Deep Fluid Tracer in Ordos Basin: Characteristics and Origin of High Natural Gamma Sandstone in Triassic Yanchang Formation
详细信息
- 责任者：Liu Xingjun (Department of Geology ; Northwest University ; Xi’an 710069 ; China) ; Liu Yiqun
- 刊名：Earth Science Frontiers
- 出版年：2013
- 卷期：20(5
- 关键词：砂体 ; sand bodies ; 自然伽玛测井 ; gamma-ray logging ; 鄂尔多斯盆地 ; Ordos Basin
- 页码：p.149-165
- 图表：7 illus., 4 tables, 58 refs.
- 分类号：1003
- issnNo：ISSN1005-2321
- isbnNo：CN11-3370/P
摘要
The Member Chang 6of Triassic Yanchang Formation in central Ordos Basin is an important layer for petroleum exploration and exploitation.In this member high natural gamma sandstones are wide-spread,but they are poorly studied.Previous studies suggest that the high natural gamma anomaly is related with feldspar,biotite,clay mineral contents and volcanic tuff.However,through the microscopic thin section study,X-diffraction analysis of clay minerals,electron microprobe and mass spectrometer analysis of chemical elements in minerals,and the study of distribution characteristics of sediments we found that in contrast with conventional sandstones the high natural gamma sandstones are higher in K-feldspar,chlorite and ferruginous clay matrix contents while the content of quartz is significantly lower.The contents of biotite and calcite is slightly increased.Feldspar in some high gamma sandstone is seriously kaolinized.Some high gamma sandstones are higher in lithic fragments which are commonly intensively altered forming pseudo matrix.As compared with conventional sandstones,the contents of Th,U,K in high natural gamma sandstone are higher.Among them the content of Th is significantly increased,which is mainly existed in monazite,rutile,ferruginous clay,feldspar,some of the zircon,apatite,biotite and lithic fragments.The radioactive element of U mainly exists in most of zircon,some of apatite,biotite and magnesium calcite.The radioactive element of K is mainly contained in K-feldspar,biotite,rutile,ferruginous clay,and some of albite and lithic fragments.The sedimentary facies is not the controlling factor for the high gamma anomaly in the sandstone formation.There is not any inevitable connection between volcanic tuff and the formation of high gamma sandstone.To a certain degree,the high gamma sandstone is indigenous to the material source from northeast of the basin.On the whole,the deep hydrothermal activity may probably have resulted in the formation of high gamma sandstones.
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