Ahmed Al-Yaseri

Influence of temperature and pressure on quartz–water–CO2 contact angle and CO2–water interfacial tension

We measured water-CO2 contact angles on a smooth quartz surface (RMS surface roughness ∼40 nm) as a function of pressure and temperature. The advancing water contact angle θ was 0° at 0.1 MPa CO2 pressure and all temperatures tested (296-343 K); θ increased significantly with increasing pressure and temperature (θ=35° at 296 K and θ=56° at 343 K at 20 MPa). A larger θ implies less structural and residual trapping and thus lower CO2 storage capacities at higher pressures and temperatures. Furthermore we did not identify any significant influence of CO2-water equilibration on θ. Moreover, we measured the CO2-water interfacial tension γ and found that γ strongly decreased with increasing pressure up to ∼10 MPa, and then decreased with a smaller slope with further increasing pressure. γ also increased with increasing temperature.

CO2‐wettability of caprocks: Implications for structural storage capacity and containment security

Structural trapping, the most important CO2 geostorage mechanism during the first decades of a sequestration project, hinges on the traditional assumption that the caprock is strongly water wet. However, this assumption has not yet been verified; and it is indeed not generally true as we demonstrate here. Instead, caprock can be weakly water wet or intermediate wet at typical storage conditions; and water wettability decreases with increasing pressure or temperature. Consequently, a lower storage capacity can be inferred for structural trapping in such cases.

Impact of pressure and temperature on CO2-brine-mica contact angles and CO2-brine interfacial tension: Implications for carbon geo-sequestration

Precise characterization of wettability of CO2-brine-rock system and CO2-brine interfacial tension at reservoir conditions is essential as they influence capillary sealing efficiency of caprocks, which in turn, impacts the structural and residual trapping during CO2 geo-sequestration. In this context, we have experimentally measured advancing and receding contact angles for brine-CO2-mica system (surface roughness ∼12nm) at different pressures (0.1MPa, 5MPa, 7MPa, 10MPa, 15MPa, 20MPa), temperatures (308K, 323K, and 343K), and salinities (0wt%, 5wt%, 10wt%, 20wt% and 30wt% NaCl). For the same experimental matrix, CO2-brine interfacial tensions have also been measured using the pendant drop technique. The results indicate that both advancing and receding contact angles increase with pressure and salinity, but decrease with temperature. On the contrary, CO2-brine interfacial tension decrease with pressure and increase with temperature. At 20MPa and 308K, the advancing angle is measured to be ∼110°, indicating CO2-wetting. The results have been compared with various published literature data and probable factors responsible for deviations have been highlighted. Finally we demonstrate the implications of measured data by evaluating CO2 storage heights under various operating conditions. We conclude that for a given storage depth, reservoirs with lower pressures and high temperatures can store larger volumes and thus exhibit better sealing efficiency.

On wettability of shale rocks

The low recovery of hydraulic fracturing fluid in unconventional shale reservoirs has been in the centre of attention from both technical and environmental perspectives in the last decade. One explanation for the loss of hydraulic fracturing fluid is fluid uptake by the shale matrix; where capillarity is the dominant process controlling this uptake. Detailed understanding of the rock wettability is thus an essential step in analysis of loss of the hydraulic fracturing fluid in shale reservoirs, especially at reservoir conditions. We therefore performed a suit of contact angle measurements on a shale sample with oil and aqueous ionic solutions, and tested the influence of different ion types (NaCl, KCl, MgCl2, CaCl2), concentrations (0.1, 0.5 and 1M), pressures (0.1, 10 and 20MPa) and temperatures (35 and 70°C). Furthermore, a physical model was developed based on the diffuse double layer theory to provide a framework for the observed experimental data. Our results show that the water contact angle for bivalent ions is larger than for monovalent ions; and that the contact angle (of both oil and different aqueous ionic solutions) increases with increase in pressure and/or temperature; these increases are more pronounced at higher ionic concentrations. Finally, the developed model correctly predicted the influence of each tested variable on contact angle. Knowing contact angle and therefore wettability, the contribution of the capillary process in terms of water uptake into shale rocks and the possible impairment of hydrocarbon production due to such uptake can be quantified.

Dependence of quartz wettability on fluid density

Wettability is one of the most important parameters in multiphase flow through porous rocks. However, experimental measurements or theoretical predictions are difficult and open to large uncertainty. In this work we demonstrate that gas densities (which are much simpler to determine than wettability and typically well known) correlate remarkably well with wettability. This insight can significantly improve wettability predictions, thus derisking subsurface operations (e.g., CO2 geostorage or hydrocarbon recovery), and significantly enhance fundamental understanding of natural geological processes.

Impact of fines and rock wettability on reservoir formation damage

ABSTRACT Pore throat plugging of porous rock by fine particles causes formation damage, and thus has attracted attention in various areas such as petroleum engineering, hydrology and geothermal energy production. Despite significant efforts, the detailed pore‐scale mechanisms leading to formation damage and the associated permeability reduction are not well understood. We thus investigated plugging mechanisms and characteristics with a combination of ex situ (i.e., coreflooding measurements and scanning electron microscopy imaging) and in situ (i.e., nuclear magnetic resonance and μCT) methods, with a particular focus on the effect of wettability. The corefloods indicated that permeability drops rapidly when fines are injected; mechanistically thin pore throats are plugged first, followed by filling of adjacent pore bodies with the fine material (as evidenced by the nuclear magnetic resonance and μCT experiments, which can measure the pore size distribution evolution with fines injection). Furthermore, it is clear that wettability plays a major role: if fines and rock wettability are identical, plugging is significantly accelerated; wettability also controls the 3D distribution of the fines in the pore space. Furthermore we note that the deposited fines were tightly packed, apparently due to strong adhesion forces.

Microstructural effects on mechanical properties of shaly sandstone

AbstractUnderstanding the mechanical properties of shaly sandstone is of great importance in reservoir geomechanics. Because of the lack of core data, measurements based on acoustic wave velocities...

Carbon dioxide/brine wettability of porous sandstone versus solid quartz: An experimental and theoretical investigation

HYPOTHESIS Wettability plays an important role in underground geological storage of carbon dioxide because the fluid flow and distribution mechanism within porous media is controlled by this phenomenon. CO2 pressure, temperature, brine composition, and mineral type have significant effects on wettability. Despite past research on this subject, the factors that control the wettability variation for CO2/water/minerals, particularly the effects of pores in the porous substrate on the contact angle at different pressures, temperatures, and salinities, as well as the physical processes involved are not fully understood. EXPERIMENTS We measured the contact angle of deionised water and brine/CO2/porous sandstone samples at different pressures, temperatures, and salinities. Then, we compared the results with those of pure quartz. Finally, we developed a physical model to explain the observed phenomena. FINDINGS The measured contact angle of sandstone was systematically greater than that of pure quartz because of the pores present in sandstone. Moreover, the effect of pressure and temperature on the contact angle of sandstone was similar to that of pure quartz. The results showed that the contact angle increases with increase in temperature and pressure and decreases with increase in salinity.