Hanson, Andrew D.1, Bradley D. Ritts2
(1) University of Nevada Las Vegas, Las Vegas, NV
(2) Utah State University, Logan, UT
ABSTRACT: Oils and Source Rocks of the Ordos Basin, North-Central China
Outcrop samples from the eastern and western margins of the Ordos basin were analyzed
in order to assess their potential as hydrocarbon source rocks. Total organic carbon (TOC)
content and Rock-Eval analyzes were performed on a total of fifty-nine samples. Vitrinite
reflectance (Ro) analyses were performed on twelve samples. Most samples are lacustrine
mudstones but other samples include fluvial or deltaic mudstones and coals. Two limestones
were also analyzed.
Geochemical parameters suggest that most samples would generate gas if they were to generate any hydrocarbons. Four Upper Triassic and Middle-Upper Jurassic mudstones have values indicating they would generate oil. The Ro values for six samples from western Ordos (0.95-2.25) are, on average, more mature than samples from eastern Ordos (0.51-1.37). Upper Triassic samples are close to the oil window whereas the Jurassic samples are still slightly immature. However, these may be effective source rocks where buried deeper in the basin.
We also collected fifteen oil samples from throughout the basin. Most are dark brown-black, waxy oils that solidify at room temperature. A few samples are lighter in color and do not solidify at room temperature. Molecular organic geochemical studies indicate that although there are differences in the suite of oils we analyzed, particularly with regards to maturity, they are similar enough to be lumped into one genetic family. Biomarkers indicate the oils are derived from clay-rich source rocks containing terrestrial plant organic matter deposited in suboxic environments. Oil-source rock studies link the oils to Triassic source rock samples.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.