煤层气井渗透率时空变化规律研究及应用

Spatial-Temporal Permeability and Its Application in CBM Well

针对煤层气井排采过程中渗透率变化规律认识不清的问题,利用煤层气产出过程中的正、负效应,渗流及等温吸附理论,得到排采过程中煤储层渗透率随时间及距离变化的数学模型。研究表明:单相水流阶段,液面降速越慢,负效应导致的渗透率降幅越小;气水两相流阶段,适当提高液面降速,正效应越显著;在排采过程中,渗透率呈非对称"V"型变化;对于临储压力比较高的煤储层,采取"低降幅憋套压"的方式能够扩大煤储层的气体解吸范围。研究成果为煤层气井的现场排采控制提供理论指导。

The reservoir permeability variation during gas recovery by water drainage is unclear in CBM well. The positive-negative effects,seepage and isothermal adsorption theories during CBM production are used to establish a reservoir permeability model to predict the permeability variation with time and distance during gas recovery by water drainage. Research shows that the permeability resulting from negative effect decreases slowly with the decrease of liquid-level drawdown velocity in single-phase water flow. The positive effect increases with the appropriate increase of liquid-level drawdown velocity in water-gas two-phase flow. Reservoir permeability follows a pattern of asymmetric 'V-type'during gas recovery by water drainage.For the coal gas reservoir with relatively high critical desorption pressure,'low drawdown level and casing pressure buildup'production mode could expand the gas desorption area in coal reservoir. This research could provide certain theoretical guidance for the operation of field gas recovery by water drainage in CBM well.