A process for upgrading a petroleum-based composition while decreasing plugging comprising: mixing a supercritical water stream with a pressurized, heated petroleum-based composition in a mixing device to create a combined feed stream; introducing the combined feed stream to an upgrading reactor system to produce an upgraded product, where the upgrading reactor system operates at a temperature greater than a critical temperature of water and a pressure greater than a critical pressure of water, and where the upgrading reactor system comprises one or more upgrading reactors; passing the upgraded product out of the upgrading reactor system; cooling the upgraded product with a cooling device to create a cooled upgraded product having a temperature less than 200°C; decreasing the pressure of the cooled upgraded product with a pressure reducer to create a cooled, depressurized stream having a pressure from 0.05 megapascals (MPa) to 2.2 MPa; and injecting plug remover solution into one or more injection locations at a temperature within 200°C of a temperature of an internal fluid at the injection locations and a pressure of 100% to 120% of the pressure of the internal fluid at the injection location, where the plug remover solution comprises an aromatic solvent and less than 500 parts per million (ppm) of water, and where the injection locations include one or more of: an injection port on a process line connecting the mixing device with the upgrading reactor system; an injection port on a process line connecting the upgrading reactor system with the cooling device; or an injection port on a process line connecting the cooling device with the pressure reducer. mixing a supercritical water stream with a pressurized, heated petroleum-based composition in a mixing device to create a combined feed stream; introducing the combined feed stream to an upgrading reactor system to produce an upgraded product, where the upgrading reactor system operates at a temperature greater than a critical temperature of water and a pressure greater than a critical pressure of water, and where the upgrading reactor system comprises one or more upgrading reactors; passing the upgraded product out of the upgrading reactor system; cooling the upgraded product with a cooling device to create a cooled upgraded product having a temperature less than 200°C; decreasing the pressure of the cooled upgraded product with a pressure reducer to create a cooled, depressurized stream having a pressure from 0.05 megapascals (MPa) to 2.2 MPa; and injecting plug remover solution into one or more injection locations at a temperature within 200°C of a temperature of an internal fluid at the injection locations and a pressure of 100% to 120% of the pressure of the internal fluid at the injection location, where the plug remover solution comprises an aromatic solvent and less than 500 parts per million (ppm) of water, and where the injection locations include one or more of: an injection port on a process line connecting the mixing device with the upgrading reactor system; an injection port on a process line connecting the upgrading reactor system with the cooling device; or an injection port on a process line connecting the cooling device with the pressure reducer. an injection port on a process line connecting the mixing device with the upgrading reactor system; an injection port on a process line connecting the upgrading reactor system with the cooling device; or an injection port on a process line connecting the cooling device with the pressure reducer.