEN Weizhong.Research of a bidisperse diffusion model based on adsorption hysteresis[J].Journal of China Coal Society,2016,41(S2):475-481.
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[6]赵东,冯增朝,赵阳升.高压注水对煤体瓦斯解吸特性影响的试验研究[J].岩石力学与工程学报,2011,30(3):547-555.ZHAO Dong,FENG Zengchao,ZHAO Yangsheng.Experimental study of effects of high pressure water injection on desorption charactistic of coal-bed methane(CBM)[J].Chinese Journal of Rock Mechanics and Engineering,2011,30(3):547-555.
[7]蒋长春.负压采气新工艺改进[J].天然气工业,1996,16(5):86-87.JIANG Changchun.Improvement of new negative pressure gas production technology[J].Natural Gas Industry,1996,16(5):86-87.
[8]黄君权.四川龙泉山侏罗系浅气藏负压采气技术[J].天然气工业,1992,12(5):53-60,8.HUANG Junquan.Negative pressure gas producting technique for Jurassic Shallow gas pool in Longquan Mountains of Sichuan[J].Natural Gas Industry,1992,12(5):53-60,8.
[9]牛国斌.煤层气地面负压排采模式研究及应用[C]//第十届全国煤炭工业生产一线青年技术创新文集.北京:中国煤炭学会,2016.
[10]程远平,董骏,李伟,等.负压对瓦斯抽采的作用机制及在瓦斯资源化利用中的应用[J].煤炭学报,2017,42(6):1466-1474.CHENG Yuanping,DONG Jun,LI Wei,et al.Effect of negative pressure on coalbed methane extraction and application in the utilization of methane resource[J].Journal of China Coal Society,2017,42(6):1466-1474.
[11]DONG Jun,CHENG Yuanping,JIN Kan,et al.Effects of diffusion and suction negative pressure on coalbed methane extraction and a new measure to increase the methane utilization rate[J].Fuel,2017,197:70-81.
[12]张洪良,王兆丰,陈向军.负压环境下煤的瓦斯解吸规律试验研究[J].河南理工大学学报:自然科学版,2011,30(6):634-637.ZHANG Hongliang,WANG Zhaofeng,CHEN Xiangjun.Study on the law of gas desorption under negative pressure[J].Journal of Henan Polytechnic University:Natural Science,2011,30(6):634-637.
[13]杨小鹏.负压抽采条件下孔隙率对动态加载构造煤渗透率影响的实验研究[J].煤矿安全,2016,47(9):4-7.YANG Xiaopeng.Experiment on effect of porosity and dynamic loading on permeability of tectonic coal under negative pressure drainage[J].Safety in Coal Mines,2016,47(9):4-7.
[14]焦义.负压下构造煤加卸载过程瓦斯渗透率变化研究[J].煤炭工程,2016,48(9):106-108,112.JIAO Yi.Study on gas permeability variation of tectonic coal in loading-unloading process under negative pressure[J].Coal Engineering,2016,48(9):106-108,112.
[15]王公忠,孙光中.负压条件下构造煤原煤样瓦斯渗透性实验[J].煤矿安全,2015,46(10):11-14.WANG Gongzhong,SUN Guangzhong.Gas permeability experiment for raw samples of tectonic coal under the condition of negative pressure[J].Safety in Coal Mines,2015,46(10):11-14.
[16]DU Yunfei,CHEN Xiangjun,LI Liyang,et al.Characteristics of methane desorption and diffusion in coal within a negative pressure environment[J].Fuel,2018,217:111-121.
[17]郑吉玉,田坤云,王振江.负压对煤的瓦斯气体流动影响研究[J].煤炭技术,2016,35(3):175-177.ZHENG Jiyu,TIAN Kunyun,WANG Zhenjiang.Influence of negative pressure on gas flow of coal[J].Coal Technology,2016,35(3):175-177.
[18]杨宏民,沈涛,王兆丰.伏岩煤业3#煤层瓦斯抽采合理孔口负压研究[J].煤矿安全,2013,44(12):11-13.YANG Hongmin,SHEN Tao,WANG Zhaofeng.Study on reasonable orifice negative pressure of gas drainage in No.3 coal seam of Fuyan coal mine[J].Safety in Coal Mines,2013,44(12):11-13.
[19]张遂安.有关煤层气开采过程中煤层气解吸作用类型的探索[J].中国煤层气,2004,1(1):26-28,20.ZHANG Sui’an.Views on types of desorption effect in the process of CBM production[J].China Coalbed Methane,2004,1(1):26-28,20.
[2]马东民.煤层气吸附解吸机理研究[D].西安:西安科技大学,2008.
[3]亓宪寅,杨典森,陈卫忠.煤层气解吸滞后定量分析模型[J].煤炭学报,2016,41(S2):475-481.QI Xianyin,YANG Diansen,CHEN Weizhong.Research of a bidisperse diffusion model based on adsorption hysteresis[J].Journal of China Coal Society,2016,41(S2):475-481.
[4]田伟兵,李爱芬,韩文成.水分对煤层气吸附解吸的影响[J].煤炭学报,2017,42(12):3196-3202.TIAN Weibing,LI Aifen,HAN Wencheng.Effect of water content on adsorption/desorption of coalbed methane[J].Journal of China Coal Society,2017,42(12):3196-3202.
[5]陈向军.外加水分对煤的瓦斯解吸动力学特性影响研究[D].徐州:中国矿业大学,2013.
[6]赵东,冯增朝,赵阳升.高压注水对煤体瓦斯解吸特性影响的试验研究[J].岩石力学与工程学报,2011,30(3):547-555.ZHAO Dong,FENG Zengchao,ZHAO Yangsheng.Experimental study of effects of high pressure water injection on desorption charactistic of coal-bed methane(CBM)[J].Chinese Journal of Rock Mechanics and Engineering,2011,30(3):547-555.
[7]蒋长春.负压采气新工艺改进[J].天然气工业,1996,16(5):86-87.JIANG Changchun.Improvement of new negative pressure gas production technology[J].Natural Gas Industry,1996,16(5):86-87.
[8]黄君权.四川龙泉山侏罗系浅气藏负压采气技术[J].天然气工业,1992,12(5):53-60,8.HUANG Junquan.Negative pressure gas producting technique for Jurassic Shallow gas pool in Longquan Mountains of Sichuan[J].Natural Gas Industry,1992,12(5):53-60,8.
[9]牛国斌.煤层气地面负压排采模式研究及应用[C]//第十届全国煤炭工业生产一线青年技术创新文集.北京:中国煤炭学会,2016.
[10]程远平,董骏,李伟,等.负压对瓦斯抽采的作用机制及在瓦斯资源化利用中的应用[J].煤炭学报,2017,42(6):1466-1474.CHENG Yuanping,DONG Jun,LI Wei,et al.Effect of negative pressure on coalbed methane extraction and application in the utilization of methane resource[J].Journal of China Coal Society,2017,42(6):1466-1474.
[11]DONG Jun,CHENG Yuanping,JIN Kan,et al.Effects of diffusion and suction negative pressure on coalbed methane extraction and a new measure to increase the methane utilization rate[J].Fuel,2017,197:70-81.
[12]张洪良,王兆丰,陈向军.负压环境下煤的瓦斯解吸规律试验研究[J].河南理工大学学报:自然科学版,2011,30(6):634-637.ZHANG Hongliang,WANG Zhaofeng,CHEN Xiangjun.Study on the law of gas desorption under negative pressure[J].Journal of Henan Polytechnic University:Natural Science,2011,30(6):634-637.
[13]杨小鹏.负压抽采条件下孔隙率对动态加载构造煤渗透率影响的实验研究[J].煤矿安全,2016,47(9):4-7.YANG Xiaopeng.Experiment on effect of porosity and dynamic loading on permeability of tectonic coal under negative pressure drainage[J].Safety in Coal Mines,2016,47(9):4-7.
[14]焦义.负压下构造煤加卸载过程瓦斯渗透率变化研究[J].煤炭工程,2016,48(9):106-108,112.JIAO Yi.Study on gas permeability variation of tectonic coal in loading-unloading process under negative pressure[J].Coal Engineering,2016,48(9):106-108,112.
[15]王公忠,孙光中.负压条件下构造煤原煤样瓦斯渗透性实验[J].煤矿安全,2015,46(10):11-14.WANG Gongzhong,SUN Guangzhong.Gas permeability experiment for raw samples of tectonic coal under the condition of negative pressure[J].Safety in Coal Mines,2015,46(10):11-14.
[16]DU Yunfei,CHEN Xiangjun,LI Liyang,et al.Characteristics of methane desorption and diffusion in coal within a negative pressure environment[J].Fuel,2018,217:111-121.
[17]郑吉玉,田坤云,王振江.负压对煤的瓦斯气体流动影响研究[J].煤炭技术,2016,35(3):175-177.ZHENG Jiyu,TIAN Kunyun,WANG Zhenjiang.Influence of negative pressure on gas flow of coal[J].Coal Technology,2016,35(3):175-177.
[18]杨宏民,沈涛,王兆丰.伏岩煤业3#煤层瓦斯抽采合理孔口负压研究[J].煤矿安全,2013,44(12):11-13.YANG Hongmin,SHEN Tao,WANG Zhaofeng.Study on reasonable orifice negative pressure of gas drainage in No.3 coal seam of Fuyan coal mine[J].Safety in Coal Mines,2013,44(12):11-13.
[19]张遂安.有关煤层气开采过程中煤层气解吸作用类型的探索[J].中国煤层气,2004,1(1):26-28,20.ZHANG Sui’an.Views on types of desorption effect in the process of CBM production[J].China Coalbed Methane,2004,1(1):26-28,20.
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