松辽盆地徐家围子断陷大型断裂带对天然气成藏的控制作用

Control effect of three large faults on the gas pools in the Xujiaweizi faulted depression,Songliao Basin

解剖松辽盆地徐家围子断陷天然气藏的控藏要素对于该区下一步天然气勘探具有重要的指导意义,而过去较少从徐西、徐中、徐东三大断裂入手来开展这一研究。为此,在精细解释该区三维地震资料的基础上,根据上述三大断裂发育及分布特征,采用三大断裂与天然气成藏条件叠合分析的方法,探讨了三大断裂对天然气成藏与分布的控制作用。结果表明:1三大断裂共同控制了该区下白垩统沙河子组煤系烃源岩的发育,烃源岩存在3个厚度高值区(最大厚度可超过1 000m),气源供给充足,三大断裂为天然气向上覆各套储层中运移提供了输导通道;2三大断裂是徐家围子断陷地下岩浆在下白垩统营城组沉积时期向地壳浅部上侵的主要输导通道,其附近广泛分布火山岩体,并发育优质火山岩裂缝性储层;3三大断裂为火山岩中天然气的聚集提供了有效的遮挡条件,如果错断营一段火山岩圈闭的断裂两盘为火山岩储层与砂砾岩对接,断裂侧向封闭,则有利于天然气聚集成藏,钻探时为气层;当断裂两盘是火山岩与火山岩对接时,其侧向不封闭,就不利于天然气聚集成藏,钻探时为水层。

The study of the major controlling factors of gas accumulation in the Xujiaweizi faulted depression of the Songliao Basin is of great significance to future gas exploration. However, they were seldom studied in the context of major faults including Xuxi, Xuzhong and Xudong. Based on fine interpretation of 3D seismic data acquired in this area, the control effect of these three major faults on the gas pools was studied through a composite analysis of the three faults and the gas accumulation conditions based on the characteristics of development and distribution of the said major faults. The following conclusions were obtained. （1） These major faults jointly controlled the development of coal-seam source rocks in the Lower Cretaceous Shahezi Fm. Thickness of hydrocarbon source rocks exist three high-value areas （with the maximum thickness of over 1000 m） and have a large potential of hydrocarbon generation. The three major faults acted as carriers for the migration of gas upwards to the overlying reservoirs. （2） The three major faults also acted as the pathways for magma to protrude upwards into the shallow crust during the Early Cretaceous Vingcheng period. Volcanic rocks are well-developed around the faults and consist of fractured volcanic reservoirs of high quality. （3） These faults provided effective sealing conditions for the gas accumulation in the volcanic reservoirs. If the volcanic rocks in the one fault bock are juxtaposed with sandstone or conglomerate in the other fault bock, the lateral seal of the fault is favorable for gas accumulation, thus gas reservoirs can be formed. In contrast, if the volcanic rocks in the one fault block are juxtaposed with volcanic rocks in the other fault block, no lateral seal exists, thus being favorable for the formation aquifers instead of gas reservoirs.