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Correlation Study on the Geochemical Characteristics and Brittleness of Tight Sandstone in the Longmenshan Foreland Basin
Author(s) -
CHEN Bin,
WANG Weiming
Publication year - 2015
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.12302_2
Subject(s) - foreland basin , geology , structural basin , brittleness , geochemistry , petrology , geomorphology , materials science , composite material
Variability (ICV) and Chemical Index of Alteration (CIA) about Xujiahe Formation sandstone in the Longmenshan foreland basin. To show the brittle characteristics of the sandstone. Make an analysis of pore development and fracking potential in the tight sandstone gas reservoir. In order to ensure reducing the effect of modern weathering, the sandstone samples all are fresh. And through the microscope to analysis the components of sandstone. The geochemical sample processing and testing were completed in the ALS Chemex Laboratory in Guangzhou. The samples need no pollution and grind to 200 mesh in dry spare. The test of whole rock bulk elements in the Xray Fluorescence Spectrometer (AXIOS). Analysis of trace elements and rare elements on the Inductively Coupled Plasma Mass Spectrometry (ICPMS-X Series II). The accuracy is better than 5%. The bulk elements of Upper Triassic Xujiahe Formation sandstone in the Longmenshan foreland basin is show in Table 1. The content of SiO2 (66.82%–80.39%. The average 71.93%), The content of Al2O3 (6.48%–13.68%, the average 9.95%), (Fe2O3+MgO) (3.98%–8.65%, the average 4.40%), TiO2 (0.18%–0.67%, the average 0.41%), K2O/Na2O(0.29–3.30, the average1.2), close to the characteristics of passive continental margin. Cox et al. (1995) proposed the index of compositional variability: ICV=(Fe2O3+K2O+Na2O+ CaO+MgO+MnO +TiO2)/Al2O3(percentage) (Table 1). The decrease of the non-clay minerals and the growth of the clay minerals will decrease the ICV during the cycling process. So there is a positive correlation between the ICV and the level of brittleness. Nesbitt and Young (1982) indicate that feldspar is the maximum content of the crustal unstable minerals. Dissolution of K, Na and Ca in feldspar during weathering process, Make the increase of Al and alkali metal in weathering products. And proposed microclastic rocks Chemical Index of Alteration: CIA=[Al2O3 / (Al2O3+CaO*+Na2O+K2O)]×100(molar quantity). CaO* CHEN Bin and WANG Weiming, 2015. Correlation Study on the Geochemical Characteristics and Brittleness of Tight Sandstone in the Longmenshan Foreland Basin. Acta Geologica Sinica (English Edition), 89(supp.): 3-4.