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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]

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]