## 5 Discussion
### Mechanism Analysis of Influence on Gas Production Efficiency  
While workover operations are essential for maintaining the normal function of CBM wells, improper conduct can significantly reduce their service life and gas production capacity (Figure 10 and Table 3). Post-workover, the ionic environment rapidly reverted to its pre-workover state, indicating a minimal impact on the reservoir. The degree of influence from workover operations on the reservoir was characterized by the mean square error (MSE) of ion concentrations over a period following the workover. A higher MSE indicates less ionic contamination and a reduced chemical impact on the reservoir. Thus, does the MSE affect gas and water production? The answer is affirmative. Analyzing the MSE data for ions from 15 to 105 days post-workover across three wells (Table 3), the variance in TDS, Na\({}^{+}\), and Cl\({}^{-}\) levels indicated the extent of reservoir contamination. In particular, GC-10 displayed the largest changes in TDS, Na\({}^{+}\), and Cl\({}^{-}\) among the three wells, suggesting minimal chemical pollution. Moreover, the ratios of daily gas and water production 105 days post-workover to those 105 days pre-workover demonstrate that GC-10 achieved the best recovery rates in both categories among the studied wells. Figures 4-9 illustrate that the composition of the produced fluids from CBM wells altered significantly before and after the workover operation. This suggests that frequent flushing and switching of wells during these operations prompted changes in the internal structure of the coal reservoir. Coal, comprising both organic macromolecules and inorganic minerals, is susceptible to depressurization damage [10; 28; 45], making the deep coal seam prone to compound damage. This damage increases interactions between solid-phase particles and the coal and rock, thereby reducing the effective permeability of the coal seam [28; 37]. The sand-washing operation generated a considerable impact force, causing the coal body to break and produce fine particles or pulverized coal. Additionally, the existing pulverized coal migrated within the fissure channels of the coal reservoir, potentially blocking these channels and further reducing permeability [23; 37; 45]. The introduction of new liquid components, due to the differing compositions of the workover fluid and the native liquids in the coal reservoir, inevitably leads to reactions between minerals like clay and water. If clay migration and expansion occur within the reservoir channels, they can cause blockage and consequent reservoir damage. Furthermore, frequent workover operations induce significant pressure differences, with the resulting shock waves agitating pulverized coal within the seam, leading to pressure-sensitive and velocity-sensitive effects. Such events can cause irreversible damage to the permeability of the coal reservoir [20; 23; 43]. Moreover, secondary migration of previously stable pulverized coal towards the wellbore [28], if not adequately discharged, can block channels and further decrease permeability. The reactions from migrated pulverized coal and pressure sensitivity also result in rougher coal cleavage surfaces, impairing fluid transport efficiency. Post-workover, equipment such as rod tube pumps influence the flow direction of the formation and wellbore liquids, with reverse fluid flow exacerbating damage to the coal reservoir [10; 46]. This study observed changes in the material composition phases of the produced liquid from CBM wells pre- and post-workover, revealing transformations in the microstructure  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Well ID**} & \multirow{2}{*}{**Ions and Time**} & \multirow{2}{*}{ \begin{tabular}{c} **Mean Square Error of** \\ **Each Ion from 15 to** \\ **105 Days after Workover** **before Workover (\%)** \\ \end{tabular}  } & \multicolumn{2}{c}{\