碳酸盐岩储层渗透率与孔隙度、喉道半径的关系

碳酸盐岩储层渗透率与孔隙度的相关性差,与喉道半径的相关性较好,但喉道半径的分布范围通常较大,究竟哪一种喉道半径对渗透率起主要的控制作用,对此还没有形成统一的认识。为此,有必要探讨碳酸盐岩储层渗透率与喉道半径之间深层次的关系,建立渗透率、孔隙度、喉道半径三者之间的关系模型。根据碳酸盐岩储层非均质性强、孔隙结构差异较大的特点,利用毛细管压力曲线特征参数对研究样品进行了分类,针对不同孔隙结构的样品分别研究上述三者之间的关系,避免了把所有样品放在一起研究而掩盖掉非均质性影响的情况。通过对压汞实验基本原理的深入分析,认为毛细管压力曲线的拐点所对应的喉道半径对渗透率起主要的控制作用,并首次提出了拐点喉道半径的概念。将各种喉道半径与渗透率进行相关性分析,证实了拐点喉道半径与渗透率的相关性最好,最终建立了拐点喉道半径与渗透率、孔隙度三者之间的关系模型。利用该模型计算的渗透率与岩心分析渗透率相关性较好,相关系数达到0.79。

Correlation among permeability,porosity and pore throat radius of carbonate reservoirs

For carbonate reservoirs, permeability is poorly correlated with porosity but positively correlated with pore throat radius. With a wide range of pore throat radii, it is uncertain that which pore throat radius controls the permeability. Accordingly, it is necessary to clarify the correlation between permeability and pore throat radius in carbonate reservoirs and construct a model for correlation among permeability, porosity and pore throat radius. Since carbonate reservoirs have strong heterogeneity and very different pore structures, characteristic parameters of capillary pressure plots were used to classify samples. By studying correlation among permeability, porosity and pore throat radius of samples with different pore structures, negative impacts related to heterogeneity for studies with all samples together were eliminated effectively. Through an in-depth analysis of fundamental principles related to mercury penetration tests, it was determined that pore throat radius corresponding to the inflexion point of capillary pressure plots controls permeability. In addition, the concept of pore throat radius at inflexion point was put forward for the first time. Correlation analysis involving various pore throat radii and permeability confirmed the favorable correlation between pore throat radius at inflexion point and permeability. Eventually, the correlation model for pore throat radius at inflexion point, permeability and porosity was constructed. Satisfactory correlations with correlation coefficients up to 0.79 were observed between permeability determined by using the model and those determined through core analysis.