Genesis of Dolomitization of Permian Maokou Formation in Langzhong Area, Northeastern Sichuan Basin

doi:10.7657/XJPG20200201

Abstract

Abstract:

As an important oil and gas reservoir in Langzhong area of northeastern Sichuan basin, the second member of Permian Maokou formation is primarily composed of dolomite. There is no general understanding on dolomite genesis due to limited research literatures. Based on thin section authentication, cathodoluminescence analysis, quantitative analysis on inclusions and isotopes of carbon, oxygen and strontium, and combined with regional geological setting, the paper studies the petrologic and geochemical features of the dolomite in the second member of Maokou formation in Langzhong area, and discusses the genesis and significance of the dolomite. The results show that the dolomite in the study area is dominated by fine-medium crystalline, automorphic-semi-automorphic dolomite with relatively flat surface, which indicates the temperature of diagenetic environment was not high. The fine-medium crystalline dolomite in the study area is characterized by dark cathodoluminescence, low positive value of δ ¹³C and high negative value of δ ¹⁸O, ⁸⁷Sr/ ⁸⁶Sr slightly higher than that of the seawater of the same period, indicating a shallow burial and unobvious influences of high-temperature fluid. The fluid in the dolomitized rocks came from the seawater of the shallow-burial period, took grain-limestone as a carrier and then laminar and layered dolomite formed. Large scale reservoir spaces formed due to the dolomitization in the shallow-burial period, which is one of the most important diagenetic modes of carbonate reservoirs.

Key words: northeastern Sichuan basin, Langzhong area, Maokou formatin, dolomitization, geochemistry, reservoir genesis

CLC Number:

TE112.23

LI Rong, HU Hao, SHI Guoshan, XI Chengwei. Genesis of Dolomitization of Permian Maokou Formation in Langzhong Area, Northeastern Sichuan Basin[J]. Xinjiang Petroleum Geology, 2020, 41(2): 127-132.

Figures/Tables 6

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