Fine regulation method and system for wellhead throttling pressure considering inlet and outlet density measurement

Abstract

The present invention relates to a method and system for fine control of wellhead throttling pressure considering the measurement of inlet and outlet density, which includes: obtaining the initial wellhead backpressure value based on the bottomhole target pressure and the initial bottomhole pressure value; performing fine cyclic control on the wellhead throttling pressure according to the initial wellhead backpressure value and the density difference of drilling fluid at the inlet and outlet of the operating well, adjusting the wellhead backpressure to the target value, and obtaining the density distribution of drilling fluid in the wellbore; accurately calculating the bottomhole pressure based on the density distribution of drilling fluid in the wellbore, updating the wellhead backpressure value according to the bottomhole pressure and the bottomhole target pressure, adjusting the wellhead backpressure to the target value, and cyclically updating the density distribution in the wellbore, the bottomhole pressure and the wellhead backpressure value until the drilling is completed. The present invention can achieve the purpose of precise control of wellbore pressure, avoid the occurrence of complex accidents such as well kicks and losses during drilling and completion; and can be applied in the field of drilling and completion engineering for oil and gas development.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas development drilling and completion engineering, and particularly to a method and system for fine control of wellhead throttling pressure considering density measurement at the inlet and outlet. Background Art

[0002] The fine pressure control drilling technology is a new drilling technology developed in recent years. This technology combines the real-time calculation of wellbore hydraulic parameters during the drilling process with the wellhead backpressure control equipment to finely control the wellbore pressure in real time, keeping the wellbore pressure always within the safe operating window range of the formation, preventing complex accidents such as well kick and blowout, and making up for the deficiencies of traditional drilling technologies.

[0003] The core of the fine pressure control drilling technology is to accurately predict the bottom hole pressure and give the target wellhead backpressure value based on it, so as to achieve the purpose of finely controlling the wellbore pressure. During the drilling process, the configuration of the drilling fluid is affected by factors such as the solid content of the drilling fluid and on-site configuration equipment, resulting in difficulty in stably maintaining the drilling fluid density at the designed value. In actual drilling, the drilling fluid density always fluctuates around the designed value. Especially for deep wells, the change in the drilling fluid density will significantly affect the accurate prediction of the bottom hole pressure, thus posing challenges to the precise control of the wellbore pressure. Summary of the Invention

[0004] Aiming at the above problems, the purpose of the present invention is to provide a method and system for fine control of wellhead throttling pressure considering density measurement at the inlet and outlet, which can achieve the purpose of precise regulation of the wellbore pressure. At the same time, it avoids the occurrence of complex accidents such as well kick and loss during drilling and completion.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: A method for fine control of wellhead throttling pressure considering density measurement at the inlet and outlet, which includes: obtaining the initial wellhead backpressure value according to the bottom hole target pressure and the initial bottom hole pressure value; finely and circularly regulating the wellhead throttling pressure according to the initial wellhead backpressure value and the density difference of the drilling fluid at the inlet and outlet of the operating well, adjusting the wellhead backpressure to the target value, and obtaining the density distribution of the drilling fluid in the wellbore; accurately calculating the bottom hole pressure according to the density distribution of the drilling fluid in the wellbore, updating the wellhead backpressure value according to the bottom hole pressure and the bottom hole target pressure, adjusting the wellhead backpressure to the target value, and circularly updating the density distribution in the wellbore, the bottom hole pressure and the wellhead backpressure value until the drilling is completed.

[0006] Further, the bottom hole target pressure is: according to the three-pressure profile of the formation of the operating well, record the formation pore pressure P p and fracture pressure P f at the bottom hole. From the formation pore pressure P p and fracture pressure P f at the bottom hole, obtain the bottom hole target pressure;

[0007] P aim = (P p + P f ) / 2,

[0008] wherein, P aim is the bottom-hole target pressure.

[0009] Furthermore, the initial value of the bottom-hole pressure is:

[0010] Obtain the designed density of the drilling fluid according to the basic data of the well under operation, and calculate the initial value of the bottom-hole pressure from the designed density of the drilling fluid and the wellbore structure;

[0011]

[0012] wherein, p b0 is the initial value of the bottom-hole pressure, Pa; h is the well depth, m; f is the annular friction coefficient; v is the flow velocity of the drilling fluid in the annulus, m / s; d w is the wellbore diameter, m; d po is the outer diameter of the drill pipe, m; g is the acceleration due to gravity; ρ0 is the designed density of the drilling fluid, which is default equal to the designed density of the drilling fluid at the initial moment.

[0013] Furthermore, the fine circulation control of the wellhead throttling pressure includes:

[0014] At the initial moment, the density of the drilling fluid in the wellbore is considered to be equal to the designed density ρ0 of the drilling fluid;

[0015] Set a time interval, read the density ρ n of the drilling fluid at the inlet, the density ρ' n of the drilling fluid at the outlet, and the drilling fluid displacement Q to calculate the height h in of the newly injected drilling fluid column during this time period and the height h out of the flowing-out drilling fluid column during this time period;

[0016] According to the density difference between the inlet and outlet, the height h in of the injected drilling fluid column and the height h out of the flowing-out drilling fluid column, update the target value of the wellhead back pressure and adjust the wellhead back pressure to the target value, and then the density distribution of the drilling fluid in the wellbore can be obtained.

[0017] Furthermore, the accurate calculation of the bottom-hole pressure based on the density distribution of the drilling fluid in the wellbore includes:

[0018]

[0019] wherein, M is the number of annular fluid space grids; p b is the bottom-hole pressure; f i is the annular friction coefficient in the i-th annular fluid space grid; ρ′i is the density within the i-th annulus fluid space grid; h i is the height of the annulus fluid space grid.

[0020] A system for implementing the above-mentioned fine regulation method of wellhead throttle pressure considering inlet and outlet density measurement, comprising: a derrick, arranged at the upper part of the wellbore center; an inlet densitometer, arranged at the output end of the drilling fluid tank for real-time measurement of the density of the injected drilling fluid; an automatic pressure control throttle device, one end of which is connected to the wellhead outlet end of the wellbore, and the internal pressure of the wellbore is adjusted through the automatic pressure control throttle device; an outlet densitometer, connected to the other end of the automatic pressure control throttle device for real-time measurement of the density of the drilling fluid at the wellhead outlet; a fine pressure control drilling control system, configured to receive the density of the injected drilling fluid and the density of the drilling fluid at the wellhead outlet transmitted by the inlet densitometer and the outlet densitometer, and obtain a control signal according to the received drilling fluid density and transmit it to the automatic pressure control throttle device to control the automatic pressure control throttle device to adjust the internal pressure of the wellbore.

[0021] Further, it further includes a blowout preventer, arranged at the wellhead outlet end.

[0022] Further, it further includes a drilling pump and a flowmeter;

[0023] The drilling pump is arranged at the output end of the drilling fluid tank, used to provide power for injecting the drilling fluid into the wellbore and adjust the displacement during the injection process;

[0024] The flowmeter is connected to the outlet densitometer for real-time measurement of the drilling circulation displacement, and the drilling fluid circulated out of the wellbore is sequentially transmitted to the mud pit through the automatic pressure control throttle device, the outlet densitometer and the flowmeter.

[0025] A computer-readable storage medium storing one or more programs, characterized in that the one or more programs include instructions that, when executed by a computing device, cause the computing device to execute any of the above methods.

[0026] A computing device, comprising: one or more processors, a memory and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing any of the above methods.

[0027] Due to the above technical solutions adopted by the present invention, it has the following advantages:

[0028] 1. The present invention installs density measuring devices at the inlet and outlet of the drilling fluid respectively to obtain the density of the drilling fluid at the inlet and outlet in real time, thereby obtaining the spatio-temporal distribution of the drilling fluid in the wellbore, giving a precise prediction method for the bottom-hole pressure, and then regulating the wellhead backpressure in real time to achieve the purpose of precise regulation of the wellbore pressure.

[0029] 2. The present invention can effectively prevent the occurrence of complex accidents such as well kicks and losses during drilling and completion, and makes up for the deficiencies of traditional drilling technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flow chart of a fine regulation method for wellhead throttle pressure considering density measurement at the inlet and outlet in an embodiment of the present invention;

[0031] Figure 2 is a schematic structural diagram of a fine regulation system for wellhead throttle pressure considering density measurement at the inlet and outlet in an embodiment of the present invention;

[0032] Figure 3 is a flow chart of real-time recording of the density of wellbore drilling fluid in an embodiment of the present invention;

[0033] REFERENCE SIGNS

[0034] 1. Derrick; 2. Blowout preventer; 3. Wellbore; 4. Drill pipe; 5. Inlet densitometer; 6. Drilling pump; 7. Drilling fluid tank; 8. Automatic pressure control throttle device; 9. Outlet densitometer; 10. Flowmeter; 11. Fine pressure control drilling software system; 12. Mud pit. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention fall within the scope of protection of the present invention.

[0036] It should be noted that the terms used herein are only for describing the specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of the described features, steps, operations, devices, components, and / or their combinations.

[0037] In an embodiment of the present invention, a fine regulation method for wellhead throttle pressure considering density measurement at the inlet and outlet is provided. In this embodiment, as Figure 1 shown, the method includes the following steps:

[0038] 1) Obtain the initial wellhead backpressure value according to the bottom-hole target pressure and the initial bottom-hole pressure value.

[0039] 2) According to the initial wellhead backpressure value and the density difference of the drilling fluid at the inlet and outlet of the operation well, finely adjust and control the wellhead throttling pressure in a cycle, adjust the wellhead backpressure to the target value, and obtain the density distribution of the drilling fluid in the wellbore.

[0040] 3) Accurately calculate the bottom-hole pressure based on the density distribution of the drilling fluid in the wellbore. According to the bottom-hole pressure and the bottom-hole target pressure, update the wellhead backpressure value, adjust the wellhead backpressure to the target value, and cycle to update the density distribution in the wellbore, the bottom-hole pressure, and the wellhead backpressure value until the drilling is completed.

[0041] In the above step 1), the bottom-hole target pressure is: according to the three-pressure profile of the formation of the operation well, record the formation pore pressure P p and the fracture pressure P f at the bottom hole. Obtain the bottom-hole target pressure from the formation pore pressure P p and the fracture pressure P f at the bottom hole.

[0042] P aim =(P p +P f ) / 2,

[0043] In the formula, P aim is the bottom-hole target pressure. In the above step 1), the initial bottom-hole pressure value is: obtain the designed density ρ0 of the drilling fluid according to the basic data of the operation well, and calculate the initial bottom-hole pressure value from the designed density of the drilling fluid and the wellbore structure.

[0044]

[0045] In the formula, p b0 is the initial bottom-hole pressure value, Pa; h is the well depth, m; f is the annular friction coefficient; v is the annular drilling fluid flow velocity, m / s; d w is the wellbore diameter, m; d po is the outer diameter of the drill pipe, m; g is the acceleration due to gravity; ρ0 is the designed density of the drilling fluid, and it is default equal to the designed density of the drilling fluid at the initial moment.

[0046] In this embodiment, the basic data of the operation well includes: wellbore trajectory, wellbore structure, formation temperature gradient, circulation displacement, etc.

[0047] In the above step 1), according to the bottom-hole pressure and the bottom-hole target value, obtain the initial wellhead backpressure value P a0 =P aim -P b .

[0048] In step 2) above, the wellhead throttling pressure is finely cyclically regulated, including the following steps:

[0049] 2.1) As Figure 2 shown, at the initial moment, the density of the drilling fluid in the wellbore is considered equal to the designed density ρ0 of the drilling fluid;

[0050] 2.2) Set a time interval, and read the density ρ n of the drilling fluid at the inlet, the density ρ’ n of the drilling fluid at the outlet, and the drilling fluid displacement Q to calculate the height h in of the newly injected drilling fluid column during this time period and the height h out of the drilling fluid column flowing out during this time period;

[0051] For example, the time interval Δt = 30 s.

[0052] In this embodiment, the height h in of the newly injected drilling fluid column is:

[0053]

[0054] In the formula, h in is the height of the newly injected drilling fluid column, m; Δt is the data reading time interval, s; Q is the drilling displacement, m 3 / s; A p is the cross-sectional area inside the drill pipe, m 2 .

[0055] The height h out of the drilling fluid column flowing out during this time period is:

[0056]

[0057] In the formula, h out is the height of the drilling fluid column flowing out, m; A a is the cross-sectional area inside the annulus, m 2 .

[0058] 2.3) According to the density difference between the inlet and outlet, the height h in of the injected drilling fluid column, and the height h out of the drilling fluid column flowing out, update the wellhead backpressure target value, and adjust the wellhead backpressure to the target value, enter the next time point, until the first cycle is completed. As Figure 2 shown, the density distribution of the drilling fluid in the wellbore can be obtained.

[0059] In this embodiment, the formula for updating the wellhead backpressure target value is:

[0060] p a = p a0 + (ρ n ghin -ρ' n gh out ) (4)

[0061] In the formula, p a is the new wellhead back pressure value, m.

[0062] In step 3) above, the bottom hole pressure is accurately calculated according to the density distribution of the drilling fluid in the wellbore, including:

[0063]

[0064] In the formula, M is the number of annulus fluid space grids; p b is the bottom hole pressure; f i is the annulus friction coefficient in the i-th annulus fluid space grid; ρ′ i is the density in the i-th annulus fluid space grid; h i is the height of the annulus fluid space grid.

[0065] In step 3) above, update the wellhead back pressure value, adjust the wellhead back pressure to the target value, and cycle to update the density distribution, bottom hole pressure and wellhead back pressure value in the wellbore until the drilling is completed. Specifically:

[0066] 3.1) According to the bottom hole pressure and the bottom hole target value, update the wellhead back pressure value P a = P a0 +(P aim - P b ), and use the automatic pressure control throttle device 8 to adjust the wellhead back pressure to the target value.

[0067] 3.2) Enter the next time point, update the density distribution in the wellbore, and re-update the bottom hole pressure and wellhead back pressure value until the drilling is completed.

[0068] In an embodiment of the present invention, a fine regulation system for wellhead throttle pressure considering density measurement at the inlet and outlet is provided. This system is used to implement the fine regulation method for wellhead throttle pressure considering density measurement at the inlet and outlet provided in the above embodiments. In this embodiment, as Figure 3 shown, this system includes:

[0069] A derrick 1, which is arranged at the upper center of the wellbore 3 and provides an operating platform for drilling workers; a drill pipe 4 is arranged in the wellbore 3;

[0070] An inlet densitometer 5, which is arranged at the output end of the mud tank 7 and is used to measure the density of the drilling fluid injected into the drill pipe 4 in real time;

[0071] An automatic pressure control throttle device 8, one end of which is connected to the wellhead outlet end of the wellbore 3, and the internal pressure of the wellbore 3 is adjusted through the automatic pressure control throttle device 8;

[0072] The outlet densitometer 9 is located downstream of the automatic pressure control throttle device 8 and is connected to the other end of the automatic pressure control throttle device 8 for real-time measurement of the density of the drilling fluid at the wellhead outlet.

[0073] The fine pressure control drilling control system 11 is configured to receive the density of the injected drilling fluid and the density of the drilling fluid at the wellhead outlet transmitted by the inlet densitometer 5 and the outlet densitometer 9, and obtain a control signal based on the received drilling fluid density and transmit it to the automatic pressure control throttle device 8 to control the opening degree of the throttle valve inside the automatic pressure control throttle device 8 to dynamically adjust the wellhead back pressure, thereby realizing the regulation of the pressure inside the wellbore 3.

[0074] In the above embodiment, the system further includes a blowout preventer 2 disposed at the wellhead outlet end for closing the wellbore 3 in case of an emergency.

[0075] In the above embodiment, the system further includes a drilling pump 6 and a flowmeter 10. Among them:

[0076] The drilling pump 6 is disposed at the output end of the drilling fluid tank 7 for providing power for injecting the drilling fluid into the wellbore 3 and regulating the displacement during the injection process. The drilling fluid tank 7 is used for storing the drilling fluid.

[0077] The flowmeter 10 is connected to the outlet densitometer 9 for real-time measurement of the drilling circulation displacement. The drilling fluid circulated out of the wellbore 3 is sequentially transmitted to the mud pit 12 through the automatic pressure control throttle device 8, the outlet densitometer 9, and the flowmeter 10.

[0078] In the above embodiment, the fine pressure control drilling control system 11 is pre-programmed with the wellhead throttle pressure fine regulation method considering the inlet and outlet density measurements in the above embodiments, and controls the opening degree of the throttle valve inside the automatic pressure control throttle device 8 according to this regulation method.

[0079] The system provided in this embodiment is used to execute the above method embodiments. For the specific process and detailed content, please refer to the above embodiments and will not be elaborated here.

[0080] In an embodiment of the present invention, a computing device structure is provided. The computing device may be a terminal, which may include: a processor, a communications interface, a memory, a display screen, and an input device. Among them, the processor, the communications interface, and the memory complete communication with each other through a communication bus. The processor is used to provide computing and control capabilities. The memory includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. When the computer program is executed by the processor, it realizes a fine regulation method for wellhead throttle pressure considering the measurement of inlet and outlet density. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface is used to communicate with an external terminal in a wired or wireless manner. The wireless manner can be achieved through WIFI, a carrier network, NFC (Near Field Communication), or other technologies. The display screen may be a liquid crystal display screen or an electronic ink display screen. The input device may be a touch layer covering the display screen, or a button, a trackball, or a touchpad provided on the housing of the computing device, or an external keyboard, touchpad, or mouse, etc. The processor can call the logical instructions in the memory to execute the following method: obtain the initial wellhead backpressure value according to the bottomhole target pressure and the initial bottomhole pressure value; perform a fine cyclic regulation on the wellhead throttle pressure according to the initial wellhead backpressure value and the drilling fluid density difference between the inlet and outlet of the operating well, adjust the wellhead backpressure to the target value, and obtain the drilling fluid density distribution in the wellbore; accurately calculate the bottomhole pressure according to the drilling fluid density distribution in the wellbore, update the wellhead backpressure value according to the bottomhole pressure and the bottomhole target pressure, adjust the wellhead backpressure to the target value, and cyclically update the density distribution in the wellbore, the bottomhole pressure, and the wellhead backpressure value until the drilling is completed.

[0081] In addition, when the logical instructions in the above-mentioned memory are implemented in the form of a software functional unit and sold or used as an independent product, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes: various media such as a USB flash drive, a mobile hard disk, a read-only memory (ROM, Read-Only Memory), a random access memory (RAM, Random Access Memory), a magnetic disk, or an optical disc that can store program codes.

[0082] Those skilled in the art can understand that the structure of the above computing device is only a part of the structure related to the solution of this application, and does not constitute a limitation on the computing device to which the solution of this application is applied. The specific computing device may include more or fewer components, or combine some components, or have different component arrangements.

[0083] In an embodiment of the present invention, a computer program product is provided. The computer program product includes a computer program stored on a non-transitory computer-readable storage medium. The computer program includes program instructions. When the program instructions are executed by a computer, the computer can execute the methods provided in the above method embodiments. For example, it includes: obtaining an initial wellhead backpressure value according to the bottomhole target pressure and the initial bottomhole pressure value; performing fine cyclic regulation on the wellhead throttling pressure according to the initial wellhead backpressure value and the density difference of the drilling fluid at the inlet and outlet of the operating well, adjusting the wellhead backpressure to the target value, and obtaining the density distribution of the drilling fluid in the wellbore; accurately calculating the bottomhole pressure according to the density distribution of the drilling fluid in the wellbore, updating the wellhead backpressure value according to the bottomhole pressure and the bottomhole target pressure, adjusting the wellhead backpressure to the target value, and cyclically updating the density distribution in the wellbore, the bottomhole pressure, and the wellhead backpressure value until the drilling is completed.

[0084] In an embodiment of the present invention, a non-transitory computer-readable storage medium is provided. The non-transitory computer-readable storage medium stores server instructions. The computer instructions cause the computer to execute the methods provided in the above embodiments. For example, it includes: obtaining an initial wellhead backpressure value according to the bottomhole target pressure and the initial bottomhole pressure value; performing fine cyclic regulation on the wellhead throttling pressure according to the initial wellhead backpressure value and the density difference of the drilling fluid at the inlet and outlet of the operating well, adjusting the wellhead backpressure to the target value, and obtaining the density distribution of the drilling fluid in the wellbore; accurately calculating the bottomhole pressure according to the density distribution of the drilling fluid in the wellbore, updating the wellhead backpressure value according to the bottomhole pressure and the bottomhole target pressure, adjusting the wellhead backpressure to the target value, and cyclically updating the density distribution in the wellbore, the bottomhole pressure, and the wellhead backpressure value until the drilling is completed.

[0085] For the computer-readable storage medium provided in the above embodiment, its implementation principle and technical effects are similar to those of the above method embodiment, and will not be elaborated here.

[0086] This application is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of this application. It should be understood that each process and / or block in the flowchart and / or block diagram, and the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate for implementation in the processFigure 1 one process or multiple processes and / or blocks Figure 1 a device for the functions specified in one block or multiple blocks.

[0087] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including an instruction device that implements the functions in the process Figure 1 one process or multiple processes and / or blocks Figure 1 specified in one block or multiple blocks.

[0088] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to produce a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in the process Figure 1 one process or multiple processes and / or blocks Figure 1 specified in one block or multiple blocks.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fine regulation method for wellhead throttling pressure considering the measurement of inlet and outlet density, characterized in that, including: Obtain the initial wellhead backpressure value according to the bottomhole target pressure and the initial bottomhole pressure value; According to the initial wellhead backpressure value and the density difference of the drilling fluid at the inlet and outlet of the operating well, finely circulate and control the wellhead throttling pressure, adjust the wellhead backpressure to the target value, and obtain the density distribution of the drilling fluid in the wellbore; Precisely calculate the bottomhole pressure based on the density distribution of the drilling fluid in the wellbore. According to the bottomhole pressure and the bottomhole target pressure, update the wellhead backpressure value, adjust the wellhead backpressure to the target value, and cyclically update the density distribution in the wellbore, the bottomhole pressure, and the wellhead backpressure value until the drilling is completed; The fine cyclic control of the wellhead throttling pressure includes: At the initial moment, the density of the drilling fluid in the wellbore is considered equal to the designed density ρ0 of the drilling fluid; Set the time interval and read the drilling fluid density ρ at the inlet n , the drilling fluid density ρ' at the outlet n and the drilling fluid displacement Q to calculate the height h of the newly injected drilling fluid column during this time period in and the height h of the drilling fluid column flowing out during this time period out ; Based on the density difference between the inlet and outlet, the height h of the injected drilling fluid column in and the height h of the outflowing drilling fluid column out , update the target value of the wellhead backpressure and adjust the wellhead backpressure to the target value, and the density distribution of the drilling fluid in the wellbore can be obtained; The precise calculation of the bottomhole pressure based on the density distribution of the drilling fluid in the wellbore includes: Where M is the number of annular fluid space grids; p b is the bottom hole pressure; f i is the annular friction coefficient in the i-th annular fluid space grid; ρ′ i is the density in the i-th annular fluid space grid; h i is the height of the annular fluid space grid.

2. The fine regulation method of wellhead throttling pressure considering the measurement of inlet and outlet density according to claim 1, characterized in that The bottom-hole target pressure is as follows: according to the three-pressure profile of the formation of the operation well, record the formation pore pressure P at the bottom hole p , the fracture pressure P f , and obtain the bottom-hole target pressure from the formation pore pressure P at the bottom hole p , the fracture pressure P f ; P aim = (P p + P f ) / 2, Where P aim is the bottom-hole target pressure.

3. The fine regulation method of wellhead throttling pressure considering the measurement of inlet and outlet density as described in claim 1, characterized in that The initial bottomhole pressure value is: Obtain the designed density of the drilling fluid according to the basic data of the operating well, and calculate the initial bottomhole pressure value from the designed density of the drilling fluid and the wellbore structure; where p b0 is the initial bottom hole pressure, Pa; h is the well depth, m; f is the annulus friction coefficient; v is the annulus drilling fluid velocity, m / s; d w is the wellbore diameter, m; d po is the drill pipe outer diameter, m; g is the acceleration due to gravity; ρ0 is the designed density of the drilling fluid, which is default equal to the designed density of the drilling fluid at the initial moment.

4. A system for implementing the method for fine regulation of wellhead throttling pressure considering inlet and outlet density measurement as described in any one of claims 1 to 3, characterized in that, including: A derrick, arranged above the center of the wellbore; An inlet densitometer, arranged at the output end of the drilling fluid tank, for measuring the density of the injected drilling fluid in real time; An automatic pressure control throttling device, one end of which is connected to the wellhead outlet end of the wellbore, and the internal pressure of the wellbore is adjusted through the automatic pressure control throttling device; An outlet densitometer, connected to the other end of the automatic pressure control throttling device, for measuring the density of the drilling fluid at the wellhead outlet in real time; A fine pressure control drilling control system, for receiving the density of the injected drilling fluid and the density of the drilling fluid at the wellhead outlet transmitted by the inlet densitometer and the outlet densitometer, and obtaining a control signal according to the received drilling fluid density and transmitting it to the automatic pressure control throttling device to control the automatic pressure control throttling device to adjust the internal pressure of the wellbore.

5. The system according to claim 4, wherein It also includes a blowout preventer, arranged at the wellhead outlet end.

6. The system according to claim 4, wherein It also includes a drilling pump and a flowmeter; The drilling pump is arranged at the output end of the drilling fluid tank, for providing power for injecting the drilling fluid into the wellbore and adjusting the displacement during the injection process; The flowmeter is connected to the outlet densitometer, for measuring the drilling circulation displacement in real time. The drilling fluid circulated out in the wellbore is transmitted to the mud pit through the automatic pressure control throttling device, the outlet densitometer, and the flowmeter in sequence.

7. A computer-readable storage medium storing one or more programs, characterized in that, The one or more programs include instructions that, when executed by a computing device, cause the computing device to execute any of the methods described in claims 1 to 3.

8. A computing device, characterized in that, including: One or more processors, a memory, and one or more programs, where the one or more programs are stored in the memory and configured to be executed by the one or more processors. The one or more programs include instructions for executing any of the methods described in claims 1 to 3.

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