勘探早期断层封闭性快速评价方法及应用

Quick Evaluation Method and Its Application of Fault Seal During Early Exploration Period

断层垂向和侧向封闭的主因是剪切型泥岩涂抹发育且保持连续性。SSF为断距与其范围内泥岩厚度的比值、物理模拟和野外露头均证实,当SSF大于一个定值时,泥岩涂抹失去连续性,断层垂向开启。海拉尔-塔木察格盆地塔南凹陷断层遮挡型油藏控藏断裂垂向封闭与开启临界SSF值为5.0,塔南凹陷大部分控圈断裂垂向封闭,能够有效封堵油气。但必须考虑断层形成时间和后期活动性质,盆地回返抬升期形成的断裂不容易形成剪切型泥岩涂抹,断层反转造成泥岩涂抹封闭失效。卷入到断裂带中的泥质不仅是剪切型泥岩涂抹,还有砂岩中硅酸盐,因此SSF不完全代表断裂中泥质含量。SGR是表征断裂带中泥质含量最有效的参数,可以弥补SSF对评价砂-砂对接窗口的不足。将断层遮挡油藏油层对应的断层面最小的SGR值作为断层侧向封闭的临界,将临界SGR值对应的断距称之为风险断距,断距低于风险断距的断层侧向封闭风险性很大。利用这2种方法可以在勘探早期对断层圈闭风险性快速做出评价,以减少钻探风险性。

Development and continuity of shear clay smear is the main cause of lateral and vertical seal of faults.And SSF is referred as the ratio of throw of fault to thickness of mudstone.Physical modeling and outcrop observation confirm the clay smear is not continuous combined with faults vertically leakage when SSF is greater than a constant value.The critical SSF value of the vertical fault seal is 5.0 of faults-related trap in Tanan depression,Hailar-Tamuchage basin.Most of faults are sealed vertically for oil and gas.However,formation period and post-action of faults must be taken into consideration.Shear clay smear couldn＇t develop during basin inversion and uplift,and fault inversion causes failure of the clay smear and hydrocarbon leakage.The gouge in the fault zone comes not only from clay smear,but also phyllosilicate from sandstones,therefore SSF is not fully representative of clay content in fault zone,and SGR is the most effective parameter of the clay content in fault zone,especially for sand-sand juxtaposition seal.Considering the minimum SGR of fault plane as the critical value of faults lateral seal in fault-controlling oil reservoir,we regard the throw corresponding to the critical SGR as risk throw,then,faults with throw smaller than risk throw are at high risk of laterally sealing.Using these two methods,we can rapidly evaluate the risk of fault-traps during early exploration,and then reduce the risk of drilling.