Introduction

The Energy & Climate International Unit has published a report that the carbon emissions must be reduced in order to halt climate change. Currently, the reduction in carbon emissions is not sufficient and the “net zero emission” has been proposed (Unit 2020). To realize the global carbon neutrality as soon as possible, every country of the world should respond rapidly and design an appropriate strategy to take the needed action. CO2 emission reduction by geological sequestration is regarded as an important and efficient strategy. In the scenario of CO2 storage under the subsurface, CO2 can be sequestered by physical mechanisms such as structural trapping, residual trapping, and adsorption trapping, and can also be immobilized with dissolution and mineralization. CO2 carbonatization is a key process of the global carbon cycle in which atmospheric CO2 is stored (Berner and Raiswell 1983), which is also recognized as the safest way to store CO2 in the subsurface since the resulting carbonate minerals are stable and provide environmentally low risk over geological time scales (Ragnheidardottir et al. 2011).

Basaltic rock is one of the most promising reservoirs for efficient and rapid CO2 carbonatization, when compared with the conventional CO2 storage sites, e.g., the deep saline aquifers, depleted oil/gas reservoirs, unconventional shale gas reservoirs, and coal-bed methane reservoirs (Zhu et al. 2016). Basalt is a type of rock containing abundance of minerals such as olivine and pyroxene which are rich in Ca, Mg, and Fe bearings, which is the source of precipitation of carbonates including calcite, aragonite, magnesite, siderite, ankerite, and dolomite (Li et al. 2004; Nicolas et al. 2003). Studies of basalt-CO2 interactions in aqueous media indicated that pyroxene dissolution in the acidic aqueous can release Mg2+ ions to form magnesite (Gislason 2001), while plagioclase can release Ca2+ to form calcite through dissolution (Nicolas et al. 2003). It is estimated that ~ 60% of the global surface is occupied by basalt and the total CO2 storage capacity in basalt from the deep-sea can be as high as ~ 13800 to 127800 Gt (Gislason et al. 2010; Marieni et al. 2013). Basalt-CO2 reaction can occur rapidly. The onshore pilot project of CO2 sequestration in basalt conducted at the Hellisheidi geothermal power plant in Iceland, the so-called CarbFix project, initiated the injection of CO2 in January 2012. Two hundred thirty tons of CO2 was co-injected with 7000t of H2O into the targeted basalt formation which is composed of basalt lavas with an olivine tholeiitic composition with an age ranging from 500,000 to 125,000 years before present (Callow et al. 2018). It was observed that > 95% of the injected CO2 mineralized within a couple of months of the initial CO2 injection (Matter et al. 2016). Apart from basalt from the Carbfix project, it has been reported that CO2–H2O mixtures were allowed to react with the Columbia River, Central Atlantic Mafic, Newark Basin, Karoo, and Deccan basalt (Kumar and Shrivastava 2019a).

The Deccan basalt from India is one of the largest terrestrial flood basalt formations in the world which has immense accumulations of tholeiitic basalt magmas erupted over a relatively short time span straddling the Cretaceous-Tertiary boundary (Pattanayak 2002; Shrivastava et al. 2014). The isolated Mandla lobe, located in northeast of the Deccan volcanic province, is reported to have 37 major petrography distinct lava flows spread in the ~ 900-m-thick volcano-sedimentary sequences, and the uppermost part of the lava flow is highly vesicular which can provide structural pathways for CO2 and are conducive to CO2 sequestration. The availability of CO2 emission sources around the Deccan basalt is also a requisite for the feasibility of CO2 storage (Abraham-A and Tassinari 2021). It is reported that 26% of the total coal-fueled generation capacity in India is located on or in close proximity to the Deccan basalts (McGrail et al. 2006). According to the IPCC report (2005), power generation by coal combustion is the largest source for generation of CO2 (78% of the CO2 produced by large sources) (Talman 2015).

In recent years, several experimental and numerical studies on the CO2 storage in the Deccan basalt have been conducted. Shrivastava’s research group conducted lab-scale experiment of Deccan flood basalt specimens from the Eastern Mandla lobe reacting them with CO2 under different pressure (5 and 10 bars) and temperature in a time duration of 50, 60, 70, and 80 h (Kumar and Shrivastava 2019a; Rani et al 2013). They also studied the long-term CO2 capture-induced calcite crystallographic changes in Deccan basalt (Kumar and Shrivastava, 2019a). Prasad et al. (2009) reported the laboratory-scale experimental results to determine the CO2 sequestration potential of picritic basalts from the Deccan basalt volcanic province Maharashtra. Shrivastava and Pathak (2016) and Kumar and Shrivastava (2019b) have obtained both experimental and numerical results of CO2-water-Deccan basalt reaction from the Mandla lobe. Kumar et al. (2017) employed the transition-state-theory based on numerical model to simulate the basalt-CO2-water-saturated interaction under hydrothermal-like conditions in the Deccan basalt. However, the purpose of these computational simulations was to explain the experimental results from the point of view of mineral thermodynamic reactions.

The acid dissolution of silica-aluminum minerals such as plagioclase and pyroxene not only releases divalent cations to promote carbonate precipitation, but also releases abundance of silica and aluminum at the same time. The combination of irons enriched from the dissolution of basalt under mildly acdic conditions tends to lead to the formation of clays and zeolites. Clays, zeolites, and oxides are widely observed to co-precipitate with carbonates in the context of CO2-water-basalt reactions, and reported to clog narrow fractures and pore throats of the basalt potentially reducing permeability and reservoir conductivity thus to change the transport of fluid in the subsurface. Mineral precipitation in natural joints and fractures in basalt has been observed to partly or fully inhibit fluid flow. The transport of CO2 can dictate both the speed and extent of mineral carbonatization which would impact the CO2 storage potential (Andreani et al 2009; Liu et al. 2019; Menefee et al. 2017; Peuble et al 2015). As a result, to comprehensively and accurately assess the CO2 storage potential of the Deccan basalt, it is critical to combine CO2-water-basalt reaction with fluid transport and consider the effect of clay precipitation.

The specific objective of this study is to evaluate the CO2 mineralization potential of the Deccan basalt from the Eastern India. The laboratory-scale experiment of CO2-water-Deccan basalt reaction at different CO2 pressures conducted by Kumar and Shrivastava (2019c) is first reconstructed with the numerical method to obtain the appropriate mineral thermodynamic parameters. Based on the validated lab-scale model, a 2-D homogeneous field-scale model with size of 200 m in horizontal and 120 m in vertical direction is then established by collecting needed hydrological data of the Deccan basalt from the Mandla lobe. A total of 1.2096 × 104 tons of CO2 dissolved water (equivalent to 184.24 tons of carbon) is injected into the Deccan basalt at a rate of 1.0 kg/s for 140 days. By controlling the existence of clay minerals especially smectite and chlorite, role of clay minerals on CO2 carbonatization efficiency and fluid transport in the Deccan basalt are explored. In addition, impact of fluid flow rate on CO2 carbonatization and reservoir pressure perturbation is also discussed. It should be noted that although this study is based on a specific site, uncertainty exists in the selection of the represented basalt mineral composition, reservoir porosity, permeability, initial pressure and temperature, etc.; the obtained conclusions still provide important guidance for the CO2 geological sequestration potential in India.

Material and methods

Geological background of the Mandla lobe basalt

The Deccan volcanic province is an important large igneous province in the world. It marks the Cretaceous-Palaeogene boundary which witnessed the global climate and bio-geosphere change (Keller et al. 2008). The Deccan volcanic province constitutes one of the largest continental flood basalt in the world which covers a large part of the peninsular India with an area of nearly 500,000 km2 (Krishnamurthy 2020). As an isolated lobe, the Mandla lobe is located in northeast of the Deccan volcanic province and extends over a distance of 344 km in the E-W strike direction and 156 km across the N-S direction (Fig. 1). It is tectonically controlled by the rift-bounded basin fault system of the Son-Narmada and Tapi rivers in the north and south of the Manda lobe, respectively. Furthermore, it lies towards the southeastern part of the central Indian Suture Zone.

Fig. 1
figure 1

Location of the Mandla lobe in the eastern Deccan volcanic province and Geological section of the Deccan basalt from north to south (A) and west to east (B) (Revised according to Krishnamurthy 2020)

Full size image

On the basis of regional mapping, physical characters, petrography, and lateral tracing of the lava flows, there are 37 major petrography distinct lava flows spread in the ~ 900-m-thick volcano-sedimentary sequences around Mandla. Among all different lava flows, the fourth lava flow of the eastern Deccan basalt is found to have plentiful columnar and jointed structures. They are often marked with prolific cracks and possess well-developed colonnade and entablature structures within the lava flow. It is reported that the uppermost part of the lava flow is highly vesicular which can provide structural pathways for CO2 and are conducive to CO2 sequestration.

Simulator description

TOUGHREACT is employed to conduct the reactive transport modeling. The details of the code’s capabilities, governing equations, calculation procedures, and limitations are available in the user’s manual. All flow and transport equations are obtained based on the principles of mass and energy conservation. The detailed discussion on models for fluid and heat flow can be found in Pruess (1991) and Pruess et al. (1999).

Geochemical reaction calculation

For geochemical calculation, a subset of aqueous species is selected as basis species, and all other species including aqueous complexes, minerals, and gaseous species are called secondary species (Steefel 1994; Yeh and Tripathi 1991). Chemical transport equations are derived from the total dissolved concentration of chemical components which is the sum of their basis species and their associated aqueous secondary species. The advection and diffusion mechanisms are considered for the chemical transport calculation. The kinetic rate law is employed to describe the mineral dissolution and precipitation reactions, the expression of which (Eq. (1)) is referenced to Lasaga et al. (1994). At each time step, the reaction rate constants, \({k}_{n}\); total surface area,\({A}_{n}\); and the kinetic mineral saturation ratio, \({\Omega }_{n}\) of each mineral are used to calculate the overall reaction rate. The positive values of \({r}_{n}\) in Eq. (1) indicate dissolution and negative values stand for precipitation. The explanation of each parameter is included in the nomenclature.

$${r}_{n}=\mathrm{f}\left(\mathrm{c}1,\mathrm{c}2,\dots , {c}_{{N}_{c}}\right)=\pm {k}_{n}{A}_{n}{\left|1-{\Omega }_{n}^{\theta }\right|}^{\eta }$$
(1)

The reaction rate constants considered here are calculated based on the reaction rate constant at 25℃, k25, and activation energy, Ea., with different mechanisms through model calibration or published by other authors (Eq. (2)). The mechanisms include the neutral, acid, and base mechanisms. For the acid and base mechanisms, dissolution and precipitation of minerals are catalyzed by H+ and OH− respectively.

$${k}_{n}={k}_{25}^{\mathrm{nu}}\mathrm{exp}\left[\frac{{-E}_{a}^{\mathrm{nu}}}{R}\left(\frac{1}{T}-\frac{1}{298.15}\right)\right]+{k}_{25}^{\mathrm{H}}\mathrm{exp}\left[\frac{{-E}_{a}^{\mathrm{H}}}{R}\left(\frac{1}{T}-\frac{1}{298.15}\right)\right]{a}_{\mathrm{H}}^{{\sigma }_{\mathrm{H}}}+{k}_{25}^{\mathrm{OH}}\mathrm{exp}\left[\frac{{-E}_{a}^{\mathrm{OH}}}{R}\left(\frac{1}{T}-\frac{1}{298.15}\right)\right]{a}_{\mathrm{OH}}^{{\sigma }_{\mathrm{OH}}}$$
(2)

Mineral reaction–induced porosity and permeability changes

The porosity changes due to mineral alterations are described with the following expressions in the simulator (Xu et al. 2006):

$${\mathrm{\varnothing }}_{i}=1.0-\sum\nolimits_{m=1}^{k}{F}_{k}^{i}-{F}_{n}^{i}$$
(3)

A simplified Kozeny-Carman equation was implemented to describe the relation between porosity and permeability.

$$\frac{{k}_{i}}{{k}_{0}}={(\frac{{\varnothing }_{i}}{{\varnothing }_{0}})}^{3}\times {(\frac{1-{\varnothing }_{0}}{1-{\varnothing }_{i}})}^{2}$$
(4)

Initial mineral and water chemistry

For regional-scale reactive-transport modeling, the credibility of results is dependent on the initial mineral composition and its thermodynamic data. To obtain the representative mineral composition of the Deccan basalt from the Mandla lobe, the CO2 sequestration experiment conducted by Kumar and Shrivastava (2019c) was reconstructed with numerical method. To perform the high pressure–temperature experiments, 10-g hypocrystalline and vesicular basalt specimen from the Mandla lobe and 100 ml of deionized water were kept inside a 600-ml columned reactor with a height of 0.12 m and diameter of 0.08 m. The reaction temperature was set as 100 and two scenarios of pCO2 at 5 bar and 10 bar were explored respectively as shown in Fig. 2(A).

Fig. 2
figure 2

Schematic of the simulation lab-scale model and field-scale model. (A) The generalization of the lab-scale model from the experiment and (B) the gridding of the mesh, and (C) the concept map of the field-scale model. The mineral thermodynamic data calibrated through the lab-scale simulation was implemented directly into the field-scale model

Full size image

To mimic the experimental condition, the section of column reactor filled with water was considered equivalent to 41 grids in vertical direction as shown in Fig. 2(B), with size of 0.07 m × 0.07 m × 0.0005 m. It was assumed that 10 g of basalt specimens in the experiment was completely homogeneously distributed in the deionized water, and the porosity can be calculated as 96%. A pressure boundary consisting of pure water equilibrated with CO2 at a constant pressure of 5 bars and 10 bars and temperature of 100℃ was imposed at the top inlet to match experimental condition. A no-flux boundary was set at the bottom and lateral direction of the model to represent the sealed wall of the reaction vessel.

As reported by Kumar and Shrivastava (2019c), the experimental basalt was composed of pyroxene, plagioclase, magnetite, olivine, chlorophaeite, and glass. But only the volume fraction of clinopyroxene as 44.75% was given. During the model calibration, we found that olivine is very critical to match the rapid decline of pH; as a result, 3% fayalite and 2% forsterite were added in the primary minerals to represent olivine and the ratio of fayalite:forsterite was determined based on the Fe:Mg = 0.38:0.29 in olivine. Because the clinopyroxene is usually composed of diopside and hedenbergite, these two minerals were selected to represent pyroxene and the content of diopside and hedenbergite was calculated according to the molar ratio of Fe:Mg = 0.24:0.19 in clinopyroxene. Albite, anorthite, and k-feldspar were set to represent plagioclase, glass, and other minerals. The ratio Ca:Na = 0.016484:0.00665 of the Ca plagioclase in the original basalt specimens was kept for anorthite and albite. The volume fraction of k-feldspar and magnetite was set as 0.0025 and 0.0955 according to the calculation of Kumar and Shrivastava (2019c).

The choice of secondary precipitated minerals is also crucial for the model validation. The observed secondary minerals in the experiments include carbonates such as aragonite, calcite, ankerite, siderite, magnesite, some phyllosilicates like chlorite and saponite, and also some wustite. To accurately depict the CO2-water-basalt interaction at different CO2 partial pressures, all these minerals were selected as the secondary minerals. Because of the richness of Ca, Na, and Mg in this basalt, Ca-smectite, Na-smectite, and Mg-smectite were all included in the secondary minerals list.

To validate the simulation model with the experimental results, the major source of uncertainty comes from the mineral reaction kinetic parameters including kinetic constants at 25℃, activation energy, and reactive surface area. The mineral reaction kinetic parameters of the major primary and secondary minerals were obtained by adjusting the aqueous pH of the model to fit the experimental results; these are listed in Table 1. To accelerate the CO2-rock reaction rate, the experiments is conventionally conducted at stirring condition which will enhance the gaseous and aqueous diffusion rate, but not impact the mineral reaction kinetics. As a result, the aqueous diffusion coefficient was enhanced into two orders of magnitude larger than the 7.5 × 10−9 m2/s (Cadogan et al 2014).

Table 1 Summary of primary and secondary mineral specific surface area and reaction kinetics
Full size table

Field-scale model establishment

It was mentioned previously that the fourth lava flow of the eastern Deccan basalt shows columnar and jointed structures and the uppermost part of which is highly vesicular which can provide structural pathways for CO2. The forth lava flow was selected as the target CO2 storage site. Because some of the specific properties related to CO2 storage efficiency are not available for this formation, some approximate data were employed. The contact between the base of the basalt in the Mandla lobe and underlying sedimentary beds is at 364 m above mean sea level near Jabalpur and the maximum elevation of basalts is 1177 m at Badargarh (Shrivastava et al. 2014). In the simulation, an average elevation of 770 m and a thickness of 100 m for the basalt formation were selected. The normal pressure gradient of 9.81 MPa/km and the average geothermal gradient of the Deccan basalt in Jabalpur of the Mandla lobe (4.25℃/100 m) (Srinivas et al. 2019) were employed.

A large numbers of studies on the Deccan basalt’s petrophysical and hydrological conditions have been conducted for the central part, but are missing for the eastern part. It is reported that the Mandla lobe has Ambenali- and broadly Poladpur-like formation characteristics similar to the central part. Perumal (2014) have collected fresh samples of the Deccan basalt to document the variation in physical properties of the rock with depth within and between rock formations that are arranged in the Deccan basalt stratigraphic sequence and the basement rocks. The porosity of basalt varies between 0 ~ 6.3%; as a result, a relatively large porosity of 6.3% were used in the CCS field-model establishment. Some of the other needed information for the field-model establishment was directly obtained as the average value of the other part of the Deccan basalt. The detailed parameters can be found in Table 2.

Table 2 Data used in field-scale model
Full size table

A 2-D rectangular model with lateral distance of 200 m and vertical depth of 120 m was established to simulate the CO2 storage potential in the field-scale Deccan basalt (Fig. 3). The grid size was equally divided into 5 m × 5 m × 5 m, and the total grids were 40 in horizontal and 24 in vertical direction. The top side was set as a constant boundary by assigning infinite volume to those grids. The bottom boundary was set as no-flux boundary. The CO2 saturated water was injected from the left side at a depth of 72.6 m, while groundwater flowed out from the right side at a typical groundwater flow rate of 10−5 kg/s/m2 (USGS, 2020).

Fig. 3
figure 3

Comparison of pH evolution (a) and total CO2 sequestered in mineral phase (b) at CO2 pressure of 3.0 bars, 5.0 bars, 8 bars, and 10 bars. The experimental data on pH evolution at CO2 pressure of 5 bars and 10 bars is also plotted in sub-figure (a)

Full size image

Initial water and boundary water

Except for the initial hydrological data, the initial chemical condition of the formation water is also a requisite for the reactive transport modeling. Because of lack of directly drilled groundwater data for the Mandla lobe basalt, 72 groundwater sample compositions collected under phreatic conditions in the weathered zone, fractured and vesicular basalts, and under semi-confined to confined conditions in the fractured zone from the northern part of the Deccan plateau were utilized (Pawar et al. 2008). The average pH of pre-monsoon and post-monsoon season of 7.86 was employed for the groundwater of Mandla lobe basalt in this simulation. To accelerate CO2 and basalt reaction rate, the water and CO2 are mixed at a designated point in the borehole (P = 7.546 MPa, T = 57℃). The injecting water composition was calculated with PHREEQC; the detailed determination method can be found in SI. The water saturated with CO2 at a pressure of nearly 7.7 MPa at the bottom of the established model will then be injected at a rate of 1 kg/s for 140 days. The detailed information of the initial water and boundary water is listed in Table 2.

Simulation scenarios setup

A total of 1.2096 × 104 tons CO2 dissolved formation water (equivalent to 184.24 tons of carbon) was injected into the Deccan basalt reservoir at an injection rate of 1 kg/s in the duration of 140 days (scenario 1 and named as case_base). To assess the CO2 carbonatization potential of the Deccan basalt in the Mandla lobe and elucidate the impact of other alumino-silicate minerals’ precipitation and injection rate on CO2 storage efficiency, another two scenarios were set up. In scenario 2, four simulation cases were set up to explore the impact of clay precipitation on CO2 mineralization and migration by controlling the existence of clays as the secondary minerals. In scenario 3, another four simulation cases with different injection rate of 0.4 kg/s, 0.5 kg/s, 2.0 kg/s, and 3.0 kg/s were added based on the baseline cases to analyze the sensitivity of injection rate on CO2 carbonatization efficiency and security. The total injected CO2 capacity was kept the same for all the cases. The specific simulation case setups are summarized in Table 3.

Table 3 Simulation model setup
Full size table

CO2 mineralization efficiency calculation

During the field-scale simulation, the individual carbonates’ volume fraction of each grid can be generated automatically; as a result, the total mass of carbon \({\mathrm{m}}_{k}^{t}\) in precipitated carbonates k at time t can be calculated by Eq. (5), and the total dissolved inorganic carbon (DIC) at time t can be calculated by Eq. (6). Then the CO2 mineralization efficiency (E) can be obtained accordingly as shown in Eq. (7).

$${m}_{k}^{t}=\sum\nolimits_{i}^{n}{aV}_{i}{F}_{k}^{i}{\rho }_{k}/{M}_{k}$$
(5)
$${{m}_{\mathrm{DIC}}}^{t}=rt\left({c}_{\mathrm{co}2\left(\mathrm{aq}\right)}^{\mathrm{inj}}+{c}_{\mathrm{hco}3-}^{\mathrm{inj}}\right)+\sum\nolimits_{i}^{n}{12{p}_{i}^{0}V}_{i}{\rho }_{iw}^{0}\left({c}_{\mathrm{co}2\left(\mathrm{aq}\right)}^{\mathrm{ini}}+{c}_{\mathrm{hco}3-}^{\mathrm{ini}}\right)$$
(6)
$$E=\frac{{\sum }_{k}^{l}{m}_{k}^{t}}{{{m}_{\mathrm{DIC}}}^{t}}$$
(7)

Results

Benchmark-model calibration and lab-scale CO2 carbonization

To obtain the appropriate mineral reaction kinetics of the field-scale model, the high temperature and pressure CO2-water–rock reaction experiment based on the Deccan basalt samples collected from the Mandla lobe was calibrated with modeling. The pH variation with time at CO2 pressure of 5 bars and 10 bars in the modeled system was compared with the experimental results as shown in Fig. 3. To further analyze the variation in carbonization efficiency with CO2 pressure, two additional lab-scale simulation cases with CO2 pressure of 3 bars and 8 bars were also conducted. The pH evolution in both the experiment and simulation is in good agreement at short time, e.g., within 100 h. But for a longer time of 1000 h, the simulation results only capture the pH variation tendency and possess a deviation of 6.9% and 11.4% for 5 bars and 10 bars separately.

pH is an important index to illustrate the geochemical reaction between CO2 and basalt. As shown in Fig. 3, within the reaction period of 1000 h, pH of the system fluctuates with time. Pyroxene and olivine respond rapidly to CO2 injection; they dissolve and release significant Ca2+, Mg2+, and Fe2+ and consume H+. Because of this interaction, pH increases continually in the first 3 days. CO2 dissolving into water can not only provide H+ needed by the pyroxene and olivine, but also provide enough HCO3−, which to some extent can precipitate with the divalent ions, Ca2+, Mg2+, and Fe2+, to form calcite, aragonite, siderite, and ankerite, for example. In addition, the precipitation of carbonates can release H+ into the system at the same time, and the decrease in pH observed in Fig. 3 was mainly caused by the precipitation of these carbonates. Higher CO2 pressure induces more acidified system in the beginning which can lead to more pyroxene and olivine dissolution. It provides more divalent cations and promotes the mineral carbonatization of CO2. However, there is an exception for the case of CO2 pressure at 8 bars. The minimum pH at this condition is about 6.26, which was even lower than the case with CO2 pressure at 10 bars. The reason lies in that more carbonates precipitated at 8 bars; they lead to more H+ releasing into the system as shown in Fig. 3b.

The major precipitated carbonates of the Deccan basalt when reacted with CO2 at low CO2 pressure are aragonite, calcite, ankerite, siderite, and small amount of magnesite (Fig. S1 in SI). Kumar and Shrivastava (2019c) reported that at 100℃, the XRD analysis shows the formation of calcite > ankerite > aragonite > siderite when CO2 pressure was 5 bars and 10 bars, which is in agreement with the simulation results. In addition to carbonates, some clay minerals, zeolite, and oxides were also observed both in the experiment and in the simulation. Within the experiment, the formation of chlorite, saponite, chabazaite, and wustite was observed. The precipitation of these minerals will compete with carbonates for Ca2+, Mg2+, and Fe2+, and their presence has been widely reported from experiments, modeling, and field observations (Gysi and Stefánsson 2012a; b; Snæbjörnsdóttir et al 2018; Wolff-Boenisch and Galeczka 2018). All studies agree that the precipitation of clays, oxides, or zeolites will clog narrow fractures and pore throats of the basalt, potentially reducing permeability and CO2 injectivity. Such physical alterations are critical in predicting ultimate CO2 trapping potential of a basalt reservoir. However, this competition was only observed in limited spatial and temporal scale through experiments. To elucidate the large-scale aqueous CO2 storage potential of the Deccan basalt, a two-dimensional field-scale model was established based on this calibrated model.

Field-scale CO2 carbonatization

Baseline case

A total of 1.2096 × 104 ton CO2 saturated water was injected into the 2-D field-scale Deccan basalt model at a rate of 1.0 kg/s for 140 days. The DIC concentration of the injected water, which is 1.285 mol/kg H2O, was obtained with PHREEQC equilibrium calculation at 74.5 atm. and 57 ℃. It denotes that a total of 184.24 tons carbon has been injected at 140 days. Over 50% of injected carbon mineralized within 140 days for the Deccan basalt in the Mandla lobe was observed (as shown in Fig. 4). The total precipitated carbonates, including ankerite, siderite, and calcite, are 818.18 tons when CO2 injection stopped. Apart from those carbonates, significant clays including chlorite and smectite also precipitated and the capacity of which was equivalent to 1784.42 tons at 140 days.

Fig. 4
figure 4

Evolution of CO2 mineralization efficiency (a) and the major precipitated carbonates (b) and clays (c) for the Deccan basalt from the Mandla lobe, India

Full size image

Cases with different setting on secondary mineral precipitation

To quantify the competition of clay precipitation on CO2 carbonatization and explore the effect of chlorite and smectite, the results of base_case, case_ncwp, case_chl, and case_sm were compared (as shown in Table 4). By comparison, the precipitation of chlorite and/or smectite promoting the carbonatization of CO2 was observed in this study. Limiting the formation of chlorite and/or smectite, the CO2 carbonatization efficiency decreased from 49.55 to 49.24%, 48.92%, and 44.23%, respectively. Figure 5 shows the capacity evolution of the major precipitated carbonates and dissolved divalent source minerals. Chlorite precipitation promotes the dissolution of the majority divalent source minerals including diopside, fayalite, and forsterite by releasing H+ into the system as well, which echoed well with the pH evolution of different simulation cases as shown in Fig. S2 in SI. The chlorite precipitation reduced the total predicted siderite mass by ~ 24% after 140 days. Similarly, the competition of Ca2+ between smectite and calcite was also observed as shown in Fig. 5(b), and ~ 49% of calcite was reduced due to the precipitation of smectite. Both chlorite and smectite compete with magnesite for Mg2+. However, there is an exception for anorthite, the dissolution of which can release the needed divalent cations and alumino-silicate cations for smectite precipitation. Anorthite combined with diopside is also the major Ca2+ providers for the precipitation of ankerite and calcite. As seen in Fig. 5(f), the precipitation of chlorite and smectite both promoted the dissolution of anorthite, so as to promote the carbonatization of CO2 into calcite and ankerite.

Table 4 Summary of the CO2 carbonatization capacity of different simulation cases
Full size table
Fig. 5
figure 5

source minerals (f, g, h, i) for base_case, case_sm, case_chl and case_ncwp

Precipitation of the major carbonates (a, b, c, d, e) and dissolution of the divalent cations

Full size image

Figure 6 shows the spatial distribution of porosity, HCO3−, and pressure at 140 days for different simulation cases. The result of permeability distribution was not showed because it displayed with the same tendency with porosity. As seen, the competitive precipitation of clays can dramatically affect the evolution of reservoir porosity and permeability. The basalt showed a self-limiting trend in conductivity when clays were competitvely precipitated. However, a self-enhacing mode occurred when clays did not exist. It is reported that the smectite formation will clog narrow fractures and pore throats of the basalt, so as to decrease rock conductivity (Menefee et al. 2017), which is also the case in this study. Injectivity is closely related with the reservoir pressure perturbation (Heath et al. 2014; Liu et al. 2016, 2017). As shown in Fig. 6e and f, clay precipitation impacts the reservoir pressure evolution to a pronounced extent. To quantify the impact of clay precipitation on CO2 injectivity, the peak pressure buildup of case_base and case_ncwp, which was 4.37 MPa and 2.76 MPa, was compared.

Fig. 6
figure 6

Impact of clay precipitation on basalt porosity (a, b), CO2 migration (c, d), and reservoir pressure perturbation (e, f). a, c, e Case without consideration of clay precipitation; b, d, f case considering the precipitation of clays

Full size image

Cases with different injection rate

As shown in Fig. 7a, CO2 mineralization efficiency increases with the decreasing of injection rate. Injection rate not only plays a vital role on the determining of the CO2-water-basalt reaction extent but also exerts some effect on the reaction direction. As seen in Fig. 7b, the competing reactions between carbonates and clays for major divalent cations were affected by the extent of reaction with smectites and chlorite (Gysi and Stefánsson 2012a). The precipitation capacity of calcite and ankerite both decrease with the injection rate, but siderite displays a negative relationship with the injection rate. The reduction precipitation of chlorite with injection rate leads to the enhancement of siderite precipitation. Although smecite will also compete for Ca2+ with calcite, extended retention times (lower injection rate) mainly strengthen the precipitation of smectite and promote the disssolution of the two minerals (diopside and anorthite) serving as Ca source, thus to enhance calcite and ankerite precipitation. But higher injection rate limits the precipitation of smectite and reduce the formation of calcite and ankerite. Figure 7a also illustrated that the peak pressure of reservoir responded to CO2 saturated water injection not monotonously increasing with injection rate. There is a critical injection rate, rc, that existed. When r < rc, pressure buildup decreases with the injection rate, but if r > rc, pressure buildup increases with the injection rate.

Fig. 7
figure 7

CO2 carbonatization efficiency and reservoir peak pressure variation with injection rate (a); evolution of the capacity of major secondary minerals with injection rate (b); porosity distribution along the horizontal of the injection site at different injection rates (c)

Full size image

Discussion

CO2 sequestration potential of the Deccan basalt from the Mandla lobe

The CO2 mineralization efficiency of the Deccan basalt in the Mandla lobe is about 50% at this specific condition within the duration of 140 days. It is similar to the first phase of the CarFix2 project which was reported that 50% of injected carbon and 76% of sulfur mineralized within 4 to 9 months (Clark et al 2020). The majority of the aqueous CO2 is sequestered in ankerite, siderite, and calcite, which occupies a percent of 65%, 28%, and 7%, respectively. Apart from those carbonates, significant clays including chlorite and smectite also precipitated, among which chlorite is the major precipitated clays (57%) and smectite dominated the percentage of 43%. The results of Ca2+ resealing from the dissolution of olivine, pyroxene, and plagioclase being incorporated into calcite and ankerite, and Mg, Fe, and Si into smectite and chlorite, is similar to the study of Gysi and Stefánsson (2012b).

However, the results of the field-scale model are different from the lab-scale results, where calcite and aragonite were the dominated precipitated carbonates. Kanakiya et al. (2017) investigated the secondary mineralogy of basalt cores under CO2(aq) imbibition and also observed ankerite to be the key secondary carbonate phase in their study, at CO2 partial pressure of 4.5 MPa and temperature of 100 ℃. The CO2 pressure of the field-scale model was set about 7.7 MPa according to the reservoir initial pressure, while only 5 bar and 10 bars of CO2 pressure was set for the lab-scale experiment. It is conjectured that the discrepancy of precipitated carbonate type was mainly caused by the injected CO2 concentration and ankerite was preferring to precipitate at higher CO2 concentration.

Effect of clay precipitation on CO2 carbonatization

Clays, zeolites, and oxides are widely observed to co-precipitate with carbonates in the context of CO2-water-basalt reactions. Reaction path modeling have predicted precipitation of smectites and zeolites along with chalcedony, kaolinite, and goethite (Pham et al. 2012; Gysi and Stefánsson 2008). Several experimental studies also observed the formation of smectite at lower pH (Xiong et al. 2017; Hellevang et al. 2017). Some of the studies argued that the Mg2+ and Fe2+ cations released from the primary source minerals were incorporated into clay minerals such as smectites and oxides, and compete with the formation of magnesite and other carbonate minerals (Phukan et al 2020), whereas zeolites compete with calcite for dissolved Ca (Aradottir et al. 2012). Other studies also show that smectite or zeolite precipitation makes no contribution to the carbonatization of CO2 (Menefee et al. 2017). In this study, we found that the precipitation of clays could enhance the mineralization of CO2 in two pathways.

Firstly, the precipitation of smectite and chlorite will consume significant amount of divalent cations including Ca, Mg, Fe, and remarkable Si and Al in acid environment (Amram and Ganor, 2005; Bontognali et al. 2014; Peretyazhko et al. 2018). The formation water can be also acidified with chlorite precipitation so as to promote the dissolution of pyroxene, olivine, and plagioclase. Consequently, the precipitation of calcite was promoted by the generation of chlorite. It is reported that siderite was the most favorable carbonate precipitate under low pH conditions given comparable amount of available Ca2+, Mg2+, and Fe2+ (Adeoye et al. 2017). However, higher pH is more advantageous for the formation of siderite in this study (Fig. 5(c)). That is because at lower pH, chlorite will compete for Fe2+ with siderite, so as to limit the precipitation of siderite. Smectite precipitation will improve the dissolution of Ca-bearing minerals (diopside and anorthite) and to increase the precipitation capacity of calcite and ankerite.

Secondly, the clay precipitation will reduce reservoir conductivity to prolong the retention time for geochemical reactions. Clay precipitation not only exerts influence on the carbonatization of CO2, but also impacts the porosity and permeability of basalt, potentially reduce CO2 injectivity and affect the transportation of CO2 (Hellevang et al. 2017). Menefee et al. (2017) and Liu et al. (2019) all indicated that increasing the retention time of aqueous CO2 in the pore space can strengthen the mineralization of CO2. Compared with the case_base, the total precipitated carbonates for case without consideration of porosity reduction response to conductivity (case_wcnp) were 815.58 tons, with a decline of 0.32% on CO2 mineralization efficiency. However, 10.74% CO2 carbonatization efficiency was reduced for case without consideration of the clay precipitation (case_ncwp).

Basalt conductivity evolution response to aqueous CO2 injection

Except for clay precipitation, injection rate also impacts the mineralization of CO2 in basaltic reservoir. A large numbers of studies reported the positive correlation between reservoir pressure buildup and fluid injection rate (Liu et al. 2017, 2016; Buscheck et al 2012, 2014). However, in basaltic reservoir, lower injection rate lead to longer retention time of dissolved CO2 in the pore space, so as to exaggerate the geochemical reaction between CO2-water-basalt and enhance the pressure. Conventionally, the reservoir pressure buildup is determined with the injection rate for CO2 sequestration in deep saline aquifer. However, in basaltic reservoir, the pressure buildup was not only caused by the expansion of reservoir pore space and compression of fluid in response to ex-situ fluid injection (occupies a weight of 63% for the baseline case), but also induced by the permeability and porosity reduction responding to clays precipitation and dominate a weight of 37% (Fig. 7c).

The pressure buildup is in positive relation with CO2 injection rate and negative to rock conductivity (Liu et al. 2016), and the minimum pressure buildup will be obtained at the critical injection rate (as shown in Fig. 7a). To maximize CO2 mineralization efficiency, it is reasonable to decrease the CO2 injection rate; however, lower injection rate leads to the larger pressure buildup. In this study, the CO2 mineralization efficiency variation deviation was only ~ 1.6% at the injection rate between 0.4 ~ 3.0 kg/s. Therefore, from the perspective of pressure supervision, to maintain the minimum pressure buildup while ensuring high CO2 mineralization efficiency, 1.0 kg/s is much superior than 0.4 kg/s as well as 3.0 kg/s in this study.

Uncertainty analysis

Due to the lack of detailed data on the geological and hydrological conditions of the Deccan basalt from the Mandla lobe, this study is a robust preliminary assessment of the aqueous CO2 geological sequestration potential. Although the benchmark model was established and reliable mineral reaction parameters were obtained by validating with the experimental data, the mineral composition of the basalt was only represented by one shale sample from the Mandla lobe. Uncertainty still existed on the selection of the basalt mineral compositions. It is reported that despite containing similar mineralogy, major oxides, and dissolution kinetics, different basalt types, e.g the Columbia River, Central Atlantic Mafic, Newark Basin, Deccan, and Karoo basalt, show different rates of CO2 mineralization, composition, and morphologies of the neo-formed carbonates and silicates (Schaef et al 2010, 2009). CO2 transport in basalt is also an important factor affecting CO2 carbonatization, which is quite dependent on the rock porosity and permeability. Studies reported that pure advection flow with shorter retention times promotes rapid initial carbonatization, while pure diffusion sustains mineral reactions for longer time frames and generates greater net carbonatization net volumes (Liu et al. 2019; Menefee et al. 2017). In addition, the uncertainty on formation salinity and in situ reservoir temperature should also be considered. A series of studies have revealed that increased temperature and salinity enhanced the dissolution of the divalent-bearing minerals (Adeoye et al. 2017; Hellevang et al 2017). These uncertainties should be considered in the future studies.

Conclusions

In this study, reactive transport models are developed and verified based on the static batch lab-scale experiments and extended to the 2-D field-scale model to evaluate the CO2 mineralization efficiency of the Deccan basalt from the Mandla lobe in India. Over 50% of the injected carbon can be mineralized into ankerite, siderite, and calcite within 140 days, and occupies a percent of 65%, 28%, and 7%, respectively. Apart from those carbonates, significant clays including chlorite and smectite also precipitated, among which chlorite is the major precipitated clays (57%) and smectite dominated the percentage of 43%. Precipitation of clays enhanced the mineralization of CO2 in three pathways via (a) releasing H+ to promote the dissolution of pyroxene, olivine, and plagioclase by chlorite precipitation; (b) consuming Si and Al to improve the dissolution of Ca source minerals including diopside and anorthite and increase the precipitation of calcite and ankerite; and (c) reducing reservoir conductivity to prolong the retention time for geochemical reactions. But the competition for Ca2+, Mg2+, and Fe2+ between smectite, chlorite, and calcite, and siderite also occurred. In basaltic reservoir, CO2 mineralization efficiency as well as the pressure build-up increases with the reduction of injection rate. However, extreme pressure perturbation will limit the injectivity and enhance the storage security; thus, the CO2 injection rate should be precisely designed to maximize the CO2 carbonatization efficiency and ensure safety. Due to the lack of detailed data on the geological and hydrological conditions of the Deccan basalt from the Mandla lobe, uncertainty on the basalt mineral composition, reservoir porosity and permeability, reservoir initial temperature and pressure, etc. still existed. To obtain a more accuracy evaluation results, detailed and complicated 3-D model should be established in the future.