东营凹陷古近系膏盐岩沉积特征及发育模式

    Sedimentary characteristics and development model of Paleogene gypsum salt rocks in Dongying Depression

    • 摘要: 膏盐岩多与深层、超深层油气资源相互伴生,且富含大量盐矿资源。在资源开发时,如果不厘清膏盐岩空间展布,容易发生溶解垮塌、膨胀缩径等复杂工程事故,会制约油气及盐矿资源的高效开发。以地震、测井、录井及地球化学为研究手段,对东营凹陷古近系沙河街组四段(简称沙四段)膏盐岩进行研究,揭示岩石矿物特性及其地球物理响应规律,梳理不同尺度膏盐岩的识别方法,查明膏盐岩纵向上的演化规律及平面上的展布特征,阐明膏盐岩的沉积环境及发育模式。研究结果显示: ①岩心尺度的膏盐岩识别主要通过其吸水膨胀、硬度较低、易溶于水、味咸等物理性质,井筒尺度的电性特征有自然电位曲线负异常、自然伽马值低、声波时差值小及电阻率值高,可结合井径扩大或缩小综合判断膏盐岩位置,在井间及区域上则利用地震强反射振幅对膏盐岩进行空间位置标定及追踪; ②研究区沙四段膏盐岩系纵向上发育3套典型的沉积旋回,平面上膏盐岩分布在东营凹陷中北部沉积沉降中心附近,自下而上、自边缘向中心岩性依次由碎屑岩类向碳酸盐岩类、膏盐岩类转化; ③膏盐岩在古盐度较高、古气候干燥、古水深较浅、还原环境的盐湖中形成,干燥气候下降水量减少,造成湖内水体变浅和盐度上升,矿物质及卤化离子浓缩而析出结晶,在湖中心底部易形成膏盐岩系。探明东营凹陷古近系膏盐岩的沉积特征及发育模式,对于深层、超深层油气及盐矿资源的高效开发具有指导意义。

       

      Abstract: Gypsum salt rock is often associated with deep and ultra-deep oil and gas resources, and it is rich in a large number of salt resources. Due to the unclear description of the spatial distribution characteristics of gypsum salt rocks, it is easy to cause complex engineering accidents such as dissolution collapse, expansion and shrinkage during resource development, which will restrict the efficient development of oil, gas and salt resources. The Paleogene gypsum salt rock in 4th member of Shahejie Formation (Sha-4 Member) of Dongying Depression was analyzed based on seismic, well logging, well logging and geochemical data. The rock mineral characteristics and geophysical response laws were revealed, and the different scale gypsum salt rock identification methods were reviewed. Besides, the longitudinal evolution and plane distribution characteristics were clarified, and the sedimentary environment and development model of gypsum salt rock were reviewed. The results are as follows: ① The identification of the core size of gypsum salt rocks was mainly based on physical properties such as water absorption and expansion, soft properties, water solubility and salty taste. At the wellbore scale, the gypsum salt rocks had the special electrical characteristics of negative anomaly of spontaneous potential curve, low natural gamma value, low acoustic transit time value, high resistivity value. The gypsum salt rock location was determined by the expansion or contraction of the well diameter. The strong seismic reflection amplitude was used to calibrate and trace the spatial position at the well and region level. ② There were three typical sedimentary evolution cycles along the vertical orientation in gypsum salt rocks of Sha-4 Member in Dongying Depression. Gypsum salt rocks were distributed near the sedimentation center in the central and northern part of the depression. The lithology changed from clastic rock to carbonate rock and then to gypsum rock from bottom to top and from edge to center. ③ The formation of gypsum salt rocks was in high paleosalinity, arid paleoclimate, shallow paleowater depth, reducing salt lake environment, and the dry climate would cause precipitation reduction, resulting in shallow water and rising salinity in the lake. The minerals and halogenated ions were concentrated and crystallized. And the gypsum salt rocks strata easily formed at the bottom of the lake center. Ascertaining the sedimentary characteristics and development model of Paleogene gypsum salt rocks in Dongying Depression could provide guiding significance for the efficient development of deep and ultra-deep oil, gas and salt resources.

       

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