降压速率对沁水盆地南部高阶煤产气能力的影响
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摘要
参照山西晋城地区大宁煤矿3号煤层,设计模拟地层条件下解吸仿真实验,进行相同流体饱和状态、不同降压速率下的解吸模拟实验,对产气量及样品两端压力变化进行分析,并对部分实验现象进行机理探讨。实验结果表明,无论快速降压还是慢速降压,高阶煤吸附的甲烷均能有效解吸,解吸效率均能达到90%以上;解吸过程中产气量曲线存在明显拐点,均出现在煤块整体降至解吸压力之后;高阶煤甲烷解吸主要受压差驱动,高压差有利于快速解吸;快速降压出现解吸拐点时间更早,且快速解吸段产气速率更高。实验结论对原公认的煤层气井排采需要坚持"缓慢、长期"的原则提出了质疑,认为对于高阶煤层,快速排水降压可有效提高煤层气开采的经济效益。沁水盆地南部樊庄区块和郑庄区块快速降压排采现场试验结果显示,提高排水降压速率可以显著提高气井的峰值产量并缩短气井达到经济产量的时间;相比慢速排采策略,快速降压排采的气井平均达产时间缩短一半,高峰产气量更高。图8表5参22
A desorption simulation experiment with the condition of simulated strata was designed. The experiment, under different depressurizing rates and the same fluid saturation, was conducted on the sample from 3# coal of Daning coal mine in Jincheng, Shanxi Province. The gas production rate and pressure change at both ends of the sample were studied systematically, and the mechanisms of some phenomena in the experiment were discussed. The experimental results show that, whether at fast or slow depressurizing rate, the methane adsorbed to high-rank coal can effectively desorb and the desorption efficiency can reach above 90%. There is an obvious inflection point on the gas yield curve during the desorption process and it appears after the pressure on the lump of coal reduces below the desorption pressure. The desorption of methane from high-rank coal is mainly driven by differential pressure, and high pressure difference is conducive to fast desorption. In the scenario of fast depressurization, the desorption inflection appears earlier and the gas production rate in the stage of rapid desorption is higher. It is experimentally concluded that the originally recognized strategy of long-term slow CBM production is doubtful and the economic benefit of CBM exploitation from high-rank coal can be effectively improved by rapid drainage and pressure reduction. The field experiment results in pilot blocks of Fanzhuang and Zhengzhuang show that by increasing the drainage depressurization rate, the peak production of gas well would increase greatly, the time of gas well to reach the economic production shortened, the average time for a gas well to reach expected production reduced by half, and the peak gas production is higher.
A desorption simulation experiment with the condition of simulated strata was designed. The experiment, under different depressurizing rates and the same fluid saturation, was conducted on the sample from 3# coal of Daning coal mine in Jincheng, Shanxi Province. The gas production rate and pressure change at both ends of the sample were studied systematically, and the mechanisms of some phenomena in the experiment were discussed. The experimental results show that, whether at fast or slow depressurizing rate, the methane adsorbed to high-rank coal can effectively desorb and the desorption efficiency can reach above 90%. There is an obvious inflection point on the gas yield curve during the desorption process and it appears after the pressure on the lump of coal reduces below the desorption pressure. The desorption of methane from high-rank coal is mainly driven by differential pressure, and high pressure difference is conducive to fast desorption. In the scenario of fast depressurization, the desorption inflection appears earlier and the gas production rate in the stage of rapid desorption is higher. It is experimentally concluded that the originally recognized strategy of long-term slow CBM production is doubtful and the economic benefit of CBM exploitation from high-rank coal can be effectively improved by rapid drainage and pressure reduction. The field experiment results in pilot blocks of Fanzhuang and Zhengzhuang show that by increasing the drainage depressurization rate, the peak production of gas well would increase greatly, the time of gas well to reach the economic production shortened, the average time for a gas well to reach expected production reduced by half, and the peak gas production is higher.
引文
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[10]李金海,苏现波,林晓英,等.煤层气井排采速率与产能的关系[J].煤炭学报,2009,34(3):376-380.LI Jinhai,SU Xianbo,LIN Xiaoying,et al.Relationship between discharge rate and productivity of coalbed methane wells[J].Journal of China Coal Society,2009,34(3):376-380.
[11]段品佳,王芝银,翟雨阳,等.煤层气排采初期阶段合理降压速率的研究[J].煤炭学报,2011,36(10):1690-1692.DUAN Pinjia,WANG Zhiyin,ZHAI Yuyang,et al.Research on reasonable depressurization rate in initial stage of exploitation to coal bed methane[J].Journal of China Coal Society,2011,36(10):1690-1692.
[12]杨兆彪,张争光,秦勇,等.多煤层条件下煤层气开发产层组合优化方法[J].石油勘探与开发,2018,45(2):297-304.YANG Zhaobiao,ZHANG Zhengguang,QIN Yong,et al.Optimization methods of production layer combination for coalbed methane development in multi-coal seams[J].Petroleum Exploration and Development,2018,45(2):297-304.
[13]李梦溪,王立龙,崔新瑞,等.沁水煤层气田樊庄区块直井产出特征及排采控制方法[J].中国煤层气,2011,8(1):11-13.LI Mengxi,WANG Lilong,CUI Xinrui,et al.Output characteristics of vertical wells and dewatering control method used in Fanzhuang Block of Qinshui CBM Field[J].China Coalbed Methane,2011,8(1):11-13.
[14]李仰民,王立龙,刘国伟,等.煤层气井排采过程中的储层伤害机理研究[J].中国煤层气,2010,7(6):39-43.LI Yangmin,WANG Lilong,LIU Guowei,et al.Study on coal reservoir damage mechanism in dewatering and extraction process of CBM wells[J].China Coalbed Methane,2010,7(6):39-43.
[15]刘会虎,桑树勋,冯清凌,等.沁水盆地南部煤层气井排采储层应力敏感研究[J].煤炭学报,2014,39(9):1873-1878.LIU Huihu,SANG Shuxun,FENG Qingling,et al.Study on stress sensitivity of coal reservoir during drainage of coal-bed methane well in Southern Qinshui Basin[J].Journal of China Coal Society,2014,39(9):1873-1878.
[16]张遂安,曹立虎,杜彩霞.煤层气井产气机理及排采控压控粉研究[J].煤炭学报,2014,39(9):1927-1931.ZHANG Suian,CAO Lihu,DU Caixia.Study on CBM production mechanism and control theory of bottom-hole pressure and coal fines during CBM well production[J].Journal of China Coal Society,2014,39(9):1927-1931.
[17]李来成,傅雪海,罗斌.大块煤样逐次降压解吸实验研究[J].中国煤炭地质,2015,27(9):18-21.LI Laicheng,FU Xuehai,LUO Bin.Experimental study on large coal sample desorption under successive depressurization[J].Coal Geology of China,2015,27(9):18-21.
[18]康永尚,孙良忠,张兵,等.中国煤储层渗透率分级方案探讨[J].煤炭学报,2017,42(S1):186-194.KANG Yongshang,SUN Liangzhong,ZHANG Bing,et al.Discussion on classification of coalbed reservoir permeability in China[J].Journal of China Coal Society,2017,42(S1):186-194.
[19]康永尚,邓泽,刘洪林.我国煤层气井排采工作制度探讨[J].天然气地球科学,2008,19(3):423-426.KANG Yongshang,DENG Ze,LIU Honglin.Discussion about the CBMwell draining technology[J].Natural Gas Geoscience,2008,19(3):423-426.
[20]许小凯.煤层气直井排采中煤储层应力敏感性及其压降传播规律[D].北京:中国矿业大学,2016.XU Xiaokai.Stress sensitivity and pressure drop propagation law of coal reservoir during drainage process of CBM vertical well[D].Beijing:China University of Mining and Technology,2016.
[21]高彩霞,苏雪峰,刘俊英,等.沁水盆地高阶煤应力敏感性渗透率变化特征研究[J].中国煤层气,2017,14(5):11-13.GAO Caixia,SU Xuefeng,LIU Junying,et al.Study on characteristics of stress sensitivity and permeability variations of high-rank coal in Qinshui Basin[J].China Coalbed Methane,2017,14(5):11-13.
[22]李梦溪,王立龙,胡秋嘉,等.沁水盆地樊庄区块煤层气井开发特点及管理方法[J].中国煤层气,2013,10(3):3-8.LI Mengxi,WANG Lilong,HU Qiujia,et al.Coalbed methane development characteristics and management in Fanzhuang Block of Qinshui Basin[J].China Coalbed Methane,2013,10(3):3-8.
[2]吴世跃.煤层瓦斯扩散渗流规律的初步探讨[J].山西矿业学院学报,1994,12(3):259-263.WU Shiyue.Preliminary approach on the low of gas diffussion and permeation on coal seams[J].Journal of Shanxi Mining Institute,1994,12(3):259-263.
[3]李相方,石军太,杜希瑶,等.煤层气开发降压解吸运移机理[J].石油勘探与开发,2012,39(2):203-213.LI Xiangfang,SHI Juntai,DU Xiyao,et al.Transport mechanism of desorbed gas in coalbed methane reservoirs[J].Petroleum Exploration and Development,2012,39(2):203-213.
[4]聂百胜,张力.煤层甲烷在煤孔隙中扩散的微观机理[J].煤田地质与勘探,2000,28(6):20-22.NIE Baisheng,ZHANG Li.Diffusion micro-mechanism of coal bed methane in coal pores[J].Coal Geology&Exploration,2000,28(6):20-22.
[5]ANNA L O.Ground water flow associated with coalbed gas production,Ferron sandstone,east central Utah[J].International Journal of Coal Geology,2003,56(3):69-95.
[6]ANDREW R S.Hydrogeologic factors affecting gas content distribution in coal beds[J].International Journal of Coal Geology,2002,50(2):363-387.
[7]KOHLER T E.Development and application of a compositional coalbed methane production model[D].Pennsylvania:The Pennsylvania State University,1999.
[8]赵庆波,孙粉锦,李五忠.中国煤层气勘探的新思路[J].天然气工业,1996,16(5):25-28.ZHAO Qingbo,SUN Fenjin,LI Wuzhong.New theory for coalbed gas exploration in China[J].Natural Gas Industry,1996,16(5):25-28.
[9]赵群,王红岩,李景明,等.快速排采对低渗透煤层气井产能伤害的机理研究[J].山东科技大学学报(自然科学版),2008,27(3):27-31.ZHAO Qun,WANG Hongyan,LI Jingming,et al.Study on mechanism of harm to CBM well capability in low permeability seam with quick drainage method[J].Journal of Shandong University of Science and Technology(Natural Science),2008,27(3):27-31.
[10]李金海,苏现波,林晓英,等.煤层气井排采速率与产能的关系[J].煤炭学报,2009,34(3):376-380.LI Jinhai,SU Xianbo,LIN Xiaoying,et al.Relationship between discharge rate and productivity of coalbed methane wells[J].Journal of China Coal Society,2009,34(3):376-380.
[11]段品佳,王芝银,翟雨阳,等.煤层气排采初期阶段合理降压速率的研究[J].煤炭学报,2011,36(10):1690-1692.DUAN Pinjia,WANG Zhiyin,ZHAI Yuyang,et al.Research on reasonable depressurization rate in initial stage of exploitation to coal bed methane[J].Journal of China Coal Society,2011,36(10):1690-1692.
[12]杨兆彪,张争光,秦勇,等.多煤层条件下煤层气开发产层组合优化方法[J].石油勘探与开发,2018,45(2):297-304.YANG Zhaobiao,ZHANG Zhengguang,QIN Yong,et al.Optimization methods of production layer combination for coalbed methane development in multi-coal seams[J].Petroleum Exploration and Development,2018,45(2):297-304.
[13]李梦溪,王立龙,崔新瑞,等.沁水煤层气田樊庄区块直井产出特征及排采控制方法[J].中国煤层气,2011,8(1):11-13.LI Mengxi,WANG Lilong,CUI Xinrui,et al.Output characteristics of vertical wells and dewatering control method used in Fanzhuang Block of Qinshui CBM Field[J].China Coalbed Methane,2011,8(1):11-13.
[14]李仰民,王立龙,刘国伟,等.煤层气井排采过程中的储层伤害机理研究[J].中国煤层气,2010,7(6):39-43.LI Yangmin,WANG Lilong,LIU Guowei,et al.Study on coal reservoir damage mechanism in dewatering and extraction process of CBM wells[J].China Coalbed Methane,2010,7(6):39-43.
[15]刘会虎,桑树勋,冯清凌,等.沁水盆地南部煤层气井排采储层应力敏感研究[J].煤炭学报,2014,39(9):1873-1878.LIU Huihu,SANG Shuxun,FENG Qingling,et al.Study on stress sensitivity of coal reservoir during drainage of coal-bed methane well in Southern Qinshui Basin[J].Journal of China Coal Society,2014,39(9):1873-1878.
[16]张遂安,曹立虎,杜彩霞.煤层气井产气机理及排采控压控粉研究[J].煤炭学报,2014,39(9):1927-1931.ZHANG Suian,CAO Lihu,DU Caixia.Study on CBM production mechanism and control theory of bottom-hole pressure and coal fines during CBM well production[J].Journal of China Coal Society,2014,39(9):1927-1931.
[17]李来成,傅雪海,罗斌.大块煤样逐次降压解吸实验研究[J].中国煤炭地质,2015,27(9):18-21.LI Laicheng,FU Xuehai,LUO Bin.Experimental study on large coal sample desorption under successive depressurization[J].Coal Geology of China,2015,27(9):18-21.
[18]康永尚,孙良忠,张兵,等.中国煤储层渗透率分级方案探讨[J].煤炭学报,2017,42(S1):186-194.KANG Yongshang,SUN Liangzhong,ZHANG Bing,et al.Discussion on classification of coalbed reservoir permeability in China[J].Journal of China Coal Society,2017,42(S1):186-194.
[19]康永尚,邓泽,刘洪林.我国煤层气井排采工作制度探讨[J].天然气地球科学,2008,19(3):423-426.KANG Yongshang,DENG Ze,LIU Honglin.Discussion about the CBMwell draining technology[J].Natural Gas Geoscience,2008,19(3):423-426.
[20]许小凯.煤层气直井排采中煤储层应力敏感性及其压降传播规律[D].北京:中国矿业大学,2016.XU Xiaokai.Stress sensitivity and pressure drop propagation law of coal reservoir during drainage process of CBM vertical well[D].Beijing:China University of Mining and Technology,2016.
[21]高彩霞,苏雪峰,刘俊英,等.沁水盆地高阶煤应力敏感性渗透率变化特征研究[J].中国煤层气,2017,14(5):11-13.GAO Caixia,SU Xuefeng,LIU Junying,et al.Study on characteristics of stress sensitivity and permeability variations of high-rank coal in Qinshui Basin[J].China Coalbed Methane,2017,14(5):11-13.
[22]李梦溪,王立龙,胡秋嘉,等.沁水盆地樊庄区块煤层气井开发特点及管理方法[J].中国煤层气,2013,10(3):3-8.LI Mengxi,WANG Lilong,HU Qiujia,et al.Coalbed methane development characteristics and management in Fanzhuang Block of Qinshui Basin[J].China Coalbed Methane,2013,10(3):3-8.
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