Sensitivity of high-rank coal-bed methane reservoir in the Southern Qinshui Basin

In order to achieve a high-efficient exploitation of CBM in the southern Qinshui Basin,the velocity sensitivity,water sensitivity,alkaline sensitivity and stress sensitivity of the main coalbed 3 were investigated and analysed. The results show that:the degree of velocity sensitivity damage at the coalbed 3 varies from medium to weak. In the actual CBM development process,the velocity sensitivity damage is due to the transportation of coal powder produced by the coalbed washout of the fracturing fluid containing sand. The degree of water sensitivity damage at the coalbed 3 varies from medium to weak. Adding a small amount of KCl to the working fluid can reduce the water sensitivity effect. The coalbed 3 is a weak alkaline sensitive reservoir,however,the high pH fluids will dissolve quartz sand and reduce the support effect. The coalbed 3 is a strong stress sensitivity reservoir. According to the comparison of permeability change in the step-up and step-down phases,the irreversible damage rate is 55. 88%. In the coalbed methane development process,in theory,strengthening reservoir protection can increase the coalbed methane production.