CN116371266A - System and method for controlling density of well cementation cement paste - Google Patents

Abstract

The invention discloses a well cementation cement paste density control system and a well cementation cement paste density control method. The system comprises: the first PID control module generates a first output signal according to the cement paste density set value and the first density; the second PID control module generates a second output signal according to the first output signal and the second density; the dry cement ash flow calculation module calculates a dry cement ash mass flow estimation value which enters the slurry mixing tank according to the first density, the second density and the clear water flow meter; the feedforward control module generates a third output signal according to the clear water flow; the third PID control module generates a fourth output signal according to the second output signal, the third output signal and the dry cement ash mass flow estimation value; the cement ash flow control valve executes a fourth output signal to control the dry cement ash flow. By adopting the scheme, the density of the well cementation cement slurry produced by the well cementation continuous slurry mixing system can be quickly stabilized near a set value, and the stability and the accuracy of well cementation continuous slurry mixing density control are improved.

Description

System and method for controlling density of well cementation cement paste

Technical Field

The invention relates to the technical field of exploration, in particular to a well cementation cement paste density control system and method.

Background

The well cementation is a key link for connecting a drilling engineering and an oil extraction engineering, and is an operation process of pumping cement paste with set density and a certain volume into a well bottom at a certain speed under a certain high pressure condition, so that the purposes of sealing an oil layer, a gas layer and a water layer in a well hole, protecting a casing of an oil-gas well, prolonging the service life of the oil-gas well, improving the oil-gas yield and the like are achieved.

In the well cementation process, the density control of the well cementation cement paste has important significance on well cementation quality, exploration safety, oil and gas reservoir protection, corrosion prevention, channeling prevention and the like. In the prior art, a single-loop PID control method is generally adopted to realize the density control of the well cementation continuous slurry mixing. However, the density control method for the well cementation continuous slurry has the defects of insufficient precision, low stability and low control efficiency.

Disclosure of Invention

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a system and method for controlling the density of a cement slurry that overcomes or at least partially solves the above problems.

According to one aspect of the present invention, there is provided a well cementing slurry density control system for controlling the slurry density of a well cementing continuous slurry system, the well cementing slurry density control system comprising: the system comprises an equalizing tank pump outlet line densimeter, a slurry mixing tank circulating line densimeter, a clear water flowmeter, a first PID control module, a second PID control module, a feedforward control module, a dry cement ash flow calculation module, a third PID control module and a cement ash flow regulating valve;

The balance tank pump-out pipeline densimeter is used for measuring the first density of cement slurry in the balance tank pump-out pipeline in the well cementation continuous slurry mixing system; the slurry mixing tank circulating pipeline densimeter is used for measuring the second density of the cement slurry in the slurry mixing tank circulating pipeline in the well cementation continuous slurry mixing system; the clear water flowmeter is used for measuring clear water flow in the well cementation continuous slurry mixing system;

the first PID control module is connected with the pump-out pipeline densimeter of the equalizing tank and is used for generating a first output signal according to the cement paste density set value and the first density;

the second PID control module is connected with the slurry mixing tank circulating pipeline densimeter and the first PID control module and is used for generating a second output signal according to the first output signal and the second density;

the dry cement ash flow calculation module is connected with the balance tank pump-out pipeline densimeter, the slurry mixing tank circulation pipeline densimeter and the clear water flowmeter and is used for calculating a dry cement ash mass flow estimated value which enters the slurry mixing tank according to the first density, the second density and the clear water flowmeter;

the feedforward control module is connected with the clear water flowmeter and is used for generating a third output signal according to the clear water flow;

the third PID control module is connected with the second PID control module, the dry cement ash flow calculation module and the feedforward control module and is used for generating a fourth output signal according to the second output signal, the third output signal and the dry cement ash mass flow estimation value;

The cement ash flow regulating valve is connected with the third PID control module and is used for executing the fourth output signal to control the dry cement ash flow.

In an alternative embodiment, the first PID control module is specifically configured to:

calculating a first deviation of the cement paste density set value at the kth sampling moment from a first density at the kth sampling moment;

the first output signal at the kth sample time is calculated based on the first offset at the kth sample time, the first offset at the kth-1 sample time, the first offset at the kth-2 sample time, and the first output signal at the kth-1 sample time.

In an alternative embodiment, the second PID control module is specifically configured to:

calculating a second deviation of the first output signal at the kth sampling instant from the second density at the kth sampling instant;

the second output signal at the kth sample time is calculated based on the second offset at the kth sample time, the second offset at the kth-1 sample time, the second offset at the kth-2 sample time, and the second output signal at the kth-1 sample time.

In an alternative embodiment, the dry cement ash flow calculation module is specifically configured to:

Calculating the mass flow of overflow cement slurry overflowed from the slurry mixing tank to the equalizing tank at the kth sampling moment;

and calculating an estimated value of the dry cement ash mass flow entering the slurry mixing tank at the kth sampling moment according to the overflow cement slurry mass flow at the kth sampling moment, the second density at the kth-1 sampling moment and the clear water flow at the kth sampling moment.

In an alternative embodiment, the dry cement ash flow calculation module is specifically configured to:

and calculating the mass flow of the overflow cement slurry overflowed from the slurry mixing tank to the balance tank at the kth sampling time according to the first density at the kth sampling time and the first density at the kth-1 sampling time.

In an alternative embodiment, the well cementing slurry density control system further comprises:

the equalizing tank liquid level meter is used for measuring the liquid level of the equalizing tank;

and the balance tank pump-out pipeline displacement detector is used for measuring the cement paste displacement in the balance tank pump-out pipeline.

In an alternative embodiment, the dry cement ash flow calculation module is connected with the balance tank liquid level meter and the balance tank pump outlet displacement detector and is used for calculating the overflow cement slurry mass flow overflowed from the slurry mixing tank to the balance tank at the kth sampling time according to the first density at the kth sampling time, the first density at the kth-1 sampling time, the balance tank liquid level at the kth sampling time and the cement slurry displacement at the kth sampling time.

In an alternative embodiment, the feedforward control module is specifically configured to:

and generating a third output signal according to the cement paste density set value at the kth sampling moment and the clear water flow at the kth sampling moment.

In an alternative embodiment, the third PID control module is specifically configured to:

calculating a third deviation of the kth sampling moment according to the second output signal of the kth sampling moment, the third output signal of the kth sampling moment and the dry cement ash mass flow estimation value of the kth sampling moment;

the fourth output signal at the kth sample time is calculated based on the third offset at the kth sample time, the third offset at the kth-1 sample time, the third offset at the kth-2 sample time, and the fourth output signal at the kth-1 sample time.

According to another aspect of the present invention, there is provided a well cementing slurry density control method for controlling the slurry density of a well cementing continuous slurry mixing system, the well cementing slurry density control method comprising:

the first PID control module generates a first output signal according to a cement paste density set value and a first density measured by the balance tank pump outlet densimeter;

The second PID control module generates a second output signal according to the first output signal and the second density measured by the slurry mixing tank circulating pipeline densimeter;

the dry cement ash flow calculation module calculates a dry cement ash mass flow estimated value which enters the slurry mixing tank according to the first density, the second density and the clear water flow measured by the clear water flow meter;

the feedforward control module generates a third output signal according to the clear water flow;

and the third PID control module generates a fourth output signal according to the second output signal, the third output signal and the dry cement ash mass flow estimated value, and the fourth output signal is executed by the cement ash flow regulating valve to control the dry cement ash flow.

In an alternative embodiment, the first PID control module generating the first output signal based on the cement slurry density setpoint and the first density measured by the equalization tank pump-out line densitometer further comprises:

the first PID control module calculates a first deviation of a cement paste density set value at a kth sampling time and a first density at the kth sampling time; the first output signal at the kth sample time is calculated based on the first offset at the kth sample time, the first offset at the kth-1 sample time, the first offset at the kth-2 sample time, and the first output signal at the kth-1 sample time.

In an alternative embodiment, the second PID control module generates the second output signal based on the first output signal and a second density measured by a mix tank recycle line densitometer further comprises:

calculating a second deviation of the first output signal at the kth sampling instant from the second density at the kth sampling instant; the second output signal at the kth sample time is calculated based on the second offset at the kth sample time, the second offset at the kth-1 sample time, the second offset at the kth-2 sample time, and the second output signal at the kth-1 sample time.

In an alternative embodiment, the dry cement ash flow calculation module calculates a dry cement ash mass flow estimate into the mixing tank from the first density, the second density, and the clear water flow measured by the clear water flow meter further comprising:

calculating the mass flow of overflow cement slurry overflowed from the slurry mixing tank to the equalizing tank at the kth sampling moment;

and calculating an estimated value of the dry cement ash mass flow entering the slurry mixing tank at the kth sampling moment according to the overflow cement slurry mass flow at the kth sampling moment, the second density at the kth-1 sampling moment and the clear water flow at the kth sampling moment.

In an alternative embodiment, calculating the overflow cement slurry mass flow from the mixing tank to the equalization tank at the kth sampling time further comprises: and calculating the mass flow of the overflow cement slurry overflowed from the slurry mixing tank to the balance tank at the kth sampling time according to the first density at the kth sampling time and the first density at the kth-1 sampling time.

In an alternative embodiment, calculating the overflow cement slurry mass flow from the mixing tank to the equalization tank at the kth sampling time based on the first density at the kth sampling time and the first density at the kth-1 sampling time further comprises: and calculating the mass flow of overflow cement slurry overflowed from the slurry mixing tank to the equalizing tank at the kth sampling moment according to the first density at the kth sampling moment, the first density at the kth-1 sampling moment, the equalizing tank liquid level at the kth sampling moment and the cement slurry displacement at the kth sampling moment.

In an alternative embodiment, the feedforward control module generating the third output signal based on the fresh water flow further includes: and generating a third output signal according to the cement paste density set value at the kth sampling moment and the clear water flow at the kth sampling moment.

In an alternative embodiment, the third PID control module generates a fourth output signal based on the second output signal, the third output signal, and the dry ash mass flow estimate, further comprising: calculating a third deviation of the kth sampling moment according to the second output signal of the kth sampling moment, the third output signal of the kth sampling moment and the dry cement ash mass flow estimation value of the kth sampling moment;

the fourth output signal at the kth sample time is calculated based on the third offset at the kth sample time, the third offset at the kth-1 sample time, the third offset at the kth-2 sample time, and the fourth output signal at the kth-1 sample time.

In the system and the method for controlling the density of the well cementation cement slurry, the control mode of combining cascade control and feedforward control is adopted, a first PID control module is used as a main controller, a loop formed by the first PID control module and a pump-out pipeline densimeter of an equalizing tank is used as a main control loop, a second PID control module is used as a secondary controller, a loop formed by the second PID control module and a circulating pipeline densimeter of a slurry mixing tank is used as a first secondary control loop, a third PID control module is used as another secondary controller, a loop formed by a third PID control module, a dry cement ash flow calculation module and a cement ash flow regulating valve is used as a second secondary control loop, and clear water flow is introduced by a feedforward module as feedforward information, so that the accuracy and stability of controlling the density of the well cementation cement slurry are improved. Therefore, the system can be used for quickly stabilizing the density of the well cementation cement slurry produced by the well cementation continuous slurry mixing system near a set value and improving the stability and accuracy of well cementation continuous slurry mixing density control.

The foregoing description is only an overview of the present invention, and is intended to be implemented in accordance with the teachings of the present invention in order that the same may be more clearly understood and to make the same and other objects, features and advantages of the present invention more readily apparent.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to designate like parts throughout the figures. In the drawings:

FIG. 1 shows a schematic diagram of a system for controlling density of a well cementing slurry according to an embodiment of the present invention;

FIG. 2 shows a schematic diagram of setting positions of a pump-out line densimeter of an equalization tank, a circulating line densimeter of a slurry mixing tank, a clear water flowmeter and a cement ash flow regulating valve according to an embodiment of the invention;

fig. 3 shows a schematic flow chart of a method for controlling density of a well cementing slurry according to an embodiment of the present invention.

Detailed Description

Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

In order to meet the requirement of large-displacement well cementation operation, the production mode of the well cementation cement paste which is commonly used at present is a continuous slurry mixing mode, and a system for producing the well cementation cement paste by adopting the continuous slurry mixing mode is a well cementation continuous slurry mixing system. Because cement paste is usually mixed by cement ash and clear water, a well cementation continuous slurry mixing system usually comprises an ash supply device, a water supply device, a slurry mixing tank and an equalizing tank. The cement mortar mixing device comprises a cement mortar feeding device, a cement mortar mixing tank, a water supply device, a mortar mixing tank, a balance tank and a mortar balancing tank, wherein the cement mortar feeding device is used for providing cement mortar, the water supply device is used for providing clear water, the mortar mixing tank is used for mixing and stirring the cement mortar and the clear water, and the balance tank is used for mixing and stirring the mortar which overflows from the mortar mixing tank again. The embodiment of the invention mainly aims at controlling the density of the well cementation continuous slurry mixing system.

Fig. 1 shows a schematic structural diagram of a well cementing slurry density control system according to an embodiment of the present invention. The cement paste density control system for well cementation provided by the embodiment of the invention is mainly used for controlling the cement paste density of the well cementation continuous slurry mixing system 200.

As shown in fig. 1, the well cementing slurry density control system 100 includes: the equalization tank pump-out line densitometer 110, the slurry tank circulation line densitometer 120, the clear water flow meter 130, the first PID control module 140, the second PID control module 150, the dry cement ash flow calculation module 160, the feedforward control module 170, the third PID control module 180, and the cement ash flow control valve 190.

Equalization tank pump-out line densitometer 110 is used to measure a first density of cement slurry in the equalization tank pump-out line in a well cementing continuous slurry system. Specifically, the equalization tank pump-out line densitometer 110 is disposed in the equalization tank pump-out line of the well cementation continuous slurry system, and the cement slurry is pumped out of the equalization tank to the bottom of the well, whereby the first density is the density of the cement slurry pumped downhole.

The mix tank circulation line densitometer 120 is used to measure a second density of the cement slurry in the mix tank circulation line in the well cementing continuous mix system. Specifically, the mix tank circulation line densitometer 120 is disposed in the mix tank circulation line of the well cementation continuous mixing system, whereby the second density is the density of cement slurry in the mix tank.

The clean water flow meter 130 is used to measure the clean water flow in a well cementing continuous slurry system. Specifically, the clean water flow meter 130 may be installed at the front end of the clean water inlet of the high-energy mixer, and the measured clean water flow is specifically the clean water flow currently supplied to the cement paste for mixing.

The first PID control module 140 is coupled to the equalization tank pump-out line densitometer 110 for generating a first output signal based on the cement slurry density set point and the first density. The balance tank pump-out line densimeter 110 transmits the measured first density of the cement slurry in the balance tank pump-out line to the first PID control module 140 through the communication connection with the first PID control module 140, and the first PID control module 140 uses the first density as a controlled variable, uses a cement slurry density set value as a set value of the module, and outputs a first output signal. The first PID control module 140 and the balance tank pump outlet densimeter 110 form a main control loop of the well cementation cement slurry density control system 100, so as to realize accurate control of the well cementation cement slurry density.

In an alternative embodiment, the first PID control module 140 is specifically configured to: calculating a first deviation of the cement paste density set value at the kth sampling moment from a first density at the kth sampling moment; and calculating a first output signal at the kth sampling moment according to the first deviation corresponding to the kth sampling moment, the first deviation corresponding to the kth-1 sampling moment, the first deviation corresponding to the kth-2 sampling moment and the first output signal of the kth-1 sampling moment. The deviation between the cement paste density set value at the kth sampling time and the first density at the kth sampling time is called the first deviation at the kth sampling time. In addition, the PID control module in the embodiment of the present invention is a controller based on a PID (Proportional-Integral-Derivative) control scheme, where the PID is a control scheme for controlling the Proportional, integral and Derivative of errors generated by comparing information collected by real-time data of a controlled object with a given value.

Further alternatively, the first deviation of the cement paste density set value at the kth sampling time from the first density at the kth sampling time may be calculated by the following formula 1:

e ₁ (k)＝p(k)-ρ ₁ (k) (equation 1)

In formula 1, e ₁ (k) For the first deviation of the kth sampling time, ρ (k) is the cement paste density set value of the kth sampling time, ρ ₁ (k) A first density at a kth sampling instant. Wherein, the unit of each density index in the embodiment of the invention can be kg/m ³ 。

Further alternatively, the first output signal at the kth sampling instant may be calculated by the following equation 2:

in formula 2, u ₁ (k) For the first output signal of k sampling instants, u ₁ (k-1) a first output signal of k-1 sampling instants, e ₁ (k) For the first deviation, e, of the kth sampling instant ₁ (k-1) is the first deviation of the (k-1) th sampling instant, e1 (k-2) is the (k-2) th sampling instantFirst deviation of sampling time, K _p1 T is the scaling factor in the first PID control module 140 _i1 T is the integral time coefficient in the first PID control module 140 _d1 Is the derivative time coefficient in the first PID control module 140, ts is the step size. Wherein the first output signal and the first deviation can be kg/min, k is an integer greater than or equal to 1, e ₁ (0)＝e ₁ (-1)＝0，u ₁ (0) Is the second density in the initial state. Preferably, K _p1 ＝8.5，T _i1 ＝0.5，T _d1 ＝0.1。

The second PID control module 150 is coupled to the mix tank recycle line densitometer 120 and the first PID control module 140 for generating a second output signal based on the first output signal and the second density. Specifically, the slurry tank circulation line densimeter 120 transmits the measured second density of the cement slurry in the slurry tank circulation line to the second PID control module 150 through the communication connection with the second PID control module 150, and the second PID control module 150 further uses the second density as the controlled variable of the module; the first PID control module 140 transmits the generated first output signal to the second PID control module 150 through communication connection with the second PID control module 150, the second PID control module 150 further uses the first output signal as a set value of the module, the cement slurry density in the slurry mixing tank is adjusted to achieve that the cement slurry pumped out by the equalizing tank is always controlled near the density set value, and finally, the second output signal is generated based on the second density and the first output signal. The second PID control module 150 and the mixing tank circulation pipeline densimeter 120 form a first secondary loop in the well cementation cement slurry density control system, so that the disturbance of the vacuum jet pump characteristic change, the circulation pump characteristic change and the like on the density control can be eliminated.

In an alternative embodiment, the second PID control module 150 is specifically configured to: calculating a second deviation of the first output signal at the kth sampling instant from the second density at the kth sampling instant; the second output signal at the kth sample time is calculated based on the second offset at the kth sample time, the second offset at the kth-1 sample time, the second offset at the kth-2 sample time, and the second output signal at the kth-1 sample time. Wherein the deviation between the first output signal at the kth sampling instant and the second density at the kth sampling instant is referred to as a second deviation at the kth sampling instant.

Further alternatively, the second deviation of the first output signal at the kth sampling instant from the second density at the kth sampling instant may be calculated by the following formula 3:

e ₂ (k)＝u ₁ (k)-p ₂ (k) (equation 3)

In equation 3, e ₂ (k) For the second deviation (kg/min) of the kth sampling instant, u ₁ (k) For a first output signal of k sample instants ρ ₂ (k) A second density for the kth sample time.

Further alternatively, the first output signal at the kth sampling instant may be calculated by the following equation 4:

in formula 4, u ₂ (k) For the second output signal of k sampling instants, u ₂ (k-1) a second output signal of k-1 sampling instants e ₂ (k) For the second deviation of the kth sampling instant e ₂ (k-1) is the second deviation of the (k-1) th sampling time, e ₂ (K-2) is the second deviation of the (K-2) th sampling time, K _p2 T is the scaling factor in the second PID control module 150 _i2 T is the integral time coefficient in the second PID control module 150 _d2 Is the derivative time coefficient in the second PID control module 150, ts is the step size. Wherein the second output signal and the second deviation may have a unit of kg/m ³ K is an integer greater than or equal to 1, e ₂ (0)＝e ₂ (-1)＝0，u ₂ (0) =0. Preferably, K _p2 ＝25.8，T _i2 ＝2，T _d2 ＝0.8。

The dry cement ash flow calculation module 160 is coupled to the equalization tank pump-out line densitometer 110, the mix tank recycle line densitometer 120, and the clean water flow meter 130 for calculating a dry cement ash mass flow estimate into the mix tank based on the first density, the second density, and the clean water flow meter. Specifically, the equalization tank pump-out line densimeter 110 transmits the measured first density of the cement slurry in the equalization tank pump-out line to the dry cement ash flow calculation module 160 through a communication connection with the dry cement ash flow calculation module 160, the mixing tank circulation line densimeter 120 transmits the measured second density of the cement slurry in the mixing tank circulation line to the dry cement ash flow calculation module 160 through a communication connection with the dry cement ash flow calculation module 160, and the clean water flow meter 130 transmits the measured clean water flow to the dry cement ash flow calculation module 160 through a communication connection with the dry cement ash flow calculation module 160. The dry cement ash flow calculation module 160 obtains a dry cement ash mass flow estimate into the mixing tank based on the obtained measurements.

In an alternative embodiment, the dry cement ash flow calculation module 160 is specifically configured to: calculating the mass flow of overflow cement slurry overflowed from the slurry mixing tank to the equalizing tank at the kth sampling moment; and calculating an estimated value of the mass flow of the dry cement ash entering the mixing tank at the kth moment according to the mass flow of the overflow cement slurry at the kth sampling moment, the second density at the kth-1 sampling moment and the clear water flow at the kth sampling moment.

Further alternatively, the mass flow rate of overflow cement slurry from the mixing tank to the equalization tank at the kth sampling time may be calculated based on the first density at the kth sampling time and the first density at the kth-1 sampling time.

The cementing slurry density control system 100 also includes, among other things, a equalization tank level gauge (not shown) and an equalization tank pump-out line displacement detector (not shown). The equalizing tank liquid level meter is arranged in the equalizing tank and is used for measuring the liquid level of the equalizing tank; the balance tank pump-out pipeline is arranged in the pump-out pipeline at the bottom of the balance tank and used for measuring the cement paste displacement in the balance tank pump-out pipeline.

The dry cement ash flow calculation module is connected with the balance tank liquid level meter and the balance tank pump outlet discharge capacity detector and is used for calculating the overflow cement slurry mass flow from the slurry mixing tank to the balance tank at the kth sampling moment according to the first density at the kth sampling moment, the first density at the kth-1 sampling moment, the balance tank liquid level at the kth sampling moment and the cement slurry discharge capacity at the kth sampling moment. Specifically, the mass flow rate of the overflow cement slurry overflowed from the slurry mixing tank to the balancing tank can be calculated by the following formula 5:

In formula 5, F ₁₂ (k) For the k sampling instant, the mass flow (kg/min) of overflow cement slurry overflowed from the slurry mixing tank to the equalizing tank, F _out (k) Equalizing cement slurry displacement (kg/min) in tank pump-out line for kth sampling time, A ₁ To equalize the cross-sectional area (m) ² ) H (k) is the equalization tank level (m), ρ at the kth sampling instant ₁ (k) For the first density, ρ, at the kth sampling instant ₁ (k-1) is the first density at the (k-1) th sampling instant, ts is the step size, and ρ is set when k=1 ₁ (0)＝0。

Further alternatively, the estimated dry cement ash mass flow into the mixing tank at the kth sampling time can be obtained from the mass flow of overflow cement slurry overflowed from the mixing tank to the equalizing tank at the kth sampling time according to the following formula 6:

in formula 6, F _c (k) For the estimated value (kg/min) of the mass flow of the dry cement ash entering the slurry mixing tank at the kth sampling moment, F ₁₂ (k) For the k sampling instant, the mass flow (kg/min) of overflow cement slurry overflowed from the slurry mixing tank to the equalizing tank, F _w (k) For the fresh water flow (kg/min) at the kth sampling time, A ₂ Is the cross section area (m) ² )，h ₀ The height (m) and ρ of the overflow baffle between the slurry mixing tank and the equalizing tank ₂ (k) A second density, ρ, for the kth sampling instant ₂ (k-1) is the second density at the kth-1 sampling instant, ts is the step size, when k= 1, set ρ ₂ (0)＝0。

The feedforward control module 170 is connected to the clean water flow meter 130 for generating a third output signal according to the clean water flow. The clear water flow meter 130 transmits the measured clear water flow to the feedforward control module 170 through communication connection with the feedforward control module 170, and the feedforward control module 170 generates a third output signal according to the clear water flow, so that the clear water flow is introduced into the control loop, and the dry cement ash flow is correspondingly regulated when the clear water flow changes, so that the stability of the density of the well cementation cement slurry in the control process is realized.

In an alternative embodiment, the feedforward control module 170 is specifically configured to: and generating a third output signal according to the cement paste density set value at the kth sampling moment and the clear water flow at the kth sampling moment. For example, the third output signal may be calculated by the following equation 7:

in formula 7, F _f (k) For the third output signal (kg/min) at the kth sampling instant, F _w (k) For the k-th sampling instant clear water flow (kg/min), ρ _c Is dry cement ash density (kg/m) ³ ),ρ _w Density of clear water (kg/m) ³ ) ρ (k) is the cement paste density set value (kg/m) at the kth sampling time ³ )。

The third PID control module 180 is connected to the second PID control module 150, the dry ash flow calculation module 160, and the feedforward control module 170, and is configured to generate a fourth output signal according to the second output signal, the third output signal, and the dry ash mass flow estimation value. The second PID control module 150 transmits the generated second output signal to the third PID control module 180 through a communication connection with the third PID control module 180, the dry cement ash flow calculation module 160 transmits the generated dry cement ash mass flow rate estimation value to the third PID control module 180 through a communication connection with the third PID control module 180, and the feedforward control module 170 transmits the generated third output signal to the third PID control module 180 through a communication connection with the third PID control module 180. The third PID control module 180 is used as a second secondary controller in the well cementing slurry density control system and forms a second secondary loop with the dry cement ash flow calculation module 160. The third PID control module 180 specifically uses the second output signal and the third output signal as the set values of the module, and adjusts the flow rate of the dry cement entering the slurry mixing tank to control the cement slurry density in the slurry mixing tank.

In an alternative embodiment, the third PID control module 180 is specifically configured to: calculating a third deviation of the kth sampling moment according to the second output signal of the kth sampling moment, the third output signal of the kth sampling moment and the dry cement ash mass flow estimation value of the kth sampling moment; the fourth output signal at the kth sample time is calculated based on the third offset at the kth sample time, the third offset at the kth-1 sample time, the third offset at the kth-2 sample time, and the fourth output signal at the kth-1 sample time.

Further alternatively, the third deviation of the kth sampling instant may be calculated by the following equation 8:

e ₃ (k)＝u ₂ (k)+F _f (k)-F _c (k) (equation 8)

In equation 8, e ₃ (k) For the third deviation (kg/min) of the kth sampling instant, u ₂ (k) For the second output signal of k sampling instants, F _f (k) A third output signal F for the kth sampling time _c (k) The estimated value (kg/min) of the mass flow of the dry cement ash entering the slurry mixing tank at the kth sampling moment.

Further alternatively, the fourth output signal at the kth sampling instant may be calculated by the following equation 9:

in formula 9, u ₃ (k) A fourth output signal (kg/min) of k sampling instants, u ₃ (k-1) a fourth output signal of k-1 sampling instants e ₃ (k) Is the kthThird deviation of sampling time, e ₃ (k-1) is the third deviation of the (k-1) th sampling time, e ₃ (K-2) is the third deviation of the (K-2) th sampling time, K _p3 T is the scaling factor in the third PID control module 180 _i3 For the integral time coefficient, T, in the third PID control module 180 _d3 Is the derivative time coefficient in the third PID control module 180, ts is the step size. Wherein the unit of the fourth output signal and the third deviation can be kg/min, k is an integer greater than or equal to 1, e ₃ (0)＝e ₃ (-1) =0. Preferably, K _p3 ＝40.2，T _i2 ＝0.1，T _d2 ＝1。

The cement ash flow control valve 190, which may also be referred to as a lower ash valve, is coupled to the third PID control module 180 for executing a fourth output signal to control the dry cement ash flow.

In an alternative embodiment, the setting positions of the pump-out line densitometer of the equalization tank, the circulating line densitometer of the slurry mixing tank, the clear water flowmeter and the cement ash flow regulating valve are shown in fig. 2. As shown in fig. 2, after the balance tank pump-out line densimeter 110 is disposed at the filling pump of the balance tank pump-out line, the slurry mixing tank circulation line densimeter 120 is disposed at the slurry mixing tank circulation line, the clean water flow meter 130 is disposed at the front end of the clean water inlet of the high-energy mixer, and the cement ash flow rate adjusting valve 190 is disposed below the ash supplying device. In addition, the ash supply device, the water purge valve, the high-energy mixer, the slurry mixing tank, the equalizing tank, the circulating pump and the filling pump shown in fig. 2 can refer to the structure and the function in the prior art, and the present invention is not repeated herein.

Therefore, the system for controlling the density of the well cementation cement slurry provided by the embodiment of the invention adopts a control mode of combining cascade control and feedforward control, takes the first PID control module as a main controller and takes a loop formed by the first PID control module and the balance tank pump-out pipeline densimeter as a main control loop, takes the second PID control module as a secondary controller and takes a loop formed by the second PID control module and the slurry mixing tank circulating pipeline densimeter as a first secondary control loop, takes the third PID control module as another secondary controller and takes a loop formed by the third PID control module, the dry cement ash flow calculation module and the cement ash flow regulating valve as a second secondary control loop, and takes the feedforward module to introduce clear water flow as feedforward information, thereby improving the accuracy and stability of controlling the density of the well cementation cement slurry. Therefore, the system can be used for quickly stabilizing the density of the well cementation cement slurry produced by the well cementation continuous slurry mixing system near a set value and improving the stability and accuracy of well cementation continuous slurry mixing density control.

Fig. 3 shows a schematic flow chart of a method for controlling density of a well cementing slurry according to an embodiment of the present invention. The well cementation cement paste density control method is used for controlling the cement paste density of a well cementation continuous slurry mixing system, and as shown in figure 3, the well cementation cement paste density control method comprises the following steps:

In step S310, the first PID control module generates a first output signal based on the cement slurry density set point and the first density measured by the equalization tank pump-out line densitometer.

In step S320, the second PID control module generates a second output signal according to the first output signal and a second density measured by the slurry tank circulation line densimeter.

Step S330, the dry cement ash flow calculation module calculates the dry cement ash mass flow estimation value of the slurry mixing tank according to the first density, the second density and the clear water flow meter measured by the clear water flow meter.

In step S340, the feedforward control module generates a third output signal according to the flow of clean water.

In step S350, the third PID control module generates a fourth output signal according to the second output signal, the third output signal and the estimated dry cement ash mass flow rate, so as to execute the fourth output signal by the cement ash flow rate adjusting valve to control the dry cement ash flow rate.

The specific functions of each module and the sensor related to the method may be described with reference to the embodiment of fig. 1, which is not described herein.

In an alternative embodiment, the first PID control module generating the first output signal based on the cement slurry density setpoint and the first density measured by the equalization tank pump-out line densitometer further comprises:

The first PID control module calculates a first deviation of a cement paste density set value at a kth sampling time and a first density at the kth sampling time; the first output signal at the kth sample time is calculated based on the first offset at the kth sample time, the first offset at the kth-1 sample time, the first offset at the kth-2 sample time, and the first output signal at the kth-1 sample time.

In an alternative embodiment, the second PID control module generates the second output signal based on the first output signal and a second density measured by a mix tank recycle line densitometer further comprises:

calculating a second deviation of the first output signal at the kth sampling instant from the second density at the kth sampling instant; the second output signal at the kth sample time is calculated based on the second offset at the kth sample time, the second offset at the kth-1 sample time, the second offset at the kth-2 sample time, and the second output signal at the kth-1 sample time.

In an alternative embodiment, the dry cement ash flow calculation module calculates a dry cement ash mass flow estimate into the mixing tank from the first density, the second density, and the clear water flow measured by the clear water flow meter further comprising:

Calculating the mass flow of overflow cement slurry overflowed from the slurry mixing tank to the equalizing tank at the kth sampling moment;

and calculating an estimated value of the dry cement ash mass flow entering the slurry mixing tank at the kth sampling moment according to the overflow cement slurry mass flow at the kth sampling moment, the second density at the kth-1 sampling moment and the clear water flow at the kth sampling moment.

In an alternative embodiment, calculating the overflow cement slurry mass flow from the mixing tank to the equalization tank at the kth sampling time further comprises: and calculating the mass flow of the overflow cement slurry overflowed from the slurry mixing tank to the balance tank at the kth sampling time according to the first density at the kth sampling time and the first density at the kth-1 sampling time.

In an alternative embodiment, calculating the overflow cement slurry mass flow from the mixing tank to the equalization tank at the kth sampling time based on the first density at the kth sampling time and the first density at the kth-1 sampling time further comprises: and calculating the mass flow of overflow cement slurry overflowed from the slurry mixing tank to the equalizing tank at the kth sampling moment according to the first density at the kth sampling moment, the first density at the kth-1 sampling moment, the equalizing tank liquid level at the kth sampling moment and the cement slurry displacement at the kth sampling moment.

In an alternative embodiment, the feedforward control module generating the third output signal based on the fresh water flow further includes: and generating a third output signal according to the cement paste density set value at the kth sampling moment and the clear water flow at the kth sampling moment.

In an alternative embodiment, the third PID control module generates a fourth output signal based on the second output signal, the third output signal, and the dry ash mass flow estimate, further comprising: calculating a third deviation of the kth sampling moment according to the second output signal of the kth sampling moment, the third output signal of the kth sampling moment and the dry cement ash mass flow estimation value of the kth sampling moment;

the fourth output signal at the kth sample time is calculated based on the third offset at the kth sample time, the third offset at the kth-1 sample time, the third offset at the kth-2 sample time, and the fourth output signal at the kth-1 sample time.

Therefore, the adoption of the scheme can enable the density of the well cementation cement slurry produced by the well cementation continuous slurry mixing system to be quickly stabilized near the set value, and improve the stability and accuracy of the well cementation continuous slurry mixing density control.

The algorithms or displays presented herein are not inherently related to any particular computer, virtual system, or other apparatus. Various general-purpose systems may also be used with the teachings herein. The required structure for a construction of such a system is apparent from the description above. In addition, embodiments of the present invention are not directed to any particular programming language. It will be appreciated that the teachings of the present invention described herein may be implemented in a variety of programming languages, and the above description of specific languages is provided for disclosure of enablement and best mode of the present invention.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Similarly, it should be appreciated that in the above description of exemplary embodiments of the invention, various features of the embodiments of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. However, the disclosed method should not be construed as reflecting the intention that: i.e., the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Those skilled in the art will appreciate that the modules in the apparatus of the embodiments may be adaptively changed and disposed in one or more apparatuses different from the embodiments. The modules or units or components of the embodiments may be combined into one module or unit or component and, furthermore, they may be divided into a plurality of sub-modules or sub-units or sub-components. Any combination of all features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the processes or units of any method or apparatus so disclosed, may be used in combination, except insofar as at least some of such features and/or processes or units are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.

Furthermore, those skilled in the art will appreciate that while some embodiments herein include some features but not others included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the following claims, any of the claimed embodiments can be used in any combination.

Various component embodiments of the invention may be implemented in hardware, or in software modules running on one or more processors, or in a combination thereof. Those skilled in the art will appreciate that some or all of the functionality of some or all of the components according to embodiments of the present invention may be implemented in practice using a microprocessor or Digital Signal Processor (DSP). The present invention can also be implemented as an apparatus or device program (e.g., a computer program and a computer program product) for performing a portion or all of the methods described herein. Such a program embodying the present invention may be stored on a computer readable medium, or may have the form of one or more signals. Such signals may be downloaded from an internet website, provided on a carrier signal, or provided in any other form.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the unit claims enumerating several means, several of these means may be embodied by one and the same item of hardware. The use of the words first, second, third, etc. do not denote any order. These words may be interpreted as names. The steps in the above embodiments should not be construed as limiting the order of execution unless specifically stated.

Claims (10)

1. A well cementing slurry density control system for controlling the slurry density of a well cementing continuous slurry mixing system, the well cementing slurry density control system comprising: the system comprises an equalizing tank pump outlet line densimeter, a slurry mixing tank circulating line densimeter, a clear water flowmeter, a first PID control module, a second PID control module, a feedforward control module, a dry cement ash flow calculation module, a third PID control module and a cement ash flow regulating valve;

the balance tank pump-out pipeline densimeter is used for measuring the first density of cement slurry in the balance tank pump-out pipeline in the well cementation continuous slurry mixing system; the slurry mixing tank circulating pipeline densimeter is used for measuring the second density of the cement slurry in the slurry mixing tank circulating pipeline in the well cementation continuous slurry mixing system; the clear water flowmeter is used for measuring clear water flow in the well cementation continuous slurry mixing system;

the first PID control module is connected with the pump-out pipeline densimeter of the equalizing tank and is used for generating a first output signal according to the cement paste density set value and the first density;

the second PID control module is connected with the slurry mixing tank circulating pipeline densimeter and the first PID control module and is used for generating a second output signal according to the first output signal and the second density;

The dry cement ash flow calculation module is connected with the balance tank pump-out pipeline densimeter, the slurry mixing tank circulation pipeline densimeter and the clear water flowmeter and is used for calculating a dry cement ash mass flow estimated value which enters the slurry mixing tank according to the first density, the second density and the clear water flowmeter;

the feedforward control module is connected with the clear water flowmeter and is used for generating a third output signal according to the clear water flow;

the third PID control module is connected with the second PID control module, the dry cement ash flow calculation module and the feedforward control module and is used for generating a fourth output signal according to the second output signal, the third output signal and the dry cement ash mass flow estimation value;

the cement ash flow regulating valve is connected with the third PID control module and is used for executing the fourth output signal to control the dry cement ash flow.

2. The well cementing slurry density control system of claim 1, wherein the first PID control module is specifically configured to:

calculating a first deviation of the cement paste density set value at the kth sampling moment from a first density at the kth sampling moment;

the first output signal at the kth sample time is calculated based on the first offset at the kth sample time, the first offset at the kth-1 sample time, the first offset at the kth-2 sample time, and the first output signal at the kth-1 sample time.

3. The well cementing slurry density control system of claim 2, wherein the second PID control module is specifically configured to:

calculating a second deviation of the first output signal at the kth sampling instant from the second density at the kth sampling instant;

the second output signal at the kth sample time is calculated based on the second offset at the kth sample time, the second offset at the kth-1 sample time, the second offset at the kth-2 sample time, and the second output signal at the kth-1 sample time.

4. A cement paste density control system according to any one of claims 1 to 3, wherein the dry cement ash flow calculation module is specifically configured to:

calculating the mass flow of overflow cement slurry overflowed from the slurry mixing tank to the equalizing tank at the kth sampling moment;

and calculating an estimated value of the dry cement ash mass flow entering the slurry mixing tank at the kth sampling moment according to the overflow cement slurry mass flow at the kth sampling moment, the second density at the kth-1 sampling moment and the clear water flow at the kth sampling moment.

5. The well cementing slurry density control system of claim 4, wherein the dry cement ash flow calculation module is specifically configured to:

And calculating the mass flow of the overflow cement slurry overflowed from the slurry mixing tank to the balance tank at the kth sampling time according to the first density at the kth sampling time and the first density at the kth-1 sampling time.

6. The well cementing slurry density control system of claim 5, further comprising:

the equalizing tank liquid level meter is used for measuring the liquid level of the equalizing tank;

and the balance tank pump-out pipeline displacement detector is used for measuring the cement paste displacement in the balance tank pump-out pipeline.

7. The well cementing slurry density control system of claim 6, wherein the dry cement ash flow calculation module is coupled to the equalization tank level gauge and the equalization tank pump outlet displacement detector for calculating an overflow cement slurry mass flow from the mixing tank to the equalization tank at the kth sampling time based on the first density at the kth sampling time, the first density at the kth-1 sampling time, the equalization tank level at the kth sampling time, and the cement slurry displacement at the kth sampling time.

8. A well cementing slurry density control system according to any one of claims 1 to 3, wherein the feedforward control module is specifically configured to:

And generating a third output signal according to the cement paste density set value at the kth sampling moment and the clear water flow at the kth sampling moment.

9. A cement slurry density control system according to any one of claims 1 to 3, wherein the third PID control module is specifically configured to:

calculating a third deviation of the kth sampling moment according to the second output signal of the kth sampling moment, the third output signal of the kth sampling moment and the dry cement ash mass flow estimation value of the kth sampling moment;

the fourth output signal at the kth sample time is calculated based on the third offset at the kth sample time, the third offset at the kth-1 sample time, the third offset at the kth-2 sample time, and the fourth output signal at the kth-1 sample time.

10. The well cementation cement paste density control method is used for controlling the cement paste density of a well cementation continuous slurry mixing system and is characterized by comprising the following steps:

the first PID control module generates a first output signal according to a cement paste density set value and a first density measured by the balance tank pump outlet densimeter;

The second PID control module generates a second output signal according to the first output signal and the second density measured by the slurry mixing tank circulating pipeline densimeter;

the dry cement ash flow calculation module calculates a dry cement ash mass flow estimated value which enters the slurry mixing tank according to the first density, the second density and the clear water flow measured by the clear water flow meter;

the feedforward control module generates a third output signal according to the clear water flow;

and the third PID control module generates a fourth output signal according to the second output signal, the third output signal and the dry cement ash mass flow estimated value, and the fourth output signal is executed by the cement ash flow regulating valve to control the dry cement ash flow.

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