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2014-78DETERMINATION OF CO2 AND H2S INFLUENCEON MINERALOGICAL COMPOSITION AND PETROPHYSICAL PARAMETERS OF AQUIFER AND CAP ROCKS
2014-78DETERMINATION OF CO2 AND H2S INFLUENCEON MINERALOGICAL COMPOSITION AND PETROPHYSICAL PARAMETERS OF AQUIFER AND CAP ROCKSKrzysztof Labus1), Renata Cicha-Szot2), Grzegorz Leśniak2)
1) Silesian University of Technology; 2) Oil and Gas Institute-NRI
Krzysztof Labus1), Renata Cicha-Szot2), Grzegorz Leśniak2)
1) Silesian University of Technology; 2) Oil and Gas Institute-NRI
IntroductionAcid gas (mainly CO2 and, H2S) interactions with rocks became of interest during the last decades
due to greenhouse effect abatement (e.g. Holloway, 2005), and in the case of carbon dioxide - enhanced oil and gas recovery and energized fluid fracturing (Sinal, Lancaster, 1987). Although a considerable research and published work on this subject, there are still uncertainties about the behaviour of rocks under the influence of gases, in such artificial geochemical systems. In order to investigate these phenomena in selected aquifers and low permeability rock formations of Central Europe, we designed and performed a comprehensive study, enabling the hydrochemical models, calibrated on the basis of experiments, considering the impact of acid gases: CO2 and H2S.
Materials and methodsCore samples represent Upper Carboniferous sandstones and mudstones of the Upper Silesian Coal Basin, Jurassic marls the Mikulov Formation of the Vienna Basin, gas shales of Lower Paleozoic of the East European Craton.Composition of mineral assemblages determined by means of petrographic and planimetric analysis of thin sections, and XRD analysis Porosimetric properties determined by the Mercury Intrusion Porosimetry.Samples were placed in the autoclave filled with artificial brine (composition equivalent to the formation fluid), and acid gas injected to the desired pressure. The experiment was carried on for 100 days in order to simulate the initial period of storage, and reproduced water-rock-gas interactions at the PVT regime of possible storage site.Scanning electron microscope with EDX analyzer was used in examination of mineral phases in the bare samples before and after autoclave experiments.Modeling of water-rock-gas interactions was performed in two stages. The first one was aimed at simulating the immediate changes in the aquifer and insulating rocks impacted by the beginning of CO2 and/or H2S injection, the second – enabled assessment of long-term effects of sequestration. The reactions quality and progress were monitored and their effects on formation porosity and mineral sequestration capacity were calculated.
The research leading to these results has received funding from the Polish-Norwegian Research Programme, operated by the National Centre for Research and Development
under the Norwegian Financial Mechanism 2009-2014, in the frame of Project Contract No Pol-Nor/196923/49/2013.
Experimental resultsVerified process of skeletalgrains dissolution (the most intense in carbonates).
MICROSCOPY
Short-termGeochemical
Model
Long-termGeochemical
ModelSample Mineralogy
POROSIMETRY
Experiment comparisonNatural Analogue
Model
Water chemistry
SEM, XRD
PETROLOGICAL EVALUATION HYDROGEOCHEMICAL MODELING
Cavities parallel to cleavage planes in microcline, formed due to selective etching of the K-lamellae relative to Na -lamellae
Amongst the secondary minerals also the pyrite wasare found. Pits developed on quartz grains, initiate the crystals destruction
Dawsonite observed only after experiments is formed in the pore space between framework grains and within clay mineral blades.
Pressure of 150 bar, exerted at T 80°C on clay mineral sheets, forced water to be expelled. This, further enabled oxidation of pyrite. Desorbed cations form secondary minerals – e.g. gypsum, celestite
Elemental sulfur, surrounded by FeS2 crystals cover mudstones reacted in brine with H2S-CO2 mixture, no other secondary minerals observed.
0 +10 +20 +30 +40 +50 +60 +70 +80 +90 +100.238.239
.24.241.242.243.244.245
Time (day)
Por
osity
+1 +10 +100 +1000 +1e4.22
.225
.23
.235
.24
.245
Time (yr)
Por
osity
+1 +10 +100 +1000 +1e40
.5
1
1.5
2
2.5
3
3.5
4
Time (yr)
Som
e m
iner
als
(del
ta m
ol)
Dawsonite
Dolomite
Calcite
Siderite
First stage - 100 days injection of CO2, - increases gas fugacity, CO2(aq) concentrations; pH drops at the same time. Porosity increase is controlled by dissolution of carbonates and kaolinite. During 20 000 years of storage the total porosity decreases in sandstones due to precipitation of calcite, dolomite and dawsonite - NaAlCO3(OH)2, in CO2 experiment.Minerals precipitating in CO2
experiment are chalcedony and dawsonite while iron sulfides and elemental sulfur are secondary minerals in H2S-CO2 sequestration experiment.
Modeling acid gas impact on geochemical systems
PT data
Formation PT data
Formation PT data
Geochemical modeling
Geochemical modeling
Primaryformation
water composition
Primaryformation
water composition
Secondary:- minerals- water composition- porosity
Secondary:- minerals- water composition- porosity
Primary:- minerals- porosity
Primary:- minerals- porosity
Sequestration capacity
Sequestration capacity
Fresh coreFresh coreFormation
waterFormation
water
Sequestration capacity assessment
Example 1 Example 2
Caprock Aquifer Caprock Aquifer
B6 B4 B9 B7
np -primary – 0 ka 0.029 0.050 0.029 0,113 Porosity
nf - final - 20 ka 0.025 0.041 0.037 0,116
Dawsonite - 3.133 0.212 0,635
Dolomite 0.064 0.025 - - Precipitating
Minerals mol/UVR*
Siderite 0.127 - - -
Siderite - 1.638 0.004 - Dissolution mol/UVR* Kalcite - - - 0,229
mol/UVR 0.255 1.595 0.208 0,406 CO2 Mineral trapping kg/m3 rock matrix 1.090 6.669 0.889 1,585
as HCO3- g/l 0.2 42.7 31.9 48,6 CO2
Solubility trapping kg CO2/m3 rock matrix 0.004 1.263 0.851 4.067
SUM [kg CO2/m3] 1,094 7.932 1.740 5.562
*)UVR-10dm3 (rock matrix + pore space)
For most of the sandstone aquifers calculated mineral-trapping capacity varies between 1.2 and nearly 1.9 kgCO2/m3, and for cap rocks is between 0.89 and 1.42 kgCO2/m3, which is 2-3 times lower than for instance the Gulf Coast arenaceous sediments considered as perspective CO2 repositories. Solubility trapping capacity is the highest for the aquifers of high final porosities, and reaches over 4.0 kgCO2/m3.