Organic Geochemical Characteristics of the Upper Cretaceous Qingshankou Formation Oil Shales in the Fuyu Oilfield, Songliao Basin, China: Implications for Oil-Generation Potential and Depositional Environment

Abstract

The Cretaceous Era has always been a focus of geologic and palaeoenvironmental studies. Previous researchers believed that the impact of the global carbon cycle represents significant short-term global biogeochemical fluctuations, leading to the formation of a large number of organic rich sediments in the marine environment. During the Turonian, a large number of organic-rich oil shales were deposited in the lakes of the Songliao Basin in the Qingshankou Formation. How the depositional environment affected the formation of oil shales in continental lakes and the characteristics of these oil shales remain controversial. In this paper, through sampling of Qingshankou Formation strata, various testing methods are used to provide a variety of new data to study the characteristics of oil shales and palaeoenvironment evolution history in the Songliao Basin. The research of the sediments in the Qingshankou Formation in the Fuyu oilfield, Songliao Basin, via result analysis revealed that the oil shales possess an excellent oil-generation potential with moderate-high total organic carbon (TOC) levels (0.58–9.43%), high hydrogen index (HI) values (265–959 mg hydrocarbons (HC)/g TOC), high extractable organic matter (EOM) levels (2.50–6.96 mg/g TOC) and high hydrocarbon fractions (48–89%). The sources of the organic matter were mainly zooplankton, red algae and higher plants (including marine organisms). The aqueous palaeoenvironment of the Qingshankou Formation was a saline water environment with a high sulfate concentration, which promoted an increase in nutrients and stratification of the water density in the lake basin. Oxygen consumption in the bottom water layer promoted the accumulation and burial of high-abundance organic matter, thus forming the high-quality oil shales in the Qingshankou Formation. The global carbon cycle, warm-humid palaeoclimate, dynamic local biogeochemical cycling and relative passive tectonism were the most likely reasons for the TOC increase and negative δ13Corg deviation.

Geochemical Characteristics and Oil Generation Potential Evaluation of Lower Cretaceous Xiahuapidianzi Formation Shale in the Southeastern Sankeyushu Depression, Tonghua Basin: Evidence from Shale Pyrolysis Experiments and Biomarkers

“…Previous studies have shown that the conventional steroids C 27 , C 28 , and C 29 are all specific to different types of organic matter sources, and the relative proportions of these compounds can be used to study the contributions of various organic matter sources in shale oil. − The proportions of the C 27 , C 28 , and C 29 (C 29 : 40–64%, average 49.7%; C 28 : 17–26%, average 22.7%; and C 27 : 12–38%, average 27.5%; Table ; Figure ) were calculated for the Xiahuapidianzi formation. Previous studies on the specificity of the organic matter sources for the steroids C 27 , C 28 , and C 29 have found that C 27 steroids are from zooplankton and red algae; C 28 steroids are believed to be from diatoms, green algae, and higher plants; and C 29 steroids are from higher plants, some brown algae and green algae. ,,− In the light of the relative contents of the steroids C 27 , C 28 , and C 29 , it is speculated that the source rock samples from the Xiahuapidianzi formation are dominated by plankton and higher plants and may include some marine organic matter …”

“…Projection plot of Pr/Ph and C 27 /C 29 regular steranes . Adapted with permission from ref , copyright 2015.…”

“…Projection plot of Pr/Ph and C 27 /C 29 regular steranes . Adapted with permission from ref , copyright 2015. College of Construction Engineering, Jilin University, Changchun, China; Youhong Sun.…”

Sequence Stratigraphy and Geochemistry of Oil Shale Deposits in the Upper Cretaceous Qingshankou Formation of the Songliao Basin, NE China: Implications for the Geological Optimization of In Situ Oil Shale Conversion Processing

“…A significant amount of recent research has focused on the development of environmentally friendly and effective technologies and approaches for in situ conversion processing (ICP) [1,4,5]. The in situ conversion processing (ICP) of oil shale underground at the depth ranging from 300 to 3000 m is a physical and chemical process caused by using horizontal drilling and electric heating technology, which converts heavy oil, bitumen, and various organic matter into light oil and gas in a large scale, which can be called "underground refinery" [1].…”

“…Previous research has indicated that the oil yield during the ICP of oil shales is affected by the oil shale layer thicknesses and brittleness, and the abundance, type, and maturity of organic matter (OM). Therefore, this study focuses on the distribution of these oil shales within the sequence stratigraphic framework of the basin, the mineralogy of the oil shales, and the organic geochemical characteristics of the OM within these units, all of which are key for successful ICP [4][5][6][7][8]. The sequence stratigraphy of the study area can determine the distribution of source rocks by analyzing eustatic lake level changes with depth [9,10], providing a guide for future exploration.…”