Assessing risk to fresh water resources from long term 

CO2 injection- laboratory and field studies 

GCCC Digital Publication Series #08-03j 

Rebecca C. Smyth 

Susan D. Hovorka 

Jiemin Lu 

Katherine D. Romanak 

Judson W. Partin 

Corrine Wong 

Changbing Yang 

Cited as: 

Smyth, R.C., Hovorka, S.D., Lu, J., Romanak, K.D., Partin, J.W., Wong, C., 

Assessing risk to fresh water resources from long term CO2 injection- laboratory 

and field studies: presented at the 9th International Conference on Greenhouse 

Gas Control Technologies (GHGT-9), Washington, D.C., November 16-20, 2008. 

GCCC Digital Publication Series #08-03j. 

Keywords: 

Geologic sequestration, water resources, laboratory experiments, increased pH,

cations, groundwater sampling 
 

 

Assessing risk to fresh water resources from long term CO2

injection – laboratory and field studies 

Rebecca C. Smytha*, Susan D. Hovorkaa, Jiemin Lua, Katherine D. Romanaka, 

Judson W. Partinb

, Corrine Wongb, and Changbing Yanga

a

Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, P.O. Box X, Austin, TX, 78713, USA b

Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX,78705, USA 

Abstract 

In developing a site for geologic sequestration, one must assess potential consequences of failure to adequately contain 

injected carbon dioxide (CO2). Upward migration of CO2 or displacement of saline water because of increased pressure might 

impact protected water resources 100s to 1000s of meters above a sequestration interval. Questions posed are: (1) Can changes in 

chemistry of fresh water aquifers provide evidence of CO2 leakage from deep injection/sequestration reservoirs containing brine 

and or hydrocarbons? (2) What parameters can we use to assess potential impacts to water quality? (3) If CO2 leakage to 

freshwater aquifers occurs, will groundwater quality be degraded and if so, over what time period? 

 Modeling and reaction experiments plus known occurrences of naturally CO2-charged potable water show that the 

common chemical reaction products from dissolution of CO2 into freshwater include rapid buffering of acidity by dissolution of 

calcite and slower equilibrium by reaction with clays and feldspars. Results from a series of laboratory batch reactions of CO2

with diverse aquifer rocks show geochemical response within hours to days after introduction of CO2. Results included decreased 

pH and increased concentrations of cations in CO2 experimental runs relative to control runs using argon (Ar). Some cation (Ba, 

Ca, Fe, Mg, Mn, and Sr) concentrations increased over and an order of magnitude during CO2 runs. Results are aquifer dependant 

in that experimental vessels containing different aquifer rocks showed different magnitudes of increase in cation concentrations. 

 Field studies designed to improve understanding of risk to fresh water are underway in the vicinity of (1) SACROC 

oilfield in Scurry County, Texas, USA where CO2 has been injected for enhanced oil recovery (EOR) since 1972 and (2) the 

Cranfield unit in Adams County, Mississippi, USA where CO2 EOR is currently underway. Both field studies are funded by the 

U.S. Department of Energy (DOE) regional carbon sequestration partnership programs and industrial sponsors. Preliminary 

results of groundwater monitoring are currently available for the SACROC field study where researchers investigated 68 water 

wells and one spring during five field excursions between June 2006 and July 2008. Results to date show no trend of preferential 

degradation below drinking water standards in areas of CO2 injection (inside SACROC) as compared to areas outside of the 

SACROC oil field. 

 

Keywords: geologic sequestration, water resources, laboratory experiments, increased pH, cations, groundwater sampling 
1. Introduction 

Site selection for geologic sequestration (GS) is the key element in assuring that carbon dioxide (CO2) will be 

retained in an appropriate receiving formation for geologically significant periods of time. Restriction of fluid 

injection permits to properly selected sites is mandated by the Safe Drinking Water Act of 1974 (U.S. House of 

Representatives, 1974), and managed by the United States Environmental Protection Agency (USEPA) 

Underground Injection Control (UIC) Program. In a correctly selected GS site there should be negligible transport of 

CO2 out of the injection formation, and migration would be limited to diffusion into confining zones. Underground 

sources of drinking water (USDWs) near a correctly selected site would not be impacted by CO2 injection, thereby 

meeting USEPA requirements to protect human drinking water supplies. However, it is prudent to assess potential 

impacts of (1) failure to contain injected CO2 in the receiving formation, and (2) displacement of high-salinity fluid 

(brine) into USDWs. Potential errors in site selection considered here are presence of moderate to high permeability 

flow paths such as a vertically transmissive fault or improperly plugged well, along which CO2 and/or brine could 

migrate. The possibility of impacts to USDWs is the focus of this brief paper. A USDW is defined in the USEPA 

Proposed Rule for Permitting Full-Scale Geologic Sequestration Projects (July 2008) as: An aquifer or portion of an 

aquifer that supplies any public water system or that contains a sufficient quantity of groundwater to supply a public 

water system, and currently supplies drinking water for human consumption, or that contains fewer than 10,000 

mg/l total dissolved solids and is not an exempted aquifer .By regulation CO2 would be injected below the deepest 

USDW and separated from it by a confining zone (i.e. low permeability seal). 

In the following sections we present results from laboratory experiments conducted to assess chemical by-products 

of reactions between injected CO2, aquifer host rocks, and fresh groundwater. We then present results from a fieldbased study of groundwater quality overlying the Scurry Area Canyon Reef Operators Committee (SACROC) 

oilfield in Scurry County, Texas, U.S.A. CO2 has been injected at SACROC for enhanced oil recovery (EOR) since 

1972 making this an ideal natural laboratory in which to observe potential impacts of CO2 to groundwater. This 

work has been funded by (1) the Gulf Coast Carbon Center (GCCC) industrial sponsor program at the Bureau of 

Economic Geology (BEG) at The University of Texas at Austin, (2) the Department of Energy National Energy 

Technology Laboratory (DOE/NETL) through the Southwest Regional Partnership for Carbon Sequestration (SWP) 

administered by New Mexico Tech, and (3) Kinder Morgan CO2 pipeline and production companies. 

2. CO2-rock reaction fundamentals 

Most studies of how CO2 dissolves in water and reacts with the host rock have considered injection zones at greater 

than 1 km depth and focused on the trapping of CO2 in mineral phases (Rochelle et al, 2004, Gunter et al., 2004, 

Worden and Smith, 2004). CO2-solubility dependence on pressure, temperature, and salinity is well known. Field 

observations at the Frio (e.g. Karaka et al., 2006 and Hovorka et al., 2006) and Weyburn (IEA, 2005) test sites, and 

simulations based on observations at the sites, have documented rock-brine-CO2 reactions at 1,500 m depths in 

100,000 mg/L basinal brines. Under these conditions, fluids are strongly reducing (methane saturated) and CO2 is 

supercritical (Knauss et al., 2005). Under most circumstances CO2 will dissolve in water and lower pH. In a system 

containing reactive mineral phases, the decrease in pH is buffered by dissolution of Ca/Mg/Fe-bearing silicate 

minerals (Gunter et al., 1993). High CO2 content causes continued dissolution of silicates, and precipitation of clay 

minerals, carbonates, and quartz when the acidity has been reduced by silicate dissolution (Gunter et al., 1997; 

Hitchon et al., 1999). Dissolution or precipitation of carbonates depends upon rock mineralogy and water chemistry. 

In each case the dissolution and precipitation reactions are a function of thermodynamics and the rates of these 

reactions are controlled by chemical kinetics. 

There have been few studies of CO2 introduced into a potable aquifer setting. Shallow aquifer conditions are unlike 

studies done at depth where (1) rocks have generally been flushed by fresh water, (2) CO2 will be a gas rather than a 

supercritical fluid, and (3) temperature, pressure, and salinity are lower than in deep reservoirs. While potable waters 

that are high in CO2 occur in nature (e.g. the Perrier region of France), these rock-water aquifer systems have had a 

long period in which to react and equilibrate with CO2. Hence, they may be an imperfect analogue for short tem 

reactions that could result from accidental leakage of CO2 into a freshwater aquifer. 
 

3. Laboratory Experiments 

BEG researchers conducted laboratory batch experiments to investigate the extent to which injected CO2 migrating 

upward into a shallow aquifer could mobilize major and minor ions bound to aquifer host rocks. A series of batch 

experiments was designed to react diverse aquifer rocks with CO2 in the medium of water. We selected core samples

from the Core Research Center at the BEG with the goal of representing various aquifers present in Texas and

throughout the Gulf Coast region. For each reactor 95 g of disaggregated, unwashed rock sample was combined

with 500 ml of deionized (DI) water in a wide mouth 500 ml Erlenmeyer flask. Rubber stoppers facilitated airtight

placement of inflow and outflow tubes. To minimize the corrosiveness of DI water, sodium chloride (NaCl) was

added to approximate natural groundwater activity (~40 ppm Cl-

). The experiment was split into two periods where

in the first period argon (Ar) gas was bubbled through the reactors for two weeks. CO2 was bubbled through the 

reactors for a second 2-week period immediately following. When the gas supply was switched from Ar to CO2 at 

Day 14, 70 ml of DI water was added to each reactor to replace the water that was removed during the Ar run 

(dilution factor 1.14). Ten flasks containing samples of aquifer rock and a blank (DI water only) were run 

simultaneously. The outflow manifold system was open to room atmospheric pressure. During Ar injection 2-ml

water samples were taken at 1, 5, 12 hour, 1 day, 2, 4, 7, 10, 12, and 14 day time intervals for ion analysis. Water

was sampled on the same schedule during the CO2 run. After every sampling period, the pH, oxidation-reduction 

potential (ORP), dissolved oxygen (DO), and conductivity were measured using a multiparameter probe (Hanna

Instruments 9828). Cation analysis was done at the University of Texas at Austin Department of Geological

Sciences on an Agilent 7500ce Quadrupole ICP-MS. The cation concentrations measured from the reactors with

rock samples were subtracted by the measurements of the blank reactor to reduce or eliminate procedural 

contamination effects. Sodium and chloride were normalized to the amount of NaCl added at the beginning of the 

experiment and subtracted. 

Results show that cation concentrations were generally elevated in the CO2 experimental run relative to the Ar run. 

Rapid geochemical response occurred within hours to days after introduction of CO2 with significant liberation of 

the cations: Ca, Mg, K, Si, Sr, Mn, Ba, B, Fe, and Al. Concentrations of some cations (e.g. Ca, Mg, Mn, Fe, Sr, Ba)

increased over an order of magnitude. Different aquifer rock reactors displayed different magnitudes of increase in

cation concentrations. Results of the reactor containing Dockum aquifer rock from Randall County, Texas, U.S.A. 

are included as an example (Figure 1). Figure 1 shows rapid elevation in concentrations of many of the cations after 

CO2 was introduced on day 14. Release rate of all cations decreased towards the end of experiment, where their

concentrations increased slowly or remained at a constant level. Good correlation between the concentrations of Ca

and Mg suggest dolomite as their source mineral. K and Si may be released from K-feldspar. Two types of cation

concentration profiles were recognized after introduction of CO2 to reactor vessels (1) Type I – concentrations 

increased rapidly then increased slowly or remained at constant concentrations and (2) Type II – concentrations

increased rapidly followed by a gradual decrease. Type I cations include B, Ba, Ca, Co, K, Mg, Mn, Sr and Zn. Type 

II cations include Al, As, Cs, Cu, Fe, Mo, Ni, Rb, U, and V. 

 Figure 1. Cation concentrations through the process of 

experiment. CO2 was introduced into the system at

Day 14. 

Figure 2. pH through the experiment for all the reactors. 

CO2 was introduced into the system at Day 14. 
Drop in concentration of Type II cations (e.g. Fe and Al) was unexpected and suggests that cation mobilization 

reached a maximum concentration followed by resorbption and/or reprecipitation. The decline in cation 

concentrations is tentatively interpreted as a result of reprecipitation or sorption on reactive grain coatings. In the 

case of stagnant water, resorption suggests that some cation mobilization could be self-mediated by the system. This 

transience was also detected at the Frio, TX site. The elevation of concentrations of Type II cations, such as, Fe, Al, 

Mo, U, Cs, Cu, may be a short-term perturbation and therefore a limited risk to water quality. As expected, pH 

dropped at the start of CO2 flux for most of the reactors (Figure 2). In most cases, pH rebounded after abrupt 

decrease at the beginning of CO2 run, then stayed relatively constant. In general, CO2 reduced pH values up to 3 

units relative to Ar gas. In Reactor 1, for example, pH dropped from over 7.9 to 4.8 within hours after introduction 

of CO2, then rebounded and remained at ~5.4. The pH rebound is probably due to mineral buffering, in this case, 

dissolution of dolomite and, to a lesser extent, potassium feldspar. The experimental results provide initial data for 

the degree and rate at which cations would be mobilized from aquifer host rocks if they are affected by CO2 leakage. 

These data can be used for sensitivity analysis in design of field testing experiments to determine if any of the 

constituents elevated in the laboratory tests are detectable in groundwater that has or might have come in contact 

with injectate CO2. However, significance of elevated minor cations from samples in solution with minimally 

reactive gas (Ar) shows that the concentrations measured cannot be transferred directly to aquifer conditions. Three 

hypothesis are proposed to explain overall high cation concentrations (1) DI water with small amount of NaCl added 

(Cl ~40 ppm) was used in the experiment instead of aquifer water for each sediment, so some dissolution of reactive 

minerals occurred to reach rock-water equilibrium, (2) disagregation of the rocks exposed more reactive surfaces 

than would be exposed in the aquifer setting, and (3) some contamination from the experimental design was noted 

and factored out, however contamination from sample handling (for example drilling mud introduced during coring 

or oxidation of core during storage) cannot be removed. If a geometry was created where the same volume of water 

was charged with excess gas and migrated though many rock volumes, cation concentrations might become quite 

high. Cation concentrations could also decrease as the reacted groundwater moved away from the CO2 source and 

pH was buffered. 

4. Field Studies 

BEG researchers are currently involved in two field studies in which groundwater monitoring is designed to improve 

understanding of risk to fresh water from CO2 injection operations. These studies are located at (1) the SACROC 

oilfield in Scurry County, Texas, U.S.A. where CO2 has been injected for EOR since 1972 and (2) the Cranfield unit 

in Adams County, Mississippi, U.S.A. where CO2 EOR is currently underway. SACROC offers a great opportunity 

to study potential impacts to fresh water resources because of the long time span over which to observe effects of 

engineered CO2 injection. Since CO2 EOR began at SACROC, approximately 50% of the 150 million metric tons 

(MMt) of injected CO2 has been recovered. The majority of remaining CO2 is likely trapped in the deep subsurface, 

but studies to demonstrate CO2 has been sequestered at SACROC are still in progress. The SACROC oilfield covers 

a ~90 mi2

 area in central Scurry County, TX (Figure 3). Geologic units present at the surface range from Permian to 

Quaternary in age. Two significant water-bearing units crop out at the surface within the study area. The Triassicage Dockum Fm. (TrD in Figure 3) hosts the Dockum aquifer, which is designated a minor aquifer by the Texas 

Water Development Board (TWDB). The second significant water-bearing unit is the Ogallala Fm. (P-EOg in 

Figure 3). This erosional outlier of the Ogallala Fm. is isolated from the Ogallala aquifer of the Texas High Plains, 

but provides significant fresh water resources in Scurry and surrounding counties. Smaller quantities of fresh 

groundwater are produced from Permian-age units in eastern portions of the study area. 

We have sampled freshwater from wells constructed in Ogallala Fm., Dockum Fm., Permian-age units, and 

combinations of these geologic units within an ~1,800 mi2

 area. Depth of wells sampled by BEG and TWDB ranges 

from 30 to 700 ft. Sampled wells are located over such a large region for several reasons. Limited data on 

groundwater quality prior to development of oil and gas fields, do not provide adequate background (i.e. prior to 

CO2 injection) data against which to compare post-CO2-injection groundwater quality data. Water wells in the 

region are completed in numerous different and sometimes multiple geologic units; hence groundwater chemistry is 

highly variable. In order to determine if freshwater resources over the SACROC oilfield have been impacted by over 

35 years of CO2 injection, we must first define the regional variability in Dockum aquifer groundwater chemistry. In 

lieu of sampling before and after CO2 injection, we have sampled inside and outside of SACROC. 
 

Figure 3. Surface geologic units and water wells in vicinity of the SACROC oilfield. 

During the SWP SACROC groundwater study BEG researchers have (1) compiled historical groundwater chemistry 

data from the TWDB online database (196 freshwater wells) and (2) collected multiple samples from 60 freshwater 

wells, one freshwater spring, and eight production-zone-brine wells. We completed five sampling events between

June 2006 and July 2008 within a 1,275 mi

2 area (Figure 3). Water well sampling methodology included continuous 

measurement of field chemical parameters (temperature, pH, specific conductivity, and dissolved oxygen) in a flow

cell and monitoring of discharge rate. We did not collect groundwater samples until after field chemical parameters

stabilized to ensure that samples were from the formation and not stagnant casing-volume-water. Our sampling 

protocol included field alkalinity titrations in November 2007, March 2008, and July 2008. Laboratory analytes 

measured in BEG groundwater samples by Los Alamos National Laboratory (LANL) are: Al, Ag, As, B, Ba, Be, Br, 

Ca, Cd, Cl, CO3, Co, Cr, Cs, Cu, d13C, dD, d18O, F, Fe, HCO3, Hg, K, Li, Mg, Mn, Mo, Na, Ni, NO3, Pb, PO4, Rb, 

Sb, Se, Si, Sn, SO4, Sr, Th, Ti, Tl, U, V, and Zn. Laboratory analytes measured in The University of Texas at Austin

Department of Geological Sciences (UT DGS) are dissolved inorganic carbon (DIC), dissolved organic carbon

(DOC), methane (CH4) and CO2 from headspace gas in selected samples. The chemistry of Dockum groundwater is 

highly variable. Figure 4 is a Piper plot of BEG Dockum aquifer freshwater samples collected inside and outside of 

SACROC combined with data from wells completed in underlying zones. Permian well data are from both deeper

wells near SACROC and wells located east of SACROC where Permian units crop out at the surface (Figure 4). 

Samples of produced water (brines) are from SACROC oilfield wells completed at depths between 6,000 and 7,000

ft. There is no distinct grouping of BEG well samples inside versus outside of SACROC (Figure 4). Production zone

samples are clearly shown to be sodium-chloride-type waters distinct from most of the BEG samples in all portions

of Figure 4. 

Figure 4. Piper plot of all BEG freshwater samples, BEG and Kinder Morgan produced water.
Trends of major element concentrations suggest mixing of Dockum aquifer groundwater and water with Permian

and production zone geochemical signatures. Mixing models from Dr. Changbing Yang (2008, personal 

communication) at BEG predict that <1 % produced oilfield brine or 12 % Permian water could mix with the lowest

TDS BEG Dockum freshwater sample to produce the highest TDS Dockum sample. Several mechanisms can be

used to explain such mixing, especially in an oil field that has been operating since the early 1950s. 

The main question remains: Has Dockum aquifer water been impacted by the long history of CO2 injection at

SACROC? If conduit flow along leaking well bores is responsible for increased TDS in Dockum aquifer water 

overlying SACROC, we would also expect to see impacts to Dockum water from injectate CO2. Laboratory

experiments and field observations show that pH will decrease and cation concentrations will increase in fluid

reservoirs exposed to injected CO2. Methods for interpreting Dockum groundwater chemistry include spatial 

plotting of concentration contours. For analytes such as pH, we have valid data spanning pre- and post-injection 

periods. Pre-1980 pH-data from the TWDB database are shown in Figure 5. Dockum aquifer water pH ranged from

~6.5 to 9.0 in samples collected between 1936 and 1978. 

(a). (b). 

Figure 5. (a) pH values measured in freshwater well samples before 1980 (TWDB). Data points denoted by green triangles. 

(b) pH values measured in freshwater wells between 1995 (TWDB) and 2008 (BEG&TWDB). 

Dockum aquifer pH measured in samples collected from 1995 to 2008, after CO2 injection had been ongoing for

over 20 years, is shown in Figure 5. Careful comparison with pre-1980 contours reveals either no change or a slight

increase in pH near SACROC between the two time periods (Figure 5). We would expect to see pH fall if injectate 

CO2 had leaked into Dockum freshwater zones or if reservoir brine with lowered pH and increased cation

concentrations (as documented at SACROC by Han, 2008) had been displaced upward into Dockum freshwater. 

If pH change has been buffered by dissolution of silicate minerals in the Dockum aquifer, cation concentrations

would be higher over SACROC. We do not see systematic increases in cation concentrations measured in Dockum

aquifer samples inside versus outside of SACROC (figures 5 and 6). However, we are still evaluating the data from

the perspective of regional flow paths and reactive transport modeling. Another way to evaluate data from Dockum

groundwater samples is to assess degradation of water quality by comparing analyte concentrations to EPA drinking 

water standards. Data summarized in Table 1 are from BEG samples that were filtered (0.2 to 0.45 μm) in the field.

Cation samples were preserved with nitric acid to pH 2. No preservative was added to the anion samples. The 

percentage of BEG Dockum aquifer samples with analytes exceeding USEPA primary maximum contaminant levels 

(MCLs) and secondary drinking water standards are highlighted in yellow in Table 1. Without exception, the 

percentage of samples with analytes in excess of USEPA standards is higher outside than inside of SACROC (Table 

1). Arsenic (As) and lead (Pb) are listed as contaminants of particular concern in the July 2008 EPA proposed rule

because these constituents might be leached from rocks in GS reservoirs and mobilized to impact USDWs. Of the 

9.8 percent of wells with As levels above MCLs, only 1.6 percent of these are inside SACROC (Table 1). Only ~12

percent of the filtered BEG Dockum samples had Pb levels above a detection limit of 0.002 mg/L. Forty two percent 

of these samples are from wells inside versus 58% outside of SACROC. 
 

Table 1. Comparison of EPA drinking water standards with BEG Dockum aquifer well data. 

BEG researchers are studying stable carbon isotopes of fresh water, produced water, injectate CO2, and plant matter,

which forms the substrate for microbial oxidation of CO2. Solid carbonate phase is also important but analytical

results are not yet available from LANL. Potential contributions to the carbon isotope signature include mixing with

Permian and produced water, microbially-produced CO2, carbonated dissolution, and injectate CO2. A plot of carbon 

isotope ratios versus dissolved inorganic carbon (DIC) shows an increase in light carbon with increasing DIC. This

is consistent with input from microbial CO2 but does not rule out the presence of injectate CO2. Further studies are 

in progress at BEG. 

5. Summary 

Laboratory experiments and field observations show that pH will decrease and cation concentrations will increase in

fluid reservoirs exposed to injected CO2. This has been shown to be true in the 6,000 to 7,000 ft deep

injection/production zones of the SACROC oilfield (Han, 2008). Underground sources of drinking water overlying

SACROC are contained within multiple stratigraphic horizons of the Dockum aquifer. Chemical constituents 

measured in samples of Dockum groundwater suggest minor mixing with more saline (higher TDS) Permian water

or co-produced oilfield brines. However, this does not imply that CO2 injected for EOR at SACROC has mixed with

Dockum groundwater. Analysis of BEG/LANL stable carbon isotopic data to trace various sources of CO2 in the 

subsurface above SACROC is in progress. Dockum aquifer chemical concentrations inside of SACROC fall within 

the range of TWDB groundwater chemical analyses in samples taken from a multi-county region surrounding 

SACROC. We do not see evidence of As or Pb having been mobilized from injection zones at SACROC into

overlying USDWs (Dockum aquifer zones). There are Dockum wells with chemical constituents in excess of EPA 

drinking water standards within our study area. However, a larger percentage of these wells are located outside of

the SACROC oilfield. The main conclusion is that no widespread degradation of water quality exists inside the 

SACROC oilfiled as a result of CO2-injection. Work is in progress to determine if CO2 injection at SACROC is 

changing regional Dockum aquifer groundwater flow patterns. 

6. Acknowledgements 

We gratefully acknowledge support for much of this work from the Department of Energy National Energy

Technology Laboratory and Kinder Morgan CO2-pipeline and production companies. LANL performed most of the 

chemical analyses on groundwater samples collected by BEG as part of the SWP phase 2 project at SACROC. Batch
reactor experiments were funded by the industrial sponsors of the Gulf Coast Carbon Center (www.gulfcoastcarbon.org). 

We thank Bob Reedy for advice in setting up the batch reactor technique and Bridget Scanlon for assistance with ion 

analysis. 

7. References 

Gunter W.D., Perkins E.H. and McCann T.J., 1993. Aquifer disposal of CO2-rich greenhouse gases: reaction design for added capacity. Energy 

Conversion and Management, v. 34 (9-11), p. 941-948. 

Gunter W.D., Wiwchar B., Perkins E.H., 1997. Aquifer disposal of CO2-rich greenhouse gases: extension of the time scale of experiment for 

CO2-sequestering reactions by geochemical modelling. Mineralogy and Petrology, v. 59, p. 121-140. 

Gunter, W.D., Bachu, S. and Benson, S., 2004, The role of hydrogeological and geochemical trapping in sedimentary basins for secure geological 

storage of carbon dioxide, in Baines, S and Worden, R., eds, Geological Society Special Publications No. 233, p. 129-146. 

Han, W.S., 2008, Evaluation of CO2 Trapping Mechanisms at the SACROC Northern Platform: Site of 35 Years of CO2 Injection, Ph.D. 

Dissertation, New Mexico Institute of Mining and Technology, Socorro. 465 pp. 

Hitchon B., Gunter W.D., Gentzis T. and Bailey R.T., 1999. Sedimentary basins and greenhouse gases: a serendipitous association. Energy 

Conversion and Management, v. 40, p. 825 – 843. 

Hovorka et al., 2004, The impact of geological heterogeneity on storage in brine formations: a case study from the Texas Gulf Coast, in Baines, S 

and Worden, R., eds, Geological Society Special Publications No. 233, p.147-164. 

Hovorka S.D., C. Doughty, S.M. Benson, B.M. Freifeld, S. Sakurai, T.M. Daley, Y.K. Kharaka, M.H. Holtz, R.C. Trautz, H.S. Nance, L.R. Myer 

and K.G. Knauss. 2006. “Measuring Permanence of CO2 Storage in Saline Formations: The Frio Experiment.” Environmental Geosciences 

13(2):105-121. 

IEA, 2005, IEA GHG Weyburn CO2 Monitoring and Storage Project. IEA Greenhouse Gas R&D Programme. July 2005. http: 

//www.ieagreen.org.uk/glossies/weyburn.pdf. 

Kharaka, Y.K., Cole, D.R., Hovorka, S.D., Gunter, W.D., Knauss, K.G. and Freifeld, B.M., 2006, Gas-water-rock interactions in Frio Formation 

following CO2 injection: Implications for the storage of greenhouse gases in sedimentary basins, Geology, v. 34 (7), p. 577-580. 

Knauss, K.G., Johnson, J.W. and Kharaka, Y.K., 2005, Preliminary Reactive Transport Modeling and Laboratory Experiments Conducted in 

Support of the Frio Pilot Test, Fourth Annual Conference on Carbon Capture and Sequestration, 

http://www.beg.utexas.edu/mainweb/presentations/2005_presentations/CO2 [Flag: Subscript 2] /preliminary.pdf. 

Rochelle, C. A., Czernichowski-Lauriol, I. and Milodowski, A. E., 2004, The impact of chemical reactions on CO2 storage in geological 

formations: a brief review, in Baines, S and Worden, R., eds, Geological Society Special Publications No. 233, p.87-106. 

United States House of Representatives, 1974, Endangerment of drinking water sources: House Report 93-1185, p. 32. 

Worden et al., 2004, Geological sequestration of CO2 in the subsurface: lessons from CO2 injection enhanced oil recovery projects in oil fields, 

in Baines, S and Worden, R., eds, Geological Society Special Publications No. 233, p. 211-224.