柴达木盆地英雄岭南带断裂活动特征及其控藏作用

柴达木盆地英雄岭南带断裂发育,但断裂控制油气成藏的规律不太清楚。通过重新解释该地区地震剖面,分析了5条主要断裂:狮子沟断裂、Ⅰ号断裂、Ⅱ号断裂、油砂山断裂、Ⅺ号断裂,研究了断裂级次、构造样式、活动强度和演化过程,以及通过分析英雄岭南带油藏生物标志物特征和油气充注期次,探讨了断裂对油气成藏的控制作用。结果表明:①Ⅰ号、Ⅱ号、Ⅺ号断裂属于软弱层(膏盐岩+泥岩)之下断裂,形成于古近纪,其中Ⅱ号、Ⅺ号断裂由多条断裂叠加生长形成,狮子沟与油砂山断裂属于软弱层之上断裂,形成于新近纪,由单一断裂生长形成。②浅层构造带油气是深层油气向上运移的结果,控藏断裂的活动性与油气生烃期和圈闭的形成期相匹配。③断裂控藏演化分为3个阶段:下干柴沟组上段沉积期,基底断裂控制烃源岩形成;下油砂山组沉积期,滑脱断裂控制低熟油气成藏;上油砂山组沉积期,滑脱断裂控制成熟油气成藏,同时对早期低熟油气藏进行改造。不同断裂活动特征的差异性是造成英雄岭南带成藏差异性的主控因素之一。

Characteristics of fault activity and its control on hydrocarbon accumulation in southern Yingxiongling area,Qaidam Basin

Faults are widely distributed in southern Yingxiongling area,Qaidam Basin.The control of the faults on hydrocarbon accumulation is unclear.Through reinterpretation of seismic profiles in this area,five main faults were analyzed:Shizigou fault,Ⅰfault,Ⅱfault,Youshashan fault andⅪfault.The fault grade,structural style,activity intensity and evolution process were studied,and the control effect of faults on hydrocarbon accumulation was discussed by analyzing the characteristics of biomarkers and oil and gas filling periods in southern Yingxiongling area.The results show that:(1)Ⅰ,ⅡandⅪfaults belong to the faults under the weak layer(gypsum salt rock+mudstone)and formed in Paleogene,among whichⅡfault andⅪfault were formed by superposition of multiple faults,while Shizigou and Youshashan faults belong to faults above the weak layer,and be formed by single fault growth in Neogene.(2)Oil and gas in shallow structural belt are the result of upward migration of deep oil and gas.The activity of reservoir controlling faults matches with hydrocarbon generation period and the formation period of traps.(3)The evolution of the fault-controlling reservoir model can be divided into three stages:basement faults control the formation of source rocks in the upper Xiaganchaigou Formation;detachment faults control the accumulation of low-mature oil and gas reservoirs in the lower Youshashan Formation.detachment faults control mature hydrocarbon accumulation in the upper Youshashan Formation,and reform the early low mature oil and gas reservoirs.The difference of different fault activity characteristics is one of the main controlling factors for the difference of hydrocarbon accumulation in southern Yingxiongling area.