温度压力对煤中甲烷解吸速率影响的试验研究

Experimental study of effect of temperature and pressure on the desorption rate of coal bed methane

解吸速率对煤层瓦斯涌出规律、煤层气井见气时间和服务年限有重要影响。随着煤层埋藏深度的增加,温度压力对甲烷吸附量有明显的控制作用,当前对于温度压力对解吸速率的影响关注相对不足。为了研究温度压力对煤层甲烷解吸速率的影响,用同一样品开展不同温度压力条件下的等温吸附/解吸试验,获得不同平衡压力段的吸附量-时间数据,利用吸附动力学模型拟合出解吸速率-时间曲线,甄选出3个评价参数研究温度压力对解吸速率的影响。研究表明:不同压力下的解吸速率均随着时间推移呈现指数降低的变化规律。解吸速率常数、相对初始解吸速率、中值解吸量时间能够从不同角度反映解吸速率的变化过程,其中解吸速率常数和相对初始解吸速率均随着温度和压力的升高而增加,中值解吸量时间随温度和压力的升高而减小。结合鄂尔多斯盆地保德区块的温度/压力梯度可知,在1000 m以浅时解吸速率受温度和压力的双重控制,随深度增加而不断增高;1000~1735 m随深度增加压力效应逐渐降低,温度效应依然明显。

Desorption rates have an important influence on coal seam gas emergence patterns,the time to gas and the service life of coal bed methane wells.As the depth of the coal seam increases temperature and pressure have a significant control on methane adsorption,but relatively little attention has been paid to the effect of temperature and pressure on desorption rates.To investigate the effect of temperat-ure and pressure on the desorption rate of coalbed methane,isothermal adsorption/desorption experiments were carried out with the same sample at different temperature and pressure conditions to obtain adsorption amount-time data at different equilibrium pressures.It is shown that the desorption rate at different pressures decreases exponentially with time.The desorption rate constant,the relative initial de-sorption rate and the median desorption time can reflect the change of desorption rate from different perspectives,where the desorption rate constant and the relative initial desorption rate increase with increasing temperature and pressure,and the median desorption time de-creases with increasing temperature and pressure.Combined with the temperature/pressure gradient of the Baode Block in the Ordos Basin,it can be seen that the desorption rate is controlled by both temperature and pressure at shallower depths of 1000 m,and increases with depth;the pressure effect gradually decreases with depth between 1000 and 1735 m,while the temperature effect remains obvious.