琼东南盆地北部新近系三亚组Ophiomorpha-Thalassinoides遗迹组构的储层改造效应

Reservoir modification effect of Ophiomorpha-Thalassinoides ichnofabric in the Neogene Sanya Formation in northern Qiongdongnan Basin

琼东南盆地北部新近系三亚组储集层中生物扰动非常发育。在岩心详细观测和描述的基础上,利用偏光显微镜、扫描电镜和微米CT等方法分别对含生物扰动样品和不含生物扰动样品的微观孔隙进行了定量表征和连通性分析,并重点对Ophiomorpha-Thalassinoides遗迹组构的储层改造效应进行了研究。结果表明:(1)琼东南盆地北部新近系三亚组Ophiomorpha-Thalassinoides遗迹组构发育,且生物潜穴对储集层的原始结构具有重要的改造作用,岩心上最显著特征是其破坏了原生层理;(2)生物潜穴充填物主要为石英、长石及少量海绿石和黏土矿物,孔隙发育,以粒间孔和少量粒内溶孔为主,而围岩基质泥质含量较高,孔隙发育较差;(3)孔喉形态特征较为一致,孔隙体积、孔隙面积、孔隙等效半径和喉道面积均呈左偏单峰分布,喉道等效半径和喉道长度呈近似双峰分布,含生物扰动样品的大孔隙和喉道数量、有效孔隙度、渗透率和配位数平均值都要明显大于不含生物扰动样品。上述结果揭示Ophiomorpha-Thalassinoides遗迹组构增强了研究区三亚组储集层微观孔隙的储集能力和连通性,这对于分析生物扰动对油气储层的改造效应及推进研究区油气增储、上产和提高采收率具有重要意义。

Bioturbation is well deve loped in the reservoir of the Neogene Sanya Formation in the northern Qiongdongnan Basin.Based on detailed observations of cores,quantitative characterization and connectivity analysis of the microscopic pores of reservoir rock samples with and without bioturbation were carried out using polarized light microscopy,scanning electron microscopy and micro-CT.The reservoir modification effect reflected by the Ophiomorpha-Thalassinoides ichnofabric was studied in detail.The results show that the Ophiomorpha-Thalassinoides ichnofabric in the Neogene Sanya Formation is well deve loped in northern Qiongdongnan Basin.The burrows obviously modified the initial sedimentary structure of the reservoirs,and the primary sedimentary bedding was destroyed.The burrows are mainly filled with quartz,feldspar,chlorite and a small amount of clay minerals.Many intergranular pores and a small amount of intra-grain dissolution pores developed,while the mud content of the surrounding rocks is high,and the pores were poorly developed.Quantitative analysis shows that the morphological characteristics of the pores and pore throats are consistent.The pore volume,pore area,equivalent radius of pore and throat area all present left-skewed unimodal distribution,while the equivalent radius of throat and throat length show approximate bimodal distribution.The number of large pores and throats,effective porosity,permeability and average coordination number of samples with bioturbation are significantly greater than those of samples without bioturbation.This reveals that the Ophiomorpha-Thalassinoides ichnofabric enhances the reserve capacity and connectivity of microscopic pores in the Sanya Formation reservoir.This study is of great significance for analyzing the modification effect of bioturbation on oil and gas reservoirs,increasing reserve capcity,production and recovery of oil and gas in the study area.