CN114622900A - Underground information transmission device and method based on micro-current - Google Patents

Abstract

The invention provides a micro-current-based underground information transmission device and a method, wherein the underground information transmission device comprises a central metal pipe, an underground alternating micro-current source, a sensor and a ground signal receiver, wherein the central metal pipe is axially arranged in a shaft; the underground alternating micro-current source is fixedly arranged on the central metal pipe, and underground alternating micro-current output by the underground alternating micro-current source can carry underground signal data; the sensor is connected with the underground alternating micro-current source and can measure underground signal data and transmit the underground signal data to the underground alternating micro-current source for signal loading; the ground signal receiver is connected with a wellhead and can receive underground signal data transmitted by the underground alternating micro-current source and demodulate and extract the underground signal data. The invention has the advantages of avoiding the shielding effect of the underground metal casing on electromagnetic wave signals, expanding the application scene of underground electric signal transmission modes, promoting the digital information development of shaft wells in the oil and gas industry and the like.

Description

A device and method for downhole information transmission based on microcurrent

technical field

The invention relates to the technical field of oil and gas well information and control engineering, and in particular, relates to a micro-current-based downhole information transmission device and method.

Background technique

Oil and natural gas exist in deep formations, involving complex and harsh environments such as high pressure, high temperature, oil and gas water media, etc. Taking the Sichuan Basin as an example, there are 27 oil and gas layers in the Jurassic-Sinian from top to bottom that alternate between high and low pressure, and the safe density window Narrow and unstable, the highest formation pressure is 147MPa (well LT1), high sulfur content (Luojiazhai-Gunziping Feixianguan Formation: 135～200g/m ³ ), and the test yield is high (the test yield of Moxi 009-X1 well is 263.47 ×104m ³ /d), in order to achieve safe, stable and efficient oil and gas exploration and development, it is necessary to master the downhole conditions in the early drilling process and the later oil and gas test production process, and the most important thing to master the downhole conditions is how to Information transmission ground. With the vigorous development of the digital transformation of the petroleum industry, the establishment of digital wellbore has become an inevitable trend. How to connect the underground and the surface and build an information channel is imminent.

At present, wellbore signal transmission technologies mainly include cable transmission, optical fiber transmission, intelligent drill pipe transmission, mud pulse transmission, acoustic wave transmission, and electromagnetic wave transmission. Among them, the cable and optical fiber transmission have the characteristics of high speed, but they cannot be used due to the rotation of the drill pipe during the drilling process. During the completion of the well, the cable transmission and optical fiber transmission face the risk of release of high pressure (105MPa) at the wellhead, the risk of being damaged by the friction of the wellbore, and the risk of damage caused by downhole vibration in the later stage. , downhole corrosion risk and other problems, and the cost is high, currently only tentative applications have been carried out in China, such as distributed temperature measurement data transmission in Xinjiang Oilfield.

The publication number is "CN112593864A" and the name is "self-powered intelligent drill pipe system and downhole data transmission method" discloses a self-powered intelligent drill pipe system, which also has the characteristics of fast transmission distance, but it is still in the experimental stage in China. , the transmission stability needs to be improved, and the whole wellbore needs to be customized for a dedicated cable-through drill pipe and a corresponding signal induction joint for each drill pipe, and the application cost is very high. Mud pulse transmission MWD is relatively stable, but its data transmission needs to rely on downhole pulse transmitters to generate pulses again and again, the transmission rate is 3-5bit/s slow, and it can only be used under the environment of wellbore mud circulation, during drilling and shut-in , completion stage and oil and gas test production stage can not be used. The downhole electromagnetic wave signal transmission technology has the characteristics of fast speed, convenient operation, low cost, and does not rely on wellbore mud circulation. Compared with the above centralized signal transmission methods, the electromagnetic wave signal transmission is mainly transmitted to the surface through the formation.

The publication number is "CN201386571Y", and the name is "relay transmission while drilling signal transmitting and receiving device"; the publication number is "CN111677496A", and the name is "a coal mine underground electromagnetic wave logging while drilling instrument". An electromagnetic wave signal receiving and sending device for wireless relay transmission, and a wireless electromagnetic wave logging-while-drilling instrument in a coal mine. The above-mentioned signal transmission receiving device and detection device have better transmission effect when the antenna is in the open-hole section, but when the antenna is located in the well section with metal casing, the antenna is shielded. Due to the shielding and absorption effect of the metal casing on electromagnetic waves, It is difficult to transmit signals, and metal casing has been installed on the wellbore wall during the downhole oil and gas testing stage, well completion stage, and oil and gas production stage, so it is difficult to transmit electromagnetic waves; and in the drilling stage, there is also metal in the upper well section For casing, when the transmitting antenna is raised from the lower open hole section to the well section where the metal casing is installed, the signal is also difficult to transmit.

After the drilling is completed, the site will be transferred to the stage of test completion and oil and gas production. During this period, downhole temperature and pressure data are the main basis for formation productivity assessment, oil and gas production system adjustment and wellbore risk control, which are related to the long-term safety of wellbore service and oil and gas recovery. At present, the storage type downhole pressure gauge is used in the oil test operation. The temperature and pressure data can only be obtained after the oil test is completed, and the oil and gas reservoir cannot be evaluated in time, and the efficiency needs to be improved. The downhole dynamic data during oil and gas production mainly uses steel wire or cable run-in sensors. Recording at the bottom of the well has a large workload and a short data coverage time, which makes it difficult to realize real-time grasp of the long-term downhole dynamic laws of a large number of wells in the vast well area of the oil and gas field. At present, the ground calculation and prediction method is generally used for downhole working condition data, which has a large error and a high risk for complex deep well construction. Traditional MWD signal transmission relies on wellbore fluid circulation to be used, and in the stage of oil testing and completion and oil and gas production, there is generally no wellbore fluid circulation like drilling operations, so MWD cannot be applied, and downhole electromagnetic wave signal transmission.

The publication number is "CN201386571Y", and the name is "relay transmission while drilling signal transmitting and receiving device" discloses a device for receiving and forwarding data measured by near-bit measuring instruments in the process of drilling, directional well or horizontal well using gas medium. Relay transmission while drilling signal transmitting and receiving device. However, due to the installation of metal casing in the whole wellbore during the oil testing, completion and production stages, the signal is shielded, so it is difficult to send out a signal or the signal is extremely weak, so it cannot be used.

Based on the above problems, the present invention provides a downhole information transmission device and method based on micro-current, which is applied to the transmission and acquisition of downhole signals in the stages of oil testing and completion and oil and gas production, taking into account the transmission rate, adapting to more wellbore operating environments, operating simplicity, cost, etc.

SUMMARY OF THE INVENTION

Aiming at the deficiencies existing in the prior art, the purpose of the present invention is to solve one or more problems existing in the prior art mentioned above. For example, one of the objectives of the present invention is to provide a microcurrent-based downhole information transmission device using wellbore microcurrent as a signal carrier.

In order to achieve the above object, one aspect of the present invention provides a micro-current-based downhole information transmission device, the downhole information transmission device is suitable for the installation of metal casing in the wellbore during oil testing and completion and oil and gas production, and electromagnetic wave transmission has a shielding effect. Signal transmission of oil and gas wells, the downhole information transmission device includes a central metal pipe, a downhole alternating microcurrent source, a sensor and a ground signal receiver, wherein,

The central metal pipe is axially arranged in the wellbore;

The downhole alternating microcurrent source is fixedly arranged on the central metal pipe, and the downhole alternating microcurrent output by the downhole alternating microcurrent source can carry downhole signal data;

The sensor is connected to the downhole alternating microcurrent source, and the sensor can measure downhole signal data and transmit it to the downhole alternating microcurrent source for signal loading;

The ground signal receiver is connected to the wellhead, and the ground signal receiver can receive the downhole signal data transmitted by the downhole alternating micro-current source, and demodulate and extract the downhole signal data.

In an exemplary embodiment of an aspect of the present invention, the downhole alternating microcurrent source may include an alternating current driver, a signal conduction tool, and a metal pipe stub, wherein,

The metal tube sub-section includes an upper metal tube and a lower metal tube that are fixedly arranged from top to bottom, and the metal tube sub-section transmits the downhole alternating micro-current signal generated by the alternating current driver to the signal conduction tool;

The signal conduction tool transmits downhole alternating microcurrent signals to the casing.

In an exemplary embodiment of an aspect of the present invention, the signal conducting tool may include an upper signal conducting tool and a lower signal conducting tool, the upper signal conducting tool is disposed on the upper end of the upper metal pipe and is connected to the sleeve contact, the lower signal conduction tool is arranged on the lower end of the lower metal tube and is in contact with the sleeve.

In an exemplary embodiment of an aspect of the present invention, the alternating current driver may include a driver circuit board, a coil, a driver housing, and a driver center tube, wherein,

The two ends of the driver central tube are respectively fixedly connected with the oil pipe, the driver shell and the driver central tube form a sealed cavity, and the coil and the driving circuit board are fixedly arranged in the sealed cavity.

In an exemplary embodiment of an aspect of the present invention, the downhole information transmission device may further include a repeater, the repeater is fixedly arranged on the central metal pipe and is located above the downhole alternating micro-current source, so The repeater can and can receive the micro-current signal sent by the downhole alternating micro-current source and transmit it to the ground signal receiver.

In an exemplary embodiment of an aspect of the present invention, the repeater may include a driving circuit board, a signal receiving circuit board, a coil, a repeater housing and a repeater center tube, wherein,

The two ends of the repeater central tube are respectively fixedly connected with the central metal tube, the repeater shell and the repeater central tube form a sealed cavity, and the signal receiving circuit board, the coil and the driving circuit board are fixedly arranged in the sealed cavity in the body.

In an exemplary embodiment of an aspect of the present invention, the downhole signal data may include at least one of temperature, pressure, flow rate, water cut, and salinity.

In an exemplary embodiment of an aspect of the present invention, the ground signal receiver may include two signal lines, a data acquisition card, and a signal demodulation module, wherein,

One end of the two signal lines is respectively connected to the signal acquisition point, and the other end is respectively connected to the data acquisition card, and the data acquisition card collects the voltage signal and transmits it to the signal demodulation module.

Another aspect of the present invention provides a micro-current-based downhole information transmission method, which can be implemented by the micro-current-based downhole information transmission device described in any of the above, and the method includes the steps of:

Run the tubing installed with the downhole alternating microcurrent source and sensor into the predetermined position downhole;

Using the downhole alternating microcurrent generated by the downhole alternating microcurrent source as a signal source, the sensor measures the downhole signal data and loads the signal onto the downhole alternating microcurrent;

Using the wellbore metal casing and the formation as the composite medium for downhole alternating microcurrent conduction, select any two points in the "wellbore metal casing-strata" composite medium network as the signal acquisition point, and use the ground signal receiver to measure the distance between these two points. The voltage value is obtained, the voltage fluctuation law is obtained, and then the downhole signal data is extracted by demodulation according to the signal coding method.

In an exemplary embodiment of another aspect of the present invention, the signal loading refers to encoding the downhole signal data on the downhole alternating microcurrent, so that the fluctuation mode of the downhole alternating microcurrent can represent the downhole signal data value .

In an exemplary embodiment of another aspect of the present invention, the method may further include the step of estimating downhole transmit power and surface signal received strength downhole:

By analyzing the resistance distribution of the "wellbore metal casing-stratum" composite medium network, and using Ampere's theorem to calculate the voltage between each position point, the downhole transmission power and the ground signal reception strength are determined.

Compared with the prior art, the beneficial effects of the present invention may include at least one of the following:

(1) The present invention provides a micro-current-based downhole information transmission device, which provides a feasible method for downhole signal transmission in the stage of oil testing and completion and oil and gas production (the entire wellbore is installed with metal casing), communicating the downhole and Information channels on the ground to facilitate digital transformation;

(2) The micro-current-based downhole information transmission method of the present invention avoids the traditional downhole signal transmission relying on electromagnetic waves (the electromagnetic wave emitted by the electromagnetic wave antenna needs to be radiated to the formation, and then transmitted from the formation to the ground). When the electromagnetic wave transmitting antenna is in the metal casing , the underground metal casing has a shielding effect on the electromagnetic wave signal, and the signal transmission distance is short or even cannot be transmitted; instead, the present invention uses the micro-current signal transmission method, and the micro-current transmitter just uses the conductivity of the metal casing to transmit the signal from the metal. The casing is passed out, on the one hand, it mainly flows from the metal casing to the ground, and on the other hand, a small part flows from the formation to the ground;

(3) The present invention takes into account the transmission rate, adapts to more wellbore operating environments, and has the advantages of simple operation, low cost, and wide application range.

Description of drawings

The above and other objects and features of the present invention will become more apparent from the following description in conjunction with the accompanying drawings, wherein:

1 shows a schematic structural diagram of a microcurrent-based downhole information transmission device according to an exemplary embodiment of the present invention;

FIG. 2 shows a schematic structural diagram of an exemplary embodiment of the alternating current driver in FIG. 1;

Fig. 3 shows an equivalent circuit diagram of the resistance distribution of the "wellbore metal casing-strata" composite medium network in the microcurrent-based downhole information transmission method according to an exemplary embodiment of the present invention.

Reference number:

1-surface, 2-wellhead, 3-wellbore, 4-center metal pipe, 5-metal pipe short joint, 51-upper metal pipe, 52-lower metal pipe, 6-casing, 7-upper signal conduction tool, 8- Down signal conduction tool, 9- Alternating current driver, 91- Driver housing, 92- Driver circuit board, 93- Coil, 94- Driver center tube, 95- Sensor, 10- Downhole alternating current micro-current source, 11 -Ground signal receiver, 111-ground point, 112-signal demodulation module, 113-first signal line, 114-second signal line, 12-repeater, R1~R15-equivalent resistance, I-downhole crossover The oscillating current output by the variable micro current source to the outside.

Detailed ways

Hereinafter, the microcurrent-based downhole information transmission device and the microcurrent-based downhole information transmission method of the present invention will be described in detail with reference to the exemplary embodiments.

It should be noted that "upper", "lower", "inner" and "outer" are only for the convenience of description and constitute a relative orientation or positional relationship, and do not indicate or imply that the referred component must have the specific orientation or position.

Fig. 1 shows a schematic structural diagram of a micro-current-based downhole information transmission device according to an exemplary embodiment of the present invention; Fig. 2 shows a structural schematic diagram of an exemplary embodiment of the alternating current driver in Fig. 1; Fig. 3 shows The equivalent circuit diagram of the resistance distribution of the "wellbore metal casing-formation" composite medium network in the microcurrent-based downhole information transmission method according to an exemplary embodiment of the present invention is presented.

In the first exemplary implementation example of the present invention, as shown in FIG. 1 , the downhole information transmission device based on micro-current is equipped with metal casing for the whole wellbore of oil testing, completion and oil and gas production stages, and traditional electromagnetic wave signal transmission is used. , the electromagnetic wave signal transmitter has a shielding effect in the metal casing, the electromagnetic wave cannot be emitted, and the signal transmission of the oil and gas wells that cannot use MWD for signal transmission because the circulation cannot be established. The microcurrent-based downhole information transmission device mainly includes a central metal pipe 4 , a downhole alternating microcurrent source 10 , a sensor and a ground signal receiver 11 .

Wherein, the central metal pipe 4 is arranged in the wellbore 3 along the axial direction, and the entire wellbore 3 is wrapped by the metal casing 6 .

The downhole alternating microcurrent source 10 (that is, the downhole signal emission source) is fixedly arranged on the central metal pipe 4, and the downhole alternating microcurrent output by the downhole alternating microcurrent source 10 can be used to carry downhole signal data and carry downhole signal data. The downhole alternating microcurrent is then transmitted to the surface through a signal conduction path (ie, casing 6 ).

The sensor is fixed on the central metal pipe 4 or the downhole alternating micro-current source 10. The sensor and the down-hole alternating micro-current source 10 are connected by wires to transmit the measured down-hole signal data to the down-hole alternating micro-current source for signal loading.

The ground signal receiver 11 is disposed on the ground 1 and connected to the wellhead 2. The ground signal receiver can receive the downhole signal data transmitted by the downhole alternating microcurrent source 10 and demodulate and extract the downhole signal data.

In this exemplary embodiment, as shown in FIG. 1 , the downhole alternating current microcurrent source 10 may include an alternating current driver 9 , a signal conducting tool and a metal tube short section 5 , which constitute an oscillating current loop.

Wherein, the metal pipe short joint 5 includes an upper metal pipe 51 and a lower metal pipe 52 which are fixedly arranged up and down. The metal pipe sub-section transmits the downhole alternating microcurrent signal generated by the alternating current driver to the signal conducting tool. The signal conduction tool then transmits the downhole alternating microcurrent signal to the casing. By loading the downhole signal data to the downhole alternating microcurrent signal generated by the alternating current driver, the downhole signal data will flow into the upper and lower casings and the formation along with the alternating microcurrent signal through the metal short pipe and the signal conduction tool. The conductivity of the casing is better than that of the formation. The current mainly goes up from the casing, and a small part flows into the formation. With the appropriate power supply, the downhole alternating microcurrent can flow to the ground, so that the loaded signal data is also transmitted to the ground.

In the present exemplary embodiment, as shown in FIG. 1 , the signal conducting tool may include an upper signal conducting tool 7 and a lower signal conducting tool 8 . The upper signal conducting tool 7 is disposed on the upper end of the upper metal pipe 51 and is in contact with the sleeve 6 , and the lower signal conducting tool 8 is disposed on the lower end of the lower metal pipe 52 and is in contact with the sleeve 6 . Here, both the upper signal conducting tool and the lower signal conducting tool are in contact with the sleeve in the form of spring sheets.

In this exemplary embodiment, as shown in FIG. 2 , the alternating current driver 9 may include a driver circuit board 92 , a coil 93 , a driver housing 91 and a driver center tube 94 .

The upper and lower ends of the driver central tube 94 are respectively fixedly connected to the upper central metal tube and the lower central metal tube, a sealed cavity is formed between the driver housing 91 and the driver central tube 94, and the coil 93 and the driving circuit board 92 are fixed Disposed in the sealed cavity, the coil 93 and the driving circuit board 92 are connected by wires. Of course, the center tube of the driver can also use the center metal tube itself. Here, the alternating current driver adopts the coil coupling driving method. The signal oscillating current generated by the alternating current driver is connected to the coil, and the coil is installed on the center tube of the driver. The signal oscillating current induces the coil to induce a changing magnetic field, and the changing magnetic field drives the driver. The central tube generates an oscillating electromotive force, which is used to drive the vibrating current loop of the downhole alternating micro-current source. In particular, the alternating current driver housing and the driver center tube need to be insulated, such as applying insulating varnish on the button. As shown in FIG. 2 , the sensor 95 is fixedly arranged under the driver housing 91 and is connected to the driving circuit board 92 through wires.

In this exemplary embodiment, as shown in FIG. 1 , the downhole information transmission device may further include a repeater 12 , and the repeater 12 is fixedly arranged on the central metal pipe 4 (here, the central metal pipe may be The tubing (and possibly other wellbore tubing) is positioned above the downhole alternating microcurrent source 10 . The repeater 12 can and can receive the microcurrent signal sent by the downhole alternating microcurrent source 10 and transmit it to the surface signal receiver 11 . By setting more than one repeater, the transmission distance of the downhole alternating microcurrent generated by the downhole alternating microcurrent source can be greatly increased.

In this exemplary embodiment, the repeater may include a driving circuit board, a signal receiving circuit board, a coil, a repeater housing, and a repeater center tube.

1 and 2, the structure of the repeater is similar to the downhole alternating micro-current source 10, the difference is that a signal receiving circuit board is added to the repeater, one end of the signal receiving circuit board is connected to the coil, and the other end is connected to the coil. connected to the driver circuit board. When the coil in the repeater transmits the alternating microcurrent signal in the underground well, it will generate an induced current in it. The induced current signal is transmitted to the signal receiving circuit board, and the signal receiving circuit board transmits the received induced current signal to the driver. The circuit board, which drives the circuit board to perform the corresponding signal tasks.

In this exemplary embodiment, the downhole signal data may include at least one of temperature, pressure, flow rate, containment rate, and salinity. In this exemplary embodiment, as shown in FIG. 1 , the ground signal receiver 11 may include a first signal line 113 , a second signal line 114 , a data acquisition card, and a signal demodulation module 112 .

Among them, one end of the two signal lines is respectively connected to the signal acquisition point, and the other end is connected to the data acquisition card respectively, and the data acquisition card collects the voltage signal and transmits it to the signal demodulation module. The signal demodulation module can be signal demodulation software, and the signal demodulation software can perform signal inverse decoding according to the coding mode adopted by the downhole signal data to obtain the downhole data value. The two signal lines are respectively connected to the signal acquisition point, and the other end is connected to the data acquisition card, and the data acquisition card collects the voltage signal and transmits it to the signal demodulation software. In particular, one signal line can be connected to the derrick of the wellhead 2, and the other signal line can be connected to the ground point 111 of the apogee, and then the other ends of the two signal lines can be connected to the signal demodulation module to finally form a ground Signal reception and demodulation unit. Here, the signal acquisition point can be any two points on the metal tube, or between the metal tube and the earth, or between the earth and the earth. In particular, the signal acquisition on the ground mainly adopts the ground metal pipe between the ground outcrop and the ground.

In the second exemplary embodiment of the present invention, the downhole information transmission method based on microcurrent can be implemented by the microcurrent-based downhole information transmission device described in the first exemplary embodiment, and the method includes the steps of:

Run the tubing installed with the downhole alternating microcurrent source and sensor into the predetermined position downhole;

Using the downhole alternating microcurrent generated by the downhole alternating microcurrent source as a signal source, the sensor measures the downhole signal data and loads the signal onto the downhole alternating microcurrent;

Using the wellbore metal casing and the formation as the composite medium for downhole alternating microcurrent conduction, select any two points in the "wellbore metal casing-strata" composite medium network as the signal acquisition point, and use the ground signal receiver to measure the distance between these two points. The voltage value is obtained, the voltage fluctuation law is obtained, and then the downhole signal data is extracted by demodulation according to the signal coding method.

In this exemplary embodiment, the signal loading refers to encoding the downhole signal data on the downhole alternating microcurrent, so that the fluctuation mode of the downhole alternating microcurrent can represent the downhole signal data value.

In this embodiment, the method may further include the step of estimating downhole transmit power and ground signal reception strength:

By analyzing the resistance distribution of the "wellbore metal casing-stratum" composite medium network, and using Ampere's theorem to calculate the voltage between each position point, the downhole transmission power and the ground signal reception strength are determined. Specifically, the resistances of the microcurrent-based downhole information transmission devices were analyzed first, and the circuit diagrams of the “wellbore metal casing-strata” composite medium network were equivalent to those shown in Figure 3. Ampere’s theorem was used to calculate the The voltage of the resistors (that is, R1-R15) is used to determine the transmit power of the downhole alternating microcurrent source and the signal strength received by the ground receiver. Among them, I represents the oscillating current output by the downhole alternating micro-current source to the outside.

In this embodiment, in order to avoid electromagnetic interference of electrical equipment such as generators at the well site, it is recommended to use a metal shielding fence to set isolation in front of the large electrical equipment.

In order to better understand the above-mentioned exemplary embodiments of the present invention, they are further described below with reference to specific examples.

Taking Well GS19 as an example, this well is located somewhere in Anyue County, Sichuan Province. Due to the complex downhole conditions of this well, conventional operation methods cannot accurately grasp the downhole conditions of this well’s oil testing, and accidents are prone to occur. The micro-current-based downhole information transmission device of the present invention is used for downhole monitoring to provide support for engineers. Among them, the launch depth of the transmitter: 4512m, and the design depth of the repeater: 2995m. Test date: 20XX.3.28～4.17.

Experimental results: The device worked for 456 hours, acquired 2281 sets of temperature and pressure data at a depth of 4512m in real time, and the average signal strength received from the ground downhole was 2.5×10 ^-5 V. During this period, the wellhead and surface process pipelines were blocked due to formation spray cuttings and previously lost drilling fluid. If the existing information acquisition methods are used, the wellhead cannot infer the bottom hole situation. However, using the micro-current-based downhole information transmission device of the present invention realizes running downhole and continuously monitors and displays the bottomhole pressure in real time, which plays an early warning role in preventing well control accidents and ensures operation safety. At the same time, after the downhole information transmission device is pulled out later, the data stored in the downhole pressure gauge is compared with the data received on the ground, and the two data are consistent, indicating the reliability of the monitoring device and method.

To sum up, the beneficial effects of the present invention may include at least one of the following:

(1) The present invention provides a micro-current-based downhole information transmission device, which provides a feasible method for downhole signal transmission in the stage of oil testing and completion and oil and gas production (the entire wellbore is installed with metal casing), communicating the downhole and Information channels on the ground to facilitate digital transformation;

(2) The micro-current-based downhole information transmission method of the present invention avoids the traditional downhole signal transmission relying on electromagnetic waves (the electromagnetic wave emitted by the electromagnetic wave antenna needs to be radiated to the formation, and then transmitted from the formation to the ground). When the electromagnetic wave transmitting antenna is in the metal casing , the underground metal casing has a shielding effect on the electromagnetic wave signal, and the signal transmission distance is short or even cannot be transmitted; instead, the present invention uses the micro-current signal transmission method, and the micro-current transmitter just uses the conductivity of the metal casing to transmit the signal from the metal. The casing is passed out, on the one hand, it mainly flows from the metal casing to the ground, and on the other hand, a small part flows from the formation to the ground;

(3) The present invention takes into account the transmission rate, adapts to more wellbore operating environments, and has the advantages of simple operation and low cost.

Although the present invention has been described above in connection with the exemplary embodiments, it will be apparent to those skilled in the art that various modifications and variations can be made in the exemplary embodiments of the present invention without departing from the spirit and scope defined by the appended claims. Change.

Claims (11)

1. A micro-current based underground information transmission device is characterized by comprising a central metal pipe, an underground alternating micro-current source, a sensor and a ground signal receiver, wherein the underground information transmission device is provided with a metal sleeve aiming at a shaft in the oil testing completion and oil gas production stages, and electromagnetic wave transmission exists in the signal transmission of an oil gas well with shielding effect,

the central metal tube is axially arranged in the shaft;

the underground alternating micro-current source is fixedly arranged on the central metal pipe, and underground alternating micro-current output by the underground alternating micro-current source can carry underground signal data;

the sensor is connected with the underground alternating micro-current source and can measure underground signal data and transmit the underground signal data to the underground alternating micro-current source for signal loading;

the ground signal receiver is connected with a wellhead and can receive underground signal data transmitted by the underground alternating micro-current source and demodulate and extract the underground signal data.

2. The micro-current based downhole information transfer device of claim 1, wherein the downhole alternating micro-current source comprises an alternating current driver, a signal conducting tool and a metal tubing sub, wherein,

the metal pipe short section comprises an upper metal pipe and a lower metal pipe which are fixedly arranged from top to bottom, and the metal pipe short section transmits underground alternating micro-current signals generated by the alternating current driver to the signal conduction tool;

the signal conducting tool transmits a downhole alternating micro-current signal to the casing.

3. The micro-current based downhole information transmission device according to claim 2, wherein the signal conducting tool comprises an upper signal conducting tool disposed at an upper end of the upper metal pipe and contacting the casing and a lower signal conducting tool disposed at a lower end of the lower metal pipe and contacting the casing.

4. The micro-current based downhole information transfer device of claim 1, wherein the alternating current driver comprises a driver circuit board, a coil, a driver housing, and a driver center tube, wherein,

the two ends of the driver central tube are respectively fixedly connected with the central metal tube, the driver shell and the driver central tube form a sealed cavity, and the coil and the driving circuit board are fixedly arranged in the sealed cavity.

5. The downhole information transmission device based on micro-current according to claim 1, further comprising a repeater fixedly arranged on the central metal pipe and above the downhole alternating micro-current source, wherein the repeater is capable of receiving and transmitting micro-current signals sent by the downhole alternating micro-current source to a surface signal receiver.

6. The micro-current based downhole information transfer device of claim 5, wherein the repeater comprises a driving circuit board, a signal receiving circuit board, a coil, a repeater housing, and a repeater center tube, wherein,

two ends of the repeater central tube are fixedly connected with the central metal tube respectively, a repeater shell and the repeater central tube form a sealed cavity, and the signal receiving circuit board, the coil and the driving circuit board are fixedly arranged in the sealed cavity.

7. The micro-current based downhole information transfer device of claim 1, wherein the downhole signal data comprises at least one of temperature, pressure, flow rate, water cut, and mineralization.

8. The micro-current based downhole information transmission device according to claim 1, wherein the surface signal receiver comprises two signal lines, a data acquisition card and a signal demodulation module, wherein the two signal lines are respectively connected with the signal acquisition point, the other end of the two signal lines is connected to the data acquisition card, and the data acquisition card acquires voltage signals and transmits the voltage signals to the signal demodulation module.

9. A micro-current based downhole information transmission method, characterized in that the method is realized by the micro-current based downhole information transmission device according to any one of claims 1-8, and the method comprises the steps of:

an oil pipe provided with an underground alternating micro-current source and a sensor is put into an underground preset position;

the method comprises the following steps of (1) utilizing an underground alternating micro-current generated by an underground alternating micro-current source as a signal source, and loading signals of underground signal data measured by a sensor onto the underground alternating micro-current;

the method comprises the steps of utilizing a shaft metal sleeve and a stratum as composite media for conducting underground alternating micro-current, selecting any two points in a shaft metal sleeve-stratum composite media network as signal acquisition points, utilizing a ground signal receiver to measure voltage values between the two points to acquire a voltage fluctuation rule, and demodulating and extracting underground signal data according to a signal coding mode.

10. The method of claim 9, wherein the signal loading is encoding the downhole signal data on downhole alternating micro-current such that the fluctuation pattern of the downhole alternating micro-current is representative of the downhole signal data value.

11. The method of claim 9, further comprising the step of downhole estimating downhole transmit power and surface signal received strength:

by analyzing the resistance distribution of the composite medium network of the metal casing pipe of the shaft and the stratum, the voltage between each position point is calculated by utilizing the ampere theorem, so that the underground transmitting power and the ground signal receiving intensity are determined.

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