基于X-CT技术对黔西滇东区域煤储层物性特征的研究

黔西滇东区域是我国煤层气勘探开发的资源潜力区,近年来煤层气勘探和矿场试验显示该区具有良好的煤层气勘探开发潜力。通过X-CT技术系统研究了该区的煤储层物性特征。研究表明,X-CT扫描技术可以很好地识别矿物、暗煤、镜煤和孔隙这4种介质,它们的CT数分别为:>1 800,1 500~1 800,1 000~1 500,<1 000 HU,但是具体CT数又因样品而异;通过X-CT扫描技术估算得到的煤孔隙度值为3.33%~7.14%,矿物含量为0.11%~89.03%,与氦气法和工业分析法得到的结果相关性很好; X-CT切片分析结果显示在应力作用下,原生煤具有最强的均质性,糜棱煤具有最强的非均质性,初碎裂煤和碎裂煤介于两者之间,表明煤岩在没有受到应力作用之前,煤岩组成在轴向上的均质性相对较好,后期的应力作用造成了煤中的煤岩组分、孔裂隙以及矿物的分布不均匀,煤岩非均质性增强;通过煤储层三维模型的建立,定量表征了研究区煤中矿物质、孔隙以及裂隙的空间分布特征,实现了煤储层的三维可视化。

Characterization of the physical properties of coal reservoirs in the western Guizhou and eastern Yunnan by X-ray computed tomography

The western Guizhou and eastern Yunnan are potential exploration areas for coal bed methane (CBM) in South China, and their favorable CBM potential has been demonstrated by CBM exploration and pilot tests. In this paper, the physical properties of coal reservoirs in the study area were systematically studied by means of X-ray computed tomography (X-CT). The research showed that X-CT could identify 4 kinds of media: mineral, durain, vitrain and pore. The CT number of mineral, durain, vitrain and pore were approximately >1 800, 1 500-1 800, 1 000-1 500 and <1 000 Hounsfield unit (HU), respectively. Their specific CT number varied from sample to sample. The estimated porosity values of coals ranged from 3.33% to 7.14%, and mineral contents ranged from 0.11% to 89.03% by means of X-CT, which correlated well with the porosities determined using the helium gas method and proximate analysis. X-CT scans showed that under the influence of stress, undeformed coal has the highest homogeneity, mylonitic coal has the highest heterogeneity, and proto-cataclastic and cataclastic coals were between them. If coals were not affected by stress, their composition heterogeneity in the axial direction was relatively good. The later stress action caused the uneven distribution of coal components, pores, fractures and minerals, which enhanced the heterogeneity of coals. A three-dimensional model of coals was built to show the quantification and 3D visualization of the spatial disposition of minerals, pores and fractures of coals in these areas.