US Patent 10113394 Multi-stage flow device

A multi-stage flow sub usable in wellbore operations provides for flow of fluid from a tool string to a wellbore annulus, and may provide for one or more of controlling wellbore pressure during a tool operation, or preventing stripping of wet string. The multi-stage flow sub may include a housing having an axial bore and at least one flow passage. A sleeve within the housing may have an axial bore, a shoulder acting as a ball seat, and first and second axially offset flow passages. A first burst disc may be in fluid communication with the first flow passage, and a second burst disc may be in fluid communication with the second flow passage, the second burst disc having a higher burst pressure than the first burst disc.