TY - THES

T1 - Effects of Salt Precipitation on the Hydraulic Properties of Porous Media due to Supercritical CO2 Injection via Microfluidics

AU - Kabogozza, Reagan

N1 - no embargo

PY - 2022

Y1 - 2022

N2 - Carbon Capture and Storage in deep saline aquifers (CCS) is one of the most favoured technical solutions for mitigating global CO2 emission levels to achieve global CO2 reduction goals and curb climate change. However, saline aquifers have highly mineralized brines whose minerals (salts such as halite, sylvite and others) precipitate during CO2 injection due to the vaporization of the brine into the dry supercritical CO2 phase. Salt precipitation can reduce the hydraulic properties of porous media, such as porosity and permeability, and cause major injectivity impairment or reduction, especially in the near-wellbore area where complete clogging has been reported to occur. This causes CO2 storage operations to be less cost-effective, especially when a single well cannot accommodate the injection of several million metric tons of CO2 per year. To correctly predict and simulate with the right clogging model how and when salt precipitation occurs during CCS in saline aquifers, understanding the physical mechanisms leading to and enhancement of salt precipitation is vital. It is also important to understand the nature of salt crystallization, the patterns of precipitation, and, therefore, the resulting change in hydraulic properties of porous media. Many ambiguities exist in the literature regarding the critical inputs into salt clogging models, and this has led to discrepancies in predictions of salt precipitation and what is observed in the field. This thesis examines salt precipitation on a microscopic level using lab-on-a-chip microchips to challenge some of these ambiguities and establishes what happens from a microscopic point of view. Air and dry supercritical CO2 were injected into fully brine-flooded microchips to achieve complete drying under observation. Two types or forms of salt crystallization were observed to occur in different phases, while also having different patterns of salt precipitation. The influence of injection rate and brine salinity on the patterns and nature of salt precipitation is also examined. The obtained results were used to ascertain the amount of change in the hydraulic properties of the porous media (microchip) and then compared to the commonly used clogging models for salt precipitation simulation in saline environments.

AB - Carbon Capture and Storage in deep saline aquifers (CCS) is one of the most favoured technical solutions for mitigating global CO2 emission levels to achieve global CO2 reduction goals and curb climate change. However, saline aquifers have highly mineralized brines whose minerals (salts such as halite, sylvite and others) precipitate during CO2 injection due to the vaporization of the brine into the dry supercritical CO2 phase. Salt precipitation can reduce the hydraulic properties of porous media, such as porosity and permeability, and cause major injectivity impairment or reduction, especially in the near-wellbore area where complete clogging has been reported to occur. This causes CO2 storage operations to be less cost-effective, especially when a single well cannot accommodate the injection of several million metric tons of CO2 per year. To correctly predict and simulate with the right clogging model how and when salt precipitation occurs during CCS in saline aquifers, understanding the physical mechanisms leading to and enhancement of salt precipitation is vital. It is also important to understand the nature of salt crystallization, the patterns of precipitation, and, therefore, the resulting change in hydraulic properties of porous media. Many ambiguities exist in the literature regarding the critical inputs into salt clogging models, and this has led to discrepancies in predictions of salt precipitation and what is observed in the field. This thesis examines salt precipitation on a microscopic level using lab-on-a-chip microchips to challenge some of these ambiguities and establishes what happens from a microscopic point of view. Air and dry supercritical CO2 were injected into fully brine-flooded microchips to achieve complete drying under observation. Two types or forms of salt crystallization were observed to occur in different phases, while also having different patterns of salt precipitation. The influence of injection rate and brine salinity on the patterns and nature of salt precipitation is also examined. The obtained results were used to ascertain the amount of change in the hydraulic properties of the porous media (microchip) and then compared to the commonly used clogging models for salt precipitation simulation in saline environments.

KW - CCS

KW - Carbon Capture and Storage

KW - Saline Aquifer

KW - salt precipitation

KW - Hydraulic parameters

KW - porosity

KW - permeability

KW - clogging model

KW - porous medium

KW - microfluidics

KW - microchip

KW - porosity-permeability modal

M3 - Master's Thesis

ER -