基于孔隙分形特征的低渗透储层孔隙结构评价

储层孔隙结构对低渗透储层的渗流能力和油气产能有重要影响，是低渗透储层研究的热点。 目前，急需一种在储层宏观尺度上反映强非均质性储层孔隙结构优劣的储层孔隙结构定量评价方法。 以塔南凹陷白垩系低渗透储层为例，在薄片观察、孔渗测试和毛管压力测试的基础上，将分形算法应用于储层孔隙结构评价，建立了利用压汞测试求取孔隙分形维数，进而定量评价储层孔隙结构的方法。 研究认为，该区发育粗态型、偏粗态型、偏细态型和细态型 4 种类型孔隙结构。 利用毛管压力对数与润湿相饱和度对数的线性关系可求取孔隙分形维数，且分形维数越小，孔隙结构越好。 结合薄片和试油资料建立了该区孔隙结构分类的分形维数标准，同时发现该区储层非均质性强，部分样品整体分形特征不明显，储层中的大孔隙和小孔隙均具有良好的分形特征，但是具有不同的孔隙结构特点，表现为毛管压力与润湿相饱和度关系的分段性。

Pore structure evaluation of low permeability reservoir based on pore fractal features

Pore structure is an important factor that influences percolation capacity and oil production of low permeabttlty reservoir. It is a hot spot in low permeability reservoir study. A quantitative method for pore structure evaluation which can characterize pore structure of heterogeneous reservoir on macro-scale is needed. Taking low permeability reservoir of Cretaceous in Tanan Depression as an example, based on thin slices observation, porosity and permeability test and capillary pressure test, this paper applied fractal algorism to reservoir pore structure evaluation, and established a quantitative pore structure evaluation method based on pore fractal dimension from mercury intrusion test. The result shows that there are four types of pore structures developed in the study area, including coarse shape type, subcoarse shape type, subfine shape type and fine shape type. Pore fractal dimension can be calculated according to the linear relationship between logarithm of capillary pressure and logarithm of wetting phase saturation. The smaller the porefractal dimension is, the better the pore structure will be. The pore fractal dimension criteria for pore structures classification was built up with thin slice and oil testing. It is also found that large pores and small pores have different fractal characters in high heterogeneous reservoirs in the study area, which performs as the segmental character in the relationship between capillary pressure and wetting phase saturation.