Oil & Gas Geology ›› 2014, Vol. 35 ›› Issue (6): 870-882.doi: 10.11743/ogg20140614

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Lithofacies, diagenesis zone and reservoir origin of the Ordovician in eastern tectonic belt of the Maigaiti slope

Qian Yixiong1, Yu Tengxiao2, Zhou Linfang1, Yue Yong2, Qiao Guilin1, You Donghua1, Shao Zhibing1, Jing Ting1   

  1. 1. Wuxi Institute of Geology, Exploration & Production Research Institute, SINOPEC, Wuxi, Jiangsu 214151, China;
    2. Exploration & Production Research Institute, Northwest Oilfield Company, SINOPEC, Urumqi, Xinjiang 830011, China
  • Received:2014-11-19 Revised:2014-11-29 Online:2014-12-08 Published:2015-01-27

Abstract: Through the detailed research of fracture style, strata feature, sedimentary facies (microfacies), diagenisis process and reservoir characteristics of two exploratory wells in carbonate rocks of Maigaiti slope, the following conclusions can be obtained. The Yingshan Formation consists of a set of intra-platform beaches-inter-beach seas of open platform, and the Penglaiba Formation consists of dolomite flat, dolomite-limestone flat and granule shoal. The diagentic processes in Lower and Middle Ordovician mainly include submarine cementation, early atmospheric fresh water dissolution and cementation, compaction and pressure solution, two periods of atmospheric water karstification, burial and hydrothermal modification. Due to the influence of multiphase tectonic movements, open and relative closed diagenetic facies could coexist in the same limestone. The open diagenetic facies feature in small thickness and multiple intervals. In contrast, the closed diagenetic facies is characterized by large thickness and less intervals. The quality of reservoir was controlled by muti-phases unconformities, faults, fractures and water-rock interaction, so the effective reservoir diagenetic sequences were submarine cementation, compaction and pressure solution-two periods atmospheric water karstification, buried dissolution and hydrothermal reformation. Karst reservoir facies zones were mainly distributed in the superimposed tectonic belt between fault fold top, folding wing or fracture with high frequency sequence boundary, and show a karstification model featuring in superimposition of vadose zone and water hole under the control of multiphase tectonic movements.

Key words: sedimentary subfacies, diagentic belt, carbonate, Ordovician, Maigaiti slope, Tarim Basin

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