致密油储层微观孔隙结构定量表征——以鄂尔多斯盆地新安边油田长7储层为例

Quantitative characterization of microscopic pore throat structure in tight sandstone oil reservoirs:A case study of Chang 7 reservoir in Xin'anbian oil field,Ordos Basin

鄂尔多斯盆地新安边油田长7致密油储层具有较好的开发潜力,由于微观孔隙结构研究的薄弱制约了致密油勘探开发进程,对后期开采具有较大影响。该文采用扫描电镜、铸体薄片、高压压汞、微纳米CT扫描等技术,对新安边油田长7致密油储层的储集空间特征及微观孔隙结构参数进行定量表征。结果表明,长7致密油储层孔隙类型主要分为三类:粒间孔、溶孔、微裂缝。研究区发育大量纳米级孔喉,其对储层的储集及渗流能力具有较大贡献。依据不同样品的排驱压力划分:排驱压力小于1 MPa时,微米尺度孔隙丰富且连通性好,孔喉形态多为粗大管状、条带状,喉道半径主要集中在100~380 nm;排驱压力介于1~3 MPa之间,局部孔隙连通性好,纳米尺度孔喉多发育于粒内溶孔,孔喉形态表现为管束状、球状,喉道半径主要分布于75~250 nm;排驱压力大于3 MPa时,大量孤立的小球状孔喉聚集,垂向连通性差,仅局部微裂缝发育区提供储集空间,喉道半径主要集中为15~75 nm。

The Chang7 tight sandstone oil reservoir in the Xin＇anbian oil field in the Ordos Basin has good potential for hydrocarbon exploration. However,the studies of microscopic pore throat structure were limited,which restricted tight oil exploration and long-term development. Size,shape and spatial distribution of pore throats in tight oil reservoirs were studied in this paper by using scanning electron microscope（ SEM）,casting thin section,high-pressure mercury injection and Nano-CT technologies. Pores in the Chang7 tight oil reservoir in the Xin＇anbian oil field were divided into three categories,namely intergranular pores,dissolution pores and microfractures. A large number of nanoscale pore throats developed in this area,which contributed to reservoir capacity and permeability. Pore throat distributions on capillary pressure curves of different samples showed that when threshold pressure is less than 1 MPa,there are many micron-sized pores with a good connectivity and pore throats are large tubular and striped with throat diameters being in the range of 100-380 nm. When the threshold pressure ranges from 1 to 3 MPa,there are many nanoscale pores with a good connectivity locally,intragranular dissolution pores are developed and pore throats are tube bundle and spherical shape with throat diameter being in the range of 75-250 nm. When the threshold pressure is greater than 3 MPa,small isolated spherical nanopores occur,leading to a poor vertical connectivity,only local microfracture development provides storage space,and throat diameter is concentrated in the range of 15-75 nm.