Coalbed methane reservoir damage and its control in the drainage stage of a block in southern Junggar Basin

Abstract

Aiming at the reservoir damage of low-yield coalbed methane wells in Junggar Basin block during the drainage stage, in this paper, the drainage situation of typical coalbed methane wells in the block is systematically analyzed and reservoir damage types and prevention and control methods of coalbed methane wells in the drainage stage are discussed. The results show that the main types of reservoir damage at the drainage stage in the study area include stress sensitivity, velocity sensitivity and water lock damage. The low mechanical strength of coal reservoirs, improper fracturing fluid, and high drainage intensity are the important reasons for these damages. During the drainage stage of CBM wells, drainage is carried out according to the “continuous, slow and stable” guidelines, increasing the expansion range of the pressure drop funnel and keeping the fluid flow rate below the particle start flow rate will help prevent the three types of reservoir damage. In addition, the use of low-damage fracturing fluid with low surface tension and strong wettability can promote the rapid sedimentation and aggregation of particles. The pore capillary pressure is significantly reduced in the reservoir in the reconstruction stage, thereby inhibiting reservoir velocity sensitivity and water blocking damage. Meanwhile, the coal reservoir is retrofitted by surrounding rock, which helps to reduce the impact of stress-sensitive damage on the production of coalbed methane.

Keywords

• coalbed methane
• stress sensitive damage
• speed sensitive damage
• water blocking damage
• drainage control