笔石碎屑对页岩气生成和储集特性的影响

笔石作为奥陶纪和志留纪的标准生物化石之一,在中国南方下古生界上奥陶统五峰组—下志留统龙马溪组中广泛存在。虽然这套地层显示出巨大的页岩气资源勘探开发潜力,但关于笔石碎屑对这套地层页岩气生成和储集的贡献目前仍存在着较大的分歧。通过对四川盆地威远—长宁地区威页1井五峰组—龙马溪组页岩进行酸处理,提取笔石碎屑,开展了显微傅里叶红外光谱、扫描电镜和透射电子显微镜分析,揭示了笔石有机质的成分及孔隙发育特征,探讨了笔石体对页岩气储集能力的贡献。结果表明,笔石体的成分可能主要为胶原蛋白类的有机质所组成,其生气潜力较低;但笔石体内部胎管呈中空状,体腔内发育草莓状黄铁矿,这些空隙结构有利于页岩气的储集;并且笔石体相互叠置形成多层结构,笔石表皮中纵横纹和纳米矿物的隔档可在叠置的笔石表皮间形成空隙,从而提高了页岩气储集和运移的能力。因此认为五峰组—龙马溪组页岩中笔石大量发育是影响该段页岩气富集的重要原因之一。

Influence of graptolite debris on shale gas generation and accumulation

As one of the standard fossils of the Ordovician and Silurian, graptolites are widely distributed in the Upper Ordovician Wufeng Formation to the Lower Silurian Longmaxi Formation in the Lower Paleozoic of South China. This stratum shows a good potential for shale gas exploration; however, there is a disagreement about the contribution of graptolite debris to the generation and storage of shale gas. Acid treatment was carried out on shale samples from the Wufeng-Longmaxi formations in well Weiye 1 in the Weiyuan and Changning areas of the Sichuan Basin. Graptolite debris was collected and analyzed with Microscopic Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy and Transmission Electron Microscopy. The composition and pore development characteristics of the organic matter in graptolites were examined, and the contribution of graptolite bodies to shale reservoir capacity was discussed. The graptolite bodies were mainly composed of organic matter of collagen, which shows a poor gas potential. However, the inner fetal tube of the graptolite body is hollow, and strawberry-like pyrite is developed in the body cavity, which is favorable for the storage of shale gas. The graptolite bodies are superposed on each other to form a multi-layer structure, and the vertical and horizontal stripes and the nano-mineral partitions in the graptolite skin form gaps between the stacked graptolite skins, thereby improving shale gas storage. Therefore, it is believed that the large number of graptolites in the Wufeng-Longmaxi formation shale is one of the important reasons that affect the shale gas enrichment in this segment.