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Zhang, X.; He, J.; Ren, Z.; Zhou, T.; Shi, S., and Zhao, Y., 2019. Paleo-lake water stratification in the Chang 7 Age of the triassic and its significance for shale gas accumulation in the Ordos Basin. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 170–177. Coconut Creek (Florida), ISSN 0749-0208. As the second largest sedimentary basin in China, the Ordos Basin experienced a peak age of paleo-lake transgression during Chang 7 Age of Triassic. The best source rocks of Mesozoic in the whole basin have been formed together with this transgression. The relationship between water stratification of the paleo-lake in Chang 7 Age and the shale development characteristics of Chang 7 formation can provide a scientific basis for researches of shale gas reservoir formation. In this paper, the paleo-climatic, depth, distribution and salinity of paleo-lake in Chang 7 Age, as well as the geochemical and mineralogical characteristics of the Chang 7 shale, are analyzed. Comparing with water stratification characteristics in present-day oceans and lakes from previous studies, the water stratification characteristics of paleo-lake in Chang 7 Age has been concluded. The water stratification was widely distributed by temperature stratification, which could lead indirectly to salinity stratification. Large areas of stably stratified water increased the abundance of organic matter, the content of brittle minerals in the shales, and resulted in well-developed laminated organic shales. All of these are of great significance to the formation of Chang 7 shale gas reservoir. [ABSTRACT FROM AUTHOR]

Zhang, X.; He, J.; Ren, Z.; Zhou, T.; Shi, S., and Zhao, Y., 2019. Paleo-lake water stratification in the Chang 7 Age of the triassic and its significance for shale gas accumulation in the Ordos Basin. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 170–177. Coconut Creek (Florida), ISSN 0749-0208. As the second largest sedimentary basin in China, the Ordos Basin experienced a peak age of paleo-lake transgression during Chang 7 Age of Triassic. The best source rocks of Mesozoic in the whole basin have been formed together with this transgression. The relationship between water stratification of the paleo-lake in Chang 7 Age and the shale development characteristics of Chang 7 formation can provide a scientific basis for researches of shale gas reservoir formation. In this paper, the paleo-climatic, depth, distribution and salinity of paleo-lake in Chang 7 Age, as well as the geochemical and mineralogical characteristics of the Chang 7 shale, are analyzed. Comparing with water stratification characteristics in present-day oceans and lakes from previous studies, the water stratification characteristics of paleo-lake in Chang 7 Age has been concluded. The water stratification was widely distributed by temperature stratification, which could lead indirectly to salinity stratification. Large areas of stably stratified water increased the abundance of organic matter, the content of brittle minerals in the shales, and resulted in well-developed laminated organic shales. All of these are of great significance to the formation of Chang 7 shale gas reservoir. [ABSTRACT FROM AUTHOR]

The Ordos Basin is an important intracontinental sedimentary basin in western China for its abundant Mesozoic crude oil resources. The southern part of the Tianhuan Depression is located in the southwestern marginal area of this Basin, in which the Jurassic and Triassic Chang-3 are the main oil-bearing strata. Currently, no consensus has been reached regarding oil source and oil migration in the area, and an assessment of oil accumulation patterns is thus challenging. In this paper, the oil source, migration direction, charging site and migration pathways are investigated through analysis of pyrrolic nitrogen compounds and hydrocarbon biomarkers. Oil source correlations show that the oils trapped in the Jurassic and Chang-3 reservoirs were derived from the Triassic Chang-7 source rocks. The Jurassic and Chang-3 crude oils both underwent distinct vertical migration from deep to shallow strata, indicating that the oils generated by Chang-7 source rocks may have migrated upward to the shallower Chang-3 and Jurassic strata under abnormally high pressures, to accumulate along the sand bodies of the ancient rivers and the unconformity surface. The charging direction of the Jurassic and Chang-3 crude oils is primarily derived from Mubo, Chenhao, and Shangliyuan, which are located northeast of the southern Tianhuan Depression, with oils moving toward the west, southwest, and south. The results show that an integration of biomarker and nitrogen-bearing compound analyses can provide useful information about oil source, migration, and accumulation. [ABSTRACT FROM AUTHOR]