If oxygen is used instead of air, the BTU of the resultant gas...

If oxygen is used instead of air, the BTU of the resultant gas is generally higher. Oxygen is preferred for deeper wells. In shallower coals (<1,000ft.), both the injection and production wells are vertical and drilled in a grid. For deeper coals, directional wells with CRIP technology are preferred. CRIP refers to “controlled retractable injection point” and is a key innovation developed through US research. It allows for multiple ignition points along the path of a horizontal wellbore. AIR is used in shallower coals, but overseas trials have show that UCG can pose a potentially significant risk to groundwater when the trial is at shallow depth, this will not be the case for Oxygen blown - deeper wells, the risk is MUCH LOWER!