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CO2 flooding is a proven enhanced oil recovery (EOR) technique and is also considered as a potential method for CO2 sequestration. Despite having successful field trials on CO2 EOR, the effects of reservoir wettability and permeability heterogeneity on the efficiency of miscible CO2 flooding are not well understood. In this work, laboratory investigations have been carried out to evaluate the influence of these properties on the miscible CO2 EOR performance. The wettability of hydrophilic Berea core samples was altered to be oil-wet by vacuum saturation of the clean and dry core samples with n-hexadecane. The permeability heterogeneity was obtained by combining two half pieces of axially split water-wet core samples of different permeabilities. Core flooding experiments were conducted for n-hexadecane - synthetic brine - CO2 systems at 1400 psig backpressure to achieve minimum miscibility pressure (MMP) of CO2 in n-hexadecane at the test temperature (24 ± 1 °C). It was found that wettability strongly influences CO2 EOR. For the alternate cases of previously brine flooded (to remaining oil saturation) oil-wet and water-wet core samples, five pore volumes (PVs) of CO2 recovered 100% and only 43% of remaining oil in place (ROIP) respectively. Three PVs of CO2 could recover only about 0-5% ROIP from the split core samples. The mechanisms underlying these results are discussed. This study sheds light on the significant influence of reservoir wettability and permeability heterogeneity on the performance of miscible CO2 EOR.

The storage potential of hydrocarbon reservoirs in the central Gulf of Mexico (GOM) makes future development of CO2 storage projects in those areas promising for secure, large-scale, and long-term storage purposes. Focusing on the producing and depleted hydrocarbon fields in the continental slope of the central GOM, this paper analyzed, assessed, and screened the producing sands and evaluated their CO2 storage potential. A live interactive CO2 storage site screening system was built in the SAS® Viya system with a broad range of screening criteria combined from published studies. This offers the users a real-time assessment of the storage sites and enables them to adjust the filters and visualize the results to determine the most suitable filter range. The CO2 storage resources of the sands were estimated using a volumetric equation and the correlation developed by the National Energy Technology Laboratory (NETL). The results of this study indicate that 1.05 gigatons of CO2 storage resources are available in the developed reservoirs at the upper slope area of the central GOM. The Mississippi Canyon and Green Canyon protraction areas contain the fields with the largest storage resources. [ABSTRACT FROM AUTHOR]

Nucleation is the formation of a new phase that has the ability to irreversibly and spontaneously grow into a large-sized nucleus within the body of a metastable parent phase. In this experimental work, the effect of wettability on the incipiation of vacuum-driven bubble nucleation, boiling, and the consequent rate of evaporative cooling are studied. One hydrophilic (untreated), and three hydrophobic (chlorinated polydimethylsiloxane, chlorinated fluoroalkylmethylsiloxane and (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane) glass vials of different wettabilities were filled with degassed deionized water and exposed to a controlled vacuum inside a transparent desiccator. The vacuum was increased by 34 mbar abs. (1 inHg rel.) steps with 15-min waiting period to observe bubble nucleation. The average onset pressures for gas/vapor bubble nucleation in CM, CF, and HT vials were 911 ± 30, 911 ± 34, and 925 ± 17 mbar abs., respectively. Bubble nucleation was not observed in hydrophilic vial even at 65 mbar abs. pressure. During the vacuum boiling at 65 mbar abs., the average temperatures of water in hydrophilic, CM, CF, and HT vials reduced from room temperature (~22.5 °C) to 15.2 ± 0.9, 13.1 ± 0.9, 12.9 ± 0.5, and 11.2 ± 0.3 °C, respectively. The results of this study show that the wettability of the container surface has a strong influence on the onset vacuum for vapor/gas bubble nucleation, rate of vacuum boiling, and evaporative cooling. These findings are expected to be useful to develop wettability-based vacuum boiling technologies. [ABSTRACT FROM AUTHOR]

When the concentration of a gas exceeds the equilibrium concentration in a liquid, the gas–liquid system is referred as a supersaturated system. The supersaturation can be achieved by either changing the pressure and/or temperature of the system. The gas from a supersaturated liquid escapes either through bubble nucleation that usually occurs on solid surface and/or gas diffusion through the gas–liquid interface. The bubble nucleation requires a minimum threshold supersaturation. A waiting time is required to observe whether the applied supersaturation is sufficient to initiate bubble nucleation. When the supersaturation is not sufficient to cause bubble nucleation, some or all of the supersaturated gas may diffuse out from the liquid through the gas–liquid interface before further reducing the pressure in order to increase the supersaturation. In this article, using Fick's second law of diffusion and Henry's law, an analytical method is proposed to estimate the level of supersaturations generated in three gas–liquid systems at different step-down pressures. Characteristic times of the gas–liquid systems were estimated to validate whether the waiting times used in this study are in accordance with the semi-infinite diffusion model used to estimate the supersaturations generated. [ABSTRACT FROM AUTHOR]

Abstract: This work presents contact angle measurements for CO2–water–quartz/calcite systems at general sequestration pressure and temperature conditions (200–3000psig and 77–122°F). The effect of drop volume, repeated exposure of the substrates to dense water saturated CO2, pressure and temperature on the contact angles is examined. In the 1st measurement cycle, the contact angles for the quartz substrate varied from 46 to 48° and 47 to 46° for gaseous (water saturated) CO2 and liquid (water saturated) CO2 respectively, at 77°F. For calcite substrate, these values varied from 45 to 48° and 42 to 40°, respectively. Remarkably, this work highlights a characteristic permanent shift in the contact angle data with repeated exposure to dense, water saturated, CO2. The contact angle data trends after repeated exposure to the dense, water saturated CO2 varied from 89 to 91° and 85 to 80° for the quartz substrate for gaseous (water saturated) CO2 and liquid (water saturated) CO2 respectively, at 77°F. For calcite substrates, these values varied from 60 to 59° and 54 to 48°, respectively. This important observation has serious implications towards the design and safety issues, as a permanent positive contact angle shift indicates lower CO2 retention capabilities of sequestration sites due to a reduction in the capillary pressure. It is further confirmed that the permanent shift in the contact angle is due to surface phenomena. With an increase in temperature (from 77 to 122°F), the contact angle shift is reduced from about 45° to about 20° for quartz substrates. Other observations in the contact angle data with respect to pressure are in good agreement with the trends reported in the literature. [Copyright &y& Elsevier]

Recently, geomaterial-functionalized microfluidic chips have been receiving increased attention as they facilitate material representation to mimic surface mineralogy in addition to direct visualization and quantification of multiphase flow and transport processes in a porous media. In particular, calcite-coated glass surfaces have been used to mimic the solid-fluid interactions involved in carbonate reservoirs. The coating procedure usually involves the deposition of calcium carbonate layers on a functionalized glass surface. Depending upon experimental conditions, the deposited calcium carbonate could be one or more of the three polymorphs: calcite, vaterite, and aragonite. Hence, it is essential to analyze and control the formation of the desired calcium carbonate polymorph. In this study, we transformed glass surfaces into carbonate surfaces by growing calcium carbonate particles in-situ using a layer-by-layer deposition procedure. The influences of process parameters involved in the deposition procedure on the formation of calcium carbonate polymorphs were analyzed. The parameters evaluated were: initial glass surface cleaning phase – DI water, plasma, piranha and NaOH as substrate cleaners; surface functionalization phase – DI water and chloroform as silane solvents; and calcite crystals growth phase – effect of number of coating cycles and concentration of CaCl 2 and Na 2 CO 3 solutions on the coating. After CaCO 3 deposition, strategies to transform kinetically favorable vaterite to thermodynamically stable calcite are discussed. Coating uniformity, morphology, elemental atomic percentage of coating, and the CaCO 3 polymorphs were examined by optical microscopy, Scanning Electron Microscopy (SEM), SEM Energy Dispersive X-Ray Spectroscopy (SEM EDS), and Raman spectroscopy, respectively. Image 1 • Influence of initial cleaning, silanization solvents, and supersaturation on CaCO 3 deposition on glass surfaces were studied. • Deposited CaCO 3 polymorphs were aragonite, calcite, and/or vaterite with vaterite being the major component of the coating. • Vaterite was transformed to calcite to create glass surfaces coated with only calcite to better replicate carbonate surfaces. [ABSTRACT FROM AUTHOR]

Microfluidic porous media systems are used for various applications ranging from chemical molecule detection to enhanced oil recovery studies. Absolute permeability data of the microfluidic porous media are important for those applications. However, it is a significant challenge to measure the permeability due to the difficulty in accurately measuring the ultra-low pressure drop across the pore network. This article presents a semi-experimental procedure to estimate the permeability of a microfluidic pore network. The total pressure drop across the porous media chip (ΔP chip ) at a given flow rate of a single-phase liquid was obtained from the difference in the inlet pressures at the microfluidic pump with and without the pore network chip connected. The pressure drops in the inlet (ΔP inlet channel ) and outlet (ΔP outlet channel ) channels of the pore network are estimated using the hydraulic resistance equation for Poiseuille flow in a wide rectangular cross section. Then the pressure drop across the pore network of the chip (ΔP pore network ) is obtained by subtracting (ΔP inlet channel  + ΔP outlet channel ) from ΔP chip . Subsequently the permeability of the pore network is calculated using the Darcy's law. •The proposed method is applicable for both homogenous and heterogeneous pore networks.•This method does not require a differential pressure sensor across the microfluidic chip.•This method eliminates the possibility of gas entrapment that can affect the permeability measurement.