An array laterolog tool and its measurement method

Abstract

The present invention provides an array laterolog tool and a measurement method thereof. The method includes: independently applying a driving signal source to each driving circuit, and each driving circuit independently driving its corresponding electrode so that the potential on the electrode is consistent with the potential of the driving signal source applied on the driving circuit; one driving circuit drives the main electrode to emit a measurement current to the formation, and the other driving circuits drive the corresponding shielding electrodes to emit shielding currents to the formation; the shielding currents constrain the flow path of the measurement current so that the measurement current flows horizontally along the formation; by measuring the current value of the measurement current emitted by the main electrode to the formation and the voltage drop generated by the measurement current passing through the formation, the resistivity value of the formation is calculated. In the present invention, the main electrode and each shielding electrode are independently driven respectively, which does not increase the driving burden on the driving circuits of other electrodes, improves the focusing effect on the measurement current emitted by the main electrode, and fully ensures the measurement accuracy for low-resistivity formations.

Description

Technical Field

[0001] The present invention relates to the technical field of lateral logging, and more specifically, to an array lateral logging tool and a measurement method thereof. Background Art

[0002] Array lateral logging refers to a focused resistivity logging method. By means of current focusing, the current emitted by the shielding electrodes arranged on both sides of the main electrode restricts the flow path of the current emitted by the main electrode, forcing the current emitted by the main electrode not to flow up and down in the wellbore at a certain position away from the wellbore, but to flow horizontally into the formation in the lateral direction. Because of the shunting effect of the wellbore and the influence of the surrounding rock, the measurement results can be used to distinguish the electrical characteristics of strata at different distances from the wellbore in a stepped manner. The dual lateral logging tool is a special implementation of the array lateral logging tool, which provides the formation resistivity at two detection depths with a (deep, shallow) minimum array.

[0003] The array lateral logging tool first needs to drive multiple electrodes to emit current into the formation to form a controllable electric field in the formation to achieve the function of focused measurement. The existing array lateral technology (including dual lateral, not elaborated hereinafter) drives the electrodes in a relative driving manner. The specific implementation method is as Figure 1 shown, which is to cascade-drive multiple electrodes A1 - A4 through multiple driving transformers L1 - L3, that is, the secondaries of adjacent transformers are connected in series, and the current is driven from one of the two electrodes connected to the secondary of the driving transformer to the other electrode. The main disadvantage of this driving method is that if both of the two driven electrodes are shielding electrodes, or one of the two driven electrodes is a shielding electrode and the other is a main electrode, the two electrodes need to emit current into the formation simultaneously, and the returned current must form a loop through the secondary of the outermost transformer, which adds an extra load to the driving circuit of the outermost transformer and easily causes the load of the outermost driving circuit to be overweight. In fact, the problem of insufficient driving ability of the outermost driving circuit has become a bottleneck factor affecting the performance of the array lateral logging tool.

[0004] Overweight load is a serious drawback of this driving method. Especially when the number of electrode arrays in lateral logging is large and the formation resistivity is low, it is more likely to cause the overload of the outermost driving circuit, thereby affecting the measurement accuracy of the instrument. Therefore, it is necessary to study a solution that can improve the performance of the array lateral logging tool. Summary of the Invention

[0005] The present invention aims at the technical problems existing in the prior art, and provides an array lateral logging tool and a measurement method thereof to solve the problems of overweight load and poor performance of the existing array lateral logging tool.

[0006] According to a first aspect of the present invention, there is provided an array lateral logging tool, comprising:

[0007] A control circuit, a sampling circuit, and multiple electrodes;

[0008] The multiple electrodes include a main electrode and multiple shielding electrodes, and the multiple shielding electrodes are dispersedly arranged on both sides of the main electrode; the main electrode is used for emitting a measurement current to the formation; the shielding electrodes are used for emitting a shielding current to the formation; the shielding current and the measurement current compete for a flow channel, thereby restricting the flow path of the measurement current to achieve detection of the resistivity of a formation at a specific depth by the measurement current.

[0009] The control circuit includes multiple driving circuits, and the input ends of the multiple driving circuits are respectively connected to multiple driving signal sources in one-to-one correspondence; the output ends of the multiple driving circuits are respectively connected to the multiple electrodes in one-to-one correspondence, and each driving circuit independently drives the electrode connected to its output end so that the potential of the electrode is consistent with the potential of the driving signal source connected to the input end of the driving circuit.

[0010] The sampling circuit is connected to the main electrode and is used for measuring the magnitude of the measurement current flowing into the formation through the main electrode and measuring the magnitude of the voltage drop generated by the measurement current passing through the formation to calculate the resistivity value of the formation.

[0011] Based on the above technical solutions, the present invention can also be improved as follows.

[0012] Optionally, the driving circuit includes a first operational amplifier, and the non-inverting input end of the first operational amplifier is connected to a driving signal source; the output end of the first operational amplifier is connected to the corresponding electrode for outputting a driving signal to the corresponding electrode; the inverting input end of the first operational amplifier is connected to the corresponding electrode, so that the first operational amplifier operates in a voltage follower mode.

[0013] Optionally, a transformer is further arranged between the driving circuit and the electrode. One end of the primary of the transformer is connected to the output end of the driving circuit and the other end is grounded; one end of the secondary of the transformer is connected to the electrode and the other end is grounded; the transformer is used for applying the driving signal output by the driving circuit to the corresponding electrode.

[0014] Optionally, a signal superposition unit is respectively arranged at the front end of each driving circuit to provide a driving signal source for the driving circuit; the signal superposition unit includes a specific channel measurement signal input end, a basic signal input end, and a mixed signal output end.

[0015] The specific channel measurement signal input terminal is used to receive an externally input specific channel measurement signal; the mixed signal output terminal of the signal superposition unit is connected to the non-inverting input terminal of the first operational amplifier in the drive circuit, and is used to superpose the signal of the specific channel measurement signal input terminal and the signal of the basic signal input terminal through the signal superposition unit, and use the mixed signal formed after superposition as the drive signal source of the drive circuit and output it to the drive circuit;

[0016] Taking the main electrode as the central position, according to the positional relationship of the shielding electrode relative to the main electrode, determine the inner and outer relationships between the electrodes; regard the signal superposition unit that provides the drive signal source for the drive circuit, the drive circuit, and the functional unit formed by connecting the electrodes driven by the drive circuit in series as an excitation path, and determine the inner and outer relationships between the excitation paths according to the inner and outer relationships between the electrodes included in each excitation path;

[0017] The basic signal input terminal of the signal superposition unit included in each excitation path is connected to the electrode in the adjacent outer excitation path, and is used to introduce the drive signal of the adjacent outer excitation path as the basic signal of this excitation path into the signal superposition unit.

[0018] Optionally, the signal superposition unit includes an adder; the electrode in the relatively outer excitation path is connected to the non-inverting input terminal of the adder of the signal superposition unit in the adjacent relatively inner excitation path to provide the basic signal for the adder; the non-inverting input terminal of the adder of the signal superposition unit in the relatively inner excitation path is also connected to the specific channel measurement signal input terminal for inputting the specific channel measurement signal; the output terminal of the adder is connected to the non-inverting input terminal of the first operational amplifier of the drive circuit in the same excitation path; the adder superposes the signal on the electrode in the relatively outer excitation path and the specific channel measurement signal in the adjacent relatively inner excitation path, and outputs it to the non-inverting input terminal of the first operational amplifier of the drive circuit in the relatively inner excitation path to drive the electrode in the relatively inner excitation path.

[0019] Optionally, the signal superposition unit includes a subtractor; the electrodes in the outermost excitation path are connected to the non-inverting input terminal of the subtractor of the signal superposition unit in the adjacent inner excitation path, providing a basic signal for the subtractor; the inverting input terminal of the subtractor of the signal superposition unit in the inner excitation path serves as the specific channel measurement signal input terminal for inputting the specific channel measurement signal; the output terminal of the subtractor is connected to the non-inverting input terminal of the first operational amplifier of the drive circuit in the same excitation path; the subtractor superimposes the signals on the electrodes in the outermost excitation path and the specific channel measurement signals in the adjacent inner excitation path, and outputs to the non-inverting input terminal of the first operational amplifier of the drive circuit in the inner excitation path to drive the electrodes in the inner excitation path.

[0020] Optionally, the sampling circuit includes a sampling resistor. One end of the sampling resistor is connected to the output terminal of the first operational amplifier corresponding to the main electrode, and the other end of the sampling resistor is connected to the common node of the inverting input terminal of the first operational amplifier and the main electrode. The sampling resistor is used to sample the current value of the measurement current flowing through the main electrode.

[0021] Optionally, the sampling circuit further includes a signal separation unit. The signal separation unit is connected to the main electrode and is used to separate the superimposed signals collected from the main electrode into multiple specific channel signals; the resistivity of different depth formations is detected through each specific channel signal respectively.

[0022] Optionally, a monitoring electrode is arranged at a position adjacent to the main electrode and / or the shielding electrode, and the monitoring of the voltage on the main electrode and / or the shielding electrode is replaced by the monitoring of the voltage on the monitoring electrode.

[0023] According to the second aspect of the present invention, based on the above array laterolog tool, a measurement method of the array laterolog tool is further provided, including:

[0024] Drive signal sources are independently applied to each drive circuit respectively, and each drive circuit independently drives its corresponding electrode to make the potential on the electrode consistent with the potential of the drive signal source applied on the drive circuit;

[0025] A certain drive circuit drives the main electrode to emit a measurement current to the formation, and the other drive circuits drive the corresponding shielding electrodes to emit shielding currents to the formation; the shielding currents constrain the flow path of the measurement current to make the measurement current flow horizontally along the formation;

[0026] The resistivity value of the formation is calculated by measuring the current value of the measurement current emitted by the main electrode to the formation and the voltage drop generated by the measurement current passing through the formation.

[0027] An array laterolog tool and its measurement method provided by the present invention independently drive the main electrode and each shielding electrode respectively. The current generated by driving each electrode forms a loop directly through the power supply and / or ground of the driving circuit of the current electrode. Compared with the prior art where the loop is formed through the secondary of the transformer driving other electrodes, it will not increase the driving burden on the driving circuits of other electrodes. For the array laterolog tool adopting this driving method, when the measurement current and shielding current required are very large in a low-resistivity formation, the driving ability of each electrode can still be ensured to be sufficient, improving the focusing effect of the measurement current emitted by the main electrode and fully ensuring the measurement accuracy for the low-resistivity formation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 FIG. is a schematic diagram of relative driving of each electrode in the prior art;

[0029] Figure 2 FIG. is a schematic diagram of the principle of the independent driving circuit of an array laterolog tool according to an embodiment provided by the present invention;

[0030] Figure 3 FIG. is a schematic diagram of the principle of an array laterolog tool provided by the present invention in which a magnetic device is provided in an embodiment;

[0031] Figure 4 FIG. is a schematic diagram of the circuit principle of an array laterolog tool with power driving provided by the present invention in an embodiment;

[0032] Figure 5 FIG. is a schematic diagram of the circuit principle of an array laterolog tool adopting a monitoring electrode provided by the present invention in an embodiment;

[0033] Figure 6 FIG. is a schematic diagram of the principle of an array laterolog tool with more shielding electrodes provided by the present invention in an embodiment; Figure 1 ;

[0034] Figure 7 FIG. is a schematic diagram of the principle of an array laterolog tool with more shielding electrodes provided by the present invention in an embodiment; Figure 2 . DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The following further describes in detail the specific embodiments of the present invention with reference to the drawings and embodiments. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0036] Figure 1 FIG. is a schematic diagram of relative driving of multiple electrodes in the prior art. As Figure 1As shown, electrodes A1 to A4 are driven by drive transformers L1 to L3. Among them, the secondaries of drive transformers L1 to L3 are connected in series, forming a load cascade between each drive circuit (2111, 2112, 2113). The current is driven from one of the two electrodes connected to the secondary of the drive transformer to the other electrode. Assume A4 is the outer electrode. Sampling points B21 and B22 are used to sample the voltage difference between electrode A1 and electrode A2, and compensate this voltage difference into the drive signal of drive transformer L1 for driving electrode A1 relative to A2; sampling points B31 and B32 are used to sample the voltage difference between electrode A2 and electrode A3, and compensate this voltage difference into the drive signal of drive transformer L2 for driving electrode A2 relative to A3; sampling points B41 and B42 are used to sample the voltage difference between electrode A3 and electrode A4, and compensate this voltage difference into the drive signal of drive transformer L3 for driving electrode A3 relative to A4; and so on, to show the relative drive between all electrodes. Assume a detection mode where A1 - A3 are driven at the same potential, and all the current emitted by A1 - A3 has to return from A4, flowing through the secondary of transformer L3, forming the load of drive circuit 2113. Figure 1 The shown technical solution has the drawback that an additional load is applied to the drive circuit of the drive transformer corresponding to the outermost electrode, which easily causes the load of the outer drive circuit to be too heavy, thus affecting the driving ability of the outer drive circuit.

[0037] The basic idea to overcome this drawback is to connect the wire that was originally connected to A2 of L1 to A4, and connect the wire that was originally connected to A3 of L2 to A4. The drive circuits 2111, 2112, and 2113 directly drive A1, A2, and A3 respectively (or drive relative to the loop electrode A4), rather than driving relative to A2 and A3 respectively. One embodiment of the present invention is like this, and A4 is grounded.

[0038] Specifically, based on the defects in the background technology, as Figure 2 shown, an embodiment of the present invention provides an array laterolog tool, including:

[0039] A control circuit, a sampling circuit, and multiple electrodes;

[0040] The multiple electrodes include a main electrode and multiple shielding electrodes, and the multiple shielding electrodes are dispersedly arranged on both sides of the main electrode; as Figure 2 shown, on one side of the main electrode A0, shielding electrode A1 and shielding electrode A2 are arranged in sequence along the well depth direction; the main electrode is used to emit a measurement current to the formation; the shielding electrode is used to emit a shielding current to the formation; the shielding current and the measurement current compete for the flow channel, and then restrict the flow path of the measurement current to achieve the detection of the resistivity of the formation at a specific depth by the measurement current.

[0041] The control circuit includes a plurality of drive circuits, and the input ends of the plurality of drive circuits are respectively connected to a plurality of drive signal sources one by one (for example Figure 2 , Figure 4 the output of operational amplifier U1, the output of operational amplifier U2, and the sampling point A1R on the electrode in Figure 3 , Figure 5 the output of operational amplifier U1, the output of operational amplifier U2, and the monitoring electrode M2 in Figure 6 the output of operational amplifier U1, the output of operational amplifier U2, the output of operational amplifier U21, the output of operational amplifier U22, the output of operational amplifier U23, and the output of operational amplifier U24 in Figure 7 the output of operational amplifier U1, the output of operational amplifier U2, the output of operational amplifier U21, the output of operational amplifier U22, the output of operational amplifier U23, and the sampling point A1R on the electrode in

[0042] The sampling circuit is connected to the main electrode and is used to measure the magnitude of the measurement current flowing into the formation through the main electrode and the magnitude of the voltage drop generated by the measurement current passing through the formation, so as to calculate the resistivity value of the formation.

[0043] It can be understood that the number of shielding electrodes can be flexibly arranged according to actual needs to form laterolog tools with different array scales. Among them, the dual laterolog tool is a type of array laterolog tool with a very small array scale but a very wide application range. Figures 2 - 5 Taking the scheme of a dual laterolog tool with two shielding electrodes respectively arranged on both sides of the main electrode A0 as an example, Figures 2 - 5 only the shielding electrode A1 and the shielding electrode A2 located on one side of the main electrode A0 are shown in Figures 6 - 7In the technical solution, taking the example of arranging shielding electrodes A1 to A6 on one side of the main electrode A0, the number of shielding electrodes on the other side of the main electrode A0 not shown in the figure can be set according to actual measurement requirements. The array laterolog tool proposed in the embodiment of the present invention improves the driving performance of the laterolog tool. Specifically, for the array laterolog tool of this embodiment, the main electrode and each shielding electrode are independently driven, and the current generated by driving each electrode directly forms a loop through the power supply and / or ground of the driving circuit of the current electrode. Compared with the prior art where the loop is formed through the secondary of the transformer driving other electrodes, the tool of this embodiment does not increase the driving burden on the driving circuits of other electrodes. The array laterolog tool adopting the driving method of this embodiment can still ensure the driving ability of each electrode in low-resistivity formations, fully guarantee the measurement accuracy for low-resistivity formations, and effectively improve the measurement performance of the tool.

[0044] Sometimes different driving methods need to be paired with different control methods. Figure 1 The control method paired with the relative driving method shown is to detect the potential difference between two adjacent driven electrodes and drive this potential difference to be consistent with a preset target. Specifically, it is to drive the potential difference between B21 and B22 to be consistent with in1; drive the potential difference between B31 and B32 to be consistent with in2, and drive the potential difference between B41 and B42 to be consistent with in3.

[0045] The currently widely used control technology is to judge whether the potential difference between two electrodes contains signals that need to be suppressed. If there are signals that need to be suppressed, feedback suppression is performed on them. In this way, a complex signal extraction circuit must be introduced in the feedback loop, making the focusing link extremely unstable.

[0046] The feedback control technology paired with the independent driving in this embodiment drives the potential on the driven electrode to be consistent with a preset target through an extremely simple follower driving circuit. This driving control method can fully ensure the stability and reliability of the system.

[0047] The independent driving proposed by the present invention is also very easy to achieve flexible focusing (under-focusing or over-focusing), providing direct support for zoom logging.

[0048] It should be particularly noted that it is impossible to perform "independent driving" on the electrodes in an absolute sense. The so-called "independent driving" we mentioned is also driving relative to the ground or a common loop electrode.

[0049] Based on the above technical solution, the following improvements can also be made in this embodiment.

[0050] In a possible embodiment, the driving circuit includes a first operational amplifier. The non-inverting input terminal of the first operational amplifier is connected to a driving signal source, and the inverting input terminal of the first operational amplifier is connected to the corresponding electrode. The output terminal of the first operational amplifier is connected to the corresponding electrode for outputting a driving signal to the corresponding electrode. As Figure 2 shown, a first operational amplifier U3 is provided in the driving circuit of the shielding electrode A2, and a first operational amplifier U4 is provided in the driving circuit of the shielding electrode A1. The driving signal source of the shielding electrode A2 comes from the output terminal of the operational amplifier U1 and is input to the non-inverting input terminal of the first operational amplifier U3. The output terminal of the first operational amplifier U3 is connected to the inverting input terminal of the first operational amplifier U3 to form a signal negative feedback. The output terminal of the first operational amplifier U3 outputs a driving signal to the shielding electrode A2. Similarly, the driving signal source of the shielding electrode A1 comes from the output terminal of the operational amplifier U2 and is input to the non-inverting input terminal of the first operational amplifier U4. The output terminal of the first operational amplifier U4 is connected to the inverting input terminal of the first operational amplifier U4 to form a signal negative feedback. The output terminal of the first operational amplifier U4 outputs a driving signal to the shielding electrode A1. The driving signal source of the main electrode A0 comes from the access point A1R on the A1 electrode and is input to the non-inverting input terminal of the first operational amplifier U5. The output terminal of the first operational amplifier U5 is connected to the inverting input terminal of the first operational amplifier U5 through a sampling resistor R1 to form a signal negative feedback. The output terminal of the first operational amplifier U5 outputs a driving signal to the main electrode A1 through the sampling resistor R1.

[0051] In this embodiment, the signal of the driving signal source is followed by the first operational amplifier, and the feedback point of the follow-up is set on the driven electrode to ensure the compliance between the potential on the driven electrode and the potential of the driving signal source. Each driving circuit respectively follows the signal input to its non-inverting input terminal through a first operational amplifier to ensure the compliance between the potential on each electrode and the potential of each driving signal source. In the actual implementation process, as Figure 4 shown in FIG. 4 or 5, if the driving ability of the selected first operational amplifier is insufficient, functional modules such as power driving can also be added behind the first operational amplifier to improve the driving ability of the driving circuit for the electrode. After adding circuits such as power driving behind the operational amplifier, a generalized operational amplifier is formed. If the newly added subsequent circuit changes the phase of the signal, for example, including but not limited to introducing an inverting link through a transformer, the definitions of the non-inverting terminal and the inverting terminal of the generalized operational amplifier should also be modified accordingly. For Figure 4 example, Figure 4In this case, a power driving module is provided at the output end of the driving circuit of each electrode. For example, at the output end of the driving circuit of the main electrode A0, a power driving module composed of transistors Q1 to Q2, diodes D1 to D2, resistors R6 to R9, and a ±12V working power supply is provided. The power driving modules in the remaining shielding electrodes have the same principle as the power driving module in the driving circuit of the main electrode A0. Here, only the power driving module in the driving circuit of the main electrode A0 will be described in detail. The collector of transistor Q1 is connected to the +12V working power supply. The emitter of transistor Q1, resistor R7, resistor R9, the collector of transistor Q2, and the -12V working power supply are connected in series in sequence. The +12V working power supply, resistor R6, diode D1, diode D2, resistor R8, and the -12V working power supply are connected in series in sequence. Among them, diodes D1 and D2 are set with forward bias. The common node of resistor R6 and the anode of diode D1 is connected to the base of transistor Q1. The common node of the cathode of diode D2 and resistor R8 is connected to the base of transistor Q2. The common node of the cathode of diode D1 and the anode of diode D2 serves as the signal input end of this power driving module and is connected to the output end of the first operational amplifier U5. The common node of resistor R7 and resistor R9 serves as the signal output end of this power driving module and is used to output the amplified driving signal to realize the driving of the main electrode A0. It should be noted that the driving signal feedback point of the electrode should be directly connected to the corresponding electrode, that is, the inverting input end of the first operational amplifier should be directly connected to the corresponding driven electrode. For example, the driving signal feedback point A0R of the main electrode is directly connected to the main electrode A0 to obtain the most accurate feedback signal to ensure that the final driving effect is that the potential on the electrode is consistent with the potential of the driving signal source. When necessary, a monitoring electrode can be used to directly introduce a feedback signal from the formation to ensure that the potential of the feedback point in the formation is consistent with the potential of the driving signal source. As long as the feedback point is regarded as the driving target point of the first operational amplifier, it is feedback following in principle. Improving the driving ability of the operational amplifier itself is not the focus of this invention and will not be elaborated herein.

[0052] In this embodiment, the output end of the first operational amplifier or the output end of the power driving at the rear end of the first operational amplifier can be directly connected to the corresponding electrode to distinguish from the situation in the traditional technical solution where a driving transformer is connected to the driven electrode. Since the logging instrument works in a high-temperature environment, there are few magnetic devices that can work normally in a high-temperature environment, and they work unstably with large parameter drifts. The transformer is a magnetic device, and magnetic devices are an important factor causing the instability and unreliability of high-temperature instruments and equipment. Therefore, in this embodiment, by directly connecting the driving signal output by the driving circuit to the driven electrode, the problems brought by the above-mentioned magnetic devices are solved, making the instrument in this embodiment more adaptable to the high-temperature environment. At the same time, not using magnetic devices can also reduce the volume of the electronic circuit and lower the power consumption.

[0053] In a possible embodiment, in order to maintain consistency with existing instrument parameters to the greatest extent, including ensuring high electrical isolation indicators, this embodiment also presents an embodiment that retains magnetic devices (transformers) and incorporates independent drives. Specifically, based on the above technical solution, as Figure 3 shown, a transformer is also provided between the drive circuit and the corresponding driven electrode. For example, Figure 3 in Figure 3 , transformer T2 corresponding to shield electrode A1 and transformer T1 corresponding to shield electrode A2; one end of the primary of the transformer is connected to the output end of the drive circuit and the other end is grounded; one end of the secondary of the transformer is connected to the electrode and the other end is grounded; the transformer is used to apply the drive signal output by the drive circuit to the corresponding electrode.

[0054] It can be understood that this embodiment is different from Figure 1 the way of electrical isolation through transformers in the traditional lateral logging tool shown in Figure 1 . In this embodiment, one end of the secondary of each transformer is grounded, and of course, it can also be connected to another common connection point, avoiding the problem of excessive load on the outer drive circuit caused by the traditional scheme. Similarly, for sampling the current of the main electrode A0, the traditional mutual inductor sampling method can also be retained. For example, Figure 3 in Figure 3 , current transformer T3 connected to the main electrode A0. The current transformer T3 is also a magnetic device and is used to convert the primary side current into the secondary side current to realize the current measurement of the main electrode A0.

[0055] In a possible embodiment, a signal superposition unit is respectively provided at the front end of each of the drive circuits to provide a drive signal source for the drive circuit. For example, Figures 2 - 7 U1 and / or U2 in Figures 2 - 7 , and Figures 6 - 7 U21 - U24 in Figures 6 - 7 are all signal superposition units; the signal superposition unit includes a specific channel measurement signal input end (such as Figures 2 - 7 S1 and S2 in Figures 2 - 7 , Figure 6 S3 - S6 in Figure 6 , Figure 7 S21, S22, S23 in Figure 7 ), a basic signal input end, and a mixed signal output end;

[0056] The specific channel measurement signal input end is used to receive the externally input specific channel measurement signal; the mixed signal output end of the signal superposition unit is connected to the non-inverting input end of the first operational amplifier in the drive circuit, and is used to use the mixed signal formed by superimposing the signal at the specific channel measurement signal input end and the signal at the basic signal input end through the signal superposition unit as the drive signal source of the drive circuit and output it to the drive circuit; it should be noted here that the drive signal source refers to a signal or a signal port, not a component, assembly, or element;

[0057] Taking the main electrode as the central position, determine the inner and outer relationships between the electrodes according to the positional relationship of the shielding electrode relative to the main electrode; take the signal superimposing unit that provides the drive signal source for the drive circuit, the drive circuit, and the functional unit composed of the electrodes driven by the drive circuit connected in series front and back as an excitation path, and determine the inner and outer relationships between the excitation paths according to the inner and outer relationships between the electrodes included in each excitation path;

[0058] The basic signal input terminal of the signal superimposing unit included in each excitation path is connected to the electrode in the adjacent outer excitation path, and is used to introduce the drive signal of the adjacent outer excitation path as the basic signal of this excitation path into the signal superimposing unit.

[0059] More specifically, taking Figure 6 as an example, for the signal superimposing unit U1 at the front end of the drive circuit of the shielding electrode A5, its specific channel measurement signal input terminal, that is, the inverting input terminal of the signal superimposing unit U1, is used to receive the specific channel measurement signal S1 externally applied, and its basic signal input terminal, that is, the non-inverting input terminal of the signal superimposing unit U1, is used to receive the signal on the more outer electrode as the basic signal. Since there is no shielding electrode outside the shielding electrode A5, it is defaulted that its more outer electrode is the grounding electrode A6. Ground the basic signal input terminal of the signal superimposing unit U1, that is, a mixed signal superimposing the specific channel measurement signal S1 and the grounding signal is output at the output terminal of the signal superimposing unit U1. The mixed signal output by the signal superimposing unit U1 serves as the drive signal source for its corresponding drive circuit. As shown by Figure 6 the connection relationships of each signal superimposing unit in, by the same token, for the shielding electrode A4 inside the shielding electrode A5, the shielding electrode A3 inside the shielding electrode A4, the shielding electrode A2 inside the shielding electrode A3, the shielding electrode A1 inside the shielding electrode A2, and the main electrode A0 inside the shielding electrode A1, the principle of signal superimposition is similar. The drive signal source for the shielding electrode A4 is obtained by superimposing the specific channel measurement signal S2 and the drive signal of the shielding electrode A5 through the signal superimposing unit U2. The drive signal source for the shielding electrode A3 is obtained by superimposing the specific channel measurement signal S3 and the drive signal of the shielding electrode A4 through the signal superimposing unit U21. The drive signal source for the shielding electrode A2 is obtained by superimposing the specific channel measurement signal S4 and the drive signal of the shielding electrode A3 through the signal superimposing unit U22. The drive signal source for the shielding electrode A1 is obtained by superimposing the specific channel measurement signal S5 and the drive signal of the shielding electrode A2 through the signal superimposing unit U23. The drive signal source for the main electrode A0 is obtained by superimposing the specific channel measurement signal S6 and the drive signal of the shielding electrode A1 through the signal superimposing unit U24.

[0060] It can be understood that the purpose of separately arranging signal superposition units at the front end of each drive circuit is to superpose the signals on adjacent outer electrodes onto the inner electrodes (including the innermost main electrode). When examining the drive electrodes of the array laterolog tool, the drive corresponding to the outer electrode is generally a shielding current, and there must be a corresponding and consistent drive on the inner electrode (including the main electrode). Therefore, regardless of whether a new signal is introduced on the inner electrode, it is always necessary to introduce the signal on the outer electrode to the inner electrode. That is to say, once a specific channel measurement signal (i.e., an externally input signal) is introduced on a certain electrode, a signal superposition unit is generally arranged at the front end of the drive circuit corresponding to the electrode on its inner side, and the basic signal input terminal of this signal superposition unit is connected to this outer electrode to copy the signal on this outer electrode to the inner electrode. For electrodes that do not require the introduction of new specific channel measurement signals, such as the main electrode, a signal superposition unit may not be arranged at the front end of its drive circuit, and the outer electrode is directly connected to the input terminal of the drive circuit to copy and drive the signal on the outer electrode to the inner electrode, as Figures 2 - 5 、 Figure 7 。

[0061] It should be noted that the array laterolog tool generally uses several signals with different frequencies to complete the detection of formations at different depths. On the premise that the size of the electrodes is certain, the number of shielding electrodes outside the main electrode determines the restraint strength of the shielding current on the detection current and also determines the detection depth of the detection current on the formation. It should be noted that not all the electrodes arranged outside the main electrode constitute the shielding electrodes of the main electrode. Only when the current emitted by the outer electrode to the formation is the same as the current emitted by the main electrode to the formation does this outer electrode constitute the shielding electrode of the main electrode. Therefore, in this embodiment, the shielding relationship between the shielding electrode and the main electrode is distinguished according to the "specific channel measurement signal". In specific implementation, in this embodiment, the shielding current is first set, and then the main current is set according to the magnitude and direction of the shielding current; when there are multiple shielding currents, the outermost shielding current is first set, and the inner shielding current is set according to the outermost shielding current.

[0062] The so-called "specific channel measurement signal" in this embodiment is generally a signal with a single frequency. Once it is introduced on a pair of shielding electrodes, each pair of shielding electrodes inside this shielding electrode, all the way to the main electrode, will contain this frequency signal. That is to say, for the signal with which frequency is first introduced at a more outer position and the introduction time is earlier, the more electrodes (shielding electrodes) contain this frequency signal, the wider the flow channel occupied by the shielding current, the better the focusing effect on the main current, and the deeper the detection depth of the current with this frequency on the formation resistivity.

[0063] If frequency division measurement is adopted, the measurement signals of each specific channel need to be orthogonal in the frequency domain to ensure that the measurement signals of each path do not interfere with each other and can ultimately be separated by the sampling circuit. Of course, time-division measurement can also be adopted, where measurement signals are applied to each excitation path in different time periods to achieve time-division measurement of the formation. Although time-division measurement seems relatively old-fashioned and has low measurement efficiency on the surface, it can reduce the frequency impact and can also play a specific role in instrument maintenance.

[0064] In a possible embodiment, as Figure 7 shown, the signal superposition unit includes an adder, that is, an adder circuit is used to implement the function of superposing two signals; the electrodes in the outer excitation path are connected to the non-inverting input terminal of the adder of the signal superposition unit in the adjacent inner excitation path to provide a basic signal for the adder; the non-inverting input terminal of the adder in the signal superposition unit in the inner excitation path is also connected to the specific channel measurement signal input terminal for inputting the specific channel measurement signal; the output terminal of the adder is connected to the non-inverting input terminal of the first operational amplifier of the drive circuit in the same excitation path; the adder superposes the signal on the electrode in the outer excitation path and the specific channel measurement signal in the adjacent inner excitation path, and outputs it to the non-inverting input terminal of the first operational amplifier of the drive circuit in the inner excitation path to drive the electrode in the inner excitation path.

[0065] As Figure 7 shown is a specific embodiment of using an adder to implement the function of superposing the specific channel measurement signal and the adjacent outer electrode drive signal. Figure 7 Among them, U1, U2, U21, U22, U23 and the supporting resistors respectively constitute signal superposition units corresponding to the drive circuits of electrodes A5 to A1 one by one, and U1, U2, U21, U22, U23 and the supporting resistors all constitute adders. The inverting input terminal of the adder is connected to the negative feedback network, and the non-inverting input terminal of the adder inputs the specific channel measurement signal through R51, R61, R71, R81, R91 and inputs the basic signal through R60, R70, R80, R90. Taking Figure 7 the adder U2 in it as an example for illustration. The inverting input terminal of the adder U2 is grounded through the resistor R62 and connected to the output terminal of the adder U2 through the resistor R63 to form a negative feedback to determine the amplification gain of the adder; the non-inverting input terminal of the adder U2 is connected to the external specific channel measurement signal S2 through the resistor R61, and the non-inverting input terminal of the adder U2 is connected to the adjacent outer electrode A5 through the resistor R60, and the signal collected at the signal collection point on the A5 electrode is used as the basic signal for driving the electrode A4. By setting the parameters of the resistors R60 to R63 and the adder U2, the gain factor of the adder U2 can be adjusted so that the signal introduced from the outer electrode A5 is mixed into the mixed signal output from the output terminal of the adder U2 with a proportional factor of 1.

[0066] The independent driving method for the counter electrode proposed by the present invention provides a driving guarantee for realizing various flexible focusing. An example: while keeping the potential difference between the main electrode and the return electrode unchanged, by increasing (or decreasing) the potential difference between the shielding electrode and the return electrode, overfocusing (or underfocusing) can be achieved, and the detection depth of the instrument can be increased (or decreased). Taking Figure 7 adder U2 in it as an example for illustration, by setting the parameters of resistors R60 to R63 and adder U2, the gain factor of adder U2 can be adjusted, so that the signal introduced from the outer electrode A5 is mixed into the mixed signal output from the output end of adder U2 with a scale factor less than 1 (or greater than 1), achieving overfocusing (or underfocusing), and increasing (or decreasing) the detection depth of the instrument. Special focusing or even zoom logging can be achieved in this way.

[0067] It can be understood that the setting of the adder is to ensure that the driving signal of a certain frequency introduced to the outer electrode can continue to be introduced to all the inner electrodes (including the main electrode) in the same phase manner. It should be noted here that the driving signal is introduced in the same phase manner, so as to ensure that the electrodes introducing signals of the same frequency can be in step when emitting current to the formation, so as to achieve the screen current effect.

[0068] In a possible embodiment, as Figure 6 shown, the signal superposition unit includes a subtractor. That is, as an Figure 7 alternative solution, the signal superposition unit can also use a subtractor to achieve the expected signal superposition function; the electrodes in the outer excitation path are connected to the non-inverting input terminal of the subtractor of the signal superposition unit in the adjacent inner excitation path to provide a basic signal for the subtractor; the inverting input terminal of the subtractor of the signal superposition unit in the inner excitation path is connected to the specific channel measurement signal input terminal for inputting the specific channel measurement signal; the output terminal of the subtractor is connected to the non-inverting input terminal of the first operational amplifier of the driving circuit in the same excitation path; the subtractor superimposes the signal on the electrode in the outer excitation path and the specific channel measurement signal in the adjacent inner excitation path, and outputs it to the non-inverting input terminal of the first operational amplifier of the driving circuit in the inner excitation path to drive the electrodes in the inner excitation path.

[0069] It can be understood that, as a parallel embodiment in which the signal superposition unit is implemented by an adder, the signal superposition unit can also be implemented by a subtractor to achieve the signal superposition function. Whether an adder or a subtractor is used to implement signal superposition, the ultimate goal is to ensure that the phases of the signals excited on the main electrode and the shielding electrode by the same-frequency drive signal are consistent, and the potentials on the shielding electrode and the main electrode of the electric field excited in the formation are consistent. It should be noted that the consistency mentioned here is for the measurement signal of a certain frequency. For measurement signals of different frequencies, the corresponding shielding electrodes are different, which is common sense in this field and will not be elaborated further.

[0070] It should be specifically noted that Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 In the circuits shown, the signal superposition unit adopts the subtractor scheme. In the subtractor scheme, the gain of the signal mixed in from the non-inverting terminal is always greater than or equal to 1 when it reaches the output terminals of U2, U21, U22, U23, and U24. If it is directly used as the drive signal source without attenuation, the effect is always underfocused. If balanced focusing is required, the signals output from U2, U21, U22, U23, and U24 in the subtractor scheme can be first divided and attenuated and then used as the drive signal source. Of course, signal attenuation can also be achieved in other positions in other ways, which is common sense in this field and will not be elaborated further.

[0071] In a possible embodiment, as shown in Figure 2 、 Figures 6 - 7 the sampling circuit includes a sampling resistor R1. One end of the sampling resistor is connected to the output terminal of the first operational amplifier U5 corresponding to the main electrode A0, and the other end of the sampling resistor R1 is connected to the common node of the inverting input terminal of the first operational amplifier U5 and the main electrode A0. The sampling resistor R1 is used to sample the current value of the measurement current flowing through the main electrode A0.

[0072] It can be understood that this embodiment shows the connection position of the sampling resistor in the circuit. The output terminal of the first operational amplifier is connected to the main electrode through the sampling resistor. It should be noted that the sampling resistor is arranged inside the drive circuit corresponding to the main electrode. Specifically: 1. The inverting input terminal of the first operational amplifier is connected to the main electrode across the sampling resistor, so as to ensure that the accurate drive of the potential on the main electrode is not affected by adding the sampling resistor; 2. No circuit branch that requires a large current can be connected to the common node connected between the sampling resistor and the main electrode. Only a measurement branch with a high input impedance can be connected to this node to ensure the accurate measurement of the current passing through the main electrode.

[0073] In this embodiment, by measuring the voltage across the sampling resistor R1 and referring to the resistance value of the sampling resistor R1, the magnitude of the current flowing through the sampling resistor R1 can be calculated, which is also the magnitude of the measurement current emitted by the main electrode A0, that is, the magnitude of the current flowing from the main electrode A0 to the formation. Of course, if the influence of the high-temperature environment on the performance of the magnetic device is not considered here, as Figure 3 shown, the current transformer T3 can also be used to replace the sampling resistor R1 to measure the magnitude of the current flowing from the main electrode to the formation.

[0074] The voltage drop of the current flowing through the formation can be measured by measuring the pressure difference between the main electrode and the outermost electrode; it can also be measured by measuring the pressure difference between the main electrode and the armored cable sheath; it can also be measured by measuring the pressure difference between the main electrode and the ground electrode. The measurement of the voltage drop of the main current flowing through the formation is neither the focus of the present invention nor difficult, so it will not be elaborated in this article.

[0075] In a possible embodiment, a monitoring electrode may also be provided at a position adjacent to the main electrode and / or the shielding electrode, and the monitoring of the voltage on the main electrode and / or the shielding electrode is replaced by monitoring the voltage on the monitoring electrode. As Figure 5 shown, M1 is the monitoring electrode of the main electrode A0, and both M2 and A1* are the monitoring electrodes of the shielding electrode A1, and the two are arranged on both sides of the shielding electrode A1. When the driving signal of the shielding electrode A1 is superimposed on the driving circuit of the main electrode A0, the monitoring electrode M2 can be connected to the input end of the driving circuit corresponding to the main electrode A0 to obtain the driving signal of the shielding electrode A1 through the monitoring electrode M2.

[0076] That is to say, when selecting the potential reference point representing each electrode, we can directly select the electrode, or we can select the monitoring electrode arranged around the electrode. These details that can be flexible in the specific implementation process do not change the basic content and essence of the present invention, and those skilled in the art can flexibly select them during the implementation process. The purpose of setting the monitoring electrode is to ensure that the electric field excited in the formation forms an equipotential, rather than just to ensure an equipotential between the driving electrodes, which is more in line with the focusing principle of laterolog. Sampling the voltage using the monitoring electrode can avoid the error caused by the voltage drop on the wire when directly measuring the voltage on the driving electrode, improve the focusing effect and measurement accuracy. After adopting the direct driving method and the negative feedback depth is high enough, the use of the monitoring electrode is not required, and sufficient accuracy of focusing and the acquisition of the formation electric field potential can also be achieved. In this embodiment, the monitoring electrode is set mainly to maximize the compatibility between the instrument provided by the present invention and the instruments provided by the prior art, including instrument components.

[0077] In a possible embodiment, the sampling circuit further includes a signal separation unit, which is connected to the main electrode and is configured to separate the superimposed signal collected from the main electrode into multiple specific channel signals; the resistivity of the formation at different depths is detected by each of the specific channel signals respectively.

[0078] It can be understood that signals of various frequency components introduced to the electrode through the specific channel measurement signal input ends of each excitation path will all appear on the more inner electrodes, especially on the main electrode. In other words, signals of various frequencies applied to all electrodes can be measured on the main electrode. The signal measured on the main electrode is a superimposed signal or a mixed signal of specific channel measurement signals of various frequencies. As described above, these superimposed signals or mixed signals are either orthogonal in the frequency domain and can be separated by Fourier transform, or do not overlap in the time domain and can also be distinguished by time-sharing control logic. In short, separating the signal collected from the main electrode by the signal separation unit for specific channel measurement signals and calculating the resistivity values of the formation at different depths based on the separated current and / or voltage signals is a mature technology in this field. It is not difficult for those skilled in the art to implement signal separation, and the specific implementation methods will not be elaborated in this specification.

[0079] It can be understood that there is a clear inner and outer relationship between the electrodes of the array laterolog. Generalizing the inner and outer relationship between the electrodes to the signal superposition unit and the drive circuit is helpful for clarifying the structural relationship of the system. To avoid comparing the inner and outer relationships between different types of objects, the concept of excitation path is introduced in this specification. Each excitation path includes a corresponding signal superposition unit, a drive circuit, and an electrode. The output of the signal superposition unit in the same excitation path is connected to the input end of the drive circuit in the same excitation path, and the output of the drive circuit in the same excitation path is connected to the electrode in the same excitation path. In this way, we can determine the inner and outer relationships between the excitation paths according to the inner and outer relationships of the electrodes included in the excitation path, and further generalize to the inner and outer relationships between the elements included in the excitation path, without causing logical confusion.

[0080] Based on the above embodiments of the array laterolog, this embodiment further provides a measurement method for an array laterolog, including the following steps:

[0081] Drive signals are independently applied to each drive circuit respectively, and each drive circuit independently drives its corresponding electrode to make the potential of the electrode consistent with the potential of the drive signal applied to the drive circuit.

[0082] A driving circuit drives a main electrode to emit a measurement current into the formation, and another driving circuit drives a corresponding shielding electrode to emit a shielding current into the formation; the shielding current constrains the flow path of the measurement current, causing the measurement current to flow horizontally in the formation.

[0083] By measuring the current value of the measurement current emitted by the main electrode into the formation and the voltage drop generated by the measurement current passing through the formation, the resistivity value of the formation is calculated.

[0084] Now, a specific measurement implementation case is combined to illustrate the array laterolog tool. To simplify the description of the workflow as much as possible, the dual laterolog tool in the array logging tool is used as an example in this embodiment.

[0085] As Figure 2 shown, the main electrode A0 is centered, and two layers of shielding electrodes A1 and A2 are sequentially arranged outside the main electrode A0. Shielding electrodes A1’ (not shown in the figure) corresponding to the shielding electrode A1 and shielding electrodes A2’ (not shown in the figure) corresponding to the shielding electrode A2 are symmetrically arranged with respect to the main electrode A0. Figure 2 The 10# in is a metal armored cable, which is used as a zero potential reference point. M1 is the monitoring electrode of the main electrode A0, and the monitoring electrode M1 is arranged adjacent to the main electrode A0; M2 and A1* are both the monitoring electrodes of the shielding electrode A1. The monitoring electrode M2 and A1* are respectively arranged on both sides of the shielding electrode A1 and are adjacent to the shielding electrode A1. The monitoring electrodes M2 and A1* are both used to sample the voltage of the shielding electrode A1. Monitoring electrodes can also be set for the shielding electrode A2. According to experience, for the outer electrodes far from the main electrode, monitoring electrodes are generally not set. Shielding electrode A1’ monitoring electrodes and shielding electrode A2’ monitoring electrodes are symmetrically arranged with respect to the main electrode A0. Only the working conditions on one side of the main electrode A0 are used as an example when describing the working principle of this embodiment. Therefore, the shielding electrode A1’ and its monitoring electrodes, and the shielding electrode A2’ and its monitoring electrodes on the other side of the main electrode A0 are not shown in the figure. During measurement, the voltage of its corresponding main electrode or shielding electrode can be sampled through the monitoring electrode, or the voltage of the main electrode or shielding electrode can be directly sampled. The specific electrode voltage sampling method will not be elaborated here.

[0086] A specific channel measurement signal S1 from an external source is applied to the drive circuit of the shield electrode A2 through a coupling capacitor C1, while a specific channel measurement signal S2 from an external source is applied to the drive circuit of the shield electrode A1 through a coupling capacitor C2. The specific channel measurement signal S1 passes through a signal superposition unit U1 and a first operational amplifier unit U3, and then outputs a drive signal to the shield electrode A2, and the shield electrode A2 emits a shield current. The drive signal of the shield electrode A2 and the specific channel measurement signal S2 are superimposed by a signal superposition unit U2, and the obtained mixed signal is output to the first operational amplifier unit U4 of the drive circuit of the shield electrode A1. The first operational amplifier unit U4 outputs a drive signal to the shield electrode A1, and the shield electrode A1 emits a shield current. The drive signal of the shield electrode A1 is then output to the first operational amplifier unit U5 of the drive circuit of the main electrode A0, and the mixed signal superimposed with the specific channel measurement signal S1 and the specific channel measurement signal S2 is used as the drive signal source of the main electrode A0 to realize the drive of the main electrode A0, and the main electrode A0 emits a measurement current. The current value of the main electrode A0 is sampled through a sampling resistor R1. Taking the metal armored cable 10# as the reference point of the far-end potential of the formation, a loop is formed between the main electrode A0 and the metal armored cable 10# (as Figures 2 - 5 The five lines on the right side in the figure indicate the situation of current passing through the formation. Among them, the thinner lines indicate the current channels corresponding to the deep exploration current, and the thicker lines indicate the current channels corresponding to the shallow exploration current; the lines connected to the main electrode indicate the flow path of the measurement current, and the other lines indicate the flow path of the shield current; it can be seen from the figure that the shallow lateral corresponds to only one shield current, and the deep lateral corresponds to two shield currents), measure the voltage between the main electrode A0 and the metal armored cable 10#, and then combine the measured current value of the main electrode A0 to obtain the real-time resistance value of the measured formation. Specifically, assuming that the single-harmonic deep exploration signal with frequency f1 is input for S1, and the single-harmonic shallow exploration signal with frequency f2 is input for S2, as long as f1 and f2 are orthogonal, the signals with frequencies f1 and f2 can be separated from the original acquisition signal through the Fourier algorithm to obtain the measurement results of two detection depths, deep and shallow.

[0087] In this measurement process, the drive signals of the outer electrodes are superimposed layer by layer on the inner electrodes, and the more types of signals are superimposed on the inner electrodes. Therefore, a current loop is also formed between the inner electrode and the outermost electrode (as Figure 2The current channel connected to the 10# electrode on the right side of the middle), the current that is not connected to the main electrode squeezes the flow channel of the measurement current emitted by the main electrode, so that the current emitted by the main electrode flows out towards the formation as much as possible, thus realizing the current concentration of the current emitted from the main electrode. In the schematic diagram, there is no thick line connected to the 10# electrode, indicating that the shallow detection signal does not pass through the 10# electrode. The thin lines connecting A1, A2 and the 10# electrode indicate the deep shielding current, and the thin lines connecting A0 and the 10# electrode indicate the deep measurement current; the thick line connecting A1 and A2 indicates the shallow shielding current, and the thick line connecting A0 and the A2 electrode indicates the shallow measurement current. Taking the 10# electrode as a reference, examining the potentials on each electrode, the A2 electrode contains the deep shielding signal, the A1 electrode contains both the deep and shallow shielding signals, and the A0 electrode contains both the deep and shallow measurement signals. In the actual situation, there will also be some current flowing back through the 10# in the shallow lateral direction, etc. Since it does not affect the fundamental principle display, it is omitted in the figure.

[0088] By the same token, Figures 6 - 7 More layers of shielding electrodes are adopted in it, and its measurement principle is also to layer by layer superimpose the driving signals of the outer layer electrodes onto the inner layer electrodes until all the driving signals are superimposed onto the main electrode. Since the measurement principle is the same, no detailed examples will be given here.

[0089] It should be particularly noted that the dual laterolog tool is only a special example of the array laterolog tool; the dual laterolog tool measures the resistivity of the formation using two frequencies, providing two formation resistivity curves, namely the deep lateral and the shallow lateral. Among them, the shallow lateral uses one-layer shielding current, and the deep lateral uses two-layer shielding current. Generally, the armored cable sheath is used as the return electrode for the deep lateral. All these can be flexibly implemented according to specific application requirements and the focus of the implementation engineer.

[0090] An array laterolog tool and its measurement method provided by the present invention independently drive the main electrode and each shielding electrode respectively. The current generated by driving each electrode forms a loop directly through the power supply and / or ground of the driving circuit of the current electrode. Compared with the prior art where the loop is formed through the secondary of the transformer driving other electrodes, it will not increase the driving burden on the driving circuits of other electrodes. For the array laterolog tool adopting this driving method, the driving ability of each electrode can still be ensured in low-resistivity formations, fully guaranteeing the measurement accuracy for low-resistivity formations. The technical solution of the present invention directly superimposes the driving signal of the outermost electrode on the innermost electrode, improving the consistency of the current emitted by the outermost electrode and the main electrode to the formation, ensuring the accurate measurement of the current passing through the main electrode, and improving the focusing effect of the tool. Compared with the method of compensating signals by sampling the voltage difference between adjacent electrodes in the traditional technology, the debugging method and the instrument composition of the present invention are simpler, improving the measurement performance and hardware cost of the instrument. The present invention can also omit magnetic devices such as transformers and mutual inductors, further saving the instrument cost, making the instrument more adaptable to high-temperature environments, and enhancing the detectable depth of the instrument for the formation.

[0091] It should be noted that in the above embodiments, the descriptions of each embodiment have their own emphases. For the parts not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0092] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic inventive concept. Including but not limited to connecting the electrode and the inverting terminal of the first operational amplifier through a resistor, grounding the inverting terminal of the first operational amplifier by combining or separately using a resistor, etc. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0093] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these changes and modifications.

Claims

1. An array laterolog tool, characterized in that, It includes a control circuit, a sampling circuit and multiple electrodes; The multiple electrodes include a main electrode and multiple shielding electrodes, and the multiple shielding electrodes are dispersedly arranged on both sides of the main electrode; the main electrode is used to emit a measurement current to the formation; the shielding electrodes are used to emit a shielding current to the formation; the shielding current and the measurement current compete for a flow channel, thereby constraining the flow path of the measurement current to achieve the detection of the resistivity of a formation at a specific depth by the measurement current; The control circuit includes multiple driving circuits, and the input ends of the multiple driving circuits are correspondingly connected to multiple driving signal sources one by one; The output ends of the multiple driving circuits are correspondingly connected to the multiple electrodes one by one, and each driving circuit independently drives the electrode connected to its output end, so that the potential of the electrode is kept consistent with the potential of the driving signal source connected to the input end of the driving circuit; A signal superposition unit is respectively arranged at the front end of each driving circuit; the signal superposition unit includes a specific channel measurement signal input end, a basic signal input end and a mixed signal output end; The specific channel measurement signal input end is used to receive an externally input specific channel measurement signal; the mixed signal output end of the signal superposition unit is connected to the non-inverting input end of the first operational amplifier in the driving circuit, and is used to superpose the signal at the specific channel measurement signal input end and the signal at the basic signal input end through the signal superposition unit, and use the mixed signal formed after superposition as the driving signal source of the driving circuit and output it to the driving circuit; Taking the main electrode as the central position, the inner and outer relationships between the electrodes are determined according to the positional relationship of the shielding electrodes relative to the main electrode; The functional unit composed of connecting the signal superposition unit that provides the driving signal source for the driving circuit, the driving circuit and the electrode driven by the driving circuit in sequence is regarded as an excitation path, and the inner and outer relationships between the excitation paths are defined according to the inner and outer relationships between the electrodes included in each excitation path; The basic signal input end of the signal superposition unit included in each excitation path is connected to the electrode in the adjacent outer excitation path, and is used to introduce the driving signal of the adjacent outer excitation path as the basic signal of this excitation path into the signal superposition unit; The signal superposition unit includes an adder; the electrode in the relatively outer excitation path is connected to the in-phase input terminal of the adder of the signal superposition unit in the adjacent relatively inner excitation path to provide a basic signal for the adder; the in-phase input terminal of the adder of the signal superposition unit in the relatively inner excitation path is further connected to the specific channel measurement signal input terminal for inputting a specific channel measurement signal; the output terminal of the adder is connected to the in-phase input terminal of the first operational amplifier of the drive circuit in the same excitation path; the adder superimposes the signal on the electrode in the relatively outer excitation path and the specific channel measurement signal in the adjacent relatively inner excitation path, and outputs it to the in-phase input terminal of the first operational amplifier of the drive circuit in the relatively inner excitation path to drive the electrode in the relatively inner excitation path. The sampling circuit is connected to the main electrode and is used to measure the magnitude of the measurement current flowing into the formation through the main electrode and to measure the magnitude of the voltage drop generated by the measurement current passing through the formation, so as to calculate the resistivity value of the formation. The sampling circuit includes a sampling resistor. One end of the sampling resistor is connected to the output terminal of the first operational amplifier corresponding to the main electrode, and the other end of the sampling resistor is connected to the common node of the inverting input terminal of the first operational amplifier and the main electrode. The sampling resistor is used to sample the current value of the measurement current flowing through the main electrode.

2. The array laterolog tool according to claim 1, wherein The drive circuit includes a first operational amplifier. The in-phase input terminal of the first operational amplifier is connected to the drive signal source; the output terminal of the first operational amplifier is connected to the corresponding electrode for outputting a drive signal to the corresponding electrode. The inverting input terminal of the first operational amplifier is connected to the corresponding electrode, so that the first operational amplifier operates in a voltage follower mode.

3. The array laterolog tool according to claim 2, characterized in that A transformer is further provided between the drive circuit and the electrode. One end of the primary of the transformer is connected to the output terminal of the drive circuit and the other end is grounded; one end of the secondary of the transformer is connected to the electrode and the other end is grounded; the transformer is used to apply the drive signal output by the drive circuit to the corresponding electrode.

4. An array laterolog tool according to claim 2 or 3, characterized in that, Replace the adder in the signal superposition unit with a subtractor; the electrode in the relatively outer excitation path is connected to the in-phase input terminal of the subtractor of the signal superposition unit in the adjacent relatively inner excitation path to provide a basic signal for the subtractor; the inverting input terminal of the subtractor of the signal superposition unit in the relatively inner excitation path serves as the specific channel measurement signal input terminal for inputting a specific channel measurement signal; the output terminal of the subtractor is connected to the in-phase input terminal of the first operational amplifier of the drive circuit in the same excitation path; the subtractor superimposes the signal on the electrode in the relatively outer excitation path and the specific channel measurement signal in the adjacent relatively inner excitation path, and outputs it to the in-phase input terminal of the first operational amplifier of the drive circuit in the relatively inner excitation path to drive the electrode in the relatively inner excitation path.

5. The array laterolog tool according to claim 2, wherein The sampling circuit further includes a signal separation unit, which is connected to the main electrode and is configured to separate the superimposed signal collected from the main electrode into multiple specific channel signals; the resistivity of different depth formations is detected by each of the specific channel signals respectively.

6. The array laterolog tool according to claim 5, wherein A monitoring electrode is arranged at a position adjacent to the main electrode and / or the shielding electrode, and the monitoring of the voltage on the main electrode and / or the shielding electrode is replaced by monitoring the voltage on the monitoring electrode.

7. A measurement method for an array laterolog tool, based on the array laterolog tool according to any one of claims 1 to 6, characterized in that, It includes: The driving signal source is independently applied to each of the driving circuits, and each of the driving circuits independently drives its corresponding electrode so that the potential on the electrode is consistent with the potential of the driving signal source applied on the driving circuit; One of the driving circuits drives the main electrode to emit the measurement current into the formation, and the other driving circuits drive the corresponding shielding electrodes to emit shielding currents into the formation; The shielding current constrains the flow path of the measurement current so that the measurement current flows horizontally along the formation; The resistivity value of the formation is calculated by measuring the current value of the measurement current emitted by the main electrode into the formation and the voltage drop generated by the measurement current passing through the formation.

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