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中南大学学报(英文版)

Journal of Central South University

Vol. 26    No. 7    July 2019

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Discovery and prediction of high natural gamma sandstones in Chang 73 Submember of Triassic Yanchang Formation in Ordos Basin, China
ZHENG Qing-hua(郑庆华)1, LIU Xing-jun(刘行军)2, YOU Ji-yuan(尤继元)1, 3, BAI Yun-yun(白云云)1, WANG Jing-hui(王镜惠)1, CHEN Xiao-liang(陈小亮)1

1. School of Chemistry & Chemical Engineering, Yulin University, Yulin 719000, China;
2. Changqing Division, China Petroleum Well Logging Limited Company, Xi’an 710201, China;
3. Department of Geology, Northwest University, Xi’an 710069, China

Abstract:The large scale development of high natural gamma sandstones has been discovered in the Chang 73 Submember of the Triassic Yanchang Formation in the Ordos Basin, China. High natural gamma sandstones consist of terrigenous detrital rocks with particle sizes ranging from silt to sand. They represent turbidite deposits characterized by high gamma ray values that are more than 180 American Petroleum Institute (API) units on a natural gamma ray log profile. For a long time, very high natural gamma sandstones had been identified as high-quality source rocks, such as oil shales, from conventional well log profiles, such as natural gamma ray well logs. Therefore, predicting the distribution of high natural gamma sandstones was studied. The sedimentary, lithological, and well log characteristics, as well as the genesis of the high radioactivity of high natural gamma sandstones were analyzed in the Chang 73 Submember. Thorium (Th), uranium (U) and other radioactive elements were found, carried by deep hydrothermal activity, and probably resulted in the formation of a relatively high radioactive zone in the cross-section, where high natural gamma sandstones usually develop in large quantities. This caused many turbidite sand bodies, which should have a continuous distribution in the cross-section, to appear to have a discontinuous distribution, when using conventional well log profiles, such as natural gamma ray well logs. From the above mentioned apparent discontinuous distribution of turbidite sand bodies in the cross-section, a continuous distribution can be predicted. It is obvious that the prediction of areas of continuous turbidite sand bodies in the cross-section usually corresponds with areas where high natural gamma sandstones are developed in large quantities. Exploration and development practice demonstrated that the developed method is fast and effective in predicting high natural gamma sandstones in the Chang 73 Submember.

 

Key words: Ordos Basin; Chang 73 Submember; high-quality source rock; high natural gamma sandstone; prediction

中南大学学报(自然科学版)
  ISSN 1672-7207
CN 43-1426/N
ZDXZAC
中南大学学报(英文版)
  ISSN 2095-2899
CN 43-1516/TB
JCSTFT
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