基于Visual Modflow沁水盆地南部水动力条件及其对煤层气富集控制机理的研究
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摘要
水动力条件是控制煤层气富集成藏的重要因素之一，评价水动力条件也可以作为优选煤层气勘探开发有利目标区的重要依据。沁水盆地太原组15号煤储层资源量达到1.28×10~(12)m~3，占全盆地的60%。但15号煤层顶板K_2灰岩含水层对煤层水进行持续补给，导致煤层气井排采过程中产水量大，产气量低。本文以位于沁水盆地南部的柿庄南区块为目标区，通过分析K_2灰岩含水层的水动力模式及其对煤层气富集的控制机理，为将来的煤层气勘探开发和提高煤层气井产量提供理论依据。
研究区柿庄南区块位于沁水盆地南部，总体构造形态为北倾箕状斜坡带，地层总的趋势是由东南向西北倾斜。构造环境比较简单，区内断层不甚发育，存在有较多规模和幅度较小的褶皱。
利用Visual Modflow4.2软件，研究了以15号煤层为开采层的煤层气井排采过程中地下水流场的变化情况。在研究过程中，概化了目的层太原组15号煤系承压含水层岩溶—裂隙系统，建立了水文地质概念模型，即非均质各向同性二维非稳定流模型。并在此基础上，进一步建立了符合15号煤K_2含水层实际情况的三维地下水流系统模型，总结了该地区的水动力条件对煤层气富集的控制机理。在此基础止，分别对太原组15号K_2含水层未来流场变化进行了3年后、6年后的预测，根据预测结果，推测煤层气富集区的变化。
研究结果表明，柿庄南区块太原组15号煤地下流场为汇流型；研究区的东侧为出露区，接受补给，径流强度较大，然后顺层由东向西径流，径流强度逐渐减弱。寺头正断层导气、导水能力极差，不会发生水力交换。高村—樊庄一带，存在地下分水岭，地下分水岭使由东径流而来的地下水分别向北和南径流。分水岭以北，形成了一个以柿庄—枣园一带为中心的水位等势面低地，径流条件极弱。分析认为，本区15号煤储层主要受两种控气模式的影响，在盆地边缘补给区及部分径流区带，以水力封堵控气作用为主；在远离补给区的径流区及滞流区域，为水力封闭控气作用。枣园—柿庄一带形成的“低洼”地下水等势面，出现汇流区储层压力升高的现象，形成煤层气含气量高值区。这种高压力分布区与高含气量分布区的吻合，说明了地下水汇流区十分有利于煤层气的富集。
而预测结果显示，尽管受煤层气井排采的影响，到2014年时地下水流场变化很小，只有分水岭位置稍微向北移动了一些；而在枣园—柿庄一带，汇流区位置基本没有改变。到2017年时地下水流场的变化受煤层气井排采影响较大，总体水头比2011年下降了8～12m，研究区西侧的地下水等势面有向北移动的趋势，地下分水岭明显的北移。预测15号煤煤层气含气量高的区域在未来几年内，仍为有利目标区，但面积在逐渐减小。
Hydrodynamic condition controls the enrichment and accumulation of coal bedmethane and the evaluation of hydrodynamic condition could provide important basisfor optimizing favorable target zone. The coal bed methane resources in15coal seamof Taiyuan Fm in Qinshui basin is1.28×10~(12)m~3，60%of the gross of the wholebasin. Because of the continuous water supply from the limestone roof aquifer K_2of15coal seam, the coal bed methane wells appears high water production while lowgas production. Focusing the south Shizhuang in Qinshui basin as the target area, onthe basis of analysing the hydrodynamic model of K_2limestone roof aquifer and itscontrolling mechanism for CBM enrichment, this paper provides theoretical basis forcoal bed methane exploration and development in the future.
The underground water flow field changing during the CBM wells producingprocess of15coal seam was studied by using the Visual Modflow4.2software.Generalizing the15coal series confined aquifer Karst-fissure system and building the2D hydrogeology conceptual model and the3D underground water flow systemmodel coinciding with15coal seam and K_2aquifer. On the basis of these work, thehydrodynamic condition of this field and its controlling mechanism for CBMenrichment was summarizing and the prediction of favorable developing area wasmade according to the changing of underground water dynamic field in the future.
The research result shows the underground water flow field of15coal seam inTaiyuan Fm is confluence type in south Shizhuang field. The east side is outcrop aeraand has a stronger runoff intensity by receiving replenishment and becomes fromstrong to weak from east to west. The Sitou normal fault has bad capacity intransmitting water and gas and does not have hydraulic exchange. The undergrounddivide in Gaocun to Fanzhuang area makes the underground water from the east flowto the south and north part, which produces a low water level equipotential surfacearea with center of Daning—Shizhuang—Zaoyuan region. The analysis indicates thatthe CBM enrichment of15coal reservoir has two kinds of controlling mode. At thebasin edge area gives priority to hydraulic plugging mode, while the place far from the recharge area and stagnation area gives priority to hydraulic sealing. The reservoirpressure rises and forms the CBM content high level region in the Shizhuang—Zaoyuan area with low water level equipotential surface. The coincidence of highreservoir pressure area and high CBM content area explains the groundwaterconfluence area is in favor of CBM enrichment.
The prediction result shows the groundwater flow field will not change but thedivide move a little to the north to2014, though influenced by CBM wells producing.The location of doab area will state unchanged in the Shizhuang—Zaoyuan area. Thechanging of groundwater flow field to2017will be strongly influenced by CBM wellsproducing with the head fall by30～40m. Meanwhile, the groundwater equipotentialsurface has a trend to move to the north and the divide move to the north apparently.The region with high CBM content of15coal reservoir will still be favorable in thenext few years except the decreasing.
研究区柿庄南区块位于沁水盆地南部，总体构造形态为北倾箕状斜坡带，地层总的趋势是由东南向西北倾斜。构造环境比较简单，区内断层不甚发育，存在有较多规模和幅度较小的褶皱。
利用Visual Modflow4.2软件，研究了以15号煤层为开采层的煤层气井排采过程中地下水流场的变化情况。在研究过程中，概化了目的层太原组15号煤系承压含水层岩溶—裂隙系统，建立了水文地质概念模型，即非均质各向同性二维非稳定流模型。并在此基础上，进一步建立了符合15号煤K_2含水层实际情况的三维地下水流系统模型，总结了该地区的水动力条件对煤层气富集的控制机理。在此基础止，分别对太原组15号K_2含水层未来流场变化进行了3年后、6年后的预测，根据预测结果，推测煤层气富集区的变化。
研究结果表明，柿庄南区块太原组15号煤地下流场为汇流型；研究区的东侧为出露区，接受补给，径流强度较大，然后顺层由东向西径流，径流强度逐渐减弱。寺头正断层导气、导水能力极差，不会发生水力交换。高村—樊庄一带，存在地下分水岭，地下分水岭使由东径流而来的地下水分别向北和南径流。分水岭以北，形成了一个以柿庄—枣园一带为中心的水位等势面低地，径流条件极弱。分析认为，本区15号煤储层主要受两种控气模式的影响，在盆地边缘补给区及部分径流区带，以水力封堵控气作用为主；在远离补给区的径流区及滞流区域，为水力封闭控气作用。枣园—柿庄一带形成的“低洼”地下水等势面，出现汇流区储层压力升高的现象，形成煤层气含气量高值区。这种高压力分布区与高含气量分布区的吻合，说明了地下水汇流区十分有利于煤层气的富集。
而预测结果显示，尽管受煤层气井排采的影响，到2014年时地下水流场变化很小，只有分水岭位置稍微向北移动了一些；而在枣园—柿庄一带，汇流区位置基本没有改变。到2017年时地下水流场的变化受煤层气井排采影响较大，总体水头比2011年下降了8～12m，研究区西侧的地下水等势面有向北移动的趋势，地下分水岭明显的北移。预测15号煤煤层气含气量高的区域在未来几年内，仍为有利目标区，但面积在逐渐减小。
Hydrodynamic condition controls the enrichment and accumulation of coal bedmethane and the evaluation of hydrodynamic condition could provide important basisfor optimizing favorable target zone. The coal bed methane resources in15coal seamof Taiyuan Fm in Qinshui basin is1.28×10~(12)m~3，60%of the gross of the wholebasin. Because of the continuous water supply from the limestone roof aquifer K_2of15coal seam, the coal bed methane wells appears high water production while lowgas production. Focusing the south Shizhuang in Qinshui basin as the target area, onthe basis of analysing the hydrodynamic model of K_2limestone roof aquifer and itscontrolling mechanism for CBM enrichment, this paper provides theoretical basis forcoal bed methane exploration and development in the future.
The underground water flow field changing during the CBM wells producingprocess of15coal seam was studied by using the Visual Modflow4.2software.Generalizing the15coal series confined aquifer Karst-fissure system and building the2D hydrogeology conceptual model and the3D underground water flow systemmodel coinciding with15coal seam and K_2aquifer. On the basis of these work, thehydrodynamic condition of this field and its controlling mechanism for CBMenrichment was summarizing and the prediction of favorable developing area wasmade according to the changing of underground water dynamic field in the future.
The research result shows the underground water flow field of15coal seam inTaiyuan Fm is confluence type in south Shizhuang field. The east side is outcrop aeraand has a stronger runoff intensity by receiving replenishment and becomes fromstrong to weak from east to west. The Sitou normal fault has bad capacity intransmitting water and gas and does not have hydraulic exchange. The undergrounddivide in Gaocun to Fanzhuang area makes the underground water from the east flowto the south and north part, which produces a low water level equipotential surfacearea with center of Daning—Shizhuang—Zaoyuan region. The analysis indicates thatthe CBM enrichment of15coal reservoir has two kinds of controlling mode. At thebasin edge area gives priority to hydraulic plugging mode, while the place far from the recharge area and stagnation area gives priority to hydraulic sealing. The reservoirpressure rises and forms the CBM content high level region in the Shizhuang—Zaoyuan area with low water level equipotential surface. The coincidence of highreservoir pressure area and high CBM content area explains the groundwaterconfluence area is in favor of CBM enrichment.
The prediction result shows the groundwater flow field will not change but thedivide move a little to the north to2014, though influenced by CBM wells producing.The location of doab area will state unchanged in the Shizhuang—Zaoyuan area. Thechanging of groundwater flow field to2017will be strongly influenced by CBM wellsproducing with the head fall by30～40m. Meanwhile, the groundwater equipotentialsurface has a trend to move to the north and the divide move to the north apparently.The region with high CBM content of15coal reservoir will still be favorable in thenext few years except the decreasing.
引文
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D.C. Gupta. Environmental aspects of selected trace elements associated with coal andnatural waters of Pench Valley coalfield of India and their impacton human health. InternationalJournal of Coal Geology1999(40):133–149.
E.C.P. Kinnon, S.D. Golding, C.J. Borehamb, K.A. Baublys, J.S. Esterle. Stable isotopeand water quality analysis of coal bed methane production waters and gases from the BowenBasin, Australia. International Journal of Coal Geology,2009:1-13.
McBeth, Ian H., Katta J. Reddy, and Quentin D. Skinner,2003. Coalbed Methane ProductWater Chemistry in Three Wyoming Watersheds. Journal of the American Water ResourcesAssociation39(3):575-585.
Scott A.R. et al. Hydrogeologic factors affecting gas content distribution in coal beds.International Journal of coal Geology.2002(50):363-387.
S.W.Lambert. The1989Coalbed Methane Symposium Proceedings,The University ofAlabama, et al, Tuscaloosa,1989:253-264.
Tom Myers. Groundwater management and coal bed methane development in the PowderRiver Basin of Montana. Journal of Hydrology2009(368):178–193.
Wayne A. Van Voast. Geochemical signature of formation waters associated with coalbedmethane. AAPG Bulletin,2003.87(4):667–676.
Zebrowitz M. et al. Coalbed stimulation are optimized in Alabama basin. OGJ,1989,87(4):61-72
池卫国.沁水盆地煤层气的水文地质控制作用.石油勘探与开发.1998,25(3):15-18
冯三利,胡爱梅,叶建平.中国煤层气勘探开发技术研究.北京:石油工业出版社,2007:18-40
傅雪海,秦勇,王文峰,等.沁水盆地中-南部水文地质控气特征.中国煤田地质.2001,13(1):31-34
傅雪海,秦勇,韦韬奋,等.沁水盆地水文地质条件对煤层含气量的控制作用.煤层气地质理论与选区评价.2007:61-69
傅雪海,王爱国,陈锁忠,等.寿阳-阳泉煤矿区控气水文地质条件分析.天然气工业.2005,25(1):33-36
付江伟,傅雪海,胡晓,等.焦作矿区煤层气开发的水文地质条件分析.中国矿业.2011,20(4):106-109
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