Abstract
Clarifying the origin of dolomite and its impact on reservoirs in ultra-deep carbonates is essential for petroleum exploration. This study investigates Middle-Lower Ordovician dolomites in the Shunnan area, Tarim Basin, using petrography, geochemistry, fluid inclusions, and in-situ U-Pb dating. Four dolomite types are identified: stylolite-associated (DAS), microfracture-filling (DAMF), vug-filling (FMD and saddle dolomite, SD), and matrix dolomite (MD). Geochemical signatures indicate dolomitizing fluids derived from seawater, shallow to deep burial formation waters, and Mg-rich hydrothermal sources. U-Pb ages define a paragenetic sequence from Caledonian to early Hercynian: FMD (462 ± 13 Ma), DAS (449 ± 32 Ma), MD (420 ± 19 Ma), DAMF (355 ± 18 Ma), and SD (352 ± 13 Ma). Corresponding genetic mechanisms include mixed-water, shallow-burial, deep-burial, and hydrothermal dolomitization. Reservoir analysis reveals that MD enhances both porosity and permeability, DAMF and vug-filling dolomites significantly improve permeability, whereas DAS degrades reservoir quality. This work innovatively constrains the multi-stage dolomitization history and fluid evolution in an ultra-deep setting, providing a predictive framework for reservoir quality and supporting hydrocarbon exploration in tight carbonate sequences of the Tarim Basin.
Paper Information：
Jian Wang, Mingyu Tang, Mingfeng Xie, Yingchang Cao, Dongping Tan, Jun Han. Origin and reservoir response of dolomites in ultra-deep limestone formations: Insights from the Middle-Lower Ordovician in the Shunnan area, Tarim basin. Marine Geoscience and Energy Resources, 2026, 193: 207836. https://doi.org/10.1016/j.marger.2026.207836
