Pore-fillings of dolomite reservoirs in Sinian Dengying Formation in Sichuan basin

Abstract

The Sinian Dengying Formation in the Sichuan basin is an important potential reservoir for oil and gas exploration in the periphery of the Sichuan basin. Its reservoirs were well developed. And many kinds of fillings which lead to the decrease of pores can be seen in reservoir pores and caves. In this paper, the pore fillings of the Dengying Formation reservoir in Sichuan basin are the object of study. The types and characteristics of the fillings are studied in detail by means of rock slices analysis, cathode luminescence, trace elements and inclusion temperature measurement. The study shows that the fillings include dolomite fillings and siliceous quartz fillings and bitumen fillings. Among them, dolomite fillings can be divided into botryoidal dolomite fillings, foliated dolomite fillings, finely-medium crystalline dolomite fillings and coarse crystalline dolomite fillings. 50%-80% of the pores are filled by the dolomite fillings with botryoidal structure, and the pores can be partially full filled; 0%-20% of pores are filled by foliated dolomite fillings; 20-80% of the pores are filled by finely-medium dolomite fillings; 20-80% of the pores are filled by coarse crystalline dolomite fillings. 1%-5% of secondary pores are often filled by siliceous quartzs, and the pores can be partially full filled. Bitumen fillings often occur after the above-mentioned fillings, and the residual pores are often semi-filled by bitumens, which makes the original pores and throat smaller and reduces the effective porosity and permeability of the reservoir. So, it is a destructive diagenesis. The pore fillings make the secondary porosity in the reservoir significantly lower, which is not conducive to the formation and preservation of the Dengying Formation reservoir.

Keywords

Pore fillings / Reservoir / Dengying formation / Sichuan basin

Acknowledgements

This research was supported by National Science and technology major project (2017ZX05001001-002), PetroChina Innovation Foundation (2018D-5007-0105), Open Fund of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Chengdu University of Technology) (PLC20180304), open fund of Shandong Provincial key laboratory of Depositional mineralization (No. DMsMzO1TO35) and scientific research starting project of SWPU (No. 2017QHZ005).

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