低渗透气藏相对渗透率影响因素的孔隙网络模型

实验测量相对渗透率受许多条件的限制,为了在保持其他控制参数不变的条件下研究某一变量对相对渗透率的影响,采用孔隙网络模型模拟的方法,以苏里格气田盒8段储层的孔隙结构为参照,构造了喉道半径为0.05～2.50μm的孔隙网络;研究了孔喉比、润湿性、初始含水饱和度和残余水饱和度对气相相对渗透率的影响。结果表明:①孔喉比对气相相对渗透率的影响明显,随着孔喉比增大,相同水饱和度下的气相相对渗透率降低;②当水饱和度大于0.4时,气体的相对渗透率按照水湿→弱水湿→弱气湿→气湿的顺序依次增加,但当水饱和度小于0.4时,相对渗透率增加的次序性被打乱,在弱水湿情况下表现为最小;③随着初始含水饱和度增加,气相相对渗透率总体呈下降趋势;④残余水饱和度越大,气相相对渗透率曲线越陡,下降越快。这对用改变岩石润湿性的方法来提高油气采收率时具有指导意义。

Pore network modeling for the investigation of factors affecting relative permeability of low-permeability reservoirs

Experimental measuring of relative permeability is affected by many parameters. To study the influence of a single parameter with the other parameters remaining unchanged, taking the pore structure of the He 8 reservoir (the eighth member of the Lower Shihezi Formation) at the Sulige Gas Field as a reference, a method of pore network simulation is adopted and pore networks are constructed with the throat radius varying from 0.05 to 2.50 μm. The studies on the influences of pore throat ratio, rock wettability, initial water saturation and residual water saturation on the relative permeability are carried out. The results indicate that the pore throat ratio shows a notable influence on the relative permeability. As the pore throat ratio increases, the gas phase relative permeability decreases under the circumstances of the same water saturation. When water saturation is higher than 0.4, the gas relative permeability increases with water wet, weakly water wet, weakly gas wet and gas wet sequentially. However, when water saturation is lower than 0.4, the above order will be shuffled with a minimum relative permeability obtained under the circumstances of weakly water wet. Along with the increase of initial water saturation, the gas phase relative permeability takes on a downtrend on the whole. The higher the residual water saturation, the steeper (i.e. the faster the decrease) the curve of the relative permeability becomes. The results will help improve the recovery with the method of changing the rock wettability.