页岩气成藏动力特点及其平衡方程

Accumulation dynamic characteristics and the dynamic equations of shale gas

针对页岩气吸附加游离的成藏方式对其成藏动力特点进行了系统分析。与特定的储集物性条件与相应的气源压力相匹配时,页岩气藏中游离气具有与根缘气或常规储层气相似的作用力类型,包括生烃膨胀力、连续气柱顶界静水柱压力、连续气柱底界静水柱压力、连续气柱重力、毛细管压力和动水头压力等,而造成气体分子在有机质颗粒及岩石矿物表面进行吸附与游离相态转换的作用力类型则为吸附作用力和解吸作用力。天然气动力类型存在运移动力与成藏动力的区别,页岩气作为源储一体的聚集模式,其运移动力和成藏动力具有方向相反特点。根据页岩热演化程度、生气强度、构造条件、物性条件等,将页岩气成藏划分为4个阶段,对每一阶段的成藏动力特点进行了系统分析,据此建立了成藏(运移)动力平衡方程,并采用权重系数赋值方法建立了页岩气成藏(运移)动力平衡方程通式。

The accumulation dynamic characteristics of shale gas are systemically analyzed according to the spe- cial accumulation pattern of both absorbed and free gases. The free gas of shale gas accumulation has similar dynamic types compared with source-contacting gas and conventional reservoir gas with expansive pressure of gas generation, hydrostatic pressure at the top of gas column, hydrostatic pressure at the bottom of gas col umn, gravity of gas column, capillary pressure, dynamic water-head pressure, etc. ; while adsorption force and desorption force are the cause of gas phase state changing between absorbed gas and free gas at the surface of organic grains and rock minerals. There are two types of gas dynamics： migration dynamics and accumula tion dynamics. As a gas whose source rock and reservoir are the same body, the migration dynamic and accu- mulation dynamic directions of the shale gas are reversed. The accumulation of shale gas is divided into four stages, and the accumulation dynamic characteristics of each stage are systemically analyzed. Accumulation （migration） dynamic equations are established according to the dynamic characteristics, and a general equation of shale gas accumulation （migration） dynamics is established using the method of coefficient assignment.