›› 2017, Vol. 38 ›› Issue (3): 1-1.doi: 10.7657/XJPG20170302

   

Discussions on Sandstone Densification TimeA Case Study from Shanxi Formation in Zhidan Area, Ordos Basin

LI YanxiaLIU Jieqi   

  1. (Xian Shiyou University, a.School of Earth Science and Engineering; b.Key Laboratory of National Petroleum and Petrochemical Industry, Xian, Shaanxi 710065, China)
  • Online:2019-01-01 Published:1905-07-15

Abstract: By means of polarized-light and fluorescence microscopes, petrological characteristics of the tight sandstones of Shanxi formation in Zhidan area, Ordos basin are observed. Meanwhile, temperatures of the inclusion in the quartz overgrowth edges are measured by using microscopic heating-freezing stages and components of the inclusion are analyzed with laser Raman spectroscopy. The study shows that four types of inclusions are developed in the quartz overgrowth edges of the tight sandstones in Shanxi formation of Zhidan area, namely, inorganic brine inclusion, hydrocarbon-bearing brine inclusion, gaseous and liquid hydrocarbon inclusion, and gaseous hydrocarbon inclusion. The homogenization temperature of the brine inclusion occurred in the quartz overgrowth edges of Stage Ⅰ ranges from 80℃ to 100℃ and its freezing temperature is -4~-2℃. Based on which, it is assumed that the quartz overgrowth edge was formed 200×106~190×106 years ago; brine inclusion in the quartz overgrowth edges of Stage Ⅱ has a homogenization temperature of 105~125℃ and freezing temperature of -6~-4℃, whose gaseous components are dominated by CO2 with minor C2H6, indicating the time for Stage Ⅰ natural gas charging and initial sandstone densification was 190×106~160×106 years ago. The homogenization temperature and freezing temperature of the brine inclusion in the quartz overgrowth edges of Stage Ⅲ are 135~155℃ and -10~-8℃, respectively. The gasceous components are dominated by CH4 and C2H6, accompanied by large amount of high-matured natural gas charging at the late stage. Then it is assumed that the time for natural gas accumulation and further sandstone densification occurred 160×106~140×106 years ago. Natural gas charging was accompanied by late-stage sandstone densification

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