致密砂岩储层孔隙结构成因机理分析及定量评价——以鄂尔多斯盆地姬塬地区长8油层组为例

利用普通薄片、铸体薄片、物性分析和压汞曲线等资料,对姬塬地区长8油层组储层的微观孔隙结构特征及其成因机理等进行了研究.结果表明沉积物在地质历史时期经历的压实、胶结、溶蚀和破裂等一系列成岩作用对储集岩孔喉特征影响显著,成岩作用的不均一性导致了储层宏观物性和微观孔隙结构的差异.通过视压实率、视胶结率、视溶蚀率和视微孔隙率等参数的计算阐明了压实、胶结、溶蚀等对排驱压力和分选系数等孔隙结构特征参数的定量控制.选取成岩综合系数作为成岩作用强度及其组合的定量表征参数,其与排驱压力、分选系数、储集层品质指数和分形维数等均具良好的统计相关关系,不同的孔隙结构类型具有不同的成岩作用组合特征以及成岩综合系数值,因此成岩综合系数可作为不同孔隙结构类型的定量表征参数.在对影响孔隙结构特征的成岩作用类型和强度组合深入剖析的基础上,通过成岩综合系数可实现储集岩孔隙结构的定性划分和定量评价.

Mechanism Analysis and Quantitative Assessment of Pore Structure for Tight Sandstone Reservoirs: An Example from Chang 8 Oil Layer in the Jiyuan Area of Ordos Basin

The microscopic pore structure characteristic and its genetic mechanism of Chang 8 oil layer in the Jiyuan region are analyzed by making full use of normal thin section, casting thin section, physical property analysis and mercury injection data. The results show that sediments experienced compaction, cementation, dissolution and fracturing diagenesis during the geological history, which had significant effect on pore structure characteristics. The heterogeneity of diagenesis led to difference between macroscopic physical property and microscopic pore structure. The effects of compaction, cementation and dissolution on quantitative control of pore structure parameters such as displacement pressure and sorting coefficient can be illustrated, through calculation of apparent compaction rate, apparent cementation rate, apparent dissolution rate, and apparent micropore rate parameters. The comprehensive coefficient of diagenesis was selected to act as the quantitative characterization parameter of diagenetic strength and diagenesis combination, and it exhibits good statistical correlation with displacement pressure, soring coefficient, reservoir quality index (RQI) and fractal dimension. Different pore structure types have different diagenesis combination characteristics and comprehensive coefficients of diagenesis. The comprehensive coefficients of diagenesis can be regarded as the quantitative characterization parameters of different pore structure types. Based on diagenetic types and thorough analysis of impact on pore structure characteristics, the qualitative division and quantitative evaluation can be implemented through comprehensive coefficients of diagenesis.