Bashir, HB
2018,
Methane adsorption into sandstones and its role in gas recovery from depleted reservoirs
, PhD thesis, University of Salford.
Abstract
Depleted gas reservoirs represent the most viable option for research and development and are the most preferred method for Enhanced gas recovery and sequestration application. The adsorption process acts as a displacement mechanism in the enhanced gas recovery, therefore investigating this process will lead to a better understanding of methane recovery in the EGR-CO2 process. Despite many pilot studies on EGR-CO2 in depleted reservoirs, no projects have moved to commercial phase, due to both technical and economic issues. This research demonstrated the role of adsorption as a mechanism for gas displacement in the EGR-CO2 process by investigating the interaction of the mineral components of sandstones (i.e. Quartz, Plagioclase, feldspar and clays), with methane (CH4), the effect of pressure and the interaction between water/brine and methane (CH4) gas in a competitive sorption environment for sandstones and their constituents.
The first series of tests were conducted using commercial helium pycnometer to quantify the effect of experimental parameters (pressure, contact time) and water on void volume of sandstone core samples. The average of the measured void volume using helium was 8.017cm3 for Bandera and 4.5171cm3 for the Scioto sandstones with a deviation of less than 0.002 cm3 and 0.001 cm3 indicating little dependence on pressure in void volume measurement. Water content of 5.62 wt. % and 5.48wt. % for both samples respectively can reduce the dry capacity by as much as 12.53% and 11.20%.
Subsequently, a manometric adsorption apparatus was self-fabricated specifically for this research to quantify the methane adsorption capacity of sandstone cores samples. The experiments were conducted using dry sandstone core samples. Methane (CH4) adsorption capacity of sandstones was investigated using dry sandstone samples. The methane (CH4) adsorption capacity varied for the different sandstone types, which for the present studies Bandera and Scioto are considered. The Scioto sandstone has the largest CH4 adsorption capacity of the tested samples with a maximum amount of adsorbed CH4 of 0.110 mmol/g while the Bandera sandstone had significantly less CH4 sorption capacity with a maximum amount of adsorbed CH4 of 0.089 mmol/g. Using X-ray diffraction (XRD) results, the Scioto sample had the highest total amount of clays present (22%) compared to Bandera (14%) and had the highest adsorption capacity. The previous analyses imply that high content of clay minerals in the Scioto sample relative to the Bandera provides extra surface area for adsorption of methane (CH4). As a result, it can be concluded that there exists a correlation between methane (CH4) adsorption capacity and surface area of clay present in the samples.
Finally, the methane (CH4) adsorption capacity of sandstones saturated with water or brine at a particular water/ brine content (33, 65 and 91%) was investigated. The analysis showed that for water saturated core samples the CH4 adsorption capacity decreased by 47.21, 54.47 and 60.89 % for Scioto and 10.26, 24.36, and 38.03% for Bandera relative to dry core samples. The loss of methane adsorption capacity was due to increase in water content (33, 65 and 91%) and was much lower than that of dry samples at the same experimental pressure (0 - 400 psia). The presence of brine in sandstone samples caused an overall decrease in methane adsorption capacity of 30.17,43.57 and 69.83% for Scioto and 28.90, 42.58 and 52.85% for Bandera compared to dry samples. These results indicate that methane adsorption of clay minerals found in a combined state with sandstone rock fabric as the case in real reservoirs will be influenced by its structural, physical, geotechnical, and geological properties.
Experimental data verification were conducted using the repeatability and best fit method. Two replicate runs were conducted to investigate the reproducibility of the isotherm measurements. The average data deviation was 0.33 and 0.42 for dry Scioto and Bandera samples respectively, while the deviations were 3.85 and 3.59 for samples saturated with water and brine respectively between the first and repeat experiments. Excellent repeatability of experimental data for both sandstone samples (Scioto and Bandera) was observed.
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