RESUMEN
The biodegradation of guar gum by microorganisms sourced from coalbeds can result in low-temperature gel breaking, thereby reducing reservoir damage. However, limited attention has been given to the influence of salinity on the synergistic biodegradation of coal and guar gum. In this study, biodegradation experiments of guar gum and lignite were conducted under varying salinity conditions. The primary objective was to investigate the controlling effects and mechanisms of salinity on the synergistic biodegradation of lignite and guar gum. The findings revealed that salinity had an inhibitory effect on the biomethane production from the co-degradation of lignite and guar gum. The biomethane production declined with increasing salinity levels, decreasing from 120.9 mL to 47.3 mL. Even under 20 g/L salt stress conditions, bacteria in coalbeds could effectively break the gel and the viscosity decreased to levels below 5 mPa s. As salinity increased, the removal rate of soluble chemical oxygen demand (SCOD) decreased from 55.63% to 31.17%, and volatile fatty acids (VFAs) accumulated in the digestion system. High salt environment reduces the intensity of each fluorescence peak. Alterations in salinity led to changes in microbial community structure and diversity. Under salt stress, there was an increased relative abundance of Proteiniphilum and Methanobacterium, ensuring the continuity of anaerobic digestion. Hydrogentrophic methanogens exhibited higher salt tolerance compared to acetoclastic methanogens. These findings provide experimental evidence supporting the use of guar gum fracturing fluid in coalbeds with varying salinity levels.
RESUMEN
With the increase of the burial depth of the no. 3 coal seam in the Zhengzhuang minefield of Qinshui Basin, the production of surface coal bed methane (CBM) vertical wells was low. By means of theoretical analysis and numerical calculation, the causes of low production of CBM vertical wells were studied from the aspects of reservoir physical properties, development technology, stress conditions, and desorption characteristics. It was found that the high in situ stress conditions and stress state changes were the main controlling factors of the low production in the field. On this basis, the mechanism of increasing production and reservoir stimulation was explored. An L-type horizontal well was constructed alternately among the existing vertical wells on the surface to initiate a method to increase the regional production of fish-bone-shaped well groups. This method has the advantages of a large fracture extension range and a wide pressure relief area. It could also effectively connect the pre-existing fracture extension area of surface vertical wells, realizing the overall stimulation of the low-yield area and increasing the regional production. Through the optimization of the favorable stimulation area in the minefield, 8 L-type horizontal wells that adopted this method were constructed in the area with high gas content (greater than 18 m3/t), a thick coal seam (thicker than 5 m), and relatively rich groundwater in the north of the minefield. The average production of a single L-type horizontal well reached 6000 m3/d, which was about 30 times that of the surrounding vertical wells. The length of the horizontal section and the original gas content of the coal seam had a significant influence on the production of the L-type horizontal wells. This method for increasing the regional production of fish-bone-shaped well groups was an effective and feasible low-yield well stimulation technology, which provided a reference for increasing the production and efficiently developing CBM under the high-stress conditions in mid-deep high-rank coal seams.
RESUMEN
For the problem where numerous coalbed methane (CBM) stripper wells exist in China, this paper analyzes the genesis of the stripper wells from the aspects of geological conditions and development technologies combined with the CBM development of some typical blocks. A series of key secondary stimulation technologies for CBM stripper wells are put forward, including low-damage fracturing fluid for preventing reservoir damages, proppants with multigraded sizes for supporting multilevel fractures, large-scale fracture network stimulation (FNS) for improving reservoir permeability, and coal measure gas development for increasing the exploitable resources within a single well scope, as well as coordinated stimulation of parent-child wells for the overall production improvement of low-yield blocks. Also, it is pointed out that all types of stripper wells could adopt the low-damage fracturing fluid and multigraded proppant and optimize the drainage schedule to inhibit reservoir damage and promote the maintenance of fracture conductivity. For resource-controlled stripper wells, large-scale FNS of coal seams, coal measure gas development, and coordinated stimulation of parent-child wells could be adopted according to the differences in resource abundance and coal seam distribution. For the stripper wells controlled by the coal structure and ground stress, FNS of the surrounding rock could be conducted to construct stable and efficient channels for CBM migration. In addition, by conducting large-scale FNS, the stimulation effect of fracturing-controlled stripper wells improves, while after unblocking and reopening the existing reservoir fractures of the drainage-controlled stripper wells, an optimized drainage schedule could be adopted to prevent reservoir damages and promote the maintenance of fracture conductivity.
