Investigations of Structural and Residual Trapping Phenomena during CO 2 Sequestration in Deccan Volcanic Province of the Saurashtra Region, Gujarat

This work aims to study the structural and residual trapping mechanisms on the Deccan traps topography to elucidate the possible implementation of CO 2 geological sequestration. This study provides an insight into a selection of stairsteps landscape from Deccan traps in the Saurashtra region, Gujarat, India. Various parameters aﬀect the eﬃciency of the structural and residual trapping mechanisms. Thus, the parametric study is conducted on the modeled synthetic geological domain by considering the suitable injection points for varying injection rates and petrophysical properties. The outcomes of this study will provide insights into the dependencies of structural and residual trapping on the Deccan traps surface topography and injection rates. It can also establish a protocol for selecting the optimal injection points with the desired injection rate for the safe and eﬃcient implementation of CO 2 sequestration. The simulation results of this study have shown the dependencies of structural and residual trapping on the geological domain parameters.


Introduction
According to the International Energy Agency (IEA), the atmospheric CO 2 concentration has reached an alarming level of 410 ppm, in which the energy-related CO 2 emissions rose to a historic high [1]. e increase in the CO 2 concentration has led to a rise in the average temperature on the Earth's surface, resulting in deleterious phenomena like the melting of ice caps in polar regions, thereby creating ecological imbalance. Scientists and researchers are looking for various measures to reduce the effects of CO 2 and control global warming to an extent by reducing the amount of CO 2 reaching the atmosphere [2]. Among the significant measures, CO 2 sequestration is a promising strategy to reduce carbon emissions. CO 2 sequestration is the only storage technique that reduces the CO 2 concentration in the atmosphere without reducing the consumption of fossil fuels, and it is becoming popular among researchers and environmentalists [3]. CO 2 storage requires careful consideration of location and effective predictive analysis [4]. Depending on the storage types, CO 2 sequestration is classified into geologic sequestration, ocean sequestration, and terrestrial sequestration. Geologic sequestration involves storing captured CO 2 in deep geologic formations. Some suitable geologic formations for storage are mature oil and gas reservoirs, coal beds, saline aquifers, and basalt formations [3][4][5]. is work aims to simulate CO 2 geological sequestration in Deccan volcanic province.
e Deccan volcanic province in India is spread across 5,00,000 km 2 [6]. Its petrophysical and geochemical properties are considered one of the largest sinks for the CO 2 geological sequestration [7]. In 1970, the Indian government planned to store nuclear waste in these traps, but the idea was abandoned due to water contamination possibilities [8]. An old survey conducted by the Indian government in collaboration with Pacific Northwest National Laboratory (PNNL) estimated that about 150 gigatons of CO 2 could be stored in the Deccan volcanic provinces with strategic implementation of CO 2 sequestration [8].
e Deccan volcanic basalt rock layers are formed due to the cooling and solidification of molten lava, which came out due to volcanic eruption at the end of the Cretaceous period [9,10]. ere are nearly 11 types of basalt rock formations found in India.
ese basalt rock formations are somewhat similar to the basalt formation found in Iceland and Columbia River basalts of the north-western United States [11][12][13]. e geological subsurface arrangement of the Basalt layers and Mesozoic sediment layers with other geological layers made Deccan volcanic provinces the exemplary candidate for the CO 2 geological sequestration [7]. Deccan volcanic province possesses vast geological heterogeneity with a sequential arrangement of basalt layers with the availability of vesicular basalt and massive basalt. e massive basalt layer should act as caprock due to its fault-free and thick enough layer so that it can act as an impermeable seal [7]. e mineral composition of the Deccan basalts is dominated by the Pyroxene, Plagioclase, and Olivine mineral groups [11,[14][15][16][17]. Basalt rock formation consists mainly of the divalent cation like Ca 2+ , Mg 2+ , and Fe 2+ , which is advantageous in forming the secondary minerals. When these divalent cations react with dissolved CO 2 , minerals like calcite, magnesite, and siderite are formed [11,12,15,17,18]. Due to the availability of favorable minerals, Deccan traps can be considered a potential candidate for CO 2 sequestration. e Deccan volcanic region considered in this work is based on the Saurashtra Peninsula with the precise location of 21.50°N-23°N and 69.75°E-71.50°E longitude [19]. e major part of the Saurashtra Peninsula is excepted to be covered by the Deccan traps. e fate of injected CO 2 during the geological sequestration is classified into four categories. First, when the CO 2 is injected into the domain, the formation's top impermeable layer provides the primary trap. It prevents CO 2 from escaping to Earth's surface; this type of trapping mechanism is called structural trapping. e second is residual trapping, where CO 2 migrating through a porous medium gets trapped in the migration pathway or confined inside a porous structure. e third is solubility trapping; the residual CO 2 will interact with resident water to solubilize and form weak carbonic acid. e fourth is mineral trapping; the weak carbonic acid will begin to react with mineral rocks and form secondary carbonate minerals [20]. e efficiency of the CO 2 geological sequestration is determined by structural and residual trapping mechanisms [21]. erefore, understanding the movement of CO 2 and its spreading in various forms is vital for a specific geological formation. As more CO 2 gets trapped in the rigid porous formation, a higher amount of CO 2 will undergo solubility trapping leading to a surge in the production of carbonic acid, which leads to an increase in the mineral reaction and mineral trapping in the formation domain [22,23]. e obtained percentages of structural and residual trapping results can provide a vigorous interpretation for the solubility and mineral trapping. erefore, this article aims to enhance the understanding of the structural and residual trapping mechanisms for CO 2 sequestration in the Deccan volcanic formation domain. Investigation on structural and residual trapping alone will help understand the fate of CO 2 in the geological formation and assist in further studies on the field-scale application [24].
In situ pressures and temperatures of deep geological formations are favorable to operate the geological sequestration process in the supercritical state. e main advantage of storing CO 2 in a supercritical state (ScCO 2 ) is that it consumes less storage volume than the CO 2 present in the gaseous state. Furthermore, in this article, the reference CO 2 means the carbon dioxide is present in a supercritical state. e CO 2 injected at the deepest geological formation will remain in the supercritical condition due to in situ pressures and temperatures [23,25,26]. When injected into the deep subsurface formation, CO 2 in the form of a plume tends to move upwards due to the buoyancy force. In this process, while injecting CO 2 percolate through the formation layer, it encounters porous channels and traps and leaves residuals in the migration pathway [27,28]. e traps are within the more prominent geological formation, which serves as storage spaces or minireservoirs [29].
To explain the structural and residual trapping phenomena, a geological formation is considered, as illustrated in Figure 1(a). Most of the naturally formed formation layers contain geological perturbations. In geological terminology, it is typically referred to as anticline and syncline sequences. When the injected CO 2 tends to move laterally with the top surface, these perturbations of anticline and syncline primarily affect the migration and movement of the CO 2 plume. ese perturbations of the geological domain act as a trap, which restricts the movement of CO 2 in the anticline dome. is phenomenon further contributes to the trapping mechanisms of CO 2 sequestration [30][31][32]. e injected CO 2 forms a plume that will move upwards due to buoyancy; this phenomenon is pictorially represented in Figure 1(a). e CO 2 plume displaces water and moves freely in the formation domain with the influences of injection pressure; this quantity of CO 2 plume is classified as movable plume; see Figure 1(b). e CO 2 plume moves upwards and gets restricted by an impermeable layer, caprock, and starts moving in the lateral direction. e part of the plume that comes under the influence of caprock will lose its momentum and spread in the lateral direction; see Figure 1(c). During injection, CO 2 accumulated under the one anticline dome will overflow to the next anticline dome. which causes CO 2 movement under the caprock; see Figures 1(d) and 1(e). After the injection period, the CO 2 under the caprock will lose its momentum and get structurally trapped under the anticline domes.
is quantity of CO 2 is classified as structural trapping. In the postinjection period (Figure 1(e)), movable plume starts losing momentum and tends to be trapped in the geological domain. e appreciable amount of CO 2 gets trapped in the migration pathway during the upward movement of the plume and is confined inside the porous structure. is quantity of trapped CO 2 is classified as residual trapping. e fate of CO 2 injection during the postinjection period over the geological time is shown in Figure 1(e). After the injection of CO 2 , there is an apparent transformation of the movable plume to structural and residual trapping. e residual trapped CO 2 coexist with water, solubilized in water to interact with minerals in the formations. erefore, an increase in the percentage of residuals in the formation domain is favorable to CO 2 solubility and then to mineralization [31,33,34].
Most of the research conducted on the structural and residual trapping mechanisms is taken with the aspect of CO 2 saturation to estimate the trapping efficiency in the geological domain [31,33,35,36]. e parameters considered in their studies mostly deal with the reservoir parameters such as pore aspect ratio [37,38], rock type [39], capillary pressure [40][41][42], saturation [27,43], porosity [33], and flow rate [44,45]. In the pore aspect ratio study, the influences of the pore size and throat size of the porous domain are studied on the trapping mechanism and plume migration [37,38]. e influences of the rock structure and rock composition on CO 2 entrapment (both structural and residual trapping) are studied [39]. e influences of porosity are studied regarding the saturation distribution of nonwetting fluid and variation on capillary pressure of the domain [33, 40-42, 46, 47]. Most of these studies were conducted with numerical simulations or/and experimental investigation under controlled parameters by considering the core samples of the geological domain [31,48]. Most researchers use experimental techniques like core-flooding techniques and X-ray microtomography to study the trapping capacity at the lab scale [27,44,46,49].
In the literature, research is conducted on geomorphological structures to study their influences and impact on the structural and residual trapping mechanisms. e SINTEF researchers have developed a reservoir toolbox called MRST-co2lab [33], which can study the influences of the various topographical formations of the Norwegian continental shelf. e techniques like vertical equilibrium and spill-point analysis were used to evaluate and estimate trapping and storage  International Journal of Chemical Engineering capacities of various formations [31,50]. Nearly the topographies of 14 geological formations are saved in this toolbox, in which some of the popular formation topographies are Sleipner [33,51], Sandes [33,52], Utsira [22,32], and Statfjord [33,50]. Nilsen et al. [53] conducted a study on the combined stratigraphic scenarios of different formation morphologies by considering the flooded marginal marine setting and buried offshore sand ridges structures. e spill-point analysis was carried out to analyze the influences of the migration pathway. Moreover, this study is carried out by examining the structural and residual trapping percentages. e author in this research concluded that the uncertainty on top-surface morphology has a clear impact on the CO 2 migration and structural and residual trapping entrapment [53]. Allen et al. [52] performed a similar simulation analysis on the Utsira and Sandnes formations. e study was focused on the caprock elevation, migration of CO 2, and petrophysical properties. Additionally, the perturbation influences on the topography of the formations were explained with a synthetic smooth and wavy top surface of a domain. It was found that the topographical perturbations and caprock elevation have an impact on the structural trapping percentage and CO 2 migration in the domain [52]. Ahmadinia et al. [54] conducted a simulation study on a top-surface structure shaped as a sinusoidal wave. is research by the author was conducted to study the influences of the sloping nature of an aquifer. e structural, residual, and solubility trapping percentages were considered a parameter of evaluation to study the influences of the sloping angle of the top surface. It was observed that the dissolution of CO 2 was less in the highly tilted formation domain due to the uncertainty in residual trapping in the lower formation layers [54]. In this current research, for the first time, a stairsteps kind of structure is considered to conduct a simulation analysis to study the influences of the topography of Deccan traps located in the Saurashtra region, India [19]. is numerical study will provide insight into selecting the injection point and injection rate at the safe range of petrophysical properties to safely implement CO 2 sequestration in the Deccan volcanic province. To achieve this, first, the synthetic geological domain of Deccan traps is modeled. en, the appropriate boundary conditions and petrophysical properties are assigned to the simulation domain. Further, the CO 2 sequestration simulations are carried out at various injection rates, injection points, and petrophysical properties. e structural and residual trapping percentages at discrete times are evaluated and studied. By illustrating the lateral movement of the injected CO 2 in the sizeable geological domain, it has provided an intuition on the influences of Deccan traps topography and geological parameters on the entrapment percentage of structural and residual trapping mechanism in geological time scale.

Model Description
Geological sequestration of CO 2 occurs in a subsurface porous structure that involves several processes, including flow and transport of CO 2 . e solubility and mineral trapping mechanisms are neglected in this work to elucidate the influence of the structural and residual trapping mechanisms, meaning the transport due to chemical reactions is not considered.

Multiphase Flow Equations.
Immiscible displacements of CO 2 and water are occurring in a complex porous geological formation at reservoir conditions. Each phase can involve more than one chemical species and can still be considered a single component because there is no mass transfer (dissolution of CO 2 in water) between phases. Hence, their compositions remain constant over a geological time scale. So, the incompressible flow is cogitated in the simulation domain [34]. e general mass conservation equations governing the multiphase flow is given by e subscript α denotes phases {l, g} (where g is for CO 2 and l is for water). ∅ is the porosity; S α and ρ α are α phase saturation and density, respectively. e term ] → α is Darcy's velocity of α phase, which is given by where K represents permeability, k α represents relative permeability, µ α is viscosity, and z is height. e following equation illustrates the saturation relation for all phases for a singular component:

Brooks-Corey Relation.
e Brooks-Corey relation is used to relate the capillary pressure P c to effective invading fluid saturation S eα . In this current simulation study, CO 2 is the invading fluid in the reservoir [34]. e Brooks-Corey relation is given by where P e is the entry pressure; P c (� (ρ l − ρ g )gh � Δρgh) is the capillary pressure; ρ l and ρ g are the densities of water and injected CO 2 ; S e,g is the effective CO 2 saturation; n b is the parameter related to the pore size distribution. Its value is taken as 2.5, and its range is between 0.2 and 5 [34]. Brooks-Corey-Mualem model gives the relationship equation between relative permeability and effective saturation, as shown in the following equations.
k r,l � S e,l n 1 +n 2 n 3 , where n 1 , n 2, and n 3 are constants, the value of n 1 is 1, n 2 is 1 + 1/n b, and n 3 is 2, which are obtained by the experimental fitting. From the above equation, S e,l is effective water saturation. e effective saturation fluid should be considered normal saturation of fluid in this simulation analysis because it is considered that there is no presence of isolation pore space [34]. Further, the methodology for solving the equations is through discretization. Backward discretization along with discrete derivative operators for grad and div is defined to obtain the following implicit system of equations for a phase "α": e fluid movement is primarily defined by the action of buoyancy and capillary forces, which will govern the movement of injected CO 2 in the geological structure domain [34].

Modeling the Synthetic Computation Domain.
e domain considered in this research is the Saurashtra Peninsula with the precise location of 21.50°N-23°N and 69.75°E-71.50°E longitude adapted from Murthy et al. [19]. e major part of the Saurashtra Peninsula is excepted to be covered by the Deccan traps. e word "traps" in this context represent the stairsteps and stairsteps are like structures formed due to geological stretching, rifting, and uplifting happening from geological past [55] that happened nearly 65 million years ago [11,[56][57][58]. Figures 2(a)-2(c) illustrate the contour plot of the domain (see Figure 2(a) with high range stairsteps traps [19]. From Figures 2(b) and 2(c), a heavy dip can be seen at one corner of the domain. e dip section is related to the Kachchh rift, which shares its boundaries with the Saurashtra Peninsula. One can visualize and analyze the modeled domain as an integrated geomorphological structure of anticline dome and trap structure [11,[56][57][58][59].
e top surface of the domain is modeled by using the MATLAB image processing technique. First, by using the contour plot obtained by literature, the elevation of the structure is extracted. en, by plotting the mesh grid in MATLAB, the top surface of the domain is modeled. Further, the whole grid structure is modeled and simulated using MRST-co2lab. e geological cracks and faults of the domain were not induced in the modeled domain to minimize the complexity of the simulation. e illustration of the synthetic simulation domain can be seen in Figure 2(d).
e physical dimensions of the domain are 160 km × 160 km × 1.8 km.
e domain is discretized into 2,56,000 (160 × 160 × 10) grid cells. An attempt was made to model the domain to an accurate demonstration of the realistic case.

Petrophysical Properties.
e petrophysical properties, i.e., porosity and permeability, need to be assigned to generate the synthetic geological computation domain. e porosity range of the geological domain is maintained between 0.2 and 0.4 (Figure 2(e)); the range of porosity considered is with respect to Deccan basalt [6,60].
e porosity values to each grid cell are assigned randomly by the Gaussian function. e permeability is evaluated for the respective porosity value by utilizing the Carmen-Kozeny relation and assigned to the individual grid cell [34].
where τ represents the tortuosity and A ϑ is the specific surface area. For basalt formation, the value considered for the tortuosity is 1, and the specific surface area is equal to 2.4 × 10 5 μm −1 , which are obtained from A. Navarre-Sitchler et al. [61]. e range of permeability for simulation is evaluated in between 10 and 1500 mD. Figures 2(e) and 2(f ) illustrate the porosity and permeability of the geological domain. e hydrostatic boundary conditions are specified for all the outer boundaries except the top surface, which has a no-flow condition. e depth of the synthetic domain starts from 800 m, as illustrated in Figure 2(d). is indicates that the sequestration of CO 2 in the simulation domain is carried out below 800 m from the surface [62,63]. As the geological domain considered for the simulation is a sloping domain, a uniform initial reservoir pressure cannot be taken for the whole simulation domain. e synthetic domain modeled is the sloping landscape, so the depth value "h" for each grid cell changes. e initial reservoir pressure for each grid cell varies depending on the depth of the grid. e initial reservoir pressure in the reservoir is calculated by ρ w gh. As the density of water considered in the geological domain is constant, the pressure is dependent only on the depth factor, h. e reservoir pressure varies from 0.707 to 22.068 MPa in the geological domain.

Trapping Capacity Calculation.
e flow in the reservoir domain is characterized using conservation of mass, a modified Darcy's law, based on the concept of relative permeability. e entrapment percentage calculations are performed based on the porosity, pore-volume, and CO 2 saturation of the grid cells. Further in the text, the word entrapment percentage means the total trapping percentage (both structural and residual trapping percentages). Structural trapping is calculated using the following formula: Residual trapping is calculated using the following formula: Residual trapping � nf n�1 ∅V r ρ co 2 × min S co 2 , S rco 2 .

Base Case Scenario.
In this section, a numerical simulation is presented for the base case scenario of injecting CO 2 at point B (see Figure 2)(a) of the synthetic computation domain. e CO 2 injection is carried out continuously for the first 20 years at the volumetric flow rate of 99 × 10 5 m 3 / day and the pressure of 22.068 MPa. e density and viscosity of water are 975.86 kg/m 3 and 0.3086 × 10 −3 Pa s and those of CO 2 are 686.54 kg/m 3 and 0.0566 × 10 −3 Pa s, respectively [34]. Simulations were conducted for 3000 years to observe the structural and residual trapping phenomenon. e geological domain consists of a different range of perturbation cognates, with a peak characteristically referred to as an anticline dome in geology. e fate of CO 2 due to structural and residual trapping in the geological domain is thoroughly analyzed and illustrated in Figure 3, which consists of two congener results. e first column represents the CO 2 saturation in the transparent 3D domain, which can analyze the spreading and displacement of CO 2 in the geological domain. e second column illustrates the saturated CO 2 height in the domain. For an economically adhered CO 2 sequestration project, the lateral spreading should be high during the initial period so that it can cover a large volume of the geological domain.
is sizeable spreading can influence the economics of CO 2 sequestration in a virtuous way by reducing the number of injection points. e histogram plot, Figure 4, represents the percentages of structural trapping, residual trapping, and movable plume over a geological time scale. In this particular result, it is observed that the CO 2 plume that is formed after CO 2 injection has moved towards the highest elevation region of an anticline dome. e movement was rapid until the injection period (20 years); this is because the injection force also acts on the CO 2 plume, in addition to the buoyancy forces. e CO 2 plume reaches the highest elevation of the anticline dome within 500 years, but to spread through the anticline top surface, it takes about 2500 years. From this specific observation, it can be suggested that the injection force plays a vital role in the lateral spreading of the CO 2 plume during the preliminary phase of CO 2 injection. During the postinjection period, in the absence of injection pressure, the movement of CO 2 slows down drastically. e movable plume, which is then in the significant portion, transforms into structural trapping and residual trapping (see Figure 4). After a protractive time, there might be a possible transformation of structural trapping into residual trapping. is phenomenon of percentage increase in structural trapping and residual trapping over a geological time scale is observed in Figure 4. e increase in the percentage of residual CO 2 will significantly facilitate the coexistence of CO 2 with water to favor the dissolution of CO 2 to instigate solubility trapping phenomena.

Influence of Injection Location.
e injection location in the geological domain plays a significant role in the CO 2 entrapment in the domain. Figure 5 shows the dynamic evolution of the CO 2 trapping during pre-and postinjection periods at each injection point. From Figure 5, two keen observations are noticed; i.e., movable plume gradually decreases over a geological time scale. Also, structural trapping and residual trapping are increasing over the geological time scale. e order of increment of structural trapping and residual trapping is different for all the injection points. is difference is due to the topographical variation of the Deccan traps. e modeled domain is categorized into three parts to explain the influences of the Deccan trap topographical variation. e first part of categorization is the flat bottom of the domain, the second categorized part is the sloping stairsteps traps of the domain, and the third part is the highest elevation of the structural domain. When the CO 2 is injected at the highest elevation point at injection points C, E, and F, as illustrated in Figure 6, due to the low availability of migration volume and traps, the trapping percentage recorded is low, as observed in Figure 5.
Two injection points are selected to elucidate the influences of the sloping traps. One injection point is at the lowest point of the sloping traps (B injection point, see Figure 2(d)), and another one is located at the top section of sloping traps (A injection point, see Figure 2(d)). e results show that the entrapment percentage recorded at injection point B is highest compared to all injection points. When the CO 2 is injected at the lowest point, the CO 2 spends more time migrating upwards. During this process, the plume encounters a greater number of traps than the A injection point. us, the A injection point has a low total entrapment percentage compared to injection point B despite injecting on the sloping trap region, as illustrated in Figure 5. When the CO 2 is injected at the flat bottom (at injection point D), the CO 2 does not undergo as much migration as the B injection point. e lateral spreading of the CO 2 plume for the D injection point highly depends on the injection force. However, for the B injection point addition to the injection force, the sloping nature of the domain helps achieve greater migration and lateral spreading.
By the end of 3000 years for the cases of A, B, C, and D injection points, the total entrapment percentage is International Journal of Chemical Engineering dominating compared to the E and F injection points (see Figure 5). is is due to the position of injection points, where more quantity of CO 2 undergoes migration and entrapment. e injection point, which is far away from the anticline dome, takes a lot more time in the migration, and for this reason, the movable plume will reduce over time.
From this significant observation, it is understood that positioning the injection points near the sloping traps region yields a higher amount of entrapment (both structural and residual trapping) due to higher CO 2 migration. However, when the CO 2 is injected at the top of the anticline, the decline of lateral movement of CO 2 plume took place, due to

Influence of Deccan Traps
Topography. e naturally available Deccan traps contain geological sloping stairsteps traps, which are integrated and form an anticline structure. In the present synthetic computation domain, these traps are elevated (highlighted in white in all surface plots in Figure 6) into the direction of an enormous anticline dome. From the results of various injection points, as shown in Figure 6, it can be seen that from the injection point (highlighted dark red point), the CO 2 plume is moving towards the highest elevation point. It means that the elevation of the anticline dome dominates the injected CO 2 to move through the sloping traps. When the CO 2 moves through these sloping traps, a higher amount of CO 2 is expected to get trapped in this region. is illustration of trapping on the Deccan traps can be seen in Figure 6 at the B injection point. e higher the amount of CO 2 gets trapped at this structure, the higher the solubility and mineral trapping mechanism entrapment are expected in the long run.
From these observations, it can be concluded that the naturally available topography segments like stairsteps geological traps and perturbation of the geological domain have a significant impact on the structural and residual trapping mechanisms of CO 2 storage in the geological formation.
ese observations give a glimpse of the importance of selecting the geological site based on geological arrangements and topography.

Influence of Injection Rates on Structural and Residual
Trapping.
e influence of injection rates on the trapping mechanisms presented in a histogram plot of the trapping percentage is shown in Figure 7. As the injection rate decreases, the results show that the structural and residual trapping contributions increase, while there is a significant decrease in movable plume contribution. Because the geological domain consists of a finite number of traps, a higher amount of CO 2 is injected into the domain if the injection rate increases. Still, only a finite amount of CO 2 plume can be trapped in the geological domain. e remaining amount of plume will freely move in the domain. For this reason, as the injection rate decreases, the trapping percentage is slightly observed to give an increasing trend and, in contrast, movable plume is decreasing. During the simulations, it was observed that, above 99 × 10 5 m 3 /day injections rate, there is no considerable increase in the structural and residual trapping volume of CO 2 . In CO 2 sequestration, the structural and residual trapping mechanisms play a significant role in facilitating the interaction with the aqueous phase for solubility and mineral trapping mechanisms. erefore, the dominant presence of more structural and residual trapping than movable plume at any time for any point of injection represents the favorable CO 2 sequestration; see also Figure 5 and therein Figure 7 for percentage contributions.

Effect of Petrophysical Properties on Sweeping Efficiency.
A simulation analysis is conducted to study the effects of porosity and permeability on the sweeping efficiency of the geological domain. is study will understand the impact of CO 2 sequestration in the Deccan traps at a low range of International Journal of Chemical Engineering 9 petrophysical properties. e two sets of porosity and permeability ranges are considered in these simulations.
ese simulations are carried out at injection point B with the injection rate of 99 × 10 5 m 3 /day, which is continued up to the initial 20 years. e remaining 2980 years are reserved for postinjection analysis. e porosity ranges for simulation set 1 are considered between 0.05 and 0.1, and the permeability range is between 1 and 10 mD. e range of porosity and permeability for simulation set 2 is considered from 0.2 to 0.4 and 10 to 1500 mD, respectively. e sweeping efficiency deals with the amount of lateral spreading of nonwetting or injected CO 2 into the geological domain. As the lateral spreading increases, the sweeping efficiency of the CO 2 also increases, which will reduce the required number of injection points in the establishment of CCS. Ultimately, this will have a positive impact on the financial aspects of the implementation of CO 2 sequestration projects. From Figure 8(a), it is observed that the simulation set 1 has lower sweeping efficiency than the simulation set 2 for 99 × 10 5 m 3 /day injection rate at injection point B. is variation in the sweeping efficiency is due to the different petrophysical properties used for both simulation sets. Due to the low petrophysical properties range in the simulation set 1, the injected CO 2 will experience high restriction while percolating through the porous domain, and this will reduce the lateral spreading of the CO 2 in the geological domain. As the lateral spreading and plume displacement are low, the percentage of CO 2 entrapment for the structural and residual trapping will be recorded less over geological time. As the CO 2 plume movement is low, it will take time to explore the traps in the geological domain. is phenomenon can be seen in the histogram plots of Figure 8  structural and residual trapping percentages for the geological time are illustrated at the end of the 3000 th year. e percentage of entrapment recorded for the structural and residual trapping provides a clear indication of the sweeping efficiency. In simulation set 2, as the CO 2 lateral movement (sweep efficiency) is high compared to that in the simulation set 1, more CO 2 will percolate and explore more traps of a computational domain and get structurally and residually trapped. Due to this, the structural and residual trapping entrapment percentages are recorded high in simulation set 2 when compared to simulation set 1; these results are clearly illustrated in Figure 8(b). In simulation set 1, due to the low range of petrophysical properties, the lateral movement of injected CO 2 is low in the geological domain. e movable plume dominates compared to simulation set 2. e low lateral movement of CO 2 in the geological sequestration process due to the low petrophysical properties range can affect the structural integrity of the geological domain. Even if the structural arrangement of geological storage is not affected, the strangled CO 2 will undergo solubility and mineral reaction in the region. In the mineral reactions, if the dissolution reaction dominates, it may weaken the injection well point and the surrounding region; if the precipitation reactions dominate, it may affect the storage capacity due to decreasing porosity.

Conclusions
is study investigates the possible implementation of CO 2 geological sequestration in the Deccan volcanic province of the Saurashtra region, Gujarat. e numerical analysis is carried out to analyze the influences of specific sequestration parameters, such as the petrophysical properties, injection rate, and the injection point. Utilizing the optimal injection rate at an optimal injection point can result in maximum storage for a more extended period without compromising the caprock integrity. Structural and residual trapping mechanisms contribute significantly to store CO 2 for a relatively significant period. In this simulation analysis, it is observed that the percentage of structural trapping and residual trapping is increasing by decreasing the injection rates. is trend was consistent at all the injection points due to the finite amount of trap capacity. e dominance of residual trapping depends on the proximity of the formation traps near the injection points, as formation traps act as minireservoirs and contribute significantly to the entire trapping phenomena. Furthermore, this study has demonstrated the structural and residual trapping dependencies on the petrophysical properties. e lower petrophysical properties range of a geological domain has shown a higher restriction for the CO 2 movement. Our preliminary investigations on structural trapping and residual trapping mechanisms are promising for further studies to implement CO 2 sequestration in the Deccan volcanic province. Future works include the reactive transport modeling of solubility trapping and mineral trapping mechanisms on various geological domains of Deccan volcanic province to comprehend the feasibility of CO 2 sequestration.

Data Availability
e data used to support the findings of this study are included within the article.