柴达木盆地西南缘乌南油田新近系古地震纪录及储集性能研究

Reservoir Characters and Paleoseismic Records in Neogene Wunan Oilfield,Southwestern Margin of the Qaidam Basin

柴达木盆地为一新生代以来形成的叠合盆地,由于多期构造活动,盆内形成了多组断裂系统。受新近纪昆仑山北侧断裂活动的影响,盆地西南缘乌南地区地震活动强烈,发育一系列与地震有关的震积岩,形成多种类型的与地震活动有关的软沉积物变形构造。乌南油田新近系的软沉积物变形构造主要包括重荷模、火焰构造、震积砂枕、砂球构造、假结核、枕状层、液化砂泥岩脉、泄水构造、层内错断、地裂缝、串珠状构造、微褶皱纹理等。本区震积岩的岩石类型主要包括震褶岩、震裂岩、震塌岩、自碎屑角砾岩等。地震活动使岩层产生大量的微裂缝,裂缝沟通了原有的孔隙。尽管储集层孔隙度没有大幅度增加,但能够极大地改善储集层渗透性,使渗透率大幅度增加。震积岩特别是震裂岩和震碎角砾岩是一种潜在的油气储层,为油气勘探和开发提供了新的视角和领域。

Qaidam Basin is a superimposed basin developed under the different tectonic backgrounds during Cenozoic. Because of multi-stage tectonic activities, multiple sets of rift system developed. The Wunan area in the southwestern margin of the Qaidam Basin was intensely affected by a series of faulting movement of Neocene in the north of Kunlun Mountain, and developed seismite presented serious seismicrelated soft-sediment deformation structures. The Neocene soft-sediment deformation structures in the Wunan oilfield consist of load casts, flame structures, pillow structures, ball structures, pseudonodules, pillow beds, liquefied sandstone vein, liquefied mudstone vein, water-escape structures, micro-fault, micro-fracture, pinch and swell structures, micro corrugated lamination. Seismites can be subdivided into many types, such as seismic corrugated rocks, shattered rocks, seismic collapse rocks and autoclastic breccias. When earthquake was active, a great amount of micro fractures formed and connected with original pore. Though the porosity of reservoirs would not be improved greatly, the permeability of reservoirs can be improved obviously. Seismites, especially the shattered rocks and seismic breccias, are potential reservoirs and will become new exploration areas in the near future.