塔西南阿其克背斜地质构造特征及与油气关系

Geological Structure and Petroleum Geology Features of Aqike Anticline in Southwest Tarim Basin

阿其克背斜是塔里木盆地西南坳陷南缘的一个横向转换构造,该构造的特殊性在于其枢纽走向与造山带总体是垂直的,而非平行。笔者通过分析阿其克背斜南、中、北3段地质剖面及各剖面中核部与两翼地层的极射赤平投影,揭示了阿其克背斜的几何学、运动学、动力学特征。结合地震解释剖面、区域构造背景及前人研究成果,建立了阿其克背斜形成过程的地质模型,认为它是在断层传播褶皱和断层转折褶皱共同作用下,以断层传播作用为主分3个阶段形成的断坡背斜构造,垂向上自下而上分原地系统、准原地系统和外来系统中的推覆体3个构造层次。塔里木盆地的菱形边界性质造成阿其克地区EW向的挤压应力场。由于背斜上部外来系统中的推覆体南部翘起遭受剥蚀,东侧被阿其克断层破坏,因此对油气圈闭不利,但在北部异地推覆体之下,原地系统中过熟烃源岩及毗邻凹陷内的烃源岩可以通过断层、不整合面向上部准原地系统中的宽缓背斜圈闭供给油气。

The Aqike anticline is a transitional structure on the southern margin of the southwest depression of Tarim Basin. The particularity of this structure lies in the fact that the strike of its axis is vertical to rather than parallel to the mountain belt. Through the analysis of southern, middle and northern sections in combination with the stereographic projection, the authors identified geometric features of the anticline. Based on seismic data interpretation and regional development history, this paper has built up a model for the formation of the anticline. The model holds that the Aqike anticline was formed by both fault-propagation fold process and fault-bend fold process. It is a fault-anticline structure formed by three stages and composed vertically of three parts, i.e., autochthonous system, para-autochthonous system, and allochthonous thrust block. The boundary property of Tarim Basin leads to the WE-trending compressive stress field. Affected by the allochthonous thrust block, the southern part of the anticline is exposed and is transected by the Aqike fault on the east side, thus unfavorable for petroleum trapping. However, in the autochthonous system, the petroleum-bearing rocks may provide oil and gas for the upper traps of the para-autochthonous system through faults and discontinuous surfaces.