摘要:
平衡剖面技术是一种遵循几何守恒原则而反演地质构造演化过程的剖面、亦是恢复重建地质演化历史活动及过程的一种方法,同时也是构造演化定量分析的有效手段。准噶尔盆地西北缘是典型的前陆冲断带,由于其地质条件复杂、地震波速横向变化大等原因,故对该区构造演化及动力学机制研究与油气地质条件的分析一直不能深入进行,因而严重制约了油气勘探进程。针对以上症结所在,从技术层面提出了更好的利用平衡剖面技术进行构造演化恢复的方法,进而为深刻认识该区构造发育史、分析油气运移及聚集规律等提供了依据。通过平衡剖面恢复的结果表明,研究区经历了挤压—伸展—挤压三期构造运动,并由此构成了一个完整的构造旋回。其中,晚二叠世存在一个小幅度的快速挤压期,而三叠纪为整个构造演化中最强烈的构造挤压时期,其对该区构造演化及构造格架形成与油气运聚成藏等均具重要影响和控制作用。
Abstract:
The balanced cross-section is an effective tool for quantitative restoration of structural evolution under the guidance of a constant geometry. The northwestern margin of the Junggar Basin is a typical foreland thrust belt. Due to the complexity of geological conditions and the horizontal variation of seismic wave velocity,the study of tectonic evolution and its dynamic mechanism is not deep enough in the basin that constraints effective oil exploration. In order to obtain the reliable results, adequate methods should be adopted on the basis of actual geological conditions. For the reliable restoration of structural evolution by balanced cross-section in foreland thrust belt in northwestern China, 4 critical steps are suggested from technical point of view in this paper: Firstly it is necessary to select a suitable seismic line; Secondly, use variable velocity parameters in time-depth conversion to have reliable geologic profiles; Thirdly, adopt the flexural-slip mechanism for middle and upper strata, and then apply the vertical mechanism to deeper strata; Finally, decompact the strata by segment where the lithologic characters vary intensively in the horizon to decrease the decompaction errors. The northwestern margin of the Junggar Basin in Northwest China, which is a typical foreland thrust belt, is discussed in this paper as an example. The result suggests that the study area experienced a complete tectonic cycle consisting of three tectonic movements of compression- extension- compression. There is a rapid low amplitude compression stage in late Permian, and the strongest compression of tectonic evolution in Triassic. All the above has important impact on the formation of structural framework and the migration and accumulation of hydrocarbons.
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