Cement slurry density control system and method

Abstract

The present invention discloses a density control system and method for cement slurry in cementing. The system includes: a first PID control module generates a first output signal based on the set value of the cement slurry density and a first density; a second PID control module generates a second output signal based on the first output signal and a second density; a dry cement ash flow calculation module calculates an estimated mass flow rate of dry cement ash entering the mixing tank according to the first density, the second density, and the clear water flow rate; a feedforward control module generates a third output signal according to the clear water flow rate; a third PID control module generates a fourth output signal based on the second output signal, the third output signal, and the estimated mass flow rate of dry cement ash; a cement ash flow regulating valve executes the fourth output signal to control the dry cement ash flow rate. By adopting this solution, it is possible to quickly stabilize the density of the cement slurry for cementing produced by the continuous cement mixing system near the set value, and improve the stability and accuracy of the density control of the continuous cement mixing for cementing.

Description

Technical Field

[0001] The present invention relates to the field of exploration technology, and particularly to a density control system and method for cement slurry in cementing operation. Background Art

[0002] Cementing is a key link connecting drilling engineering and oil production engineering. It is a process of pumping a certain density and a certain volume of cement slurry into the bottom of the well at a certain rate under specific high-pressure conditions, so as to isolate oil layers, gas layers and water layers in the wellbore, protect the casing of oil and gas wells, extend the service life of oil and gas wells, and increase oil and gas production, etc.

[0003] During the cementing process, the density control of the cement slurry in cementing is of great significance for cementing quality, exploration safety, oil and gas reservoir protection, anti-corrosion and anti-channeling. In the prior art, a single-loop PID control method is usually used to achieve the density control of continuous cement slurry mixing in cementing. However, the accuracy of the density control of continuous cement slurry mixing by this density control method is insufficient, the stability is low, and the control efficiency is low. Summary of the Invention

[0004] In view of the above problems, the present invention is proposed to provide a density control system and method for cement slurry in cementing that overcomes the above problems or at least partially solves the above problems.

[0005] According to one aspect of the present invention, a density control system for cement slurry in cementing is provided. The density control system for cement slurry in cementing is used to control the density of the cement slurry in the continuous cement slurry mixing system. The density control system for cement slurry in cementing includes: a density meter for the pump-out pipeline of the equalizing tank, a density meter for the circulation pipeline of the mixing tank, 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;

[0006] Among them, the density meter for the pump-out pipeline of the equalizing tank is used to measure the first density of the cement slurry in the pump-out pipeline of the equalizing tank in the continuous cement slurry mixing system; the density meter for the circulation pipeline of the mixing tank is used to measure the second density of the cement slurry in the circulation pipeline of the mixing tank in the continuous cement slurry mixing system; the clear water flowmeter is used to measure the clear water flow in the continuous cement slurry mixing system;

[0007] The first PID control module is connected to the density meter for the pump-out pipeline of the equalizing tank, and is used to generate a first output signal according to the set value of the cement slurry density and the first density;

[0008] The second PID control module is connected to the density meter for the circulation pipeline of the mixing tank and the first PID control module, and is used to generate a second output signal according to the first output signal and the second density;

[0009] The dry cement ash flow calculation module is connected to the density meter of the balanced tank pump-out pipeline, the density meter of the mud mixing tank circulation pipeline, and the clean water flow meter, and is used to calculate the estimated mass flow rate of dry cement ash entering the mud mixing tank according to the first density, the second density, and the clean water flow rate;

[0010] The feedforward control module is connected to the clean water flow meter and is used to generate a third output signal according to the clean water flow rate;

[0011] The third PID control module is connected to the second PID control module, the dry cement ash flow calculation module, and the feedforward control module, and is used to generate a fourth output signal according to the second output signal, the third output signal, and the estimated mass flow rate of dry cement ash;

[0012] The cement ash flow regulating valve is connected to the third PID control module and is used to execute the fourth output signal to control the dry cement ash flow rate.

[0013] In an alternative embodiment, the first PID control module is specifically configured to:

[0014] Calculate the first deviation between the set value of the cement slurry density at the k-th sampling moment and the first density at the k-th sampling moment;

[0015] Calculate the first output signal at the k-th sampling moment according to the first deviation at the k-th sampling moment, the first deviation at the (k - 1)-th sampling moment, the first deviation at the (k - 2)-th sampling moment, and the first output signal at the (k - 1)-th sampling moment.

[0016] In an alternative embodiment, the second PID control module is specifically configured to:

[0017] Calculate the second deviation between the first output signal at the k-th sampling moment and the second density at the k-th sampling moment;

[0018] Calculate the second output signal at the k-th sampling moment according to the second deviation at the k-th sampling moment, the second deviation at the (k - 1)-th sampling moment, the second deviation at the (k - 2)-th sampling moment, and the second output signal at the (k - 1)-th sampling moment.

[0019] In an alternative embodiment, the dry cement ash flow calculation module is specifically configured to:

[0020] Calculate the mass flow rate of the overflow cement slurry overflowing from the mud mixing tank to the balanced tank at the k-th sampling moment;

[0021] Calculate the estimated mass flow rate of dry cement ash entering the mud mixing tank at the k-th sampling moment according to the mass flow rate of the overflow cement slurry at the k-th sampling moment, the second density at the k-th sampling moment, the second density at the (k - 1)-th sampling moment, and the clean water flow rate at the k-th sampling moment.

[0022] In an alternative embodiment, the dry cement ash flow calculation module is specifically configured to:

[0023] Calculate the mass flow rate of the overflow cement slurry flowing from the mud mixing tank to the equalizing tank at the k-th sampling moment based on the first density at the k-th sampling moment and the first density at the (k - 1)-th sampling moment.

[0024] In an alternative embodiment, the cement slurry density control system for well cementing further includes:

[0025] An equalizing tank level gauge for measuring the level of the equalizing tank;

[0026] A displacement detector for the pump-out pipeline of the equalizing tank for measuring the displacement of the cement slurry in the pump-out pipeline of the equalizing tank.

[0027] In an alternative embodiment, the dry cement ash flow calculation module is connected to the equalizing tank level gauge and the displacement detector for the pump-out pipeline of the equalizing tank, and is configured to calculate the mass flow rate of the overflow cement slurry flowing from the mud mixing tank to the equalizing tank at the k-th sampling moment based on the first density at the k-th sampling moment, the first density at the (k - 1)-th sampling moment, the level of the equalizing tank at the k-th sampling moment, and the displacement of the cement slurry at the k-th sampling moment.

[0028] In an alternative embodiment, the feedforward control module is specifically configured to:

[0029] Generate a third output signal based on the set value of the cement slurry density at the k-th sampling moment and the flow rate of clear water at the k-th sampling moment.

[0030] In an alternative embodiment, the third PID control module is specifically configured to:

[0031] Calculate the third deviation at the k-th sampling moment based on the second output signal at the k-th sampling moment, the third output signal at the k-th sampling moment, and the estimated value of the dry cement ash mass flow rate at the k-th sampling moment;

[0032] Calculate the fourth output signal at the k-th sampling moment based on the third deviation at the k-th sampling moment, the third deviation at the (k - 1)-th sampling moment, the third deviation at the (k - 2)-th sampling moment, and the fourth output signal at the (k - 1)-th sampling moment.

[0033] According to another aspect of the present invention, there is provided a method for controlling the density of well cementing cement slurry. The method for controlling the density of well cementing cement slurry is used to control the density of the cement slurry in a continuous mud mixing system for well cementing, and the method for controlling the density of well cementing cement slurry includes:

[0034] The first PID control module generates a first output signal based on the set value of the cement slurry density and the first density measured by the density gauge for the pump-out pipeline of the equalizing tank;

[0035] The second PID control module generates a second output signal based on the first output signal and the second density measured by the density meter in the circulation pipeline of the mud mixing tank;

[0036] The dry cement ash flow calculation module calculates an estimated value of the mass flow rate of dry cement ash entering the mud mixing tank based on the first density, the second density, and the clear water flow rate measured by the clear water flow meter;

[0037] The feedforward control module generates a third output signal based on the clear water flow rate;

[0038] The third PID control module generates a fourth output signal based on the second output signal, the third output signal, and the estimated value of the dry cement ash mass flow rate, for the cement ash flow regulating valve to execute the fourth output signal to control the dry cement ash flow rate.

[0039] In an alternative embodiment, the first PID control module generating the first output signal based on the set value of the cement slurry density and the first density measured by the density meter in the pump-out pipeline of the equalizing tank further includes:

[0040] The first PID control module calculates a first deviation between the set value of the cement slurry density at the k-th sampling moment and the first density at the k-th sampling moment; based on the first deviation at the k-th sampling moment, the first deviation at the (k - 1)-th sampling moment, the first deviation at the (k - 2)-th sampling moment, and the first output signal at the (k - 1)-th sampling moment, calculates the first output signal at the k-th sampling moment.

[0041] In an alternative embodiment, the second PID control module generating the second output signal based on the first output signal and the second density measured by the density meter in the circulation pipeline of the mud mixing tank further includes:

[0042] Calculates a second deviation between the first output signal at the k-th sampling moment and the second density at the k-th sampling moment; based on the second deviation at the k-th sampling moment, the second deviation at the (k - 1)-th sampling moment, the second deviation at the (k - 2)-th sampling moment, and the second output signal at the (k - 1)-th sampling moment, calculates the second output signal at the k-th sampling moment.

[0043] In an alternative embodiment, the dry cement ash flow calculation module calculating the estimated value of the mass flow rate of dry cement ash entering the mud mixing tank based on the first density, the second density, and the clear water flow rate measured by the clear water flow meter further includes:

[0044] Calculates the mass flow rate of the overflow cement slurry overflowing from the mud mixing tank to the equalizing tank at the k-th sampling moment;

[0045] Calculate the estimated mass flow rate of dry cement ash entering the mud mixing tank at the k-th sampling moment based on the mass flow rate of overflowing cement slurry at the k-th sampling moment, the second density at the k-th sampling moment, the second density at the (k - 1)-th sampling moment, and the water flow rate at the k-th sampling moment.

[0046] In an alternative embodiment, calculating the mass flow rate of overflowing cement slurry from the mud mixing tank to the equalizing tank at the k-th sampling moment further includes: calculating the mass flow rate of overflowing cement slurry from the mud mixing tank to the equalizing tank at the k-th sampling moment based on the first density at the k-th sampling moment and the first density at the (k - 1)-th sampling moment.

[0047] In an alternative embodiment, calculating the mass flow rate of overflowing cement slurry from the mud mixing tank to the equalizing tank at the k-th sampling moment based on the first density at the k-th sampling moment and the first density at the (k - 1)-th sampling moment further includes: calculating the mass flow rate of overflowing cement slurry from the mud mixing tank to the equalizing tank at the k-th sampling moment based on the first density at the k-th sampling moment, the first density at the (k - 1)-th sampling moment, the liquid level of the equalizing tank at the k-th sampling moment, and the cement slurry displacement at the k-th sampling moment.

[0048] In an alternative embodiment, the feedforward control module generating the third output signal based on the water flow rate further includes: generating the third output signal based on the set value of the cement slurry density at the k-th sampling moment and the water flow rate at the k-th sampling moment.

[0049] In an alternative embodiment, the third PID control module generating the fourth output signal based on the second output signal, the third output signal, and the estimated mass flow rate of dry cement ash further includes: calculating the third deviation at the k-th sampling moment based on the second output signal at the k-th sampling moment, the third output signal at the k-th sampling moment, and the estimated mass flow rate of dry cement ash at the k-th sampling moment;

[0050] Calculate the fourth output signal at the k-th sampling moment based on the third deviation at the k-th sampling moment, the third deviation at the (k - 1)-th sampling moment, the third deviation at the (k - 2)-th sampling moment, and the fourth output signal at the (k - 1)-th sampling moment.

[0051] In the cement slurry density control system and method disclosed by the present invention, the provided cement slurry density control system adopts a control method combining cascade control and feedforward control. The first PID control module serves as the main controller, and the loop formed by the first PID control module and the density meter on the pump-out pipeline of the equalizing tank serves as the main control loop. The second PID control module serves as a secondary controller, and the loop formed by the second PID control module and the density meter on the circulation pipeline of the mud mixing tank serves as the first secondary control loop. The third PID control module serves as another secondary controller, and the loop formed by the third PID control module, the dry cement ash flow calculation module, and the cement ash flow regulating valve serves as the second secondary control loop. In addition, the feedforward module introduces the clear water flow as feedforward information, improving the accuracy and stability of the cement slurry density control for well cementing. Therefore, using this system can quickly stabilize the density of the well cementing cement slurry produced by the continuous mud mixing system for well cementing near the set value, and improve the stability and accuracy of the density control of the continuous mud mixing for well cementing.

[0052] The above description is only an overview of the technical solution of the present invention. In order to understand the technical means of the present invention more clearly, it can be implemented according to the content of the specification. In order to make the above and other purposes, features, and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention are given below. Brief Description of the Drawings

[0053] By reading the detailed description of the preferred embodiments below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0054] Figure 1 shows a schematic structural diagram of a cement slurry density control system for well cementing provided by an embodiment of the present invention;

[0055] Figure 2 shows a schematic diagram of the installation positions of a density meter on the pump-out pipeline of the equalizing tank, a density meter on the circulation pipeline of the mud mixing tank, a clear water flowmeter, and a cement ash flow regulating valve provided by an embodiment of the present invention;

[0056] Figure 3 shows a schematic flowchart of a cement slurry density control method for well cementing provided by an embodiment of the present invention. Detailed Description of the Embodiments

[0057] Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present invention can be more thoroughly understood and the scope of the present invention can be fully conveyed to those skilled in the art.

[0058] To meet the requirements of large-displacement cementing operations, the currently commonly used method for producing cement slurries for cementing is the continuous mixing method, and the system for producing cement slurries for cementing using the continuous mixing method is the continuous cementing mixing system. Since cement slurries are usually formed by mixing cement ash and fresh water, the continuous cementing mixing system generally includes an ash supply device, a water supply device, a mixing tank, and a balancing tank. Among them, the ash supply device is used to provide cement ash, the water supply device is used to provide fresh water, the mixing tank is used to mix and stir the cement ash and fresh water, and the balancing tank is used to remix and stir the slurry that overflows from the mixing tank. Then, the embodiments of the present invention mainly focus on density control of the above-mentioned continuous cementing mixing system.

[0059] Figure 1 The structural schematic diagram of a density control system for cement slurries for cementing provided by an embodiment of the present invention is shown. Among them, the density control system for cement slurries for cementing provided by the embodiments of the present invention is mainly used to control the density of the cement slurries in the continuous cementing mixing system 200.

[0060] As Figure 1 shown, the density control system 100 for cement slurries for cementing includes: a density meter 110 for the pump-out pipeline of the balancing tank, a density meter 120 for the circulation pipeline of the mixing tank, a fresh water flow meter 130, a first PID control module 140, a second PID control module 150, a dry cement ash flow calculation module 160, a feedforward control module 170, a third PID control module 180, and a cement ash flow regulating valve 190.

[0061] The density meter 110 for the pump-out pipeline of the balancing tank is used to measure the first density of the cement slurry in the pump-out pipeline of the balancing tank in the continuous cementing mixing system. Specifically, the density meter 110 for the pump-out pipeline of the balancing tank is arranged in the pump-out pipeline of the balancing tank of the continuous cementing mixing system, and the cement slurry is pumped out from the balancing tank and sent to the bottom of the well. Therefore, this first density is the density of the cement slurry pumped to the bottom of the well.

[0062] The density meter 120 for the circulation pipeline of the mixing tank is used to measure the second density of the cement slurry in the circulation pipeline of the mixing tank in the continuous cementing mixing system. Specifically, the density meter 120 for the circulation pipeline of the mixing tank is arranged in the circulation pipeline of the mixing tank of the continuous cementing mixing system. Therefore, this second density is the density of the cement slurry in the mixing tank.

[0063] The fresh water flowmeter 130 is used to measure the fresh water flow rate in the continuous cementing slurry mixing system. Specifically, the fresh water flowmeter 130 can be installed at the front end of the fresh water inlet of the high-energy mixer, and the measured fresh water flow rate is specifically the fresh water flow rate currently supplied for cement slurry mixing.

[0064] The first PID control module 140 is connected to the density meter 110 of the equalizing tank pump-out pipeline, and is used to generate a first output signal according to the set value of the cement slurry density and the first density. The density meter 110 of the equalizing tank pump-out pipeline transmits the measured first density of the cement slurry in the equalizing tank pump-out pipeline to the first PID control module 140 through the communication connection with the first PID control module 140. The first PID control module 140 takes the first density as the controlled variable, takes the set value of the cement slurry density as the set value of this module, and outputs a first output signal. Among them, the first PID control module 140 and the density meter 110 of the equalizing tank pump-out pipeline constitute the main control loop of the cementing cement slurry density control system 100, so as to realize the precise control of the cementing cement slurry density.

[0065] In an alternative embodiment, the first PID control module 140 is specifically used for: calculating a first deviation between the set value of the cement slurry density at the kth sampling moment and the first density at the kth sampling moment; according to the first deviation corresponding to the kth sampling moment, the first deviation corresponding to the k-1th sampling moment, the first deviation corresponding to the k-2th sampling moment, and the first output signal at the k-1th sampling moment, calculating the first output signal at the kth sampling moment. Among them, the deviation between the set value of the cement slurry density at the kth sampling moment and the first density at the kth sampling moment is called the first deviation at the kth sampling moment. In addition, the PID control module in the embodiments of the present invention is a controller based on the PID (Proportional-Integral-Derivative) control scheme, and PID is a control scheme that performs control according to the proportion, integral, and differential of the error generated by comparing the information collected from the real-time data of the controlled object with the given value.

[0066] Further optionally, the first deviation between the set value of the cement slurry density at the kth sampling moment and the first density at the kth sampling moment can be calculated by the following formula 1:

[0067] e1(k) = p(k) - ρ1(k) (Formula 1)

[0068] In Formula 1, e1(k) is the first deviation at the kth sampling moment, ρ(k) is the set value of the cement slurry density at the kth sampling moment, and ρ1(k) is the first density at the kth sampling moment. Among them, the unit of each density index in the embodiments of the present invention can be kg / m 3 .

[0069] Further optionally, the first output signal at the k-th sampling moment can be calculated by the following formula 2:

[0070]

[0071] In formula 2, u1(k) is the first output signal at the k-th sampling moment, u1(k - 1) is the first output signal at the (k - 1)-th sampling moment, e1(k) is the first deviation at the k-th sampling moment, e1(k - 1) is the first deviation at the (k - 1)-th sampling moment, e1(k - 2) is the first deviation at the (k - 2)-th sampling moment, K p1 is the proportionality coefficient in the first PID control module 140, T i1 is the integral time coefficient in the first PID control module 140, T d1 is the derivative time coefficient in the first PID control module 140, Ts is the step size. Wherein, the units of the first output signal and the first deviation can be kg / min, k is an integer greater than or equal to 1, e1(0) = e1(-1) = 0, and u1(0) is the second density in the initial state. Preferably, K p1 = 8.5, T i1 = 0.5, T d1 = 0.1.

[0072] The second PID control module 150 is connected to the density meter 120 of the mud mixing tank circulation pipeline and the first PID control module 140, and is used to generate a second output signal according to the first output signal and the second density. Specifically, the density meter 120 of the mud mixing tank circulation pipeline transmits the measured second density of the cement slurry in the mud mixing tank circulation pipeline 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 then takes this second density as the controlled variable of this module; the first PID control module 140 transmits the generated first output signal 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 then takes this first output signal as the set value of this module, adjusts the density of the cement slurry in the mud mixing tank to ensure that the cement slurry pumped out from the equalizing tank is always controlled near the density set value, and finally generates a second output signal based on the second density and the first output signal. Among them, the second PID control module 150 and the density meter 120 of the mud mixing tank circulation pipeline form the first secondary loop in the cement slurry density control system for well cementing, which can eliminate the interference of changes in the characteristics of the vacuum injection pump, the characteristics of the circulation pump, etc. on the density control.

[0073] In an alternative embodiment, the second PID control module 150 is specifically configured to: calculate the second deviation between the first output signal at the k-th sampling moment and the second density at the k-th sampling moment; calculate the second output signal at the k-th sampling moment according to the second deviation at the k-th sampling moment, the second deviation at the (k-1)-th sampling moment, the second deviation at the (k-2)-th sampling moment, and the second output signal at the (k-1)-th sampling moment. Wherein, the deviation between the first output signal at the k-th sampling moment and the second density at the k-th sampling moment is called the second deviation at the k-th sampling moment.

[0074] Further optionally, the second deviation between the first output signal at the k-th sampling moment and the second density at the k-th sampling moment can be calculated by the following formula 3:

[0075] e2(k) = u1(k) - p2(k) (Formula 3)

[0076] In Formula 3, e2(k) is the second deviation at the k-th sampling moment (kg / min), u1(k) is the first output signal at the k-th sampling moment, and ρ2(k) is the second density at the k-th sampling moment.

[0077] Further optionally, the first output signal at the k-th sampling moment can be calculated by the following formula 4:

[0078]

[0079] In Formula 4, u2(k) is the second output signal at the k-th sampling moment, u2(k-1) is the second output signal at the (k-1)-th sampling moment, e2(k) is the second deviation at the k-th sampling moment, e2(k-1) is the second deviation at the (k-1)-th sampling moment, e2(k-2) is the second deviation at the (k-2)-th sampling moment, K p2 is the proportionality coefficient in the second PID control module 150, T i2 is the integral time coefficient in the second PID control module 150, T d2 is the derivative time coefficient in the second PID control module 150, Ts is the step size. Wherein, the units of the second output signal and the second deviation can be kg / m 3 , k is an integer greater than or equal to 1, e2(0) = e2(-1) = 0, u2(0) = 0. Preferably, K p2 = 25.8, T i2 = 2, T d2 = 0.8.

[0080] The dry cement ash flow calculation module 160 is connected to the density meter 110 of the equalizing tank pump-out pipeline, the density meter 120 of the mud mixing tank circulation pipeline, and the clean water flow meter 130, and is used to calculate the estimated mass flow rate of dry cement ash entering the mud mixing tank according to the first density, the second density, and the clean water flow rate. Specifically, the density meter 110 of the equalizing tank pump-out pipeline transmits the measured first density of the cement slurry in the equalizing tank pump-out pipeline to the dry cement ash flow calculation module 160 through the communication connection with the dry cement ash flow calculation module 160. The density meter 120 of the mud mixing tank circulation pipeline transmits the measured second density of the cement slurry in the mud mixing tank circulation pipeline to the dry cement ash flow calculation module 160 through the communication connection with the dry cement ash flow calculation module 160. The clean water flow meter 130 transmits the measured clean water flow rate to the dry cement ash flow calculation module 160 through the communication connection with the dry cement ash flow calculation module 160. The dry cement ash flow calculation module 160 obtains the estimated mass flow rate of dry cement ash entering the mud mixing tank according to the obtained measured values.

[0081] In an alternative embodiment, the dry cement ash flow calculation module 160 is specifically configured to: calculate the mass flow rate of the overflow cement slurry overflowing from the mud mixing tank to the equalizing tank at the k-th sampling moment; calculate the estimated mass flow rate of dry cement ash entering the mud mixing tank at the k-th moment according to the mass flow rate of the overflow cement slurry at the k-th sampling moment, the second density at the k-th sampling moment, the second density at the (k - 1)-th sampling moment, and the clean water flow rate at the k-th sampling moment.

[0082] Further alternatively, the mass flow rate of the overflow cement slurry overflowing from the mud mixing tank to the equalizing tank at the k-th sampling moment can be calculated according to the first density at the k-th sampling moment and the first density at the (k - 1)-th sampling moment.

[0083] Wherein, the cement slurry density control system 100 for well cementing further includes an equalizing tank level gauge (not shown in the figure) and an equalizing tank pump-out pipeline displacement detector (not shown in the figure). The equalizing tank level gauge is arranged in the equalizing tank and is used to measure the level of the equalizing tank. The equalizing tank pump-out pipeline is arranged in the pump-out pipeline at the bottom of the equalizing tank and is used to measure the displacement of the cement slurry in the equalizing tank pump-out pipeline.

[0084] Then the dry cement ash flow calculation module is connected to the equalizing tank level gauge and the equalizing tank pump-out pipeline displacement detector, and is used to calculate the mass flow rate of the overflow cement slurry overflowing from the mud mixing tank to the equalizing tank at the k-th sampling moment according to the first density at the k-th sampling moment, the first density at the (k - 1)-th sampling moment, the level of the equalizing tank at the k-th sampling moment, and the displacement of the cement slurry at the k-th sampling moment. Specifically, the mass flow rate of the overflow cement slurry overflowing from the mud mixing tank to the equalizing tank can be calculated by the following formula 5:

[0085]

[0086] In Formula 5, F 12 (k) is the mass flow rate of the overflowing cement slurry from the mixing tank to the equalizing tank at the k-th sampling moment (kg / min), and F out (k) is the displacement of the cement slurry in the pump-out pipeline of the equalizing tank at the k-th sampling moment (kg / min). A1 is the cross-sectional area of the equalizing tank (m 2 ), h(k) is the liquid level of the equalizing tank at the k-th sampling moment (m), ρ1(k) is the first density at the k-th sampling moment, ρ1(k - 1) is the first density at the (k - 1)-th sampling moment, Ts is the step size. When k = 1, ρ1(0) is set to 0.

[0087] Further optionally, the estimated mass flow rate of the dry cement ash entering the mixing tank at the k-th sampling moment can be obtained according to the following Formula 6 based on the mass flow rate of the overflowing cement slurry from the mixing tank to the equalizing tank at the k-th sampling moment:

[0088]

[0089] In Formula 6, F c (k) is the estimated mass flow rate of the dry cement ash entering the mixing tank at the k-th sampling moment (kg / min), and F 12 (k) is the mass flow rate of the overflowing cement slurry from the mixing tank to the equalizing tank at the k-th sampling moment (kg / min), and F w (k) is the flow rate of clear water at the k-th sampling moment (kg / min). A2 is the cross-sectional area of the mixing tank (m 2 ), h0 is the height of the overflow baffle between the mixing tank and the equalizing tank (m), ρ2(k) is the second density at the k-th sampling moment, ρ2(k - 1) is the second density at the (k - 1)-th sampling moment, Ts is the step size. When k = 1, ρ2(0) is set to 0.

[0090] The feedforward control module 170 is connected to the clear water flowmeter 130 and is used to generate a third output signal according to the clear water flow rate. Among them, the clear water flowmeter 130 transmits the measured clear water flow rate to the feedforward control module 170 through the communication connection with the feedforward control module 170. The feedforward control module 170 generates a third output signal according to the clear water flow rate, thereby introducing the clear water flow rate into the control loop, so that when the clear water flow rate changes, the dry cement ash flow rate is adjusted correspondingly, and the stability of the density of the cement slurry for well cementing during the control process is realized.

[0091] In an alternative embodiment, the feedforward control module 170 is specifically configured to: generate a third output signal according to the set value of the cement slurry density at the k-th sampling moment and the clear water flow rate at the k-th sampling moment. For example, the third output signal can be calculated by the following Formula 7:

[0092]

[0093] In Formula 7, F f (k) is the third output signal (kg / min) at the k-th sampling moment, F w (k) is the clear water flow rate (kg / min) at the k-th sampling moment, ρ c is the dry cement ash density (kg / m 3 ), ρ w is the clear water density (kg / m 3 ), and ρ(k) is the set value of the cement slurry density at the k-th sampling moment (kg / m 3 ).

[0094] The third PID control module 180 is connected to the second PID control module 150, the dry cement ash flow calculation module 160, and the feedforward control module 170, and is used to generate a fourth output signal according to the second output signal, the third output signal, and the estimated value of the dry cement ash mass flow rate. The second PID control module 150 transmits the generated second output signal to the third PID control module 180 through the communication connection between the two. The dry cement ash flow calculation module 160 transmits the estimated value of the dry cement ash mass flow rate to the third PID control module 180 through the communication connection between the two. The feedforward control module 170 transmits the generated third output signal to the third PID control module 180 through the communication connection between the two. The third PID control module 180 serves as the second secondary controller in the well cementing cement slurry density control system and forms a second secondary loop with the dry cement ash flow calculation module 160. Specifically, the third PID control module 180 uses the second output signal and the third output signal as the set values of this module to adjust the dry cement flow rate entering the mixing tank to control the cement slurry density in the mixing tank.

[0095] In an optional implementation manner, the third PID control module 180 is specifically configured to: calculate the third deviation at the k-th sampling moment according to the second output signal at the k-th sampling moment, the third output signal at the k-th sampling moment, and the estimated value of the dry cement ash mass flow rate at the k-th sampling moment; calculate the fourth output signal at the k-th sampling moment according to the third deviation at the k-th sampling moment, the third deviation at the (k - 1)-th sampling moment, the third deviation at the (k - 2)-th sampling moment, and the fourth output signal at the (k - 1)-th sampling moment.

[0096] Further optionally, the third deviation at the k-th sampling moment can be calculated by the following Formula 8:

[0097] e3(k) = u2(k) + F f (k) - F c(k) (Formula 8)

[0098] In Formula 8, e3(k) is the third deviation at the k-th sampling moment (kg / min), u2(k) is the second output signal at the k-th sampling moment, F f (k) is the third output signal at the k-th sampling moment, F c (k) is the estimated mass flow rate of dry cement ash entering the slurry mixing tank at the k-th sampling moment (kg / min).

[0099] Further optionally, the fourth output signal at the k-th sampling moment can be calculated by the following Formula 9:

[0100]

[0101] In Formula 9, u3(k) is the fourth output signal at the k-th sampling moment (kg / min), u3(k - 1) is the fourth output signal at the (k - 1)-th sampling moment, e3(k) is the third deviation at the k-th sampling moment, e3(k - 1) is the third deviation at the (k - 1)-th sampling moment, e3(k - 2) is the third deviation at the (k - 2)-th sampling moment, K p3 is the proportionality coefficient in the third PID control module 180, T i3 is the integral time coefficient in the third PID control module 180, T d3 is the derivative time coefficient in the third PID control module 180, Ts is the step size. Among them, the units of the fourth output signal and the third deviation can be kg / min, k is an integer greater than or equal to 1, and e3(0) = e3(-1) = 0. Preferably, K p3 = 40.2, T i2 = 0.1, T d2 = 1.

[0102] The cement ash flow regulating valve 190 can also be called the ash discharging valve, which is connected to the third PID control module 180 and is used to execute the fourth output signal to control the dry cement ash flow rate.

[0103] In an optional implementation manner, the installation positions of the equalizing tank pump-out pipeline densitometer, the slurry mixing tank circulation pipeline densitometer, the fresh water flowmeter, and the cement ash flow regulating valve are as Figure 2 shown. As Figure 2 shown, the equalizing tank pump-out pipeline densitometer 110 is arranged behind the perfusion pump of the equalizing tank pump-out pipeline, the slurry mixing tank circulation pipeline densitometer 120 is arranged in the slurry mixing tank circulation pipeline, the fresh water flowmeter 130 is arranged in front of the fresh water inlet of the high-energy mixer, and the cement ash flow regulating valve 190 is arranged below the ash supply device. In addition, Figure 2The ash supply device, water supply device, clean water valve, high-energy mixer, slurry mixing tank, equalizing tank, circulation pump, and perfusion pump shown in the figure can refer to the structures and functions in the prior art, and will not be elaborated in this invention.

[0104] It can be seen that the cement slurry density control system provided by the embodiment of the present invention adopts a control method combining cascade control and feedforward control. The first PID control module is used as the main controller, and the loop composed of the first PID control module and the density meter on the pump-out pipeline of the equalizing tank forms the main control loop. The second PID control module is used as a secondary controller, and the loop composed of the second PID control module and the density meter on the circulating pipeline of the slurry mixing tank forms the first secondary control loop. The third PID control module is used as another secondary controller, and the loop composed of the third PID control module, the dry cement ash flow calculation module, and the cement ash flow regulating valve forms the second secondary control loop. The feedforward module introduces the clean water flow as feedforward information, improving the accuracy and stability of the cement slurry density control for well cementing. Therefore, using this system can quickly stabilize the density of the well cementing cement slurry produced by the continuous slurry mixing system for well cementing near the set value, and improve the stability and accuracy of the density control of the continuous slurry mixing for well cementing.

[0105] Figure 3 The flowchart of a cement slurry density control method for well cementing provided by the embodiment of the present invention is shown. This cement slurry density control method is used to control the density of the cement slurry in the continuous slurry mixing system for well cementing. As Figure 3 shown, the cement slurry density control method for well cementing includes:

[0106] Step S310, the first PID control module generates a first output signal according to the set value of the cement slurry density and the first density measured by the density meter on the pump-out pipeline of the equalizing tank.

[0107] Step S320, the second PID control module generates a second output signal according to the first output signal and the second density measured by the density meter on the circulating pipeline of the slurry mixing tank.

[0108] Step S330, the dry cement ash flow calculation module calculates the estimated mass flow rate of the dry cement ash entering the slurry mixing tank according to the first density, the second density, and the clean water flow measured by the clean water flowmeter.

[0109] Step S340, the feedforward control module generates a third output signal according to the clean water flow.

[0110] 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 mass flow rate of the dry cement ash, for the cement ash flow regulating valve to execute the fourth output signal to control the dry cement ash flow.

[0111] Among them, for the specific functions of each module and sensor involved in this method, reference can be made to Figure 1 the description in the embodiments, which will not be elaborated here.

[0112] In an optional implementation manner, the first PID control module generating a first output signal based on the set value of the cement slurry density and the first density measured by the density meter on the pump-out pipeline of the equalizing tank further includes:

[0113] The first PID control module calculates the first deviation between the set value of the cement slurry density at the k-th sampling moment and the first density at the k-th sampling moment; according to the first deviation at the k-th sampling moment, the first deviation at the (k - 1)-th sampling moment, the first deviation at the (k - 2)-th sampling moment, and the first output signal at the (k - 1)-th sampling moment, calculates the first output signal at the k-th sampling moment.

[0114] In an optional implementation manner, the second PID control module generating a second output signal based on the first output signal and the second density measured by the density meter on the circulation pipeline of the mud mixing tank further includes:

[0115] Calculates the second deviation between the first output signal at the k-th sampling moment and the second density at the k-th sampling moment; according to the second deviation at the k-th sampling moment, the second deviation at the (k - 1)-th sampling moment, the second deviation at the (k - 2)-th sampling moment, and the second output signal at the (k - 1)-th sampling moment, calculates the second output signal at the k-th sampling moment.

[0116] In an optional implementation manner, the dry cement ash flow rate calculation module calculating the estimated mass flow rate of dry cement ash entering the mud mixing tank based on the first density, the second density, and the clear water flow rate measured by the clear water flow meter further includes:

[0117] Calculates the mass flow rate of the overflow cement slurry overflowing from the mud mixing tank to the equalizing tank at the k-th sampling moment;

[0118] Based on the mass flow rate of the overflow cement slurry at the k-th sampling moment, the second density at the k-th sampling moment, the second density at the (k - 1)-th sampling moment, and the clear water flow rate at the k-th sampling moment, calculates the estimated mass flow rate of dry cement ash entering the mud mixing tank at the k-th sampling moment.

[0119] In an optional implementation manner, calculating the mass flow rate of the overflow cement slurry overflowing from the mud mixing tank to the equalizing tank at the k-th sampling moment further includes: calculating the mass flow rate of the overflow cement slurry overflowing from the mud mixing tank to the equalizing tank at the k-th sampling moment according to the first density at the k-th sampling moment and the first density at the (k - 1)-th sampling moment.

[0120] In an alternative embodiment, calculating the mass flow rate of the overflow cement slurry overflowing from the mud mixing tank to the equalizing tank at the k-th sampling moment based on the first density at the k-th sampling moment and the first density at the (k - 1)-th sampling moment further includes: calculating the mass flow rate of the overflow cement slurry overflowing from the mud mixing tank to the equalizing tank at the k-th sampling moment according to the first density at the k-th sampling moment, the first density at the (k - 1)-th sampling moment, the liquid level of the equalizing tank at the k-th sampling moment, and the displacement of the cement slurry at the k-th sampling moment.

[0121] In an alternative embodiment, the feedforward control module generating the third output signal according to the clear water flow rate further includes: generating the third output signal according to the set value of the cement slurry density at the k-th sampling moment and the clear water flow rate at the k-th sampling moment.

[0122] In an alternative embodiment, the third PID control module generating the fourth output signal according to the second output signal, the third output signal, and the estimated value of the dry cement ash mass flow rate further includes: calculating the third deviation at the k-th sampling moment according to the second output signal at the k-th sampling moment, the third output signal at the k-th sampling moment, and the estimated value of the dry cement ash mass flow rate at the k-th sampling moment;

[0123] Calculating the fourth output signal at the k-th sampling moment according to the third deviation at the k-th sampling moment, the third deviation at the (k - 1)-th sampling moment, the third deviation at the (k - 2)-th sampling moment, and the fourth output signal at the (k - 1)-th sampling moment.

[0124] It can be seen that adopting this solution can quickly stabilize the density of the cement slurry produced by the cementing continuous mud mixing system near the set value, and improve the stability and accuracy of the density control of the cementing continuous mud mixing.

[0125] The algorithms or displays provided herein are not inherently related to any particular computer, virtual system, or other device. Various general-purpose systems can also be used in conjunction with the teachings herein. The structure required to construct such systems will be apparent from the above description. In addition, the embodiments of the present invention are not directed to any specific programming language. It should be understood that the content of the present invention described herein can be implemented using various programming languages, and the description of the specific language above is to disclose the best mode of the present invention.

[0126] In the specification provided herein, a large number of specific details are set forth. However, it can be understood that the embodiments of the present invention can be practiced without these specific details. In some instances, well-known methods, structures, and technologies have not been shown in detail so as not to obscure the understanding of this specification.

[0127] Similarly, it should be understood that, for the purpose of streamlining the present invention and facilitating the understanding of one or more of the various inventive aspects, in the foregoing description of the exemplary embodiments of the present invention, the various features of the embodiments of the present invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, the disclosed method should not be construed as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as reflected in the following claims, the inventive aspects lie in less than all the features of the single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate embodiment of the present invention.

[0128] Those skilled in the art will appreciate that the modules in the devices in the embodiments can be adaptively changed and disposed in one or more devices different from the embodiments. The modules or units or components in the embodiments can be combined into one module or unit or component, and in addition, they can be divided into multiple sub-modules or sub-units or sub-components. Except that at least some of such features and / or processes or units are mutually exclusive, any combination can be used to combine all the features disclosed in this specification (including the accompanying claims, abstract, and drawings) and all the processes or units of any method or device so disclosed. Unless otherwise expressly stated, each feature disclosed in this specification (including the accompanying claims, abstract, and drawings) can be replaced by an alternative feature that provides the same, equivalent, or similar purpose.

[0129] In addition, those skilled in the art will be able to understand that although some of the embodiments herein include certain features included in other embodiments rather than other features, the combination of the features of different embodiments means that it is within the scope of the present invention and forms different embodiments. For example, in the following claims, any one of the claimed embodiments can be used in any combination.

[0130] The various component embodiments of the present invention can be implemented in hardware, or in software modules running on one or more processors, or in a combination thereof. Those skilled in the art should understand that a microprocessor or a digital signal processor (DSP) can be used in practice to implement some or all of the functions of some or all of the components according to the embodiments of the present invention. The present invention can also be implemented as a device or apparatus program (for example, a computer program and a computer program product) for executing part or all of the methods described herein. Such a program for implementing the present invention can be stored on a computer-readable medium, or can be in the form of one or more signals. Such signals can be downloaded from an Internet website, or provided on a carrier signal, or provided in any other form.

[0131] It should be noted that the above embodiments illustrate the present invention rather than limit the present invention, and those skilled in the art can 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 the claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The present invention can be implemented by means of hardware including several different elements and by means of a suitably programmed computer. In a unit claim listing several devices, several of these devices can be embodied by the same item of hardware. The use of the words first, second, and third, etc. does not denote any order. These words can be interpreted as names. The steps in the above embodiments, unless otherwise specified, should not be construed as limiting the order of execution.

Claims

1. A density control system for cement slurry in cementing, the density control system for cement slurry in cementing being used to control the density of cement slurry in a continuous cementing mixing system, characterized in that The cement slurry density control system for well cementing includes: a density meter for the pump-out pipeline of the equalizing tank, a density meter for the circulation pipeline of the mud mixing tank, a clean 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; Among them, the density meter for the pump-out pipeline of the equalizing tank is used to measure the first density of the cement slurry in the pump-out pipeline of the equalizing tank in the continuous mud mixing system for well cementing; the density meter for the circulation pipeline of the mud mixing tank is used to measure the second density of the cement slurry in the circulation pipeline of the mud mixing tank in the continuous mud mixing system for well cementing; the clean water flowmeter is used to measure the clean water flow in the continuous mud mixing system for well cementing; The first PID control module is connected to the density meter for the pump-out pipeline of the equalizing tank, and is used to generate a first output signal according to the set value of the cement slurry density and the first density; The second PID control module is connected to the density meter for the circulation pipeline of the mud mixing tank and the first PID control module, and is used to generate a second output signal according to the first output signal and the second density; The dry cement ash flow calculation module is connected to the density meter for the pump-out pipeline of the equalizing tank, the density meter for the circulation pipeline of the mud mixing tank, and the clean water flowmeter, and is used to calculate the estimated mass flow rate of dry cement ash entering the mud mixing tank according to the first density, the second density, and the clean water flow; The feedforward control module is connected to the clean water flowmeter, and is used to generate a third output signal according to the clean water flow; The third PID control module is connected to the second PID control module, the dry cement ash flow calculation module, and the feedforward control module, and is used to generate a fourth output signal according to the second output signal, the third output signal, and the estimated mass flow rate of dry cement ash; The cement ash flow regulating valve is connected to the third PID control module, and is used to execute the fourth output signal to control the dry cement ash flow.

2. The density control system of the well cement slurry according to claim 1, wherein The first PID control module is specifically used for: Calculating the first deviation between the set value of the cement slurry density at the kth sampling moment and the first density at the kth sampling moment; Calculating the first output signal at the kth sampling moment according to the first deviation at the kth sampling moment, the first deviation at the (k - 1)th sampling moment, the first deviation at the (k - 2)th sampling moment, and the first output signal at the (k - 1)th sampling moment.

3. The density control system for the cement slurry used in well cementing according to claim 2, wherein, The second PID control module is specifically used for: Calculating the second deviation between the first output signal at the kth sampling moment and the second density at the kth sampling moment; Calculating the second output signal at the kth sampling moment according to the second deviation at the kth sampling moment, the second deviation at the (k - 1)th sampling moment, the second deviation at the (k - 2)th sampling moment, and the second output signal at the (k - 1)th sampling moment.

4. The density control system of the cement slurry for well cementing according to any one of claims 1-3, characterized in that, The dry cement ash flow calculation module is specifically used for: Calculating the mass flow rate of the overflow cement slurry overflowing from the mud mixing tank to the equalizing tank at the kth sampling moment; Calculating the estimated mass flow rate of dry cement ash entering the mud mixing tank at the kth sampling moment according to the mass flow rate of the overflow cement slurry at the kth sampling moment, the second density at the kth sampling moment, the second density at the (k - 1)th sampling moment, and the clean water flow at the kth sampling moment.

5. The density control system for well cement slurry according to claim 4, wherein, The dry cement ash flow calculation module is specifically used for: Calculate the mass flow rate of the overflow cement slurry flowing from the mud mixing tank to the equalizing tank at the k-th sampling moment based on the first density at the k-th sampling moment and the first density at the (k - 1)-th sampling moment.

6. The density control system of the cement slurry for well cementing according to claim 5, wherein, The well cement slurry density control system further includes: An equalizing tank level gauge for measuring the level of the equalizing tank; An equalizing tank pump-out pipeline displacement detector for measuring the displacement of the cement slurry in the equalizing tank pump-out pipeline.

7. The density control system of the well cement slurry according to claim 6, characterized in that, The dry cement ash flow calculation module is connected to the equalizing tank level gauge and the equalizing tank pump-out pipeline displacement detector, and is used to calculate the mass flow rate of the overflow cement slurry flowing from the mud mixing tank to the equalizing tank at the k-th sampling moment based on the first density at the k-th sampling moment, the first density at the (k - 1)-th sampling moment, the level of the equalizing tank at the k-th sampling moment, and the displacement of the cement slurry at the k-th sampling moment.

8. The density control system for well cement slurry according to any one of claims 1-3, characterized in that The feedforward control module is specifically used for: Generating a third output signal based on the cement slurry density set value at the k-th sampling moment and the fresh water flow rate at the k-th sampling moment.

9. The density control system of the cement slurry for well cementing according to any one of claims 1 to 3, characterized in that, The third PID control module is specifically used for: Calculating the third deviation at the k-th sampling moment based on the second output signal at the k-th sampling moment, the third output signal at the k-th sampling moment, and the estimated value of the dry cement ash mass flow rate at the k-th sampling moment; Calculating the fourth output signal at the k-th sampling moment based on the third deviation at the k-th sampling moment, the third deviation at the (k - 1)-th sampling moment, the third deviation at the (k - 2)-th sampling moment, and the fourth output signal at the (k - 1)-th sampling moment.

10. A method for controlling the density of cement slurry for well cementing, which is used to control the density of cement slurry in a continuous cement mixing system for well cementing, and is characterized in that, The well cement slurry density control method includes: The first PID control module generates a first output signal based on the cement slurry density set value and the first density measured by the equalizing tank pump-out pipeline densitometer; The second PID control module generates a second output signal based on the first output signal and the second density measured by the mud mixing tank circulation pipeline densitometer; The dry cement ash flow calculation module calculates the estimated value of the dry cement ash mass flow rate entering the mud mixing tank based on the first density, the second density, and the fresh water flow rate measured by the fresh water flowmeter; The feedforward control module generates a third output signal based on the fresh water flow rate; The third PID control module generates a fourth output signal based on the second output signal, the third output signal, and the estimated value of the dry cement ash mass flow rate, for the cement ash flow regulating valve to execute the fourth output signal to control the dry cement ash flow.

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