泥岩非构造裂缝与现代水下收缩裂缝相似性研究

泥岩非构造裂缝与现代水下收缩裂缝在形态结构、形成机理方面都十分相近.通过对现代泥质沉积物水下收缩裂缝的深入研究,初步探讨了成岩收缩作用、异常高压作用、层间滑动作用以及裂缝充填物沉积模式等对泥岩非构造裂缝的发育特征、发育机理以及油气初次运移等方面可能产生的重要影响.通过对比分析可知:(1)地层倾角较大的泥岩层段,主要发育矩形收缩裂缝;倾角较缓的层段,则以网状收缩裂缝为主.(2)在异常高压带内,油气初次运移分先后2个阶段,首先是爆发式混相涌流,其次为隙壁渗流.(3)高压带内的砂质地层不但有利于高压形成,可以为油气初次运移提供储集空间,而且具有很好的保护作用.(4)在泥、砂厚度比为3~4时,砂层的润滑作用更有利于上下泥岩层收缩裂缝的发育.早期裂缝内充填物沉积模式对后期裂缝的发育规律、渗透性以及油气初次运移等具有深远的影响.

Study on the similarity of the non-tectonic cracks in mud-shale to underwater shrinkage cracks in present muddy sediments

The non-tectonic cracks in mud-shale (NCMS) are similar to the underwater shrinkage cracks in present muddy sediments (USCM) in morphologic features and forming mechanism.Based on the studies on USCM by geologic modeling,the effects of diagenesis contraction,overpressure,interlayer gliding and the sedimentation mode of crack fillings on the growth mechanism,distribution law and connectedness of NCMS and the primary migration of hydrocarbon are studied in detail.It is found that (1) there are more rectangular shrinkage cracks (longitudinal crack) in the mud intervals with greater formation dip,but there are more reticular cracks (chicken wire crack) in those with less formation dip;(2) in overpressure zone,there are two phases in the hydrocarbon primary migration,the migration is burst mixing-phase inrush in the first phase,and it is the seepage through pore walls in the second phase;(3) the sand bed within the overpressure zone is not only favorable to the formation of the overpressure,but also it can supply reservoir space for the hydrocarbon primary migration and the good protection from loss and decomposition for the hydrocarbon;(4) when the thickness ratio of mad bed to sand bed is 3～4,the sand bed between mud beds can also play an important role as lubricant,which is favorable to the development of the shrinkage cracks in the mud beds;(5) the sedimentary mode of earlier crack fillings has great effect on the growth law and permeability of the later developed cracks and the hydrocarbon primary migration.