## 2 Oil Shale Properties  
### Oil Shale Geology  
Oil shale is a type of sedimentary rock that contains organic matter known as kerogen, which can be converted into liquid hydrocarbons through thermal processing. It is considered an unconventional source of oil due to its low energy density and high production costs. According to the U.S. Energy Information Administration, global oil shale resources are estimated to be around 6 trillion barrels, with the largest deposits located in the United States, Russia, and China [5; 6]. Oil shale is formed through the accumulation of organic matter in fine-grained sedimentary rocks over millions of years. The organic matter, primarily composed of algae and other aquatic organisms, undergoes chemical and physical changes under high pressure and temperature, resulting in the formation of kerogen. According to a study by Dyni (2010), the organic content of oil shale can range from 3% to 60%, with higher organic content leading to greater potential for hydrocarbon production [7]. Deposits of oil-shale can be found across numerous global locations. These deposits span from the Cambrian to Tertiary periods and originated in diverse marine, terrestrial, and lake-related settings for deposition. China's major oil shale deposits are located in Fushun, Maoming, and Xinjiang, with estimated reserves of approximately 354 billion barrels [8]. These oil shale deposits are typically found in lacustrine or marine sedimentary environments and are characterized by their low permeability and fine-grained matrix. In the United States, the Green River Formation is one of the largest oil shale deposits, with an estimated 4.28 trillion barrels of in-place oil shale resources, according to a report by the U.S. Department of Energy (DOE) [9]. During the early to middle Eocene epoch, extensive lakes formed the Green River Formation's lacustrine deposits, spanning 65,000 km\({}^{2}\) throughout Colorado, Wyoming, and Utah. Closures and fluctuations in these lakes led to high salinity and varying water  
Figure 1: Scope of the oil shale review in this study. levels, which caused diverse mineral precipitation and sulfate depletion by sulfate-reducing microorganisms [10]. The warm, alkaline conditions promoted the flourishing of blue-green algae, the main contributor to the oil shale's organic content. Home to various aquatic life and surrounded by rich land ecosystems, the Green River lake system thrived for over 10 million years in a warm temperate to subtropical climate, playing a significant role in the formation of oil shale deposits. Situated in northeast China's Liaoning Province, the Fushun basin is a modest-sized, investigated Cenozoic fault basin recognized for its coal and oil shale reserves. The basin is primarily composed of Eocene swamp to lacustrine deposits belonging to the Guchengzi and Xilutian Formations and hosts Asia's most expansive opencast oil shale mine. The Eocene climate in the Fushun basin transformed from a warm temperate environment to a north subtropical one, generally transitioning from warm, humid conditions to subhumid-semiarid [10; 11]. When comparing the geology of Fushun oil shale with the Green River Formation, both basins contain Eocene lacustrine deposits. However, while the Green River Formation was marked by significant salinity fluctuations and water level variations, the Fushun basin experienced a warm, humid climate with substantial precipitation in the Jijuntun Formation before shifting to a sub-humid to semiarid climate during the Xilutian Formation. In the Fushun basin, the warm and humid climate during the Jijuntun Formation led to high initial productivity in lake water and a subsequent stable stratification. This resulted in oxygen deficiency at the bottom of the lake, facilitating the preservation of organic matter and the formation of the Jijuntun Formation's thick oil shale deposits.