Methods, apparatus and systems for in-situ heating fluids with electromagnetic radiation are provided. An example tool includes a housing operable to receive a fluid flowed through a flow line and a heater positioned within the housing. The heater includes a number of tubular members configured to receive portions of the fluid and an electromagnetic heating assembly positioned around the tubular members and configured to generate electromagnetic radiation transmitted to heat the tubular members. The heated tubular members can heat the portions of the fluid to break emulsion in the fluid. Upstream the heater, the tool can include a homogenizer operable to mix the fluid to obtain a homogenous fluid and a stabilizer operable to stabilize the fluid to obtain a linear flow. Downstream the heater, the tool can include a separator operable to separate lighter components from heavier components in the fluid after the emulsion breakage.