Investigation of thermal stimulation of coal seam gas fields for accelerated gas recovery

In coal seam gas production, interventions to increase well productivity from poorly performing wells need to be matched to the nature of the coal, which may include: fracture stimulation if the permeability is low; and matrix stimulation if gas flow is restricted by the matrix diffusion. Increasing the coal bed temperature will assist in matrix stimulation by increasing the diffusion flux and in-turn enhance the well productivity. Four different coal samples were studied against the temperature influence on methane storage as well as its transport inside the pores. It is found that a change in temperature, for e.g. ΔT ∼ 40 °C, may be expected to cause a three to four fold improvement in diffusivity. The experimental data was utilized in theoretical simulation of coal seam bed. By increasing the bed temperature, the total amount of methane recovered is higher, however, the economic benefit of extra methane produced is too small to justify the thermal stimulation of the bed. The true benefit of thermal stimulation lies in the enhanced rate of recovery which results in improving the NPV of the produced gas. Several production-well case scenarios were examined to determine the favourable conditions for implementing thermal stimulation technique and to determine if such a method could be commercially implemented on the field