大宁-吉县区块深层煤岩多尺度孔缝结构特征

针对单一技术手段难以定量表征大宁-吉县区块深层煤岩储层复杂的多尺度孔缝结构问题,基于全直径CT扫描、微米CT扫描、FIB-SEM电镜扫描、氩离子抛光场发射扫描电镜等多种实验方法,利用多尺度的数字岩心技术对煤岩样品进行扫描及分析。结果表明:大宁-吉县区块深层煤岩发育多尺度孔缝系统,纳米尺度以气孔和组织孔发育为主,微米尺度以微裂缝和矿物溶孔发育为主,毫米尺度发育有高角度裂缝和割理组合;全直径CT扫描技术可有效识别毫米级的裂缝、割理及溶孔;建立了D20井煤岩段岩心孔-缝模型,计算得到裂缝孔隙度为1.55%,裂缝密度为22.5条/m,裂缝平均开度为1.1 mm;微米孔隙平均半径为2.99~4.15 μm,微米喉道平均半径为1.16~1.80 μm;微裂缝平均开度为3.75~4.84 μm;纳米孔隙平均半径为51.21~80.65 nm,纳米喉道平均半径为19.44~32.06 nm;通过微、纳米孔隙数据拼接,获得多尺度分布特征,小孔数量最多,平均表面积占比为63.68%,大孔(大于103 nm)数量少但贡献了大量的孔隙体积。研究成果可为深层煤层气勘探开发提供技术支撑。

Characteristics of Multi-Scale Pore-Fracture Structure of Deep Coal Rocks in the Daning-Jixian Block

In response to the problem that it is difficult to quantitatively characterize the complex multi-scale pore-fracture structure of deep coal rock reservoirs in the Daning-Jixian Block with a single technical method, a multi-scale digital core technology is adopted to scan and analyze coal and rock samples based on full-diameter CT scanning, micro-CT scanning, FIB-SEM scanning, and argon ion polishing field emission scanning electron microscopy and other experimental methods. The result shows: The multi-scale pore-fracture systems develop in the deep coal rocks in the Daning-Jixian Block. The nano-scale development is dominated by stomatal and tissue pores, the micro-scale development is dominated by micro-fractures and mineral dissolved pores, and the millimeter-scale development is high-angle fractures and cleat assemblages. The full-diameter CT scanning technology can effectively identify millimeter-scale fractures, cleats and dissolved pores. The core hole-fracture model of the coal section of Well D20 is established, and the calculated fracture porosity is 1.55%, the fracture density is 22.5 pieces/m, and the average opening of fractures is 1.1mm; the average radius of micro-pores is 2.99-4.15 μm, the average radius of micro-throat is 1.16-1.80μm; the average opening of micro-fractures is 3.75-4.84 μm; the average radius of nano-pores is 51.21-80.65 nm, the average radius of the nano-throat is 19.44-32.06 nm; the multi-scale distribution characteristics are obtained through the splicing of micro- and nano-pore data. The number of micro-pores is the largest, with the average surface area accounting for 63.68%, while the number of macro-pores (greater than 103 nm) is small but contributes a large amount of pore volume. The research results can provide technical support for the exploration and development of deep coalbed methane.