Experimental Study of CO2-Water-Mineral Interactions and Their Influence on the Permeability of Coking Coal and Implications for CO2-ECBM

Abstract

Abstract:Coal permeability is one of the most critical parameters affecting gas flow behavior during coalbed methane (CBM) production. However, little research has been conducted on how permeability evolves after CO 2 injection in coking coal. Hence, examining possible chemical interactions between coal minerals, water, and injected CO 2 can be very helpful to better characterize coking coal. In this study, coking coal specimens obtained from the Malan and Tunlan mines located in the Gujiao block of the Qinshui basin were treated with water and CO 2 to achieve a better understanding of their dissolution kinetics, pore structure, and permeability. It was found that the relative carbonate mineral content decreases with time, while the relative clay mineral content increases after the reaction with CO 2 and water. Scanning electron microscopy (SEM) confirmed these mineral alteration phenomena. Carbonate minerals (calcite, dolomite) dissolve faster than clay minerals (montmorillonite, illite and kaolinite). In particular, the dissolution rates of Ca 2+ in carbonate minerals increases with decreasing temperature (25-45 • C) and pH (4.3-6.3), and the dissolution rate of Ca 2+ ions in the calcite reaction solution is higher than that in the dolomite solution. In addition, the results of low-pressure nitrogen adsorption analysis showed that CO 2 injection can enlarge smaller size pores into larger size pores and change the overall pore size distribution. Therefore, CO 2 injection can increase the porosity of coal beds and ultimately their permeability, which in turn facilitates CBM production.

Gas Migration Patterns with Different Borehole Sizes in Underground Coal Seams: Numerical Simulations and Field Observations

“…In future studies, for the CO 2 injection times and CO 2 injection well design, this study can be referred to. Meanwhile, attention should be paid to the permeability reduction effects [44,45]. The adsorption capacity of coal to CO 2 is 2-5 times higher than that of coal to methane [46,47].…”

Influences of supercritical carbon dioxide fluid on pore morphology of various rank coals: A review

“…Therefore, the change in the pore morphology of coals, due to ScCO 2 exposure, during longer time scale has gained interest in recent years. Guo et al (2018) examined the interaction between ScCO 2 , H 2 O and coals for 5-6 months and found that the average pore diameter, porosity and microfracture of coals increased due to dissolution of calcite and dolomite. Particularly, S meso/mac and V meso/mac of all the coal samples were observed to increase by approximately 30-73% and 40-54%, respectively.…”

“…Thus, the pore structure of coals has been considered to get further enhanced (Li, 2018;Liu et al, 2018). Therefore, injecting CO 2 , H 2 S Source: reproduced with permission from Guo et al, 2018. and SO 2 fluid is considered to enhance the intensity of dissolution effect, thereby increasing the pore volume of coals and to mitigate the hazardous gaseous pollutants emitted into the atmosphere. With respect to secondary minerals, they are not considered to be precipitated, when the saturation index (SI), is less than zero.…”

Influence of H2O on Adsorbed CH4 on Coal Displaced by CO2 Injection: Implication for CO2 Sequestration in Coal Seam with Enhanced CH4 Recovery (CO2-ECBM)

“…Furthermore, the H 2 O-induced swelling effect and blocking effect also have a profound impact on fluid migration. , Due to the unstable organic macromolecule structure of the coal matrix, H 2 O adsorbed on coal is able to trigger its volume expansion . Accordingly, the induced coal matrix swelling further compresses cleat space of the coal reservoir, resulting in decreasing porosity and permeability and further impeding adsorption, desorption, diffusion, and flow of CO 2 and CH 4 in the coal reservoir. , With regard to the latter effect, H 2 O retention in pores may block channels for CH 4 desorption from coal. , Particularly, H 2 O is capable of producing capillary force directed toward the fluid with the coal matrix via surface tension. Providing this pressure differential between inside and outside of the pore cannot overcome capillary force, and the permeability of the coal reservoir will decrease, thus making CH 4 desorption more difficult …”