致密砂岩储层束缚水饱和度影响因素——以鄂尔多斯盆地临兴地区为例

Influencing Factors of Irreducible Water Saturation in Tight Sandstone Reservoirs:A Case Study of Linxing Area in Ordos Basin

为了有效指导储层描述、评价及产能预测,为致密砂岩油气勘探和开发提供理论依据,以鄂尔多斯盆地临兴地区致密砂岩储层为例,利用铸体薄片、X射线衍射、核磁共振、高压压汞、气水相渗及扫描电镜等实验,分析了致密砂岩中束缚水饱和度的影响因素。结果表明:研究区致密砂岩束缚水饱和度为34.77%~83.78%,平均值为63.86%,T_(2)谱截止值(T_(2cutoff))为3.86~65.60 ms,平均值为20.96 ms;致密砂岩束缚水饱和度受储层物性、润湿性、敏感性、黏土矿物类型、质量分数和粒径共同作用;致密砂岩粒径越细,黏土矿物质量分数越高,岩石亲水性越强,岩石比表面积和水膜厚度越大,则毛细管束缚水和薄膜束缚水越高;水敏和盐敏是造成致密储层渗透率改变的主要因素;致密砂岩发育残余粒间孔、粒间溶蚀孔、粒内溶蚀孔、晶间孔和微裂缝;充填于孔隙中黏土矿物的类型、形态存在差异,致使致密砂岩储层的孔隙结构复杂,微观非均质性强,束缚水饱和度变化大。

With the tight sandstone gas exploration and development,to study the influencing factors of tight sandstone irreducible water saturation becomes important,as it can effectively guide reservoir description,evaluation,and productivity prediction.As an example of the tight sandstone reservoir in Linxing area in Ordos basin,the influencing factors of irreducible water saturation in tight sandstone were analyzed by casting thin section,X-ray diffraction,nuclear magnetic resonance,high pressure mercury injection,gas-water phase permeability,and scanning electron microscope experiments.The results show that the irreducible water saturation of tight sandstone in the study area is 34.77%-83.78%,with an average of 63.86%,and the T_(2 cutoff) is 3.86-65.60 ms with an average of 20.96 ms.The irreducible water saturation of tight sandstone is affected by physical properties,wettability,sensitivity,clay mineral type,mass fraction,and particle size in reservoirs.The smaller the tight sandstone size is,the higher the clay minerals content,and the stronger the rock hydrophilicity;The greater the specific surface area and water film thickness of the rock,the higher the capillary and membrane irreducible water.Water sensitivity and salt sensitivity are the main factors causing the damage of permeability.Residual intergranular pores,dissolution intergranular pores,dissolution within grains,intercrystalline pores and micro-fractures are developed in the research area.The types and forms of clay minerals filled in the pores are different,resulting in the complex pore structure of tight sandstone,strong micro-heterogeneity,and large irregular changes in water saturation.