基于孔隙结构控制的致密砂岩可动流体评价——以鄂尔多斯盆地华庆地区上三叠统长6致密砂岩为例

Fluid mobility evaluation based on pore structure investigation in tight sandstones:Case study of Upper Triassic Chang 6tight sandstones in Huaqing area,Ordos Basin

以鄂尔多斯盆地华庆地区长6致密砂岩为研究对象,利用QEMSCAN、光学显微镜、场发射扫描电镜、微米CT、高压压汞、核磁共振等方法对孔隙结构与可动流体进行了研究。结果表明,华庆地区长6储层发育原生粒间孔、颗粒溶蚀孔与粒间溶蚀扩大孔,以钾长石、岩屑、方解石溶蚀为主;CT三维孔喉模型指示孔喉连通性中等-好,连通孔隙体积比例与储层物性呈正相关关系。长6致密砂岩可动流体饱和度介于70%~90%之间,可动油饱和度介于40%~65%之间,与储层物性呈正相关关系。不同渗透率样品可动流体与可动油分布的优势孔喉尺寸具有差异性,当空气渗透率从大于1×10^-3μm^2到(0.1~1)×10^-3μm^2再到小于0.1×10^-3μm^2,可动流体饱和度分布的优势孔喉半径从0.1~1μm减小到0.01~0.1μm再到0.001~0.01μm,可动油饱和度分布的优势孔喉半径从1~10μm减小到0.1~1μm再到0.001~0.01μm。研究结果有助于进一步明确致密砂岩储层微观孔隙结构与可动流体的关系,为鄂尔多斯盆地致密油勘探开发提供参考依据。

Characteristics of pore structures and movable fluids of tight sandstones of the Upper Triassic Chang 6 member in Huaqing area of the Ordos Basin were analyzed based on the data from QEMSCAN,optical microscope,FE-SEM,Micro-CT,MICP and NMR.Inter-particle pores,particle-dissolution pores,and inter-particle dissolved pores were dominated in the storage space,and K-feldspar,rock fragments and calcite were the main dissolution components.CT data indicated that the connectivity of 3 Dpore system was medium to good,and the ratio of connected pores was positively related to physical properties.The ranges of movable fluid saturation and movable oil saturation of Chang 6 member was 70%-90% and 40%-65%,which showed positive correlations with porosity and permeability.The movable fluid saturation changed among samples with different permeability values.As the air permeability of Chang 6 member decreased from over 1×10-3μm2 to 0.1×10-3μm2 and less than 0.1×10-3μm2,the radius of storage space for movable fluid decreased from 0.1-1μm to 0.01-0.1μm and 0.001-0.01μm.Moreover,the radius of storage space for movable oil decreased from 1-10μm to 0.1-1μm and 0.001-0.01μm,respectively.The results can help to further define the relationship between pore structure and movable fluids of tight sandstones,as well as provide technical support for petroleum exploration and development in Huaqing area.