The discovery and control of slug flow in coalbed methane reservoir

Slug flow, which can cause severe velocity sensitivity damage to coalbed methane (CBM) reservoirs, tends to happen at the gas-liquid two-phase flow stage during the CBM production process. However, little attention has been paid to this phenomenon. This paper investigates the factors which can influence the forming of slug flow in CBM reservoirs systematically via a series of laboratory experiments and production data from two CBM wells. Results show that a slug flow is more likely to be formed under the conditions of high reservoir permeability, high fluid surface tension and high producing differential pressure. This is because that both the high permeability and high production differential pressure would lead to a high fluid flow velocity that can cause strong Kelvin-Helmholtz instability effect of the interface wave. Then, the strong Kelvin-Helmholtz instability effect will cause the slug flow. Meanwhile, a high fluid surface tension means that the liquid will form slug flow more easily. The most effective way to restrain slug flow is to utilize a fracturing fluid with low surface tension in combination with continuous, slow and stable productions.