致密储层渗吸特征与孔径分布的关系

致密油气藏资源量巨大,作为重要的替代能源可以极大地缓解中国的原油对外依存度。致密储层微纳米孔隙发育,毛细管力渗吸作用强,充分发挥渗吸排驱作用对提高致密油气产出至关重要。然而,由于致密储层孔隙结构复杂,目前对于渗吸特征与孔径分布之间的关系尚不清楚。选取致密火山岩和页岩开展实验,并与致密砂岩进行对比。通过高压压汞测试和自发渗吸实验分别获得致密储层孔径分布和渗吸特征参数,并建立两者之间的相关关系。结果显示致密储层渗吸体积与时间的双对数坐标系下,自发渗吸曲线呈现三段式特征:初期直线段、曲线段和后期直线段。其中初期直线渗吸段为主要阶段,吸水速度大大超过扩散段,且吸水量占总吸水量的比例超过90%,可采用渗吸指数和扩散指数对渗吸特征进行表征。渗吸指数和扩散指数与孔径分布特征关系密切;渗吸指数约为0. 5,主要反映了宏孔孔径分布特征,渗吸指数越大,宏孔越发育;扩散指数低于0. 3,主要反映了中孔分布特征,扩散指数越大,中孔越发育。本文研究有助于理解致密储层渗吸特征与孔径分布的关系,对发挥渗吸驱替作用和提高致密油气高效产出具有重要意义。

The studies on the relationship between imbibition characteristics and pore size distribution

The pores of tight reservoirs are in the micro-nano level, and the capillary imbibition plays an important role in improving the tight oil and gas production. However, due to the complex pore structure of tight reservoirs, the relationship between the imbibition characteristics and the pore size distribution is still unclear. This paper selects tight volcanic rocks and shale to conduct experiments and compare them with conventional sandstones. The pore size distribution and permeability parameters of tight reservoirs were obtained by high pressure mercury intrusion test and spontaneous imbibition experiments, and the correlation between the two was established. The results show that the spontaneous imbibition curve exhibits three-stage characteristics in the double-logarithmic coordinate: imbibition stage, transition stage and diffusion stage. The imbibition stage is the main stage and the water flow speed in imbibition stage greatly exceeds the diffusion stage. The ratio of water volume to total water volume exceeds 90%. The imbibition exponent and diffusion exponent can be used to characterize the imbibition characteristics. The imbibition exponent and diffusion exponent are closely related to the pore size distribution characteristics; the imbibition exponent is about 0.5, which mainly reflects the pore size distribution characteristics of macropores. The larger imbibition exponent, the more macropores; the diffusion exponent is lower than 0.3, which mainly reflects the pore size distribution of mesopores. The larger the diffusion exponent, the more mesopores. This study is helpful to understand the relationship between the imbibition characteristics of tight reservoirs and the pore size distribution. It is of great significance for exerting the effect of displacement and improving the efficient production of tight oil and gas.