银根—额济纳旗盆地改造动力与油气成藏

TRANSFORMATION DYNAMIC FORCES AND HYDROCARBON ACCUMULATION OF THE YINGEN-EJINAQI BASIN

王新民 李相博 郭彦如 李天顺

WANG Xin-min LI Xiang-bo GUO Yan-ru LI Tian-shun

中国石油, 勘探开发研究院, 北京, 100083 2. 中国科学院, 兰州地质研究所, 甘肃, 兰州, 730000 3. 中国石油, 勘探开发研究院, 西北分院, 甘肃, 兰州, 730020 4. 中国科学院, 研究生院, 北京, 100039

Research Institute of Petroleum Exploration and Development, CNPC, Beijing 100083, China 2. Lanzhou Research Institute of Geology, Chinese Academy of Sciences, Lanzhou, Gansu 730000, China 3. Northwest Branch, Research Institute of Petroleum Exploration and Development, CNPC, Lanzhou, Gansu 730020, China 4. Graduate School, Chinese Academy of Sciences, Beijing 100039, China

银根—额济纳旗盆地地应力、重力和热力3种动力对盆地具有改造作用并影响油气成藏。地应力改造作用在盆地主要表现为抬升、挤压、伸展和走滑4种改造方式。其中抬升作用延缓了剥蚀区油气成藏的进程,使烃源岩热演化停滞于剥蚀前的热演化状态,这种改造对早生早排古油气藏的保存有利;挤压改造作用产生褶皱与断裂甚至构造反转等现象,为油气成藏储备了大量各种类型圈闭条件的同时,也为油气运移提供了动力和通道,有利于油气成藏;伸展作用在盆地表现为早白垩世断陷以不同叠合(叠置)形式叠置在侏罗纪断陷之上,这种改造有利于提高侏罗系烃源岩的热演化程度,使源岩有机质向烃类转化并运聚成藏,同时,张性贯通断裂可使原有古油气藏保存条件部分改变或破坏,形成次生油气藏;大型走滑作用可形成一系列张扭性与压扭性构造样式,在走滑伸展沉降带内形成走滑拉分盆地,并对前期盆地产生走滑分割改造,对油气成藏的影响主要表现为提供成藏环境及条件和改造破坏正反作用两个方面。重力改造作用以深埋及压实为具体表现形式,为盆地成烃、成藏提供了地温场、地压场和保存条件,深埋作用的快速发生还为盆地形成流体压力封存箱提供了条件,异常超压及其流体压力封存箱的存在有利于保存原生孔隙、发育次生孔隙并形成压力封闭成藏条件,这对油气生成、运移和聚集成藏有积极作用。热力改造作用在盆地主要表现为多期岩浆侵入和喷发活动对沉积盖层的改造,为油气成烃、成藏提供了有利条件。

Three dynamic forces-ground stress, gravity and thermal dynamic force cause the transformation of basin and influence the hydrocarbon accumulation in the Yingen-Ejinaqi Basin. The transformation effect of ground stress is shown in 4 ways: uplift, extrusion, expansion and strike slip. Among which, the uplift postpones hydrocarbon accumulation in the denudation area, thus the thermal evolution of source rock remains the state before denudation, which is favorable for the preservation of palaeoaccumulation early generated and discharged. The extrusion effect results in fold, fracture and even tectonic reversal, offering not only various traps for hydrocarbon accumulation, but also force and passage for hydrocarbon migration. The expansion effect is shown by superposition of the Early Cretaceous rifts on the Jurassic ones. This transformation promotes the thermal evolution of Jurassic source rock, helping organic matters in source rock convert to hydrocarbon and migrate and accumulate. Meanwhile, extentional linked fractures partially change or destroy the original preservation condition of palaeoaccumulation, forming (secondary) hydrocarbon accumulation. The large-scale strike slip effect may form a series of transtensional and compresso-shear tectonic patterns, resulting in strike-slip pull-apart basin in the strike-slip expanding subsiding belt, and transforming preliminary basin. The influences on bydrocarbon accumulation include: a) providing environment and condition for accumulation; b) transformation and destruction. The gravity transformation effect is shown by deep burial and compaction, providing terrestrial heat field, geopressure field and preservation condition for hydrocarbon generation and accumulation. The quick occurrence of deep burial is also helpful for confining liquid pressure, resulting in abnormal overpressure, which is favorable for preserving primary pore, generating secondary pore and forming pressure seal, thus promoting hydrocarbon generation, migration and accumulation. The transformation effect of thermal dynamic force is shown by the transformation of sedimentary cover by multistage magma intrusion and effusion activity, providing favorable condition for hydrocarbon generation and accumulation.

中国石油"九五"油气勘探科技工程项目北方侏罗系油气勘探项目(970207-34-2).

https://doi.org/10.11781/sysydz200405442