Wells – Processes – With indicating – testing – measuring or locating
Reexamination Certificate
1999-09-17
2001-09-25
Neuder, William (Department: 3672)
Wells
Processes
With indicating, testing, measuring or locating
C166S053000, C166S372000
Reexamination Certificate
active
06293341
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for controlling a liquid and gaseous hydrocarbons production well activated by injection of gas from a source of pressurized gas, the hydrocarbons produced being processed in a downstream treatment unit fed by the well.
STATE OF THE PRIOR ART
Document GB 2,252,797 describes a method for controlling the production flow rate of an oil well, which well comprises a hydrocarbons production string leading to a well head and defining, with the wall of the well, an annular space, the string being fitted with at least one gas inlet valve communicating with a source of pressurized gas via a control valve which allows the flow rate of gas towards the inside of the production string to be controlled, and with an outlet choke for governing the flow of hydrocarbons in the production string, the method consisting in controlling the control valve and the outlet choke as a function of the temperature and pressure measurements taken at the surface and in the annular space and as a function of measurements of pressure and flow rate of the gas emanating from the source.
Document EP 0,756,065 describes a system for controlling the production of hydrocarbons through an outlet pipe which extends to a production well activated by injection of gas.
This system comprises:
an outlet choke for controlling the flow rate of hydrocarbons through the outlet pipe, and
a control module for dynamically controlling the aperture of the outlet choke.
The control module dynamically controls the aperture of the choke as a function of the variations in pressure in the gas injection pipe.
According to a particular embodiment, the control module comprises a PID algorithm which stabilizes and minimizes the pressure in the gas injection pipe on the basis of the pressure in this pipe measured by means of a sensor, this pressure being used as an input signal, and which at output, delivers a signal of the position of the outlet choke.
This method and this device are not able to achieve efficient control over the production of hydrocarbons when a plug of gas forms when the well enters a production phase as a result of the opening of the outlet choke, or when a plug of liquid forms when the injected gas starts to rise, particularly when the pressure of the injected gas is very high.
These plugs have the effect of initiating disturbances, particularly cyclic disturbances, in the production of hydrocarbons, which are manifested in an irregular supply to the hydrocarbons-treatment units downstream, such as the liquid/gas separation unit, gas recompression and treatment units.
The consequences of this irregular supply to the downstream hydrocarbons-treatment units are, among other things, a reduction in the amount of gas available for activating the well and an increase in the risks of tripping, which are manifested by a reduction in production.
Another consequence of these disturbances is that wear on the hole-layer connection is accentuated, particularly in wells with unconsolidated reservoirs, which leads to the ingress of sand which requires sand control equipment and frequent and expensive restoration of damaged wells.
Something else that these methods are unable to achieve is optimum stable production after the start-up phase with a minimum gas flow rate, or efficient compensation for disturbances resulting from the random behaviour of the reservoir, failure of string equipment, or bringing the well into a production phase efficiently when gas availability is low.
The object of the present invention is precisely to alleviate these drawbacks. To this end, it provides a 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 being characterized in that, with the control valve and the outlet choke closed, it comprises a start-up phase which consists in performing the following sequence of steps:
a step of initiating the production of hydrocarbons consisting:
in comparing the pressure downstream of the control valve with two predetermined thresholds PCH
1
and PCH
2
, PCH
2
being higher than PCH
1
, and
a) if this pressure is below the threshold PCH
1
, in opening the control valve so as to insect gas into the annular space at a predetermined flow rate Q
1
,
b) if this pressure is between the thresholds PCH
1
and PCH
2
, in opening the control valve so as to inject gas into the annular space at a predetermined flow rate Q
2
higher than Q
1
, and
c) when this pressure reaches the threshold PCH
2
, in adjusting the flow rate of gas injected into the annular space to a predetermined value Q
3
higher than Q
1
,
in gradually opening the choke to a predetermined value so as to achieve a predetermined minimum produced-hydrocarbons flow rate,
a step of ramping up to production speed, which consists in performing the following operations:
comparing the produced-hydrocarbons flow rate with a predetermined threshold T
1
and, if the said flow rate exceeds the said threshold continuously for a predetermined length of time D
1
, increasing the aperture of the choke to a predetermined value, and if not, repeating the comparison,
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 threshold T
2
which is higher than T
1
and comparing the pressure upstream of the choke with a predetermined pressure P
1
and, if the said flow rate and the said pressure simultaneously exceed the said thresholds continuously for the length of time D
1
, finishing the start-up phase, and if not, repeating the comparison.
According to another feature of the invention, the step of ramping up to speed in the start-up phase additionally consists in 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 threshold and with a predetermined positive threshold, and
if the derivative of pressure is below the negative threshold, increasing the injected-gas flow rate by a predetermined amount,
if the derivative of pressure is above the positive threshold, decreasing the injected-gas flow rate by a predetermined amount.
According to another feature of the invention, the start-up phase is followed by a production phase which consists in performing the following operations in parallel:
comparing the produced-hydrocarbons flow rate with four predetermined thresholds SR
1
, SR
2
, SR
3
and SR
4
, SR
2
being higher than SR
1
, SR
4
being higher than SR
3
, and:
if the produced-hydrocarbons flow rate is below SR
1
and if the injected-gas flow rate is below a predetermined threshold, increasing the said flow rate by a predetermined amount,
if the produced-hydrocarbons flow rate is above SR
2
and if the injected-gas flow rate is above a predetermined threshold, decreasing the said flow rate by a predetermined amount,
if the produced-hydrocarbons flow rate is below SR
3
and if the aperture of the outlet choke is below a predetermined threshold, increasing the aperture of the said choke by a predetermined amount,
if the produced-hydrocarbons flow rate is above SR
4
and if the aperture of the outlet choke is above a predetermined threshold, reducing the aperture of the said choke by a predetermined amount,
repeating the previous comparison,
comparing the produced-hydrocarbons flow rate with a predetermined threshold and, if the said flow rate is below the said threshold, resuming the start-up phase.
According to another feature of the invention, the production phase consists in also periodically performing the following operations:
calculating t
Blank Rome Comisky & McCauley LLP
Elf Exploration Production
Neuder William
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