Oil & Gas Geology ›› 2022, Vol. 43 ›› Issue (5): 1167-1179.doi: 10.11743/ogg20220513

• Petroleum Geology • Previous Articles     Next Articles

Oil enrichment law of the Jurassic Yan’an Formation, Hongde block, Longdong area, Ordos Basin

Shuai Yin1,2(), Zhonghu Wu3(), Xiaoming Wu4, Jianping Liu5, Chengqian Tan1, Ruyue Wang6, Hui Yuan1, Yawei Dai1,2   

  1. 1.School of Earth Sciences and Engineering,Xi’an Shiyou University,Xi’an,Shaanxi 710065,China
    2.Shaanxi Key Laboratory of Petroleum Accumulation Geology,Xi’an Shiyou University,Xi’an,Shaanxi 710065,China
    3.College of Civil Engineering,Guizhou University,Guiyang,Guizhou 550025,China
    4.No. 7 Oil Production Plant,Changqing Oilfield Company,PetroChina,Xi’an,Shaanxi 710086,China
    5.Changqing Oilfield Company,PetroChina,Xi’an,Shaanxi 710018,China
    6.Petroleum Exploration and Production Research Institute,SINOPEC,Beijing 102206,China
  • Received:2021-09-11 Revised:2022-08-11 Online:2022-10-01 Published:2022-09-02
  • Contact: Zhonghu Wu E-mail:speedysys@163.com;wuzhonghugzu@163.com

Abstract:

The Jurassic in the Hongde block, Longdong area, Ordos Basin, has been less explored until some oil discoveries were made in the same system of nearby blocks. The Yan’an Formation in the Hongde block is taken as the subject of study to reveal conditions for possible oil accumulations in the formation based on relevant core, logging, seismic and testing data as well as analyses of sedimentary systems, tectonics and paleo geomorphology-the three most likely controlling factors for oil pooling. The results indicate that from the Yan’an Formation to the Yanchang Formation in the area there are three local unconformities respectively between the Fuxian Formation and the Yanchang Formation, the Yan 10 sub-member (Yan’an Formation) and Yanchang Formation, and the Yan 9 sub-member (Yan’an Formation)and Yanchang Formation. Five types of pre-Jurassic paleomorphologic units are also recognized:the paleovalley, inter-channel hill, ancient terrace, slope belt and low residual hill. Among them, the slope belt and low residual hill are conducive to hydrocarbon accumulation,and the ancient terrace and valley in the Yan 10 sub-member also have certain hydrocarbon accumulation potential. In addition, favorable conditions for oil accumulation also exist in the slope mouth where sandbodies have low shale content as several tributaries converged here and washed shale away. Oil caps and oil-water contacts are easily recognized. From a plan view, fault zones are intersecting sandbodies. The hanging walls of faults form perfect traps for oil, while the footwalls, without effective sealing, are usually barren in terms of oil pool. Normal faults are comparatively better oil pool holders than reverse ones. High-quality sedimentary reservoirs are necessary but insufficient conditions for the Yan’an Formation to contain oil pools. Based on the understanding, a method for identifying reservoirs in the Jurassic Yan’an Formation in the Hongde block is proposed.

Key words: sedimentary reservoir, Yan’an Formation, paleomorphology, structure, Jurassic, Ordos Basin

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