Controlling factors and formation mechanism of fractures in the tight-gas sandstones of the Upper Triassic Xujiahe Formation, western Sichuan Basin, China

2020 ◽  
Author(s):  
Wenya Lyu ◽  
Lianbo Zeng ◽  
Shuangquan Chen ◽  
Lei Tang ◽  
Yunzhao Zhang
Keyword(s):  
Formation Mechanism ◽  
Isotope Analysis ◽  
Late Triassic ◽  
Burial History ◽  
Thin Sections ◽  
Xujiahe Formation ◽  
Western Sichuan ◽  
Mechanical Stratigraphy ◽  
Filling Sequence ◽  
Western Sichuan Basin

<p>Based on cores, image logs and thin sections, five sets of fractures are developed in the study area, where faults are developed. Most of fractures are open without fillings, and some fractures are filled with calcite, quartz, bitumen, pyrite and mud. Fractures are mainly controlled by lithology, mechanical stratigraphy and faults. Based on mutual crosscutting relationships of fractures, mineral filling sequence of fracture fillings, fluid inclusion and carbon-oxygen isotope analysis of calcite fillings in fractures, and quartz spintronic resonance analysis of quartz fillings in fractures, in combination with thermal and burial history, the formation sequence and time of fractures were analyzed. The results show that fractures mainly formed over three period, that is, the late Triassic, Middle to Late Jurassic, and Late Cretaceous to Paleogene. Then，combined with the paleostress evolution and fracture characteristics of the study area, the formation mechanism of fractures was discussed.</p>

Characteristics and Sequences of Fractures in the Tight Conglomerate Reservoirs of Jiulongshan Structure

2014 ◽  
Vol 900 ◽  
pp. 689-692
Author(s):  
Lei Gong ◽  
Shuai Gao ◽  
Shu Ju Guo ◽  
Jian Guo Huang ◽  
Xian Xian Tao
Keyword(s):  
Fractal Dimension ◽  
Fractal Dimensions ◽  
Areal Density ◽  
Lower Jurassic ◽  
Fracture Origin ◽  
Thin Sections ◽  
Western Sichuan ◽  
The North ◽  
Western Sichuan Basin ◽  
Natural Gas Reservoirs

Fracture is an important controlling factor for the distribution of natural gas reservoirs in the tight conglomerate reservoirs in the Lower Jurassic Zhenzhuchong Formation at the north of Western Sichuan basin. Using the data of outcrops, cores, image logs and thin sections, combined with experimental analysis, we analyze the fracture origin types, distribution characteristics and formation sequences. There are three types of fractures, i.e. tectonic fractures, diagenetic fractures and original fractures in the tight conglomerate reservoirs. Among them, tectonic fractures are dominant, which can be classified into four sets, i.e. E-W, nearly S-W, NWW-SEE, NEE-SWW orientations. According to the statistics of areal density and fractal dimension, the average fracture areal density is 0.31cm/cm2, with the bulk in the range of 0.15-0.60cm/cm2. The fracture fractal dimensions are distributed at 0.95-1.70. There is a well positive correlation between fracture areal density and fractal dimension. Micro-fractures are important channels that connect matrix intergranular pores and intragranular dissolved pores, which improve the connectivity among pores. The tectonic fractures in the study area were formed in two periods, i.e. the end of Cretaceous and the end of Neogene.

scholarly journals Late Triassic tectonic inversion in the upper Yangtze Block: Insights from detrital zircon U-Pb geochronology from south-western Sichuan Basin

2018 ◽  
Vol 31 (1) ◽  
pp. 92-113 ◽  
Author(s):  
Zhaokun Yan ◽  
Yuntao Tian ◽  
Rui Li ◽  
Pieter Vermeesch ◽  
Xilin Sun ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
Sichuan Basin ◽  
Late Triassic ◽  
Yangtze Block ◽  
Western Sichuan ◽  
Tectonic Inversion ◽  
Western Sichuan Basin

scholarly journals The Origin of Quartz Cement in the Upper Triassic Second Member of the Xujiahe Formation Sandstones, Western Sichuan Basin, China

Water ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 1890
Author(s):  
Jie Ren ◽  
Zhengxiang Lv ◽  
Honghui Wang ◽  
Jianmeng Wu ◽  
Shunli Zhang
Keyword(s):  
Sichuan Basin ◽  
Secondary Ion Mass Spectrometry ◽  
Trace Element Composition ◽  
Upper Triassic ◽  
Al2o3 Content ◽  
Xujiahe Formation ◽  
Western Sichuan ◽  
Rock Fragments ◽  
Quartz Cement ◽  
Western Sichuan Basin

High-precision in situ δ18O values obtained using secondary ion mass spectrometry (SIMS) for μm-size quartz cement are applied to constrain the origin of the silica in the deep-buried Upper Triassic second member of Xujiahe Formation tight sandstones, western Sichuan Basin, China. Petrographic, cathodoluminescence (CL), and fluid inclusion data from the quartz cements in the Xu2 sandstones indicate three distinct, separate quartz precipitation phases (referred to as Q1, Q2, and Q3). The Q1 quartz cement was formed at temperatures of approximately 56–85 °C and attained the highest δ18O values (ranging from 18.3 to 19.05‰ Vienna Standard Mean Ocean Water (VSMOW)). The Q2 quartz cement was generated at temperatures of approximately 90–125 °C, accompanying the main phase of hydrocarbon fluid inclusions, with the highest Al2O3 content and high δ18O values (ranging from 15 to 17.99‰ VSMOW). The Q3 quartz cement was formed at temperatures of approximately 130–175 °C, with the lowest δ18O values (ranging from 12.79 to 15.47‰ VSMOW). A portion of the Q2 and Q3 quartz cement has a relatively high K2O content. The dissolution of feldspar and volcanic rock fragments was likely the most important source of silica for the Q1 quartz cement. The variations in δ18O(water) and trace element composition from the Q2 quartz cement to the Q3 quartz cement suggest that hydrocarbon emplacement and water-rock interactions greatly altered the chemistry of the pore fluid. Feldspar dissolution by organic acids, clay mineral reactions (illitization and chloritization of smectite), and pressure dissolution were the main sources of silica for the Q2 and Q3 quartz cements, while transformation of the clay minerals in the external shale unit was a limited silica source.

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