Influence of Geochemistry on Toughening Behavior of Organic-Rich Shale

TL;DR

This study investigates how geochemical composition affects the fracture behavior of organic-rich shale across multiple scales, revealing correlations between mineral content and fracture toughness, and emphasizing the need for advanced modeling and fracturing techniques.

Contribution

It provides new experimental data and insights into the multiscale fracture behavior of organic-rich shale influenced by geochemistry, extending fracture toughness evaluation methods.

Findings

Fracture toughness correlates positively with kerogen, clay, and calcite content.

Shale rich in TOC, clay, and calcite shows higher fluid lag and lower crack width.

Geochemistry influences hydraulic fracture propagation timescale and regime.

Abstract

Our research objective is to understand the influence of geochemistry on the fracture behavior of organic-rich shale at multiple length-scales. Despite an increasing focus on the fracture behavior of organic-rich shale, the relationships between geochemistry and fracture behavior remain unclear and there is a scarcity of experimental data available. To this end, we carry out 59 mesoscale scratch-based fracture tests on 14 specimens extracted from 7 major gas shale plays both in the United States and in France. Post-scratch testing imaging reveal fractures with small crack width of about 400 nm. The fracture toughness is evaluated using the energetic size effect law, which is extended to generic axisymmetric probes. A nonlinear anisotropic and multiscale fracture behavior is observed. In addition, a positive correlation is found between the fracture toughness and the presence of of kerogen, clay and calcite. Moreover, the geochemistry is found to influence the timescale and the regime of propagation of the hydraulic fracture at the macroscopic length-scale. In particular, shale systems rich in TOC, clay and calcite are more likely to exhibit high values of the fluid lag and low hydraulic crack width. Our findings highlight the need for advanced constitutive models for organic-rich shale systems and advanced hydraulic fracturing solutions that can fully integrate the complex fracture response of organic-rich shale materials.