沁水盆地南部高阶煤气水相对渗透特征

Characteristics of gas-water relative permeability in high-rank coals of southern Qinshui Basin

文中通过对比分析核磁共振T2谱分布和基于非稳态法气水相对渗透率测试,研究了沁水盆地高阶煤样的孔隙结构及气水两相渗流特征。结果表明:研究煤样以贫煤、无烟煤为主,其核磁共振T2谱分别对应单峰和双峰2种分布形态;贫煤以微孔和超微孔为主,无烟煤以小孔为主,含部分微孔和超微孔;煤中微孔和超微孔之间的连通性较好,而小孔与微孔和超微孔之间的连通性很差,导致无烟煤中束缚水饱和度很高,有效孔隙度较低;煤体的渗流特征受煤中孔径分布和孔隙连通性的双重影响,孔隙度越大,大孔径孔隙越发育且孔隙连通性越好,则煤体两相共渗区越宽,煤体渗流能力越好。研究煤样相渗特征表现为残余水饱和度高、残余水条件下气相相对渗透率低、气水两相共渗区间窄等特点,揭示了研究区煤层气开发面临着解吸与渗流瓶颈问题。

Based on the comparative analysis of the n uclear magnetic resonance （NMR） T2 spectrum d istribution and gas-water relative permeability, this study described the high rank coal reservoir pore structure and gas-water flow characteristics in Qinshui Basin. The results show that this area is dominated by lean coal and anthracite with the NMR T2 spectrum corresponding to single and bimodal distribution respectively; lean coal prioritizes micro pores and ultramicroscopic pores and anthracite prioritizes transition pores, including part of micro pores and ultramicroscopic pores; the connectivity between the micro pores and ultramicro scopic pores is good, however the connectivity between the transition pores and micro pores/ultramicroscopic pores is very poor, which leads to high irreducible water saturation and low effective porosity; the seepage characteristics of the coal are affected by the pore distribution and pore connectivity, greater porosity, more development of the large aperture and better connection of the pore lead to the wider two phase flow region and the better seepage ability of the coal. The gas-water relative permeability characteristics of the research area present high residual water saturation, low gas permeability under residual water saturation and narrow two phase flow region, revealing the research area CBM development is faced with desorption and seepage bottleneck.