Method of controlling a hydrocarbons production well activated by injection of gas

Method for controlling a liquid and gaseous hydrocarbons production well activated by injecting gas, which well comprises at least one production string inside a casing and defining, with the said casing, an annular space connected by a pipe for injecting gas, through a control valve, to a source of pressurized gas, the said production string being fitted with at least one gas inlet valve and extended by an outlet pipe fitted with an adjustable-aperture outlet choke, the method comprising, with the control valve and the outlet choke closed, a start-up phase which comprises performing the following sequence of steps:

• initiating the production of hydrocarbons comprising:
• comparing the pressure downstream of the control valve with two predetermined pressure thresholds PCH1 and PCH2, PCH2 being higher than PCH1, and
• a) if this pressure is below the threshold PCH1, opening the control valve so as to inject gas into the annular space at a predetermined flow rate Q1,
• b) if this pressure is between the thresholds PCH1 and PCH2, opening the control valve so as to inject gas into the annular space at a predetermined flow rate Q2 higher than Q1, and
• c) when this pressure reaches the threshold PCH2, adjusting the flow rate of gas injected into the annular space to a predetermined value Q3 higher than Q1,
• gradually opening the choke to a predetermined value so as to achieve a predetermined minimum produced-hydrocarbons flow rate,
• ramping up to production speed, which comprises performing the following operations:
• comparing the produced-hydrocarbons flow rate with a predetermined flow rate threshold T1 and, if the said flow rate exceeds the said threshold continuously for a predetermined length of time D1, increasing the aperture of the choke to a predetermined value, and if not, repeating the comparison of the produced-hydrocarbons flow rate with the threshold T1,
• waiting for a predetermined length of time to allow the minimum hydrocarbons flow rate to become established,
• comparing the produced-hydrocarbons flow rate with a flow rate threshold T2 which is higher than T1 and comparing the pressure upstream of the choke with a predetermined pressure P1 and, if the said flow rate and the said pressure simultaneously exceed the said thresholds continuously for the length of time D1, performing a production phase, and if not, repeating the comparison of the produced hydrocarbon flow rate with the threshold T1 and the comparison of the pressure upstream of the choke with the predetermined pressure P1.