• Energy Research

Rock wetting behaviour and CO2/brine interfacial tension (IFT) have significant impacts on enhanced hydrocarbon recovery (EOR) and carbon geo-sequestration (CGS) projects. Influence of nanoparticles/surfactant solutions (NPS) flooding on EOR and CGS in sandstone and carbonate formation have been examined in recent studies. But the impact of NPS on carbon dioxide (CO2) and methane (CH4) wettabilities of organic-rich shale and CO2/brine IFT is presently unclear. Thus, we measured contact angles, [advancing (θa)and receding (θr)] for CO2/brine and CH4/brine on Marcellus shale with high total organic carbon (14.8 wt%), as well as CO2/brine IFT with Krüss drop shape analyzer (DSA 100) through the sessile drop and pendant drop techniques. Prior to IFT and contact angles measurement, the shale samples were aged in NPS solutions to evaluate the impact of NPS treatment on CO2 geo-storage. Low-cost rice husk silica nanoparticles and saponin surfactant were used for the study due to their environmental friendliness and economic attractiveness. At geo-storage conditions (25 MPa and 353 K), the advancing contact angle of untreated shale was measured as θa=116.22° (CO2-wet condition), whereas the receding contact angle was measured as θr=82.88° (near neutral wettability). However, θareduced by 56.34° whereas θrreduced by 56.76° when the shale substrate was treated with 0.1 wt% SiO 2 and 0. 2 wt% saponin solutions. CO2/NPS IFT were lower than CO2/brine IFT and the CH4 wettability of the Marcellus shale was significantly lower than the CO2 wettability at all investigated conditions. Contact angles decreased with temperature and increased with CO2/CH4 pressure, whereas CO2/NPS IFT exhibited an opposite trend. The reduction in contact angles and CO2/brine IFT by NPS have significant impacts on adsorption trapping of CO2in organic-rich shale and hydrocarbon recovery from unconventional shale reservoirs.

Abstract CO2 geo-storage in basaltic formations has recently been demonstrated as a viable solution to rapidly sequester and mineralize CO2. In case CO2 is injected into such basalt reservoirs in supercritical form, a two-phase system (reservoir brine and supercritical CO2) is created, and it is of key importance to specify the associated CO2-basalt wettability so that fluid distributions and CO2 flow through the reservoir can be predicted. However, there is a serious lack of data for basalt CO2-wettability. We therefore measured water contact angles on basalt substrates in CO2 atmosphere. The results indicate that at shallow depth (below 500 m) basalt is strongly water-wet. With increasing depth the basalt becomes less hydrophilic, and turns intermediate-wet at a depth of 900 m. We conclude that basalt is more CO2-wet than chemically clean minerals (quartz, calcite), especially at depths below 900 m. However, the basalt had a CO2-wettability similar to some caprock samples and a gas-reservoir sandstone. The data presented in this paper will thus aid in the prediction and optimization of CO2 geo-storage in basalt formations.

Abstract Rock mechanical properties are of key importance in coal mining exploration, coal bed methane production and CO2 storage in deep unmineable coal seams; accurate data is required so that geohazards (e.g. layer collapse or methane/CO2 leakage) can be avoided. In this context it is well established that coal matrix swelling due to water adsorption significantly changes the coal microstructure. However, how water adsorption and the associated with microstructural changes affect the mechanical properties is only poorly understood, despite the fact that micro-scale mechanical properties determine the overall geo-mechanical response as failure initiates at the weakest point. Thus, we measured nanoscale rock mechanical properties via nanoindentation tests and compared the results with traditional acoustic methods on heterogeneous medium rank coal samples in both dry and brine saturated conditions. The microscale heterogeneity of the rock mechanical properties was mapped and compared with the morphology of the sample (measured by SEM and microCT). While the nanoindentation tests measured decreasing indentation moduli after water adsorption (−60% to −66%), the traditional acoustic tests measured an increase (+17%). We concluded that acoustic tests failed to capture the accurate rock mechanical properties changes for the heterogeneous coal during water adsorption. It is thus necessary to measure the coal rock mechanical properties at the microscale to obtain more accurate data and reduce the risk of geohazards.

Abstract Geomechanical properties are of great importance in coal mining exploration, (enhanced) coal bed methane production and carbon geosequestration in deep unmineable coal seams. However, coal highly heterogeneous rocks, and conventional experimental methods (e.g. acoustic, seismic or unconfined compressive strength tests) only measure the cm-m scale bulk properties. Thus, we measured the geomechanical properties at nanoscale of Western Australian Collie coal. We mapped the nanoscale mechanical heterogeneity and correlated it with the sample's morphology (measured by SEM-EDS). It was found that the quartz and siderite in the coal had higher Young's moduli (up to 28.6 GPa), while the organic coal matrix had lower Young's moduli (from 3 GPa to 5 GPa), while the soft material kaolinite had the lowest Young's moduli (

Abstract The affinity of the basalt surfaces towards CO2, quantified as wettability functions, is one of the most important driving factors for CO2 trapping capacity and containment security. SiO2 is a minor constituent, often found in traces in the seawater and formation brine injected or reinjected into the sub-surface formations. This work, thus, evaluates the effect of nano-sized SiO2 (100, 1000, and 2000 mg. L−1) on the wettability of the basalt rock surface in the pressure range of 5-20 MPa. The results from brine/CO2/rock wettability measurements show that SiO2 nanoparticles turn the CO2-wet basalt surface to weakly water-wet upon aging with nanofluids. About 40% reduction in the measured brine contact angle takes place upon treatment of the rock sample with 1000 mg. L−1 nanoparticles. We hypothesize that this change in wettability may facilitate enhanced capillary or residual trapping of CO2 in the basalt formation having adequate porosity and permeability to enhance the basalt CO2 trapping capacity.

Abstract Microstructures and geomechanical properties are of key importance in coal mining, coal bed methane production and CO 2 storage in deep coal seams. Full characterization of the microstructures needs multiscale methods and accurate mechanical data to avoid geohazards (e.g. coal seam layer collapse, fault reactivation or methane leakage). However, standard methods (i.e. acoustic, seismic or USC tests) measure only cm-km bulk properties, while it is clear that the nano-micrometre scale coal heterogeneity plays a vital role. Thus, we used the SEM, microCT, and NMR to characterized the microstructure of a Chinese sub-bituminous coal, and measured nanoscale geomechanical properties via nanoindentation tests and compared the results with the traditional acoustic method. We found that such coal had few cleats, while nanopores constituted the main pores. Furthermore, clear heterogeneity in geo-mechanical properties was observed and mapped, which was not reflected in the bulk acoustic measurements (which provide only averaged data). Such small scale heterogeneity, however, clearly highly correlated with the morphology of the sample, where the mineral phase in the coal had higher indentation moduli (up to 60 GPa for well consolidated), while the coal matrix had lower indentation moduli (lower than 6 GPa). We conclude that such nanoscale rockmechanical property was highly correlated with the morphology of the microstructure; and importantly, it is necessary to measure geomechanical coal properties at small scale to appreciate their large variation and highly heterogeneous character, and to reliably assess and eventually reduce the risk of geohazards.

Wettability is one of the main parameters controlling CO2 injectivity and the movement of CO2 plume during geological CO2 sequestration. Despite significant research efforts, there is still a high uncertainty associated with the wettability of CO2/brine/rock systems and how they evolve with CO2 exposure. This study, therefore, aims to measure the contact angle of sandstone samples with varying clay content before and after laboratory core flooding at different reservoir pressures, of 10 MPa and 15 MPa, and a temperature of 323 K. The samples’ microstructural changes are also assessed to investigate any potential alteration in the samples’ structure due to carbonated water exposure. The results show that the advancing and receding contact angles increased with the increasing pressure for both the Berea and Bandera Gray samples. Moreover, the results indicate that Bandera Gray sandstone has a higher contact angle. The sandstones also turn slightly more hydrophobic after core flooding, indicating that the sandstones become more CO2-wet after CO2 injection. These results suggest that CO2 flooding leads to an increase in the CO2-wettability of sandstone, and thus an increase in vertical CO2 plume migration and solubility trapping, and a reduction in the residual trapping capacity, especially when extrapolated to more prolonged field-scale injection and exposure times.