Method for measuring the resistivity of the homogeneity of a hydrate

Abstract

The application discloses a kind of hydrate uniformity resistivity measurement methods, including probe rod, probe rod array and measurement system, the probe rod includes probe rod outside and probe rod inside, the probe rod array is designed into resistivity horizontal array measurement unit with angle ring electrode angle corresponding equal division in a horizontal direction, the measurement system includes constant current source unit, data acquisition unit, wire gating unit, inclination monitoring unit.The application adopts a kind of hydrate uniformity resistivity measurement methods, multiple angle ring electrode probe rod cooperation can improve measurement accuracy, probe rod array and angle ring electrode resistivity probe rod cooperate, it is convenient for hydrate saturation calculation, constructs wire gating unit, it is convenient for control measurement unit, realizes the selection between power supply electrode and measurement electrode of electrode.

Description

Technical Field

[0001] This invention relates to the field of in-situ measurement technology of seabed natural gas hydrates, and in particular to a method for measuring the resistivity of hydrate uniformity. Background Technology

[0002] Natural gas hydrates are a clean and efficient energy source, and their importance and attention are constantly increasing worldwide. To better understand the occurrence and distribution of natural gas hydrates and lay the foundation for their rational development, resistivity, with its highly sensitive electrical response, is widely used in the study of natural gas hydrate-bearing reservoirs. Gas bubbles and natural gas hydrates cause an abnormal increase in sediment resistivity. By arranging resistivity probes in a specific pattern in the area to be monitored, the resistivity values ​​in the horizontal or vertical directions at a certain depth are measured, thus obtaining a three-dimensional resistivity distribution map of the measurement area. The distribution of hydrates and bubbles can then be determined by identifying resistivity anomalies.

[0003] Current resistivity measurement devices and methods cannot accurately measure the inhomogeneity of hydrate formation and decomposition processes in seabed sediments, leading to significant errors in hydrate saturation estimation and hindering the development and utilization of hydrate resources. A comparative analysis of patents related to resistivity measurement probes and detection methods is as follows:

[0004] Invention patent CN202011258781.6 discloses a spiral electrode resistivity probe and its monitoring method. This invention comprises a probe body consisting of a conical probe tip, several spiral electrode modules, a probe tail end, an electrode reset device, and a penetration device. The invention uses an electrode reset device to allow the probe to switch between penetration and measurement modes. When the probe reaches the measurement position, the spiral electrode transforms into a ring electrode, enabling the measurement of resistivity in the vertical direction. The device has a simple structure and ingenious design. However, its primary application is in soil resistivity measurement. The penetration method involves the spiral electrode rotating and penetrating the soil. Furthermore, when switching from penetration to measurement mode, the spiral electrode on the outer surface of the probe transforms into a ring electrode. This series of processes causes significant agitation of the soil near the outer surface of the probe, resulting in considerable damage to the in-situ measurement environment, making it unsuitable for use in seabed environments.

[0005] Invention patent CN202210186613.3 discloses a method for in-situ measurement of the vertical distribution range of shallow gas bubbles in seabed sediments. The invention provides a method for in-situ measurement of the vertical distribution range of shallow gas bubbles in seabed sediments. The device consists of a top chamber, a probe rod, a probe body, an electrode sequence, a counterweight, wires, a battery compartment, and a hook. The electrode sequence is a ring-shaped array of electrodes arranged vertically on the outer surface of the probe rod. This invention utilizes the highly sensitive electrical response of resistivity, using the ring-shaped electrode array to measure the resistivity of sediments and the increase in sediment resistivity due to shallow gas bubbles. It analyzes whether the measured resistivity and resistivity change ratio are abnormal, thereby achieving in-situ and rapid measurement of shallow gas bubbles in seabed sediments. While this device can detect the presence of vertical bubbles, because it uses ring electrodes, anomalies in resistivity values ​​can only indicate the presence of surrounding bubbles or hydrates, and cannot accurately determine the uneven distribution of hydrates, resulting in low resolution.

[0006] Invention patent CN202210185900.2 discloses a method for in-situ measurement of the gas content of bubble-type shallow seabed gas based on a point-electrode probe. The device comprises a top chamber, a probe rod, a probe body, an electrode sequence, a counterweight, wires, a battery compartment, and a hook; the electrode sequence is a horizontally arranged array of point electrodes on the outer surface of the probe rod. However, point electrodes have poor monitoring capabilities for the spatial diffusion of permeable gas, making it difficult to monitor changes in gas diffusion channels during hydrate formation and decomposition. Summary of the Invention

[0007] The purpose of this invention is to provide a method for measuring the resistivity of hydrate uniformity. The use of multiple corner ring electrode probes can improve measurement accuracy. The use of probe arrays and corner ring electrode resistivity probes facilitates the calculation of hydrate saturation. A wire selection unit is constructed to facilitate the control of the measurement unit and realize the selection of electrodes between power supply electrodes and measurement electrodes.

[0008] To achieve the above objectives, the present invention provides a method for measuring the resistivity of hydrate uniformity, comprising a probe, a probe array, and a measurement system. The probe includes an outer probe and an inner probe. The probe array is designed in a horizontal direction as a resistivity horizontal array measurement unit that is equally divided with respect to the angle of the corner ring electrode. The measurement system includes a constant current source unit, a data acquisition unit, a wire selection unit, and a tilt angle monitoring unit.

[0009] Preferably, the probe rod exterior includes a cone tip probe, a corner ring electrode, a probe rod body, an outer cabin, and a first cable. The cone tip probe and the probe rod body are connected sequentially from bottom to top on the probe rod exterior. The corner ring electrode, the outer cabin, and the first cable are located on a straight line along the vertical direction of the probe rod.

[0010] Preferably, the probe rod includes a multi-way switch and internal wires, the probe rod array includes several probe rods, a second cable, and a probe rod bracket. The number of wires inside the probe rod, from bottom to top, is equal to the number of the corner ring electrodes. The multi-way switch is connected to the electronic compartment.

[0011] Preferably, the probe array consists of, from bottom to top, the probe, the probe bracket, and the second cable.

[0012] Preferably, multiple corner ring electrodes of equal shape and size can be arranged at the same horizontal position on the probe rod, and the separation angle of two adjacent corner ring electrodes is the same.

[0013] Preferably, four adjacent corner ring electrodes in the same vertical position along the vertical direction of the probe rod can be measured once, with the two middle electrodes being the measuring electrodes and the two side electrodes being the power supply electrodes. The number of measurements that can be taken at the same horizontal position of the probe rod depends on the number of corner ring electrodes in the horizontal position when the probe rod is designed.

[0014] Preferably, the method includes the following steps: The probe has n corner ring electrodes (3, 4, or 6) at a horizontal position, and the electrode curvature and the separation angle between two adjacent electrodes are set as α and β, respectively. Then:

[0015]

[0016] The theoretical formula for measuring the resistivity of a corner ring electrode is derived as follows: Assume an infinitely long cylinder of radius b with resistivity ρ is embedded within a homogeneous and isotropic conductive medium. A corner ring electrode, as described above, is mounted on the cylinder, and its thickness is negligible. One electrode, C1, is used as the power supply electrode and connected to a constant current source. The other power supply electrode, C2, is located at infinity. The constant current source forms an equipotential surface with the insulating probe as its boundary. The current density at a point ρ(r,z) on this equipotential surface is:

[0017]

[0018] In the formula, V is the voltage at point P;

[0019] Combining equations (1) and (2), we get:

[0020]

[0021] Based on the arrangement of the electrodes on the probe, electrodes C1 and C2 on both sides are the power supply electrodes, and the two middle electrodes P1 and P2 are used to measure the potential difference. All electrodes are arranged at equal intervals, with a spacing of 'a'.

[0022] make Then we have:

[0023]

[0024] The device coefficient is used in the theoretical calculation formula for the resistivity of a angular ring electrode with an electrode curvature of α.

[0025] Before using the probe to measure resistivity, the device coefficients should be calibrated. The resistivity measured by a high-precision conductivity meter should be used as the standard resistivity. The standard resistivity and the resistivity measured by the probe... The ratio of is the corrected device coefficient.

[0026] Preferably, the feature is that: a single probe has n electrodes at a certain horizontal position, and when n=3, four corner ring resistivity units are used to form an equilateral triangle and a horizontal array measurement unit at the center point.

[0027] Preferably, the measurement system includes a constant current source unit, a data acquisition unit, a conductor selection unit, and an inclination monitoring unit.

[0028] Therefore, the present invention employs a resistivity measurement method for hydrate uniformity using the above-described structure. The use of multiple corner ring electrode probes in combination can improve measurement accuracy. The probe array, in combination with the corner ring electrode resistivity probes, facilitates the calculation of hydrate saturation. A wire selection unit is constructed to facilitate the control of the measurement unit and realize the selection of the electrode between the power supply electrode and the measurement electrode.

[0029] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0030] Figure 1 A cross-sectional view of the probe in an embodiment of the resistivity measurement method for hydrate uniformity according to the present invention;

[0031] Figure 2 This is a schematic diagram of the electrode measurement principle of a method for measuring the resistivity of hydrate uniformity according to the present invention.

[0032] Figure 3 The resistivity of a hydrate uniformity measurement method according to the present invention is shown in the probe array diagrams for n=3 and n=4.

[0033] Figure 4 The resistivity measurement method for hydrate uniformity according to the present invention is shown in the equipotential surface diagram of the corner ring electrode.

[0034] Figure 5 This is a system control structure diagram of a method for measuring the resistivity of hydrate uniformity according to the present invention;

[0035] Figure 6 This invention relates to a method for measuring the resistivity of hydrate uniformity using an angled ring electrode probe structure.

[0036] Figure 7 This is a cross-sectional schematic diagram of the angle ring electrode probe used in the resistivity measurement method for hydrate uniformity according to the present invention.

[0037] Figure 8 This is a schematic diagram of the probe array structure for a method of measuring the resistivity of hydrate uniformity according to the present invention.

[0038] Figure 9 This invention provides a method for measuring the resistivity of hydrate homogeneity. Figure 6 Schematic diagram of the central corner ring electrode sequence structure;

[0039] Figure 10 This is a flowchart illustrating the process of measuring the resistivity of a hydrate uniformity method according to the present invention. Detailed Implementation

[0040] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0041] Example 1

[0042] like Figure 1-10 As shown, a method for measuring the resistivity of hydrate uniformity includes a probe, a probe array, and a measurement system. The probe includes an outer probe and an inner probe. The probe array is designed in a horizontal direction as a resistivity horizontal array measurement unit that is equally divided with respect to the angle of the corner ring electrode. The measurement system includes a constant current source unit, a data acquisition unit, a wire selection unit, and a tilt angle monitoring unit.

[0043] The probe rod exterior includes a cone tip probe, a corner ring electrode, a probe rod body, an outer compartment, and a first cable. The cone tip probe and the probe rod body are connected sequentially from bottom to top on the probe rod exterior. The corner ring electrode, the outer compartment, and the first cable are located on a straight line along the vertical direction of the probe rod.

[0044] The probe rod contains a multi-way switch, internal wires, and the probe rod array includes several probe rods, a second cable, and a probe rod support. The number of wires inside the probe rod, arranged from bottom to top, is equal to the number of corner ring electrodes. It also includes a multi-way switch and an electronic compartment.

[0045] The probe array consists of, from bottom to top, the probe, the probe support, and the second cable.

[0046] Multiple corner ring electrodes of equal shape and size can be arranged at the same horizontal position on the probe rod, with the same separation angle between two adjacent corner ring electrodes.

[0047] Four adjacent corner ring electrodes in the same vertical position along the probe rod can be used for one measurement. The two middle electrodes are the measuring electrodes, and the two side electrodes are the power supply electrodes. The number of measurements that can be taken at the same horizontal position of the probe rod depends on the number of horizontal corner ring electrodes designed for the probe rod.

[0048] The steps include: Given n angle ring electrodes (3, 4, or 6) at a horizontal position on the probe rod, with the electrode curvature and the separation angle between two adjacent electrodes set as α and β respectively, then:

[0049]

[0050] The theoretical formula for measuring the resistivity of a corner ring electrode is derived as follows: Assume an infinitely long cylinder of radius b with resistivity ρ is embedded within a homogeneous and isotropic conductive medium. A corner ring electrode, as described above, is mounted on the cylinder, and its thickness is negligible. One electrode, C1, is used as the power supply electrode and connected to a constant current source. The other power supply electrode, C2, is located at infinity. The constant current source forms an equipotential surface with the insulating probe as its boundary. The current density at a point ρ(r,z) on this equipotential surface is:

[0051]

[0052] In the formula, V is the voltage at point P;

[0053] Combining equations (1) and (2), we get:

[0054]

[0055]

[0056] Based on the arrangement of the electrodes on the probe, electrodes C1 and C2 on both sides are power supply electrodes, and the two middle electrodes P1 and P2 are used to measure the potential difference. All electrodes are arranged at equal intervals of 'a', then:

[0057] make Then we have:

[0058]

[0059] The device coefficient is used in the theoretical calculation formula for the resistivity of a angular ring electrode with an electrode curvature of α.

[0060] Before using the probe to measure resistivity, the device coefficients should be calibrated. The resistivity measured by a high-precision conductivity meter should be used as the standard resistivity. The standard resistivity and the resistivity measured by the probe... The ratio of is the corrected device coefficient.

[0061] A single probe has n electrodes (3, 4, or 6) at a certain horizontal position. For n=3, four corner ring resistivity units are used, forming a horizontal array measurement unit with an equilateral triangle and a center point. That is, the four corner ring resistivity probes are inserted into the sediment for measurement according to the arrangement of the three points and the center point of the equilateral triangle. For n=4, five corner ring resistivity units are used, forming a horizontal array measurement unit with a square and a center point. That is, the five corner ring resistivity probes are inserted into the sediment for measurement according to the arrangement of the four points and the center point of the square. The corner ring electrodes at the horizontal position of the center probe are respectively aligned with one electrode of the probe at the point of the regular polygon. By comparing the resistivity values ​​measured by the center probe and the probe at that point with the general resistivity value of the sediment in the measurement area, if the resistivity values ​​are approximately equal, the sediment distribution between the two aligned electrodes can be considered uniform. If the resistivity values ​​differ too much, the two aligned electrodes can be considered... The deposits between the electrodes are unevenly distributed, with hydrates distributed on the side with higher resistivity. This allows for the determination of whether the hydrate distribution is uniform in a horizontal direction. For cases where the horizontal measurement area is large, an appropriate value of n can be selected, and multiple horizontal array measurement units can be combined to expand the horizontal measurement area. Along the vertical direction of the probe rod, each probe rod in this array consists of at least two sets of corner ring resistivity units (eight corner ring electrodes on a straight line along the vertical direction of the probe rod) to measure the non-uniformity of hydrates in the vertical direction. For cases where the vertical measurement depth is large, the number of corner ring resistivity measurement units can be increased. The resolution of this measurement method is determined by the following parameters: the number of corner rings in the horizontal position of the corner ring resistivity unit (3, 4, or 6), the distance between the two electrodes of the corner ring resistivity unit, and the side length of one resistivity horizontal array measurement unit (equilateral triangle, square, or regular hexagon).

[0062] The measurement system comprises a constant current source unit, a data acquisition unit, a conductor selection unit, and an inclination monitoring unit. The constant current source unit uses a voltage-controlled constant current source. During operation, the control circuit samples the load current in real time and uses an algorithm to maintain a constant current based on the set current value. The inclination monitoring unit uses an inclination sensor to detect and correct the tilt angle of the probe as it sinks and penetrates seabed sediment. The conductor selection unit consists of an internal control chip and multiple parallel multiplexers. All conductors connected to the electrodes are connected to the electronic compartment and the multiplexers. By controlling the on / off state of the multiplexers, the measurement unit is selected. The conductor selection unit reduces the number of conductors to two power lines and two signal lines. These four conductors are connected to the mother ship on the sea surface via cables from the outer compartment. The data acquisition unit filters, amplifies, and converts the received signals into digital quantities, performs calculations, and stores the data on an SD card.

[0063] (1) First, use conventional geological exploration methods to determine whether there are hydrates and gases in the sediments of the area to be tested;

[0064] (2) Vertically insert the angled ring electrode probe array into the sediment containing hydrates and gas;

[0065] (3) To begin measurement, first measure probe A. The main control circuit first controls the constant current source unit to generate a precise and constant current source. After the current source stabilizes, data acquisition begins. The conductor selection unit first controls the four electrodes vertically distributed at the top of the probe, such as... Figure 9 As shown, C11, C12, P11, P12, C21, C22, P21, P22, and C31, C32, P31, P32 constitute three measurement points. First, measurement point 1 (electrodes C11, C12, P11, P12) is connected. After its measurement is completed, the electrode is disconnected and measurement point 2 is connected. After measurement 3 is completed, the electrode is disconnected and measurement point 3 is connected. At this point, resistivity values ​​in three different directions at a horizontal position are obtained. Then, the working electrode is moved down one position sequentially, and the original P11, P12, C12 electrodes become C11, P11, P12. The measurement steps above are repeated. A single probe can measure a total of 15 resistivity values ​​at different depths along three different directions at a horizontal position. This process is repeated for probes B, C, and D, completing one resistivity value acquisition.

[0066] (4) Repeat step (3) at intervals and store the collected data in the SD card;

[0067] (5) Analyze the collected data and draw three-dimensional resistivity distribution maps for different time periods. By comparison, construct distribution maps of the formation and decomposition process of space hydrates, and analyze the changes in the leakage and diffusion channels of decomposition gas.

[0068] It should be noted that this embodiment only illustrates one application of the corner ring electrode resistivity probe. The probe radius b, the vertical distance a between the two electrodes, the corner ring electrode arc α, the separation angle β, the number of horizontal electrodes n on a single probe, and the number of corner ring resistivity measurement units can all be changed according to actual measurement needs. The device coefficient of the corresponding resistivity theoretical calculation formula will also change with α. The probe array composed of multiple probes is a regular n-gon. When the horizontal measurement area of ​​the sediment to be measured is large, by analyzing the different shapes of probe arrays and the horizontal orientation of each probe electrode on the array, it can be seen that using probe arrays with n=4 and n=6 to combine multiple arrays is the most suitable. That is, the probe on the side of one probe array of this shape can be directly used as a side probe of another probe array at the same time.

[0069] Therefore, the present invention employs a resistivity measurement method for hydrate uniformity using the above-described structure. The use of multiple corner ring electrode probes in combination can improve measurement accuracy. The probe array, in combination with the corner ring electrode resistivity probes, facilitates the calculation of hydrate saturation. A wire selection unit is constructed to facilitate the control of the measurement unit and realize the selection of the electrode between the power supply electrode and the measurement electrode.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for measuring the resistivity of hydrate homogeneity, characterized in that: The device includes a probe rod, a probe rod array, and a measurement system. The probe rod includes an outer probe rod and an inner probe rod. The probe rod array is designed as a resistivity horizontal array measurement unit that is equally divided in one horizontal direction corresponding to the angle of the corner ring electrode. The measurement system includes a constant current source unit, a data acquisition unit, a conductor gating unit, and an tilt angle monitoring unit. Multiple corner ring electrodes of equal shape and size are arranged at the same horizontal position on the probe rod, and the separation angle of two adjacent corner ring electrodes is the same. A measurement is performed on four adjacent corner ring electrodes at the same vertical position along the vertical direction of the probe rod. The two middle electrodes are measuring electrodes, and the two side electrodes are power supply electrodes. The number of measurements performed at the same horizontal position of the probe rod depends on the number of corner ring electrodes at the horizontal position when the probe rod is designed. The steps include: The probe has n angle ring electrodes in a horizontal position, where n is 3, 4, or 6. The electrode curvature and the separation angle between two adjacent electrodes are set as α and β, respectively. Then: （1） The theoretical formula for measuring resistivity of a corner ring electrode is derived as follows: Assume an infinitely long cylinder of radius b with resistivity ρ is embedded within a homogeneous and isotropic conductive medium. A corner ring electrode, as described above, is mounted on the cylinder, and its thickness is negligible. One electrode, C1, is used as the power supply electrode connected to a constant current source. The other power supply electrode, C2, is located at infinity. The constant current source forms an equipotential surface with the insulating probe as its boundary. A point on this equipotential surface... The current density is: （2） In the formula, V is the voltage at point P; Combining equations (1) and (2), we get: ； ； （3） Based on the arrangement of the electrodes on the probe, electrodes C1 and C2 on both sides are the power supply electrodes, and the two middle electrodes P1 and P2 are used to measure the potential difference. All electrodes are arranged at equal intervals, with a spacing of 'a'. make Then we have: （4） The device coefficient is used in the theoretical calculation formula for the resistivity of a angular ring electrode with an electrode curvature of α. Before using the probe to measure resistivity, the device coefficients should be calibrated. The resistivity measured by a high-precision conductivity meter should be used as the standard resistivity. The standard resistivity and the resistivity measured by the probe... The ratio is the corrected device coefficient; A single probe has n electrodes at a certain horizontal position. When n=3, four corner ring resistivity units are used to form a horizontal array measurement unit consisting of an equilateral triangle and a center point; that is, four corner ring resistivity probes are inserted into the sediment for measurement according to the arrangement of three points of an equilateral triangle and the center point. When n=4, five corner ring resistivity units are used to form a horizontal array measurement unit consisting of a square and a center point; that is, five corner ring resistivity probes are inserted into the sediment for measurement according to the arrangement of four points of a square and the center point.

2. The method for measuring the resistivity of hydrate uniformity according to claim 1, characterized in that: The probe rod is connected in sequence from bottom to top to the cone-shaped probe and the probe rod body. Along a straight line in the vertical direction of the probe rod are the corner ring electrode, the outer cabin and the first cable.

3. The method for measuring the resistivity of hydrate uniformity according to claim 1, characterized in that: The probe rod includes a multi-way switch and internal wires. The probe rod array includes several probe rods, a second cable, and a probe rod support. The number of wires, the multi-way switch, and the electronic compartment are arranged from bottom to top inside the probe rod, equal to the number of the corner ring electrodes.

4. The method for measuring the resistivity of hydrate uniformity according to claim 3, characterized in that: The probe array, from bottom to top, includes the probe, the probe bracket, and the second cable.

5. The method for measuring the resistivity of hydrate uniformity according to claim 1, characterized in that: The measurement system includes a constant current source unit, a data acquisition unit, a conductor selection unit, and an inclination monitoring unit.

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