玛湖凹陷百口泉组致密砂砾岩储层孔隙结构特征

Pore structure characteristics of tight glutenite reservoirs of Baikouquan Formation in Mahu Sag

玛湖凹陷百口泉组是重要的砂砾岩油气聚集区。为了研究玛湖凹陷百口泉组致密砂砾岩储层的孔隙结构特征,开展了压汞、核磁共振、铸体薄片等分析,结合微米CT扫描技术、扫描电镜矿物定量评价(QEMSCAN)及MAPS显微图像拼接技术,从尺度与精度、二维与三维综合开展其微观孔隙结构特征研究。结果表明:①玛湖凹陷百口泉组致密砂砾岩储层孔喉尺度分布广泛,呈现较明显双峰特征,大尺度孔喉为亚微米—微米级,而小尺度孔喉为纳米—亚微米级,以0.5~4.0μm喉道贡献率最高,微米级孔喉对渗流的贡献较大。②微米尺度下,孔隙结构具有强非均质性,复模态等特点,孔隙类型以溶蚀孔、粒间孔及微裂缝为主,孔隙展布状态主要有条带状和孤立状2种,孔隙连通性比孔隙尺度对渗流的贡献更大。③纳米尺度下,扫描电镜确定其主要矿物为石英和长石,粒间压实作用充分,颗粒形状结合紧密,不同孔渗的样品基质内纳米级微孔形态各异,多以分布于矿物颗粒(晶体)内部蜂窝状长石溶蚀孔或填隙物表面微孔为主,可见方解石颗粒解理缝,对微米级球状微孔及纳米级溶孔起到较好的沟通作用。该研究成果可为致密砂砾岩储层孔隙结构表征及“甜点”预测提供借鉴。

The Baikouquan Formation in Mahu Sag is an important oil and gas accumulation area of glutenite.In order to study the pore structure characteristics of tight glutenite reservoir of Baikouquan Formation in Mahu Sag.The analyses of mercury injection,nuclear magnetic resonance and cast thin sections were carried out.Combined with micro-CT scanning technology,quantitative evaluation of minerals by scanning electron microscope(QEMSCAN)and MAPS micro-image splicing technologies,the comprehensive study of microscopic pore structure characteristics from scale and precision,two-dimension and three-dimension were carried out.The results show that:(1)The pore throat scales of tight glutenite reservoirs of Baikouquan Formation in Mahu Sag are widely distributed,showing obvious bimodal characteristics.The large-scale pore throats are submicron to micron scale,while small scale pore throats are nano to submicron scale.The contribution rate of 0.5-4.0μm throat is the highest,and the contribution rate of micron scale pore throat to seepage is greater.(2)On micron scale,the pore structure has the characteristics of strong heterogeneity and complex mode.The main pore types are dissolution pore,intergranular pore and micro fracture.The distribution states of pores are mainly banded and isolated.The contribution of pore connectivity to seepage is greater than pore scale.(3)On nano scale,scanning electron microscope show that the main mineral components are quartz and feldspar.The compaction between grains is sufficient,and the grain shape is closely combined.The morphology of nano pores in the samples matrix with different porosity and permeability are distinctive,mainly the honeycomb feldspar dissolution pores in mineral grains(crystals)or micropores on the surface of interstitial materials,and the cleavage fracture of calcite particles can be observed,which play a good role in communicating the micro spherical pores and nano dissolved pores.The research results can provide reference for the pore structure characterization and"sweet spot"prediction of tight glutenite reservoirs.