坳陷湖盆湖泛层沉积特征及其石油地质意义——以鄂尔多斯盆地三叠系延长组为例

以鄂尔多斯盆地延长组为例,运用高分辨率层序地层学理论,综合利用露头、岩心、测井等资料,在延长组内识别出了6层三级层序级别的湖泛层(Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ、Ⅵ),研究了其沉积相类型、沉积厚度及其平面展布等沉积特征,从发育层位、露头、岩电响应等方面建立了其识别标志.研究结果表明,湖泛层主要具有4方面的石油地质意义:①湖泛层具有在测井和地震资料上易识别和对比的特征,可作为湖盆层序地层划分和对比的辅助标志层,对湖盆层序地层研究具有一定辅助作用;②利用湖泛泥岩类型及其厚度平面展布特征,反映不同时期湖水分布和演化规律;③借助湖泛层厚度沉积中心的分布和迁移,研究湖盆沉积洼陷的分布和迁移规律,对认识整个湖盆的演化具有重要意义;④湖泛层作为油藏的主要烃源岩和盖层,其时空分布特征控制着油藏组合类型和成藏规律.

Depositional features and petroleum geological significance of the flooding layers in depression lake basins:a case study of Triassic Yanchang Formation in Ordos Basin

Six lake flooding layers of third-order sequence(Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ、Ⅵ) were identified from Yanchang Formation in Ordos Basin based on high resolution sequence stratigraphy and the data of outcrop,core,logging,etc.Their sedimentary facies types,thickness and plane distribution were studied,and their identification marks were established from several aspects of developing strata,outcrops and lithlogy-electricity responses.The results show that,the lake flooding layers are of four aspects of petroleum geological significances:① the lake flooding layers can easily be identified and contrasted from logging and seismic data,and therefore they can be as the assist marked beds for the sequence stratigraphic division and contrast of lake basins,which is of assistant effect to the sequence stratigraphy research of lake basin;② the types and the thickness plane distribution of the lake flooding mudstone can reflect the distributions of the lake water in different stages and the evolution law of the lake water distribution;③ the distribution and the migration law of the depositional sags in lake basins can be studied according to the distribution and the migration law of the thickness sedimentation centers of the lake flooding layers,which is of significance to knowing the evolution of the lake basins;④ the lake flooding layers were the reservoir’s primary source rocks and cap rocks,whose spatial and temporal distribution features control the assemblage types and the forming rules of oil reservoirs.