以往的煤层气藏物质平衡法未考虑地解压差问题,对此进行了改进,提出了新方法.首先对煤层的原始吸附气含量采用临界解吸压力(而非前人采用的原始地层压力)下的Langmuir方程进行表征；然后通过近似化和线性化处理,将基本物质平衡方程转化为视平均储层压力(P/Z)和累积产气量(GP)的直线方程.该直线在直角坐标系横坐标上的截距为原始地质储量,在纵坐标上的截距为视临界解吸压力(而非前人的视原始地层压力).运用该物质平衡法,计算Eclipse建立的一个煤层气藏模型的储量,发现误差仅为0.35％.这表明在参数准确的情况下,Langmuir体积和压力、原始割理孔隙度和某些时刻的平均地层压力等在数模中可准确获知,该方法是准确可靠的.%The pressure difference between initial coal seam pressure and critical desorption pressure was neglected in previous material balance methods. Therefore, a modified method has been presented in this paper. In the derivation, the initial gas content is expressed as a Langmuir's equation about the critical desorption pressure, rather than the initial coal seam pressure. Finally, a linear material balance equation of the pseudo average reservoir pressure (P/Z*) versus cumulative gas production (Gp) is obtained, whose intercept on horizontal axis yields the initial gas reserves, and intercept on vertical axis gives the pseudo critical desorption pressure, instead of the pseudo initial reservoir pressure. By using this method to evaluate a simulated reservoir, its reserves can be obtained with an error less than 0.35%, which indicates the method is reliable when the Langmuir's volume and Langmuir's pressure, average reservoir pressure, initial cleat porosity are accurate.
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