吉木萨尔凹陷二叠系芦草沟组页岩储层孔隙结构定量表征

吉木萨尔凹陷二叠系芦草沟组是重要的页岩油气聚集区。通过铸体薄片、压汞及核磁共振等分析，结合医用CT、微米CT扫描技术、扫描电镜矿物定量评价（QEMSCAN）及Avizo可视化软件先进的数学算法，构建了吉木萨尔凹陷芦草沟组页岩储层的三维数字岩心并提取了孔隙网络模型参数，获取全尺度孔径分布曲线，从多个维度综合开展其微观孔隙结构定量表征研究。研究结果表明：①研究区芦草沟组页岩储层的孔隙度平均为7.6%，渗透率平均为0.37 mD，为“低孔-特低渗”型致密页岩储层，其主要储集空间类型为次生溶蚀孔，含残余粒间孔、生物体腔孔和成岩微裂缝。②孔喉尺度为纳米—微米级不等，以0.12~1.75 μm喉道贡献率最高，亚微米—微米级孔喉对渗流的贡献较大，孔隙展布形态多为孤立状和条带状，孔隙半径大多为4.5~12.5 μm；喉道半径大多为1.3~5.1 μm，喉道长度为5~15 μm；孔喉配位数为1~2，孔隙结构具有非均质性强、连通性差等特点，孔喉连通性比孔隙尺度对渗流的贡献更大。③纳米尺度下，基质矿物主要为石英和钠长石，纳米级微孔大多分布于矿物颗粒（晶体）内部有机质孔及胶结物微孔隙，孔径为0.015~5.000 μm。

Quantitative characterization of pore structure of shale reservoirs of Permian Lucaogou Formation in Jimsar Sag

The Permian Lucaogou Formation in Jimsar Sag is an important shale oil and gas accumulation area. Based on the analyses of cast thin sections,mercury injection and nuclear magnetic resonance,combined with medical CT,micro-CT scanning technology,quantitative evaluation of minerals by scanning electron microscope(QEMSCAN)and advanced mathematical algorithms of Avizo visualization software,a three-dimensional digital core of shale reservoirs of Lucaogou Formation in Jimsar Sag was constructed,and the pore network model parameters were extracted,and the full-scale pore size distribution curves were obtained. The comprehensively quantitative characterization of microscopic pore structure from multiple dimensions was carried out. The results show that:(1)The average porosity of the shale reservoirs of Lucaogou Formation in the study area is 7.6%, and the average permeability is 0.37 mD,which belongs to low porosity and ultra-low permeability tight shale reservoir. The main reservoir space is secondary dissolved pores,including residual intergranular pores,biological cavity pores and diagenetic microfractures.(2)The pore throat scale ranges from nanometers to micrometers. The throats within 0.12-1.75 μm have the highest contribution rate,and the submicron-micron pore throats have a greater contribution to seepage. The pores are mainly distributed in isolated and banded shape. The pore radius is mostly 4.5-12.5 μm,the throat radius is mostly 1.3-5.1 μm,and the throat length is 5-15 μm. The pore throat coordination number is mainly 1-2. The pore structure has the characteristics of strong heterogeneity and poor connectivity,and the contribution of pore connectivity to seepage is greater than that of pore scale.(3)On the nano scale,the matrix minerals are mainly quartz and albite,the main nano micropores are organic matter pores in mineral particles(crystals)and cement micropores, and the pore radius is 0.015-5.000 μm.