裂陷盆地断层相关圈闭含油气性控制因素分析——以海拉尔-塔木察格盆地塔南凹陷为例

ANALYSIS ON CONTROLLING FACTORS OF OIL/GAS-BEARING PROPERTIES OF FAULT-RELATED TRAPS IN RIFTING BASINS --TAKINC TANAN SAC IN HAILAR-TAMTSAG BASIN AS AN EXAMPLE

塔南凹陷中西部发育典型的断圈，形成典型的断层遮挡型油藏。在有油气来源的前提下，影响断层相关圈闭含油性的因素主要有三方面：一是充注的程度；二是侧向封闭能力；三是后期改造的程度。充注程度表现为“供烃”、“输导”和“聚集”三方面的耦合，高效供烃有两种模式：即侧向运移持续供烃模式，砂泥薄互层烃源岩早期分散型聚集之后断裂活动高效汇聚模式。沿断裂运移的油气必须在“顶封”作用下才能大规模聚集。断层侧向封闭性影响断圈的有效性，分为三种情况：一是断层封闭的烃柱高度大于断圈的幅度，断圈完全有效；二是断层封闭的烃柱高度小于断圈的幅度，断圈部分有效；三是断层开启，断圈无效。断圈油气保存受控于成藏期后断裂活动性，成藏关键时刻之后活动断裂将破坏盖层连续性，在浅层形成次生油藏或散失，不活动的断圈油气得以保存。因此，断圈含油性需要从断裂输导、遮挡和保存三个方面进行评价，三个条件必须合理匹配，油气才能大规模成藏。

In the Middle-west of Tanan Sag, the typical fault trap is developed, and the typical fault-screened reservoirs are formed. Under the prerequisite of existing hydrocarbon sources, there are three factors that influence oil/gas bearing properties of fault-related traps ： the first one is the degree of hydrocarbon filling; the second is the lateral seal ability ; the third is the degree of late reformation. The degree of hydrocarbon filling displays as the coupling of ＂hydrocarbon supplying＂, ＂transporting＂ and ＂accumulating＂ There are two effective hydrocarbon supplying patterns： the continuous hydrocarbon supplying by lateral migration and the high effective faulting aggregation after early scattered aggregation of source rock with thin sand-shale interbeds. Only under the effect of ＂ top being sealed＂ could the oil/gas migrating along faulting form a large-scale accumulation. There exit three circumstances that the lateral seal property of faults influences the effectiveness of fault traps. The first one is that if the height of hydrocarbon column sealed by faults is greater than the amplitude of fault trap , the fault trap is fully effective; the second is that if the hydrocarbon column height sealed by faults are smaller than the amplitude of fault trap, the fault trap is partially effective ; the third is that if the fault is open, the fault trap is non-effective. The hydrocarbon preservation in fault traps is controlled by faulting activities after reservoir-forming period. After the critical reservoir-forming period, the active faults will destroy the continuity of capping formation, which leads to the formation of secondary reservoirs in shallow layers or hydrocarbon loss, and oil/gas can be preserved in the inactive fault traps. Therefore, it needs to evaluate the oil-bearing property of fault traps from three aspects, namely faulting transporting, shielding and preserving. Only when these three conditions match reasonably, the large scale hydrocarbon accumulation can be realized.