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Adaptive Slug Controller

IP.com Disclosure Number: IPCOM000247091D
Publication Date: 2016-Aug-04
Document File: 17 page(s) / 2M

Publishing Venue

The IP.com Prior Art Database

Abstract

A method and apparatus for continuously providing set point/ high and low limits for a slug-controller (Slug controller here refers to a device which mitigates slugging in a multiphase fluid stream flowing through a conduit, by regulating the position of an adjustable choke valve downstream of the slugging zone), such that it operates the production facilities at optimum stability and automatically adjusts to change in field conditions. This is achieved through three 'Automation blocks'. Set Point Automation block: This block continuously provides set point to the slug controller, the method comprising the steps of: (a) Filtering the Controlled variable or present variable - PV (dPhead / Riser bottom pressure) of the slug controller through a low pass filter with high filter time constant; (b) Measuring the differential pressure across the choke located downstream of slugging zone (which the slug controller is acting on); (c) Determining the error from a target differential pressure across the choke (user defined – for example a default value of 5 bar), by subtracting target differential pressure across choke with current differential pressure across choke from step(b); (d) Multiplying the error in differential pressure across choke obtained from step (c) with a constant factor; (e) Adding the value obtained from step(d) with the filtered PV value obtained from step (a). (f) Passing the value obtained from step (e) through a dead band, the output of which is fed as a set point to the slug controller. Low Limit Automation block: This block works on the controller output (velocity form) from the slug controller. The block limits the choke located downstream of slugging zone to either a pre-defined static 'Low Limit' or dynamically when the riser top pressure is beyond a certain high value. The method comprising steps of: (a) Measuring the pressure just upstream of choke (located downstream of slugging zone, which the slug controller is acting on); (b) Determining the error from a target pressure upstream of the choke (user input); (c) If pressure just upstream of choke is higher than target pressure then prevent the valve from closing further. Step (c) is also followed after comparing slug controller positional output with static low limit. High Limit Automation block: This block works on the controller output (velocity form) from the slug controller. The block limits the opening of riser top choke valve to either a pre-defined static 'High Limit' or dynamically to limit the differential pressure across the choke located downstream of slugging zone (which the slug controller is acting on). The method comprising steps of: (a) Calculating an average position of valve by filtering it through a low pass filter of high filter time constant; (b) Multiplying the average position with a constant factor to determine dynamic high limit; (c) Take the maximum of static and dynamic high limit; (d) If the choke position is higher than value determined from step (c) then prevent the valve from opening further.

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Adaptive Slug Controller

Abstract: A method and apparatus for continuously providing set point/ high and low limits for a slug-controller (Slug controller here refers to a device which mitigates slugging in a multiphase fluid stream flowing through a conduit, by regulating the position of an adjustable choke valve downstream of the slugging zone), such that it operates the production facilities at optimum stability and automatically adjusts to change in field conditions. This is achieved through three ‘Automation blocks’.

Set Point Automation block: This block continuously provides set point to the slug controller, the method comprising the steps of: (a) Filtering the Controlled variable or present variable - PV (dPhead / Riser bottom pressure) of the slug controller through a low pass filter with high filter time constant; (b) Measuring the differential pressure across the choke located downstream of slugging zone (which the slug controller is acting on); (c) Determining the error from a target differential pressure across the choke (user defined – for example a default value of 5 bar), by subtracting target differential pressure across choke with current differential pressure across choke from step(b); (d) Multiplying the error in differential pressure across choke obtained from step (c) with a constant factor; (e) Adding the value obtained from step(d) with the filtered PV value obtained from step (a). (f) Passing the value obtained from step (e) through a dead band, the output of which is fed as a set point to the slug controller.

Low Limit Automation block: This block works on the controller output (velocity form) from the slug controller. The block limits the choke located downstream of slugging zone to either a pre-defined static ‘Low Limit’ or dynamically when the riser top pressure is beyond a certain high value. The method comprising steps of: (a) Measuring the pressure just upstream of choke (located downstream of slugging zone, which the slug controller is acting on); (b) Determining the error from a target pressure upstream of the choke (user input); (c) If pressure just upstream of choke is higher than target pressure then prevent the valve from closing further. Step (c) is also followed after comparing slug controller positional output with static low limit.

High Limit Automation block: This block works on the controller output (velocity form) from the slug controller. The block limits the opening of riser top choke valve to either a pre-defined static ‘High Limit’ or dynamically to limit the differential pressure across the choke located downstream of slugging zone (which the slug controller is acting on). The method comprising steps of: (a) Calculating an average position of valve by filtering it through a low pass filter of high filter time constant; (b) Multiplying the average position with a constant factor to determine dynamic high limit; (c) Take the maximum of static and dynamic high limit; (d) If the chok...