Method for producing a flow which is rich in methane and a cut which is rich in C 2 + hydrocarbons from a flow of dehydrated feed natural gas, which is composed of hydrocarbons, nitrogen and CO 2 and which advantageously has a molar content of C 2 + hydrocarbons greater than 10%, the method comprising the following steps: - cooling the feed natural gas flow, advantageously at a pressure greater than 40 bar, in a first heat exchanger and introducing the cooled, feed natural gas flow into a first separation flask; - separating the cooled natural gas flow in the first separation flask and recovering a light fraction which is substantially gaseous and a heavy fraction which is substantially liquid; - dividing the light fraction into a flow for supplying to a turbine and a secondary flow; - dynamic expansion of the turbine supply flow in a first expansion turbine and introducing the expanded flow into an intermediate portion of a separation column; - cooling the secondary flow in a second heat exchanger and introducing the cooled secondary flow into an upper portion of the separation column; - expanding the heavy fraction, vaporisation in the first heat exchanger and introduction into a second separation flask in order to form a head fraction and a bottom fraction; - introducing the head fraction, after cooling in the second heat exchanger, in the upper portion of the separation column; - introducing the bottom fraction into an intermediate portion of the separation column; - recovering, at the bottom of the separation column, a bottom flow which is rich in C 2 + hydrocarbons and which is intended to form the cut rich in C 2 + hydrocarbons; - removing, at the head of the separation column, a head flow rich in methane; - reheating the head flow rich in methane in the second heat exchanger and in the first heat exchanger and compressing that flow in at least a first compressor which is coupled to the first expansion turbine and in a second compressor in order to form a flow rich in methane from the compressed head flow rich in methane; - removing a first recirculation flow from the head flow (82, 84, 86) rich in methane; - passing the first recirculation flow into the first heat exchanger and into the second heat exchanger in order to cool it, then introducing at least a first portion of the first cooled recirculation flow into the upper portion of the separation column; characterised in that the method comprises the following steps: - forming at least a second recirculation flow (96; 136; 168; 192) obtained from the head flow rich in methane downstream of the separation column; - forming a dynamic expansion flow (100; 136) from the second recirculation flow (96; 136; 168; 192) and introducing the dynamic expansion flow (100; 136) into an expansion turbine (22; 132) in order to produce frigories, and in that the second recirculation flow is introduced into a flow (40; 46) downstream of the first heat exchanger and upstream of the first expansion turbine in order to form the dynamic expansion flow. - cooling the feed natural gas flow, advantageously at a pressure greater than 40 bar, in a first heat exchanger and introducing the cooled, feed natural gas flow into a first separation flask; - separating the cooled natural gas flow in the first separation flask and recovering a light fraction which is substantially gaseous and a heavy fraction which is substantially liquid; - dividing the light fraction into a flow for supplying to a turbine and a secondary flow; - dynamic expansion of the turbine supply flow in a first expansion turbine and introducing the expanded flow into an intermediate portion of a separation column; - cooling the secondary flow in a second heat exchanger and introducing the cooled secondary flow into an upper portion of the separation column; - expanding the heavy fraction, vaporisation in the first heat exchanger and introduction into a second separation flask in order to form a head fraction and a bottom fraction; - introducing the head fraction, after cooling in the second heat exchanger, in the upper portion of the separation column; - introducing the bottom fraction into an intermediate portion of the separation column; - recovering, at the bottom of the separation column, a bottom flow which is rich in C 2 + hydrocarbons and which is intended to form the cut rich in C 2 + hydrocarbons; - removing, at the head of the separation column, a head flow rich in methane; - reheating the head flow rich in methane in the second heat exchanger and in the first heat exchanger and compressing that flow in at least a first compressor which is coupled to the first expansion turbine and in a second compressor in order to form a flow rich in methane from the compressed head flow rich in methane; - removing a first recirculation flow from the head flow (82, 84, 86) rich in methane; - passing the first recirculation flow into the first heat exchanger and into the second heat exchanger in order to cool it, then introducing at least a first portion of the first cooled recirculation flow into the upper portion of the separation column; - forming at least a second recirculation flow (96; 136; 168; 192) obtained from the head flow rich in methane downstream of the separation column; - forming a dynamic expansion flow (100; 136) from the second recirculation flow (96; 136; 168; 192) and introducing the dynamic expansion flow (100; 136) into an expansion turbine (22; 132) in order to produce frigories, and in that the second recirculation flow is introduced into a flow (40; 46) downstream of the first heat exchanger and upstream of the first expansion turbine in order to form the dynamic expansion flow.