珲春盆地八连城矿区煤岩孔隙分形特征

煤岩孔隙结构特征是评价煤层储集能力和选层压裂的重要参数。综合应用低温氮吸附方法、核磁共振技术和氩离子抛光成像等方法，利用分形理论定量表征孔隙的非均质性，并探讨分形维数的影响因素。结果表明，八连城矿区煤岩有机质孔主要为植物组织孔、粒间孔和气孔，矿物质孔为溶蚀孔和黏土矿物孔。I类曲线显示煤岩发育狭缝状孔和楔形孔。II类曲线表明煤岩瓶型孔发育。核磁共振双峰型T₂谱表明吸附孔较为发育，连通性差。三峰型显示渗流孔和裂隙发育，孔渗条件好。孔隙直径在2~100 nm时，水分含量和比表面积与D₁表现为正相关关系。D₂与灰分含量、平均孔径呈正相关和负相关。孔隙直径在0.1~10.0 μm时，核磁共振法获得D_N1与吸附孔表面积呈正相关，D_N2与渗流孔的孔体积呈正相关；D_M和溶蚀孔分形维数D_C，分别受到黏土矿物和长石含量的控制。因此，氮吸附I型曲线煤层和三峰型核磁T₂图谱煤层利于煤层气的开发。

Fractal Characteristics of Coal Rock Pores in the Baliancheng Mining Area,Hunchun Basin

Pore structure characteristics of coal rocks are important parameters for evaluating coal seam storage capacity and selecting fracturing layers.Low temperature nitrogen adsorption,nuclear magnetic resonance(NMR)technology,and argon ion polishing imaging enabled quantitative characterization of the pore heterogeneity by fractal theory were used to examine the influencing factors of fractal dimensions.The organic pores of the coal rocks from the Baliancheng mining area comprised mainly of plant tissue,intergranular,and gas pores,whereas the mineral pores were composed of dissolution and clay mineral pores.The type I curve indicated that the coal rock developed slit-like and wedge-shaped holes,while the type II curve indicated the development of bottle-shaped pores.The NMR bimodal T2 spectrum showed that the adsorption pores were developed only to a limited degree with poor connectivity.The trimodality indicated the development of weep holes and fissures under good pore percolation conditions.When the pore diameter ranged between 2 and 100 nm,the water content and specific surface area were positively correlated with D1,whereas D2 was positively correlated with the ash content and negatively correlated with average pore size.When the pore diameter was between 0.1 and 10.0m,DN1 obtained by NMR was positively correlated with the surface area of the pores and DN2 was positively correlated with the volume of the percolation pores.In addition,DM and the fractal dimension Dc of the dissolution pores were largely controlled by the clay mineral and feldspar contents,respectively.Therefore,coal layers exhibiting a nitrogen adsorption type I curve and trimodal nuclear magnetic T2 map are conducive to the development of coalbed methane.