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

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.

Pore-Scale Modeling of Nucleation and Growth in Porous Media

“…The simulator used in this study to perform the reactive transport simulations builds upon the porescale LB-based reactive transport simulator developed and validated in our previous works 15,20,21 .…”

“…The details of the model development can be found in our previous publications 15,20,21 and we here present the overview of the model.…”

“…The simulator used in this study to perform the reactive transport simulations builds upon the pore-scale LB-based reactive transport simulator developed and validated in our previous studies. 15,20,21 The details of the model development can be found in our previous publications 15,20,21 In the pore-scale reactive transport simulations, the advection−diffusion-reaction equation is solved to obtain the concentration of different species…”

Modeling Reactive Transport Processes in Fractures

“…This is, however, computationally expensive for finite-volume based reactive transport models. Alternative approaches, such as the Lattice Boltzmann method, have been explored (Chen et al 2014;Fazeli et al 2018). Chen et al (2014) investigated fracture evolution in a binary mineral system using a pore-scale model, and showed the development of an altered layer, in which the flow velocity is negligible.…”

Role of Mineralogy in Controlling Fracture Formation

“…However, the presence and evolution of fractures can not only pose a risk to system integrity − but can also threaten overlying groundwater resources with acidification and contamination via trace element mobilization. − While it is well understood that mineral dissolution and precipitation can alter the porosity and permeability of a formation, − whether and how fracture permeabilities will be enhanced or reduced by mineral dissolution or precipitation on the fracture surfaces ,− is unknown. Changes in transmissivity will, however, depend upon a variety of fracture parameters including aperture, roughness, and reactive mineral distributions. − − For instance, the formation of preferential flow channels is a common occurrence in fractures, − but the spatial distribution of mineral heterogeneities can both prevent and promote channelization. However, the relationship between the distribution of minerals at the fracture surface and its sealing capacity is not well understood.…”