沁水盆地煤储层微裂隙发育的煤岩学控制机理

Influence and Control of Coal Petrological Composition on the Development of Microfracture of Coal Reservoir in the Qinshui Basin

基于沁水盆地主要矿区实测煤样的分析资料,总结了煤岩显微组分、煤岩类型和煤相与微裂隙发育的关系,探讨了微裂隙的成因及煤岩学控制机理.结果表明:该区微裂隙多以长度小于300μm,宽度小于5μm的裂隙为主,裂隙密度一般都在10～50条/9cm2之间;微裂隙通常发育于均质镜质体为主的组分中,且常见于条带状亮煤或以微镜煤为主的亮煤中.潮湿、弱氧化和弱水动力的成煤环境有利于微裂隙的发育.微裂隙是煤化作用过程中烃类气体的瞬间积聚形成高压流体单元后突然破裂而形成的,其中条带状亮煤或以均质镜质体为主的流体微单元,不仅具有较好的生烃潜能,同时孔隙发育差不利于气体的扩散,这是造成这些组分中微裂隙发育的主要原因.

The developmental characteristics of coal microfracture and its correlations to coal macerals, submaeerals, coal facies, macro-and mierolithotypes were discussed based on numerous coal analyses from the Qinshui basin. The results show that the microfractures are dominated by the type of width of 〈5μm, length of 〈300μm and the frequency of 10-50 numbers/ 9 cm^2. Microfractures are selectively developed in the submacerals of telocollinites, the lithotype of banded bright coals and vitrite. The environment of low-flowing swamp water, well tissue preservation and relatively hydrogenant forest peat swamp is favorable for microfracture development. The microfractures were formed by the processes of generation, accumulation and centralized release of high pressure gas from coals. The primary selective development of microfractures in banded bright coals and vitrites are due to the higher gas yield associating with lower gas diffusion in these coals or macerals.