| With CBM production of southern Qinshui basin as an example, the fluid geochemical field of the production well area and systematic testing and analysis of geochemistry was chosen as technical method. Based on geological setting of coal reservoir, fracturing and drainage of CBM well in CBM production area, CBM components, CBM carbon and hydrogen isotopes, ion concentration of formation water, element content of formation were studied. The spatial evolutions and affecting factors of CBM components, CBM methane isotopes, ion concentration, and element content were analyzed. Coupled relation of different fluid chemical field and well interference during drainage under well pattern was discussed, the constrained mechanism of well interference was illustrated, and the geochemical response model on well interference from CBM components, methane carbon and hydrogen isotopes, ion and element of formation water were proposed. The main research achievements are concluded as follows:(1) Geochemical monitoring method of well interference during drainage under well pattern was established.The modern geochemical testing and analysis was chosen as the method. The content of CBM components, the ratio of stable isotope of CBM, ion concentration of formation, element content of formation water were tested and analyzed, the stage and the degree of well interference of CBM wells were distinguished, geochemical monitoring method of well interference during drainage of CBM under well pattern was established.(2)The evolution characteristics and coupled relation of fluid chemical field, fluid dynamic field during drainage of CBM wells were revealed.Flowing bottom-hole pressure is controlled by Hydrostatic pressure before gas generation, but is controlled by casing pressure after gas generation. Casing pressure, hydrostatic pressure, flowing bottom-hole pressure have a certain correlation with accumulative water drainage. The underground water flows from the east to the west and from the south to the north. Coal reservoir pressure undergoes three stages: reversal period, differential period, unbalanced pressure drop period in monitoring time; it is correspond to the period of without well-interference, weak well-interference period, unbalanced well-interferenced period of CBM production. The well-interference occurs, but the well interference is unbalanced, may be in the initial stage, and its interference is relatively weak. CBM components, methane carbon and hydrogen isotopes, the ion concentration, total mineralization, the conductivity, the hardness, the element content have cyclical fluctuation with drainage time. Hydrochemical types of formation water from different CBM wells are mainly Na-HCO3, but partial hydrochemical type of formation water of partial CBM wells are Na-Cl with some special period, the sources of formation water are mainly coalbed water, the mixed water of coalbed water and sandrock water. The fluctuation of CBM components, the stable isotopes of methane may be related to component fractionation, isotope fractionation, drainage and well interference. The fluctuation of ion concentration, the mineralization, the conductivity, the hardness and the element content may be associated with drainage of CBM wells, well interference, the source of formation water, the properties of element and ion. The fractionation of CBM components, the stable isotopes, and the consistency of the variation of ion concentration reflects the effect from well interference.The spatial distribution of methane, carbon dioxide undergoes several changes in the sampling period. The spatial distribution of the concentration of CBM components is affected by the concentration of CBM produced by partial wells. The spatial evolution of the stable isotopes of CBM undergoes the course the distribution of the north-south and the deflection of the east-worth. The spatial distribution of carbon isotope is similar to the spatial distribution of hydrogen isotope, the evolution of methane hydrogen isotope falls behind methane carbon isotope. The decreasing difference of CBM components, methane carbon and hydrogen isotopes reveal the effect of well interference. The variability of the spatial evolution of CBM components and methane isotopes reveal that well interference in the initial stage, and the interference. The spatial distribution ion, element of formation water is characterized by cyclical deflection with the NS trending and the ES trending. The spatial distribution of the mineralization decrease from the south to the north, it is not sensitive than the spatial evolution of ion concentration on well interference, the spatial evolution of element falls behind the spatial evolution of ion. The spatial evolution of ion and element, their inconsistency are related to the properties of ions and elements, the source of formation water, well interference.The composite between the spatial distribution of methane and carbon dioxide shows the distribution and evolution of them is basically asynchronous, because the spatial distribution of methane and carbon dioxide are mainly related to component fractionation of CBM, the supply of CBM caused by the instable fluid field in the initial stage of well interference. The spatial evolution of carbon isotope ratio is consistent with the spatial evolution of hydrogen isotope ratio, but the spatial evolution of hydrogen isotope lags behind the spatial evolution. The composite relation of the spatial evolution of CBM component is consitent with the spatial evolution of methane carbon isotope demonstrates, which is related to component fractionation of CBM, isotope fractionation, the supply of gas source and the change of hydrodynamic condition of ground water.The composite analysis of different liquid fluid parameters show there are not entirely consistent in the spatial distribution of the two parameters of liquid fluid, the main reason may be related to the properties of ion and element, drainage under well pattern, well interference, the different source of formation water. The composite analysis between different liquid phase fluids also reveals the real reason of the inconsistency of different liquid phase fluid is the instability of the initial well interference. The evolution of chemical field of gas phase fluid is obviously consistent with the evolution of chemical field of liquid phase fluid, they are affected by well interference obviously, and there is an obvious positive correlation between them during coupling.That fluid chemical field is not related to the structure of coal bed directly, the length of main artificial fracture by fracturing, which reveals the variation of fluid chemical field is caused by well interference formed by drainage.(3) The geochemical response model of well interference during drainage of CBM was established.There is a response relationship between fluid chemical parameters, fluid chemical fields and well interference, fluctuation change characteristics of fluid chemical parameters responds the forming process of well interference, the distribution characteristics of fluid chemical field and evolution characteristics of fluid chemical flied also respond the different stages of well interference. The deflection and the inversion of chemical field of chemical field reflect the multiple sources of CBM, response the course of well interference.(4) The action of well interference in CBM production area and its production was assessed scientifically.On the basis of fluid dynamic field, fluid chemical parameters and chemical field during drainage of CBM, the principle and the scheme of assessment on well interference of CBM wells in production area, the stage and the degree of well interference in CBM production area during drainage was judged. The assessment scheme can apply to different CBM production area; it can provide the technical support for CBM development in production control. |
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