Effect of Pore-Scale Mineral Spatial Heterogeneity on Chemically Induced Alterations of Fractured Rock: A Lattice Boltzmann Study

Hossein Fazeli,Helge Hellevang,Ravi Patel

doi:10.1155/2018/6046182

Hossein Fazeli, Helge Hellevang + Show 1 more

Open Access

https://doi.org/10.1155/2018/6046182

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Journal: Geofluids	Publication Date: Jul 18, 2018
Citations: 13	License type: CC BY 4.0

Affiliation: University of Oslo, Paul Scherrer Institute

Abstract

Fractures are the main flow path in rocks with very low permeability, and their hydrodynamic properties might change due to interaction with the pore fluid or injected fluid. Existence of minerals with different reactivities and along with their spatial distribution can affect the fracture geometry evolution and correspondingly its physical and hydrodynamic properties such as porosity and permeability. In this work, evolution of a fracture with two different initial spatial mineral heterogeneities is studied using a pore-scale reactive transport lattice Boltzmann method- (LBM-) based model. The previously developed LBM transport solver coupled with IPHREEQC in open-source Yantra has been extended for simulating advective-diffusive reactive transport. Results show that in case of initially mixed structures for mineral assemblage, a degraded zone will form after dissolution of fast-dissolving minerals which creates a resistance to flow in this region. This causes the permeability-porosity relationship to deviate from a power-law behavior. Results show that permeability will reach a steady-state condition which also depends on transport and reaction conditions. In case of initially banded structures, a comb-tooth zone will form and the same behavior as above is observed; however, in this case, permeability is usually less than that of mixed structures.

Highlights

During reactive transport processes in tight rocks, fractures play an important role as it is the main flow path for species transport
We utilize a similar setup used in Chen et al.’s work [26], a single fracture surrounded by a rock matrix composed of two different minerals, and focus more on the effect of mineral spatial heterogeneity on fracture geometry evolution by constructing initially mixed and banded mineral structures that are conceptualizations of the structures observed by Ellis et al [2]
A previously developed LBM transport solver coupled with IPHREEQC has been extended for simulating advective-diffusive reactive transport

Summary

Introduction

During reactive transport processes in tight rocks, fractures play an important role as it is the main flow path for species transport. Existence of fractured seals in geological CO2 sequestration and fractures in the host rock of nuclear waste disposal sites are some practical examples in which hydrodynamic properties of fractures can help to better understand the long-term evolution of the system [1] These hydrodynamic properties will change due to chemical disequilibrium resulting from interactions between pore fluid and rock minerals. We utilize a similar setup used in Chen et al.’s work [26], a single fracture surrounded by a rock matrix composed of two different minerals, and focus more on the effect of mineral spatial heterogeneity on fracture geometry evolution by constructing initially mixed and banded mineral structures that are conceptualizations of the structures observed by Ellis et al [2]. This rock is representative of a carbonate-rich caprock such as some intervals in the Draupne shale [35]

Numerical Model Description

Results and Discussion

Initial Mineral Distribution

Conclusions

Validation of LBM Model