Modeling CO2–H2S–Water–Rock Interactions at Williston Basin Reservoir Conditions
University ofNorth Dakota
Grand Forks
EERCEnergy & Environmental Research Center®
Putting Research into Practice
Rock Unit Selection
To evaluate potential chemical and physical reactions between CO2 and selected Williston Basin rock units, samples representing three different formations were tested in bench-scale laboratory experiments. Numerical modeling of geochemical reactions was performed and verified with laboratory results. The samples were chosen as a part of the Williston Basin characterization effort, based on both availability and on the likelihood of future exposure to injected CO2. In previous work, five different formations were subjected to initial evaluation, and powdered rocks were used in order to obtain initial results. A further, more focused investigation of three different formations was undertaken: Madison Group (limestone- and dolostone- dominated samples), Broom Creek (dolomite and calcite cemented sandstone), and Pennsylvanian–Tyler Formation (sandstone with carbonates and clays). All Williston Basin samples were obtained through the North Dakota Geological Survey’s Core Library, located on the campus of the University of North Dakota.
Experimental Setup and Conditions
On the left: The combined mineralogical analysis of initial (unexposed) sample (blue color), sample exposed to CO2 (dark green), and sample exposed to CO2 and H2S (orange). On the right: The exposed water composition analysis for metals compared to numerical modeling.
The refined QEMSCAN image of the Broom Creek Formation rock, which illustrates the spatial distribution of iron content within the sample. On the left: unreacted sample. On the right: sample after exposure to CO2.
Summary This preliminary geochemical assessment Madison Group, Broom Creek Formations, and Tyler Formations of Williston Basin indicated that there are no immediate operational concerns for both cases of injection scenarios (pure CO2 and sour gas). The analysis of obtained reaction products suggests that 1) there is no strong evidence for higher degradation of samples exposed to a mixture of CO2 and H2S if compared to the pure CO2 stream; however, 2) carbonate rocks seem to be more unstable if exposed to the acid gas if compared to pure CO2 3) if H2S is present in the stream, it seems to be more dominant in the reactions; and 4) reactivity of the sample is strongly driven by its mineralogy.
The mineralogical analysis performed with various analytical tools (x-ray fluoresence, XRD, and QEMSCAN) required verification with numerical modeling tools. Often, the error in instrument tolerance, small-scale sample heterogeneity, or measurement error can be corrected by thermodynamic modeling suggestions.
Authors: Yevhen I. Holubnyak, Steven B. Hawthorne, Blaise A. F. Mibeck, David J. Miller, Jordan M. Bremer, James A. Sorensen, Edward N. Steadman, and John A. Harju
Abstract A series of laboratory experiments, field observations, and numerical modeling of geochemical reactions have been conducted to determine the chemical kinetics of potential mineral dissolution and/or precipitation caused by the injection of carbon dioxide (CO2) and sour gas. Kinetic experiments were conducted using core samples from potential Williston Basin storage formations and pure mineral samples (e.g., calcite, dolomite, siderite, etc.) obtained from vendors. Samples were analyzed using x-ray diffraction (XRD) and QEMSCAN® techniques. Two sample sets consisting of 16 samples each, under the same experimental conditions, were “soaked” for a period of 4 weeks at 2500 psi (172 bar) and 176°F (80°C) in synthetically generated brine. Over that time period, one set was exposed to pure carbon dioxide and the other to a mixture of CO2 (88 mol%) and H2S (12 mol%). The initial XRD mineralogical analysis of selected samples indicates the presence of the following minerals: anhydrite, calcite, dolomite, forsterite, halite, illite, magnetite, and quartz. The main objectives of this work were 1) to determine possible mineral reactions of the Madison Group, Broom Creek Formations, and Tyler Formations of Williston Basin, North Dakota with CO2 and sour gas; 2) to identify potential operational concerns; 3) to compare differences in mineral reactions between pure CO2 and sour gas injection scenarios; and 4) to adjust kinetic reaction rates for geochemical modeling tools with experimental observations. This work was performed by the Energy & Environmental Research Center through the Plains CO2 Reduction Partnership, one of the U.S. Department of Energy National Energy Technology Laboratory’s Regional Carbon Sequestration Partnerships.
CO2 Partial Pressure 2250 psi/155 bar
Temperature 158°F/70°C
Gas Mixture1) CO2 – 100 mol%2) CO2 – 67.3 mol% H2S – 32.7 mol%
Mass of Sample 10–15 g
Type of Sample Core plugs
Saturation Conditions Synthetic brineNaCI, 10% by weight
Time of Exposure 4 weeks
Mississippian Mission Canyon Limestone sample collected from a depth of 8140 ft (2481 m) saturated with brine (NaCl, 10 %) and exposed to pure supercritical CO2 and a mixture of supercritical CO2 (88 mol%) and H2S (12 mol%) under a pressure of 2100 psi (145.4 bar) and temperature of 176°F (80° C). The left side of the figure represents vacuum-dried-after-exposure samples compared with the original specimen; and the right side illustrates samples saturated in fluid after experiment completion.
Results
0
10
20
30
40
50
60
70
Ankerite Quartz Calcite Dolomite Hematite Magnetite
Rela
tive
Wei
ght,
%
Blank CO2 CO2+H S
1
10
100
1000
10000
Al Ca Mg Si
mg/
L
CO2 – Lab CO2 + H2S – Lab
CO2 – Modeling CO2 + H2S – Modeling
BackgroundFe-MineralNon-Fe Mineral
10.0 µr1000.0 µr
White River GrpGolden Valley Fm
Wood Mountain Fm
Ravenscrag Fm
Hell Creek FmFox Hills Fm
Frenchman Fm
Pierre Fm
PierreFm
Judith River Fm
Eagle Fm
Whitemud Fm
Niobrara Fm Niobrara FmCarlile Fm Carlile Fm
Greenhorn FmBelle Fourche Fm
Belle Fourche FmSecond White Specks
Fish Scales FmWestgate FmViking FmJoli Fou Fm
Mowry FmNewcastle FmSkull Creek FmInyan Kara Fm
Col
orad
oG
roup
Swift Fm
Rierdon FmPiper Fm
Spearfish Fm
Mannville GroupSuccess FmMasefield FmRierdon FmUpper Watrous Fm
Oil Fields
Lower Watrous Fm
Minnekahta FmOpeche Fm
Missing
Tyler FmAmsden Fm
Otter FmKibbey Fm Charles
FmMissionCanyon
Fm
Poplar MbrRatcliffe MbrMidale MbrFrobisher MbrAlida MbrTilston MbrSouris Valley
Charles Fm
Mission Canyon
Lodgepole Fm Lodgepole
Bakken Fm Bakken Fm
Mad
ison
Gro
up
Mad
ison
Gro
up
Min
nelu
saG
roupBroom Creek Fm
Fort Union Grp
Pennsylvanian
Mississippian
359
318
299
251200
146
66.5
1.8
Eastend FmBearpaw FmJudith River Fm
Milk River FmFirst White Speckled Shale
Coal Seams
Coal SeamsSaline Formations
Oil FieldsSaline Formations
Oil FieldsSaline Formations
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Age Units YBP(Ma) USA (ND) Canada (SK)
Rock Units (Groups, Formations) Potential Sequestration
Targets
Cen
ozoi
cM
esoz
oic
Pal
eozo
icPha
nero
zoic
Dak
ota
Gro
up
Support Rackwith Samples
Heater
Ther
moc
oupl
e
Thermocouple
A
A
0.125
Support Rack (Cut)2.5”
13”
Original SampleAfter Exposure
to CO2
After Exposureto CO2
After Exposureto CO2 + H2S
After Exposureto CO2 + H2S
WILLISTON BASIN