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This study investigates the importance of multiple organic–inorganic interactions on heterogeneous carbonate cementation patterns in Silurian deeply buried sandstones, central Tarim Basin, north‐western China, to evaluate their effects on reservoir quality. Petrographic observations and mineral geochemistry identify two stages of carbonate cementation: (i) eogenetic, poikilotopic blocky calcite precipitated at 20 to 50°C (δ13CVPDB from −0.3‰ to +6.8‰; δ18OVPDB between −6.6‰ and −2.9‰) and dolomite precipitated at 40 to 62°C (δ13CVPDB from +1.9‰ to +5.3‰; δ18OVPDB between −6.2‰ and −2.1‰); and (ii) mesogenetic, isolated pore‐filling ankerite formed at 70 to 120°C (δ13CVPDB from −14.4‰ to −6.6‰; δ18OVPDB between −11.6‰ and −7.8‰). The eogenetic carbonates are predominantly distributed as carbonate‐cemented beds or concretions along sandstone–mudstone contacts and were derived mainly from microbial methanogenesis of organic matter and dissolution of carbonate minerals in adjacent calcareous mudstones. The mesogenetic ankerite cements occur predominantly as carbonate‐cemented beds, concretions and patches, and are more concentrated in the central sections of sandstone bodies. It is inferred that ankerite cements were sourced from dissolution of eogenetic calcite and dolomite via in situ generation of organic CO2 related to thermal decarboxylation of organic acids within sandstones. Kinetic modelling results coupled with petrographic observations illustrate that mesogenetic dissolution of eogenetic calcite and dolomite cements did not enhance total reservoir porosity due to re‐precipitation of ankerite cements on a very local scale within sandstone bodies. The development of extensively carbonate‐cemented geometries (beds, concretions and patches) created by different generations of carbonate cements derived from external sources, led to reservoir heterogeneity and significant destruction of sandstone reservoir quality especially during diagenesis. The results of this study demonstrate the importance of multi‐stage, intra‐formational mass transfer induced by concentration gradients during organic–inorganic interactions in mediating a variety of spatial patterns of carbonate cementation under different diagenetic regimes. Better insights of these organic–inorganic interactions in a coupled sandstone–mudstone system could improve predictive models of heterogeneous diagenetic alterations in deeply buried sandstones of similar origin. [ABSTRACT FROM AUTHOR]

This study deciphers the origin and distribution of multiphase carbonate cementations and assesses their implications for reservoir quality of the Eocene delta hydrocarbon sandstones in the Bohai Bay Basin. Petrographic observation and stable isotopic analysis identified two phases of carbonate cementations: (1) eodiagenetic phase including non-ferroan calcite cement precipitated at 25–42 °C (δ13C VPDB : 1.0‰ to +5.7‰ and δ18O VPDB : 10.7‰ to −7.5‰); and (2) mesodiagenetic phase which includes ferroan calcite cement (δ13C VPDB : 11.8‰ to −5.7‰ and δ18O VPDB : 17.0‰ to −12.6‰) and ankerite cement (δ13C VPDB : 13.7‰ to −5.9‰ and δ18O VPDB : 17.1‰ to −12.4‰) precipitated at 90–134 °C. The eodiagenetic non-ferroan calcite cement that is mainly sourced from microbial methanogenesis of organic matter in adjoining mudrocks, extensively cemented at or near sandstone-mudstone contact. Mesodiagenetic ferroan carbonate cements are derived from predominantly thermal decarboxylation of organic acids and subordinate dissolution of eodiagenetic calcite cements in sandstones. These ferroan carbonates are preferentially concentrated at distances of 0.5–1.0 m from sandstone-mudstone contacts. Kinetic modelling reproduces evolution pathways of different diagenetic minerals in the Es4s sandstones (the upper part of the fourth member of the Eocene Shahejie Formation). More importantly, results of modelling reveal that the dissolution of non-ferroan calcite cements would not enhance total reservoir quality due to the precipitation of more stable ferroan calcite and ankerite cements. Therefore, the occurrence of multi-phase carbonate cementations at different sections of sandstones leads to significant destruction of porosity and reservoir heterogeneity during progressive diagenesis. • The fan-delta sandstones in Es4s interval are important hydrocarbon reservoirs. • The eodiagenetic non-ferroan calcite and the mesodiagenetic ferroan carbonate cements are identified. • Different generations of carbonates are mainly sourced from the alteration of organic matter in the adjacent mudstone. • Kinetic modeling reproduces evolution pathways of different diagenetic minerals. • The multi-phased carbonate cementations lead to significant destruction in the reservoir quality. [ABSTRACT FROM AUTHOR]