塔里木盆地库车坳陷北部构造带地质结构与油气勘探领域

Geological structures and petroleum exploration fields of the northern tectonic belt in the Kuqa depression,Tarim basin

地质结构、构造演化及其与油气成藏的关系是制约塔里木盆地库车坳陷北部构造带油气勘探进程的重要因素。以地震剖面为基础,结合区域构造背景、露头地层特征以及钻井资料,对北部构造带3个构造段(吐格尔明、迪北—吐孜、巴什)的地质结构进行了详细解剖,恢复了构造演化史,并分析了变形特征,最后在构造演化与油气成藏关系的基础上,讨论了北部构造带的潜在勘探领域。结果表明,吐格尔明段为古隆起和基底卷入断层共同控制的背斜构造;迪北—吐孜段和巴什段均发育深浅两套变形系统,深层为基底逆冲断层控制的褶皱带,浅层发育相对简单的断层-褶皱体系。吐格尔明段、迪北—吐孜段、巴什段的构造活动分别始于白垩纪—古近纪早期、新近纪中期、新近纪晚期,均定型于新近系库车组沉积期—第四纪。新近系吉迪克组—康村组沉积期(23~5 Ma),迪北—吐孜段和吐格尔明段形成古油藏,巴什段下侏罗统形成大面积、低丰度的含油带;新近系库车组沉积期(5~2 Ma),早期古油藏遭到破坏,局部仍有古油藏保留,同时形成规模不等的天然气藏或凝析气藏;第四纪西域组沉积期(2 Ma~),先前形成的气藏及残留古油藏发生大规模调整改造,形成现今的成藏格局。吐格尔明段的油气勘探应避开核部剥蚀区,背斜北翼、南翼、东西倾伏端分别发育裂缝性岩性油气藏、孔隙型岩性油气藏、构造-岩性油气藏;迪北—吐孜段的迪北南斜坡是裂缝性致密砂岩油气藏勘探的重要潜在领域,依奇克里克油田是构造-岩性油气藏勘探的重要现实领域,迪北2井区和巴什段的巴什1井单斜带均为高风险勘探领域;巴什段南部克拉苏构造带的中下侏罗统可作为后备风险勘探领域。北部构造带的油气勘探应以中下侏罗统为主,兼顾浅层多目的层系,从而进一步拓宽油气勘探领域。

Geological structures, tectonic evolution and their relationships with hydrocarbon accumulation are significant factors that limit the hydrocarbon exploration of the northern tectonic belt in the Kuqa depression, Tarim basin. Based on seismic sections and combined with regional tectonic background, strata characteristic of outcrops and well drilling data, the geological structures, tectonic evolution and deformation features of three tectonic sections(i.e., the Tugerming, the Dibei-Tuzi and the Bashi sections) of the northern tectonic belt were systematically analyzed, and the potential exploration fields of the northern tectonic belt were discussed on the basis of relationship between tectonic evolution and hydrocarbon accumulation. The results show that the Tugerming section is an anticline controlled by a paleo-uplift and basement-involved faults. The Dibei-Tuzi and the Bashi sections both develop deep and shallow deformation systems, where the deep deformation system is a fold belt dominated by basement-involved thrust faults, and the shallow deformation system is a relatively simple fault-fold system. The tectonic activities of the Tugerming, the Dibei-Tuzi and the Bashi sections dated from the Cretaceous-early Paleogene, middle Neogene and late Neogene, respectively, and were all finalized in the Late Kuqa Period of Neogene-Quaternary. At the Jidike-Kangcun period of Neogene(23~5 Ma), the Dibei-Tuzi and the Tugerming sections developed paleo-oil reservoirs, while the Bashi section developed oil-bearing belts with large area and low abundance. At the Kuqa period of Neogene(5~2 Ma), early formed paleo-oil reservoirs were destroyed, but in some regions they were preserved, and in the meantime, some natural gas reservoirs or condensate gas reservoirs formed on various scales. In the Xiyu period of Quaternary(~2 Ma), previously formed gas reservoirs and residual paleo-oil reservoirs were massively adjusted and transformed, and the current accumulation pattern ultimately formed. The hydrocarbon exploration of the Tugerming section should keep away from the denuded area at the cores of anticlines. The north limb, south limb and west-east plunging crown develop fractured lithological oil-gas reservoirs, porous lithological oil-gas reservoirs and structural-lithological oil-gas reservoirs, respectively. The south Dibei slope of the Dibei-Tuzi section is a significant potential field for fractured tight sandstone oil-gas reservoir exploration, and the Yiqikelike oil field is an important practical field for the structural-lithological oil-gas reservoir exploration, while the Dibei-2 well block and the Bashi-1 monocline are the exploration fields with high risks. The Lower-Middle Jurassic of the Kelasu tectonic belt, to the south of Bashi section, can be considered as a reserve risk exploration field. The hydrocarbon exploration of the northern tectonic belt should give priority to Lower-Middle Jurassic, and consider shallow multi target formations to further broaden hydrocarbon exploration field.