碎屑石英和自生石英对页岩脆性的贡献差异(AAPG 2017 Feb)

The impact of rock composition on geomechanical properties of a shale formation: Middle and Upper Devonian Horn River Group shale, Northeast British Columbia, Canada

Tian Dong, Nicholas B. Harris, Korhan Ayranci, and Sheng Yang

AAPG Bulletin, v. 101, no. 2 (February 2017), pp. 177–204

有一个新的认识:页岩中的脆性贡献来源于自生石英(生物硅),而碎屑来源的硅质对脆性没有贡献。

大致意思:

1、元素与矿物是线性关系,具体转换应依据闭合氧化模型。

2、传统的脆性评价:①矿物组分与含量,②高杨氏模量与低泊松比代表高脆性,可以通过密度、声波(纵、横波)来计算。

Rocks with high Young’s modulus and low Poisson’s ratio are generally interpreted as brittle and more likely to fracture under stress and to maintain open fractures. In contrast, rocks with a low Young’s modulus and high Poisson’s ratio are interpreted as ductile and are more resistant to fracture initiation(Rickman et al., 2008).

3、提出用hardness来表征页岩的弹性等物理性质,hardness是通过岩心实验获得的。

4、有机质能显著的降低杨氏模量,增加泊松比,但是岩石hardness和TOC之间并未出现显著的负相关性,猜测可能是高演化程度下有机质不是影响杨氏模量的主要因素??

This suggests that organic matter is not a major factor affecting Young’s modulus at very high thermal maturities, which are approximately 1.6–2.5% Ro in the Horn River basin (Ross and Bustin, 2008,2009b).

5、如果页岩富含碎屑硅,那么也富含粘土,所以反而表现为塑性。生物硅往往是胶结物,形成一个刚性的骨架,往往则表现为脆性。

6、SiO2与Zr(锆石)交汇图表征硅的来源,正相关为碎屑硅,负相关为生物硅。

The critical distinction between detrital and biogenic quartz can be achieved by comparing the SiO2 concentration with that of Al2O3 (Ross and Bustin, 2009a) and tracing element detrital proxies such as Zr and titanium (Wright et al., 2010).

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