Although the CO2 injection for enhanced coalbed methane (ECBM) recovery is one of the potential coalbed methane production techniques, the effectiveness of the process is greatly dependent on the coal seam and method for CO2 injectivity enhancement which is still becomes one of the technical challenges. This study has therefore aimed to investigate the performance of CO2 sequestration for ECBM recovery through a horizontal well in deep unmineable coal seams. To achieve the objectives, a novel 3D numerical model was developed based on the characteristics of coal seams in Indonesia's Basins and reservoir simulation study was performed. From the results, the productivity of methane was increased by applying horizontal well instead of vertical well, especially for the coal seams with low permeability. In addition, CO2 sequestration coupled with the use of a horizontal well resulted in the volume of CO2 stored in deep unmineable coal seams increases to three times larger than a vertical well, it depends on the horizontal well length. Copyright © 2017, AIDIC Servizi S.r.l..