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通过核磁共振(NMR)与气水两相相对渗透率实验,描述黔西比德-三塘盆地煤储层NMR T2谱与气水相渗特征,并结合压汞、最大镜质体反射率以及煤物质组成等基础测试,从煤级、显微组分、孔隙结构等角度分析主要控制因素,最后通过与沁水盆地高煤阶煤储层、美国中-低煤阶煤储层相关结论进行对比,揭示本区煤层气开发潜力.研究结果表明:本区煤储层以无烟煤为主,NMR T2谱呈双峰态分布,不可动峰明显而可动峰微弱,揭示束缚水饱和度高,有效孔隙度较低,两峰相互分离,截止值T2c为10ms,对应孔隙直径约为100nm,表明扩散孔(<100nm)和渗流孔(>100nm)之间连通性差.T2谱特征与压汞孔隙结构具有良好的匹配性,即微小孔发育、中大孔不发育,中孔比例极低,孔隙类型以半封闭孔为主,连通性较差,说明煤级控制之下的孔隙结构决定了T2谱的形态特征.气水相渗特征受控于孔隙结构、煤级、显微煤岩组分等因素,本区相渗条件总体优于沁水盆地南部,但相比于美国中-低阶煤储层,仍然表现出残余水饱和度高、残余水条件下气体相对渗透率低、气水两相流区间窄等特点,揭示本区煤层气开发面临着我国高煤阶煤储层普遍存在的解吸与渗流瓶颈问题.
The NMR T2 spectrum and gas-water infiltration characteristics of coal reservoir in Qianxibeide-Santang Basin were described by NMR and gas-water relative permeability experiments. Combined with mercury injection, the maximum vitrinite reflectance and Coal material composition and other basic tests, from the coal level, microstructure, pore structure analysis of the main control factors, and finally with the Qinshui Basin high coal rank coal reservoir, the United States low coal rank correlation conclusions The results show that: the coal reservoirs in this area are mainly anthracite, the NMR T2 spectrum presents a bimodal distribution, the non-moving peak is obvious and the moving peak is weak, revealing that the irreducible water saturation is high, The effective porosity is low and the two peaks are separated from each other with a cut-off value of T2c of 10 ms and a corresponding pore diameter of about 100 nm, indicating poor connectivity between diffusion pores (<100 nm) and pores (> 100 nm) The structure has a good match, that is, the development of micro-pores, medium-large pores are not developed, the proportion of mesopores is very low, the type of pores is mainly semi-closed pores, and the connectivity is poor, indicating that the pore structure under the control of coal grade determines T2 The morphological characteristics of the spectrum. The gas-water infiltration characteristics are controlled by the pore structure and coal rank , Micro-coal and rock components and other factors, the overall permeability and permeability conditions in this area are better than those in the southern part of Qinshui Basin, but they still show high residual water saturation compared with the medium-low rank coal reservoirs in the United States. The residual gas Low relative permeability and narrow interval of gas-water two-phase flow, revealing that the development of CBM in this area faces the bottleneck of desorption and seepage that is common in high-rank coal reservoirs in China.