泥页岩孔隙类型、形态特征及成因研究

Study on morphological characteristics of micropores and microcracks in shale

泥页岩中存在丰富的微孔隙及微裂隙,这些微孔隙及微裂隙是泥页岩的存储空间与流通通道,对页岩气开采有着重要的意义。用氩离子抛光制样方法,采用场发射扫描电镜背散射模式能比较容易地观察到这些孔隙。我国泥页岩中常见微孔隙有:有机质孔隙,粘土矿物晶间孔,碳酸盐及长石溶蚀孔,微裂缝等四种类型。有机质孔隙是有机质达到一定成熟度后开始大量排烃,从而在有机质内部留下的孔隙;粘土矿物晶间孔多呈三角形或狭缝形,大小从几纳米到超过1微米;碳酸盐溶蚀孔多呈菱形,且多发生在矿物表面和边缘,长石溶蚀孔常沿长石解理方向平行分布,溶蚀孔与有机质分解过程中产生的有机酸有密切关系;微裂隙包括收缩裂缝,干裂缝,层间缝等,这些微孔隙及微裂缝为页岩气提供了重要的储存空间与流通通道。

There are many micropores and microcracks which are typically in the micrometer to nanometer size range in shale, and they are accumulation space and migration pathway of shale gas, so these microporesand microcracks play an important role in the exploitation of shale gas. It is easy to observe these micropores and microcracks in FESEM （ field emission scanning electron microscope） in BSE （ back scattered electron） mode after Ar-ion milled. The types of pores include organic matter pores, phyllosilicate framework pores, carbonate dissolution pores, and microcracks. Organic matter pores are formed from the process of oil or nature gas spilled out from the organic matter in certain maturity. Phyllosilicate framework pores are usually present triangular or slit shape with the size range from several nanometer to several micron. Carbonate dissolution pores are always in diamond shape, and usually occur in the edge of minerals. Feld spar dissolution pores are always along the direction of cleavage. Microcracks include shrinkage crack, desiccation fissure and seam between the layers.