Source rock characteristics of Permian Lucaogou Formation in the Jimusar Sag, Junggar Basin, northwest China, and its significance on tight oil source and occurrence

Significant progress has recently been made in tight oil exploration within the Permian Lucaogou (P2l) Formation of the Jimusar Sag. However, current tight oil exploration deployment of the P2l Formation is mainly based on reservoir prediction, which is high risk for tight oil exploration. In this study, the geological and geochemical characteristics of the P2l Formation source rocks, including the distribution, sedimentary environment, organic matter abundance, kerogen types and thermal maturity were investigated. Hydrocarbon generation and expulsion intensity were evaluated through an improved hydrocarbon generation potential methodology, and the significance of source rocks in tight oil source and occurrence was systematically investigated. Results indicate that P2l Formation source rocks with total organic carbon >1.0 wt% occur widely (an area up to 1500 km2), are thick (up to 160 m), were deposited in a lacustrine weakly reducing sedimentary environment with relatively low salinity, have a high total organic content with a mean value of 3.12 wt%, are dominated by type II kerogen and have reached the early mature to mature stage. Modelling results indicate that the source rocks reached the hydrocarbon generation threshold and hydrocarbon expulsion threshold at 0.48% and 0.86% vitrinite reflectance, respectively. The comprehensive hydrocarbon expulsion efficiency was approximately 30%, and the maxima of hydrocarbon generation and expulsion intensities for P2l Formation source rocks are 1200 × 104 and 425 × 104 t/km2. The tight oil is sourced from adjacent source rocks that are interbedded with, or are close to, the reservoirs. The migration of oil generated from the source rocks occurs over very short distances. The oil filling degree index (oil bearing thickness/P2l Formation thickness) is higher at a closer proximity to the source rocks, and where it is higher the hydrocarbon generation intensity of the source rocks is also elevated. In addition, the greater the hydrocarbon expulsion intensity of the source rocks, the higher the daily oil production values (ton/day) from prospect wells. Copyright © 2016 John Wiley & Sons, Ltd.

Cenozoic tectonic evolution of the Tibetan Plateau – the Nepal Himalaya and the provenance of their foreland basins

The Tibetan Plateau and the Himalayan region formed after 55–50 Ma, as a result of the intracontinental collision of the Indian and Eurasian plates, occupying the east–west trending, high‐altitude Himalaya and Karakorum ranges in the south and the vast Tibetan Plateau to the north of central Asia. The tectonic evolution of Tibet began between the late Palaeozoic and the Cenozoic, and the Himalayan mountain system evolved in a series of stages beginning 50–35 Ma and is still active.
Active tectonics significantly affect upheaval and the rate of erosion in the Himalaya. Therefore, different foreland basins of the Tibetan Plateau (e.g. the Lhasa terrane, the Hoh Xil Basin, the Qaidam Basin, and the Jiuquan Basin) and the Himalayan foreland basins (e.g. Gondwanaland Basin and the Siwalik and Quaternary basin) experience direct effects in terms of tectonic and sedimentary evolution. For the tectonic evolution and provenance analysis of foreland basins in the Tibetan Plateau and the Nepal Himalaya, researchers have adopted various techniques in past studies: This paper discusses petrography, U–Pb geochronology, and seismic reflection.
Provenance analyses have illustrated that the sediments of the Southern Tibetan foreland basin (i.e. the Lhasa terrane) derive from the Qiangtang, Tethys Himalaya, and southwest Australia. Similarly, the sediments of the Central Tibetan basin derive from the Qilian, Kunlun‐Qimantagh, and the Altyn Mountains; the sediments of northern side of the Tibetan foreland basin, from Qilian Shan Mountain; and the sediments of the Nepal Himalayan foreland basin, from the Tethys, Higher, and Lesser Himalaya. Copyright © 2016 John Wiley & Sons, Ltd.

Stratigraphic correlations and occurrence patterns of two sets of Lower Cretaceous black shales in coastal southeastern China and geological implications: insights from zircon U–Pb ages

Lower Cretaceous black shales in coastal southeastern China are of significance to the geological study of the Pacific tectonic domains. However, the stratigraphic correlations and occurrence patterns of the shales have not been well constrained so far. To address these limitations, 131 new zircon U–Pb dates were obtained from the tuff layers, which were interlayered with the shales from four outcrops. In combination with previously reported geochronological data, the stratigraphic correlations and occurrence patterns of the black shales were discussed. Results show that the black shales in the Shuidishan Formation (~145 Ma) in the Dayawan section, northern Guangdong, are older than those in the lower part of the Bantou Formation (~132 Ma) in the northward Yong’an section, southern Fujian, whereas they are roughly isochronous to the base of the Bantou Formation (~144 Ma). In contrast, the black shales in the upper part of the Bantou Formation (~117 Ma) from the Yong’an section in northwestern Fujian and the black shales in the Shixi Formation (~117 Ma) from the Yiyang section in northeastern Jiangxi can be isochronously correlated with the black shales in the Bantou Formation (~117 Ma) from the Chong’an section in northwestern Fujian, and they are slightly older than those in the Guantou Formation (~113 Ma) from the Shangzhang and Xiahuyuan sections in western Zhejiang. Black shales in Units I and II of the Shipu Group (~113–109 Ma) in northeastern Zhejiang can be isochronously correlated with those in the Guantou Formation (~113–106 Ma) in western Zhejiang. These new stratigraphic correlations indicate that the Lower Cretaceous black shales in coastal southeastern China can be divided into two regional‐scale sets. The first set was deposited during the early Early Cretaceous (Berriasian–Hauterivian) and is diachronous (i.e. 144 ± 2 Ma in the Dayawan section and 132 ± 2 Ma in the Yong’an section). The second set of black shales was deposited during the later Early Cretaceous and was roughly isochronous (~117 Ma). These results imply that the processes of the Pacific plate subduction in coastal southeastern China during the Early Cretaceous varied in two distinct stages that are identified by two volcanic–black shale cycles (i.e. ~145–120 and ~120–100 Ma). The distribution of the first set of black shales may extend to offshore basins in the South China Sea, whereas the second set may extend to the Taiwan Strait. Both sets are likely to be potential petroleum prospects. Copyright © 2016 John Wiley & Sons, Ltd.