民和盆地永登凹陷油气成藏地质特征

Geologic Feature of Hydrocarbon Accumulation in Yongdeng Sag of Minhe Basin

民和盆地勘探主体包括巴州凹陷和永登凹陷。永登凹陷勘探程度较低,为盆地沉积和生烃主体。利用露头资料、地震解释、巴州凹陷探井资料分析对比、周围煤田钻孔资料的研究,确定自盆地中燕山运动回返以来,永登凹陷长期处于构造高部位和古地温场低值区,主要目的层段埋藏浅,滨浅湖相发育宽广,储集层主要为扇三角洲砂体、滩坝砂体,物性较好,属中孔中渗-中孔低渗型,发育了断背斜、背斜等有利圈闭,并在凹陷东斜坡坡折带区发育构造-地层复合圈闭。油源断层发育,喜马拉雅运动对圈闭改造作用弱,圈闭保存条件好,具备长期捕获油气能力。

The main explorative targets in Minhe basin include Bazhou sag and Yongdeng sag. Yongdeng sag＇s exploration degree is lower, which is main body of deposition and hydrocarbon source in this area. Through a series of researches on the evolution of basin structure,field outcrop, the seismic interpretation, the analysis and correlation of geological information from Bazhou sag, it is indicated that Yongdeng sag, since the Middle Yanshanian movement, has been in structural high and province of low paleogeothermal field for a long time. Because of its shallow burial target zone, broad developed coastal shallow lake facies, fan delta sand and beach bar sand reservoirs, its physical property is comparatively better, belonging to mid-porosity and mid-low permeability type of reservoir with faulted anticline and anticline traps as well as structural-stratigraphic traps in slop belt area of the easterm Yongdeng sag. The study also shows that the preserved conditions of the traps are good, possessing long-term ability to capture oil and gas due to weak reconstruction to the traps by Himalayan movement and developed faults linked with source rock.