Influence of dvilling fluid on stress sensitivity of coalbed reservoir

During coal gas reservoir well drilling and completions and stimulations, the contact of different types of working liquid with the reservoir and interaction with each other will impact the stress sensitivity of reservoir. Coal samples tested were cored from moderate coal rank in Ningwu basin, after fracturing, the coal samples were soaked in different working fluids, and then were tested for stress sensitivity by increasing and reducing confining pressure. The results show that stress sensitivity of fractured coal sample is 0.73, the stress sensitivity of core samples with working fluid intrusion is 0.79~0.94, the stress sensitivity of coal is greater than tight sandstone and shale before and after being damaged by working fluid. In combination with rock mechanic test results, the fracture development of coal is favorable to the invasion of the working fluid, after being effected by working liquid coal strength reduces, making crack easier to close and strengthening the stress sensitivity of coal reservoirs. Research results can provide basic parameters for coalbed reservoir protection during coalbed methane well drilling and completion, stimulation and exploitation