Oil & Gas Geology ›› 2021, Vol. 42 ›› Issue (5): 1043-1055.doi: 10.11743/ogg20210503

• Petroleum Geology • Previous Articles     Next Articles

Characteristics of unconformity resulted from Huaiyuan Movement in Ordos Basin and its significance for oil and gas exploration

Xiangbo Li1(), Hongbo Wang1, Junping Huang1, Caili Zhang2, Yan Zhang3, Yating Wang2, Lei Zhang2, Jing Wang1, Huaqing Liu1   

  1. 1. Research Institute of Petroleum Exploration and Development-Northwest, PetroChina, Lanzhou, Gansu 730020, China
    2. Changqing Oilfield Branch Company Ltd., PetroChina, Xi'an, Shaanxi 710018, China
    3. China University of Petroleum (Beijing), Beijing 102249, China
  • Received:2020-06-15 Online:2021-10-28 Published:2021-10-26

Abstract:

The unconformity formed out of Huaiyuan Movement is one of the important regional unconformities in the North China Platform.Following the investigation on and analysis of the occurrence and geological characteristics of the movement, we make an in-depth analysis of the evidences and characteristics manifesting the movement-caused unconformity and its correlation with reservoirs and oil and gas accumulation in the Ordos Basin, with new understandings obtained.The results show that: ①There is a regional unconformity formed by the Huaiyuan Movement in the deep Ordovician of Ordos Basin, and it perhaps associates with a large-scale geomorphology system of karst ravines; ②The regional unconformity and ravine system serve as the paleogeomorphologic setting for the deposition of the overlying strata, to be specific, the middle-to-bottom parts of Majiagou Formation (namely, from Ma 4 to Ma 1 Members), and control the depositional pattern and favorable reservoir facies distribution, as well as the development of dolomitized and weathered crust reservoirs in the underlying Lower Ordovician to Cambrian and to Changcheng Systems; ③The regional unconformity acts as a favorable channel for the lateral migration of natural gas from different sources in certain regions, known as "highway of hydrocarbon migration"; meanwhile, it is also a favorable place for hydrocarbon accumulation, the upper and lower layers near which are conducive to natural gas accumulation and enrichment in large scale.It is possibly a new exploration area worthy of attention in replacement of weathering crust on top of the Ordovician.However, the current understandings have to be deepened on the unconformity in the study area, for which a 3D seismic acquisition is recommended to promote creative geological understandings and new exploration discoveries in the Ordos Basin.

Key words: dolomitization, weathering crust, unconformity, Huaiyuan Movement, palaeogeomorphology, Majiagou Formation, Ordos Basin

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