Multiscale Reconstructions, Effective Elastic Properties, and Ultrasonic Responses of Kerogen Matter Based on Digital Organic Shales

Ying Rao,Bo-Ye Fu,Zhi-Wei Wang,Li-Yun Fu

doi:10.1109/access.2021.3058944

Abstract

Organic shales usually present significant heterogeneities in rock textures and reservoir properties due to differing kerogen contents and morphologies, subsequently impacting shale elastic properties and acoustic responses. Numerical upscaling of digital organic shales to evaluate effective elastic properties and acoustic responses has important implications for source rocks and unconventional reservoir characterization. We propose a modeling framework that includes the multiscale reconstruction of kerogen distributions, the numerical modeling of effective elastic properties, and the acoustic response to evaluate the contribution of organic matter. Based on digitized images of the microstructure of Longmaxi black shale samples obtained by X-ray CT, the kerogen components are identified and decomposed into different-level slices in terms of organic matter sizes and morphologies. Multiscale random media reconstruction is applied to these kerogen slices, with synthetic kerogen distributions validated by original counterparts. A finite-element method is used to model the effective elastic properties of digital organic shales, by which we investigate the effect of different kerogen contents and organic matter morphologies. We use a rotated staggered-grid finite-difference method to simulate ultrasonic wave propagation in digital organic shales to evaluate the response of different kerogen contents and organic matter morphologies. Numerical examples show that the multiscale random media method can be applicable to natural organic shales for the reconstruction of kerogen distributions. The elastic properties mainly depend on kerogen contents, with less influence by organic matter morphologies. The ultrasonic scattering effects become stronger for higher kerogen contents with smaller rounding coefficients. Our results confirm the applicability of the proposed modeling framework to support unconventional reservoir characterization. The purpose of this study is to provide the possibility of indicating the sweet point of shale.

Highlights

As potential unconventional resources, organic shales have been extensively studied in the last decade
Rock physics models facilitate the interpretation of sonic measurements and seismic responses for organic shales
The aim of this study is to reconstruct the distribution of kerogen grains and model their effective elastic properties, followed by simulating ultrasonic responses to evaluate the contribution of different kerogen contents and grain morphologies [2]

Summary

INTRODUCTION

Organic shales have been extensively studied in the last decade. The aim of this study is to reconstruct the distribution of kerogen grains and model their effective elastic properties, followed by simulating ultrasonic responses to evaluate the contribution of different kerogen contents and grain morphologies [2]. For general applicability to complex organic shales in this study, a finite-element (FE) method is used to estimate the effective elastic properties from a heterogeneous digital core, with particular attention given to the distinction of elastic responses of different morphologies and distributions of organic matter. We apply the RSG-FD numerical simulation of Biot’s poroelastic equations to ultrasonic wave propagation in digital organic shales followed by a coda analysis of ultrasonic scattering with kerogen contents and their morphologies

MULTISCALE RECONSTRUCTION OF KEROGEN DISTRIBUTIONS

Findings

CONCLUSION