准噶尔盆地南缘四棵树凹陷构造特征与油气勘探

Structural Characteristics and Petroleum Exploration in Sikeshu Sag,Southern Margin of Junggar Basin

四棵树凹陷位于准噶尔盆地西北缘与南缘构造体系的交会区,构造变形复杂,落实构造圈闭是油气勘探的关键。采用构造建模思路和技术方法,通过二维和三维地震几何学以及运动学分析,结合区域构造成图,建立四棵树凹陷"两期叠加、双层构造"的变形模式。研究认为,以白垩系吐谷鲁群泥岩、古近系安集海河组泥岩滑脱层为界,四棵树凹陷发育深、浅2个构造层,深部构造层是中生代北西—南东向走滑断裂和雁列式分布褶皱,浅部构造层是新生代滑脱冲断构造。两期构造垂向叠置,平面展布继承中生代雁列式构造格局。通过油气成藏条件综合研究,提出四棵树凹陷构造"垂向叠置"油气成藏模式。浅部构造层油藏受断裂沟通影响,新生代断裂控制油藏分布;深部构造层紧邻生烃中心,构造圈闭形成早,有利于油气长期运聚,且晚期变形改造弱。2019年高探1井获日产千方油气流,证实四棵树凹陷深部构造成藏条件优越。

Sikeshu sag is located in the intersection area of the northwestern and southern margins of Junggar basin. Because of the complex structural deformation, ascertaining traps in the area is vital for petroleum exploration. Based on 2 D and 3 D seismic geometry and kinematics analysis and combined with regional structural mapping, the research adopts the ideas and techniques of structural modeling to build a deformation model of "two periods of superimposition and double layered structure" for Sikeshu sag. It is considered that deep and shallow structural layers are developed in the sag by taking the Cretaceous Tugulu mudstone and the detachment layer of mudstone of Paleogene Anjihaihe formation as boundaries. The deep structural layer is mainly composed of Mesozoic NWSE trending strikeslip faults and en echelonlike folds and the shallow structural layer is a Cenozoic detachmetn thrust structure. The two periods of structures superimposes vertically and exhibit a Mesozoic en echelonlike structural framework laterally. Based on the comprehensive research of oil and gas accumulation, a hydrocarbon accumulation model of vertical superimposition is proposed for Sikeshu sag. The reservoir in the shallow structural layer is influenced by fault connection and its distribution is controlled by Cenozoic faults;the deep structural layer is very near to hydrocarbon generation center in which structural traps formed early and late deformation was weak, which benefits longterm hydrocarbon migration. The commercial oil and gas flow with the daily production more than 1 000 tons obtained from the Well Gaotan1 in Jan., 2019 can prove that the hydrocarbon accumulation conditions of Sikeshu sag is favorable.