Chemical Characteristics And Dynamic Field Analysis Of CBM Produced Water In The Southern Qinshui Basin

By means of materials collection, hydrogeological survey, water chemicalanalysis and environmental isotope test, synthesis analysis of hydrogeochemicalcharacteristics of coal-bed methane （CBM） produced water in the southern Qinshuibasin is conducted, and filling source has been discriminated to a certain degree. Atthe same time, by adopting the Visual Modflow software, the numerical simulationmodel of groundwater flow is built up on the basis of the water level observationdata of coal-bed methane well. By means of this model seepage field distribution anddepression cone expanding are predicted in single CBM well drainage progress, and thechanges of depression cone radius with different time are obtained.Through hydrochemistry analysis on CBM produced water in study field, CBMproduced water is characterized by high chloride and high salinity, and water quality ismostly Cl HCO₃-Na type. The δD and δ¹⁸O values of environmental isotope from CBMproduced water plot slightly nearby the meteoric water line, indicating that each aquiferin mining area has unified supply water from the atmosphere precipitation. Throughmodel validation and parameter identification, the numerical simulation modelestablished corresponds with hydrogeological conditions, and is stable and reliable.Through simulation and prediction of level fluctuation during extraction of CBM wellTS-192, it shows that depression cone gradient is steep within20m around drainagewells while that is slow to extraction influence boundary, with limited transferring rangeand steep gradient influence boundary expanding outward. To change roof and floorpermeability coefficient, along with the increase of the roof and floor permeabilitycoefficient, expanding radius of depression conereduce gradually when roof and floorpermeability is less than coal permeability, and the range of depression cone is less than280m. When roof and floor permeability is over coal permeability, the flow fieldwillsoon reach stable state in coal seam, afterwards depression cone starts expandingwith increase of extraction quantity but not be dry up. When the permeability of roofand coal are on the same order, pressure transmission range are almost the same, with itsscope in the200m to220m; while depression cone expand far and expands in the coalroof, and pressure transmit indirectly in coal-bed when the roof permeability is bigger than coal permeability over one order.