CN115522915B - A downhole gas intrusion detection device and working method during rotary drilling based on gas-liquid two-phase - Google Patents

Abstract

The invention relates to a device and a working method for detecting underground gas invasion while drilling in a rotary drilling process based on gas-liquid two phases, which belong to the technical field of underground gas invasion measurement of drilling, and comprise a signal generating unit and a rotating unit, wherein the signal generating unit comprises a permanent magnet, a conductor bar and a collector disc; the conductor bar is inserted into the middle lower end of the collector disc and connected with the rotary barrel, the rotary unit comprises a blade, an insulating layer, a conductive layer and the rotary barrel, the blade is arranged on the outer side of the rotary barrel, receives rotary resistance in the rotation process of the drill rod, transmits the rotary resistance to the whole rotary unit and the drill rod to generate relative rotation to generate an electric signal, and transmits the electric signal through an access circuit; the signal generator is used for converting the direct current signal into an alternating current signal which can be transmitted, and judging that the gas invasion occurs. According to the invention, the physical properties of the drilling fluid can be measured in the rotary drilling process of the drill rod, so that the gas invasion situation of the shaft is reversely pushed out, the energy consumption is low, the long-time underground gas invasion measurement can be realized, and the monitoring accuracy is high.

Description

A downhole gas intrusion detection device based on gas-liquid two-phase rotary drilling process and working method

Technical Field

The invention relates to a downhole gas invasion detection device and a working method during rotary drilling, belonging to the technical field of downhole gas invasion measurement in drilling.

Background Art

Gas invasion refers to the phenomenon that during the oil field drilling process, the gas in the formation invades the drilling wellbore, causing the properties of the drilling fluid to change. There are three main reasons: First, when drilling into fractured or large cave formations, there will be a sudden influx of gas into the wellbore and the loss of drilling fluid. Second, when drilling into the gas layer, as the rock is broken, the gas in the formation will invade the wellbore. Third, when the downhole pressure is less than the formation pressure at the same depth, it is in an underbalanced drilling state. Due to the pressure difference, the gas in the formation will invade the wellbore in the form of gas or dissolved gas through the mud cake. Once gas invasion occurs, the density of the drilling fluid will decrease, and accidents such as overflow and blowout are prone to occur. Therefore, timely and accurate detection of downhole gas invasion and taking measures can effectively avoid accidents.

In terms of gas intrusion detection, the methods commonly used in China include the drilling fluid pool liquid level detection method (drilling fluid increment method), flow difference overflow detection method and acoustic gas intrusion monitoring method. For example, Chinese patent document CN111364979A is an ultrasonic-based downhole gas intrusion detection system. This method is to add an ultrasonic monitoring device to the drill pipe and use it in conjunction with a turbine and a gas-solid separation device. The drilling fluid pool liquid level detection method and the flow difference overflow detection method have low accuracy and slow response speed. The acoustic wave method has a faster response speed than the first two, but it also has accuracy and technical defects.

Using traditional methods to detect gas invasion, the indication results are too rough and unreliable, and there is also the problem of slow response of detection results. With the increase of drilling depth and the difficulty of drilling projects, traditional methods are difficult to meet well control requirements. For deep-sea drilling with huge costs, overflow detection requires more reliable detection results to meet more advanced well control technology.

Summary of the invention

In view of the deficiencies in the prior art, the present invention provides a downhole gas intrusion detection device and a working method during rotary drilling.

The technical solution of the present invention is as follows:

A downhole gas invasion detection device based on gas-liquid two-phase rotary drilling process, comprising a signal generating unit, a rotating unit,

The signal generating unit includes a permanent magnet, a conductor bar, and a collector plate; the permanent magnet is fixed on the collector plate to provide permanent magnetic force; the conductor bar has a T-shaped structure, the two ends of the upper cross bar are inserted into the collector plate, and the lower end is connected to a rotating barrel, which is used to cut the magnetic field under the drive of the rotating barrel to generate an induced current; the collector plate is a cylindrical body, one end of which is fixedly connected to the drill pipe, and an annular groove is provided in the middle, the upper cross bar of the conductor bar is inserted into the annular groove, and the collector plate is connected to the access circuit and the signal generator: the collector plate is used to bind the conductor bar and fix the permanent magnet, and can also collect the induced current generated by the conductor bar and transmit the electrical signal through the access circuit; the signal generator is used to convert the DC signal into an AC signal that can be transmitted;

The rotating unit includes blades, an insulating layer, a conductive layer, and a rotating barrel;

The signal generating unit is arranged in the space inside the rotating barrel, and the metal wall of the rotating barrel is used to isolate the internal signal generating unit from the external fluid;

The inner wall of the rotating barrel is provided with a conductive layer, which is a part of the rotating barrel. The conductive layer is directly connected to the conductor rod. The conductive layer, the conductor rod, the collector plate, the access circuit, and the signal generator form a conductive circuit.

An insulating layer is provided between the inner wall of the rotating barrel and the conductive layer to isolate the conductive layer from the metal wall of the rotating barrel to avoid further attenuation of the electrical signal;

The blades are arranged outside the rotating barrel, receive the rotation resistance during the rotation of the drill rod, and transmit it to generate relative rotation between the entire rotating unit and the drill rod.

Preferably, the rotating unit further comprises a conical tooth large end and an inertial one-way shaft, wherein the conical tooth large end is arranged on the upper and lower sides of the rotating barrel and connected to the metal wall of the rotating barrel to drive the inertial one-way shaft to rotate and change the transmission direction;

The inertia one-way shaft is fixedly connected to the drill pipe, and its external teeth are meshed with the large end of the conical teeth. It has large inertia, can maintain the stability of the drilling speed of the entire rotating system, and can also prevent the reverse rotation of the rotating device.

Preferably, the rotating unit further comprises a sealer slot and a sealer, and a sealer slot is provided in an annular direction on the outer side of the rotating barrel for connecting the sealer. On the one hand, it is necessary to prevent external fluid from entering the gear space, and on the other hand, the sealer can rotate in the sealer slot. The sealer is directly connected to the drill pipe to isolate the external fluid from the internal space.

Preferably, the downhole gas intrusion detection device during the rotary drilling process based on gas-liquid two-phase includes at least two signal generating units and two rotating units. The electrical signal generated by each signal generating unit is summarized by a line collecting unit and connected to a transmission cable. Specifically, multiple rotating units and signal generating units can be arranged around the drill pipe according to the size of the drill pipe. The electrical signal generated by each unit is summarized by a line collecting unit. On the one hand, the induced current at different positions of the drill pipe in the circumferential direction can be measured by multiple signal generating units and line collecting units evenly distributed in the circumferential direction, which is suitable for the case where the gas is unevenly distributed in the circumferential direction; on the other hand, when a certain signal generating unit and line collecting unit fails, it does not affect the functioning of the entire device, so the reliability of the measurement is further improved. The number of signal generating units and line collecting units is preferably determined according to the actual rotation speed of the drill pipe and the actual downhole conditions of the target well, including the drilling depth, drilling fluid displacement, drilling fluid density, drilling fluid viscosity, etc. When a stable current value can be measured, the number of selected signal generating units and line collecting units is optimal and is evenly distributed around the drill pipe.

A working method of the downhole gas intrusion detection device during the above-mentioned gas-liquid two-phase rotary drilling process comprises the following steps:

Step 1. The gas intrusion measurement device is fixed on the drill pipe and lowered into the wellbore along with the drill pipe.

Step 2. The drill pipe rotates and drills, driving the collector plate, permanent magnet, inertia one-way shaft and other components fixed to the drill pipe to rotate together; at this time, due to the large inertia of the inertia one-way shaft, there is a tendency to drive the large end of the conical tooth and the metal wall of the rotating barrel, the conductor rod, the blades and other devices connected to it as a whole to rotate together;

Step 3. When the drill string starts to rotate, it will drive the sealer, inertial one-way shaft, permanent magnet and collector plate connected to the drill string to rotate at a certain rate; the rotating unit and the conductor rod will start to rotate due to the inertia of the inertial one-way shaft at the start-up moment, and at the same time, the blades will be subject to the rotational resistance of the annular drilling fluid, and the resistance will be transmitted to the rotating barrel, and then to the entire rotating unit and the directly connected conductor rod, resulting in a rotational speed difference between the conductor rod and the permanent magnet; once a rotational speed difference occurs between the conductor rod and the permanent magnet, it is equivalent to the conductor rod cutting the magnetic flux lines, which will excite the induced current; the induced current flows from the conductor rod into the collector plate, and then into the signal generator for processing. After processing in the line collection unit, the signal will be transmitted to the transmission cable until it reaches the ground.

Preferably, in Step 3, the signal processed by the line collection unit is transmitted to the ground for calculation and analysis to predict the magnitude of the rotational resistance F _d : F _d = i _constant BL sin(α) (7)

i is _{a constant} current value, B is the magnetic induction intensity; L is the length of the conductor; α is the angle between the current direction in the conductor and the magnetic field direction.

Further preferably, in Step 3, when gas invasion occurs in the wellbore, the properties of the drilling fluid will change, thereby causing a change in the rotational resistance, and a gas invasion discrimination threshold C is set;

The gas-liquid miscible phase model is adopted, that is, it is assumed that the gas and liquid form a mixed phase, and the density of the mixed phase is:

ρ _m ＝ρ _l (1-φ)+ρ _g φ＝ρ _l +φ(ρ _g -ρ _l ) (15)

Among them, φ is the volume content of gas, ρ _l is the liquid density, and ρ _g is the gas density; therefore, the resistance expression of the whole device is:

If you remember:

Then we have:

F _total =ρ _l Q+φ(ρ _g -ρ _l )Q (18)

Among them, H is the height of the blade, D is the straight-line distance from the end of the blade to the central axis, _Cd is the drag coefficient, S is the radius of the central axis, r represents the position on the blade that is a straight-line distance r from the central axis, the central axis is the drill string with a rotating barrel, and the value of Q is related to the angular velocity ω of the drill rod rotation and the design specifications of the blade; when the blade rotates, it will drive the conductor rod in the electrical area to cut the magnetic flux lines to generate current, but the generation of current will also form an Ampere force on the conductor rod, and the direction of the Ampere force is always opposite to the cutting direction, presenting a resistance that hinders cutting. When the Ampere force is equal to the resistance of the blade, the entire device rotates stably, and the output stable current i _{is constant} , that is:

F _A = i _constant BL sin (α) = ρ _l Q + φ (ρ _g - ρ l) Q = F _total (19)

At this time, the gas content φ can be expressed as:

Wherein, B is the magnetic induction intensity; L is the conductor length; α is the angle between the current direction in the conductor and the magnetic field direction. It can be seen from the above expression that when the drilling process is stable, only the gas content φ and the stable current value i are _constant variables. Therefore, this method can be used to determine the occurrence and degree of gas invasion.

By formula (20), the wellbore gas content _φt at time t can be calculated by obtaining _{the constant} i. After a certain time interval Δt, the wellbore gas content φt _+Δt at time _t+ Δt can be obtained. The wellbore gas content φt+Δt at time t+Δt is compared with the wellbore gas content φt _{+Δt at time t+Δt. If φt+Δt>φt and φt+Δt-φt＝Δφt≥C are satisfied, it can be determined that gas invasion has occurred. When φt+Δt < φt or φt + Δt > φt} but _φt+Δt - _φt ＝ _Δφt ＜C, it means that gas invasion has not occurred and the monitoring at the next time is continued. The selected time interval Δt should be reasonably selected according to the actual drilling conditions.

Preferably, in Step 1, a gas invasion detection device is installed at intervals of 100 m in the layer section prone to gas invasion. Combined with a high-precision current sensor, multi-point measurement can be achieved in the layer section prone to gas invasion. Combined with downhole drilling parameters, the layer where gas invasion occurs can be monitored; the rate of change of the wellbore gas content φ within a certain period of time between adjacent or separated gas invasion detection devices can qualitatively reflect the movement speed of the gas, which is helpful to timely initiate well control prevention measures.

According to the fluid properties of the drilling fluid and the monitoring well depth, after determining the distribution number of the signal generating unit and the line collection unit and the installation position of the detection device, a higher-precision current sensor is selected to measure more subtle changes in the induced current. The magnitude of the downhole rotational resistance is determined by the change in the induced current. After gas invasion occurs, the viscosity of the drilling fluid will decrease, and thus the rotational resistance will also decrease. The change in the rotational resistance can be used to qualitatively analyze the degree of gas invasion. Combined with multi-point measurement, the prediction of the gas invasion position and movement speed can also be achieved.

Device Principle

When the conductor bar cuts the magnetic flux lines to generate induced current, according to Ampere's law, the conductor bar will be subjected to the Ampere force of the magnetic field. The direction of the Ampere force is opposite to the tangent direction of the relative motion of the rotating unit and the direction of the rotation resistance of the blade, and is the same as the tangent direction of the rotation of the drill pipe. We can describe the Ampere force here as follows: As long as the rotation of the drill pipe starts, the Ampere force will be generated, and it will increase with the increase of the relative drilling speed, and the direction of the Ampere force always points to the direction that is conducive to reducing the relative drilling speed between the drill pipe and the rotating unit.

When the three forces of Ampere force, annular rotation resistance and friction rotation resistance in the instrument are balanced, the relative drilling speed between the drill pipe and the rotating unit will be stable, and the output DC power will also be stable. The DC current in the process is transmitted to the signal generator for processing and becomes a transmittable AC signal, which is processed by the line collection unit and becomes a signal that can be sent to the transmission cable.

In 1831, Faraday pointed out that when a part of the conductor of a closed circuit cuts the magnetic flux lines in a magnetic field, and the movement must be at a certain angle to the magnetic flux lines and not parallel to the magnetic flux lines, a current will be generated in the conductor. This phenomenon is called electromagnetic induction. The generated current is called induced current. When a section of conductor cuts the magnetic flux lines at a uniform speed in a uniform magnetic field, regardless of whether the circuit is closed or not, the magnitude of the induced electromotive force E is only proportional to the magnetic flux density B, the conductor length L, the cutting speed v, and the sine value of the angle θ with the direction, that is:

E＝BLv sin(θ) (1)

Assuming that the internal resistance of the conductor is r, the induced current is:

When B, L, r, and θ are constant, the intensity of the induced current is proportional to the cutting speed, that is:

i∝v (3)

Ampere found through experiments that when a straight wire with a current intensity of i and a length of L is placed in a uniform external magnetic field with a magnetic induction intensity of B, the magnitude of the Ampere force on the wire is:

f＝iBL sin(α) (4)

Where α is the angle between the current direction in the wire and the direction B. Combining equations (3) and (4) we can get the instantaneous Ampere force in the process of cutting magnetic flux lines:

From formula (5), we can know that when B, L, α, and θ are constant, the Ampere force is proportional to the cutting speed v. That is:

f∝v (6)

Combining formula (4), we can conclude that when B, L, α, and θ are constant, the magnitude of the induced current reflects the magnitude of the Ampere force. When the magnitude of the rotational resistance and the Ampere force are the same, the output induced current will be a stable value and reflect the magnitude of the rotational resistance. This induced current reaches the surface through the transmission of the downhole information transmission system. By analyzing it, the magnitude of the downhole rotational resistance can be obtained: F _d = i _constant BL sin(α) (7)

Referring to the relevant formula of the vertical axis resistance type Savonius turbine, the energy capture efficiency during rotation is usually expressed by the power coefficient Cp, the torque coefficient Cm and the tip speed ratio λ:

Among them: ρ is the density of the fluid; M is the rotational torque; P _TURBING is the energy captured by the turbine; P _THEORY is the theoretical energy of the water flow in the area swept by the turbine; U is the incoming flow velocity; ω is the blade rotation speed; D is the straight-line distance from the end of the blade to the central axis, the central axis is the drill rod with a rotating barrel in this application, S is the radius of the central axis, that is, the radius of the drill rod + the length of the rotating barrel in this application, and the drill rod with a rotating barrel is regarded as the central axis that drives the blade to rotate; H is the height of the turbine, that is, the blade in this application. The structure diagram of the turbine is shown in Figures 5 and 6.

The resistance expression of the fluid on a single blade is:

In the formula, V is the relative velocity of the fluid; ρ is the density of the fluid; u is the average velocity of the blade; A is the swept area, which can also be regarded as the maximum projected area of the blade; _Cd is the drag coefficient;

However, in the present invention, since the drilling fluid system does not flow head-on, different positions on the blade receive different incoming flow velocities. The received incoming flow velocity should be the sum of the partial velocities at each position on the blade, that is, V = ωr, where ω is the rotational angular velocity of the relative motion between the blade and the drilling fluid; r represents the position on the blade with a straight line distance r from the central axis. Assuming that the blade is semicircular, then take a very small dr segment, and the resistance received by this position can be expressed as:

is the relative speed between the dr section on the blade and the incoming fluid, then: The size of dA depends on the maximum projection length of the dr segment, which can be expressed as: dA = H·dr _{maximum projection} , so the entire resistance expression can be written as:

The value of _{the maximum projection} of dr can be studied by establishing a coordinate system as shown in Figure 7.

Point O is the geometric center of the entire device, and the semicircular arc represents the shape of the blade. Since the length of the arc segment dr is very small, it can be considered that the lengths of the line segments AB and GF are both dr, and TA and TB are parallel to each other, TF and TG are parallel to each other and have ∠FGT=90°. TE and TK are the midlines of ΔTAB and ΔTFG, respectively, and the angle between them is θ. When TE is perpendicular to the X-axis, it is easy to obtain the maximum projection length of AB CD=AB=dr. When TE is rotated by an angle of θ, the maximum projection length corresponding to the chord GF at this time is dr _{maximum projection} =JH. When dr is very small, since PH is parallel to TE, it can be considered that ∠PGT=θ, then it is easy to obtain ∠QJH=θ through geometric relationships, and at this time JH=cosθdr. The value of cosθ can be obtained through ΔPTG, which is so

Therefore, the resulting resistance expression is:

Want to get the indefinite integral The original function form of the resistance F _d is very difficult to simplify into an analytical form. In actual calculations, numerical calculation methods such as Newton and Simpson formulas can be used to solve it.

The gas-liquid miscible phase model is adopted, that is, it is assumed that the gas and liquid form a mixed phase, and the density of the mixed phase is:

ρ _m ＝ρ _l (1-φ)+ρ _g φ＝ρ _l +φ(ρ _g -ρ _l ) (15)

Among them, φ is the volume content of the gas. Therefore, the resistance expression of the whole device is:

If you remember

Then we have:

F _total =ρ _l Q+φ(ρ _g -ρ _l )Q (18)

When the blades rotate, they drive the conductor rods in the electrical area to cut the magnetic flux lines and generate current. However, the current will also generate an Ampere force on the conductor rods, and the direction of the Ampere force is always opposite to the cutting direction, presenting a resistance that hinders the cutting. When the Ampere force is equal to the resistance of the blades, the entire device rotates stably and the output stable current i _{is constant} , that is:

F_安＝ _iconstantBL sin(α)＝ρ _l Q+φ(ρ _g -ρ _l )Q＝ _Ftotal (19)

At this time, the gas content φ can be expressed as:

Where B is the magnetic induction intensity; L is the length of the conductor; α is the angle between the current direction in the conductor and the magnetic field direction.

It can be seen from the above expression that when the drill string rotates stably, only the gas content φ and the stable current value i _{are constant} variables. Therefore, this method can be used to determine the occurrence and degree of gas invasion.

From formula (20), the wellbore gas content φ _t at time t can be calculated by obtaining _constant i. After a certain time interval Δt, the wellbore gas content φ _t+Δt at time t+Δt can be obtained. φ _t is compared with the wellbore gas content φ _t+Δt at time t+Δt. If φ _t+Δt >φ _t and φ _t+Δt -φ _t = Δφ _t ≥ C are satisfied, it can be determined that gas invasion has occurred; when φ _t+Δt <φ _t or φ _t+Δt >φ _t but φ _t+Δt -φ _t = Δφ _t <C, it means that gas invasion has not occurred and the monitoring at the next moment is continued. The selected time interval Δt should be reasonably selected according to the actual drilling conditions.

The beneficial effects of the present invention are:

1. The present invention can measure the physical properties of the drilling fluid during the rotary drilling process of the drill pipe, thereby inferring the gas invasion situation of the wellbore.

2. The present invention has low energy consumption, can realize long-term underground gas invasion measurement, and has high monitoring accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a cross-sectional design diagram of a signal generating unit;

Fig. 2 is a signal generating circuit diagram;

FIG3 is a schematic cross-sectional view of a rotating unit;

FIG4 is a schematic cross-sectional view of the overall device;

Fig. 5 is a simplified outline diagram of the device portion;

FIG. 6 is a bottom plan view of the device.

Figure 7 is the blade projection coordinate system.

Among them: 1. permanent magnet, 2. conductor rod, 3. collector plate, 4. blade, 5. insulating layer, 6. conductive layer, 7. rotating barrel, 8. rotating barrel metal wall, 9. large end of conical tooth, 10. sealer slot, 11. sealer, 12. inertial unidirectional shaft, 13. line collection unit, 14. signal generator, 15. drill pipe, 16. transmission cable.

DETAILED DESCRIPTION

The present invention will be further described below by way of embodiments in conjunction with the accompanying drawings, but is not limited thereto.

Embodiment 1:

A downhole gas intrusion detection device based on gas-liquid two-phase rotary drilling process, as shown in Figure 1-4, includes a signal generating unit, a rotating unit,

The signal generating unit comprises a permanent magnet 1, a conductor rod 2 and a collector disc 3; the permanent magnet 1 is fixed on the collector disc 3 to provide permanent magnetic force; the conductor rod 2 presents a T-shaped structure, the two ends of the upper cross bar are inserted into the collector disc 3, and the lower end is connected to the rotating barrel 7, which is used to cut the magnetic field under the drive of the rotating barrel to generate an induced current; the collector disc 3 is a cylindrical body, one end of which is fixedly connected to the drill rod 15, and an annular groove is provided in the middle, the upper cross bar of the conductor rod is inserted into the annular groove, and the collector disc 3 is connected to the access circuit and the signal generator 14: the collector disc is used to bind the conductor rod and fix the permanent magnet, and at the same time can collect the induced current generated by the conductor rod and transmit the electrical signal through the access circuit; the signal generator is used to convert the DC signal into an AC signal that can be transmitted;

The rotating unit includes blades 4, an insulating layer 5, a conductive layer 6, and a rotating barrel 7;

The signal generating unit is arranged in the space inside the rotating barrel, and the metal wall 8 of the rotating barrel is used to isolate the internal signal generating unit from the external fluid;

The inner wall of the rotating barrel is provided with a conductive layer 6, which is a part of the rotating barrel. The conductive layer 6 is directly connected to the conductor rod 2. The conductive layer 6, the conductor rod 2, the collector plate 3, the access circuit, and the signal generator 14 form a conductive loop.

An insulating layer 5 is provided between the inner wall of the rotating barrel and the conductive layer 6 to isolate the conductive layer from the metal wall of the rotating barrel to prevent further attenuation of the electrical signal;

The blades 4 are arranged outside the rotating barrel 7, and receive the rotation resistance during the rotation of the drill rod 15, and transmit it to generate relative rotation between the entire rotating unit and the drill rod.

The rotating unit also includes a conical tooth big end 9 and an inertial one-way shaft 12. The conical tooth big end 9 is arranged on the upper and lower sides of the rotating barrel and connected to the metal wall of the rotating barrel to drive the inertial one-way shaft to rotate and change the transmission direction.

The inertia unidirectional shaft 12 is fixedly connected to the drill rod 15, and its external teeth are meshed with the large ends of the conical teeth. It has large inertia, can maintain the drilling speed stability of the entire rotating system, and can also prevent the reverse rotation of the rotating device.

The rotating unit also includes a sealer slot 10 and a sealer 11. The sealer slot 10 is provided circumferentially on the outer side of the rotating barrel to connect the sealer 11. On the one hand, it is necessary to prevent external fluid from entering the gear space, and on the other hand, the sealer can rotate in the sealer slot. The sealer is directly connected to the drill pipe to isolate the external fluid from the internal space.

Embodiment 2:

A downhole gas intrusion detection device during rotary drilling based on gas-liquid two-phase, the structure of which is as described in Example 1, except that the downhole gas intrusion detection device during drilling includes at least two signal generating units and two rotating units, and the electrical signal generated by each signal generating unit is summarized by a line collection unit 13 and connected to a transmission cable 16. Specifically, a plurality of rotating units and signal generating units can be arranged around the drill pipe according to the size of the drill pipe, and the electrical signal generated by each unit is summarized by a line collection unit. On the one hand, the induced current at different circumferential positions of the drill pipe can be measured by a plurality of circumferentially evenly distributed signal generating units and line collection units, which is suitable for the case where the gas is unevenly distributed in the circumferential direction; on the other hand, when a certain signal generating unit and line collection unit fails, it does not affect the functioning of the entire device, so the reliability of the measurement is further improved. The number of signal generating units and line collection units is optimally determined according to the actual rotation speed of the drill pipe and the actual downhole conditions of the target well, including drilling depth, drilling fluid displacement, drilling fluid density, drilling fluid viscosity, etc. When a stable current value can be measured, the number of selected signal generating units and line collection units is optimal and is evenly spaced around the drill pipe.

Embodiment 3:

A working method of the downhole gas intrusion detection device during the gas-liquid two-phase rotary drilling process using the first embodiment includes the following steps:

Step 1. The gas invasion measuring device is fixed on the drill pipe and lowered into the wellbore along with the drill pipe. In the layer section prone to gas invasion, a gas invasion detection device is installed at intervals of 100m. Combined with a high-precision current sensor, multi-point measurement can be achieved in the layer section prone to gas invasion. Combined with downhole drilling parameters, the layer where gas invasion occurs can be monitored; the rate of change of the induced current within a certain period of time between adjacent or separated gas invasion detection devices can qualitatively reflect the movement speed of the gas, which helps to initiate well control prevention measures in a timely manner.

Step 2. The drill pipe rotates and drills, driving the collector plate, permanent magnet, inertia one-way shaft and other components fixed to the drill pipe to rotate together; at this time, due to the large inertia of the inertia one-way shaft, there is a tendency to drive the large end of the conical tooth and the metal wall of the rotating barrel, the conductor rod, the blades and other devices connected to it as a whole to rotate together;

Step 3. When the drill string starts to rotate, it will drive the sealer, inertial one-way shaft, permanent magnet and collector plate connected to the drill string to rotate at a certain rate; the rotating unit and the conductor rod will start to rotate due to the inertia of the inertial one-way shaft at the start-up moment, and at the same time, the blades will be subject to the rotational resistance of the annular drilling fluid, and the resistance will be transmitted to the rotating barrel, and then to the entire rotating unit and the directly connected conductor rod, resulting in a rotational speed difference between the conductor rod and the permanent magnet; once a rotational speed difference occurs between the conductor rod and the permanent magnet, it is equivalent to the conductor rod cutting the magnetic flux lines, which will excite the induced current; the induced current flows from the conductor rod into the collector plate, and then into the signal generator for processing. After processing in the line collection unit, the signal will be transmitted to the transmission cable until it reaches the ground.

In Step 3, the signal processed by the line collection unit is transmitted to the ground for calculation and analysis to predict the magnitude of the rotational resistance F _d : F _d = i _constant BL sin(α) (7)

i is _{a constant} current value, B is the magnetic induction intensity; L is the length of the conductor; α is the angle between the current direction in the conductor and the magnetic field direction.

In Step 3, when gas invasion occurs in the wellbore, the properties of the drilling fluid will change, resulting in changes in the rotational resistance. The impact of the wellbore gas content is predicted and the gas invasion discrimination threshold C is set;

From formula (20), the wellbore gas content φ _t at time t can be calculated by obtaining _constant i. After a certain time interval Δt, the wellbore gas content φ _t+Δt at time t+Δt can be obtained. φ _t is compared with the wellbore gas content φ _t+Δt at time t+Δt. If φ _t+Δt >φ _t and φ _t+Δt -φ _t = Δφ _t ≥ C are satisfied, it can be determined that gas invasion has occurred; when φ _t+Δt <φ _t or φ _t+Δt >φ _t but φ _t+Δt -φ _t = Δφ _t <C, it means that gas invasion has not occurred and the monitoring at the next moment is continued. The selected time interval Δt should be reasonably selected according to the actual drilling conditions.

According to the fluid properties of the drilling fluid and the monitoring well depth, after determining the distribution number of the signal generating unit and the line collection unit and the installation position of the detection device, a higher-precision current sensor is selected to measure more subtle changes in the induced current. The magnitude of the downhole rotational resistance is determined by the change in the induced current. After gas invasion occurs, the viscosity of the drilling fluid will decrease, and thus the rotational resistance will also decrease. The change in the rotational resistance can be used to qualitatively analyze the degree of gas invasion. Combined with multi-point measurement, the prediction of the gas invasion position and movement speed can also be achieved.

Claims (6)

1. A downhole gas intrusion detection device based on gas-liquid two-phase rotary drilling process, characterized in that it includes a signal generating unit, a rotating unit, The signal generating unit comprises a permanent magnet, a conductor bar and a collector plate; the permanent magnet is fixed on the collector plate to provide permanent magnetic force; the conductor bar presents a T-shaped structure, the two ends of the upper cross bar are inserted into the collector plate, and the lower end is connected to a rotating barrel, which is used to cut the magnetic field under the drive of the rotating barrel to generate an induced current; the collector plate is a cylindrical body, one end of which is fixedly connected to the drill pipe, and an annular groove is provided in the middle, the upper cross bar of the conductor bar is inserted into the annular groove, and the collector plate is connected to the access circuit and the signal generator: the collector plate is used to bind the conductor bar and fix the permanent magnet, and can also collect the induced current generated by the conductor bar and transmit the electrical signal through the access circuit; the signal generator is used to convert the DC signal into an AC signal; The rotating unit includes blades, an insulating layer, a conductive layer, and a rotating barrel; the rotating unit also includes a large end of a conical tooth and an inertial one-way shaft. The large end of the conical tooth is arranged on the upper and lower sides of the rotating barrel and connected to the metal wall of the rotating barrel. The large end of the conical tooth drives the inertial one-way shaft to rotate and change the transmission direction; the inertial one-way shaft is fixedly connected to the drill pipe, and its external teeth are meshed with the large end of the conical tooth; the rotating unit also includes a sealer slot and a sealer. The outer side of the rotating barrel is provided with a sealer slot in an annular direction for connecting the sealer, and the sealer is directly connected to the drill pipe; The signal generating unit is arranged in the space inside the rotating barrel, and the metal wall of the rotating barrel is used to isolate the internal signal generating unit from the external fluid; The inner wall of the rotating barrel is provided with a conductive layer, which is directly connected to the conductor rod. The conductive layer, the conductor rod, the collector plate, the access circuit and the signal generator form a conductive loop. An insulating layer is provided between the inner wall of the rotating barrel and the conductive layer to isolate the conductive layer from the metal wall of the rotating barrel; The blades are arranged outside the rotating barrel, receiving the rotation resistance during the rotation of the drill pipe, and transmitting the rotation resistance to the entire rotating unit and the drill pipe to generate relative rotation; The size of the downhole rotational resistance is determined by the change of the induced current. After gas invasion occurs, the viscosity of the drilling fluid will decrease, and thus the rotational resistance will also decrease. The degree of gas invasion can be qualitatively analyzed by the change of the rotational resistance. 2. The downhole gas intrusion detection device during rotary drilling based on gas-liquid two-phase according to claim 1 is characterized in that the downhole gas intrusion detection device during rotary drilling comprises at least two signal generating units and at least two rotating units, and the electrical signal generated by each signal generating unit is summarized by a line collection unit and connected to a transmission cable. 3. A working method of the downhole gas intrusion detection device based on gas-liquid two-phase rotary drilling in claim 1, characterized in that it comprises the following steps: Step 1. The gas intrusion measurement device is fixed on the drill pipe and lowered into the wellbore along with the drill pipe; Step 2. The drill pipe rotates and drills, driving the collector plate, permanent magnet, and inertial one-way shaft components fixed to the drill pipe to rotate together; at this time, due to the large inertia of the inertial one-way shaft, there is a tendency to drive the large end of the conical tooth and the metal wall of the rotating barrel, the conductor rod, and the blade device connected to it as a whole to rotate together; Step 3. When the drill string starts to rotate, it will drive the sealer, inertial one-way shaft, permanent magnet and collector plate connected to the drill string to rotate at a certain rate; the rotating unit and the conductor rod will start to rotate due to the inertia of the inertial one-way shaft at the start-up moment, and at the same time, the blades will be subject to the rotational resistance of the annular drilling fluid, and the resistance will be transmitted to the rotating barrel, and then to the entire rotating unit and the directly connected conductor rod, resulting in a rotational speed difference between the conductor rod and the permanent magnet; once a rotational speed difference occurs between the conductor rod and the permanent magnet, it is equivalent to the conductor rod cutting the magnetic flux lines, which will excite the induced current; the induced current flows from the conductor rod into the collector plate, and then into the signal generator for processing. After processing in the line collection unit, the signal will be transmitted to the transmission cable until it reaches the ground. 4. The working method of the downhole gas intrusion detection device during the gas-liquid two-phase rotary drilling process according to claim 3 is characterized in that, in Step 3, the signal processed by the line collection unit is transmitted to the ground for calculation and analysis to predict the magnitude of the rotation resistance _Fd : _Fd = i _constant BLsin(α)(7) i is _{a constant} current value, B is the magnetic induction intensity; L is the length of the conductor; α is the angle between the current direction in the conductor and the magnetic field direction. 5. The working method of the downhole gas intrusion detection device during the gas-liquid two-phase rotary drilling process according to claim 4 is characterized in that, in Step 3, when gas intrusion occurs in the wellbore, the properties of the drilling fluid will change, thereby causing a change in the rotation resistance, and the wellbore gas content φ is calculated and the gas intrusion discrimination threshold C is set; The gas content φ is expressed as: Wherein, B is the magnetic induction intensity; L is the conductor length; α is the angle between the current direction in the conductor and the magnetic field direction, ρ _l is the liquid density, ρ _g is the gas density, i is _{the constant} current value, ω is the angular velocity of the drill pipe rotation; H is the height of the blade, D is the straight-line distance from the end of the blade to the central axis, C _d is the drag coefficient, S is the radius of the central axis, r represents the position on the blade with a straight-line distance r from the central axis, and the central axis is the drill string with a rotating barrel; The wellbore gas content _φt at time t is calculated by formula (20) through the _constant i obtained. After a certain time interval Δt, the wellbore gas content _φt+Δt at time t+Δt is obtained. _φt is compared with the wellbore gas content φt _+Δt at time t+Δt. If _{φt+Δt >} φt and φt _+Δt - _φt = _Δφt≥C are satisfied, it is determined that gas invasion has occurred. When φt _+Δt < _φt or φt _+Δt > _φt but _φt+Δt - _φt = _Δφt <C, it means that gas invasion has not occurred and monitoring at the next moment is continued. 6. The working method of the downhole gas intrusion detection device during the gas-liquid two-phase rotary drilling process according to claim 3 is characterized in that, in Step 1, a gas intrusion detection device is installed at intervals of 100m in the layer section where gas intrusion is prone to occur.