Patent FR-2783557-A1 (FR)
Title: Method for controlling a liquid and gaseous hydrocarbon production well using injection gas involves using outlet choke and injection gas control valve to control start up phase, that initiates and ramps up production, and production phase
Inventor: LEMETAYER PIERRE
IPC: E21B43/12
Filed: 1998-09-21
Abstract: The method has a well (1) fitted with an adjustable-aperture outlet choke (9) into which gas, the flow rate of which can be adjusted by a control valve (6), is injected. The method comprises a start up phase that consists of a step for initiating the production of hydrocarbons and a step of ramping up production speed. A subsequent production phase uses the outlet choke and control valve to maintain stability of the flow rate. The method involves the step of initiating the production of hydrocarbons by comparing the pressure downstream of a control valve, that connects an annular space formed by a casing inside a production string to a source of pressurized gas, with two predetermined thresholds PCH1 and PCH2, with PCH2 being higher than PCH1. If this pressure is below the threshold PCH1 then the control valve is opened so as to inject gas into the annular space at a predetermined flow rate Q1 and if the pressure is between the thresholds then the control valve is opened to inject gas at a flow rate Q2, which is higher than Q1. When the pressure reaches the threshold PCH2 the flow rate of the gas injected into the annular space is adjusted to a predetermined value Q3 which is also higher than Q1. An adjustable-aperture outlet choke fitted to the outlet pipe is gradually adjusted so as to achieve a minimum produced-hydrocarbons flow rate. The production speed is then ramped up to a production speed by comparing the produced-hydrocarbons flow rate with a predetermined threshold T1 and, if the flow rate exceeds the threshold continuously for a predetermined length of time D1, the aperture of the choke is increased to a predetermined value, and if not the comparison is repeated. A predetermined length of time is left to allow the minimum hydrocarbons flow rate to become established after which the produced-hydrocarbons flow rate with a threshold T2 which is higher that T1 and comparing the pressure upstream of the choke with a predetermined pressure P1 and, if the flow rate and the pressure simultaneously exceed the thresholds continuously for a length of time D1 then the start-up phase is finished while if they do not then the comparison is repeated. Preferred Features: The step of ramping up the speed in the start up phase additionally consists of periodically calculating the derivative with respect to time of the pressure downstream of the control valve and comparing the derivative with a predetermined negative threshold and with a predetermined positive threshold. The injected gas flow rate is increased or decreased by a predetermined amount if the derivative of pressure is below the negative threshold of above the positive threshold, respectively. The start up phase is followed by a production phase which involves comparing the produced-hydrocarbon flow rate with four predetermined thresholds SR1, SR2, SR3 and SR4, where SR is higher than SR1 and SR4 is higher than SR3. If the production flow rate is below SR1 and if the injected gas flow rate is below a predetermined threshold then the flow rate is increased by a predetermined amount and if the production flow rate is above SR2 and if the injected gas flow rate is above a predetermined threshold then the flow rate is decreased by a predetermined amount. If the production flow rate is below SR3 and if the aperture of the choke is below a predetermined threshold then the aperture of the choke is reduced by a predetermined amount while if the production flow rate is above SR4 and if the aperture of the choke is above a predetermined threshold then the aperture is reduced by a predetermined threshold. This comparison is repeated and the produced hydrocarbons-production flow rate is compared with a predetermined threshold and, if the flow rate is below the threshold, the start up phase is resumed. The production phase also consists of periodically calculating the derivative with respect to time of the pressure downstream of the control valve and comparing the derivative with a predetermined negative threshold and with a predetermined positive threshold, with the injected gas flow rate being increased or decreased if the derivative of the pressure is below the negative threshold or above the positive threshold, respectively. The produced-hydrocarbons flow rate is either measured using a flow meter mounted on the outlet pipe upstream of the outlet choke, estimated on the basis of measurement of the temperature of the produced hydrocarbons upstream of the outlet choke or estimated on the basis of the pressure difference across the outlet choke and the aperture of the choke