断层对接型和断层岩型侧向封闭的差异性

在碎屑岩地层中，断裂侧向封闭分为断层岩型侧向封闭和对接型侧向封闭2种类型，过去对这2种类型封闭油气的机理、封闭能力强弱等未进行过对比研究。为正确认识断裂在油气成藏与分布中的作用，分析了断层岩型侧向封闭和对接型侧向封闭的封闭机理和封闭条件；在此基础上，对比研究了这2种断裂侧向封闭的差异性。结果发现，由于起封闭作用的遮挡物和封闭条件不同，造成了对接型与断层岩型侧向封闭的差异性主要表现在以下2个方面：①受其影响形成的圈闭，其油（气）—水界面分布的控制因素不同，受对接型侧向封闭影响形成的圈闭，油（气）—水界面分布受对接岩性控制，而受断层岩型侧向封闭影响形成的圈闭，油（气）—水界面分布受断层岩排替压力大小控制；②侧向封闭能力明显不同，断层对接型的侧向封闭能力明显强于断层岩型的侧向封闭能力。以歧口凹陷板桥断裂为例，相同条件下，板桥断裂对接型侧向封闭油气的能力为断层岩型侧向封闭油气能力的25~43倍。这一显著的差异，造成板桥断裂古近系沙河街组一段，其上部对接型侧向封闭段富集的是天然气，而在其之下的断层岩型封闭段却聚集的是原油。

Difference between fault juxtaposition and fault rock lateral seals

Lateral fault seals in clastic sequences can be divided into two types, namely fault rock and fault juxtaposition seals. In order to correctly understand the role of faults in hydrocarbon accumulation and distribution, a pioneer comparative study was performed on the sealing mechanisms and sealing conditions of the aforementioned two types of lateral seals. Findings showed that for the traps formed under the influence of lateral fault juxtaposition seals, their oil (gas) water contact distributions are controlled by the lithologies of juxtaposed rocks. In contrast, for the traps formed under the influence of lateral fault rock seals, their oil (gas) water contract distributions are controlled by the displacement pressure of fault rocks. The lateral fault juxtaposition seals are significantly better than the lateral fault rock seals in sealing capacities. In a case study of the Banqiao fault in the Qikou sag, Dagang Field, we found that under the same conditions, the sealing capacity of lateral fault juxtaposition seals is 25 to 43 times larger than that of lateral fault rock seals. This significant difference results in the accumulation of gas in the upper part of the 1^st member of the Paleogene Shahejie Fm sealed by the lateral fault juxtaposition seals, while the accumulation of oil in the lower part of the 1^st member of the Paleogene Shahejie Fm sealed by the lateral fault rock seals.