Dolomitization and Main Controlling Factors of Penglaiba Formation Reservoir in Tarim Basin

doi:10.7657/XJPG20250404

Abstract

Abstract:

The dolomites in the Lower Ordovician Penglaiba formation in the Tarim Basin have undergone a complex diagenetic evolution characterized by multi-stage and multi-genesis. To systematically study their petrological features, dolomitization mechanisms, and main factors governing reservoir quality, investigations were conducted using outcrops, core samples, thin sections, and geochemical tests. The results show the presence of four major dolomite types in the Penglaiba formation, including micritic dolomite, fine- to medium-grained dolomite, coarse-grained dolomite, and porphyritic dolomite, all of which are genetically controlled by penecontemporaneous-shallow burial and burial dolomitizations. Fine- to medium-grained dolomites display abundant intercrystalline pores with high euhedral degree, whereas coarse crystalline dolomites retain some intercrystalline pores and have strong compaction resistance. The dolomites generally formed through replacement or recrystallization under burial conditions, with Early Ordovician seawater serving as the primary dolomitizing fluid, variably modified by deep hydrothermal fluids and evaporite-derived brines. Grain-shoal deposits provide the most favorable sedimentary microfacies for reservoir development because the early intergranular pores not only act as pathways for fluid migration but also serve as initial storage space, thereby accelerating dolomitization. Sea-level fluctuations modulated the physical and chemical conditions of dolomitization by altering hydrodynamic regimes, fluid-migration patterns, and the karstification processes. Palaeogeomorphic highs experienced more intense dolomitization, and well-developed stratiform dissolution pores and vugs provide favorable conditions for high-quality reservoirs. These insights provide a sound basis for deep dolomite exploration in the Ordovician strata of the Tarim Basin, clarify dolomitization mechanisms and main reservoir-controlling factors, and offer practical guidance for future exploration and development.

Key words: Tarim Basin, Penglaiba formation, dolomite, dolomitization, carbon and oxygen isotopes, strontium isotope, controlling factor

CLC Number:

TE122

YAN Bo, LUO Fuwen, CAO Yang, CHENG Linfeng. Dolomitization and Main Controlling Factors of Penglaiba Formation Reservoir in Tarim Basin[J]. Xinjiang Petroleum Geology, 2025, 46(4): 419-428.

Figures/Tables 7

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