Wellhead back pressure control rule and device based on throttle valve opening model

Abstract

The invention provides a wellhead back pressure control rule and device based on a throttle valve opening model, and the method comprises the steps: determining the relation between the throttle pressure drop and the equivalent diameter of the overflow section of a throttle valve according to the energy conservation principle of fluid flow; according to the structure of the needle type throttle valve, the relation between the equivalent diameter and the opening and closing degree of the throttle valve is determined; joint calculation is carried out through the relational expression between the throttling pressure drop and the equivalent diameter of the overflowing section of the throttling valve and the relational expression between the equivalent diameter and the switching degree of the throttling valve, an opening degree model of the throttling valve is obtained, and a wellhead back pressure control algorithm is established based on the model; according to a well mouth back pressure control rule and device based on a throttle valve opening degree model, the well mouth back pressure is adjusted in a mode of combining open-loop rapid adjustment and PID closed-loop control. The throttle valve opening degree model and the control algorithm based on the model provide a theoretical basis for regulating and controlling the opening degree of the pressure-controlled drilling throttle valve; according to the wellhead back pressure control rule and device based on the throttle valve opening model, through combination of rapid coarse adjustment and accurate fine adjustment, the throttle valve opening adjustment accuracy is guaranteed, the throttle valve opening adjustment speed is increased, and rapid and accurate adjustment of wellhead back pressure is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of oil production, and in particular to a wellhead back pressure control law and device based on a throttle valve opening model. Background Art

[0002] With the rapid development of the oil industry, drilling technology has begun to move towards automation and intelligence. Managed pressure drilling technology is one aspect of automated drilling. Through data monitoring systems and wellhead equipment, the wellbore pressure is monitored in real time, and the wellbore pressure is adjusted to achieve safe drilling.

[0003] The throttle valve is one of the most critical equipment in the managed pressure drilling system, and it is also the core equipment of the ground throttle manifold system. The throttle valve equipment is installed in the throttle manifold part of the managed pressure drilling system. By adjusting the throttle valve opening on the throttle manifold, the wellhead back pressure can be controlled. Combined with the wellhead target back pressure, the pressure limit requirement in the time-limited adjustment process of the wellhead target back pressure is completed, ensuring the safe drilling of oil and gas wells, so that the pressure regulation part of the entire managed pressure drilling system can be maintained in an ideal pressure balance state.

[0004] During field work, it is necessary to achieve rapid and precise control of the wellhead back pressure, that is, to ensure the rapid and precise adjustment of the throttle valve opening of the pressure-controlled drilling. When the PID control method is used alone to control the throttle valve opening to adjust the wellhead back pressure, the throttle valve opening adjustment speed is too slow, resulting in a long wellhead back pressure adjustment time, resulting in a large difference between the control effect of the wellhead back pressure and the field requirements. Summary of the invention

[0005] In view of the above problems, the present invention proposes a wellhead back pressure control law and device based on a throttle valve opening model.

[0006] The present invention proposes an opening model of a pressure-controlled drilling throttle valve and establishes a wellhead back pressure control algorithm based on the model, including:

[0007] According to the energy conservation principle of fluid flow, the relationship between the throttling pressure drop and the equivalent diameter of the throttling valve flow cross section is determined;

[0008] According to the structure of needle throttle valve, the relationship between equivalent diameter and throttle valve opening and closing degree is determined;

[0009] According to the relationship between the throttling pressure drop and the equivalent diameter of the throttling valve flow cross section and the relationship between the equivalent diameter and the throttling valve opening degree, the throttling valve opening model is determined, and the wellhead back pressure control algorithm is established.

[0010] Furthermore, determining the relationship between the throttling pressure drop and the equivalent diameter of the throttling valve flow cross section includes:

[0011] The throttling principle of the needle throttle valve is determined by the theory of small hole throttling. The throttle valve changes the flow area of ​​the fluid in the valve by changing the stroke size between the valve core and the valve seat on the basis of the small hole throttling theory, and adjusts the pressure and flow size before and after the throttle valve by changing the stroke size.

[0012] The energy change of the fluid flowing through the small hole is used to explain the energy change of the fluid when it flows through the needle throttle valve. Therefore, according to the energy conservation principle of the fluid, that is, the Bernoulli equation, the theory of small hole throttling is first derived, and the small hole throttling pressure difference formula is derived. Then, the relationship between the throttling pressure drop of the throttle valve and the equivalent diameter of the flow section of the throttle valve is obtained.

[0013] According to the energy conservation principle of fluid energy, namely the Bernoulli equation, the small hole throttling pressure difference formula is derived:

[0014]

[0015] Where, ΔP is the throttling pressure difference before and after the orifice, pa; ρ is the fluid density, kg / m 3 ; Q is the fluid flow rate, m 3 / s;C d is the small hole flow coefficient; d is the small hole flow cross-sectional diameter, m.

[0016] Then, the relationship between the throttling pressure drop and the equivalent diameter of the throttling valve flow cross section is determined by the small hole throttling pressure difference formula. Their relationship is as follows:

[0017]

[0018] In the formula, is the throttle pressure difference before and after the throttle valve at time t, MPa; is the density of the fluid flowing through the throttle valve at time t, g / cm 3 ; is the fluid flow rate flowing through the throttle valve at time t, L / s; is the flow coefficient; is the equivalent diameter of the throttle valve flow cross section at time t, cm.

[0019] Furthermore, according to the structure of the needle throttle valve, the relationship between the equivalent diameter and the throttle valve opening and closing degree is determined, and their relationship is as follows:

[0020]

[0021] In the formula, is the equivalent diameter of the throttle valve flow cross section at time t, cm; is the maximum equivalent diameter of the throttle valve flow section, cm; β(t) is the throttle valve opening at time t; ω is the structural characteristic parameter.

[0022] Furthermore, the relationship between the throttling pressure drop and the equivalent diameter of the throttle valve flow cross section and the relationship between the equivalent diameter and the throttle valve opening degree are jointly calculated to obtain the throttle valve opening model and establish the wellhead back pressure control algorithm based on the model:

[0023] Through joint calculation, the throttle valve opening model is obtained as follows:

[0024]

[0025] Where, β(t) is the throttle valve opening at time t; ω is the structural characteristic parameter; is the inlet and outlet throttling pressure difference under the maximum flow diameter of the throttle valve, MPa; is the throttling pressure difference between the inlet and outlet of the throttle valve at time t, MPa.

[0026] Based on the throttle valve opening model established above, the wellhead back pressure control algorithm is established. When the pressure loss of the surface pipeline is ignored, the wellhead back pressure is approximately equal to the throttle pressure difference between the inlet and outlet of the throttle valve. Therefore, the set value of the wellhead back pressure is used to replace the throttle pressure difference between the inlet and outlet of the throttle valve in the control algorithm. According to the established throttle valve opening model, the control algorithm can be expressed as:

[0027] u(t)=u(t0)+Δu(t) (21)

[0028]

[0029] Wherein, u(t) is the output variable of the control algorithm at time t; u(t0) is the output variable of the control algorithm before the last step change at time t; Δu(t) is the change in the output variable of the control algorithm at time t; ω is the structural characteristic parameter of the throttle valve; SP(t) is the set value of the wellhead back pressure at time t, MPa; SP(t0) is the set value of the wellhead back pressure before the last step change at time t, MPa; The pressure difference before and after the throttle valve when the throttle valve has the maximum flow diameter, MPa;

[0030]

[0031] Where ΔP min is the pressure difference before and after the throttle valve when the throttle valve has the maximum flow diameter, MPa; let the moment of the throttle valve's maximum flow diameter be t1; ρ(t1) is the density of the fluid flowing through the throttle valve at t1, g / cm 3 ; Q(t1) is the fluid flow rate flowing through the throttle valve at time t1, L / s; C d is the flow coefficient; d maxis the maximum equivalent flow diameter of the throttle valve flow section, cm; H is the height of the needle throttle valve except the part blocking the throttle port when it is fully closed, cm; θ is the angle from the side of the throttle valve to the center line, °; d1 is the diameter at the throttle port, cm.

[0032] The present invention also proposes a control law and device for adjusting the wellhead back pressure by combining open-loop rapid coarse adjustment based on the above throttle valve opening model with PID closed-loop control, including:

[0033] According to the wellhead back pressure setting value at the current moment, the throttle valve target opening value corresponding to the current moment is calculated by the control algorithm based on the throttle valve opening model, the throttle valve target opening value is compared with the actual opening value of the throttle valve at this moment to obtain their difference, and the obtained difference is compared with the set threshold value, so as to select the wellhead back pressure open loop fast coarse adjustment or precise fine adjustment;

[0034] According to the control algorithm established based on the above throttle valve opening model, the throttle valve target opening value corresponding to the wellhead back pressure setting value at the current moment is calculated, and the throttle valve opening is adjusted according to the obtained throttle valve target opening value, thereby realizing rapid coarse adjustment of the wellhead back pressure;

[0035] The back pressure deviation is obtained based on the actual detected wellhead back pressure value and the set value of the wellhead back pressure, and accurate fine adjustment of the wellhead pressure is achieved through PID automatic control.

[0036] Further, the selection of rapid coarse adjustment or precise fine adjustment of the wellhead back pressure includes:

[0037] According to the wellhead back pressure setting value at the current moment, the throttle valve target opening value corresponding to the current moment is calculated by the control algorithm based on the throttle valve opening model, the throttle valve target opening value is compared with the throttle valve actual opening value to obtain their difference, and a threshold value is set at the same time;

[0038] When the difference between the target opening value and the actual opening value of the throttle valve is greater than the threshold, it means that the actual opening value of the throttle valve differs greatly from the target opening value. At this time, a control algorithm based on the throttle valve opening model is used for regulation. The opening control module regulates the throttle valve opening value according to the calculated target opening value of the throttle valve at the current moment, so that the throttle valve opening is displaced over a large range to approach the target opening. When the final actual opening reaches the vicinity of the target opening value at the current moment, that is, the difference between the actual opening value of the throttle valve and the target opening value is less than the threshold, the throttle valve has been adjusted to the vicinity of the opening corresponding to the pressure value that needs to be set at the current moment, thereby realizing rapid coarse adjustment of the wellhead back pressure.

[0039] When the difference between the target opening value and the actual opening value of the throttle valve is less than the threshold, that is, after the rough adjustment of the pressure is completed, the actual opening value of the throttle valve is slightly different from the target opening value. At this time, the measured and set back pressure deviation value is used as the input of the PID controller to perform PID automatic control to achieve accurate fine adjustment of the wellhead back pressure.

[0040] Furthermore, the rapid rough adjustment of the wellhead back pressure includes:

[0041] According to the control algorithm based on the throttle valve opening model, as shown in equations (21), (22) and (23), the throttle valve target opening value corresponding to the wellhead back pressure setting value at the current moment is calculated. When the difference between the throttle valve target opening value and the actual opening value is greater than the threshold value, the opening value is transmitted to the opening control module, and the opening control module transmits it to the hydraulic control module. The hydraulic control module adjusts the throttle valve opening according to the target opening value. When the actual opening value of the throttle valve is finally adjusted to the target opening value, the throttle valve has been adjusted to the vicinity of the opening value corresponding to the wellhead back pressure value that needs to be set at the current moment, thereby realizing rapid coarse adjustment of the wellhead back pressure.

[0042] The specific process of the control algorithm during rapid coarse adjustment is to calculate the controller output u(t0) before the step change from the wellhead back pressure setting value given at the beginning. When the wellhead back pressure setting value changes due to the step change, the change in the controller output Δu(t) is obtained according to formula (22). At this time, the controller obtains the output value at the current moment from the initial output value u(t0) at time t=t0 through a step of Δu(t). According to formula (21), the output value of the controller at the current moment is u(t), and then the cycle is repeated based on the controller output value at the current moment until the difference between the actual opening value of the throttle valve and the target opening value is less than the threshold.

[0043] Furthermore, precise adjustment of wellhead back pressure includes:

[0044] After the rapid rough adjustment of the wellhead back pressure is completed, that is, when the difference between the target opening value and the actual opening value of the throttle valve is less than the threshold, PID automatic control is used for adjustment. The PID algorithm of the pressure control loop is as follows:

[0045] Δu(k)=K p [e(k)-e(k-1)]+K i e(k)+K d [e(k)-2e(k-1)+e(k-2)] (25)

[0046] Where, Δu(k) is the PID control output variable; K p is the proportional adjustment coefficient; K i is the integral adjustment coefficient; K dis the differential adjustment coefficient; e(k) is the control deviation, that is, the difference between the control target pressure and the actual measured pressure.

[0047] The wellhead back pressure control module is connected in series with the opening control module. The control system will compare the actual detected wellhead back pressure value with the wellhead back pressure set value, generate a control deviation value and then pass it to the throttle valve opening control module, which will then be passed to the hydraulic control module. The hydraulic control module can achieve precise fine-tuning of the wellhead back pressure by adjusting the throttle valve opening.

[0048] The specific process of the control algorithm during precise fine-tuning is that when the difference between the actual throttle valve opening value and the target opening value is less than the threshold value, the control algorithm based on the throttle valve opening model is switched to the PID automatic control algorithm, that is, the controller output obtained by the throttle valve opening model control algorithm at the previous moment is added with the controller output increment Δu(k) obtained by formula (25) to obtain the controller output value at the current moment, and then the controller output increment at the next moment is calculated by formula (25) based on this controller output value, and then the controller output value at the next moment is obtained, and this cycle is repeated.

[0049] Compared with the prior art, the beneficial effects of this application are:

[0050] According to the energy conservation principle of fluid, namely Bernoulli equation, the principle of small hole throttling is analyzed, and then the theory of small hole throttling is extended to the throttling principle of needle throttle valve. Combined with the structure of needle throttle valve, the opening model of pressure-controlled drilling throttle valve is established, and the wellhead back pressure control algorithm is established based on the model, which provides a theoretical basis for the regulation of pressure-controlled drilling throttle valve opening. Then, according to the control algorithm established based on the throttle valve opening model, the throttle valve target opening value corresponding to the wellhead back pressure setting value at the current moment is calculated. According to the relationship between the difference between the actual throttle valve opening value and the target opening value and the set threshold value, the control algorithm based on the throttle valve opening model is selected to perform fast rough adjustment of wellhead back pressure or accurate fine adjustment through PID automatic control. While ensuring the accuracy of throttle valve opening adjustment through PID automatic control, the rapidity of wellhead back pressure adjustment is improved through the fast rough adjustment of wellhead back pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0052] Figure 1The present invention is a flowchart of a wellhead back pressure control law and device based on a throttle valve opening model according to an embodiment of the present invention.

[0053] Figure 2 This is a schematic diagram of the small hole throttling described in the present invention.

[0054] Figure 3 It is a structural diagram of the needle type throttle valve described in the present invention.

[0055] Figure 4 It is a schematic diagram of the working principle of the controlled pressure drilling throttle valve control system of the present invention.

[0056] Figure 5 It is a block diagram of the wellhead back pressure control principle based on the throttle valve opening model described in the present invention. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] The embodiment of the present invention is based on the energy conservation principle of fluid flow and the structure of a needle-type throttle valve, proposes an opening model of a pressure-controlled drilling throttle valve, and establishes a wellhead back pressure based on the model, then obtains a corresponding throttle valve target opening value according to the setting value based on the throttle valve opening model and the wellhead back pressure at the current moment, compares the throttle valve target opening value with the actual opening value to obtain the difference between the two, and when the difference is greater than the set threshold, allows the throttle valve opening to be displaced over a large range to approach the target opening, and performs rapid coarse adjustment of the wellhead back pressure, and when the difference is less than the set threshold, performs PID automatic control to achieve precise fine adjustment of the wellhead back pressure, thereby achieving rapid and precise control of the wellhead back pressure. The overall implementation idea is shown in the attached Figure 1 .

[0059] Embodiments of the present invention include:

[0060] S1: According to the energy conservation principle of fluid flow, determine the relationship between the throttling pressure drop and the equivalent diameter of the throttling valve flow cross section;

[0061] S2: According to the structure of the needle throttle valve, determine the relationship between the equivalent diameter and the throttle valve opening and closing degree;

[0062] S3: The throttle valve opening model is obtained by jointly calculating the relationship between the throttle pressure drop and the equivalent diameter of the throttle valve flow cross section and the relationship between the equivalent diameter and the throttle valve opening degree, and a wellhead back pressure control algorithm is established based on the model;

[0063] S4: According to the wellhead back pressure control law and device based on the throttle valve opening model, the wellhead back pressure is regulated by combining open-loop fast regulation with PID closed-loop control.

[0064] The following is a detailed description of each step:

[0065] S1: According to the energy conservation principle of fluid flow, determine the relationship between the throttling pressure drop and the equivalent diameter of the throttling valve flow cross section;

[0066] The throttling principle of the needle throttle valve is determined by the theory of small hole throttling. The throttle valve changes the flow area of ​​the fluid in the valve by changing the stroke size between the valve core and the valve seat on the basis of the small hole throttling theory, thereby changing the resistance coefficient δ under the corresponding valve opening. The pressure and flow rate before and after the throttle valve are adjusted by changing the stroke size.

[0067] When the fluid passes through a small hole, the fluid will be subject to local resistance, which will lead to energy loss due to the local resistance. This is because when the fluid passes through the small hole, the flow area is reduced, resulting in energy loss before and after the small hole throttling, and there is a change in pressure difference before and after the small hole throttling. Generally, the throttling pressure difference between the inlet and outlet of the small hole represents the energy loss caused by the fluid flowing in the small hole.

[0068] The energy change of the fluid flowing through the small hole is used to explain the energy change of the fluid when it flows through the needle throttle valve. Therefore, according to the energy conservation principle of the fluid, that is, the Bernoulli equation, the theory of small hole throttling is first derived, and the small hole throttling pressure difference formula is derived. Then, the relationship between the throttling pressure drop of the throttle valve and the equivalent diameter of the flow section of the throttle valve is obtained.

[0069] Here we take small hole throttling as an example, refer to Figure 2 , to analyze the relationship between the throttling pressure difference and the characteristic parameters of the small hole.

[0070] Assuming that the diameter of the fluid flow pipe is uniform before and after the orifice throttling, the fluid flow rate is equal, and the fluid geometric pressure head is equal at all points in the horizontal pipe, the following formula can be obtained based on the energy conservation principle of the fluid, that is, the Bernoulli equation:

[0071]

[0072] From the above formula, we can get the equation before and after throttling:

[0073]

[0074] Where v1 and v2 are the velocities of the fluid before and after the hole, respectively, m / s; ρ1 and ρ2 are the fluid densities before and after the hole, respectively, kg / m 3 ; P1 and P2 are the fluid pressures before and after the small hole, pa.

[0075] For an ideal fluid, ρ1=ρ2=ρ, so the velocity formula v after the fluid flows through the small hole can be deduced from the above formula: 20 :

[0076]

[0077] In the formula, v 20 is the velocity of the fluid after passing through the small hole without considering the fluid friction resistance loss, m / s; ρ is the fluid density, kg / m 3 .

[0078] For actual fluids, the friction loss of the fluid must be taken into account, so the actual velocity v2 of the fluid after flowing through the small hole is:

[0079]

[0080] Where ξ is the velocity coefficient.

[0081] The formula for the speed factor is as follows:

[0082]

[0083] Assuming ε is the small hole contraction coefficient, the relationship between the flow area at the small hole outlet and the small hole cross-sectional area is:

[0084] A1=εA2 (6)

[0085] The flow formula for flowing through the small hole throttle is:

[0086] Q=A1v2=εA2v2=εA2v 20 ξ=C d A2v 20 (7)

[0087] Where Q is the fluid flow rate, m 3 / s; A1 is the flow area at the orifice outlet, m 2 ; A2 is the cross-sectional area of ​​the small hole, m 2 ; C d is the small hole flow coefficient.

[0088] The orifice flow coefficient can be calculated by the following formula:

[0089] C d =ξε (8)

[0090] According to the circle area formula, the cross-sectional area of ​​the small hole is:

[0091]

[0092] Combining the above formula with formula (3) and substituting it into formula (7), we can get:

[0093]

[0094] And because:

[0095]

[0096] Where d is the diameter of the flow section of the small hole, m; D is the diameter of the flow pipe, m.

[0097] So it can be considered Then the above formula becomes:

[0098]

[0099] By transforming the above formula, we can finally get the small hole throttling pressure difference formula:

[0100]

[0101] Where, ΔP is the throttling pressure difference before and after the orifice, pa;

[0102] Based on the small hole throttling pressure difference formula, the relationship between the throttling pressure drop and the equivalent diameter of the throttling valve flow cross section can be obtained:

[0103]

[0104] In the formula, is the throttle pressure difference before and after the throttle valve at time t, MPa; is the density of the fluid flowing through the throttle valve at time t, g / cm 3 ; is the fluid flow rate flowing through the throttle valve at time t, L / s; is the flow coefficient; is the equivalent diameter of the throttle valve flow cross section at time t, cm.

[0105] S2: According to the structure of the needle throttle valve, determine the relationship between the equivalent diameter and the throttle valve opening and closing degree;

[0106] Needle throttle valve structure reference Figure 3 ,According to the structural characteristics of the needle-type throttle valve, the relationship between the equivalent diameter and the throttle valve opening and closing degree is obtained.

[0107] Maximum equivalent diameter of throttle valve flow cross section for:

[0108]

[0109] Wherein, H is the height of the needle throttle valve except the part blocking the throttle port when it is fully closed, cm; θ is the angle from the side of the throttle valve to the center line, °; d1 is the diameter at the throttle port, cm.

[0110] The structural characteristic parameter formula of the throttle valve is:

[0111]

[0112] Assume β is the opening of the throttle valve:

[0113]

[0114] Where, β is the throttle valve opening; h x It is the height of the part blocking the throttle port when the needle throttle valve is fully closed, cm.

[0115] According to the structural characteristics of the needle throttle valve, the relationship between the equivalent diameter and the throttle valve opening can be obtained as follows:

[0116]

[0117] In the formula, is the equivalent diameter of the throttle valve flow cross section at time t, cm; is the maximum equivalent diameter of the throttle valve flow section, cm; β(t) is the throttle valve opening at time t; ω is the structural characteristic parameter.

[0118] S3: The throttle valve opening model is obtained by jointly calculating the relationship between the throttle pressure drop and the equivalent diameter of the throttle valve flow cross section and the relationship between the equivalent diameter and the throttle valve opening degree, and a wellhead back pressure control algorithm is established based on the model;

[0119] Substituting equation (18) into equation (14), we can get the relationship between the pressure drop before and after the throttle valve and the throttle valve opening as follows:

[0120]

[0121] In the formula, is the throttling pressure loss calculated according to formula (14) at the maximum flow diameter of the throttling valve, MPa.

[0122] Further deducing from the relationship between the pressure drop before and after the throttle valve and the throttle valve opening, the throttle valve opening model can be finally obtained as follows:

[0123]

[0124] Where, β(t) is the throttle valve opening at time t; ω is the structural characteristic parameter; is the inlet and outlet throttling pressure difference under the maximum flow diameter of the throttle valve, MPa; is the throttling pressure difference between the inlet and outlet of the throttle valve at time t, MPa.

[0125] Based on the throttle valve opening model established above, the wellhead back pressure control algorithm is established. When the pressure loss of the surface pipeline is ignored, the wellhead back pressure is approximately equal to the throttle pressure difference between the inlet and outlet of the throttle valve. Therefore, the set value of the wellhead back pressure is used to replace the throttle pressure difference between the inlet and outlet of the throttle valve in the control algorithm. According to the established throttle valve opening model, the control algorithm can be expressed as:

[0126] u(t)=u(t0)+Δu(t) (21)

[0127]

[0128] Wherein, u(t) is the output variable of the control algorithm at time t; u(t0) is the output variable of the control algorithm before the last step change at time t; Δu(t) is the change in the output variable of the control algorithm at time t; ω is the structural characteristic parameter of the throttle valve; SP(t) is the set value of the wellhead back pressure at time t, MPa; SP(t0) is the set value of the wellhead back pressure before the last step change at time t, MPa; The pressure difference before and after the throttle valve when the throttle valve has the maximum flow diameter, MPa;

[0129]

[0130] In the formula, is the pressure difference before and after the throttle valve when the throttle valve has the maximum flow diameter, MPa; let the time when the throttle valve has the maximum flow diameter be t1; is the density of the fluid flowing through the throttle valve at time t1, g / cm 3 ; is the fluid flow rate flowing through the throttle valve at time t1, L / s; is the flow coefficient; is the maximum equivalent flow diameter of the throttle valve flow section, cm; H is the height of the needle throttle valve except the part blocking the throttle port when it is fully closed, cm; θ is the angle from the side of the throttle valve to the center line, °; d1 is the diameter at the throttle port, cm.

[0131] S4: According to the wellhead back pressure control law and device based on the throttle valve opening model, the wellhead back pressure is regulated by combining open-loop fast regulation with PID closed-loop control.

[0132] The throttle valve control system is mainly composed of a data acquisition module, an opening control module, and a hydraulic control module. The data acquisition module is composed of a displacement sensor and a pressure sensor, which are used to obtain signals such as the riser pressure, casing pressure, and throttle valve opening; the opening control module is mainly composed of an input signal source, a proportional amplifier, and a PID controller, which transmits the signal to the hydraulic control module; the hydraulic control module is mainly composed of an electro-hydraulic proportional valve, a hydraulic cylinder, and a needle-type throttle valve. The electro-hydraulic proportional valve controls the opening value and opening adjustment speed of the throttle valve through the hydraulic cylinder according to the obtained signal. For a schematic diagram of the working principle of the pressure-controlled drilling throttle valve control system, refer to Figure 4 .

[0133] The working process of the throttle valve control system is as follows: the input signal source inputs the command through the proportional amplifier and then transmits it to the electro-hydraulic proportional reversing valve. When the right coil of the electro-hydraulic proportional valve is energized, the left liquid circuit is the passage, and the hydraulic oil enters from the middle of the valve and enters the left chamber of the hydraulic cylinder, thereby pushing the hydraulic cylinder piston actuator to move in one direction, and the opening of the throttle valve changes; conversely, if the other side of the electro-hydraulic proportional valve is energized, thereby pushing the hydraulic cylinder piston actuator to move in the other opposite direction, the throttle valve opening can be adjusted in the opposite direction. It can be seen that after the electro-hydraulic proportional valve receives the signal from the proportional amplifier, the two pressure outlets are connected to the rod chamber and the rodless chamber of the hydraulic cylinder respectively, and the hydraulic oil enters the hydraulic cylinder of the throttle valve through different passages, pushing the valve core to move, and finally the throttle valve opening can be adjusted, thereby adjusting the wellhead back pressure.

[0134] Block diagram of wellhead back pressure control principle based on throttle valve opening model Figure 5 When the pressure loss of the surface pipeline is ignored, the wellhead back pressure is approximately equal to the inlet and outlet pressure difference of the throttle valve. The wellhead back pressure setting value at the current moment is substituted into the control algorithm based on the throttle valve opening model, and the corresponding target opening value of the throttle valve at the current moment is calculated. The target opening value of the throttle valve is compared with the actual opening value to obtain the difference between the two, and then a threshold is set to compare the size relationship between the difference between the two and the threshold.

[0135] When the difference between the target opening value and the actual opening value of the throttle valve at the current moment is greater than the set threshold, it means that the actual opening value of the throttle valve is significantly different from the target opening value at this time. According to the control algorithm based on the throttle valve opening model, the target opening value corresponding to the wellhead back pressure setting value at this time is calculated and transmitted to the opening control module, and the opening control module transmits it to the hydraulic control module. The hydraulic control module adjusts the actual throttle valve opening according to the target opening value, so that the throttle valve opening is displaced over a large range to approach the target opening value. When the actual opening value reaches near the target opening value, that is, the difference between the actual opening value of the throttle valve and the target opening value is less than the threshold, the throttle valve has been adjusted to near the opening corresponding to the required set pressure value, thereby realizing rapid coarse adjustment of the wellhead back pressure based on the throttle valve opening model. After completing the rapid coarse adjustment of the wellhead back pressure, the difference between the target opening value and the actual opening value of the throttle valve is less than the set threshold value. The wellhead back pressure control module is connected in series with the opening control module to measure the wellhead back pressure value. Then, the actually detected wellhead back pressure value is compared with the set value of the wellhead back pressure. A control deviation value is generated and then transmitted to the throttle valve opening control module. The opening control module then transmits it to the hydraulic control module. The hydraulic control module adjusts the throttle valve opening to change the wellhead back pressure value, thereby using PID automatic control to achieve precise fine adjustment of the wellhead back pressure.

[0136] In the process of rapid rough adjustment of the wellhead back pressure, the control algorithm based on the throttle valve opening model established above is used for open-loop adjustment. The control algorithm is shown in equations (21), (22), and (23). The controller output u(t0) before the step change is calculated by the wellhead back pressure setting value given at the beginning. When the wellhead back pressure setting value changes due to the step change, the change Δu(t) of the controller output is obtained according to equation (22). At this time, the controller obtains the output value at the current moment from the initial output value u(t0) at time t=t0 through a step of Δu(t). According to equation (21), the output value of the controller at the current moment is u(t), and then the cycle is repeated based on the controller output value at the current moment until the difference between the actual throttle valve opening value and the target opening value is less than the threshold value.

[0137] In the process of precise fine adjustment of wellhead back pressure, PID automatic control is used for adjustment. The PID automatic control algorithm can be expressed as:

[0138]

[0139] Where, u(t) is the PID control output variable at time t; t is time, s; K p is the proportional adjustment coefficient; e(t) is the control deviation; T i is the integration time constant; T d is the differential time constant.

[0140] It can be seen from formula (24) that due to the existence of the integral term, the PID control algorithm will cause the accumulation of control errors, which will increase the error of throttle valve opening adjustment. Therefore, in order to eliminate the integral term error, an incremental PID control algorithm is used here:

[0141] Δu(k)=K p [e(k)-e(k-1)]+K i e(k)+K d [e(k)-2e(k-1)+e(k-2)] (25)

[0142] Where, Δu(k) is the PID control output variable; K p is the proportional adjustment coefficient; K i is the integral adjustment coefficient; K d is the differential adjustment coefficient; e(k) is the control deviation, that is, the difference between the control target pressure and the actual measured pressure.

[0143] The specific process of the control algorithm during precise fine-tuning is that when the difference between the actual throttle valve opening value and the target opening value is less than the threshold, the control algorithm based on the throttle valve opening model is switched to the PID automatic control algorithm, that is, the controller output obtained by the throttle valve opening model control algorithm at the previous moment is added with the controller output increment Δu(k) obtained by formula (25) to obtain the controller output value at the current moment, and then the controller output increment at the next moment is calculated by formula (24) based on this controller output value, and then the controller output value at the next moment is obtained, and this cycle is repeated.

[0144] According to the control algorithm based on the throttle valve opening model, the target opening value of the throttle valve corresponding to the wellhead back pressure setting value at the current moment is calculated. When the deviation between the target opening value of the throttle valve and the actual opening value of the throttle valve is greater than the threshold value, according to the control algorithm based on the throttle valve opening model, the target opening value of the throttle valve corresponding to the wellhead back pressure setting value at the current moment is calculated, and the throttle valve opening is directly open-loop adjusted. This can greatly improve the adjustment speed of the throttle valve opening and achieve rapid coarse adjustment of the wellhead back pressure. Then, the throttle valve opening is accurately adjusted through PID automatic control. While ensuring the accuracy of the throttle valve opening adjustment, the speed of the throttle valve opening adjustment is improved, and rapid and accurate adjustment of the wellhead back pressure is achieved.

[0145] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0146] It should be noted that, in this application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0147] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A controlled pressure drilling throttle valve opening model and a wellhead back pressure control algorithm based on the model, characterized in that: include: According to the energy conservation principle of fluid flow, the relationship between the throttling pressure drop and the equivalent diameter of the throttling valve flow cross section is determined; According to the structure of needle throttle valve, the relationship between equivalent diameter and throttle valve opening and closing degree is determined; The throttle valve opening model is obtained by jointly calculating the relationship between the throttling pressure drop and the equivalent diameter of the throttle valve flow cross-section and the relationship between the equivalent diameter and the throttle valve opening degree.

2. According to the opening model of the pressure-controlled drilling throttle valve according to claim 1, a wellhead back pressure control algorithm is established based on the model, characterized in that: The relationship between the throttling pressure drop and the equivalent diameter of the throttling valve flow cross section includes: The throttling principle of the needle throttle valve is determined by the theory of small hole throttling. The throttle valve changes the flow area of ​​the fluid in the valve by changing the stroke size between the valve core and the valve seat on the basis of the small hole throttling theory, and adjusts the pressure and flow size before and after the throttle valve by changing the stroke size. The energy change of the fluid flowing through the small hole is used to explain the energy change of the fluid when it flows through the needle throttle valve. Therefore, according to the energy conservation principle of the fluid, that is, the Bernoulli equation, the theory of small hole throttling is first derived, and the small hole throttling pressure difference formula is derived. Then, the relationship between the throttling pressure drop of the throttle valve and the equivalent diameter of the flow section of the throttle valve is obtained. According to the energy conservation principle of fluid energy, namely the Bernoulli equation, the small hole throttling pressure difference formula is derived: In the formula, ΔP is the throttling pressure difference before and after the orifice, pa; ρ is the fluid density, kg / m3; Q is the fluid flow rate, m3 / s; Cd is the orifice flow coefficient; d is the orifice flow section diameter. Then, the relationship between the throttling pressure drop and the equivalent diameter of the throttling valve flow cross section is determined by the small hole throttling pressure difference formula. Their relationship is as follows: In the formula, is the throttle pressure difference before and after the throttle valve at time t, MPa; is the density of the fluid flowing through the throttle valve at time t, g / cm 3 ; is the fluid flow rate flowing through the throttle valve at time t, L / s; is the flow coefficient; is the equivalent diameter of the throttle valve flow cross section at time t, cm.

3. According to the opening model of the pressure-controlled drilling throttle valve of claim 1, a wellhead back pressure control algorithm is established based on the model, characterized in that: Determining the relationship between the equivalent diameter and the throttle valve opening degree includes: The relationship between the equivalent diameter and the throttle valve opening degree is: In the formula, is the equivalent diameter of the throttle valve flow cross section at time t, cm; is the maximum equivalent diameter of the throttle valve flow section, cm; β(t) is the throttle valve opening at time t; ω is the structural characteristic parameter.

4. According to the opening model of the pressure-controlled drilling throttle valve according to claim 1, a wellhead back pressure control algorithm is established based on the model, characterized in that: The relationship between the throttle pressure drop and the equivalent diameter of the throttle valve flow cross section and the relationship between the equivalent diameter and the throttle valve opening degree are jointly calculated to obtain the throttle valve opening model and establish the wellhead back pressure control algorithm based on the model, including: Through joint calculation, the throttle valve opening model is obtained as follows: Where, β(t) is the throttle valve opening at time t; ω is the structural characteristic parameter; is the inlet and outlet throttling pressure difference under the maximum flow diameter of the throttle valve, MPa; is the throttling pressure difference between the inlet and outlet of the throttle valve at time t, MPa. Based on the throttle valve opening model established above, the wellhead back pressure control algorithm is established. When the pressure loss of the surface pipeline is ignored, the wellhead back pressure is approximately equal to the throttle pressure difference between the inlet and outlet of the throttle valve. Therefore, the set value of the wellhead back pressure is used to replace the throttle pressure difference between the inlet and outlet of the throttle valve in the control algorithm. According to the established throttle valve opening model, the control algorithm can be expressed as u(t)=u(t0)+Δu(t) (21) Wherein, u(t) is the output variable of the control algorithm at time t; u(t0) is the output variable of the control algorithm before the last step change at time t; Δu(t) is the change in the output variable of the control algorithm at time t; ω is the structural characteristic parameter of the throttle valve; SP(t) is the set value of the wellhead back pressure at time t, MPa; SP(t0) is the set value of the wellhead back pressure before the last step change at time t, MPa; The pressure difference before and after the throttle valve when the throttle valve has the maximum flow diameter, MPa; In the formula, is the pressure difference before and after the throttle valve when the throttle valve has the maximum flow diameter, MPa; let the time when the throttle valve has the maximum flow diameter be t1; is the density of the fluid flowing through the throttle valve at time t1, g / cm 3 ; is the fluid flow rate flowing through the throttle valve at time t1, L / s; is the flow coefficient; is the maximum equivalent flow diameter of the throttle valve flow section, cm; H is the height of the needle throttle valve except the part blocking the throttle port when it is fully closed, cm; θ is the angle from the side of the throttle valve to the center line, °; d1 is the diameter at the throttle port, cm.

5. A control law and device for adjusting wellhead back pressure by combining open-loop rapid coarse adjustment based on the above throttle valve opening model with PID closed-loop control, characterized in that: include: According to the wellhead back pressure setting value at the current moment, the throttle valve target opening value corresponding to the current moment is calculated by the control algorithm based on the throttle valve opening model, the throttle valve target opening value is compared with the actual opening value of the throttle valve at this moment to obtain their difference, and the obtained difference is compared with the set threshold value, so as to select the wellhead back pressure open loop fast coarse adjustment or precise fine adjustment; According to the control algorithm established based on the above throttle valve opening model, the throttle valve target opening value corresponding to the wellhead back pressure setting value at the current moment is calculated, and the throttle valve opening is adjusted according to the obtained throttle valve target opening value, thereby realizing rapid coarse adjustment of the wellhead back pressure; the back pressure deviation is obtained based on the actually detected wellhead back pressure value and the set value of the wellhead back pressure, and accurate fine adjustment of the wellhead pressure is realized through PID automatic control.

6. The control law and device for adjusting the wellhead back pressure by combining the open-loop rapid coarse adjustment based on the above throttle valve opening model with the PID closed-loop control according to claim 5 is characterized in that: The options for quick coarse adjustment or precise fine adjustment of wellhead back pressure include: According to the wellhead back pressure setting value at the current moment, the throttle valve target opening value corresponding to the current moment is calculated by the control algorithm based on the throttle valve opening model, the throttle valve target opening value is compared with the throttle valve actual opening value to obtain their difference, and a threshold value is set at the same time; When the difference between the target opening value and the actual opening value of the throttle valve is greater than the threshold, it means that the actual opening value of the throttle valve differs greatly from the target opening value. At this time, a control algorithm based on the throttle valve opening model is used for regulation. The opening control module regulates the throttle valve opening value according to the calculated target opening value of the throttle valve at the current moment, so that the throttle valve opening is displaced over a large range to approach the target opening. When the final actual opening reaches the vicinity of the target opening value at the current moment, that is, the difference between the actual opening value of the throttle valve and the target opening value is less than the threshold, the throttle valve has been adjusted to the vicinity of the opening corresponding to the pressure value that needs to be set at the current moment, thereby realizing rapid coarse adjustment of the wellhead back pressure. When the difference between the target opening value and the actual opening value of the throttle valve is less than the threshold, that is, after the rough adjustment of the pressure is completed, the actual opening value of the throttle valve is slightly different from the target opening value. At this time, the measured and set back pressure deviation value is used as the input of the PID controller to perform PID automatic control to achieve accurate fine adjustment of the wellhead back pressure.

7. The control law and device for adjusting the wellhead back pressure by combining the open-loop rapid coarse adjustment based on the above throttle valve opening model with the PID closed-loop control according to claim 5 is characterized in that: The rapid rough adjustment of wellhead back pressure includes: According to the control algorithm based on the throttle valve opening model, as shown in equations (21), (22) and (23), the throttle valve target opening value corresponding to the wellhead back pressure setting value at the current moment is calculated. When the difference between the throttle valve target opening value and the actual opening value is greater than the threshold value, the opening value is transmitted to the opening control module, and the opening control module transmits it to the hydraulic control module. The hydraulic control module adjusts the throttle valve opening according to the target opening value. When the actual opening value of the throttle valve is finally adjusted to the target opening value, the throttle valve has been adjusted to the vicinity of the opening value corresponding to the wellhead back pressure value that needs to be set at the current moment, thereby realizing rapid coarse adjustment of the wellhead back pressure. The specific process of the control algorithm during rapid coarse adjustment is to calculate the controller output u(t0) before the step change from the wellhead back pressure setting value given at the beginning. When the wellhead back pressure setting value changes due to the step change, the change in the controller output Δu(t) is obtained according to formula (22). At this time, the controller obtains the output value at the current moment from the initial output value u(t0) at time t=t0 through a step of Δu(t). According to formula (21), the output value of the controller at the current moment is u(t), and then the cycle is repeated based on the controller output value at the current moment until the difference between the actual opening value of the throttle valve and the target opening value is less than the threshold.

8. According to claim 5, a control law and device for adjusting wellhead back pressure by combining open-loop rapid coarse adjustment based on the above throttle valve opening model with PID closed-loop control is implemented, characterized in that: Achieving precise fine-tuning of wellhead back pressure includes: After the rapid rough adjustment of the wellhead back pressure is completed, that is, when the difference between the target opening value and the actual opening value of the throttle valve is less than the threshold, PID automatic control is used for adjustment. The PID algorithm of the pressure control loop is as follows: Δu(k)=K p [e(k)-e(k-1)]+K i e(k)+K d [e(k)-2e(k-1)+e(k-2)] (25) Where, Δu(k) is the PID control output variable; K p is the proportional adjustment coefficient; K i is the integral adjustment coefficient; K d is the differential adjustment coefficient; e(k) is the control deviation, that is, the difference between the control target pressure and the actual measured pressure. The wellhead back pressure control module is connected in series with the opening control module. The control system will compare the actual detected wellhead back pressure value with the wellhead back pressure set value, generate a control deviation value and then pass it to the throttle valve opening control module, which will then be passed to the hydraulic control module. The hydraulic control module can achieve precise fine-tuning of the wellhead back pressure by adjusting the throttle valve opening. The specific process of the control algorithm during precise fine-tuning is that when the difference between the actual throttle valve opening value and the target opening value is less than the threshold value, the control algorithm based on the throttle valve opening model is switched to the PID automatic control algorithm, that is, the controller output value obtained by the throttle valve opening model control algorithm at the previous moment is added with the controller output increment Δu(k) obtained by formula (25) to obtain the controller output value at the current moment, and then the controller output increment at the next moment is calculated by formula (25) based on this controller output value, and then the controller output value at the next moment is obtained, and this cycle is repeated.

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