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

• US 6,293,341 B1
• Filed: 09/17/1999
• Issued: 09/25/2001
• Est. Priority Date: 09/21/1998
• Status: Expired due to Term

• Current Assignee: ELF Exploration Production (Cook Composites and Polymers)
• Original Assignee: ELF Exploration Production (Cook Composites and Polymers)
• Inventors: Lemetayer, Pierre
• Primary Examiner(s): NEUDER, WILLIAM P
• Application Number:
  US09/398,462
• Time in Patent Office: 739 Days
• Field of Search: 166/250.15, 166/305.1, 166/306, 166/372, 166/53
• US Class Current: 166/250.15
• CPC Class Codes: E21B 43/122 Gas lift

Abstract

The invention relates to a method for controlling a liquid and gaseous hydrocarbons production well (1) activated by injection of gas, the well comprising a production string (2) fitted with an adjustable-aperture outlet choke (9), into which gas, the flow rate of which can be adjusted by means of a control valve (6), is injected, the method being characterized in that it comprises a start-up phase which consists in performing the following sequence of steps:

a step of initiating the production of hydrocarbons

a step of ramping up to production speed followed by a production phase, during which phases the outlet choke (9) and the control valve (6) are operated in such a way as to maintain the stability of the flow rate of the produced hydrocarbons.

Claims

1. 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.

2. Method according to claim 1, wherein the step of ramping up to production speed in the start-up phase additionally comprises periodically performing the following operations:

calculating the derivative with respect to time of the pressure downstream of the control valve,

comparing this derivative with a predetermined negative pressure derivative threshold and with a predetermined positive pressure derivative threshold, and

if the derivative of pressure is below the negative pressure derivative threshold, increasing the injected gas-flow rate by a predetermined amount,

if the derivative of pressure is above the positive pressure derivative threshold, decreasing the injected-gas flow rate by a predetermined amount.

3. Control method according to claim 1 wherein during the production phase following the start-up phase the following operations are performed in parallel:

comparing the produced-hydrocarbons flow rate with four predetermined flow rate thresholds SR1, SR2, SR3 and SR4, SR2 being higher than SR1, SR4 being higher than SR3, and;

if the produced-hydrocarbons flow rate is below SR1 and if the injected-gas flow rate is below a predetermined gas flow rate threshold, increasing the said flow rate by a predetermined amount,

if the produced hydrocarbons flow rate is above SR2 and if the injected-gas flow rate is above a predetermined gas flow rate threshold, decreasing the said flow rate by a predetermined amount,

if the produced-hydrocarbons flow rate is below SR3 and if the aperture of the outlet choke is below a predetermined aperture threshold, increasing the aperture of the said choke by a predetermined amount,

if the produced-hydrocarbons flow rate is above SR4 and if the aperture of the outlet choke is above a predetermined aperture threshold, reducing the aperture of the said choke by a predetermined amount,

comparing the produced-hydrocarbons flow rate with a predetermined flow rate value and, if the said flow rate is below the said value, resuming the start-up phase.

4. Method according to claim 3, wherein the production phase comprises also periodically performing the following operations:

calculating the derivative with respect to time of the pressure downstream of the control valve,

comparing this derivative with a predetermined negative pressure derivative threshold and with a predetermined positive pressure derivative threshold, and

if the derivative of pressure is below the negative pressure derivative threshold, increasing the injected-gas flow rate by a predetermined amount,

if the derivative of pressure is above the positive pressure derivative threshold, decreasing the injected-gas flow rate by a predetermined amount.

5. Method according to claim 1, wherein the produced-hydrocarbons flow rate is measured using a flow meter mounted on the outlet pipe upstream of the outlet choke.

6. Method according to claim 1, wherein the produced-hydrocarbons flow rate is estimated on the basis of measurement of the temperature of the produced-hydrocarbons upstream of the outlet choke.

7. Method according to claim 1, wherein the produced-hydrocarbons flow rate is estimated on the basis of the pressure difference across the outlet choke and of the aperture of the said choke.