›› 2018, Vol. 39 ›› Issue (4): 1-1.doi: 10.7657/XJPG20180401

   

Geochemical Features and Geological Significance of Oil Seepages in Northeastern Wulungu Depression

WANG Qianjun1, CAO Gaoshe2,3, XING Zhou2, WANG Jinduo1   

  1. (1.Research Institute of Exploration and Development, Shengli Oilfield Company, Sinopec, Dongying, Shandong 257015, China; 2.Institute of Resources & Environment, Henan Polytechnic University, Jiaozuo, Henan 454000, China; 3.Collaborative Innovation Center of Coalbed Methane and Shale Gas for Central Plains Economic Region, Jiaozuo, Henan 454000, China)
  • Online:2019-01-01 Published:1905-07-17

Abstract: Exploration breakthrough has not been achieved in Wulungu depression in the northeastern margin of Junggar basin, this should be attributed to the absence of Permian source rock which is commonly found in Junggar basin. Although the Carboniferous basement of Wulungu depression is considered as the most likely potential source rock, it is still doubtful whether reservoirs can form here. Flame-like, disseminated and dendritic solid bitumen seepages which intrude into the earthy yellow, unconsolidated sand sediments and weathering granites of Quaternary are found in the outcrops of northeastern Wulungu depression. On the basis of the analysis of total organic carbon content, rock pyrolysis, chloroform bitumen A, vitrinite reflectance, carbon isotope of kerogen and biomarkers of steriod and terpenoid, the paper verifies the presence of the oil seepages and compares them with the source rocks and discoverded crude oil in the study area. The study shows that the oil seepages have high total organic carbon contents which indicate typical carbon isotope values of coal formed oil and the oil source is the Carboniferous black mudstone distributed in the oil seepage area; this oil is greatly different from the oil sourced from Permian, Middle—Upper Triassic and Jurassic rocks in Zhundong area, but it can be well correlated with the Carboniferous oil. The regional structural analysis indicates that the basement of Wulungu depression is a part of Central Asia Orogenic Belt, which has similar compositions and structural features with the Carboniferous strata in the areas where the oil seepages are located. Therefore, the discovery and study of the oil seepages not only have important significance for oil and gas exploration in the study area, but can provide references for oil and gas exploration in Wulugu depression in the northeastern margin of Junggar basin

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