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Geochemical characteristics and resource potential analysis of Chang 7 organic-rich black shale in the Ordos Basin

Published online by Cambridge University Press:  19 December 2018

JIANGMIN DU ,
YANDE ZHAO ,
QINGCHUN WANG ,
YANQIU YU ,
HUI XIAO ,
XIANKUI XIE ,
YUGUO DU  and
ZIMIAO SU
JIANGMIN DU*
Affiliation:
College of Resources, Hebei GEO University, Shijiazhuang 050031, China
YANDE ZHAO
Affiliation:
BaiLie School of Petroleum Engineering, Lanzhou City University, Lanzhou 730070, China Exploration & Development Research Institute of PetroChina Changqing Oilfield Company, Xi’an 710018, China National Engineering Laboratory for Exploration and Development of Low-Permeability Oil & Gas Fields, CNPC, Xi’an, Shanxi 710018, China
QINGCHUN WANG
Affiliation:
College of Resources, Hebei GEO University, Shijiazhuang 050031, China
YANQIU YU
Affiliation:
College of Resources, Hebei GEO University, Shijiazhuang 050031, China
HUI XIAO
Affiliation:
Exploration & Development Research Institute of PetroChina Changqing Oilfield Company, Xi’an 710018, China National Engineering Laboratory for Exploration and Development of Low-Permeability Oil & Gas Fields, CNPC, Xi’an, Shanxi 710018, China
XIANKUI XIE
Affiliation:
Exploration & Development Research Institute of PetroChina Changqing Oilfield Company, Xi’an 710018, China National Engineering Laboratory for Exploration and Development of Low-Permeability Oil & Gas Fields, CNPC, Xi’an, Shanxi 710018, China
YUGUO DU
Affiliation:
Exploration & Development Research Institute of PetroChina Changqing Oilfield Company, Xi’an 710018, China National Engineering Laboratory for Exploration and Development of Low-Permeability Oil & Gas Fields, CNPC, Xi’an, Shanxi 710018, China
ZIMIAO SU
Affiliation:
College of Resources, Hebei GEO University, Shijiazhuang 050031, China
*
†Author for correspondence: Jiangmindu@sohu.com
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Abstract

The Ordos Basin is the largest and most important intracontinental sedimentary depression in China, and a significant amount of crude oil resources has developed within this Mesozoic formation. High-grade organic-rich shale is prevalent in the large-scale areas of the Chang 7 sedimentary stage and provides essential hydrocarbon resources for abundant oil enrichment in the Mesozoic. This research investigated the geochemical characteristics of Chang 7 shale using core samples and well logs and via laboratory tests. In addition, the microscopic components of the shale organic matter (OM), biological marker compounds, carbon isotopes, enrichment grade of trace elements, and elemental ratio were analysed systematically. Moreover, the aspects related to the shale OM source, sedimentary environment and resource potential were evaluated. Our results revealed that spherical alginate and calcium spherical alginate were predominant in the micropetrological components of the shale. Many biomarkers, including n-alkanes, steranes and terpanes, were detected in the gas chromatography – mass spectrometry spectra. An analysis of n-alkanes, regular sterane shapes (C21−/C22− and C26+C27/C28+C29), odd–even predominance index (OEP) and carbon preference index (CPI) values and carbon isotope distributions showed that OM was produced from aquatic organisms. The indicators of trace elements, such as Sr/Ba and V/V+Ni, combined with the biomarker compound in Pr/Ph and the gammacerane index showed the presence of a semi-deep – deep lake environment containing fresh–brackish water. In addition, the hydrocarbon conversion rate index and shale rock pyrolysis parameters revealed that Chang 7 has a high hydrocarbon generation ability and hydrocarbon expulsion efficiency.

Keywords

resource potentialgeochemical characteristicsshaleTriassic Chang 7Ordos Basin
Type
Original Article
Information
Geological Magazine , Volume 156 , Issue 7 , July 2019 , pp. 1131 - 1140
Copyright
Copyright © Cambridge University Press 2018 

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