Milankovitch cycle of continental deep-water fine-grained sedimentary rocks in the lower submember of Es3 of Well FY1 in Dongying Sag and its significance for shale oil exploration

Abstract

China has recently faced significant difficulties in the exploitation of its shale oil and gas resources. An essential geological obstacle preventing the breakthrough of Chinese shale oil exploration is the precise identification of productive oil and gas pools and ideal formation. Therefore, it is crucial to examine the properties of shale reservoirs. Deep-water fine-grained sedimentary rocks in the lower member of the Well FY1 in Dongying Sag are analyzed using the Milankovitch cycle based on core, geochemical analysis, and gamma logging data. The findings demonstrate that: (1) The entire Milankovitch cycle is preserved in the Es3x of Well FY1 in Dongying Sag, and that the long Eccentricity of 405 ka and the Precession cycle of 23.2 ka are the key controlling factors in the deposition. (2) The “three-end-member” method is used to divide eight different types of lithofacies. The main vertical changes in these lithofacies are from organic massive gray mudstone to organic lamellar callitic mudstone to organic massive gray mudstone to organic lamellar gray mudstone to organic lamellar gray mudstone and back again. From shallow to deep to deeper, the entire water depth fluctuated. (3) Each of the four lengthy Eccentricity cycles has a half-cycle of warm, humid weather and cold, dry weather. Analysis was done on how the lithofacies and organic matter concentration changed with high and small eccentricities. The enrichment of biological materials in warm, wet, dry, and cold climates was hypothesized by examining the response of fine-grain sedimentary rocks to eccentricities and Precession periods. Larger Eccentricity is thought to be more suitable for storing shale oil.