Synthetic natural gas (SNG) production from black liquor gasification (BLG) replacing conventional recovery cycle at chemical pulp mills is an attractive option to reduce CO2 emissions and replace fossil natural gas. This paper evaluates the potential of SNG production from a circulating fluidized bed BLG process with direct causticization by investigating synthesis gas composition, purity requirements for SNG and process integration with the reference pulp mill producing 1000 air dried tonnes (ADt) of pulp per day. The objective of this study is to estimate the integrated process efficiency from black liquor (BL) conversion to SNG and to quantify the differences in overall process efficiencies of various bio-refinery options. The models include a BLG Island including BL gasifier, synthesis gas cooling and cleaning unit, methanation with SNG upgrading and a power boiler. The result indicates a large potential of SNG production from BL but at a cost of additional biomass import to compensate energy deficit in terms of BL conversion to SNG. In addition, the study shows a significant CO2 abatement when CO2 capture is carried out in SNG upgrading and also reducing CO2 emissions when SNG potentially replaces fossil natural gas.