Oil & Gas Geology ›› 2021, Vol. 42 ›› Issue (5): 1089-1097.doi: 10.11743/ogg20210507

• Petroleum Geology • Previous Articles     Next Articles

Source rock characterization: The dark mudstone in Chang 7 Member of Triassic, central Ordos Basin

Yaxiong Zhang()   

  1. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China
  • Received:2021-03-25 Online:2021-10-28 Published:2021-10-26

Abstract:

The seventh member of Yanchang Formation (Chang 7 Member) in Ordos Basin is typical lacustrine dark mudstone, which slims down while approaching lake rim at the central part of the basin.The study of source rocks, especially the dark mudstone as source rock in that part, has been very limited due to its thinness.Dark mudstone samples from 15 exploration wells in the area are collected and analyzed through core observation, TOC determination, rock pyrolysis, GC-MS and organic carbon isotope analysis.The results indicate a sedimentary environment of weak reduction and oxidation with mixed inputs of plankton and terrestrial plants for the dark mudstone and provide parameters that define the dark mudstone as a good source rock: high TOC (averaged at 2.39%), type Ⅱ2 and type Ⅲ dominated organic matter with an average S1+S2 at 7.65 mg/g, and moderate thermal evolution with Ro averaged at 0.98%.The total hydrocarbon generation amount, hydrocarbon expulsion amount and residual hydrocarbon amount of the dark mudstone are respectively measured to be 793, 337 and 456 million tons.And the comprehensive hydrocarbon expulsion efficiency is 42.50%.The contribution ratio of dark mudstone and shale to the oil and gas resources in the area is 1:1.8.All indicate great source rock potential of the stone.

Key words: dark mudstone, shale, source rock, Yanchang Formation, Ordos Basin

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