库车东部碎屑岩层厚和岩性对裂缝发育的影响

摘要

Layer thickness and lithology are key factors in producing structural fractures, especially in areas that tectonics is relatively simple. In order to study the distribution of fracture controlled by layer thickness and lithology, clastic rocks of middle-lower Jurassic in East Kuqa are selected as investigated subject, and the density of their structural fractures is measured. Measured fracture density shows that the layer thickness of clastic sequence has an effect on fracture density;compared with the thicker layers, the thinner layers are easier to produce structural fractures. Besides, there is an exponential relationship between fracture density and layer thickness, which is concordant with previous views that the fracture interval is proportional to the layer thickness. For the same layer thickness and different lithology, the value of fracture density from small to large follows order of conglomerate, gritrock, medium sandstone, fine sandstone and silty shale, which means in the same tectonic setting and layer thickness, the smaller the size range is, the larger the fracture density will be. The difference of fracture density in layer of diverse thickness is connected with stress concentration, and the fracture density divergence of different lithology is the result of various anti-press stress in differen lithology.%层厚和岩性是控制裂缝发育的重要因素，尤其在构造不太发育的地区，层厚和岩性与裂缝发育的规律性对储层裂缝的预测更为重要。文章以库车东部中-下侏罗统碎屑岩地层为例，重点研究层厚和岩性控制构造裂缝的分布规律，对其构造裂缝面密度进行了定量化研究。研究结果表明，层厚影响构造裂缝发育程度：薄层比厚层更易发育构造裂缝。在相同层厚条件下、不同岩性碎屑岩中，裂缝面密度由小到大依次为砾岩、粗砂岩、中砂岩、细砂岩和粉砂质页岩，即在相同构造环境和等厚地层的情况下，碎屑岩粒级越小，面密度越大。对层厚和岩性影响裂缝发育的力学机制进行了探讨：不同层厚中的裂缝发育差异与应力分布状态有关；而不同岩性中裂缝密度之所以不同，则是因为不同岩性的破裂强度不同。