关键词: 四川盆地, 凯迪期—埃隆期, 深水页岩, 层序地层, 沉积演化模式

Abstract: Shale gas is enriched in deep reservoirs in Luzhou area in southern Sichuan Basin, where the organic matter-rich marine shale in submember 1 of Member 1 of Katian Wufeng Formation and Aeronian Longmaxi Formation is the main shale gas producing layer; it is of great significance to clarify the depositional environment evolution in this area and its controlling role in organic matter enrichment for describing the accumulation mechanism of shale oil. Using the drilling, logging and well logging data, as well as the test data of major, trace and rare earth elements, this paper systematically analyzes the sequence stratigraphy and depositional environment evolution of Katian-Aeronian black shale in southern Sichuan, and establishes a state model of organic matter-enriched paleo-ocean in southern Sichuan. Based on the lithology, typical sedimentary structure, electrical properties of rock and element composition, five maximum flooding surfaces were identified from Katian stage to Aeronian stage; according to the ice age, maximum flooding surface, lithological change and graptolite belt constraint, eight fourth order sequences were divided. Under the constraint of sequence stratigraphic framework, the evolution of paleo-oxygenation facies and paleo-productivity were restored, and the substituted coefficient for identifying the paleo-oxygenation facies and paleo-productivity of high-quality shale was also established. As the shale deposited in Katian Wufeng Formation is controlled by strong stagnant water in the restricted platform, the high productivity supply at the surface is of positive significance for the development of organic matter-rich shale. Since the Rhuddanian stage, ice sheet melting during the ice age has resulted in large-scale transgressions, as well as sea level rise, thus forming a strong reducing environment with water stratification; as a result, the organic matter-rich shale is developed in the lower part of Longmaxi Formation. In the Aeronian stage, continuous marine regression continued, low sea level, sufficient terrestrial source injection, fast deposition rate and redox conditions were not conductive to the preservation of organic matters. However, the paleo-productivity was high in this stage, so that black shale with rich carbon in the upper part and high clay mineral content was formed during the short-termed transgression.

Key words: Sichuan Basin, Kadian-Aeronian, deep-water shale, sequence stratigraphy, sedimentary evolution model