For more than two centuries, the “dolomite problem” has challenged geologists and oil explorers. In 1791, French geologist Déodat de Dolomieu discovered and named the dolomite mineral in the Dolomieu mountain in Italy. These fluids caused negative shifts in the oxygen isotope compositions of the earlier dolomite.ĭolostone reservoirs are an important target for carbonate oil and gas exploration ( Dai et al., 2020 Fu et al., 2021 Liu et al., 2021 Yang et al., 2021 Yue et al., 2021). Fluids in the overlying and underlying clastic strata of the Buqu Formation were driven by the thermal hot spot during compressional tectonic setting. Cd2 has δ 13C‰ PDB of −0.09‰−3.38‰, δ 18O‰ PDB from −10.41‰ to −8.56‰, and 87Sr/ 86Sr of 0.708180–0.708876 and was related to the collisional orogeny between the Lhasa termite and the Qiangtang Basin in the late Early Cretaceous. 5) Cd1 has δ 13C‰ PDB of 3.02‰, δ 18O‰ PDB of −5.13‰, and 87Sr/ 86Sr of 0.708147 and was formed during cavern filling before the shallow-burial stage. The crystal curvature was caused by high environmental temperatures. 4) Rd4 has δ 13C‰ PDB of 3.24‰–4.14‰, δ 18O‰ PDB from −8.22‰ to −6.37‰, and 87Sr/ 86Sr of 0.707234–0.707884 and resulted from dolomitization or recrystallization at high temperatures in the medium-to deep-burial stage. Excessive dolomitization during the late shallow-burial stage caused the destruction of the dolomite crystals from euhedral to subhedral. Both were formed at low temperatures in the shallow-burial stage, when the dolomitization fluid was mainly derived from seawater. Abundant supersaturated dolomitization fluids favored the preservation of its primary dolomite texture.

2) Rd1 has δ 13C‰ PDB of 3.42‰–4.23‰, δ 18O‰ PDB from −4.22‰ to −3.37‰, and 87Sr/ 86Sr of 0.707654–0.708176 and was formed in the contemporaneous or penecontemporaneous stage at low temperatures by mimic replacement related to seawater evaporation. The dolomite filling includes fine-grained planar subhedral cave-filling dolomite (Cd1) and medium-to coarse-grained anhedral, saddle dolomite (Cd2). The primary fabric-poorly-preserved dolomite includes fine-grained euhedral dolomite (Rd2), fine-grained planar subhedral dolomite (Rd3), and medium-to coarse-grained anhedral dolomite (Rd4). The results revealed the genesis and evolution of different types of dolomite matrix and cement, as follows: 1) The dolomite texture in the study area is closely related to its formation environment and process and can be categorized as primary fabric well-preserved dolomite (Rd1), primary fabric poorly-preserved dolomite, and dolomite filling. To determine the origin of these reservoirs, petrographic study, fluid inclusion thermometry dating, and C-O and Sr isotopic dating were performed. The Qiangtang Mesozoic sedimentary basin is a new field of hydrocarbon exploration, in which the Buqu Formation dolostone reservoirs have attracted increasing attention in recent years. 3College of Earth Sciences, Chengdu University of Technology, Chengdu, China.2Chengdu Center, China Geological Survey, Chengdu, China.1Key Laboratory of Sedimentary Basin and Oil and Gas Resources, Ministry of Natural and Resources, Chengdu, China.

Youli Wan 1,2*, Jiashan Lin 1,2*, Zhan Zhao 1,2 and Zhonglin Wang 1,3

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