Article Cite This: Energy Fuels XXXX, XXX, XXX−XXX
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Carbon Dioxide/Brine, Nitrogen/Brine, and Oil/Brine Wettability of Montmorillonite, Illite, and Kaolinite at Elevated Pressure and Temperature Cut A. Fauziah,† Ahmed Z. Al-Yaseri,*,† R. Beloborodov,‡,§ Mohammed A. Q. Siddiqui,∥ M. Lebedev,§ D. Parsons,⊥ H. Roshan,∥ A. Barifcani,† and S. Iglauer†,# †
Western Australia School of Mines: Minerals, Energy and Chemical Engineering, School Discipline of Petroleum Engineering, and Western Australia School of Mines: Minerals, Energy and Chemical Engineering, School Discipline of Exploration Geophysics, Curtin University, 26 Dick Perry Avenue, 6151 Kensington, Western Australia, Australia ‡ Deep Earth Imaging Future Science Platform, CSIRO, 26 Dick Perry Avenue, 6151 Kensington, Western Australia, Australia ∥ School of Petroleum Engineering, University of New South Wales, 2052 Kensington, Sydney, Australia ⊥ School of Engineering & IT, Murdoch University, 6150 Murdoch, Western Australia, Australia # School of Engineering, Edith Cowan University, 6027 Joondalup, Western Australia, Australia
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ABSTRACT: Wettability of CO2/brine/clay is one of the most important parameters in assessing CO2 storage capacities and containment security. Despite its importance, the literature data in this context are very limited. We thus systematically measured montmorillonite, illite, and kaolinite wettability for CO2/brine, nitrogen/brine, and nitrogen/oil systems at various pressures (5, 10, 15, and 20 MPa) and temperatures (305 and 333 K). The zeta potential of each clay mineral was also measured to investigate its link to the macroscopic contact angle. The results show that both advancing and receding water contact angles for CO2/brine, nitrogen/brine, and nitrogen/oil systems increase with an increase in pressure. However, they are only slightly reduced by increasing temperature. It was also shown that montmorillonite has a higher water contact angle in the presence of CO2, followed by illite and kaolinite. The same trend was measured for nitrogen/brine and brine/oil systems. Consequently, montmorillonite is strongly oil-wet; kaolinite and illite, however, are strongly water-wet at typical storage conditions (high pressure and elevated temperature). This has important implications for CO2 geostorage in determining the flow of CO2 and its entrapment, fluid spreading, and dynamics in the reservoir.
1. INTRODUCTION CO2 capture and storage (CCS) is a promising technology to decrease atmospheric CO2 emissions and enhance production from unconventional resources.1 However, one of the essential concerns of CCS is to ensure that the buoyant CO2 remains trapped underground in the geological formation.2 Commonly, there are four CO2 trapping mechanisms:2 structural,3,4 residual,5,6 dissolution,7,8 and mineral trapping.9 Adsorption trapping in coal and organic-rich shale also has been proposed.10,11 Thus, to optimize storage efficiency and to ensure minimum CO2 leakage, specific reservoirs have to be selected.12 One of the crucial aspects, which strongly affect storage capacities and containment security, is wettability.13,14 Thus, wettability needs to be understood in detail. In this context, several studies have measured the wettability of clay minerals by contact angle measurements, especially for CO2/brine/muscovite (mica) systems.12,15−19 These studies examined the contact angle of CO2/brine on muscovite (mica) substrates at elevated pressures and temperatures. Their results show that the water contact angle increases with pressure and salinity, and decreases with an increase in temperature. Other researchers have investigated the wetting of CO2 on organic shales (Barnett Shale), which consisted mainly of clay. Conversely, they report that an increase in pressure did not show an increase in the contact angle, and an increase in temperature increased the contact angle.20 Contact angles © XXXX American Chemical Society
measured on caprock samples (siltstone, argillaceous siltstone, calcareous sandstones, and calcareous siltstone), taken from a CO2 storage site in New South Wales, again increased significantly with pressure and temperature.4 These studies suggest that there is a significant discrepancy in the reported results. This discrepancy could be attributed to different factors including chemical heterogeneity of the substrate, surface roughness, and contamination.14,21,22 To more deeply understand the underlying causes, we thus systematically measured the wettability of various clay minerals: montmorillonite, illite, and kaolinite through advancing and receding contact angle measurements. The three clay minerals were chosen for the analysis because they are essential constituents of many rock-forming minerals present in reservoir and caprocks,14,23 which are critical in CO2 sequestration. The measurements were performed for CO2/brine, nitrogen/brine, and nitrogen/oil (n-decane) fluid systems at various pressures (5, 10, 15, and 20 MPa) and temperatures (305 and 333 K). The experimental setups are relevant for geosequestration conditions.16,24,25 The characterization for nitrogen/brine and nitrogen/oil (n-decane) contact Received: August 16, 2018 Revised: November 23, 2018 Published: December 1, 2018 A
DOI: 10.1021/acs.energyfuels.8b02845 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels
applied stress). Subsamples were then oven-dried at 105 °C. Details of the samples are provided in Table 1.
angles was measured to enhance fundamental knowledge which will be applicable to oil production and fundamental understanding of the development of solid earth. Zeta potential was additionally measured to correlate the macroscopic contact angle to surface chemistry and thus wettability.13,26 We then analyzed how pressure and temperature, clay type, pore system, and surface roughness influence the contact angle. Finally, we present and discuss our results with primary reasons for the measured relations and compare them with reliable literature studies.
Table 1. Provenance and Purity of Chemicals Used chemical name montmorillonite illite kaolinite
2. EXPERIMENTAL METHODOLOGY NaCl CaCl2 MgCl2 KCl CO2 N2 n-decane DI water
2.1. Sample Preparation. The clay powder samples were mechanically compacted to create solid montmorillonite, illite, and kaolinite samples. The compaction rig used is illustrated in Figure 1
source of supply Ward’s Natural Science, USA Ward’s Natural Science, USA Ward’s Natural Science, USA Scharlab s.1., Spain Scharlab s.1., Spain Scharlab s.1., Spain Scharlab s.1., Spain BOC, Australia BOC, Australia Sigma-Aldrich David Gray’s deionized water
state
mass fraction purity
powder
≥0.950
powder
≥0.850
powder
≥0.950
powder powder powder powder gas gas liquid liquid
≥0.995 ≥0.995 ≥0.995 ≥0.995 ≥0.999 ≥0.999 ≥0.999 0.02 mS/cma
a
The conductivity of deionized water was measured with a multiparameter (HI 9823) at T = 294 K at atmospheric pressure.
2.2. Contact Angle Measurement. The contact angle measurements were conducted using the tilted plate technique32 and a hightemperature high-pressure goniometer method, as summarized in detail in refs.14,33 The schematic of the experimental setup is illustrated in Figure 2. The surface roughness of three prepared clay
Figure 1. Schematic of the mechanical compaction rig illustrating the key parts (modified from Beloborodov et al.28). and is described in detail in ref 27. The solids were prepared from a brine-based mixture of montmorillonite, illite, and kaolinite. To mimic the brine solution in the reservoir formation, we mixed 4 wt % NaCl, 4 wt % CaCl2, 1 wt % MgCl2, and 1 wt % KCl in deionized water. The brine mixture was added to each of the above clay powders. The prepared mixtures were then poured into an oedometer cell and enclosed with a semipermeable porous plate (porous alumina, 25% porosity, mean pore size < 2 μm) that retained clay particles but allowed the water to pass through during the compaction process. An automatic hydraulic pump (Isco-Teledyne 260D) was used to create constant axial stress that was applied vertically to the porous plates on either side of the oedometer. The applied stress was increased stepwise until the stabilization criterion (0.01 mm in 16 h for the sample of ∼25 mm in height) was met to prevent creep deformations and to fully consolidate the sample at a given step.28 All samples were compacted to the same porosity level of 15% estimated as a function of cell volume (V0), clay grain density (ρm), and clay mass (m) as follows
ϕ=1−
Figure 2. Schematic of the contact angle measurement apparatus: (a) CO2 cylinder (b) syringe pump-CO2, (c) syringe pump-brine, (d) high-pressure cell with the substrate housed on a tilted plate inside, (e) heating unit, (f) liquid feed/drain system (reactor controller), (g) high resolution video camera, (h) image visualization and interpretation software, and (i) pressure relief valve (adapted from Al-Yaseri et al., 201525 and Arif et al., 201616). samples was measured using atomic force microscopy (AFM; instrument model DSE 95-200). The root-mean-square (rms) surface roughness values were 180, 310, and 740 nm for montmorillonite, kaolinite, and illite, respectively, Figure 3. Subsequently, the three samples were cleaned with air plasma for 5 minutes to eliminate any potential organic surface contamination.34 The cleaning process is an essential step to evade possible biased results.21 The cleaned clay samples were then placed in the pressure chamber at a set temperature (308 or 333 K). Using a high-precision syringe pump (ISCO 500D; pressure accuracy of 0.1% FS), CO2 was injected into the chamber, and the pressure was raised to prescribed values (5, 10, 15, or 20 MPa). After reaching the set pressure, a droplet (average volume of a single drop was ∼6 ± 1 μL) of equilibrated brine (equilibrated with CO2 by using a mixing reactor;35 however, such CO2/brine equilibration did not affect contact angle measurements on quartz36) was dispensed onto the tilted surface (tilting angle of
m/ρm V0
(1)
Note that the particle size of individual clay grains is generally
