An Analysis About The Hydrodynamic Condition Of South Qinshui Basin And Its Controlling Mechanism To CBM Enrichment Based On Visual Model

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 is1.28×10¹²m³,60%of the gross of the wholebasin. Because of the continuous water supply from the limestone roof aquifer K₂of15coal 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 K₂limestone 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 K₂aquifer. 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.