摘要:
[Objective] The carbonate content is high in the source rocks of the Permian Pusige Formation in the southwestern depression of Tarim Basin, and the relationship between carbonate and organic matter remains unclear. This has hindered the evaluation of their potential for hydrocarbon generation.[Methods] Through analysis using techniques such as core examination, thin section analysis, scanning electron microscopy (SEM), whole-rock X-ray diffraction (XRD), and geochemical studies, this research investigates the storage state and origin of carbonate, the distribution patterns of organic matter, and the relationship between carbonate and organic matter in the source rocks of the Permian Pusige Formation located at the peripheral areas of Kekeya in the southwestern depression of Tarim Basin. [Results] The source rocks of Permian Pusige Formation primarily exhibit three lithofacies associations: sand-mud, gray-mud, and sand-gray-mud. Calcite in the source rock mainly exists as cement and particles, displaying a multi-scale cycloidal feature of increasing and then decreasing from bottom to top within each “sand-gray-mud” cycle. The sources of carbonate include: 1) detrital particles derived from ancient continental sediments; 2) intra-depositional detritus or carbonate laminae; and 3) cementation or replacement products formed during the diagenetic phase. By conducting detailed analysis of the multi-scale cyclothem sequences, it was observed that organic matter tends to accumulate at the tops of these sequences. The main hydrocarbon-bearing intervals could be the laminites at the top of each cyclothem. Geochemical analysis revealed a strong negative correlation between carbonate minerals like calcite and Rock-Eval parameters such as TOC (Total Organic Carbon), PG (Pyrolytic Hydrocarbon Generation Potential), and HI (Hydrogen Index), reflecting a pattern of high calcium and low Rock-Eval parameters. The underlying cause is that calcium primarily resides in sandstone and calcitic layers at the cycle's base and middle sections, where stronger hydrodynamic conditions during deposition were unfavorable for organic accumulation and preservation. [Conclusion] The high-calcium source rocks within multi-scale "sand-gray-mud" cycles may possess unique characteristics pertaining to hydrocarbon generation conditions, expulsion efficiency, and oil/gas migration processes, indicating a substantial potential for hydrocarbon generation in the source rocks of Permian Pusige Formation in the Kekeya.
Abstract:
[Objective] The carbonate content is high in the source rocks of the Permian Pusige Formation in the southwestern depression of Tarim Basin, and the relationship between carbonate and organic matter remains unclear. This has hindered the evaluation of their potential for hydrocarbon generation.[Methods] Through analysis using techniques such as core examination, thin section analysis, scanning electron microscopy (SEM), whole-rock X-ray diffraction (XRD), and geochemical studies, this research investigates the storage state and origin of carbonate, the distribution patterns of organic matter, and the relationship between carbonate and organic matter in the source rocks of the Permian Pusige Formation located at the peripheral areas of Kekeya in the southwestern depression of Tarim Basin. [Results] The source rocks of Permian Pusige Formation primarily exhibit three lithofacies associations: sand-mud, gray-mud, and sand-gray-mud. Calcite in the source rock mainly exists as cement and particles, displaying a multi-scale cycloidal feature of increasing and then decreasing from bottom to top within each “sand-gray-mud” cycle. The sources of carbonate include: 1) detrital particles derived from ancient continental sediments; 2) intra-depositional detritus or carbonate laminae; and 3) cementation or replacement products formed during the diagenetic phase. By conducting detailed analysis of the multi-scale cyclothem sequences, it was observed that organic matter tends to accumulate at the tops of these sequences. The main hydrocarbon-bearing intervals could be the laminites at the top of each cyclothem. Geochemical analysis revealed a strong negative correlation between carbonate minerals like calcite and Rock-Eval parameters such as TOC (Total Organic Carbon), PG (Pyrolytic Hydrocarbon Generation Potential), and HI (Hydrogen Index), reflecting a pattern of high calcium and low Rock-Eval parameters. The underlying cause is that calcium primarily resides in sandstone and calcitic layers at the cycle's base and middle sections, where stronger hydrodynamic conditions during deposition were unfavorable for organic accumulation and preservation. [Conclusion] The high-calcium source rocks within multi-scale "sand-gray-mud" cycles may possess unique characteristics pertaining to hydrocarbon generation conditions, expulsion efficiency, and oil/gas migration processes, indicating a substantial potential for hydrocarbon generation in the source rocks of Permian Pusige Formation in the Kekeya.
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