Geochemical studies on high-efficiency hydrocarbon expulsion of Triassic lacustrine shale in the Ordos Basin, China: implications for tight and shale oil accumulation. Issue 1 (November 2020)

• Record Type: Journal Article
• Authors: Yang, Weiwei; Zhang, Wenzheng; Li, Shixiang; Li, Shanpeng
• Is Part Of: IOP conference series. Volume 600:Issue 1(2020)
• Publication Date: 2020-11
• Subjects: Earth sciences -- Periodicals; Environmental sciences -- Congresses; Environmental sciences -- Periodicals; 550.5
• DOI: 10.1088/1755-1315/600/1/012044
• Languages: English
• ISSNs: 1755-1307

Abstract

Abstract: The organic-rich sediments developed at the bottom of Chang7 Member of the Upper Triassic Yanchang formation, which can be divided into oil shale and black mudstones, are dominate source rocks for low permeability and tight oil reservoirs in Mesozoic petroleum system of Ordos Basin. The hydrocarbon expulsion characteristics of the organic-rich sediments have been investigated by geology and geochemistry data. By comparison with the geochemical parameters of crude oil samples and mudstone extracts, Chang7 shale has many geochemical evidences on high rates of hydrocarbon expulsion. Lower conversion rate of chloroform extracted bitumen "A", especially for the samples with TOC higher than 10%; lower productivity indexes and lower hydrogen indexes reducing with TOC increasing; lower ratios of saturates/aromatics but higher contents of polar components for residual bitumen "A"; heavier stable carbon isotopes of residual hydrocarbons. It should be noted that the source rock evaluation and oil-source correlation would be misunderstood based on these abnormal geochemical data caused by high-efficiency hydrocarbon expulsion. Calculation for rock samples have shown that the expelled rates of the shale samples averaging 70% are significantly higher than those of the mudstone samples. Chang 7 shale with large amounts of hydrocarbons generated and expelled is critical for hydrocarbon accumulation in low-permeability and tight oil reservoirs. Also, Chang7 organic-rich rocks is an important exploration field of shale oil in the future.