Field experiment of stress sensitivity effect in the Mabidong CBM block, southern Qinshui Basin, China

Coalbed methane (CBM) has made significant contributions to global energy supply and carbon neutrality. The stress sensitivity effect (SSE) is an important factor that influences CBM production, and it indicates that reservoir properties change with stress. Although there is abundant research on the SSE in CBM, most studies are based on theoretical analyses or laboratory physical simulations. Only few studies focused on the SSE of CBM during field production. Therefore, this study aims to investigate the SSE through a field experiment. To this end, a field well from the Mabidong CBM block in the southern Qinshui Basin is selected. Then, the corresponding experimental installations are set up. A parametric inversion method based on the Newman product method and type curve matching is established to interpret the experimental data. The entire experimental process includes six stages of pressure build tests, lasting for 290 days. The field experiment data are inverted using the parametric inversion method. The SSE in the CBM during production is revealed by analyzing the variations in the formation parameters of each stage. The results indicate that both the permeability and fracture half-length are related to the average pressure. The average pressure declines as the production proceeds, and this leads to an increase in the effective stress and a decrease in the permeability and fracture half-length. Relationships between permeability, fracture half-length, and average pressure are derived, and they can be used to better interpret the dynamic production data of CBM wells in the Mabidong Block. Moreover, these results indicate that decreasing the flow rate can mitigate the SSE, especially when the gas desorbs. Thus, during CBM production, the flow rate needs to be strictly controlled for maintaining a stable pressure drop and reducing reservoir damage caused by the SSE.