泥岩涂抹形成演化与油气运移及封闭

泥岩涂抹是断层封闭的主要机制之一,为了建立合理的断层封闭性评价方法,系统研究了泥岩涂抹类型、形成和演化规律.结果表明:泥岩涂抹主要有3种类型:即研磨型、剪切型和注入型.泥岩、页岩、煤层、膏岩、泥质盐岩、碳酸盐岩和粉砂岩均可成为涂抹的原岩,由原岩与周围岩石的强度差异所决定的拉张型叠覆带是泥岩涂抹形成的关键地质因素.叠覆区的几何学特征、断距与泥岩厚度的比率、有效正应力控制着泥岩涂抹的连续性,亚地震断层(断距小于15m)泥岩涂抹连续临界SSF值范围很大,最大可达到50,规模较大的断层(断距大于15m)临界SSF值一般为5～8,有效正应力越大,临界SSF值越大.连续的泥岩涂抹导致断层在盖层段垂向封闭.断层侧向封闭取决于多次涂抹形成断层泥含量,可建立SGR,SSF和CSP与过断层面压力差之间的关系,从而计算断层所能封闭的最大油气柱高度,实现断层侧向封闭性定量评价.

Formation and evolution of clay smear and hydrocarbon migration and sealing

Clay smear is one of the most important mechanism for fault sealing.In order to establish a reasonable method for fault sealing assessment,we systematically studied the pattern of clay smear,formation and evolution rule.The results indicate that there are mainly three types of shale smear: shear,abrasion and injection.Mudstone,shale,coal-bed,gypsum bed,argillaceous halite,carbonate rock and siltstone can be applied to the original rock.Extensional relay,which is determined by the different strengths of the mudstones and the surrounding rocks,is the key geological factor controlling the formation of clay smear.The continuity of clay smear is controlled by overlapping zone geometry,the ratio between fault throw and thickness of mudstone and the effective normal stress.For a sub-seismic fault(a fault throw less than 15 m),the maximum critical value of shale smear factor(SSF) can be up to 50,whereas for a large scale fault(a fault throw more than 15 m),the critical value of SSF is usually 5-8.The larger the effective normal stress,the larger the critical values of SSF.A continuous shale smear results into a vertical sealing of the fault in the caprock.Fault lateral sealing depends on fault gouge content applied for several times.We could establish the relationship among the shale gouge ratio(SGR),SSF,clay smear potential(CSP) and the pressure difference across the fault plane,and consequently calculate the maximum gas column height that the fault can seal to achieve quantitative evaluation of fault sealing.