致密砂岩微观非均质性定量评价方法研究

鄂尔多斯盆地华庆地区长6油层组为深水重力流成因的致密砂岩储层，储层整体致密、非均质性强，微观评价难度较大，注水开发效果不理想。通过粒度分析、铸体薄片、高压压汞及真实砂岩两相渗流模型等常规实验手段，从岩石骨架颗粒、成岩作用及孔喉结构三方面优选非均质性特征参数，分别提出了表征骨架颗粒非均质性的粒度标准偏差σ，表征成岩作用非均质性的充填指数C和抗溶蚀指数K以及表征孔喉结构非均质性的分形维数D。在此基础上，论证并构建了微观非均质性综合指数F，F值介于0.2~3.0，F越大，代表了储层骨架颗粒分选越差、成岩作用越强、孔喉结构越复杂，微观非均质性越强，反之则相反。通过真实砂岩模型模拟油田注水开发，结果表明，F指数能够精确表征由孔隙致密区导致的储层微观特征差异，F指数与无水期及最终期驱油效率呈较好的相关性，可用于定量评价致密砂岩油藏内部微观非均质性，预测剩余油分布规律，为深水致密砂岩油藏的勘探开发提供科学依据。

Quantitative Evaluation Method for Micro Heterogeneity of Tight Sandstone:A case study of Chang-6 reservoir of Yanchang Formation in Huaqing area,Ordos Basin

The Chang-6 Reservoir in the Huaqing area is a tight sandstone reservoir resulting from deepwater gravity flow. It is generally compact， with high heterogeneity， resulting in very difficult microscopic evaluation and a poor water-flooding effect. In this study the characteristic heterogeneity parameters were selected from three aspects: rock skeleton particles， diagenesis and pore throat structures. Then conventional experimental methods were employed， including grain-size analysis， cast thin-section identification， mercury injection capillary pressure testing and a true two-phase sandstone seepage modeling， to obtain the standard deviation of grain size （σ） for describing the heterogeneity of skeleton particles， filling index （C） and corrosion resistance index （K） to determine the diagenesic heterogeneity， and ractal dimension （D） to determine the heterogeneity of pore throat structures. Based on these three parameters， a comprehensive microscopic heterogeneity index （F） was developed and modeled； 0.2 ≤ F ≤ 3.0， where the higher values indicate poorer sorting of skeleton particles of reservoir， stronger diagenesis， more complex pore-throat structure， and greater microscopic heterogeneity. The true sandstone model simulated oilfield water-flooding. The results showed that the proposed index F accurately described the difference in microscopic properties of the reservoir in dense regions of pores， and good correlation was found between F and oil displacement efficiency in the anhydrous and final periods. This indicates that F may be used to quantitatively evaluate the internal microscopic heterogeneity of tight sandstone reservoirs and predict the distribution of remaining oil， providing a scientific basis for exploration and development of deepwater tight sandstone reservoirs.