Recent Advances in Geochemical and Mineralogical Studies on CO₂–Brine–Rock Interaction for CO₂ Sequestration: Laboratory and Simulation Studies

Abstract

The urgent need to find mitigating pathways for limiting world CO₂ emissions to net zero by 2050 has led to intense research on CO₂ sequestration in deep saline reservoirs. This paper reviews key advancements in lab- and simulation-scale research on petrophysical, geochemical, and mineralogical changes during CO₂–brine–rock interactions performed in the last 25 years. It delves into CO₂ MPD (mineralization, precipitation, and dissolution) and explores alterations in petrophysical properties during core flooding and in static batch reactors. These properties include changes in wettability, CO₂ and brine interfacial tension, diffusion, dispersion, CO₂ storage capacity, and CO₂ leakage in caprock and sedimentary rocks under reservoir conditions. The injection of supercritical CO₂ into deep saline aquifers can lead to unforeseen geochemical and mineralogical changes, possibly jeopardizing the CCS (carbon capture and storage) process. There is a general lack of understanding of the reservoir’s interaction with the CO₂ phase at the pore/grain scale. This research addresses the gap in predicting the long-term changes of the CO₂–brine–rock interaction using various geochemical reactive transport simulators. Péclet and Damköhler numbers can contribute to a better understanding of geochemical interactions and reactive transport processes. Additionally, the dielectric constant requires further investigation, particularly for pre- and post-CO₂–brine–rock interactions. For comprehensive modeling of CO₂ storage over various timescales, the geochemical modeling software called the Geochemist’s Workbench was found to outperform others. Wettability alteration is another crucial aspect affecting CO₂–brine–rock interactions under varying temperature, pressure, and salinity conditions, which is essential for ensuring long-term CO₂ storage security and monitoring. Moreover, dual-energy CT scanning can provide deeper insights into geochemical interactions and their complexities.

1. Introduction

According to the Annual Energy Outlook (EIA, 2023), the United States CO₂ emissions created by energy-related emissions such as electricity generation (coal, natural gas, oil), transportation (vehicles, aviation), industrial processes, and residential and commercial processes are 25% to 38% below 2005 levels, depending on economic expansion and zero-carbon technology generation costs; see Figure 1 [1]. The energy transition’s success hinges on the widespread availability of low-cost, emissions-free electricity and the substitution of most fuel-powered devices, materials, and manufacturing processes with electric alternatives. This also involves utilizing carbon capture and storage (CCS) for structural materials and creating carbon-neutral fuels for sectors that are challenging to electrify [2]. CO₂ sequestration in deep saline reservoirs is not just a topic of current research but a pressing issue that demands immediate attention. With most large oil and gas companies and government policymakers being focused on reducing CO₂ emissions from the environment, the urgency of this research cannot be overstated. In a recent paper, Thakur et al. [3] focused on carbon storage and reservoir management as a practical example of climate change response [3]. IPCC 2023 stated that different mitigation pathways for CO₂ emissions will reach net zero by 2050 for 1.5 °C and for 2.0 °C by 2070; see Figure 2 [4]. In their paper, Farouq Ali and Soliman [5] highlighted that carbon capture and storage (CCS) has mitigated less than 0.1% of global CO₂ emissions over the past two decades. This finding underscores the urgent need for enhanced efforts, given the persistent reliance on fossil fuels. Current CCS initiatives have not achieved the desired impact, emphasizing the necessity for substantial technological advancements. Developing and implementing innovative approaches that have yet to be explored by the petroleum industry and academic engineering programs is imperative to attain net-zero emissions [5]. The research presented in this paper is comprehensive, covering key aspects of the geochemical and mineralogical issues for CO₂–brine–rock interactions for CO₂ storage. It provides a detailed review of the experimental and simulation studies, delving into the trapping mechanism of CO₂. It is divided into two parts: (1) physical trapping (less than 100 years) includes stratigraphic hydro trapping, capillary trapping, and sorption trapping; and (2) geochemical trapping includes solubility trapping (convective and diffusion processes), while mineral trapping states the chemical reactions with minerals [6,7,8,9,10,11] (see Figure 3).

Based on current trends and previous studies, extensive research has been conducted on the geochemical interactions between CO₂, brine, and rock, encompassing experimental and simulation studies. Geochemistry is the main factor in carbon storage. CO₂ dissolution occurs due to the chemical reaction between CO₂, rock, and carbonate and bicarbonate ions present in formations, and a pH drop [12,13]. GCS depends on carbon capture. This initial process determines the impurities in injected scCO₂ and injected volumes, rates, and pressures [14]. Experimental and practical data are used to understand storage processes and assess associated risks. However, knowledge gaps still exist in the field [15,16].

As detailed in Figure 4, the injectivity index of CO₂ injection affects the geochemical, thermodynamic, transport, and mechanical processes [17]. Porosity variations resulting from geochemical interactions and how this affects the CO₂ injectivity; these are validated by coupled modeling applications [18]. In the geochemical interactions between CO₂, brine, and rock, substantial changes occur depending on the type of rock. In the near-wellbore region, chemical reactions occur between the gas mixture, brine, and cement or steel. This process, known as carbonation, involves the conversion of constitutive cement minerals such as (CaO·SiO₂·H₂O) and Ca(OH)₂ by CO₂. Specifically, CO₂ reacts with the Ca(OH)₂ in the cement to form (CaCO₃), which can significantly impact the mineralogy, porosity, transport, and mechanical properties of the cement. For long-term CO₂ storage security, crucial for periods exceeding 1000 years, these changes could lead to increased permeability, diffusivity, fissures, and annular spaces between the casing and cement, thereby elevating the risk of CO₂ leakage to the surface [17,19,20,21].

Figure 5 illustrates a comprehensive overview of geological carbon storage across laboratory and spatial scales of multiphase reactive transport, focusing on A. nano-scale (mineral–fluid experiments and theoretical geochemistry involving dissolution and precipitation); B. pore-scale (bench-scale experiments and pore-scale modeling); and C. reservoir scale (core flooding and reactive transport modeling) [14,22,23,24,25,26,27,28,29].

2. Mechanisms for CO₂–Brine–Rock Interactions

The mechanism of CO₂–brine–rock interactions involves very complex chemical reactions. There is a significant lack of understanding regarding reservoir interactions with CO₂ at the pore/grain scale [11]. This knowledge gap emphasizes the potential risks of unforeseen geochemical and mineralogical changes during scCO₂ injection. In GCS conditions, there are four most impactful chemical reactions: (1) the dissolution of scCO₂ in brine; (2) the creation of secondary minerals because of reactions driven by CO₂-enriched brine; (3) water, rock, and scCO₂ interactions called wet scCO₂-induced interactions; and (4) near-wellbore reactions, which depend on several factors such as pressure, temperature, salinity, and rock mineralogy. These reactions can form in situ nanoparticles, affecting the pore throat and causing wettability alterations (see Figure 6) [14,26,30].

CO₂, brine, and rock interaction mechanisms induce various geochemical reactions that significantly influence MPD. These interactions can profoundly affect the subsurface environment in carbon sequestration, which is crucial for geochemical and mineralogical interactions among CO₂, brine, and rock.

Fluid–mineral reactions can have significant consequences:

• The rapid dissolution of carbonates can lead to the degradation of caprocks, wellbores, and fault seals, potentially allowing CO₂ to migrate into overlying formations and cause equipment leakage [31].
• Carbonate precipitation in caprocks can lower the permeability, stabilizing storage.
• Mineral dissolution or precipitation in reservoirs may change permeability, affecting the flow of CO₂ and CO₂-saturated brine.
• CO₂ sequestration into carbonate rocks and minerals contributes to long-term storage security [32,33].

Geochemical reactions between CO₂ and reservoir or caprock in deep subsurface environments are primarily driven by a decrease in pH and the formation of bicarbonate and carbonate ions due to CO₂ dissolution [12]. Despite this, the wettability interactions among CO₂, calcite, and brine remain not fully understood from a geochemical standpoint [34].

In Section 2.2 of this paper, we can correlate the above four points using CT scanning technology, which offers valuable insights. There is a direct connection between in situ visualization using CT scanning and the MPD to analyze the dissolution of scCO₂ in brine to create acidified brine, the CO₂ saturation profile in the core sample, mineral precipitation, calcite dissolution, and various time-dependent geochemical reactions during CO₂ sequestration. These chemical reaction processes are explained in more detail in Figure 6. Dual-energy and micro-CT scans can provide important visual insights into geochemical interactions. With ISSM (in situ saturation monitoring), industrial/micro-CT scanners can observe and quantify the complex structural effects of these processes and potentially mitigate the risks and challenges they pose. Mineralization, precipitation, and dissolution can be seen using ISSM techniques, offering a unique perspective. A CT scanner has the ability to monitor small changes in density and effective atomic number, Zeff, providing a window into the dynamic nature of these processes. The higher the density or Zeff of a rock, the higher the grayscale number (or Hounsfield number). Under in situ conditions, a rock sample is exposed to CO₂ and brine inside an X-ray transparent core holder. It is then scanned periodically to monitor any grayscale number changes taking place in CT slices compared with the initial scans before exposure, which can be related to saturation changes.

2.1. MPD (Mineralization, Precipitation, and Dissolution)

Carbon mineralization (conversion to solid inorganic carbonates) in the subsurface is a very impactful factor for carbon management efforts. Calcium or magnesium carbonates are formed from stoichiometric and chemo-morphological reactions [35]. Mineral dissolution and precipitation can change the permeability of the reservoir [12]. In their meticulous investigation, Rathnaweera et al. [36] looked at the impact of prolonged CO₂ injection. Their research revealed a CO₂ drying-out effect, accompanied by the precipitation of NaCl crystals in sandstone (see Figure 7a). These processes significantly impact rocks’ mineralogical properties and permeability within saline aquifers. The dissolution of minerals such as calcite, siderite, barite, and quartz was identified as the primary cause of these changes, a conclusion that was reached through rigorous scientific methods. Figure 7b shows the before-and-after images of a carbonate core subjected to scCO₂ injection; it provides the dissolution of calcite minerals after reaction with a rock to form carbonic acid. The fine particles inside the limestone core sample are dissolved by the carbonic acid [37].

When CO₂ is impure and contains other plant gases, such as oxides of sulfur and nitrogen, it can undergo geochemical interactions and reactions with the formation of rock and brine, altering the mineralogical and equilibrium thermodynamic conditions. CO₂ dissolves in brine, reducing the pH and leading to primary phase dissolution and secondary mineral precipitation. These reactions can change the permeability and porosity of the rock [38]. Figure 8 presents a practical example of CO₂ sequestration in sedimentary basins in the Frio Formation in Texas, USA, illustrating the decline in pH and the concurrent alkalinity increases following the breakthrough of CO₂ [39,40]. The dissolution of iron oxyhydroxides can mobilize toxic metals, potentially contaminating groundwater. Additionally, the presence of sulfur oxides can lead to the formation of H₂S and significantly lower the pH [41].

X-ray diffraction (XRD) and scanning electron microscopy (SEM) are analytical techniques that provide detailed insights into grain structures, pore characteristics, and the changes induced by the continuous injection of supercritical CO₂ (scCO₂) in carbon sequestration processes. Figure 9A,B visually illustrate the mineral dissolution and precipitation resulting from CO₂–brine–rock interactions [42]. These interactions led to brine acidification, evidenced by increased calcium and magnesium ions. This, in turn, caused the dissolution of carbonate minerals and increased the porosity and permeability of the formation rock [43]. Figure 10 highlights the dissolved areas, such as feldspar dissolution, pore formation, and kaolinization, and their effects on the connectivity of tight reservoir rocks [44,45]. Figure 11 illustrates the pore expansion observed in feldspar during the CO₂–rock test. Conversely, in the case of CO₂–water–rock interactions, the most significant pore expansion was observed in kaolinite, along with mass loss and alterations in permeability and porosity in tight cores following CO₂–water–rock experiments [44,46].

Rathnaweera et al. [36,47,48] investigated the interactions between CO₂, rock, and brine in a study. SEM observations revealed distinctive features in the reacted samples, including calcite dissolution textures, etching caverns, pits, and the corrosion of quartz minerals, resulting in a relatively rough surface on sandstone samples. Calcite dissolution within carbonate-cemented reservoirs led to significant alterations in pore structures.

Figure 12 illustrates various effects of CO₂ injection on cores from a limestone reservoir [49]. Point A shows dissolution occurring at the grain level; points B and D show grain breakage due to CO₂ reaction with the core; point C shows mass loss at the grain level; and point E shows cement dissolution [49]. These findings signify a loss of integrity and underscore the potential for mechanical failure in limestone reservoirs, which is a crucial aspect of the CCS project.

An additional and sometimes overlooked geochemical interaction is surface complexation and associated redox equilibrium [50]. Surface reactions, particularly for low-salinity brines, can measurably impact the CO₂ amounts being actively transported.

2.2. Advancements in Visualization through CT Scanners and In Situ Techniques

Recent advancements in visualization techniques, such as CT scanning, are revolutionizing in situ monitoring and analysis by enhancing our understanding of geochemical interactions and their role in carbon storage.

Soong et al. [42] illustrated this in their study using CT scan images of Cedar Keys/Lawson rock (carbonate formation) after one month of exposure to scCO₂ and brine. The study found that porosity decreased from 19.5% to 19.35% following the CO₂ reaction, indicating potential impacts on the rock’s stability. Dissolution was observed primarily in the outer region of the core, suggesting structural alterations. Additionally, the pore increased in volume by 21%, with the pore size expanding (equivalent diameter) from 1223 µm to 1304 µm, as shown in Figure 13. The permeability value decreased from 4.57 to 4.50 mD. Figure 14, which is the continuation of Figure 13, shows where the dissolution occurred and created another pore connected to the adjacent void space to create a channel.

The research on wormhole creation in carbonate reservoirs for CO₂–brine–rock interactions presents novel insights [51], as evidenced by the CT scan images in Figure 15 [49] and Figure 16 [52], respectively. These figures offer a unique and enlightening visual representation of wormhole formation and breakage, a phenomenon that has also been observed using a CT scan. The maximum depth of wormhole formation reached 6.3 cm. The 175% increase in absolute permeability of the sample can be attributed to dissolution and the formation of wormhole channels [52]. Another researcher documented the implication of CO₂-saturated brine salinity on wormhole generation and concluded that the low-salinity brine could induce thicker wormholes in the limestone samples [53]. Importantly, Gharbi et al. [54] discovered that creating high-conductive channels, such as wormhole formations and propagation in carbonate rocks, is associated with very high Péclet and Damköhler numbers. A Péclet number is defined as the ratio of the advection rate of a chemical species by the flow to the rate of diffusion of this quantity in the fluid mixture. A Damköhler number is defined as the ratio of the reaction rate and the diffusive mass transfer rate at the fluid/solid interface [55].

Based on the literature, our study analyzed the dissolution patterns influenced by Péclet (Pé) and Damköhler (Da₁) numbers, as shown in Figure 17.

• Figure 17a: Different dissolution patterns based on varying Péclet and Damköhler numbers.
• Figure 17b: The dissolution front remains highly stable for small Péclet numbers (Pé ≤ 10⁻²) and Da₁ > 1.
• Figure 17c: When Da₁ > 1 and injection rates are higher but within a diffusion-dominated transport regime (1 ≥ Pé > 10⁻²), the dissolution front becomes non-uniform along the vertical cross-section, forming a conical pattern due to the faster regions dragging the dissolution.
• Figure 17d: A single dominant wormhole forms for conditions where Da₁ > 1 and 10 ≥ Pé > 1. In this case, advection dominates the void space due to the acid transport mechanism.
• Figure 17e,f illustrate ramified wormhole formation for Da₁ > 1 and Pé > 10, showing complex dissolution patterns. Uniform dissolution occurs for small Damköhler numbers (Da₁ ≤ 1) irrespective of the Péclet number [55,56,57].

Various researchers discuss the Péclet and Damköhler numbers in acidizing and stimulation for wormhole creation. For example, the modeling of the wormhole creation has been processed to optimize the acidizing stimulation of production wells [58,59]. The dissolution regime is influenced by these two-dimensional numbers, as depicted in Figure 18 [60,61,62,63,64]. It is worth knowing that when we inject the scCO₂ for geochemical interactions such as MPD processes, very little research on reactive transport phenomena based on wormhole formation and propagation based on these interactions relates to the Péclet and Damköhler numbers. As Gharbi et al. [54] stated in their paper, it is worthwhile to investigate the dissolution regimes at lower Damköhler numbers and predict the reactive transport properties and wormhole propagation.

Siddiqui et al. [65] reviewed significant research conducted using both medical and micro-CT scanners for core characterization and flow visualization. Several researchers employed CT scanners with dual-energy CT scanning for the characterization of rocks [66,67]. Dual-energy CT scanning utilizes two X-ray energies—one low and one high energy—at the exact location. This technique determines bulk density and effective atomic number, which makes it possible to accurately characterize some rock properties. Some previous studies have also compared various techniques for extracting density and porosity from cuttings. Siddiqui et al. [68] highlighted using micro-CT and medical CT scanners to achieve these measurements, demonstrating their effectiveness for capturing core heterogeneities and for use in detailed rock characterization.

Limited research has been conducted using industrial CT scanners. By employing industrial CT scanners with dual-energy techniques and by analyzing cuttings or chips using micro-CT scanners, one can potentially examine MPD interactions between CO₂, brine, and rock for short- and long-term CO₂ storage. This methodology enables the observation of chemical reactions in the context of reactive transport phenomena and helps identify the critical factors influencing these reactions.

New to the area of visualization in cores is the use of positron emission tomography (PET). In this system (a more enhanced version of a CT scanner), both transmitted X-rays (CT scans) and emitted particles with associated X-rays can be observed. An example of positron emission tomography is shown in Figure 19 [69]. For CO₂ injection, the specificity of selected positron emitters in the brine, CO₂, or oil can be used to produce images when density variations are too small to produce a sufficient CT number contrast [70,71].

In situ techniques are new ways to observe geochemical changes associated with mineral precipitation and dissolution (MPD) in carbon sequestration lab studies. Perrin et al. [72] utilized in situ techniques to visualize the two-phase (CO₂/brine) experiments using X-ray CT scanning. The study’s outcomes (samples from Victoria, southwest Australia) showed that the sweep efficiency was controlled by sub-core-scale heterogeneities while using CT scanning to visualize the in situ CO₂ saturation profile. Another study [73] examined the relationship between in situ saturation profiles obtained using a CT scanner and the porosity and heterogeneity distributions, which are critical factors influencing the CO₂ storage capacity within the core. In situ data on CO₂ injection revealed anomalies in local saturation that are attributed to capillary effects at the core–sample interface [73]. Nuclear magnetic resonance (NMR) is a valuable technique for assessing changes in pore size measurements and can be utilized for in situ analyses. In their study, Wang et al. [74] investigated the application of time domain nuclear magnetic resonance (TD-NMR) by examining transverse relaxation time (T2) and diffusion coefficient (D) distributions to detect pore size alterations in rock samples undergoing CO₂ sequestration. These changes are associated with geochemical processes such as mineral precipitation and dissolution (MPD). NMR can verify pore size modifications by revealing shifts in the peak values corresponding to different pore types in T2 and D distributions before and after CO₂ sequestration. The findings from NMR are corroborated by results from other in situ measurement techniques.

Thin sections are another way to see a detailed microscopic view of the sample’s mineralogy (grain level) before and after the scCO₂ injection. Figure 20 shows the (a) cross-polarized light image of a thin section of sandstone (SS) and (b) cross-polarized light image of a thin section of limestone (LS). Thin section measurements and image-registered micro-CT scanning were used to obtain mineralogy and capture pore and matrix features to identify details of the change in rock geochemistry regarding MPD.

Acoustic and resistivity measurements are another way to monitor CO₂ sequestration. Acoustic measurement refers to velocity, including measuring the velocity of sound waves traveling through the core sample. These measurements are conducted before and after interactions between scCO₂, rock, and brine. Resistivity measurements are monitored to establish CO₂/rock equilibrium and reaction progress pre- and post-scCO₂ exposure.

3. Laboratory Studies of CO₂–Brine–Rock Interaction for Carbon Storage

Numerous laboratory experiments have investigated the geochemical interactions among CO₂, brine, and rock. These studies, conducted under specific conditions such as CO₂ acidification, examined the effects of geochemical interactions on brine and various rock types. Some experiments were conducted over short durations and at low temperatures, involving an alteration in the chemical composition of the brine. Under these conditions, significant carbonate dissolution and precipitation were observed [17,75,76,77,78]. For instance, wormholes formed in limestone cores due to CO₂–brine injection, which increased permeability and dissolution [79]. Other researchers have studied geochemical reactions at higher temperatures [80]. They found that CO₂-induced precipitation reactions occurred in fractures within cap rock, reducing the measurement of capillary pressure [81]. Additionally, mineral formations were observed on fracture planes along natural CO₂ leakage paths, and carbonates and anhydrite were present in fractures and cracks [82,83]. The precipitation reactions in natural reservoirs were attributed to dawsonite formation [84,85]. The St. John Field, spanning parts of Arizona and New Mexico, is an exemplary site for studying the long-term presence of CO₂ in natural reservoirs. Observations in this field have revealed significant mineralogical and geochemical changes, such as the formation of CaCO₃ resulting from the dissolution of limestone and dolomites. The interactions between reservoir fluids and rocks have led to the dissolution of carbonate cement and detrital feldspars, along with the formation of minerals like kaolinite and dawsonite. Geochemical simulations indicate that dawsonite deposition likely occurred when CO₂ fugacity reached 20 bars and that CO₂ fugacity decreased concurrently with the formation of kaolinite [86].

3.1. Laboratory-Scale Static Batch Reactor Experiments of CO₂–Brine–Rock Interaction for Carbon Storage

In Figure 21, the static reactor system is depicted for both one-month and six-month durations. Operating at approximately 55 °C and a pressure of 4.08 MPa, the system facilitates interactions between CO₂ and brine. The outcomes of these interactions revealed alterations in permeability, porosity, dissolution, and pore structure [42]. The batch experiment revealed various mineral dissolution patterns, resulting in increased surface area and enhanced dissolution rates, as illustrated in Figure 22 [87]. Mandalaparty [88] elucidated the chemical reactions occurring during CO₂–brine–rock interactions through batch experiments. In limestone samples, a notable dissolution occurred without any precipitation observed. Conversely, sandstone experiments exhibited the precipitation of calcite and kaolinite. A coherent correlation between simulation and laboratory findings was established, using the Geochemist’s Workbench (V3.2.2) for modeling. The lessons learned from a critical review of over 100 references reveal several key insights for understanding geochemical interactions and reactive transport phenomena.

In Appendix A,

Table A1. Summary of research findings on the MPD (mineralization, precipitation, and dissolution) on rock types based on static reactor/static batch reactors/HPHT reactors/static system (in situ condition).

Sample	Temp (°C)	Pressure (Mpa)	Experimental Setup	Research Findings
Lower Tuscaloosa Formation [115]	85	23.8	Static System (in situ condition)	The exposure time to CO2 was 180 days, resulting in a 7% decrease in φ and a 13% decrease in K due to feldspar dissolution, migration, and secondary mineral precipitation, which collectively altered the pore structure.
Vermillion Sandstone [116]	85	23.8	Static System (in situ condition)	The exposure time to CO2 was 180 days, resulting in a 50% decrease in K due to feldspar dissolution, migration, and secondary mineral precipitation, which collectively altered the pore structure of the sandstone.
Knox County [116]	85	23.8	Static System (in situ condition)	The exposure time to CO2 was 180 days, resulting in increased K linked to mineral dissolution (most likely feldspar). Mineral precipitation occurred primarily on the sample’s external surface.
Sandstone [117]	200	10	HPHT Reactor	Demonstrate that the ankerite dissolution and clay minerals can elevate the Ca2+, Mg2+, and Fe2+ concentration, ultimately leading to silicate precipitation in CO2. Additionally, these processes can induce changes in reservoir φ and K.
Sandstone [36]	40	2–6	Reactor Chamber	Long-term CO2 reactions in the aquifer result in a 49% pH drop over 1.5 years, forming carbonic acid. This process leads to significant mineral dissolution, including Ca2+ and quartz, increasing pore fluid concentrations. Consequently, drying-out effects and NaCl crystallization occur within the rock pore space of the aquifer.
Selma Chalk [115] > 90 calcite	85	23.8	Static System (in situ condition)	Selma chalk is a promising candidate as a secondary seal with unchanged K over six months.
Limestone [118]	20	0.3	Chemical Analysis and Micro-CT	The 15 h experiment, at an injection rate of 100 cc/h, revealed an uneven increase in φ, connectivity, and reactive surface area due to dissolution.
Carbonate [117]	200	10	HPHT Reactor	This finding and other significant results contribute to our understanding of CO2–brine–rock interactions and provide valuable insights for long-term carbon storage.
Carbonate [42] (gypsum and dolomite)	55	23.8	Static Batch Reactor	Mineral dissolution and precipitation alter the deposit for CO2 storage, enhancing void connectivity. Both minerals dissolved, increasing K. After six months, the total φ slightly decreased from 19.5% to 19.35%.
Calcite and Dolomite [16]	60	12	Chemical Analysis	This paper summarizes recent work on CO2 exsolution and mineral effects in GCS reservoirs, emphasizing carbon component behavior (CO2 (sc/g), CO2 (aq), HCO3−, calcite, and dolomite). The discussion emphasizes the transport mechanisms involving coupled geochemical and two-phase flow processes, addressing their implications for long-term safety. Experimental findings revealed that mineral dissolution affects both capillary pressure and permeability, which are pivotal factors in reservoir flow modeling.
Basalt (Auckland volcanic) [119]	100	5.5	Reactor Chamber	In a 140-day study on basalt samples, CO2–water–rock reactions increased φ and reduced rigidity due to dissolution; secondary mineral phases formed, including chemically zoned ankerites and aluminosilicates, creating new pores. Basalts with higher initial φ and volcanic glass content exhibited a 15.3% φ increase and a threefold K increase, suggesting potential impacts in CO2 sequestration scenarios.
Lower Tuscaloosa Sandstone [120]	85	23.8	Static Reactor	An experimental study investigated the geochemical CO2–brine–rock interactions under geologic CO2 storage conditions in a static reaction system to probe potential changes. The permeability of the sandstone formation was observed to decrease.
Marine Shale (primary sealing formation) [120]	85	23.8	Static Reactor	Marine shale permeability increased after CO2 exposure, impacting primary seal integrity in CO2 storage. The change is attributed to reactive mineral composition, sample heterogeneity, and delamination, with altered shale permeability being observed to be 1000 times less than sandstone.
Lithic Sandstone and Calcareous Mudstone (deep coal seams) [106]	160	15	Reactor	In deep coal seam CO2 storage, a 12-day experimental study revealed that cap rock actively participates in crucial chemical reactions for geological CO2 sequestration. Alterations in lithic sandstone include significant silicate dissolution, while calcareous mudstone exhibits higher reactivity, forming dolomite, siderite, illite, and chlorite. The formation of clay minerals in the cap rock reduces φ, enhancing CO2 containment security and preventing groundwater pollution.
Mafic Rock (outcrops) [121]	69.8	8.27	Batch Reactor	Carbon mineralization in mafic rocks is assessed through experiments on rock characteristics, mineralogy, pore structure, and geomechanics pre- and post-CO2 exposure. The results reveal reactivity with mafic mineral dissolution, new carbonate precipitation, reduced φ (2.2% to 4.5%), and K reaching the measurement limit. Surface rock hardness and Young’s modulus notably increase, with a maximum of 903% and 91% in one sample. An indirect correlation between φ and rock hardness/Young’s modulus is observed, while Poisson’s ratio shows no change after CO2 interaction.

provides a comprehensive overview of detailed studies, analyses, and results from static batch reactor experiments involving various rock types, including sandstone, carbonate, shale, etc.

Table A1 (Appendix A) offers an overview of detailed studies, precise analyses, and conclusive results from static batch reactor experiments involving a diverse range of rock types, including sandstone, carbonate, shale, and more. It not only provides a detailed analysis of the findings but also establishes the scientific criteria with utmost precision, mentioning the critical parameters that are indispensable for the geochemical and geochemistry of CO₂–brine–rock interactions in the context of CCS. Table A1 provides a detailed analysis of numerous experimental studies, each delving into the intricate and multifaceted effects of CO₂ exposure on various geological formations. These studies, conducted on formations such as the Lower Tuscaloosa Formation, Vermillion Sandstone, and Knox County, have revealed significant changes in permeability (K) and porosity (φ) over a span of 180 days. For instance, the Vermillion Sandstone experienced a 50% decrease in K. The high-pressure high-temperature (HPHT) reactor studies on sandstones demonstrated changes in mineral concentrations leading to silicate precipitation. Studies on Selma chalk indicated its potential as a CO₂ storage seal due to stable permeability, while basalt samples showed increased porosity and decreased rigidity from CO₂–water–rock reactions. Lithic sandstone and calcareous mudstone in deep coal seams showed significant chemical reactivity, forming minerals that enhance CO₂ containment security and prevent ground pollution. Mafic rock studies revealed substantial increases in rock hardness and the Young’s modulus post-CO₂ exposure, although porosity decreased. These findings collectively highlight the complex and dynamic interactions between CO₂ and various rock types, underscoring the importance of mineral dissolution and precipitation in altering rock properties, an essential aspect of geological carbon storage (for additional details, see Table A1 in Appendix A).

3.2. Laboratory-Scale Core Flooding Experiments of CO₂–Brine–Rock Interaction for Carbon Storage

The author [87] employed the core flooding system depicted in Figure 23, which maintained a constant brine flow rate for each sandstone, limestone, and dolomite laboratory experiment. The CO₂ flow rates varied, with rates of 2.82 mL/min and 1.41 mL/min for sandstone, 1.4 mL/min for limestone, and 0.71 mL/min for dolomite. The findings underscored the significance of iron chemistry in sandstone for CO₂ sequestration and the dissolution and wormhole formation observed in limestone and dolomite. The dissolution of iron-bearing minerals contributed to increased porosity. These results were effectively modeled using reactive transport simulators such as TOUGHREACT [87].

Table A2. Summary of research findings on the MPD (mineralization, precipitation, and dissolution) on rock types based on dynamic core flooding systems.

Sample	Temp (°C)	Pressure (Mpa)	Experimental Setup	Research Findings
Sandstone [122]	40	10	Core Flooding	The CT images of CO2 saturation reveal no significant evidence of gravity override during CO2 injection, even at the relatively low injection rate of 0.1 cc/min.
Sandstone [123]	40	10	Core Flooding	A 1D model was developed to simulate the core flooding test performed on the Berea core. Efforts were made to match the evolution of mean CO2 saturation profiles during injection, covering rates from 0.1 cc/min to 4.5 cc/min.
Sandstone [124]	40	10	Core Flooding	An experimental setup was established to investigate the scCO2 dissolution and the transfer of dissolved CO2 in mobile water within (low-K) cores. The experiments were conducted at a flow rate of 1.0 mL/min over 37 h.
Savonnières [49] > 97 Calcite	50	11.7	Core Flooding	At a rate of 0.4 mL/h, the continuous decrease in injectivity in the samples due to the dissolution and precipitation of calcite poses a greater risk, mainly if these processes occur near the wellbore, leading to reduced injectivity and potential shutdown of the CCS operation.
Carbonate [54] > 97% Calcite	50	9	Core Flooding	At a flow rate of Q = 1.667 × 10−9 m3/s and under relatively high Péclet and Damköhler numbers, we observe wormhole formation and propagation, accompanied by alterations in K and φ resulting from dissolution and precipitation.
Savonnières [37] > 97 Calcite	50	10	Core Flooding	At a formation water pH of 3 to 4, chemical reactions impact mechanical properties, leading to increased K and φ. In limestone, these reactions weaken the consolidated area and vice versa, with an injection rate of 0.5 mL/min.
Dolomite–Calcite [112]	31	18 and 22	Core Flooding	CO2 sequestration in the Asmari Formation at 1 mL/min and 2 mL/min for 2 and 4 weeks significantly alters geochemical properties, impacting the mineralogical structure. K decreases from 51.8 to 15.06 mD with a φ drop from 22.90 to 15.56. This finding suggests that formations (highly fractured) can safely store CO2, expanding storage locations globally. Long-term CO2 reactions induce dry-out effects and precipitation of NaCl in the pore space of aquifers, increasing the concentration of Na+ from 7300 to 9000 mg/L, with increments of K+ and Mg+ in the pore fluid.
Siltstone [125]	35	8.5–9.5	Core Flooding	The study investigates the impact of salinity levels in formation fluid on siltstone caprock K during scCO2 dominant advective flow. Siltstone caprock samples, saturated with synthetic brines resembling natural fluids, underwent scCO2 K experiments. The results reveal a significant reduction in scCO2 K at high salinity concentrations, attributed to evaporite deposition in rock pores, dependent on brine elemental concentration and caprock–brine interaction, known as the CO2 dry-out phenomenon.

(Appendix A) offers a detailed account of laboratory-scale core flooding experiments of CO₂–brine–rock interactions for carbon storage, with each one being a significant piece of the puzzle in our understanding of the effects of CO₂ injection under different temperatures and pressure conditions. In sandstone, experiments revealed minimal gravity override and provided significant insights into scCO₂ dissolution and mobility. Studies on calcite-rich rocks like Savonnières and carbonate samples highlighted the risks of injectivity reduction near wellbores due to calcite dissolution and precipitation, with an observable wormhole formation and mechanical property changes. The core flooding experiments in the Asmari Formation (dolomite–calcite) demonstrated significant permeability and porosity reductions, suggesting safe CO₂ storage potential in highly fractured formations. However, long-term reactions led to mineral precipitation and increased ion concentrations in pore fluids. The siltstone study emphasized the critical impact of salinity on caprock permeability, showing significant reductions due to evaporite deposition, thus illustrating the importance of brine chemistry in CO₂ storage processes. These findings underscore the intricate geochemical interactions and mechanical alterations induced by CO₂ injection, which are crucial for optimizing geological carbon sequestration strategies (for additional details, see Table A2 in Appendix A).

Figure 24, which is based on the data in Table A1 and Table A2 (Appendix A), is a summary of all pressures and temperatures used in laboratory studies. It includes 23 data points (only 16 shown here) from core flooding experiments as well as static reactors, static batch reactors, HPHT reactors, and static systems (in situ condition). The graph shows the range of reservoir depths covered in the experimental studies (500 ft to 10,000 ft). The MPD results in these studies show the most coverage for reservoirs at depths ranging from 2000 to 5000 ft. The data for higher temperatures are found to generally be at pressures below the normal hydrostatic pressures.

Figure 25 shows the experimental methodology and operational framework. The workflow comprises five pivotal components:

(1)

Petrophysical characterization involving helium porosimeter and ultra-permeability assessments.

(2)

Analytical chemistry processes, including XRD and SEM.

(3)

Utilization of a static batch reactor for investigating long-term CO₂ storage.

(4)

AFS 300 core flooding experiments to observe chemical changes using the Comet Yxlon FF20 industrial CT scanner.

(5)

Implementing reactive transport modeling to explore long-term CO₂ storage dynamics over 1 to 10,000 years using simulation, elucidating the processes governing long-term storage and sequestration integrity.

Few studies have explored the dielectric constant or dielectric permittivity in CO₂–water–porous media, making this a largely uncharted area of research. Our investigation focuses on the dielectric constant, a vital rock property, and dielectric permittivity, defined as “the product of vacuum permittivity and relative permittivity” [91]. Rabiu et al. (2020) were pioneers in examining dielectric permittivity interactions between CO₂, water, and basalt for carbon storage. Their seminal work found that bulk dielectric permittivity increased with CO₂ injection, while bulk electrical conductivity initially remained unchanged but later increased. This was attributed to the time-dependent dissolution of CO₂ in water. Consequently, pH, bulk dielectric permittivity, and bulk electrical conductivity are crucial for CO₂ monitoring [92]. Based on the above understanding, these can also affect the geochemical and mineralogical interactions pre- and post-CO₂–brine–rock reactions at the static batch reactor and how these changes occurred based on the dielectric permittivity and dielectric constant after complete exposure of scCO₂ as a time-dependent parameter. Future research direction will be based on the dielectric constant or dielectric permittivity in terms of MPD (mineralization, precipitation, and dissolution).

4. Simulation Studies of CO₂–Brine–Rock Interaction for Carbon Storage

Geochemical and solute transport modeling is a practical tool for ensuring the long-term security of CO₂ storage. As illustrated in Figure 26, this modeling comprises four key components: (1) modeling of CO₂ experiments, (2) long-term CO₂ integrity modeling, (3) CO₂ injectivity modeling, and (4) well integrity modeling. These components, measured in meters and years, are essential for understanding the fate of injected CO₂ and its effects on chemical and physical properties. This includes residual CO₂ trapping, structural tapping, mineral tapping, and dissolution trapping. Various reactive transport simulators are available to monitor these changes over extended periods. Researchers frequently utilize sedimentary rock formations, such as depleted reservoirs (oil and gas) and saline aquifers, for CO₂ storage and monitoring [17]. Petroleum reservoirs, in particular, offer the advantage of existing subsurface infrastructure for CO₂ storage and monitoring [93].

This section provides a comparative overview and introduction to the principles and performance of different simulation research tools used in CO₂–brine–rock interactions for CO₂ sequestration for reactive transport simulators, as discussed in Table 1 and Table 2. The performance of the various reactive transport simulators is based on previous research, as detailed in Table 2.

Table 1. Comparative overview of different reactive transport simulators for CO₂–brine–rock interactions for geochemical modeling for CO₂ sequestration.

Simulators	Comparative Overview
TOUGHREACT V4.13-OMP [94]	TOUGHREACT was developed by the Energy Geoscience division of Lawrence Berkely National Laboratory, University of California, Berkeley. TOUGHREACT V4.13-OMP is a simulator used for multiphase reactive transport. It is also used for other purposes, but here, it is focused on geological carbon sequestration. The Treactv413omp_eco2n module of TOUGHREACT is used for 1D and 2D cases for CO2 sequestration in a deep saline formation (executable version of the software). TOUGHREACT is written in FORTRAN 77 with FORTRAN-90 extensions.
Geochemist’s Workbench (GWB 2023) [95,96]	It includes C++, Fortran 90, and Python wrappers. GWB software was initially developed by the University of Illinois Urbana-Champaign. It is currently developed by Aqueous Solutions LLC. The software has an exemplary user interface that can do many things, such as reactive transport modeling, including X1t and X2t (1D and 2D), phase diagrams, equilibrium and kinetic reactions, graphics and animation, and more.
PHREEQC (V3) [97]	PHREEQC is developed by the US Geological Survey for geochemical modeling and chemical reactions. It is written in the C++ programming language.
CRUNCHFLOW (2009) [98]	It was developed by Carl I. Steefel, the Earth science division of Lawrence Berkely lab. It is written in Fortran programming language. It is used for multicomponent reactive flow and transport modeling, including aqueous kinetics, geochemical conditions, diffusion, dispersion, etc.
GEM-CMG (2023.40)	GEM is a reservoir simulation software package from the Computer Modeling Group, Canada. It has geochemistry modeling options, including a kinetics reaction model (mineral precipitation and dissolution reactions).

Table 1. Comparative overview of different reactive transport simulators for CO₂–brine–rock interactions for geochemical modeling for CO₂ sequestration.

Simulators	Comparative Overview
TOUGHREACT V4.13-OMP [94]	TOUGHREACT was developed by the Energy Geoscience division of Lawrence Berkely National Laboratory, University of California, Berkeley. TOUGHREACT V4.13-OMP is a simulator used for multiphase reactive transport. It is also used for other purposes, but here, it is focused on geological carbon sequestration. The Treactv413omp_eco2n module of TOUGHREACT is used for 1D and 2D cases for CO2 sequestration in a deep saline formation (executable version of the software). TOUGHREACT is written in FORTRAN 77 with FORTRAN-90 extensions.
Geochemist’s Workbench (GWB 2023) [95,96]	It includes C++, Fortran 90, and Python wrappers. GWB software was initially developed by the University of Illinois Urbana-Champaign. It is currently developed by Aqueous Solutions LLC. The software has an exemplary user interface that can do many things, such as reactive transport modeling, including X1t and X2t (1D and 2D), phase diagrams, equilibrium and kinetic reactions, graphics and animation, and more.
PHREEQC (V3) [97]	PHREEQC is developed by the US Geological Survey for geochemical modeling and chemical reactions. It is written in the C++ programming language.
CRUNCHFLOW (2009) [98]	It was developed by Carl I. Steefel, the Earth science division of Lawrence Berkely lab. It is written in Fortran programming language. It is used for multicomponent reactive flow and transport modeling, including aqueous kinetics, geochemical conditions, diffusion, dispersion, etc.
GEM-CMG (2023.40)	GEM is a reservoir simulation software package from the Computer Modeling Group, Canada. It has geochemistry modeling options, including a kinetics reaction model (mineral precipitation and dissolution reactions).

Previous studies on injecting supercritical CO₂ (scCO₂) near wellbore regions for CO₂ storage have produced significant findings. Utilizing THC (thermal, hydraulic, chemical) codes, these studies comprehensively modeled the interactions associated with injecting millions of tons of CO₂ per year, focusing on processes occurring near the wellbore region. Notably, researchers employed TOUGHREACT to investigate the critical impact of the near wellbore region on the injectivity of scCO₂, as illustrated in Figure 27 [17,18,99].

Table 2 offers insight into the role of geochemical reactions in CO₂ multiphase reactive transport. It explains the mechanisms behind chemical reactions in long-term CO₂ storage, CO₂ storage processes, leakage scenarios, and multiphase displacement (MPD) phenomena. These reactions are analyzed using reactive transport software such as TOUGHREACT V4.13-OMP, GWB 2023, CRUNCHFLOW (2009), GEM-CMG (2023.40), and PHREEQC (V3).

Table 2. Summary of previous research on the reactive transport simulator for CO₂–brine–rock interactions for CO₂ sequestration.

Sample	Simulator	Research Findings
Sandstone and Limestone [100]	Numerical simulation (GEM module of CMG)	Geochemical activity significantly impacts limestone, causing a 16.12% increase in porosity. Due to chemical activity, both limestone and sandstone experience decreased reservoir strength during the injection period. The maximum subsidence after 500 years is 0.0017 m in sandstone and 0.033 m in limestone, attributed to geochemical activities.
Sand and Shale [101]	2D radial reservoir model for two-phase flow (TOUGHREACT)	Following 10,000 years, 95% of the CO2 dissolves in the brine, while minerals absorb 5%. The mineralogy of the sand and shale is comprehensively characterized utilizing kinetics based on transition state theory.
Carbonate Rock [102]	GEM-GHG [103,104]	After 10,000 years, the percentage of CO2 trapped in minerals ranges from 40% to 100%, depending on the initial mineralogy. The rock mineralogy is determined using kinetics based on transition state theory.
Cap Rock [105]	PHREEQC (V2.6)	The alteration in porosity in the cap rock is insignificant, with a minor reduction in φ being modeled overall, except at the interface between the reservoir and cap rock after 3000 years. The entire cap rock mineralogy is assessed using kinetics based on transition state theory reactions.
Lithic Sandstone and Calcareous Mudstone (deep coal seams) [106]	TOUGHREACT	Geochemical simulation can partially reflect the dissolution and precipitation state of minerals, but it only partially aligns with experimental results. Ensuring reliability requires incorporating the actual formation’s physical properties and the rocks’ thermodynamic parameters into the simulation.
Calcite [34]	PHREEQC (V3)	This study investigated the geochemical perspective of CO2/calcite/brine wettability, considering pressure, temperature, and salinity effects through surface complexation modeling. The findings indicate that pressure, temperature, and salinity influence calcite surface species concentrations, surface potential, and disjoining pressure, impacting CO2-wetness and water-wetness dynamics.
Eagle Ford and Mancos Shales [107]	PHREEQC (V3)	A one-dimensional reactive transport model using PHREEQC simulated CO2–shale interaction. Equilibrium and kinetic models at 70 °C and 117 atm, calibrated with shale core data from Eagle Ford and Mancos fields, revealed CO2 injection triggering mineral dissolution and precipitation. The models emphasized the effectiveness of mineral trapping and significant changes occurring between 10 and 100 years. The results contribute to understanding the mineral evolution in CO2–shale interaction, but further studies are needed to address field-scale uncertainties.
Shihezi Formation [108]	TOUGHREACT V4.12-OMP (10, 20, 30, 300, 500 and 1000 years)	Numerical simulations of CO2–brine–rock interactions in the Shihezi Formation indicate K-feldspar and albite dissolution, while calcite and quartz show dissolution and precipitation patterns. Despite a low interaction rate, this proves an ideal geological storage mechanism, influencing petrophysical parameters, minimizing leakage risk, and enhancing CO2 mineralization.
Carbonate [109]	PHREEQC (V3)	This study utilized experiments that included dynamics and static and PHREEQC geochemical modeling to analyze CO2–brine–rock interaction in carbonate rocks. The findings revealed intensified CO2 dissolution, pressure-independent surface CO2 loading on calcite and dolomite, and minimal influence exchange of ions on CO2 storage in these minerals.
Gabbro-Anorthosite [110]	CRUNCHFLOW (2009)	In laboratory experiments on a gabbro-anorthosite sample, the potential for CO2 mineral carbonation was assessed under realistic pressure and temperature conditions using seawater. Geochemical modeling in CrunchFlow successfully replicated the experimental observations, revealing increased iron, magnesium, and calcium concentrations during dissolution (Stage I) and signs of carbonation during subsaturation (Stage II). The study suggests mineral carbonation potential in the Torrão–Odivelas Massif, emphasizing further research to upscale the findings to field scale for effective CO2 emissions reduction.
Shale [111]	Geochemist’s Workbench	Geochemical modeling provides calcite dissolution, an increase in shale porosity because of overall shale brine CO2 interaction, and a pH drop due to desorption of tracer elements, and calcite is the main factor in controlling the mobilization of trace elements.

Table 2. Summary of previous research on the reactive transport simulator for CO₂–brine–rock interactions for CO₂ sequestration.

Sample	Simulator	Research Findings
Sandstone and Limestone [100]	Numerical simulation (GEM module of CMG)	Geochemical activity significantly impacts limestone, causing a 16.12% increase in porosity. Due to chemical activity, both limestone and sandstone experience decreased reservoir strength during the injection period. The maximum subsidence after 500 years is 0.0017 m in sandstone and 0.033 m in limestone, attributed to geochemical activities.
Sand and Shale [101]	2D radial reservoir model for two-phase flow (TOUGHREACT)	Following 10,000 years, 95% of the CO2 dissolves in the brine, while minerals absorb 5%. The mineralogy of the sand and shale is comprehensively characterized utilizing kinetics based on transition state theory.
Carbonate Rock [102]	GEM-GHG [103,104]	After 10,000 years, the percentage of CO2 trapped in minerals ranges from 40% to 100%, depending on the initial mineralogy. The rock mineralogy is determined using kinetics based on transition state theory.
Cap Rock [105]	PHREEQC (V2.6)	The alteration in porosity in the cap rock is insignificant, with a minor reduction in φ being modeled overall, except at the interface between the reservoir and cap rock after 3000 years. The entire cap rock mineralogy is assessed using kinetics based on transition state theory reactions.
Lithic Sandstone and Calcareous Mudstone (deep coal seams) [106]	TOUGHREACT	Geochemical simulation can partially reflect the dissolution and precipitation state of minerals, but it only partially aligns with experimental results. Ensuring reliability requires incorporating the actual formation’s physical properties and the rocks’ thermodynamic parameters into the simulation.
Calcite [34]	PHREEQC (V3)	This study investigated the geochemical perspective of CO2/calcite/brine wettability, considering pressure, temperature, and salinity effects through surface complexation modeling. The findings indicate that pressure, temperature, and salinity influence calcite surface species concentrations, surface potential, and disjoining pressure, impacting CO2-wetness and water-wetness dynamics.
Eagle Ford and Mancos Shales [107]	PHREEQC (V3)	A one-dimensional reactive transport model using PHREEQC simulated CO2–shale interaction. Equilibrium and kinetic models at 70 °C and 117 atm, calibrated with shale core data from Eagle Ford and Mancos fields, revealed CO2 injection triggering mineral dissolution and precipitation. The models emphasized the effectiveness of mineral trapping and significant changes occurring between 10 and 100 years. The results contribute to understanding the mineral evolution in CO2–shale interaction, but further studies are needed to address field-scale uncertainties.
Shihezi Formation [108]	TOUGHREACT V4.12-OMP (10, 20, 30, 300, 500 and 1000 years)	Numerical simulations of CO2–brine–rock interactions in the Shihezi Formation indicate K-feldspar and albite dissolution, while calcite and quartz show dissolution and precipitation patterns. Despite a low interaction rate, this proves an ideal geological storage mechanism, influencing petrophysical parameters, minimizing leakage risk, and enhancing CO2 mineralization.
Carbonate [109]	PHREEQC (V3)	This study utilized experiments that included dynamics and static and PHREEQC geochemical modeling to analyze CO2–brine–rock interaction in carbonate rocks. The findings revealed intensified CO2 dissolution, pressure-independent surface CO2 loading on calcite and dolomite, and minimal influence exchange of ions on CO2 storage in these minerals.
Gabbro-Anorthosite [110]	CRUNCHFLOW (2009)	In laboratory experiments on a gabbro-anorthosite sample, the potential for CO2 mineral carbonation was assessed under realistic pressure and temperature conditions using seawater. Geochemical modeling in CrunchFlow successfully replicated the experimental observations, revealing increased iron, magnesium, and calcium concentrations during dissolution (Stage I) and signs of carbonation during subsaturation (Stage II). The study suggests mineral carbonation potential in the Torrão–Odivelas Massif, emphasizing further research to upscale the findings to field scale for effective CO2 emissions reduction.
Shale [111]	Geochemist’s Workbench	Geochemical modeling provides calcite dissolution, an increase in shale porosity because of overall shale brine CO2 interaction, and a pH drop due to desorption of tracer elements, and calcite is the main factor in controlling the mobilization of trace elements.

5. Discussion

This research highlights the gap in predicting the long-term changes of the CO₂–brine–rock interaction under laboratory and simulation studies using geochemical reactive transport simulators, such as TOUGHREACT, Geochemist’s Workbench, and PHREEQC. The primary focus of our review is to quantify the recent advancement in carbon storage technology, which is crucial for the environmental impact and which is one aspect of carbon storage towards net-zero technology in the petroleum industry. Building on an extensive literature review of recent advances in geochemical and mineralogical studies on CO₂–brine–rock interactions for CO₂ sequestration, we aimed to monitor and identify the optimal parameters for comprehensive understanding suitable for long-term carbon storage. These findings are significant and of utmost importance to our field of carbon capture and storage (CCS) as they contribute to our collective efforts in CO₂ sequestration.

Geochemical changes such as mineralization, precipitation, and dissolution (MPD) are crucial for carbon storage. Monitoring these processes is vital for understanding long-term carbon storage and ensuring its security. As discussed in Appendix A, Table A1 and Table A2, and Table 2, significant changes in permeability, porosity, calcite precipitation, mineral dissolution, and feldspar dissolution alter the pore structure of the core samples.

The five most vital experimental and simulation techniques for understanding the MPD are shown in Figure 28. The findings of this research are significant, providing a comprehensive understanding of various aspects of reactive transport mechanisms, including permeability, porosity, and mineralogical changes, utilizing in situ visualization with a CT scanner.

• Dual-energy CT scanning.
• Thin sections.
• Core flooding and batch reactor experiments.
• Petrophysical properties include dielectric permittivity, NMR measurements, and acoustic and resistivity measurements.
• Reactive transport phenomena modeling.

6. Conclusions

Based on a review spanning the last 25 years of geochemical studies on CO₂–brine–rock interactions, several essential parameters, considerations, and future research gaps are documented.

• CO₂–Brine–Rock interactions can create MPD (mineralization, precipitation, dissolution), permeability, and porosity changes based on the types of reservoir rocks and effects on the reactive transport phenomena for long-term CO₂ storage.
• Researchers used various simulators for geochemical reactions, including TOUGHREACT, PHREEQC, CRUNCHFLOW, and the GEM module of CMG. While the Geochemist’s Workbench is an exemplary interface for CO₂ sequestration, it must be utilized more systematically. Geochemist’s Workbench is recommended to comprehensively understand CO₂ storage over different time scales (e.g., 10, 20, 30, and up to 10,000 years), considering MPD, multiphase flow, permeability, porosity, changes, and reactive transport mechanisms.
• Rapid carbonate dissolution can corrode caprock, compromise fault seals, lead to equipment leakage, and affect CO₂ security.
• Limited research has utilized industrial/micro-CT scanners. We can examine MPD interactions between CO₂, brine, and rock for short- and long-term CO₂ storage by employing industrial/micro-CT scanners with dual-energy techniques and analyzing cuttings or chips using micro-CT scanners.
• The effects of pressure, temperature, and salinity on CO2–brine–rock wettability and interfacial tension for long-term CO₂ storage outcomes are unclear, including laboratory studies such as dynamic core flooding, static batch reactor experiments, and simulation studies, such as geochemical reactive transport modeling.
• Lab studies show that after CO₂ storage, there is a reduction in permeability and porosity in fractured reservoirs [112]. This indicates the potential applicability of CO₂ storage in fractured shale and limestone reservoirs. The chemical reactions play a crucial role in sealing fractures by reducing permeability. Further studies are required, and the topic’s applicability may extend to the Permian Basin for more CO₂ storage security, monitoring, and integrity. Abel [113] estimated significant carbon sequestration capacities in the Permian Basin of west Texas and southeastern New Mexico. The study focused on forming solid carbonates with cations from produced waters (surface mineralization) and storing CO₂ dissolved in produced waters (solubility trapping).
• Most importantly, investigating the changes before and after CO₂–brine–rock interactions, particularly considering the influence of the dielectric constant, is crucial. However, research on the dielectric constant and dielectric dispersion remains limited. The dielectric constant, or permittivity, reflects a material’s electrical polarizability [91]. It is linked to macroscopic properties such as solubility, reaction rate constants, and microscopic phenomena [114]. Therefore, further attention to the rock’s dielectric constant before and after interactions with CO₂ and brine is warranted, as it may significantly affect the rock’s geochemical and mineralogical structure.
• Several gaps exist in understanding Péclet and Damköhler Numbers concerning wormhole formation and propagation during scCO₂ injection within various core types. Both Péclet and Damköhler Numbers exhibit an increase during these processes. Further comprehensive investigations are required, mainly focusing on low Damköhler numbers and their influence on reactive transport properties [54].
• There are still gaps in studies involving CT scanners for in situ observation of chemical changes, including MPD, diffusion, dispersion, and alterations at the pore- and grain-level scales.