煤层气井排采水源分析及出水量预测——以鄂尔多斯盆地东缘韩城矿区为例

Analysis on water sources in a CBM gas well and forecast of water yield quantity:A case study from the Hancheng Mine at the eastern edge of the Ordos Basin

煤层排水降压是加速煤层气解吸的关键,查明排采出水水源并对出水量进行有效预测将有助于煤层气开发方案的合理制定。为此,利用排采、测录井等资料,基于动态刻度静态、静态预测动态的思想,通过对煤层气井排采水源和出水量的综合分析,选取煤层气井与断层之间的距离、相对构造幅度、煤层及其顶底板的含水级别这4个评价指标作为煤层气井排采出水量的主要影响因素,得出煤层气井排采出水量的预测模型,并以预测结果划分出研究区煤层出水量平面分布特征。综合评价结果认为:煤层气井排采水源来自于近断裂带、构造低幅度区、顶底板砂岩及煤层自身,出水量大的井多靠近断裂带、构造低幅度区,或存在顶底板厚层砂岩含水层,而煤层自身含水量较小;研究区5号煤层南部和北部及中部韩3-2-025井区出水量较大,呈现沿断裂带、构造低幅度区及顶底板厚层砂岩区出水量增大的趋势,与实际排采产水量吻合较好。

Pressure reduction by water drainage in a CBM gas well is a key to accelerating the coalbed methane （CBM） desorption, so it is contributive to the reasonable formulation of a CBM development program to find out water sources of drainage and effectively forecast water yield quantity. According to drainage and logging data, based on the principle of ＂static conditions determined by dy- namic conditions while hydraulic conditions forecasted with static conditions＂, and in combination with the comprehensive analysis on water sources and water yield quantity in coal bed mining, four assessment indicators （the distance from a CBM well to the fault, relative structure amplitude, water-yield grade respectively of a coal bed and its roof and floor） were used as main influencing factors of water yield quantity in CBM production to figure out a water-yield forecasting model and work out plane distribution characteristics of water yields of a CBM gas well in the research area according to the forecasting results. The comprehensive assessment shows that the water yield in CBM production is from the close fault zone, the structure low-amplitude zone, sandstones of roof and floor, or coal beds themselves; most wells with a great water yield are usually situated close to the fault zone, the structure low-amplitude zone, or the area with sandstone aquifers at roof and floor, but a water yield from coal beds is relatively low. A great amount of wa ter is found at the south, north and middle around Well H3 2-025 of No.5 coal bed in the research area, showing that the water yield is increasing gradually from the fault zone, the structure low amplitude zone to thick sandstones of coal bed roof and floor, which is consistent with that in actual CBM production with water drainage.