变形介质分形煤层气藏不稳定渗流问题

TRANSIENT FLOW OF FRACTAL COAL-BED GAS RESERVOIR IN DEFORMED MEDIUM

煤层气渗流中的许多现象都具有尺度不变性，以双重介质为基础，引入分形参数d和θ，并考虑到煤层气藏的应力敏感性，采用数值方法研究了具有分形特性的煤层气藏渗流规律。绘制并分析了分形参数和渗透率模数影响的压力动态典型曲线，通过分析表明分形参数d和分形指数θ对压力动态存在显著影响，d越小，无因次压力越大，压力导数曲线也越高；θ越大无因次压力越大，压力导数也越大；但是d和θ都对过渡段出现的时间影响不大。分形参数δ1仅影响着典型曲线过渡段出现的时间和过渡段凹兜的深浅，参数δ1越大，过渡段出现越早，凹兜也越深。压敏效应的存在使得压力及压力导数曲线出现上翘趋势，并且渗透率模数越大，上翘趋势越严重。

Many phenomena of flow in coal-bed gas have dimensional immutability. On the basis of dual medium, fractal parameters d and θ are introduced. Considering stress sensitivity of coal - bed gas reservoirs, the rule of flow in coal-bed gas reservoirs with fraetal property is studied by using numerical methods. Typical curve of pressure behavior affected by fractal parameters and permeability modulus is drawn and analyzed. Analysis indicates that pa- rameters d and θ have remarkable effect on pressure behavior, the smaller the d is, the greater the dimensionless pressure is, and the higher the differential of pressure curve is; the larger the θ is, the greater the pressure is, and the larger the differential of pressure curve is; but d and θ all do not have great effect on time of transition section appearance. The fraetal parametercrl only has effect at the time of transition section appearance of typical curve and depth of hollow bag, the large the parameter δ1 is, the earlier the transition section appearance is, and the deeper the hollow bag is. Existence of stress sensitivity causes pressure and differential of pressure curve to have an upwarping trend, and the larger the permeability modulus is, the more serious the upwarping trend is.