确定饱和型煤层气藏地质储量、可采储量和采收率方法的推导及应用

非常规的煤层气藏又称为煤层甲烷气藏,其储集空间是由原生基质孔隙系统(微观孔隙)和次生裂缝孔隙系统(宏观孔隙)所组成.在煤层中存在的气体一部分是以分子吸附状态储存于基质系统中,另一部分则是以自由状态存在于裂缝系统中.对于原始地层压力等于临界解吸压力的饱和型煤层气藏,King利用气藏在开采过程中气体摩尔数平衡的原理提出了一个物质平衡方程式.但由于该方程存在不完善性,在实际中没有得到有效应用.Ahmed应用King的研究成果得到了一个可以用于确定定容饱和型煤层气藏含气面积的直线关系式,并已应用于实际.文中基于King和Ahmed的研究方法和气藏工程原理提出了一个新的直线关系式,该公式可以同时确定吸附气和自由气的地质储量,同时还提出了确定可采储量和采收率的方法.这些方法的实用性和有效性已被实例的应用所证明.

Derivation of methods for estimating OGIP and recoverable reserves and recovery ratio of saturated coal-seam gas reservoirs

Reservoir space in unconventional coal-seam gas reservoirs,also known as coalbed methane reservoirs,consists of the primary matrix porosity system(micropores) and the secondary fracture porosity system(macropores).Some of coal-seam gas are stored in the matrix system in an adsorbed state and the rest are in the fracture system as free gas.For saturated coal-seam gas reservoirs whose initial reservoir pressure equals to the critical desorption pressure,King proposed a material balance equation by using the balance fundamental of gas mole numbers in the process of gas recovery.However,the equation was failed to be put into real practice due to its inherent limitations.Based on King's research,Ahmed proposed a linear relationship formula which may be used to determine the gas-bearing area of constant-volume saturated coal-seam gas reservoirs and has already been employed in practice.By combining the studies of King and Ahmed with the basic fundamental of gas reservoir engineering,the article presents a new linear relationship formula that may be to used to determine adsorption gas in-place and free gas in-place simultaneously.In addition,methods for determination of recoverable reserves and recovery ratio are also proposed.The practicability and effectiveness of these methods have been testified during their application.