A method for producing a methane-rich stream and a C 2 + hydrocarbon-rich stream from a feed stream containing hydrocarbons, the method comprising the following steps: - separating the feed stream into a first fraction of the feed stream and at least one second fraction of the feed stream; - cooling the first fraction of the feed stream in a first heat exchanger; - injecting the first fraction of the cooled feed stream in a first separating flask to produce a light head stream and a heavy bottoms stream; - expanding a turbine feed fraction formed from the light head stream in a first dynamic expansion turbine up to a first pressure and injecting at least part of the first expanded fraction coming from the first turbine into a first distillation column; - expanding at least part of the heavy bottoms stream to form an expanded bottoms stream and injecting the expanded bottoms stream into the first distillation column without going through the first heat exchanger between the first separating flask and the first distillation column; - recovering a bottoms stream at the bottom of the first distillation column, the C 2 + hydrocarbon-rich stream being formed from the column stream; - recovering and heating a methane-rich overhead stream; - compressing at least one fraction of the overhead stream in at least a first compressor coupled to the first dynamic expansion turbine and in at least one second compressor; - forming a methane-rich stream from the heated and compressed overhead stream; the method comprising the following steps: - expanding at least part of the second fraction of the feed stream in a second dynamic expansion turbine, separate from the first dynamic expansion turbine, up to a second pressure, to form a second expanded fraction coming from the second dynamic expansion turbine, - cooling and at least partially liquefying at least part of the second expanded fraction coming from the second dynamic expansion turbine to form a cooled reflux stream (91B; 160; 232) and inject the cooled reflux stream (91B; 160; 232) in the first distillation column; characterized in that the second pressure is substantially equal to the first pressure such that the pressure difference between the first pressure and the second pressure is less than 8 bars; and in that the entire second fraction of the feed stream is injected into the second dynamic expansion turbine, without cooling between the step for separating the feed stream and the step for injecting the second fraction of the feed stream into the second dynamic expansion turbine. - separating the feed stream into a first fraction of the feed stream and at least one second fraction of the feed stream; - cooling the first fraction of the feed stream in a first heat exchanger; - injecting the first fraction of the cooled feed stream in a first separating flask to produce a light head stream and a heavy bottoms stream; - expanding a turbine feed fraction formed from the light head stream in a first dynamic expansion turbine up to a first pressure and injecting at least part of the first expanded fraction coming from the first turbine into a first distillation column; - expanding at least part of the heavy bottoms stream to form an expanded bottoms stream and injecting the expanded bottoms stream into the first distillation column without going through the first heat exchanger between the first separating flask and the first distillation column; - recovering a bottoms stream at the bottom of the first distillation column, the C 2 + hydrocarbon-rich stream being formed from the column stream; - recovering and heating a methane-rich overhead stream; - compressing at least one fraction of the overhead stream in at least a first compressor coupled to the first dynamic expansion turbine and in at least one second compressor; - forming a methane-rich stream from the heated and compressed overhead stream; - expanding at least part of the second fraction of the feed stream in a second dynamic expansion turbine, separate from the first dynamic expansion turbine, up to a second pressure, to form a second expanded fraction coming from the second dynamic expansion turbine, - cooling and at least partially liquefying at least part of the second expanded fraction coming from the second dynamic expansion turbine to form a cooled reflux stream (91B; 160; 232) and inject the cooled reflux stream (91B; 160; 232) in the first distillation column;