富有机质页岩有机质孔发育差异性探讨——以四川盆地五峰组-龙马溪组笔石页岩为例

Difference of organic pores in organic matter:A case from graptolite shales of Wufeng Formation-Longmaxi Formation in Sichuan Basin,China

探讨富有机质页岩有机质孔发育的差异性,为页岩气勘探开发提供理论依据。在1 500倍和25 000倍电镜下,对四川盆地南部上奥陶统五峰组-下志留统龙马溪组富有机质笔石页岩进行观察。结果表明,页岩中笔石、干酪根、固体沥青等有机显微组分丰富,有机质孔总体发育;但不同有机显微组分、同一有机显微组分的有机质孔发育均存在差异,个体较大的固体沥青有机质孔最为发育,干酪根有机质孔较为发育,笔石碎片有机质孔不发育。有机质孔是随着有机碳向烃类和碳质残渣转化而形成的,笔石富碳贫氢的特征导致其有机质孔不发育;不同母质来源的干酪根生烃潜力存在差异决定了其有机质孔发育存在差异;固体沥青有机质孔是在原油裂解过程中形成的,其发育程度可能主要与原油赋存的粒间孔隙空间大小相关。

The paper discusses the difference of organic pores developing in the organic-rich shales and provides a theoretical basis for exploration and development of shale gas. By SEM with 1 500 times and 25 000 times, the organic graptolite shales of Wufeng Formation-Longmaxi Formation in Siehuan Basin are observed. The results show that the organic macerals such as graptolites, kerogens and solid bitumens are abundant and the organic pores develop well. The development of the organic pores in different organic macerals or in the same organic maceral exits differences. The organic pores in the larger individual solid bitumens develop best, that in kerogens develop better and that in graptolites do not develop. The organic pores are formed as organic carbon transforms to hydrocarbons or carbonaceous residues. The features of rich carbon and poor hydrogen in graptolites lead to organic pores to develop poor. The kerogens with different parent matter have different hydrocarbon-generating potentials and thus decide the difference of development of organic pores. The pores in solid bitumen organic matter are formed during the course of crude oil cracking and their development is related with the spaces of the intergranular pores existing in the crude oil.