Systems and methods for injecting hydrogen into a natural gas pipeline to lower the carbon intensity of the resulting fuel blend while achieving the required energy output thereof for the end user. In one embodiment a blend ratio for the blended fuel comprising hydrogen and natural gas is determined based at least in part on a minimum energy output for fuel combusted at an end-use location connected to the natural gas pipeline so that the blended fuel (i) has a lower carbon intensity than a natural gas stream flowing in the natural gas pipeline, and (ii) provides at least the minimum energy output when combusted at the end-use location. Further, one or more embodiments include adjusting a control valve of a hydrogen injection assembly connected to the natural gas pipeline upstream of the end-use location based at least in part on the blend ratio to thereby mix hydrogen into the natural gas pipeline and produce the blended fuel.