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Geochemical Characteristics and Estimation of Gas Content of the Low-middle Mature Continental Shales: A Case Study from the Ordos Basin

Tang, Xuan; Jinchuan, Zhang; Wang, Xiangzeng; Yang, Yiting; Yu, Yixing; Wang, Long; Xiong, JInyu

Widespread continental shales are the primary source rocks for the large-sized oil fields in the middle and eastern China, where conventional oil production accounts for beyond two thirds of total petroleum production in China. With the success of the shale gas development in the USA, Chinese oil industry naturally turns their eyes on the continental shales in the middle and eastern China, which are characterized by high clay mineral content, rich organic matter abundance, presently still in the oil to wet gas windows, relative lower thermal mature than those thermogeous gas shales already successively developed successively in the Unite States.. Kerogn in that thermal maturity stage are supposed not to generate gas in large amount. In reality, some vertical wells were drilled recently in the continental shales in the Ordos Basin and produced up to 3000 m3 per day by fracturing, which shows significant gas resource potential, which remind us re-examining the gas generation mode and potential in low thermal mature continental shale.

The Rock Eval (RE) pyrolysis is employed to study geochemistry of deep lacustrine shale samples from Chang-7 and Chang-9 Member of the Triassic Yanchang Formation in the southeastern part of the Ordos Basin. The results show that clays mineral account for 40% to 60% among the whole mineral compositions, vitrinite reflectance value range from 0.7% to 1.5%, Kerogen being predominantly Type II-III, and an organic abundance (TOC value) average 1.5% -4%. Isotope data shows the gas in the Chang-7 and Chang-9 member is thermogenic in origin and appears to be cogenerated with oil. Gas content amount to 3.62m3/t-5.97m3/t, in which gas absorbed amount to 46.8%-55.2%. Oil volume retained in the shale range from 5.5-7.5kg/t. Heating and pressing simulation experiments are carried out to exam the evolution of organic matter and its product, which provide mode and key parameters for predicting shale gas and oil resource and evaluate their possible producing ability.


AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013