Underground coal gasification and the ways of their admission

摘要

Underground Coal Gasification (UCG) is the conversion of coal in the seam into a combustible gas. UCG is conceptually very simple but controlling the reaction and producing a consistent gas quality under a variety of geological and coal conditions is difficult to achieve. The basic concept has two boreholes, one for the injection of oxidants and the other for the removal of the product gas. UCG requires boreholes to access the coal, and three methods have been developed to connect them, namely: 1. Air pressurisation between vertical holes 2. Man – built galleries in the coal 3. Directional drilling in the coal seam with a controlled injection. The most utilised method is the directional drilling in coal. This technology is well advanced in the hydrocarbons industry. The conventional steerable downhole motors are used for this purpose.