基于分形理论的高煤阶煤层气储层气-水相渗计算方法及应用

Application and Calculation Method of Gas-water Relative Permeability for High-rank Coalbed Methane Reservoirs Based on Fractal Theory

通过理论推理和室内实验,研究了利用分形理论计算高煤阶煤储层气-水相渗的方法,结果表明:煤样孔、渗物性越好,最大进汞饱和度越高,两相渗流区越大,等渗点水相饱和度越小;通过分形理论利用毛管压力曲线计算煤岩气-水相渗曲线是可行的,实验样品相渗曲线的计算值与实验值非常接近;分形维数主要影响水相渗透率,分形维数越大,水相渗透率曲线越向右偏移,且气水两相等渗点饱和度越大。这表明,煤储层分形维数越大,水相渗流难度越大,应控制井底流压在解吸压力以上,避免两相流出现,充分排水,扩大煤层气井降压、解吸面积。

This paper studies the calculation method of gas-water relative permeability using fractal theory,through theoretical analysis and laboratory experiments.The results show that the higher the porosity and permeability of coal sample,the higher the largest mercury saturation,the larger the two phase flowing area,and the smaller the isosmotic water-gas saturation.It is feasible to calculate gas-water relative permeability curves of coal rock by using capillary pressure curve through fractal theory.The fractal dimension mainly affects the relative permeability of water phase.The larger the fractal dimension is,the more the water phase permeability curve deviates to the right section and the greater the saturation of the isosmotic water-gas saturation points.This suggests that the bigger the fractal dimension of coal reservoir,the greater the difficulty of water seepage.So the bottom hole flowing pressure should be controlled above the desorption pressure to avoid two phase flow which can expands the de-pressured and desorption area.