Version 2 2024-01-09, 16:04Version 2 2024-01-09, 16:04
Version 1 2024-01-06, 18:03Version 1 2024-01-06, 18:03
journal contribution
posted on 2024-01-09, 16:04authored byMurilo
T. Suekuni, Mohammadamin Ezazi, Gibum Kwon, Paul R. Craddock, Alan M. Allgeier
Understanding
the wetting properties of shale reservoirs can benefit
their development for energy-related purposes and their potential
for long-term carbon dioxide injection and storage. Given its potential
volumetric abundance and high surface area, the wetting behavior of
kerogen in shale requires assessment. Despite their known limitations,
wettability studies are commonly limited to static contact angle (θ)
measurements. In this Article, the conflicting factors related to
the analysis and interpretation of kerogen wetting via static contact
angle measurements are discussed. Contact angle data for deionized
water, brine (5% NaCl), and n-dodecane are presented
for seven paleomarine type-II kerogens spanning a wide range of thermal
maturities (vitrinite reflectance, Ro:
0.55 to 2.75%) and chemical composition (aromatic carbon content,
H/C ratio, O/C ratio). Droplets of n-dodecane instantaneously
absorbed (θ* ≈ 0°) upon contact with all kerogen
pellet surfaces, showing the oleophilic nature of kerogen for all
maturities tested. Apparent contact angles of water with kerogen surfaces
were positively correlated with H/C ratios and inversely correlated
with aromatic carbon content, while the bulk and surface oxygen concentrations
did not strongly correlate with the measured data. Kerogen exhibited
hydrophobic (θwater > 90°) behavior, except
at the highest thermal maturities. For example, the least thermally
mature and most thermally mature samples studied presented apparent
contact angles for water of 123 ± 15 and 59 ± 10°,
respectively. Profilometry analyses showed roughness average values
ranging from 0.4 ± 0.1 to 3.9 ± 0.7 μm, with the indication
that sample topology can affect measured contact angles, albeit in
second order as compared to sample chemistry in this study. We recommend
caution when associating contact angle data alone with wetting behavior,
as data obtained through sessile droplet analysis are subject to known
but not always considered, caveats.