呼和湖凹陷煤储层孔隙特征及其对吸附能力的影响

Pore characteristics of coal reservoir in Huhehu Depression and its effect on adsorption capacity

综合应用扫描电镜、低温氮吸附及等温吸附实验方法,对呼和湖凹陷南部煤储层的孔隙类型及孔隙结构进行识别和分析,基于分形理论探讨分形维数与孔隙结构和吸附能力之间的关系。研究结果表明:随着煤岩变形程度的增加,煤中植物组织孔大部分被破坏,裂缝的类型和数量逐渐增多,改善了煤储层的渗流能力。呼和湖凹陷煤储层的低温氮吸附曲线表现为3种类型,分别代表不同的表面性质和孔隙分布特征,墨水瓶孔是影响吸附能力的主控因素。斜坡带的煤岩分形维数高于洼槽区,这是由于煤岩变形程度高,孔隙结构发生重组,微孔含量占主导地位,使得比表面积增大,孔隙表面粗糙度增加,为甲烷提供更多的吸附空间,增强了煤岩吸附能力。因此,斜坡带无论孔隙类型、裂缝发育程度还是煤层吸附能力都更具优势,应作为大庆探区今后煤层气勘探的重点突破区。

Scanning electron microscope,low temperature nitrogen and isothermal adsorption are used to identity the type and structure of pores in coal reservoir and to analyze the relationship between the fractal dimension and each of pore structure,gas adsorption capacity based on fractal theory.The results indicate that tissue pores are destroyed most with increasing deformation grade,the types and amounts of fractures grow in number gradually,resulting in improved pore connectivity and permeability.There are three types of low temperature nitrogen adsorption curves in Huhehu Depression,on behalf of different ratio nature and pore pattern separately,and the abundance of inkbottle-type pores is the main control on the adsorption capacity of coal.The fractal dimension is higher than that in ramp region because of higher deformation grade and pore structure recombination and increasing of micropore content,which result in the increase of surface to volume ratio and pores face roughness,trending produce adsorption space for CH4 and ultimately improving the adsorption capacity of coal.Therefore,regardless of pore types and development degree of fractures and adsorption capacity of coal,the ramp region is better than that in low region,which should be a breakthrough area of coalbed methane exploration in the future.