松辽盆地南部泉四段扶余油层致密砂岩储层微观孔喉结构特征

Microscopic pore throat characteristics of tight sandstone reservoirs in Fuyu layer of the fourth member of Quantou Formation in southern Songliao Basin

综合运用铸体薄片观察、扫描电镜、高压压汞、恒速压汞及图像分析等技术手段,对松辽盆地南部泉四段扶余油层致密砂岩储层储集空间、储集物性、微观孔喉分布及不同尺度孔喉对储层物性的贡献等特征进行精细表征,并分析不同微观孔喉参数与储层物性的相关关系。结果表明,研究区致密砂岩储层物性差、孔喉半径小;储集空间以粒内和粒间溶孔为主,含部分原生孔和黏土矿物晶间孔。储层孔隙半径分布差异不明显,而喉道半径与孔喉比分布差异较大;储层物性越好,喉道半径分布范围越宽,峰值喉道半径越大,并且右偏特征越明显;储层渗透率越高,对渗透率起主要贡献的孔喉半径越大;孔喉比分布与喉道半径分布呈现相反的特征。渗透率主要由岩石中少量的微米级孔喉贡献;纳米级孔喉所占体积很大,却只有较小的渗流能力,并且渗透率越低,纳米级孔喉所占的相对比例越大。微观孔喉结构参数对储层物性的影响主要体现在渗透率上,而对孔隙度的影响较小。

The Fuyu Oil layer of the fourth member of Quantou Formation in southern Songliao Basin was studied in detail for the reservoir space, physical property, micro pore throat distribution and contribution of different pore throat scales to reser-voir physical property of tight sandstone reservoirs. A series of techniques were used, including thin section, SEM, high pressure mercury penetration, rate-controlled mercury penetration and image analysis. The correlation of different pore throat parameters and reservoir physical property was analyzed. The results show that, the physical properties of the tight sandstone reservoirs in the study area are poor with small pore throat radius; the reservoir spaces are mainly intra-particles and inter-particles dissolved pores with some primary pores as well as inter-crystal pores in clay minerals. The pore distribution ranges have no significant difference, but the distribution ranges of throat radius and pore throat ratio had apparent difference. In the reservoirs of good physical properties, distribution ranges of throat radius are wider with larger peak values, and more obvious right-skewness. When reservoirs have higher permeability, the pore throat radius that plays major contributions to permeabili-ty are larger. Opposite distribution features exist between pore throat ratio and throat radius. Reservoir permeability is mainly contributed by a small amount of pore throat with micron sizes, although the pore throat with nanoscale sizes accounts for great volume because they hold lower filtration capacity. The lower the reservoir permeability is, the larger proportion is for the pore throat with nanoscale sizes. Micro pore throat parameters have effects mainly on permeability but less on porosity.