Modeling of fracture geometry alteration and fracture flow evolution under geostress and water-rock interaction

TL;DR

This paper presents a coupled mech-hydro-chemical model to analyze how water-rock interactions and geostress influence fracture geometry and flow evolution, highlighting the importance of the thin surface layer and hydraulic conditions.

Contribution

It introduces an approximate linearized model for pressure dissolution compatible with existing solute transport models, incorporating various processes affecting fracture evolution.

Findings

Thin surface layer is crucial for fracture deformation.

Fluid flow promotes mineral dissolution and channel development.

High stress and slow flow lead to mineral precipitation filling fractures.

Abstract

A coupled mech-hydro-chemical model for rock geometry alteration of fractures under water-rock interaction (WRI) and geostress is developed. Processes including WRI, asperity deformation, mineral chemical dissolution and pressure dissolution etc., are taken into account. A feature of this model lies in its approximate linearization to the non-linear pressure dissolution process, which makes this model compatible with existing numerical solute transport models. Case study shows that although usually only a thin layer of rock surface is invaded by WRI, the mechanical weakening of this thin layer tend to induce significant increase in rock surface deformation. Thus, the distributed flow field, mineral dissolution rates, and surface alteration increments etc., are all affected. This indicates that when fracture flow related issues are concerned, we should focus on the top thin layer of rock surface rather than the matrix. Results also show that fluid flow enhances the dissolution of rocks and development of flowing channels; however, at places where stress induces high pressure-dissolution but fluid flows slowly, minerals precipitate and fill up fracture voids. This suggests the hydraulic condition plays a key role in the development of fracture flow channels and the evolution of fracture geometry.