Overflow monitoring device and method based on flow law of multiphase flow of shaft

Abstract

The invention belongs to the technical field of overflow monitoring and judgment in the petroleum and natural gas drilling process, and discloses an overflow monitoring device and method based on a shaft multiphase flow flowing rule. A simulation switch connected with an overflow simulation device is arranged at the bottom of a simulation shaft, and gas invasion, water invasion and oil invasion can be simulated respectively; electromagnetic flow meters are installed on a wellhead drilling fluid injection manifold and a wellhead drilling fluid return manifold respectively, a liquid level pressure sensor is installed in a mud pit, dynamic change data of the electromagnetic flow meters and the liquid level pressure sensor are monitored and obtained in real time through a monitoring machine and stored, analyzed and processed in real time, and characteristic parameters of different types of overflow are determined. And on the basis, overflow monitoring and judgment are carried out, and theoretical support and guidance are provided for field well control operation. The whole device disclosed by the invention does not monitor underground, does not need expensive hardware equipment, is low in investment and operation and maintenance cost, is not limited by underground complex environmental factors, and can avoid signal transmission power loss and improve the monitoring effect.

Description

Technical Field

[0001] The invention belongs to the technical field of overflow monitoring and identification during oil and natural gas drilling, and in particular relates to an overflow monitoring device and method based on the flow law of wellbore multiphase flow. Background Art

[0002] At present, overflow is one of the main causes of underground construction safety accidents during drilling. The occurrence of overflow will have a serious impact on the drilling process, such as reducing the speed and efficiency of drilling, thereby increasing the drilling cycle and cost, affecting technical and economic indicators, etc. More seriously, it may cause accidents such as well kicks and blowouts, causing huge casualties and economic losses. Therefore, the occurrence of overflow is particularly important during the drilling process. Accurate and real-time monitoring and elimination of overflow is of great significance to the normal development of drilling construction and safety benefits.

[0003] Overflow is mainly caused by the imbalance between the density of drilling fluid and the pressure of formation fluid, so that the oil, gas and water in the formation are pressed into the wellbore, resulting in the overflow of the returned drilling fluid in the wellbore. However, the damage caused by oil invasion, water invasion and gas invasion to hydraulic drilling usually depends on many factors such as formation conditions, wellbore conditions, drilling fluid system, etc. Therefore, the damage varies from case to case. Generally speaking, for oil-based drilling fluid, the damage caused by gas invasion is far greater than that caused by oil invasion and water invasion. Taking the case where the drilling fluid system is oil-based drilling fluid and the overflow fluid of drilling fluid is natural gas as an example, due to the high temperature and high pressure environment at the bottom of the well and the chemical properties of oil-based drilling fluid and natural gas (mainly methane), natural gas is very easily soluble in drilling fluid. As the returned drilling fluid flows to the ground, the natural gas dissolved in the drilling fluid will be released only after the temperature and pressure in the near-ground annulus drop to a certain value, resulting in a lag in the formation of gas-liquid two-phase flow, making it impossible to monitor overflow early.

[0004] At present, there are many overflow judgment methods at the drilling site, such as the traditional drilling fluid pool liquid level detection method, DC index method, shale density method, torque meter detection method, acoustic time difference method, pump flushing method, etc. For example, Chinese patent CN106801602A discloses a method for real-time monitoring of gas invasion using the pressure wave signal of a while drilling measurement tool. The difference between the gas phase and the liquid phase of the pressure wave signal is used to transmit the pressure wave signal through the oil casing annulus and the drill pipe to the ground signal receiving device through the MWD downhole signal transmitting device, and the time difference experienced by the pressure wave signal in the two paths is calculated. Whether overflow occurs is determined based on the size of the time difference. However, due to the complex high temperature and high pressure environment at the bottom of the well, the installation and use conditions of the while drilling measurement tool are extremely harsh, and when transmitting signals from the bottom of the well to the ground, there are problems such as heavy signal loss, expensive transmission equipment, difficult equipment maintenance, and high maintenance cost, so this method is difficult to promote and apply.

[0005] Therefore, the existing methods mostly monitor overflow by installing measuring instruments underground, and transmit the monitoring signals to the ground for analysis through specific transmission channels. However, underground monitoring needs to consider the complex conditions of high temperature and high pressure, so the instrument operation and maintenance problems faced are difficult to solve well. In addition, gas invasion is the most difficult problem in the drilling overflow process. If some method can be used to monitor and analyze, and timely identify the overflow fluid type, rate and other information, it will be of great significance for understanding the formation characteristics, judging the cause of overflow, and subsequent wellbore pressure control. Summary of the invention

[0006] The present invention aims to solve at least one technical problem existing in the background technology, and provides an overflow monitoring device and method based on the flow law of multiphase flow in the wellbore. Through multiple experimental data collection and analysis by simulating an experimental device, a method for monitoring and distinguishing the overflow type is summarized, which can timely monitor and distinguish and identify gas invasion, water invasion and oil invasion to better guide on-site well control operations. The entire overflow monitoring device does not need to be monitored underground, and does not require expensive hardware equipment, thereby reducing investment and operation and maintenance costs. At the same time, it can avoid signal transmission power loss caused by underground monitoring and improve the monitoring effect.

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0008] An overflow monitoring device based on the study of the flow law of wellbore multiphase flow, comprising a simulated wellbore, a simulated drill string, an injection manifold, a return manifold, a circulation pump and a monitoring machine;

[0009] The simulated drill string is arranged in the simulated wellbore and forms an annular space between the wellbore wall;

[0010] A simulation switch is provided at the bottom of the simulated wellbore, and the simulation switch is connected to the overflow simulation device through a pipeline;

[0011] The upper end of the simulated drill string is connected to the injection manifold, and the top side of the simulated wellbore is connected to the return manifold; the inlet of the injection manifold and the outlet of the return manifold are both connected to the mud pool, and the mud pool is provided with drilling fluid; the injection manifold is provided with a circulation pump and a first electromagnetic flowmeter, the return manifold is provided with a second electromagnetic flowmeter, and the mud pool is provided with a liquid level pressure sensor; the first electromagnetic flowmeter, the second electromagnetic flowmeter and the liquid level pressure sensor are all connected to a monitoring machine, and the monitoring machine is used to analyze and process the received monitoring data.

[0012] Furthermore, the first electromagnetic flowmeter, the second electromagnetic flowmeter and the liquid level pressure sensor are connected to a monitoring machine via an RS485 converter.

[0013] Furthermore, the liquid level pressure sensor is a pressure sensor.

[0014] Furthermore, the overflow simulation device comprises an air source pipeline, a water source pipeline and an oil source pipeline connected in parallel, the air source pipeline is provided with a flow meter and a valve, and the water source pipeline and the oil source pipeline are respectively provided with a pump, a flow meter and a valve.

[0015] Furthermore, it also includes an image acquisition device and a controller electrically connected to the image acquisition device;

[0016] An observation window is provided on the simulated wellbore, and the image acquisition device is arranged on one side of the observation window. The image acquisition device is used to photograph the flow conditions in the simulated wellbore and transmit the photographed data to a controller for analysis and processing.

[0017] At the same time, the present invention provides a method for monitoring and distinguishing overflow types based on the study of the flow law of wellbore multiphase flow, which is implemented by using the overflow monitoring device as described in any of the above items, and the method comprises the following steps:

[0018] Step S1: adjust the depth of the simulated wellbore, turn on the circulation pump, fill the entire wellbore pipeline with drilling fluid, and start overflow monitoring after the circulation of the wellbore pipeline is stable;

[0019] Step S2: opening a simulation switch at the bottom of the simulated wellbore to fill the simulated wellbore with invading fluid;

[0020] Step S3: As the simulated overflow experiment continues, the drilling fluid return displacement data change is monitored by the second electromagnetic flowmeter installed on the return manifold, and the mud pool incremental data change is monitored by the liquid level sensor installed in the mud pool, and the monitoring data is transmitted to the monitoring machine for real-time storage;

[0021] Step S4: close the simulation switch at the bottom of the simulated wellbore, and continue to circulate the drilling fluid until all the intrusive fluid in the wellbore pipeline is discharged, and the values ​​of the first electromagnetic flowmeter, the second electromagnetic flowmeter and the liquid surface pressure sensor tend to be stable;

[0022] Step S5: repeating steps S2-S4 to complete the simulation of gas invasion, water invasion and oil invasion respectively, and obtaining the corresponding gas invasion experimental data, water invasion experimental data and oil invasion experimental data respectively;

[0023] Step S6: Summarize, analyze and process the real-time monitored and stored gas intrusion test data, water intrusion test data and oil intrusion test data, determine the characteristic parameters of different types of overflows, and use them as a basis for monitoring and identifying overflow types.

[0024] Furthermore, in step S2, the simulated wellbore is filled with invading fluid at a constant volume or a constant flow rate.

[0025] Furthermore, the invading fluid includes gas, water or oil, which are used to simulate gas invasion, water invasion or oil invasion respectively.

[0026] Furthermore, in step S6, the characteristic parameters of different types of overflow include one or more combination parameters of the following parameters:

[0027] The time point when overflow occurs, the maximum, minimum or average value of the drilling fluid return displacement, the changing speed, change amplitude and duration of the drilling fluid return displacement, the maximum, minimum or average value of the mud increment, the changing speed, change amplitude and duration of the mud increment.

[0028] In addition, the present invention also provides an overflow monitoring and identification method based on the study of the flow law of wellbore multiphase flow, which is implemented by using the overflow monitoring device as described in any of the above items, and the method comprises the following steps:

[0029] Step S01: Collect experimental data;

[0030] Conduct multiple simulated overflow experiments for different overflow types and collect drilling fluid return displacement data and mud pool increment data during overflow;

[0031] Step S02: data analysis;

[0032] Conduct statistics and analysis on the collected experimental data to determine the characteristic parameters of different types of overflow;

[0033] Step S03: Establishing a wellbore multiphase flow model;

[0034] According to the experimental data analysis results, the mathematical equation of wellbore multiphase flow is constructed, and the characteristic parameters in the experimental data are substituted into the mathematical equation of wellbore multiphase flow, and the wellbore multiphase flow model is obtained by parameterization.

[0035] Step S04: using actual monitoring data to verify and optimize the wellbore multiphase flow model;

[0036] Step S05: adjusting and correcting the wellbore multiphase flow model after verification and optimization according to the experimental results and actual needs;

[0037] Step S06: model application;

[0038] The adjusted and corrected wellbore multiphase flow model is applied to actual monitoring work to identify and distinguish the overflow conditions of different types of overflows.

[0039] Furthermore, in the step S03, the constructed gas invasion wellbore multiphase flow model includes: a continuity equation, a fluid momentum equation and a fluid energy equation that characterize the flow quality through a certain space;

[0040] The continuity equation is:

[0041]

[0042] The momentum equation for the fluid is:

[0043]

[0044] The fluid energy equation is:

[0045]

[0046] In the above formula, A is the local annular cross-sectional area, m 2 ; E g - output gas mass flow rate, kg / s; ρ g -Output gas density, kg / m 3 ; V g - Output gas return velocity, m / s; Q g -Gas production rate in the gas production section, kg / (s·m); t-time, s; s-distance from a certain point in the annulus to the wellhead, m; E m -Drilling fluid mass flow rate, kg / s; ρ m -Drilling fluid density, kg / m 3 ; V m -Drilling fluid return velocity, m / s; E c - rock cuttings volume fraction, dimensionless; ρ c -Cut density, kg / m 3 ; V c - cuttings return velocity, m / s; g-gravitational acceleration, m / s 2 ;α-inclination angle of fluid or pipe, rad;P-fluid pressure, Pa; is the friction pressure drop of the wellbore section, Pa / m; C pg - the mole fraction of a specific component in the produced gas, dimensionless; T a - annulus temperature, K; ρ l -Liquid density, kg / m 3 ; E l -Liquid volume fraction, dimensionless; C l - the mole fraction of a particular component of the formation fluid, dimensionless; -Annulus area, m 2 ;ω g -Gas phase mass flow rate, kg / s; ω l -Liquid mass flow rate, kg / s; z-depth, m; A′-drill string inner diameter area, m 2 ; B′-formation physical property coefficient, m 2 / Pa;T ei- formation temperature, K; T l - Initial temperature of the formation, K.

[0047] Furthermore, the continuity equation takes into account the three components of drilling fluid, gas and cuttings; in the process of solving the continuity equation,

[0048] The corresponding gas phase-non-gas production section mass flow calculation formula is:

[0049]

[0050] The corresponding drilling fluid mass flow calculation formula is:

[0051]

[0052] The corresponding cuttings mass flow calculation formula is:

[0053]

[0054] In the above formula, A is the local annular cross-sectional area, m 2 ; E g - output gas mass flow rate, kg / s; ρ g -Output gas density, kg / m 3 ; V g - Output gas return velocity, m / s; Q g -Gas production speed in the gas production section, kg / (s·m); E m -Drilling fluid mass flow rate, kg / s; ρ m -Drilling fluid density, kg / m 3 ; V m -Drilling fluid return velocity, m / s; E c - rock cuttings volume fraction, dimensionless; ρ c -Cut density, kg / m 3 ; V c -Cuts return velocity, m / s; Q c -cuttings mass flow rate, kg / s; t-time, s; s-distance from a point in the annulus to the wellhead, m.

[0055] Furthermore, in the process of gas invasion simulation, according to the physical shape of the multiphase flow pattern in the wellbore pipeline, the flow pattern of the multiphase flow in the vertical section pipe flow can be divided into the following four types:

[0056] Bubble flow A: In a vertical pipe flow, the continuous liquid phase contains dispersed bubbles;

[0057] Slug flow B: In the vertical pipe flow, there are one or more plug-like substances, which will hinder the normal flow of the fluid and cause the aggregation and merging of droplets, thus forming a gas-liquid two-phase flow state with alternating gas and liquid columns;

[0058] Disturbed flow C: In the vertical pipe flow, the liquid phase flow undergoes violent vortexing and mixing, the size and distribution of bubbles are uneven, there are bubbles dispersed in the liquid phase flow, and droplets are entrained in the gas phase;

[0059] Annular mist flow D: Based on the disturbance flow C, the gas velocity increases and the liquid in the vertical pipe flow is atomized;

[0060] Among them, the degree of gas invasion is from weak to strong in the order of bubbly flow A, slug flow B, disturbed flow C and annular mist flow D.

[0061] Compared with the prior art, the beneficial effects of the present invention are:

[0062] (1) The present invention is provided with a simulation switch connected to an overflow simulation device at the bottom of the simulated wellbore, which can simulate gas invasion, water invasion and oil invasion respectively; electromagnetic flowmeters are respectively installed at the wellhead drilling fluid injection manifold and the return manifold, and a liquid level pressure sensor is installed in the mud pool. The electromagnetic flowmeter and the liquid level pressure sensor are both connected to a monitoring machine through an RS485 converter. The monitoring machine can monitor and obtain the dynamic change data of the electromagnetic flowmeter and the liquid level pressure sensor in real time and store, analyze and process the data in real time, determine the characteristic parameters of different types of overflow, and monitor and identify the overflow type based on this, providing theoretical support and guidance for on-site well control operations;

[0063] (2) Compared with the existing measuring devices and methods, the entire overflow monitoring device of the present invention does not need to be monitored underground, and does not require expensive hardware equipment, thereby reducing investment and operation and maintenance costs. At the same time, the measuring tool will not be restricted by the complex environmental factors underground, and can avoid large signal transmission power loss, improve the monitoring effect, and overcome the application technical difficulties caused by installing the drilling measurement tool in the complex environment of the bottom of the well;

[0064] (3) The method of the present invention also obtains experimental data for each overflow type through multiple simulated overflow experiments, and establishes a wellbore multiphase flow model based on the experimental data analysis results, and uses actual observation results to verify, correct and optimize the wellbore multiphase flow model to clarify the flow law of the wellbore multiphase flow; finally, the constructed wellbore multiphase flow model is applied to actual monitoring work to identify and distinguish different types of overflow situations, especially for gas invasion, which is the most harmful, so that the occurrence of gas invasion can be identified in time, the flow form of the multiphase flow in the wellbore pipeline can be monitored, and the intensity of the gas invasion, the main location area of ​​the gas invasion, and the impact of the gas invasion can be judged, so as to provide a large amount of safety defense time for on-site well control operations and provide full protection for well control operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is a structural schematic diagram of an overflow monitoring device based on the study of the flow law of wellbore multiphase flow according to an embodiment of the present invention;

[0066] Figure 2 This is a flow chart of an overflow type monitoring and identification method based on a study of the flow law of wellbore multiphase flow in an embodiment of the present invention;

[0067] Figure 3 A graph showing the variation trend of the drilling fluid return discharge volume caused by different overflow types in an embodiment of the present invention;

[0068] Figure 4 is a trend diagram of the increment change of the mud pool caused by different overflow types in an embodiment of the present invention;

[0069] Figure 5 It is a schematic diagram of a gas-liquid two-phase flow pattern being a bubbly flow in an embodiment of the present invention;

[0070] Figure 6 Schematic diagram of a gas-liquid two-phase flow pattern of slug flow in an embodiment of the present invention;

[0071] Figure 7 It is a schematic diagram of a gas-liquid two-phase flow pattern being a disturbed flow in an embodiment of the present invention;

[0072] Figure 8 It is a schematic diagram of the gas-liquid two-phase flow pattern being annular mist flow in an embodiment of the present invention. DETAILED DESCRIPTION

[0073] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0074] In the description of the present invention, it is necessary to understand that the terms "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inside", "front", "center", "both ends" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0075] Example 1

[0076] Combination Figure 1 As shown, an embodiment of the present invention provides an overflow monitoring device based on the study of the flow law of multiphase flow in a wellbore, including a simulated wellbore 16, a simulated drill string 12, an injection manifold 5, a return manifold 6, a circulation pump 7 and a monitoring machine 1.

[0077] The simulated drill string 12 is arranged in the simulated wellbore 16 and forms an annular space 11 with the wellbore wall; a simulated switch is arranged at the bottom of the simulated wellbore 16, and the simulated switch is connected to the overflow simulation device through a pipeline; the upper end of the simulated drill string 12 is connected to the injection manifold 5, and the top side of the simulated wellbore 16 is connected to the return manifold 6; the inlet of the injection manifold 5 and the outlet of the return manifold 6 are both connected to the mud pool 9, and the mud pool 9 is provided with drilling fluid 10; the injection manifold 5 is provided with a circulating pump 7 and a first electromagnetic flowmeter 3, the return manifold 6 is provided with a second electromagnetic flowmeter 4, and the mud pool 9 is provided with a liquid level pressure sensor 8; the first electromagnetic flowmeter 3, the second electromagnetic flowmeter 4 and the liquid level pressure sensor 8 are connected to the monitoring machine 1 through the RS485 converter 2, and the monitoring machine 1 is used to analyze and process the received monitoring data.

[0078] Among them, the circulating pump 7 is used to pump the drilling fluid in the mud pool 9 into the simulated drill string 12, the first electromagnetic flowmeter 3 is used to monitor the drilling fluid flow in the injection manifold 5, the second electromagnetic flowmeter 4 is used to monitor the flow of the return fluid, and the liquid level pressure sensor 8 is used to measure the liquid level and liquid pressure in the mud pool 9.

[0079] The working principle of the electromagnetic flowmeter is: using the Faraday electromagnetic induction principle to measure the flow of conductive media; when the conductive medium (such as drilling fluid) flows along the pipeline, the induced electromotive force is proportional to the flow velocity of the liquid through the magnetic field in the conductor, so the flow of the liquid can be measured. The electromagnetic flowmeter can measure the volume flow of drilling fluids with different conductive properties (such as matrix fluids, pure water, liquid heavy objects, colloids, and oil and water phases), with high accuracy and reliability, and its accuracy can reach ±0.5%-±1.0% FS (full scale).

[0080] The liquid level pressure sensor 8 is preferably a pressure sensor, and its working principle is: based on the principles of wave dynamics and physics, it mainly monitors the liquid level by measuring the change in the liquid level due to the static pressure of the liquid, and has the advantages of high accuracy, strong sensitivity, and high reliability.

[0081] In some other embodiments, the flow meter and the liquid level pressure sensor may also be in other forms, which are not specifically limited here.

[0082] In an embodiment of the present invention, a simulation switch is provided at the bottom of the simulated wellbore 16, and the simulation switch is connected to an overflow simulation device through a pipeline. The overflow simulation device includes an air source pipeline, a water source pipeline and an oil source pipeline connected in parallel, and a flow meter and a valve are provided on the air source pipeline, and a pump, a flow meter and a valve are provided on the water source pipeline and the oil source pipeline respectively; the overflow simulation device can be operated by an experimenter to simulate gas invasion, water invasion and oil invasion respectively.

[0083] In addition, in an embodiment of the present invention, the overflow monitoring device further includes: an image acquisition device, and a controller electrically connected to the image acquisition device.

[0084] An observation window is provided on the simulated wellbore 16, and the image acquisition device is provided on one side of the observation window. The image acquisition device is used to photograph the flow conditions in the simulated wellbore 16 and transmit the photographed data to the controller, which analyzes and processes the photographed images.

[0085] The embodiment of the present invention can simulate gas invasion, water invasion and oil invasion respectively by providing a simulation switch connected to an overflow simulation device at the bottom of the simulated wellbore; electromagnetic flowmeters are respectively installed at the wellhead drilling fluid injection manifold and the return manifold, and a liquid level pressure sensor is installed in the mud pool. The electromagnetic flowmeter and the liquid level pressure sensor are both connected to the monitoring machine through an RS485 converter. The monitoring machine can monitor and obtain the dynamic change data of the electromagnetic flowmeter and the liquid level pressure sensor in real time, store, analyze and process the data in real time, determine the characteristic parameters of different types of overflow, and use this as a basis to monitor, distinguish, identify and prevent gas invasion, water invasion and oil invasion, which is conducive to better guiding on-site well control operations;

[0086] Compared with the existing measuring devices, the overflow monitoring device of the embodiment of the present invention does not need to be monitored underground and does not require expensive hardware equipment, thereby reducing investment and operation and maintenance costs. At the same time, the measuring tool will not be restricted by complex environmental factors underground, can avoid large signal transmission power loss, improve monitoring effects, and overcome the application technical difficulties caused by installing downhole measurement tools in complex bottom hole environments.

[0087] Example 2

[0088] The embodiment of the present invention provides an overflow type monitoring and identification method based on the study of the flow law of multiphase flow in a wellbore, and specifically adopts the overflow monitoring device in Example 1.

[0089] In the embodiment of the present invention, the drilling fluid 10 in the mud pool 9 is oil-based drilling fluid. Generally speaking, oil-based drilling fluid is prone to diffusion gas invasion. The overflow simulation device adopts diffusion gas invasion.

[0090] In the embodiment of the present invention, the simulation experiment parameters of the overflow monitoring device are: the drilling fluid displacement is 40L / S; the gas invasion speed is 600L / S; the oil-water ratio of the oil-based drilling fluid is 8:2; the mud pool volume is 1000m 3 .

[0091] like Figure 2 As shown, the method specifically comprises the following steps:

[0092] Step S1: adjust the depth of the simulated wellbore 16, turn on the circulation pump 7, fill the entire wellbore pipeline and overflow simulation with drilling fluid 10, and use the first electromagnetic flowmeter 3 and the monitoring machine 1 to monitor and control the flow; after the wellbore pipeline circulation is stable, start the overflow monitoring work.

[0093] Step S2: Open the simulation switch at the bottom of the simulated wellbore 16, and fill the simulated wellbore 16 with a gas invasion body 15 (mainly methane) at a constant volume or a constant speed. In the embodiment of the present invention, the gas invasion body is filled with a constant volume to start simulating the gas invasion situation;

[0094] Step S3: As the overflow monitoring work proceeds, the return drilling fluid 10 continues to return along the annular space 11, and the flow rate of the return drilling fluid will continue to change; the second electromagnetic flowmeter 4 installed on the return manifold 6 monitors the change of the return displacement data of the drilling fluid, and at the same time, the liquid level pressure sensor 8 installed in the mud pool 9 monitors the change of the mud increment data in the mud pool 9, and the gas invasion monitoring data is transmitted to the monitoring machine 1 through the RS485 converter 2 for real-time storage;

[0095] Step S4: close the simulation switch at the bottom of the simulated wellbore 16, and continue to circulate the drilling fluid 10 until the gas intrusion 15 in the wellbore pipeline is completely discharged, and the values ​​of the first electromagnetic flowmeter 3, the second electromagnetic flowmeter 4 and the liquid surface pressure sensor 8 tend to be stable;

[0096] Step S5: Open the simulation switch at the bottom of the simulated wellbore 16 again, inject water 13 into the simulated wellbore 16 at a constant speed, and start simulating water intrusion;

[0097] Step S6: As the overflow monitoring work proceeds, the returned drilling fluid continues to return along the annular space 11, and the flow rate of the returned drilling fluid will continue to change; the displacement data change of the returned drilling fluid 10 is monitored by the second electromagnetic flowmeter 4 installed on the return manifold 6, and at the same time, the incremental data change in the mud pool 9 is monitored by the liquid level pressure sensor 8 installed in the mud pool 9, and the water intrusion monitoring data is transmitted to the monitoring machine 1 through the RS485 converter 2 for real-time storage;

[0098] Step S7: close the simulation switch at the bottom of the simulated wellbore 16 and continue to circulate the drilling fluid 10 until all the water 13 in the wellbore pipeline is discharged and the values ​​of the first electromagnetic flowmeter 3, the second electromagnetic flowmeter 4 and the liquid level pressure sensor 8 tend to be stable.

[0099] Step S8: Open the simulation switch at the bottom of the simulated wellbore 16 again, inject the oil invasion body 14 (mainly hydrocarbon substances) into the simulated wellbore 16 at a constant speed, and start simulating the oil invasion situation;

[0100] Step S9: As the overflow monitoring work proceeds, the returned drilling fluid continues to return along the annular space 11, and the flow rate of the returned drilling fluid will continue to change; the displacement data change of the returned drilling fluid 10 is monitored by the second electromagnetic flowmeter 4 installed on the return manifold 6, and at the same time, the incremental data change in the mud pool 9 is monitored by the liquid level pressure sensor 8 installed in the mud pool 9, and the oil invasion monitoring data is transmitted to the monitoring machine 1 through the RS485 converter 2 for real-time storage;

[0101] Step S10: close the simulation switch at the bottom of the simulated wellbore 16, and continue to circulate the drilling fluid 10 until the oil invasion body 14 (mainly hydrocarbon substances) in the overflow monitoring simulation experimental device is completely discharged, and the values ​​of the first electromagnetic flowmeter 3, the second electromagnetic flowmeter 4, and the liquid surface pressure sensor 8 tend to be stable;

[0102] Step S11: the monitoring machine 1 summarizes, analyzes and processes the real-time monitored and stored gas intrusion test data, water intrusion test data and oil intrusion test data, thereby determining characteristic parameters of different types of overflows, and based on this, monitors and identifies overflow types.

[0103] The experimental data finally obtained by the embodiment of the present invention are shown in Table 1-2 below:

[0104] Table 1 Drilling fluid return displacement change data table

[0105]

[0106] Table 2 Mud pool increment change data table

[0107]

[0108] According to the above experimental data, the drilling fluid return flow rate diagram and mud pool increment change diagram under different overflow types are finally generated, as shown in the figure below: Figure 3 and Figure 4 shown.

[0109] Depend on Figure 3 and Figure 4 It can be seen that when diffusion gas invasion occurs, the return flow rate of drilling fluid and the increase in mud pool basically do not change at first, but suddenly change drastically after a period of time. Combined with the above analysis of the flow pattern change process, it can be seen that this is because diffusion gas invasion occurs when drilling with oil-based drilling fluid. Due to the characteristics of oil-based drilling fluid, most gases will dissolve in the drilling fluid, but as the dissolved gas drilling fluid migrates upward, the annular pressure gradually decreases. When it is less than the gas dissolution pressure, the gas will precipitate, causing the return flow rate of drilling fluid and the increase in mud pool to show an "explosive growth" trend.

[0110] right Figure 3 and Figure 4 Further analysis shows that:

[0111] When the overflow type is gas invasion, the drilling fluid return discharge volume changes significantly after about 82 seconds, and as the overflow simulation experiment proceeds, the drilling fluid return discharge volume will continue to increase significantly; the surface mud pool increment changes significantly after about 600 seconds, and as the overflow simulation experiment proceeds, the final mud pool increment can reach about 3m 3 , accounting for about 0.3% of the total volume of the mud pool.

[0112] When the overflow type is water invasion, the drilling fluid return discharge volume changes significantly after about 105s, and as the overflow simulation experiment proceeds, the maximum drilling fluid return discharge volume can reach about 70L / S; the surface mud pool increment changes significantly after about 720s, and as the overflow simulation experiment proceeds, the final mud pool increment can reach about 1.5m 3 , accounting for about 0.15% of the total volume of the mud pool.

[0113] When the overflow type is oil invasion, the drilling fluid return discharge volume changes significantly after about 110s, and as the overflow simulation experiment proceeds, the maximum drilling fluid return discharge volume can reach about 60L / S; the surface mud pool increment changes significantly after about 840s, and as the overflow simulation experiment proceeds, the final mud pool increment can reach about 1m 3 , accounting for about 0.1% of the total volume of the mud pool.

[0114] Through Figure 3 and Figure 4An analysis is performed to obtain characteristic parameters of significant changes in the return displacement of the drilling fluid 10 and the increment of the mud pool 9 when the overflow monitoring simulation experiment is carried out in different types of overflow simulation experiments, such as: the time node of the overflow, the maximum, minimum or average value of the return displacement of the drilling fluid, the change speed, change amplitude and duration of the return displacement of the drilling fluid, the maximum, minimum or average value of the mud increment, the change speed, change amplitude and duration of the mud increment and other parameters, so that according to the characteristic parameters, gas invasion, water invasion and oil invasion can be effectively distinguished and identified, so as to achieve the experimental purpose of monitoring and distinguishing the overflow type.

[0115] Example 3

[0116] The embodiment of the present invention provides an overflow monitoring and identification method based on the study of the flow law of multiphase flow in a wellbore, which is also implemented using the overflow monitoring device in Example 1.

[0117] Different from the embodiment 2 in which the overflow type is mainly monitored and identified, the embodiment of the present invention mainly monitors and identifies the overflow situation.

[0118] It should be additionally explained that the method of the embodiment of the present invention can further monitor and identify overflow conditions for known types of overflows; and for overflows of unknown types, the overflow type can be first identified by the method in Example 2, and then the method of the embodiment of the present invention can be further used to monitor and identify the overflow conditions.

[0119] The method specifically comprises the following steps:

[0120] Step S01: Collect experimental data;

[0121] For different overflow types (gas invasion, water invasion or oil invasion), multiple simulated overflow experiments are carried out by using the experimental device in Example 1 to collect the drilling fluid return displacement data and mud pool increment data during overflow;

[0122] Step S02: data analysis;

[0123] The collected experimental data are statistically analyzed to determine the characteristic parameters of different types of overflows, such as the rate of change of drilling fluid return flow, the pressure change in the simulated wellbore, etc.

[0124] Step S03: Establishing a wellbore multiphase flow model;

[0125] Step S031: Based on the experimental data analysis results, empirical formulas, computational fluid dynamics (CFD) methods or finite element methods are used to describe the flow behavior in the wellbore and establish a mathematical equation for the wellbore multiphase flow;

[0126] Step S032: Substituting the characteristic parameters in the experimental data into the wellbore multiphase flow mathematical equation, and parameterizing and constructing a wellbore multiphase flow model;

[0127] Step S04: verifying the optimization model;

[0128] Use actual monitoring data to verify the model and evaluate its accuracy and reliability; if there is a large deviation between the model and the actual observation results, revise and optimize the model;

[0129] Step S05: Model adjustment: according to the experimental results and actual needs, the wellbore multiphase flow model is adjusted and modified; during the adjustment and modification process, more characteristic parameters can be introduced, and / or the interaction between different substances can be considered;

[0130] Step S06: model application;

[0131] The adjusted and corrected wellbore multiphase flow model is applied to actual monitoring work to identify and judge the overflow conditions of different types of overflows, so as to clarify the intensity of the overflow, the main location area of ​​occurrence or the impact, etc., to provide a large amount of safety defense time for on-site well control operations and provide full protection for well control operations.

[0132] Example 4

[0133] Since gas invasion is a common type of drilling overflow and is the most harmful, while water invasion and oil invasion are relatively rare. At the same time, gas invasion has some unique characteristics, such as low gas density, strong fluidity, and susceptibility to temperature and pressure changes. These characteristics make the flow pattern and behavior of gas invasion in the wellbore different from other forms of fluid invasion, requiring special analysis and research. Therefore, in the embodiment of the present invention, when studying and analyzing the fluid morphology in the wellbore, emphasis is placed on the monitoring and identification of gas invasion, and taking gas invasion as an example, it is specifically introduced how to establish a wellbore multiphase flow model for gas invasion (that is, step S03 in Example 3).

[0134] During the drilling process, gas may enter the wellbore due to different mechanisms. The identification of gas invasion types and the determination of formation information are of great significance to the subsequent well killing process. The embodiment of the present invention establishes a coupling model based on multiphase flow of formation and wellbore annulus based on the mechanism of diffusion gas invasion.

[0135] Diffusion gas invasion is caused by the fact that the gas concentration in the formation is much greater than that in the wellbore. Under the action of concentration gradient, the natural gas in the formation diffuses into the wellbore through the mud cake and invades the wellbore. Therefore, diffusion gas invasion is actually a mass transfer process caused by the random thermal motion of gas molecules. The natural gas that diffuses into the well is related to factors such as the surface area of ​​the drilled gas layer and the quality of the filter cake. By considering the multiphase flow law between the formation and the wellbore, the gas invasion situation can be better simulated and analyzed.

[0136] Specifically, a wellbore multiphase flow model during gas invasion is established based on the drift model. The drift model refers to a mathematical model used to describe the gas diffusion and invasion process. It takes into account the mass transfer process of gas from the formation through the mud cake into the wellbore caused by the random thermal motion of gas molecules, which helps to understand the occurrence mechanism of gas invasion and the coupling relationship with formation information. The wellbore multiphase flow model of the present invention is based on the fluid dynamics principles and material transfer laws in the drift model, and can be used to more accurately analyze and predict gas invasion situations.

[0137] The wellbore multiphase flow model includes a continuity equation, a fluid momentum equation and a fluid energy equation that characterize the flow quality through a certain space.

[0138] (1) Continuity equation

[0139] First, in order to simplify the calculation, the model only considers three components: drilling fluid, gas and cuttings, and constructs a continuity equation that characterizes the mass of the flow through a certain space. That is, in a certain period of time, the mass flow through a certain space is equal to the fluid velocity multiplied by the fluid density. The specific calculation formula is:

[0140]

[0141] In the above formula (1), A is the local annular cross-sectional area, m 2 ; E g - output gas mass flow rate, kg / s; ρ g -Output gas density, kg / m 3 ; V g - Output gas return velocity, m / s; Q g -gas production rate in the gas production section, kg / (s·m); t-time, s; s-distance from a certain point in the annulus to the wellhead, m.

[0142] In the process of solving the continuity equation, it is necessary to find the corresponding gas phase-non-gas production section mass flow calculation formula, drilling fluid mass flow calculation formula and cuttings mass flow calculation formula.

[0143] Among them, for the gas phase-non-gas production section, the main consideration is the output gas return velocity V g and gas phase density ρ g, the output gas return velocity will decrease over time, while the gas phase density remains unchanged, so the product of the two should be equal to the mass flow rate. Therefore, the corresponding gas phase-non-gas production section mass flow calculation formula is:

[0144]

[0145] At the same time, for drilling fluid, the main consideration is the drilling fluid density ρ m and drilling fluid return velocity v m , the drilling fluid return velocity will decrease with the passage of time, while the drilling fluid density remains unchanged, so the drilling fluid mass flow rate calculation formula is:

[0146]

[0147] Similarly, for cuttings, the main consideration is the cuttings volume fraction E c and cuttings density ρ c , the cuttings volume fraction will decrease over time, while the cuttings density remains unchanged, so the cuttings mass flow rate calculation formula is:

[0148]

[0149] In the above formulas (2)-(4): A-local annular cross-sectional area, m 2 ; E g - output gas mass flow rate, kg / s; ρ g -Output gas density, kg / m 3 ; V g - Output gas return velocity, m / s; Q g -Gas production speed in the gas production section, kg / (s·m); E m -Drilling fluid mass flow rate, kg / s; ρ m -Drilling fluid density, kg / m 3 ; V m -Drilling fluid return velocity, m / s; E c - rock cuttings volume fraction, dimensionless; ρ c -Cut density, kg / m 3 ; V c -Cuts return velocity, m / s; Q c -cuttings mass flow rate, kg / s; t-time, s; s-distance from a point in the annulus to the wellhead, m.

[0150] (2) Fluid momentum equation:

[0151]

[0152] In the above formula (5): A-local annular cross-sectional area, m 2 ; Eg - output gas mass flow rate, kg / s; ρ g -Output gas density, kg / s; V g - Output gas return velocity, m / s; E m -Drilling fluid mass flow rate, kg / s; ρ m -Drilling fluid density, kg / m 3 ; V m -Drilling fluid return velocity, m / s; E c - rock cuttings volume fraction, dimensionless; ρ c -Cut density, kg / m 3 ; V c - cuttings return velocity, m / s; g-gravitational acceleration, m / s 2 ; α-inclination angle of fluid or pipeline, rad; P-fluid pressure, Pa; t-time, s; s-distance from a point in the annulus to the wellhead, m; is the friction pressure drop in the wellbore section, Pa / m.

[0153] (3) Fluid energy equation:

[0154]

[0155] In the above formula (6): t-time, s; ρ g - Density of produced gas, kg / s; E g -Output gas mass flow rate, kg / s; C pg - the mole fraction of a specific component in the produced gas, dimensionless; T a - annulus temperature, K; ρ l -Liquid phase density, kg / m 3 ; E l -Liquid volume fraction, dimensionless; C l - the mole fraction of a particular component of the formation fluid, dimensionless; -Annulus area, m 2 ;ω g -Gas phase mass flow rate, kg / s; ω l -Liquid mass flow rate, kg / s; z-depth, m; A′-drill string inner diameter area, m 2 ; B′-formation physical property coefficient, m 2 / Pa;T ei - formation temperature, K; T l - Initial temperature of the formation, K.

[0156] In the embodiment of the present invention, the simulation experiment parameters of the overflow monitoring device are: the drilling fluid displacement is 40L / S; the gas invasion speed is 600L / S; the oil-water ratio of the oil-based drilling fluid is 8:2; the mud pool volume is 1000m3 .

[0157] According to the method in Example 3, a wellbore multiphase flow model corresponding to gas invasion is finally constructed, and the model is adjusted in combination with actual needs. When applied to actual monitoring work, the occurrence of gas invasion can be identified in time, the flow pattern of multiphase flow in the wellbore pipeline can be monitored, and the intensity of gas invasion, the main location area where gas invasion occurs, and the impact of gas invasion can be judged, thereby providing a large amount of safety defense time for on-site well control operations and providing sufficient guarantee for well control operations.

[0158] Among them, in the gas invasion simulation process of the embodiment of the present invention, according to the physical shape of the multiphase flow pattern in the wellbore pipeline, the flow pattern of the multiphase flow in the vertical section pipe flow can be divided into the following four types: bubbly flow A, slug flow B, disturbed flow C and annular mist flow D, and the degree of gas invasion is from weak to strong in the order of bubbly flow A, slug flow B, disturbed flow C and annular mist flow D. When gas invasion occurs, the degree of gas invasion can be judged by observing the flow pattern of the multiphase flow in the vertical section pipe flow:

[0159] like Figure 5 The figure shows bubbly flow A: In the vertical pipe flow, the bubbles in the fluid are small and evenly distributed, with no obvious merging phenomenon, resulting in a flow containing dispersed bubbles in the continuous liquid phase. This flow pattern usually occurs when the liquid density is low, often in the low mass gas content area (the area with relatively low gas content, that is, the volume fraction of gas relative to liquid is low), and the gas invasion degree in bubbly flow A is relatively weak;

[0160] like Figure 6 The figure shows slug flow B: In the vertical pipe flow, there are one or more slug-like substances, which will hinder the normal flow of the fluid and cause the aggregation and merging of droplets, thus forming a gas-liquid two-phase flow state in which gas columns and liquid columns appear alternately; the gas invasion degree in slug flow B is relatively strong;

[0161] like Figure 7 The figure shows disturbed flow C: in the vertical pipe flow, the liquid phase flow undergoes violent vortexing and mixing, the size and distribution of bubbles are uneven, bubbles are dispersed in the liquid phase flow, and droplets are entrained in the gas phase; disturbed flow C often appears in the area of ​​relatively high mass gas content (the area with relatively high gas content, that is, the volume fraction of gas relative to liquid is high), and the degree of gas invasion is relatively strong;

[0162] like Figure 8 The figure shows annular mist flow D: based on the disturbed flow C, the gas velocity increases, and the gas flows through the tube at high speed, so that almost all the liquid is atomized. This condition is called annular mist flow D.

[0163] The above description is only an embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement and improvement made within the application scope of the present invention shall be included in the protection scope of the present invention.

Claims

1. An overflow monitoring device based on the study of wellbore multiphase flow law, characterized in that: Including simulated wellbore, simulated drill string, injection manifold, return manifold, circulation pump and monitoring machine; The simulated drill string is arranged in the simulated wellbore and forms an annular space between the wellbore wall; A simulation switch is provided at the bottom of the simulated wellbore, and the simulation switch is connected to the overflow simulation device through a pipeline; The upper end of the simulated drill string is connected to the injection manifold, and the top side of the simulated wellbore is connected to the return manifold; the inlet of the injection manifold and the outlet of the return manifold are both connected to the mud pool, and the mud pool is provided with drilling fluid; the injection manifold is provided with a circulation pump and a first electromagnetic flowmeter, the return manifold is provided with a second electromagnetic flowmeter, and the mud pool is provided with a liquid level pressure sensor; the first electromagnetic flowmeter, the second electromagnetic flowmeter and the liquid level pressure sensor are all connected to a monitoring machine, and the monitoring machine is used to analyze and process the received monitoring data.

2. The overflow monitoring device according to claim 1, characterized in that: The first electromagnetic flowmeter, the second electromagnetic flowmeter and the liquid level pressure sensor are connected to the monitoring machine via an RS485 converter.

3. The overflow monitoring device according to claim 1, characterized in that: The liquid level pressure sensor is a pressure sensor.

4. The overflow monitoring device according to claim 1, characterized in that: The overflow simulation device comprises an air source pipeline, a water source pipeline and an oil source pipeline connected in parallel, the air source pipeline is provided with a flow meter and a valve, and the water source pipeline and the oil source pipeline are respectively provided with a pump, a flow meter and a valve.

5. The overflow monitoring device according to any one of claims 1 to 4, characterized in that: Also included is an image acquisition device, and a controller electrically connected to the image acquisition device; An observation window is provided on the simulated wellbore, and the image acquisition device is arranged on one side of the observation window. The image acquisition device is used to photograph the flow conditions in the simulated wellbore and transmit the photographed data to a controller for analysis and processing.

6. A method for monitoring and distinguishing overflow types based on the study of the flow law of wellbore multiphase flow, implemented by using the overflow monitoring device according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: Step S1: adjust the depth of the simulated wellbore, turn on the circulation pump, fill the entire wellbore pipeline with drilling fluid, and start overflow monitoring after the circulation of the wellbore pipeline is stable; Step S2: opening a simulation switch at the bottom of the simulated wellbore to fill the simulated wellbore with invading fluid; Step S3: As the simulated overflow experiment continues, the drilling fluid return displacement data change is monitored by the second electromagnetic flowmeter installed on the return manifold, and the mud pool incremental data change is monitored by the liquid level sensor installed in the mud pool, and the monitoring data is transmitted to the monitoring machine for real-time storage; Step S4: close the simulation switch at the bottom of the simulated wellbore, and continue to circulate the drilling fluid until all the intrusive fluid in the wellbore pipeline is discharged, and the values ​​of the first electromagnetic flowmeter, the second electromagnetic flowmeter and the liquid surface pressure sensor tend to be stable; Step S5: repeating steps S2-S4 to complete the simulation of gas invasion, water invasion and oil invasion respectively, and obtaining the corresponding gas invasion experimental data, water invasion experimental data and oil invasion experimental data respectively; Step S6: Summarize, analyze and process the real-time monitored and stored gas intrusion test data, water intrusion test data and oil intrusion test data, determine the characteristic parameters of different types of overflows, and use them as a basis for monitoring and identifying overflow types.

7. The method according to claim 6, characterized in that In step S2, the simulated wellbore is filled with invading fluid at a constant volume or a constant flow rate.

8. The method according to claim 6, characterized in that The invading fluid includes gas, water or oil, which is used to simulate gas invasion, water invasion or oil invasion respectively.

9. The method according to claim 6, characterized in that In step S6, the characteristic parameters of different types of overflow include one or more combination parameters of the following parameters: The time point when overflow occurs, the maximum, minimum or average value of the drilling fluid return displacement, the changing speed, change amplitude and duration of the drilling fluid return displacement, the maximum, minimum or average value of the mud increment, the changing speed, change amplitude and duration of the mud increment.

10. A method for monitoring and distinguishing overflow conditions based on the study of the flow law of wellbore multiphase flow, implemented by using the overflow monitoring device according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: Step S01: Collect experimental data; Conduct multiple simulated overflow experiments for different overflow types and collect drilling fluid return displacement data and mud pool increment data during overflow; Step S02: data analysis; Conduct statistics and analysis on the collected experimental data to determine the characteristic parameters of different types of overflow; Step S03: Establishing a wellbore multiphase flow model; According to the experimental data analysis results, the mathematical equation of wellbore multiphase flow is constructed, and the characteristic parameters in the experimental data are substituted into the mathematical equation of wellbore multiphase flow, and the wellbore multiphase flow model is obtained by parameterization. Step S04: using actual monitoring data to verify and optimize the wellbore multiphase flow model; Step S05: adjusting and correcting the wellbore multiphase flow model after verification and optimization according to the experimental results and actual needs; Step S06: model application; The adjusted and corrected wellbore multiphase flow model is applied to actual monitoring work to identify and distinguish the overflow conditions of different types of overflows.

11. The method according to claim 10, characterized in that In the step S03, the constructed gas invasion wellbore multiphase flow model includes: a continuity equation, a fluid momentum equation and a fluid energy equation that characterize the flow quality through a certain space; The continuity equation is: The momentum equation for the fluid is: The fluid energy equation is: In the above formula, A is the local annular cross-sectional area, m 2 ; E g - output gas mass flow rate, kg / s; ρ g -Output gas density, kg / m 3 ; V g - Output gas return velocity, m / s; Q g -gas production rate in the gas production section, kg / (s·m); t-time, s; s-distance from a point in the annulus to the wellhead, m; E m -Drilling fluid mass flow rate, kg / s; ρ m -Drilling fluid density, kg / m 3 ; V m -Drilling fluid return velocity, m / s; E c - rock cuttings volume fraction, dimensionless; ρ c -Cut density, kg / m 3 ; V c - cuttings return velocity, m / s; g-gravitational acceleration, m / s 2 ;α-inclination angle of fluid or pipe, rad;P-fluid pressure, Pa; is the friction pressure drop of the wellbore section, Pa / m; C pg - the mole fraction of a specific component in the produced gas, dimensionless; T a - annulus temperature, K; ρ l -Liquid density, kg / m 3 ; E l -Liquid volume fraction, dimensionless; C l - the mole fraction of a particular component of the formation fluid, dimensionless; -Annulus area, m 2 ;ω g -Gas phase mass flow rate, kg / s; ω l -Liquid mass flow rate, kg / s; z-depth, m; A′-drill string inner diameter area, m 2 ; B′-formation physical property coefficient, m 2 / Pa;T ei - formation temperature, K; T l - Initial temperature of the formation, K.

12. The method according to claim 11, characterized in that The continuity equation takes into account the three components of drilling fluid, gas and cuttings; in the process of solving the continuity equation, The corresponding gas phase-non-gas production section mass flow calculation formula is: The corresponding drilling fluid mass flow calculation formula is: The corresponding cuttings mass flow calculation formula is: In the above formula, A is the local annular cross-sectional area, m 2 ; E g - output gas mass flow rate, kg / s; ρ g -Output gas density, kg / m 3 ; V g - Output gas return velocity, m / s; Q g -Gas production speed in the gas production section, kg / (s·m); E m -Drilling fluid mass flow rate, kg / s; ρ m -Drilling fluid density, kg / m 3 ; V m -Drilling fluid return velocity, m / s; E c - rock cuttings volume fraction, dimensionless; ρ c -Cut density, kg / m 3 ; V c -Cuts return velocity, m / s; Q c - cuttings mass flow rate, kg / s; t-time, s; s-the distance from a point in the annulus to the wellhead, m.

13. The method according to claim 10, characterized in that In the process of gas invasion simulation, according to the physical shape of the multiphase flow pattern in the wellbore pipeline, the flow pattern of the multiphase flow in the vertical section pipe flow can be divided into the following four types: Bubble flow A: In a vertical pipe flow, the continuous liquid phase contains dispersed bubbles; Slug flow B: In the vertical pipe flow, there are one or more plug-like substances, which will hinder the normal flow of the fluid and cause the aggregation and merging of droplets, thus forming a gas-liquid two-phase flow state with alternating gas and liquid columns; Disturbed flow C: In the vertical pipe flow, the liquid phase flow undergoes violent vortexing and mixing, the size and distribution of bubbles are uneven, there are bubbles dispersed in the liquid phase flow, and droplets are entrained in the gas phase; Annular mist flow D: Based on the disturbance flow C, the gas velocity increases and the liquid in the vertical pipe flow is atomized; Among them, the degree of gas invasion is from weak to strong in the order of bubbly flow A, slug flow B, disturbed flow C and annular mist flow D.

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