A rock physics model for the characterization of organic-rich shale from elastic properties

Ying Li,Gang Wang,Zhi-Qi Guo,Xiang-Yang Li,Cai Liu

doi:10.1007/s12182-015-0029-6

Abstract

Kerogen content and kerogen porosity play a significant role in elastic properties of organic-rich shales. We construct a rock physics model for organic-rich shales to quantify the effect of kerogen content and kerogen porosity using the Kuster and Toksoz theory and the self-consistent approximation method. Rock physics modeling results show that with the increase of kerogen content and kerogen-related porosity, the velocity and density of shales decrease, and the effect of kerogen porosity becomes more obvious only for higher kerogen content. We also find that the Poisson’s ratio of the shale is not sensitive to kerogen porosity for the case of gas saturation. Finally, for the seismic reflection responses of an organic-rich shale layer, forward modeling results indicate the fifth type AVO responses which correspond to a negative intercept and a positive gradient. The absolute values of intercept and gradient increase with kerogen content and kerogen porosity, and present predictable variations associated with velocities and density.

Highlights

Research on shale reservoirs has become more important in China (Liu et al 2009; Liu et al 2011; Zou et al 2011; Cheng et al 2013; Chen et al 2013a; Chen et al 2013b; Diao 2013; Wang et al 2013)
Kerogen content and kerogen porosity play a significant role in elastic properties of organic-rich shales
We construct a rock physics model for organic-rich shales to quantify the effect of kerogen content and kerogen porosity using the Kuster and Toksoz theory and the selfconsistent approximation method

Summary

Introduction

Research on shale reservoirs has become more important in China (Liu et al 2009; Liu et al 2011; Zou et al 2011; Cheng et al 2013; Chen et al 2013a; Chen et al 2013b; Diao 2013; Wang et al 2013). Zhu et al (2011) and Sayers (2013a) studied seismic AVO responses based on the proposed rock physics models for shale. The effect of kerogen content and kerogen porosity on elastic properties and seismic responses of shale has not been well investigated. Our objective is to build a rock physics workflow for the organic-rich shales to quantify the effects of such two factors on elastic properties, and on the seismic responses. A small amount of kerogen in weight percentage corresponds to a relevant higher volume percentage which has a significant impact on elastic properties and seismic responses of shales. The objective of this study is to build a rock physics model for organic-rich shales to quantify the effect of kerogen content and kerogen porosity.

Rock physics workflow for organic-rich shales

The effect of K and uk on elastic and geomechanical properties

Findings

Conclusions