Swelling of clay minerals and its effect on coal permeability and gas production: A case study of southern Qinshui Basin, China

Abstract

The permeability damage of high‐rank coal reservoirs is the main factor affecting the development of coalbed methane (CBM) in the late production stage. Coal core samples from southern Qinshui Basin were saturated with actual formation water, 1/2 salinity formation water, and distilled water to study the swelling of clay minerals. Then, the mechanism of permeability change caused by water sensitivity and its effect on gas production was discussed. The results show that the permeability decrease caused by flow velocity sensitivity did not occur during the water sensitivity experiments. The permeability damage caused by water sensitivity is mainly the static damage from swelling of clay minerals, especially illite/smectite mixed clays and chlorite. During the process of CBM development, the water sensitivity of coal reservoirs will lead to the sharp increase of Na+ concentration and a decrease of Mg2+ concentration in the produced water. Meanwhile, the clay minerals swell due to the adsorption of more Mg2+ and Ca2+, decreasing the reservoir permeability and gas production rate.

Permeability Loss of Bituminous Coal Induced by Water and Salinity Sensitivities: Implications of Minerals’ Occurrence and Pore Structure Complexity

“…Because research on the SS of coal is scarce, further discussions are limited. Zhao, 53 Hu et al, 54 Tao et al, 10 Gong, 52 Zuo et al, 55 Tian and Wu 56 applied anthracite samples to study WS; Wang et al 21 applied lignite samples to study WS; and Gao et al, 57 Geng et al 58 and we applied bituminous coal samples to study WS. Table 5 displays the results of these studies.…”

“…It can be seen that WS permeability damage ratios vary tremendously even for coals with the same ranks. For instance, Tao et al 10 reported WS permeability damage ratios of anthracite, which vary from 5.21 to 52.08%, and all data of anthracite from Zhao, 53 Hu et al, 54 Tao et al, 10 Gong, 52 Zuo et al, 55 and Tian and Wu 56 show that WS permeability damage ratios of anthracite vary from 5.21 to 83.06%, indicating that there is no close relationship between the WS damage degree and coal rank.…”

Characteristics of in situ stress and its influence on coalbed methane development: A case study in the eastern part of the southern Junggar Basin, NW China

“…20,27,[43][44][45][46][47] Among them, the influence of in situ stress regime on K occurs throughout the whole process of CBM exploration and development. 20,27,[43][44][45][46][47] Among them, the influence of in situ stress regime on K occurs throughout the whole process of CBM exploration and development.…”

“…As one of the most important factors in the determination of CBM productivity, K has been influenced by complex geological factors, for example, structural framework, in situ stress regime, burial depth, coal structure, and development of natural fractures. 20,27,[43][44][45][46][47] Among them, the influence of in situ stress regime on K occurs throughout the whole process of CBM exploration and development. In other words, the pore-fracture system varies with the change of in situ stress regime, along with K of coal reservoirs.…”

Soil conditioners effects on hydraulic properties, leaching processes and denitrification on a silty-clay soil

“…On the other hand, Hanson et al (1999) found that fine grained soils may be affected by reduced permeability by sodium (Na + ) induced clay swelling with consequent disruption of soil's aggregates, so attention must be paid to the Comp salinity and Na + content. In fact, clay swelling may cause a reduction of soil permeability, because clay minerals once dispersed from soil's aggregates may fill soil pores and reduce water flow (Tao et al, 2019).…”