ORIGINAL ARTICLE

Effects of feldspar and salinity on the mineral sequestrationcapacity of CO2 in high-salinity aquifers

Qi Fang1 • Yilian Li2 • Guojian Peng3 • Peng Cheng4 • Junwen Lv1

Received: 29 October 2015 / Accepted: 6 September 2016 / Published online: 16 September 2016

� Springer-Verlag Berlin Heidelberg 2016

Abstract Mineral sequestration of CO2 is considered to be

the safest mechanism in the long-term storage of CO2 in

deep saline aquifers. This study aims to investigate the

effect of feldspar and salinity on the mineral sequestration

capacity of CO2 in deep high-salinity brine aquifers by

taking Jiangling Depression of Jianghan Basin for instance.

Numerical simulation on the long-term geochemical reac-

tion and transport was performed by taking TOUGH-

REACT as the simulation tool. Simulation results indicate

that the effect of feldspar on the mineral trapping capacity

of CO2 does not depend on the total content of feldspar, but

depends on feldspar type and relative content. With Mg-

rich minerals such as chlorite or dolomite present, the

mineral composition abundant in K-feldspar is less favor-

able for the mineral sequestration capacity of CO2 for the

reason that a large amount of illite precipitates, consuming

a lot of Al3? in the aqueous solution, thereby limiting the

precipitation of dawsonite, especially for the high-tem-

perature sedimentary environment. In addition, the effect

of salinity on the mineral sequestration capacity of CO2

represents two aspects: one for the longer migration dis-

tance due to the lower solubility of higher salinity and the

other for CO2 mineral trapping capacity per 1 m3 medium

which is not in simple decreased with salinity, depending

on K-feldspar present or not. For the mineral composition

with K-feldspar present, CO2 mineral trapping capacity

decreases with salinity, while with albite instead of

K-feldspar, it increases with salinity owing to more pre-

cipitation of dawsonite.

Keywords CO2 geological storage � Mineral sequestration

capacity � Feldspar � Salinity � High-salinity aquifers

Introduction

Geologic CO2 sequestration (GCS) in deep geological

formations is increasingly regarded as a promising means

of reducing the release of greenhouse gas while still using

fossil fuels and existing or emerging energy infrastructures

(Gale 2004; IPCC 2005; Holloway 2005; Benson and Cole

2008; Schafer et al. 2012; Fang and Li 2014; Rathnaweera

et al. 2015). Suitable geological formations include

depleted oil and gas reservoirs and deep saline formations.

GCS combined with enhanced oil recovery (EOR) and

enhanced coalbed methane recovery (ECBM) may be

financially advantageous (Kuhn et al. 2012; Silva et al.

2012; Michael et al. 2013; Tao and Clarens 2013). Deep

saline formations are estimated to be the most promising

option for CGS owning to the advantages of large storage

capacity and widespread availability (Fang and Li 2014;

Rathnaweera et al. 2016). Geologic CO2 sequestration in

deep saline formations mainly relies on three trapping

mechanisms (Xu et al. 2004; Bachu et al. 2007). First, CO2

can be trapped as supercritical fluid under a low-perme-

ability caprock, referred as hydrodynamic trapping, which

is the most important form of retention in the short term.

Second, CO2 can dissolve into the formation water to be

& Qi Fang

frances2009@foxmail.com

1 School of Environmental Protection and Safety Engineering,

University of South China, Hengyang 421001, China

2 School of Environmental Studies, China University of

Geosciences, Wuhan 430074, China

3 School of Computer Science and Technology, University of

South China, Hengyang 421001, China

4 Team 217 of Hunan Nonferrous Geological Exploration

Bureau, Hengyang 421001, China

123

Environ Earth Sci (2016) 75:1265

DOI 10.1007/s12665-016-6054-y

sequestered in forms of bicarbonate ions, referred as sol-

ubility trapping. Third, CO2 can react with minerals to be

immobilized by secondary carbonate minerals, called as

mineral trapping, which is the most effective CO2

sequestration method. Xu et al. (2004) evaluated three host

rock types for long-term CO2 storage in deep aquifers and

concluded that the mineral trapping capacity depends sig-

nificantly on mineral composition. Zhang et al. (2009)

investigated the long-term fate of CO2 sequestration in

Songliao Basin of China and obtained that CO2 mineral

trapping capacity ranges from 10 to 35 kg/m3 medium.

Thibeau et al. (2009) assessed the CO2 mineral sequestra-

tion capacity of Rousse depleted gas reservoir and con-

cluded that the amount of CO2 sequestered by the

dissolution of chlorite accounts for 70 % of the total

injected CO2. Tambach et al. (2011) evaluated the CO2

sequestration potential of sandstone reservoir in the

Netherlands and found that dawsonite is the predominant

mineral to sequester CO2 in solid phase. Some studies

(Moore et al. 2005; Worden 2006; Hellevang et al.

2010, 2011) investigated the long-term stability of daw-

sonite at elevated CO2 partial pressure. Rathnaweera et al.

(2015, 2016) conducted a long-term combined experiment

related to mineralogical rock alteration and reached the

conclusion that long-term reaction with CO2 causes a sig-

nificant pH drop in the pore fluid and significant dissolution

of calcite, siderite, barite and kaolinite.

Jianghan Basin is one of the largest basins in South

China covering an area of 36.350 km2 (Fig. 1). It is a

typical salt-lake sedimentary basin with the salinity

ranging from 100,000 to 350,000 mg/L with depth. The

deposition thickness from Late Cretaceous to Quaternary

is up to 10 km. The interbedded sandstone, mudstone

and gypsum-salt rock in Shashi Formation (Es), Xin-

guizui Formation (Ex), Jingsha Formation (Ej) and

Qijiang Formation (Eq) may provide suitable reservoir

and caprock pairs for CO2 sequestration, especially the

excellent sealing ability of the thick gypsum-salt rock. In

addition, Jiangling Depression and Qianjiang Depression

are the concentration areas of highly mineralized

potassium-rich brine. Figure 2 shows the variation of

porosity, permeability and mineral composition of

sandstone with depth from ES-4 drilling in Jiangling

Depression. The porosity of Jingsha Formation ranges

from 10.91 to 13.26 % and permeability ranges from

2.76 to 6.43 mD, belonging to low-permeability reser-

voir (Fang et al. 2014). With regard to the mineral

composition of sandstone, there is no big change with

depth. The clastic constituent consists of a large amount

of quartz accounting for 80–90 % and a small quantity

of feldspar and lithic fragment with the average content

\10 %. The interstitial material in the sandstone reser-

voir accounts for 10–30 % dominated by calcite with

subordinate siliceous and ferruginous cement, gypsum

Fig. 1 Location, geological units and stratum histogram of Jianghan Basin

1265 Page 2 of 13 Environ Earth Sci (2016) 75:1265

123

and clay minerals. Brine production combined with CO2

geological storage may be a win–win method to the

investors as it will not only enhance brine production

efficiency but also improve CO2 injectivity and storage

security (Fang and Li 2014; Liu et al. 2015). Therefore,

Jianghan Basin is very likely to be a promising candidate

for CO2 geological storage. Li et al. (2012) found out

that salinity has a significant impact on the mineral

sequestration of CO2, but the influencing mechanism is

not well understood. Since the mineral sequestration

capacity of CO2 largely determines the long-term secu-

rity of CO2 storage, it is important to figure out the

mineral sequestration capacity of CO2 in high-salinity

aquifers. In this work, we aim to investigate the effect of

salinity and feldspar on the mineral sequestration

capacity of CO2 in high-salinity aquifers by taking Jin-

gling Depression of Jianghan Basin for instance.

Methodology

Model setup

The target reservoir is modeled as a homogeneous sand-

stone aquifer represented by a concentric cylindrical

geometry centered around a vertical injection well. The

maximum radial extent of the study area is set as 10 km

(far enough to avoid the disturbance to the boundary due to

CO2 injection), composed of 366 co-centered cell ele-

ments. In this study, we focus on the mineral sequestration

capacity of CO2 in per unit volume medium; therefore, the

model we built considers only one layer with a thickness of

20 m (see Fig. 3). CO2 is injected with constant rate of

1 kg/s for 30 years. The flow and geochemical transport

simulation was run for 10,000 years. The simulation was

performed using TOUGHREACT which is a numerical

simulation program for chemically reactive non-isothermal

flows of multiphase fluids in porous and fractured media

(Xu et al. 2006, 2011).

Initial and boundary conditions

The boundary condition applied to our simulations is a

Dirichlet boundary condition, which was implemented by

assigning a large volume such as 1040 to the boundary grid

element. Consequently, any influence from the influx

becomes negligible compared to the large volume of the

formation brine. The aqueous chemical composition and

thermodynamic conditions, such as temperature and pres-

sure, do not change from the original formation brine. The

sandstone layer is initially saturated with water with water

saturation equal to 1.

Hydrogeochemical conditions

The petrophysical properties used in the simulation were

taken from Jingsha Formation with depth ranging from

2244 to 2247 m. The porosity is 12 % and the permeability

is 3.81 mD. The hydrogeological parameters used in the

simulation are listed in Table 1. For lack of data, the rel-

ative permeability and capillary pressure model was taken

from previous literature (Xu et al. 2004, 2006; Zhang et al.

2009). As for the mineral composition, it mainly consists of

quartz, feldspar, calcite, anhydrite, illite, chlorite and

hematite. Because of uncertain in the composition of

feldspar and a significant impact of mineral composition on

Fig. 2 Variation in porosity, permeability (a) and mineral composition (b) with depth from ES-4 drilling

Fig. 3 Schematic diagram of the model used in this study

Environ Earth Sci (2016) 75:1265 Page 3 of 13 1265

123

the mineral trapping capacity of CO2, we looked at three

different cases corresponding to three different mineral

compositions in the geologic formation, respectively,

called as case I, case II and case III as given in Table 2.

Due to the limited amount of feldspar, we here regard it

as K-feldspar in case I, as albite in case II and both

coexist in case III. Then, in order to identify the effect

of salinity on the mineral sequestration capacity of CO2,

we considered four different initial aqueous NaCl con-

centrations, corresponding to four different salinity val-

ues (1, 2, 3 and 4 mol/L), referring to them as case Ia,

case Ib, case Ic and case Id. In addition, in order to

identify the effect of the initial feldspar content on the

mineral sequestration of CO2, the initial volume fraction

of feldspar in case I and case II is, respectively,

increased from 2 to 5 %, referring as to case I2, case I5,

case II2 and case II5. Thus, overall, we ran a total of 14

TOUGHREACT simulations. Batch geochemical mod-

eling of water–rock interaction was performed to obtain

nearly equilibrated water chemistry prior to the reactive

transport simulation by keeping pH at a fixed value, and

part of the initial concentrations of formation water is

listed in Table 3.

Kinetics of mineral dissolution and precipitation

The general kinetic rate expression used in TOUGH-

REACT is shown as follows:

rm ¼ �k Tð ÞmAm 1 � Qm

Km

� �h�����

�����g

ð1Þ

where m denotes kinetic mineral index, rm is the dissolu-

tion/precipitation rate (positive values indicate dissolution;

negative values indicate precipitation), k(T)m is the rate

constant depending on the temperature (mol/m2 s), T is the

absolute temperature, Am is the specific reactive surface

area per kg water, Km is the equilibrium constant for the

mineral–water reaction written for the destruction of 1 mol

of mineral m and Qm is the corresponding ion activity

product. The parameters h and g are two positive numbers

determined by experiments; usually, but not always, they

are taken to be equal to 1.

For many minerals, the kinetic rate constant k(T) can be

summed from three mechanisms:

k Tð Þ ¼ knu25 exp

�Enua

R

1

T� 1

298:15

� �� �

þ kH25 exp

�EHa

R

1

T� 1

298:15

� �� �anH

H

þ kOH25 exp

�EOHa

R

1

T� 1

298:15

� �� �anOH

OH

ð2Þ

where superscripts and subscripts nu, H and OH indicate

neutral, acid and base mechanisms, respectively, Ea is the

activation energy, k25 is the rate constant at 25 �C, R is the

gas constant (8.31 J/mol K), T is the absolute temperature,

a is the activity of the species and n is a power term

(constant). For all minerals, it is assumed that the precip-

itation rate equals the dissolution rate. Parameters for cal-

culating kinetic rate of minerals given in Table 4 were

taking from relative literature (Xu et al. 2006; Zhang et al.

2009). Calcite and anhydrite were assumed to react with

aqueous species at local equilibrium because their reaction

rates are typically quite rapid.

Results and discussion

Effect of feldspar on the mineral sequestration

capacity of CO2

In order to compare CO2 mineral trapping capacity and

better understand the major mineral changes, we chose a

block of 500 m away from CO2 injection well as reference.

As shown in Fig. 4, feldspar has a significant effect on the

mineral sequestration capacity of CO2, depending on not

the total content but the feldspar type and relative content

of K-feldspar. For case I with K-feldspar present, as shown

in Fig. 4a, the maximum mineral trapping capacity of CO2

reaches about 0.20 mol/L medium, corresponding to

8.8 kg/1 m3 medium after 5000 years. A significant

Table 1 Hydrogeological parameters used in the simulations

Parameters Geological formation

Porosity 0.12

Permeability (m2) 3.81 9 10-15

Pore compressibility (Pa-1) 4.5 9 10-10

Rock grain density (kg/m3) 2600

Formation heat conductivity (W/m �C) 2.51

Rock grain specific heat (J/kg �C) 920

Temperature (�C) 90

Pressure (bar) 225

Relative permeability model:

krg ¼ 1 � S� �2

1 � S2� �

S ¼ Sl � Slrð Þ

Sl � Slr � Sgr

� �

krl ¼ffiffiffiffiffiS�

p1 � 1 � S�½ �1=m

� �mn o2

S� ¼ Sl � Slrð Þ= 1 � Slrð Þ

Capillary pressure model (Van Genuchten):

Pcap ¼ �P0 S�½ ��1=m�1� �1�m

S� ¼ Sl � Slrð Þ= 1 � Slrð Þ

Slr: residual water saturation 0.05

Slr: residual water saturation 0.30

P0: strength coefficient P0 = 19.61 kPa

m: exponent 0.457

1265 Page 4 of 13 Environ Earth Sci (2016) 75:1265

123

amount of ankerite (CaMg0.3Fe0.7(CO3)2) and small

amount of magnesite (MgCO3) precipitate to sequester

CO2 in the solid phase. As for the formed clay minerals,

only illite precipitates and no kaolinite is present. In Wang

et al.’s (2016) experiment at the temperature of 180�, after

reaction with CO2 brine, the contents of quartz, plagio-

clase, illite and chlorite increased considerably, whereas

the contents of illite/smectite, biotite and kaolinite

decreased more or less. In Rathnaweera et al.’s (2015,

2016) long-term experiment, kaolinite dissolution happens

at the temperature of 40 �C. In Bolourinejad et al. (2014)

geochemical modeling, a large amount of illite also pre-

cipitates, increasing by 66 %. Therefore, it is reasonable to

generate illite in the aqueous solution abundant in K?,

Mg2? and Al3?, and the reaction increases with tempera-

ture and sediment depth. Increasing the initial volume of

K-feldspar from 2 to 5 % has little improvement on the

mineral sequestration capacity of CO2 due to the higher pH

value neutralized by more dissolution of K-feldspar

reducing the dissolution of calcite.

For case II with albite present, the maximum mineral

trapping capacity of CO2 reaches about 0.31 mol/L med-

ium, corresponding to 13.5 kg/1 m3 medium. With regard

to CO2-sequestered carbonate minerals, a significant

amount of ankerite and dawsonite and small amount of

magnesite precipitate (Fig. 4b). A certain amount of Na-

smectite and Ca-smectite precipitates. Increasing the initial

volume of albite from 2 to 5 %, the maximum mineral

trapping capacity of CO2 can rise from 13.5 to 21.3 kg/

1 m3 medium after 5000 years. The precipitation amount

of Na-smectite increases from 0.075 to 0.109 mol/L med-

ium. The precipitation amount of dawsonite increases from

0.12024 to 0.32715 mol/L medium, indicating that increase

in the volume of albite can significantly improve the

mineral sequestration capacity of CO2 since the acid

environment is not favorable for the precipitation of

smectite.

For case III with K-feldspar and albite coexist, in spite

of improving both of their initial volume to 5 %, the

maximum mineral trapping capacity of CO2 reaches about

0.32 mol/L medium corresponding to 14.1 kg/1 m3 med-

ium after 5000 years, slightly higher than that of case II2

(Fig. 4c). However, the precipitation of dawsonite only

accounts for 20 % of that in case II5 and 43 % of that in

case II. It is to be noted that a large amount of illite pre-

cipitates in this case, increased by 96 % compared with

that in case I5, indicating that most of Al3? provided by the

dissolution of albite are consumed by the precipitation of

illite, thereby leading to the decrease of dawsonite and

magnesite. Actually, it is the significant decrease in the

dissolved amount of calcite resulting from the higher pH

buffered by more dissolution of K-feldspar and albite to

keep CO2 mineral trapping capacity slightly higher than

that of case II2.

In conclusion, illite has a significant restriction on the

mineral sequestration capacity of CO2 since its

Table 2 Initial mineral volume

fractions and possible secondary

mineral phases in the

simulations

Minerals Chemical composition Volume fraction

Case I Case II Case III

Case I2 Case I5 Case II2 Case II5

Quartz SiO2 0.70 0.67 0.70 0.67 0.62

K-feldspar KAlSi3O8 0.02 0.05 0.00 0.00 0.05

Albite NaAlSi3O8 0.00 0.00 0.02 0.05 0.05

Calcite CaCO3 0.20 0.20 0.20 0.20 0.20

Anhydrite CaSO4 0.03 0.03 0.03 0.03 0.03

Chlorite Mg2.5Fe2.5Al2Si3O10(OH)8 0.01 0.01 0.01 0.01 0.01

Illite K0.6Mg0.25Al1.8(Al0.5Si3.5O10)(OH)2 0.03 0.03 0.03 0.03 0.03

Hematite Fe2O3 0.01 0.01 0.01 0.01 0.01

Kaolinite Al2Si2O5(OH) 0 0 0 0 0

Ca-smectite Ca0.145Mg0.26Al1.77Si3.97O10(OH)2 0 0 0 0 0

Na-smectite Na0.290Mg0.26Al1.77Si3.97O10(OH)2 0 0 0 0 0

Ankerite CaMg0.3Fe0.7(CO3)2 0 0 0 0 0

Dawsonite NaAlCO3(OH)2 0 0 0 0 0

Dolomite CaMg(CO3)2 0 0 0 0 0

Magnesite MgCO3 0 0 0 0 0

Siderite FeCO3 0 0 0 0 0

Pyrite FeS2 0 0 0 0 0

Environ Earth Sci (2016) 75:1265 Page 5 of 13 1265

123

precipitation preferentially consumes a lot of Al3?. K?,

Mg2? and Al3? are the three important ions to generate

illite. Chlorite is one of the most common Mg-rich min-

erals in the sedimentary rocks. Comparing the stoichio-

metric coefficient of Mg in chlorite

(Mg2.5Fe2.5Al2Si3O10(OH)8) to illite (K0.6Mg0.25Al1.8

(Al0.5Si3.5O10(OH)2), we can see that Mg stoichiometric

coefficient of chlorite is 10 times of illite, indicating that

chlorite usually could provide sufficient Mg2? to support

the precipitation of illite. For example, in this study, the

complete dissolution of 1 % volume, corresponding to

0.04185 mol/dm3 medium of chlorite, could generate

0.4185 mol/dm3 medium illite; and this quantity needs

0.2511 mol/L K? and 0.9626 mol/L Al3?. K? only

comes from the dissolution of K-feldspar (KAlSi3O8),

and Al3? is mainly from the dissolution of K-feldspar

and albite ((NaAlSi3O8). As given in Table 5, the pre-

cipitation of magnesite (MgCO3) indicates that Mg2? is

sufficient. Such K? and Al3? become the key ions to

restrain the formation of illite. One mole formation of

illite needs 0.6 mol of K? and 2.3 mol of Al3?. For case

I2 and case I5, both of the ratios of K-feldspar disso-

lution to illite precipitation are larger than 0.6, indicat-

ing that K? is sufficient; the ratio of the dissolution of

K-feldspar and albite to the precipitation of illite is

\2.3, indicating that Al3? is the limiting factor. As for

case III, the ratio of the dissolution of K-feldspar and

albite to the precipitation of illite is larger than 2.3,

indicating that Al3? is sufficient. Though the ratios of

K-feldspar dissolution to illite precipitation are 0.62,

slightly larger than 0.6, K? are still deficient for the

reason that some K? dissolve into the aqueous solution.

Compared with case II2, Al3? released from 3 % albite

is consumed by the precipitation of illite. Therefore,

with a small amount of Mg-rich minerals such as

chlorite, the mineral composition abundant in K-feldspar

is less favorable for the mineral sequestration capacity

of CO2 attributing to a significant amount of illite pre-

cipitate and consumes a large amount of Al3?, thereby

limiting the precipitation of dawsonite. In Zhang et al.

(2009), the mineral trapping capacity of CO2 only

reaches 8 kg/m3 medium after 10,000 years for the

mineral composition of 41.5 % albite, 23.3 % feldspar,

2.8 % chlorite and 3 % calcite, once again proving the

above viewpoint. In Bolourinejad et al. (2014) studies,

with the mineral composition of 1.64 % albite, 2.43 %

K-feldspar, 2.02 % dolomite and 5.14 % kaolinite, the

major modeled reactions are the formation of illite and

calcite from K-feldspar, dolomite, kaolinite and albite as

shown in reaction (3) and (4). These reactions demon-

strate that nearly 100 % of Al is conserved in the

feldspar–kaolinite–albite–illite system, in line with ear-

lier studies (Hellevang et al. 2011).Table

3In

itia

lco

nce

ntr

atio

ns

of

form

atio

nw

ater

atre

serv

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con

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so

f9

0�C

and

22

5b

ars

Ele

men

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on

cen

trat

ion

(mo

l/L

NaC

l):

Cas

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Co

nce

ntr

atio

n(m

ol/

L):

Cas

eII

Cas

eIa

:1

mo

l/L

Cas

eIb

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mo

l/L

Cas

eIc

:3

mo

l/L

Cas

eId

:4

mo

l/L

Cas

eII

a:1

mo

l/L

Cas

eII

b:

2m

ol/

LC

ase

IIc:

3m

ol/

LC

ase

IId

:4

mo

l/L

pH

6.9

6.9

6.9

6.9

6.9

6.9

6.9

6.9

Ca

6.8

959

10-

02

4.5

849

10-

02

5.5

459

10-

02

6.3

529

10-

02

3.2

069

10-

02

6.7

749

10-

02

6.1

939

10-

02

6.3

509

10-

02

Mg

6.8

979

10-

05

1.1

219

10-

04

1.3

409

10-

04

4.9

799

10-

04

1.2

369

10-

04

4.5

599

10-

04

1.0

369

10-

04

4.5

679

10-

04

Na

9.8

939

10-

01

1.9

979

10?

00

2.9

959

10?

00

3.9

959

10?

00

9.9

889

10-

01

1.9

939

10?

00

3.0

009

10?

00

4.0

029

10?

00

K3

.47

09

10-

02

3.6

289

10-

02

3.6

479

10-

02

4.1

569

10-

02

3.7

659

10-

04

2.7

669

10-

03

2.6

609

10-

02

3.4

399

10-

02

Fe

1.1

179

10-

06

1.4

839

10-

06

2.3

369

10-

06

1.1

459

10-

06

2.8

749

10-

07

2.3

449

10-

07

2.0

879

10-

06

1.4

779

10-

06

SiO

2(a

q)

9.1

009

10-

04

9.5

029

10-

04

9.8

509

10-

04

1.0

269

10-

03

9.0

959

10-

04

9.4

989

10-

04

9.9

529

10-

04

1.0

169

10-

03

C3

.35

19

10-

04

6.6

679

10-

04

6.8

269

10-

04

6.5

799

10-

04

6.8

369

10-

04

4.6

399

10-

04

5.6

809

10-

04

7.0

139

10-

04

S1

.60

09

10-

02

4.4

869

10-

02

5.4

689

10-

02

6.2

779

10-

02

3.1

479

10-

02

3.0

219

10-

02

4.8

919

10-

02

6.2

739

10-

02

Al

1.6

449

10-

08

1.7

569

10-

08

1.8

579

10-

08

1.7

079

10-

08

5.0

979

10-

08

2.9

159

10-

08

2.1

329

10-

08

1.7

689

10-

08

Cl

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2.0

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3.0

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4.0

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1.0

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2.0

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3.0

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10?

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4.0

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10?

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O2

(aq

)1

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99

10-

57

2.5

479

10-

57

2.5

449

10-

57

2.4

939

10-

55

3.9

619

10-

55

4.3

529

10-

54

2.2

149

10-

57

1.4

479

10-

55

1265 Page 6 of 13 Environ Earth Sci (2016) 75:1265

123

Table

4P

aram

eter

sfo

rca

lcu

lati

ng

kin

etic

rate

con

stan

tso

fm

iner

als

Min

eral

sS

urf

ace

area

(cm

2/g

)

Par

amet

ers

for

kin

etic

rate

law

Neu

tral

mec

han

ism

Aci

dm

ech

anis

mB

ase

mec

han

ism

k 25

(mo

l/m

2s)

Ea

(kJ/

mo

l)k 2

5Ea

n(H

?)

k 25

Ea

n(H

?)

Cal

cite

–E

qu

ilib

riu

m–

An

hy

dri

te–

Eq

uil

ibri

um

–

Qu

artz

9.8

1.2

50

0e-

14

87

.7

Kao

lin

ite

15

1.6

6.9

18

3e-

14

22

.24

.89

78

e-1

26

5.9

0.7

77

8.9

12

5e-

18

17

.9-

0.4

72

Illi

te1

51

.61

.65

96

e-1

33

5.0

1.0

47

1e-

11

23

.60

.34

3.0

20

0e-

17

58

.9-

0.4

0

Ch

lori

te9

.83

.02

00

e-1

38

8.0

7.7

62

4e-

12

88

.00

.5

Alb

ite*

low

9.8

2.7

54

2e-

13

69

.86

.91

83

e-1

16

5.0

0.4

57

2.5

11

9e-

16

71

.0-

0.5

72

K-f

eld

spar

9.8

3.8

90

5e-

13

38

.08

.70

96

e-1

15

1.7

0.5

6.3

09

6e-

22

94

.1-

0.8

23

Mag

nes

ite

9.8

4.5

70

9e-

10

23

.54

.16

87

e-0

71

4.4

1.0

Do

lom

ite

9.8

2.9

51

2e-

08

52

.26

.45

65

e-0

43

6.1

0.5

Sid

erit

e9

.81

.25

98

e-0

96

2.7

66

.45

65

e-0

43

6.1

0.5

Daw

son

ite

9.8

1.2

59

8e-

09

62

.76

6.4

56

5e-

04

36

.10

.5

An

ker

ite

9.8

1.2

59

8e-

09

62

.76

6.4

56

5e-

04

36

.10

.5

Na-

smec

tite

15

1.6

1.6

59

6e-

13

35

.01

.04

71

e-1

12

3.6

0.3

43

.02

00

e-1

75

8.9

-0

.40

Ca-

smec

tite

15

1.6

1.6

59

6e-

13

35

.01

.04

71

e-1

12

3.6

0.3

43

.02

00

e-1

75

8.9

-0

.40

Hem

atit

e1

2.8

72

.51

19

e-1

56

6.2

4.0

73

8e-

10

66

.21

.0

Py

rite

12

.87

k 25=

2.8

18

4e-

5Ea=

56

.9

n(O

2(a

q))=

0.6

k 25=

3.0

24

e-8Ea=

56

.9

n(H

?)=

-0

.5,n

(Fe3

?)=

0.5

(1)

All

rate

con

stan

tsar

eli

sted

for

dis

solu

tio

n;

(2)

Ais

spec

ific

surf

ace

area

,k

25

isth

ek

inet

icco

nst

ant

at2

5�C

,E

isth

eac

tiv

atio

nen

erg

y,

andn

isth

ep

ow

erte

rm;

(3)

the

po

wer

term

sn

for

bo

thac

idan

db

ase

mec

han

ism

sar

ew

ith

resp

ect

toH?

;an

d(4

)fo

rp

yri

te,

the

neu

tral

mec

han

ism

has

nw

ith

resp

ect

toO

2(a

q)

and

the

acid

mec

han

ism

has

two

spec

ies

inv

olv

ed:

on

en

wit

h

resp

ect

toH?

and

ano

ther

nw

ith

resp

ect

toF

e3?

Environ Earth Sci (2016) 75:1265 Page 7 of 13 1265

123

0:6KAlSi3O8 þ 0:85Al2Si2O5 OHð Þ4þ0:25CaMg CO3ð Þ2

! K0:6Mg0:25Al1:8 Si3:5Al0:5O10ð Þ OHð Þ2þ0:25CaCO3

þ 0:45H2O þ 0:25HCO�3 þ 0:25Hþ ð3Þ

0:6KAlSi3O8þ1:7NaAlSi3O8þ0:25CaMg CO3ð Þ2

þ0:4H2Oþ1:45Hþ!K0:6Mg0:25Al1:8 Si3:5Al0:5O10ð Þ OHð Þ2

þ0:25CaCO3þ1:7Naþþ3:4SiO2þ0:25HCO�3 ð4Þ

Fig. 4 Mineral dissolution (-)

and precipitation (?) for case I

with K-feldspar of 2 % (case I2)

and 5 % (case I5), case II with

albite of 2 % (case II2) and 5 %

(case II5), case III with

K-feldspar (5 %) and albite

(5 %) co-present after

5000 years

Table 5 Ratio of the dissolution of K-feldspar and albite to the precipitation of illite

Case Abundance of mineral dissolution or precipitation (mol/L) Ratio

n (Magnesite) n (K-feldspar) n (Albite) n (Illite) n (K-feldspar):n (Illite) n (K-feldspar ? Albite):n (Illite)

Case I2 0.04108 0.07577 0 0.06890 1.10 1.10

Case I5 0.03580 0.12501 0 0.09076 1.38 1.38

Case III 0.00447 0.11013 0.33893 0.17763 0.62 2.53

1265 Page 8 of 13 Environ Earth Sci (2016) 75:1265

123

Effect of salinity on the mineral sequestration

capacity of CO2

As shown in Fig. 5, the effect of salinity on the mineral

sequestration capacity of CO2 represents in two aspects: one

for the longer migration distance derived from the lower sol-

ubility with higher salinity of formation water and the other for

CO2 mineral trapping capacity per 1 m3 medium which is not

in simple decreased with salinity, depending on K-feldspar

present or not. For case I and case III with K-feldspar present

in the mineral composition, CO2 mineral trapping capacity

decreases with salinity. For case II without K-feldspar, CO2

mineral trapping capacity increases with salinity, especially

for salinity of 4 mol/L with the maximum mineral trapping

capacity of CO2 up to 15 kg/m3 medium after 5000 years.

Increasing the salinity (concentration of NaCl) will

delay or reduce the dissolution of albite, consequently

leading to the lower pH value of formation water. For case

I with no albite present, salinity has little effect on CO2

trapping capacity except for slightly higher dissolution of

K-feldspar leading to higher precipitation of illite. In spite

of abundance of Na? in the aqueous solution, no dawsonite

Fig. 5 Radial distribution of

the amount of CO2 sequestered

in solid phase (mol/L medium)

for salinity of 1, 2, 3 and 4 mol/

L of cases I, II and III

Environ Earth Sci (2016) 75:1265 Page 9 of 13 1265

123

precipitates, indicating that all the Al3? released by the

dissolution of chlorite and K-feldspar are totally consumed

by the precipitation of illite. Just as shown in Fig. 6,

dawsonite experiences a process from precipitation to

dissolution during 100–1000 years when there is no

sufficient K? in the aqueous solution to support the pre-

cipitation of illite.

For case II, salinity has little impact on the precipitation

of ankerite except for slightly longer migration distance of

CO2 plume. However, salinity has a significant effect on

Fig. 6 Time evolution of

mineral change of chlorite,

K-feldspar, illite and dawsonite

(case Ic). Chlorite and

K-feldspar dissolve; illite and

dawsonite precipitate

Fig. 7 Radial distribution of

CO2-sequestered mineral

changes in volume fraction after

5000 years for salinity of 1, 2, 3

and 4 mol/L of case II

1265 Page 10 of 13 Environ Earth Sci (2016) 75:1265

123

the precipitation of dawsonite and magnesite, manifesting

not just in the extension of radial migration, but also in the

precipitation volume per 1 m3 medium (Fig. 7). Actually,

as shown in Fig. 8, improving the initial salinity (NaCl

concentration) of aqueous solution from 1 to 3 mol/L, the

higher concentration of Na? delays the dissolution of albite

and consequently leads to the lower pH value. Low pH

environment will reduce the precipitation amount of

smectite (including Na-smectite and Ca-smectite) and

therefore increase the precipitation amount of dawsonite

and magnesite.

As for case III with K-feldspar and albite co-present in

the mineral composition, the mineral trapping of CO2

decreases significantly with salinity, from 14 kg/1 m3

medium of 1 mol/L salinity down to 11 kg/1 m3 medium

of 3 mol/L salinity. As shown in Fig. 9, improving the

initial salinity of aqueous solution from 1 to 3 mol/L

results in a large decrease in the dissolution amount of

albite, thereby leading to lower pH condition. That lower

pH condition significantly increases the dissolution amount

of calcite is the main reason accounting for the decrease in

CO2 mineral trapping capacity with salinity.

Fig. 8 Time evolution of

mineral changes of chlorite,

albite, dawsonite and Na-

smectite for salinity of 1 (case

IIa) and 3 mol/L (case IIc)

Fig. 9 Mineral dissolution (-)

and precipitation (?) for case III

with the salinity of 1 (case IIIa)

and 3 mol/L (case IIIc)

Environ Earth Sci (2016) 75:1265 Page 11 of 13 1265

123

Conclusions

The purpose of this paper is to investigate the effect of

feldspar and salinity on the mineral sequestration capacity

of CO2 in deep high-salinity brine aquifers by taking

Jiangling Depression of Jianghan Basin for instance.

Numerical simulation on long-term geochemical reaction

and transport was performed by taking TOUGHREACT as

the simulation tool. Major findings and conclusions are

summarized as follows:

1. The mineral trapping capacity of CO2 for Jiangling

Depression sandstone of Jianghan Basin ranges from

8 to 21 kg/1 m3 medium. The effect of feldspar on

the mineral trapping capacity of CO2 does not depend

on the total content of feldspar, but depends on

feldspar type and relative content. With Mg-rich

minerals such as chlorite or dolomite present, the

mineral composition abundant in K-feldspar is less

favorable for the mineral sequestration capacity of

CO2 for the reason that a large amount of illite

precipitates, consuming a lot of Al3? in the aqueous

solution, thereby limiting the precipitation of daw-

sonite, especially for the high-temperature sedimen-

tary environment.

2. The effect of salinity on the mineral sequestration

capacity of CO2 represents two aspects: one for the

longer migration distance due to the lower solubility of

higher salinity and the other for CO2 mineral trapping

capacity per m3 medium which is not in simple

decreased with salinity, depending on K-feldspar

present or not. For the mineral composition with

K-feldspar present, CO2 mineral trapping capacity

decreases with salinity, while with albite instead of

K-feldspar, it increases with salinity owing to more

dawsonite precipitates.

Acknowledgments This work was supported by National Science

Foundation of China (No. 11545016) and Science and Technology

Bureau of Hengyang City (2015KS05) as well as Doctoral Scientific

Fund of University of South China (2014XQD12). We would like to

thank the anonymous reviewers for their constructive comments and

suggestions on this manuscript.

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