--> Abstract: Abiogenic Alkane Gas Fields in the Xujiaweizi Fault Depression, Songliao Basin, China, by Jinxing Dai, Jian Li, Caineng Zou, Shuichang Zhang, Maowen Li, Xia Luo, Guoyi Hu, Yunyan Ni, Zhiqiang Feng, and Zihui Feng; #90078 (2008)

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Abiogenic Alkane Gas Fields in the Xujiaweizi Fault Depression, Songliao Basin, China

Jinxing Dai1, Jian Li1, Caineng Zou1, Shuichang Zhang1, Maowen Li2, Xia Luo1, Guoyi Hu1, Yunyan Ni1, Zhiqiang Feng3, and Zihui Feng3
1Research Institute of Petroleum Exploration and Development, PetroChina, Beijing, China
2Geological Survey of Canada, 3303-33 Street, Calgary, AB, Canada
3PetroChina Daqing Oilfield Company, Daqing, China

Recent gas discoveries in the Xujiaweizi fault depression of the Songliao Basin, 60 kms east of the Daqing oil field, are both economically and scientifically significant, as their chemical compositions of these alkane gases bear strong signatures for an abiogenic origin. This NNW-SSW trending depression, with an area of 3079km2, contains at least three deep seated basement faults (Xuxi, Xuzhong and Xudong), with oil-prone source rocks being developed in the Upper Cretaceous strata and gas-prone source rocks in the Lower Cretaceous coal measures. Biogenic gases derived from both types of source rocks are characterized by progressively higherδ13C values from C1 to C4 alkanes. In contrast, gases produced from the volcanic reservoirs of the Yingcheng Formation in the Xingcheng, Shengping and Changde gasfields display stable carbon isotope reversals for C1-C4 alkanes (δ13C1>δ13C2>δ13C3>δ13C4 ). The abiogenic origin of these gases is supported by their strong association with a positive helium isotope anomaly, with the highest R/Ra value being greater than 1. The Xingcheng gas field is believed to be the first commercial abiogenic alkane gas accumulation that has been discovered in the world, with a confirmed trap area of 62.6km2 and a recoverable gas reserve of 20.7×109m3. The precise mechanisms for the formation of these abiogenic gases remain to be determined, but the intermittent connection of the volcanic reservoirs with deep-seated basement faults and the presence of thick Upper Cretaceous-Tertiary caprocks appear to have played important roles for the gas migration, accumulation and preservation. Improved understanding of the geological processes that are responsible for the formation of the Xingcheng gas field may lead to more significant discoveries in the peripheral areas in the Songliao Basin and serve as a model for gas explorations in other parts of the world.

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas