Oil & Gas Geology ›› 2020, Vol. 41 ›› Issue (5): 953-964.doi: 10.11743/ogg20200506

• Petroleum Geology • Previous Articles     Next Articles

Origin of Cambrian dolomite from Well Milan 1 in Tadong area and its significance to dolomite reservoirs

Chuntao Guo1,2(), Haiqiang Song3, Jie Liang4, Lingmei Ni5   

  1. 1. Department of Geological and Environmental Engineering, Shanxi Institute of Technology, Yangquan, Shanxi 045000, China
    2. HRD Center of Daqing Oilfield Company, CNPC, Daqing, Heilongjiang 163453, China
    3. Petroleum International Exploration and Development Engineering Co., Ltd., Xi'an, Shaanxi 710075, China
    4. College of Architecture and Surveying Engineering, Shanxi Datong University, Datong, Shanxi 037003, China
    5. Qujing Tourism Development Research Institute, Qujing Normal University, Qujing, Yunnan 655011, China
  • Received:2018-10-18 Online:2020-10-28 Published:2020-10-22

Abstract:

Knowing reservoir distribution pattern is key to the exploration of deep dolomite reservoirs in the eastern Tarim Basin.To understand the origin of the Cambrian dolomite in the Milan area of the Tadong low uplift, we measured the rare earth elements (REE) of dolomite of various types taken from a representative well Milan 1 for geochemical characterization based on core and thin section observations.The results show that the content of all REEs in various dolostones is low, and the total mass fraction decreases with the increase of grain size.There are obvious differences in δEu anomalies for dolostones of different types.The δEu anomaly values of silty-micritic, finely-crystalline, medium-crystalline and coarse-crystalline dolostones range between 0.97-1.08, 0.77-1.05, 0.80-3.23 and 0.81-2.23, respectively.Most of the samples have negative δCe anomaly values, ranging from 0.86 to 1.02.The results show that the PAAS-normalized pattern of REEs in all samples can be divided into three types:the negative, positive and normal types.An in-depth study on the dolomitization process demonstrates that the formation of the Cambrian dolomite is essentially caused by evaporation pump mechanism.In addition, the dolomite of the negative type was also under the impact of a burial environment at a later formation stage; the positive type was modified in a hydrothermal environment at a later stage; and the normal type was mainly formed under the effect of seepage reflux.In conclusion, the formation of dolomite reservoirs is conditioned by a variety of factors, including a favorable distribution of sedimentary facies as a prerequisite; large-scale dolomitization as the foundation; dissolution as the key, and the fracture systems as versatile influencers.

Key words: rare earth element (REE), geochemistry, dolomitization, dolomite, Cambrian, Well Milan 1, Tadong area, Tarim basin

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