The latest study published in the journal Durability reflects on the influence of four distinct varieties of brine at different salt concentrations (5-25% by weight) on carbon dioxide storage.
To study: Experimental study on the interaction between different types/concentrations of brine and CO2 Injectivity for efficient CO2 Storage in deep saline aquifers. Image Credit: Dmitry Kovalchuk/Shutterstock.com
It should be borne in mind that salt deposition during CO2 sequestration in saltwater aquifers can have a significant impact on injectivity.
Carbon emissions and the importance of their reduction
Due to a sharp increase in greenhouse gas emissions, the use of fossil fuels has led to serious environmental problems such as increased global warming. Carbon dioxide (CO2) is the main cause of global warming since its quantity in the environment has increased considerably in recent decades.
Carbon Capture and Storage (CCS) Technology Offers the Opportunity to Minimize Anthropogenic CO2 emissions while safely sequestering them in geological formations such as drained oil reservoirs or deep salt deposits. This technique has the potential to reduce CO2 up to 17% by 2050. As a result, tectonic absorption or infusion of CO2 in depleted petroleum resources, underground coal seams and underground aquifers, is gaining popularity.
Schematic diagram of the experimental core flooding setup showing the path of the pressure decay test. Image credit: Edem DE et al., Sustainability
Importance of brine solutions for carbon storage
Due to their greater capacity, capture method, and widespread availability, CO2 injection into deep saline aquifers (sequestration) has the highest potential for CO capture2. Evaporation of development brine is one of the main problems facing carbon capture in aquifers.
This vaporization causes a salt deposition reaction, which can ultimately negatively influence injectivity, preventing CO2 accumulation. The infusion of a large volume of CO2 in formation water causes salt deposition in deep saline aquifers, leading to water evaporation and an increase in the molar percentage of water in CO2 flux.
The evaporation process is the main reason for the continuously increasing levels of solutes in brine. The amount of salt to some extent exceeds its absorption in the heat capacities of underground aquifers, resulting in the deposition of additional salts from the aqueous solution. This process, known as salting out, changes the pore size distribution and fluidity of the deposit.
Factors Affecting Salt Precipitation
The salt concentration, the rate of dehydration, the dispersion of the salt deposited in the crevices of the material and the properties of the rock are all elements that influence the deposition of salt. Other characteristics relevant to emulsification include ion size and charges, salt water temperatures, amount of salt, and constant dissipation factor of solvents.
CO2 dissolution in a saturated zone aquifer is pressure-sensitive, and pressure increases with lowering temperature, leading to increased CO2 absorption. Also, since absorption is directly proportional to the amount of salt in each element, an increase in dissolved salts leads to emulsification. According to the results, KCl has lower salting out impact than NaCl and CaCl2. Additionally, MgCl2 has a greater release impact than NaCl or KCl, which have a comparable effect.
Pressure decay test for different salt concentrations. Image credit: Edem DE et al., Sustainability
The most recent study investigates a wide range of brine contents for various salt varieties to obtain the optimal salt percentage group of alternative salt types for successful CO.2 sequestration in a sand reservoir of underground aquifers. In addition, saline aquifers inside the sandstones were searched.
Helium and 99% pure liquid carbon dioxide were used. Four different salts (NaCl, KCl, CaCl2, and MgCl2) were used to create brine samples. NaCl is the most common brine substance found in saline aquifers, accounting for 70-90% of the total. The Core Flooding technique was used. The fundamental physical properties of carrot were determined after drying in an oven at 75°C for 24 hours to remove all traces of solvent and moisture left by cleaning by Soxhlet extraction.
MgCl2 the brine had the earliest CO2 breakout at 15 wt. percentage concentration, followed by NaCl, KCl and CaCl2. This meant that a significant amount of CO2 was incorporated into the CaCl2 saline, which had a delayed breakthrough time compared to other brines, with all experiments being performed under identical circumstances and with extremely excellent reproducibility. In all flood situations,
NaCl exhibited the highest decomposition rates, suggesting that NaCl solutions had the maximum CO2 solubility. The results also showed that CO2 was more soluble in monovalent salts than in divalent salts (CaCl2 and MgCl2). In addition, the disintegration rate was found to be maximal in sand loaded with NaCl brine.
Rate of pressure decay versus brine concentration for all salt types and concentrations. Image credit: Edem DE et al., Sustainability
In short, research has shown that the best concentration range for carbon storage in saline groundwater aquifers is 10 wt. percent to 20% by weight. percent. However, experiments on brines containing various concentrations of different salts should be performed to find moderating salt forms in terms of storage efficiency.
Edem DE, Abba MK, Nourian A, Babaie M, Naeem Z. Experimental study on the interaction between different types/concentrations of brine and CO2 Injectivity for efficient CO2 Storage in deep saline aquifers. Durability. 2022. 14(2). 986. Available at: https://www.mdpi.com/2071-1050/14/2/986