煤层气排采局部水动力场模式及其意义——以鄂尔多斯盆地东南缘为例

煤层气排采形成的局部水动力场是对原始水动力场扰动的结果，开展局部水动力场模式及其对排采效果影响的研究对于指导煤层气排采井层的优选具有重要意义。鄂尔多斯盆地东南缘某煤层气田煤层气井排采动态表现差异很大，考虑不同排采井所处构造位置和原始水动力场背景，识别出了煤层气排采引起的3种局部水动力场模式，即有效扰动型局部水动力场、含水层入侵型局部水动力场和淡水补给型局部水动力场。在有效扰动型局部水动力场中，排出水为煤层水，煤层气井表现出见气快、产气量高等特点；在含水层入侵型局部水动力场和淡水补给型局部水动力场中，排出水有部分甚至大部分来自于邻近含水层或近地表的淡水，属无效排水，煤层气井表现出见气晚、产气量低等特点。在局部水动力场模式的指导下，对断层附近的排采井要避免射开邻近强含水层的煤层，同时，排采井的井位应避开近地表淡水补给区。

Dewatering-induced local hydrodynamic field models and their significance to CBM production : A case study from a coalfield in the southeastern margin of the Ordos Basin

The dewatering induced local hydrodynamic field is resulted from the perturbation in the original hydrodynamic field during dewatering and production of CBM. Therefore, it is of great significance to study the dewatering induced local hydrodynamic field modes and their impact on the CBM gas production, so as to provide guidance for the optimization of CBM drainage beds in production wells. The CBM gas wells in a certain coal field at the southeastern margin of the Ordos Basin present a great variance in the dynamic performance of CBM gas production. Considering the structural positions and original hydrodynamic fields of different drainage wells, three dewatering induced local hydrodynamic modes, resulted from CBM production, were identified, i.e., the effective perturbation mode, aquifer intrusion mode, and freshwater supply mode. For the local hydrodynamic field of the first mode, the outlet water comes from the coalbed water, thus the CBM well is characterized by fast gas production and high productivity; for the local hydrodynamic fields of the latter two modes, the outlet water partially or even mostly comes from the aquifer in the neighborhood or the near surface freshwater, which belongs to the invalid drainage, resulting in slow production and low productivity of CBM wells. Based on the local hydrodynamic mode, the coalbed with strong aquifer should be avoided for near fault drainage wells; meanwhile, the well sites should be laid out away from the supply areas of near surface freshwater.