高煤阶与低煤阶煤层气藏物性差异及其成因

利用扫描电镜、煤层气成藏物理模拟及热变模拟实验手段,系统研究了高煤阶、低煤阶煤储层在孔隙特征、渗透性、吸附/解吸特征等方面的根本性差异,并深入剖析了该差异的形成机制。研究结果显示,高煤阶气藏的孔隙度低,渗透性差,吸附平衡时间长且较分散,初期相对解吸率与相对解吸速率低;低煤阶气藏孔隙度高,渗透性好,吸附平衡时间短而集中,初期相对解吸率与相对解吸速率高。煤的化学分子结构、物理结构及显微组分的差异是导致其差异的主要原因。因此,高煤阶煤层气藏解吸效率较低,开发难度较大,而低煤阶煤层气藏开发较容易。同时,构造热事件对高煤阶煤储层的改造作用很显著,有利于高煤阶煤层气藏开发。

Differences and origin of physical properties of low-rank and high-rank coal-bed methanes

The differences of reservoir physical properties, including the porosity, permeability, fracture, adsorption/desorption characteristics, and the generation mechanism of characteristic differences between the low rank and high rank coal bed methane (CBM) were discussed by using the SEM, FY II CBM formation simulation system and the thermal alteration simulation. It is proved that the high rank CBM reservoir is characterized by low porosity and permeability, strong adsorption volume and slower comparison desorption speed. The low rank CBM reservoir is characterized by high porosity and permeability, weak adsorption volume and faster comparison desorption speed. It is also proved that the differences between molecular constitution, physical structure and micro lithofabric of coal are the key factors for generating the differences of reservoir physical property. So, it is easier to develop the low rank CBM reservoir. The structure thermal event can improve the physical property of high rank CBM reservoir and is favorable for the development of high rank CBM reservoirs.