中三叠世中期上扬子内克拉通古海洋环境与有机质富集模式OA

[Objective]The exploration of marlstone reservoirs represents a current frontier for expanding oil and gas resources.The recent discovery of unconventional marine oil and gas in the Lei 3-2 sub-member of the Middle Triassic Leikoupo Formation in Well CT-1 reveals a new prospective area.However,the organic matter enrichment mechanisms and exploration potential of this sub-salt lagoon marlstone remain unclear,hindering further exploration.[Methods]This study,focusing on Well CT-1 in the central Sichuan Basin,investigates the organic matter enrichment mechanism through rock mineralogy and paleo-oceanographic geochemical proxies.This study also characterizes the reservoir properties and distribution via reservoir characterization and sedimentary facies analysis to evaluate its potential.[Results]The marlstone was deposited in an anoxic,deep-water lagoon of a carbonate platform with high paleo-productivity.The enrichment of organic matter,with an average total organic carbon(TOC)content of 1.16%(reaching up to 1.78%),was co-controlled by these reducing conditions and high productivity.Analyses(CT and SEM)of the high-quality"sweet spot"intervals show that the storage space is predominantly composed of nano-to micro-scale pores and microfractures,with porosity exceeding 3%.The reservoir developed in a deep-water,marlstone-and gypsum-rich lagoon within an epicontinental sea carbonate platform.[Conclusion]The widespread distribution of deep-water lagoons during the deposition of the Lei 3-2 sub-member is associated with a maximum flooding event.Concurrently,the prevailing monsoon climate significantly enhanced weathering and nutrient input,while the overlying regressive evaporites provided a seal for long-term and efficient organic matter preservation.[Significance]Comprehensive analysis suggests that the extensively distributed,organic-rich deep-water lagoon marlstone formed during this transgression in the intracontinental sag of the Upper Yangtze Craton is not only a viable unconventional exploration target but also likely acts as a hydrocarbon source for conventional reservoirs within the Leikoupo Formation.