煤层气储层应力敏感性定量表征及影响因素研究

Controls and quantitative characterization of stress sensitivity for coal seams

煤层气储层应力敏感性较强,对煤层气开发具有重要影响。采用不同区块天然煤样开展应力敏感性室内实验,应用应力敏感性系数和渗透率伤害系数2个参数评价了各煤样应力敏感性程度,并研究了煤阶、渗透率和储层气体压力等参数对煤岩应力敏感性的影响。结果表明:镜质组反射率R_o<1.7%时,煤阶越低,应力敏感性程度越大,渗透率伤害程度越高;而镜质组反射率R_o>1.7%时,煤阶越高,应力敏感性程度越大,渗透率损害程度越高;煤岩初始渗透率越高,应力敏感性系数越低,应力敏感性越弱,利用初始渗透率与其应力敏感性系数之间的经验公式可以估算煤岩应力敏感性,方便现场应用;储层气体压力越低,渗透率越高,越有利于煤层气开发,而煤岩应力敏感性系数和渗透率伤害系数也略高,需预防应力敏感性造成的渗透率伤害。

The stress sensitivity of coalbed methane reservoirs is strong, which has an important influence on the development of coalbed methane. Natural coal samples from different blocks were used to carry out stress sensitivity experiments, and two parameters, stress sensitivity coefficient and permeability damage coefficient were applied to evaluate the degree of stress sensitivity of coal samples. The stress sensitivity effects of coal rank, permeability and the gas pressure of a coal reservoir were studied. The results showed that when Ro is lower than 1.7%, the lower the coal rank is, the greater the degree of stress sensitivity is and the higher the extent of the permeability damage. When Ro is higher than 1.7%, the higher the coal rank is, the greater the degree of stress sensitivity is and the higher the permeability damage is. The empirical formula, put forward by this paper, between initial permeability and stress sensitivity coefficient can be used to predict the stress sensitivity coefficient of coal samples, which is convenient for pilot application. The lower the pressure of a gas reservoir is, the higher the permeability, which is advanta-geous for CBM development. However, lower gas pressure results in a slightly higher stress sensitivity coefficient and permeability damage coefficient, so avoiding stress sensitivity is important.