103 / 2022-02-14 23:23:31

Types, Petrophysical Properties and Pore Evolution of Late Ediacaran Microbial Carbonates, Tarim Basin, NW China

microbial carbonate, late Ediacaran, reservoir property, pore evolution

The late Ediacaran microbial carbonates of the Tarim Basin are potential reservoir geobodies for future hydrocarbon exploration. However, no consensus has been reached regarding the types of these microbial carbonates, and little attention has been paid to the reservoir properties and pore evolution, hampering the predictions of high-quality reservoirs. Coupling petrography and in-situ U-Pb dating geochronology analysis, this study aims at clarifying the types of microbial carbonates and reconstructing the pore evolution processes of potential reservoir rocks. The late Ediacaran microbial carbonates of the Tarim Basin can be divided into four types based on different scales (macro- to micro-) of observation: microbial laminite, stromatolite, spongiomicrobialite and microbial-peloidal wackstone/mudstone. Petrophysical property results show that all these microbial carbonates have low porosity and very low permeability. Predominant diagenetic feathers include dissolution, compaction, pervasive dolomitization, cementation and fracturing. The most important reservoir spaces are vugs and solution-enlarged pores, and their formation responded to the uplift of Aksu area in the terminal Ediacaran. The fine- to medium- crystalline dolomite cement was the dominant mineral that has greatly reduced the pre-existing pores. Pore types were closely related to different microbial fabrics. This study emphasizes the importance of microbial fabrics on the pore evolution in the microbial carbonates.