从断裂带内部结构出发评价断层垂向封闭性的方法

脆性断层和塑性断层断裂带内部结构存在差异: 脆性断层断裂带由以断层岩和伴生裂缝为特征的破碎带和诱导裂缝带2部分组成; 塑性断层断裂带表现为几条充填断层泥大裂缝的组合, 诱导裂缝带不发育.破碎带内部伴生裂缝、无粘结力断层岩带和诱导裂缝带都可能成为油气运移的通道, 只有这3种通道均封闭, 脆性断层垂向才是封闭的.只要伴生裂缝封闭, 塑性断层就是封闭的.基于这种封闭机理, 分析了3种通道封闭的条件: 无粘结力断层岩带是否封闭取决于断层泥含量大小; 破碎带内部伴生裂缝的封闭性取决于断面压力和断层泥塑性强度关系; 诱导裂缝带封闭程度受控于后期成岩充填的程度.提出了利用断面压力、断层泥的含量和塑性强度、后期成岩程度综合判定不同性质断层垂向封闭性评价方法.并利用该方法对克拉2构造F₁断层垂向封闭性进行了评价, 结果表明F₁断层垂向封闭性具有分段性: ①和③段均表现为脆性, 但①段因诱导裂缝没有被充填不封闭, ③段是封闭的; ②段是塑性断层, 垂向封闭性好.这是克拉2构造有大规模天然气聚集成藏的关键因素之一. 

Method of Evaluating Vertical Sealing of Faults in Terms of the Internal Structure of Fault Zones

There is an internal structural discrepancy between plastic faults and fragile faults: a fragile fault zone consists of a crushed zone and an induced fracture zone characterized by fault rock and associated fractures; a plastic fault zone consists of several big fractures filling the fault gouge without an induced fracture zone. Associated fractures inside a crushed zone, a fault rock zone without adhesive power and induced fracture zones may all allow petroleum migration. So a fragile faultis vertically sealed only when all three migration pathways are sealed. When the associated fractures are sealed, the plastic fault is also sealed. Based on the seal mechanism, the sealing conditions of the three migration pathways are analyzed in this paper: the seal on a fault rock zone without adhesive power is dependant on the content of fault mud; the seal of an associated fracture inside a crushed zone is dependant on the relationship between the section pressure and fragile strength of the fault gouge; the seal quality of an induced fracture zone is controlled by the quantity of later rock-forming fill. This paper presents a method forevaluating the vertical seal of disparate faults using the section pressure, content and plastic strength of fault gouge and the quantity of later rock-forming fill. For example, the vertical seal of the F₁ fault of Kela 2 structure in Kuqa depression was evaluated according to this method. The results indicate that vertical seal on the F₁ fault had the following properties: section ① and section ③ show fragility, but section① is not sealed, as a result of an induced fracture that was not filled; section ③ is sealed; section ② is a plastic fault with a good vertical seal. This is one of the key reasons that natural gas gathered on a large scale and formed a field in Kela 2 stucture.