Rock resistivity test method and system suitable for ultra-low permeability sample

Abstract

The invention provides a rock resistivity test method and system suitable for an ultra-low permeability sample, and belongs to the technical field of oil and gas geology tests. According to the test device, the rock water saturation is changed in a pressurization saturation mode, then the rock resistivity at different water saturations is measured, in order to eliminate the influence of external force borne by the rock core on the resistance, the water saturation of the rock core is inversed and monitored based on the nuclear magnetic resonance technology, and the rock resistivity is measured. The change rule of the water saturation, the rock resistivity index and the rock resistivity is determined in combination with the resistivity theory, and a basis is provided for correcting a resistivity logging curve. Compared with a traditional rock resistivity test method, the method has the advantages that the saturation of an ultra-low permeability sample can be changed more easily, a measuring resistor does not need to be taken out from a rock core in the test process, and the influence of water evaporation on the saturation is eliminated; and the special clamp holder is adopted, so that the influence of different stresses at the two ends of the rock core on the resistance value is eliminated, and the test result is more accurate.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas geological testing, and in particular to a rock resistivity testing method and system suitable for ultra-low permeability samples. Background Art

[0002] As an important means of rock physics research, rock resistivity measurement mainly measures rock porosity, resistivity and saturation to obtain the four key parameters in Archie's formula and accurately calculate the formation oil and gas saturation. The change of rock resistivity can intuitively reflect the water content of the rock formation, and assist in calibrating the resistivity logging curve to characterize the oil storage capacity, seepage capacity and fluid properties.

[0003] The domestic rock resistivity measurement mainly adopts the industry standard SY / T6712-2023. After a large number of experimental studies, it is found that the displacement method or centrifugal method in the existing industry standards is not suitable for low-porosity and low-permeability rock samples. The high centrifugal force has high requirements on the equipment and is easy to cause rock sample damage. The displacement method cannot effectively measure the amount of discharged liquid, resulting in large measurement errors, high time costs, and high requirements for test instruments, thus affecting the accuracy of the test. Therefore, it is necessary to establish a set of accurate and effective test methods and systems. Summary of the invention

[0004] Based on the above problems, the purpose of the present invention is to provide a rock resistivity test method and system suitable for ultra-low permeability samples. The present invention adopts the following technical solutions:

[0005] The present invention provides a rock resistivity test method applicable to ultra-low permeability samples, comprising the following steps:

[0006] S1: Select the rock blocks required for the test and process them into standard core samples; prepare the salt solution required for the test according to the mineralization, and measure the resistivity R of the salt solution w ;

[0007] S2: vacuum the core sample. After vacuuming, measure the nuclear magnetic resonance T2 spectrum of the core sample as the base signal and record the spectrum area S0;

[0008] S3: Inject salt solution into the core sample under pressure, release the pressure after a period of time, measure the nuclear magnetic resonance T2 spectrum and rock resistivity of the core sample at this time, and record the spectrum area S1 and resistivity R 01 ;

[0009] S4: Repeat step (3) to measure the NMR T2 spectrum and rock resistivity at different times, and record the spectrum area S at that time. i and resistivity R 0i ;

[0010] S5: Repeat steps (3) and (4) until the nuclear magnetic resonance T2 spectrum of the core sample no longer changes, and the core sample reaches a fully saturated state. Measure the spectrum area S in this state. 饱 and resistivity R 0饱 ;

[0011] S6: Draw the test curve.

[0012] Preferably, in step S1, the salt solution is a sodium chloride solution.

[0013] Preferably, in step S1, the core sample is cylindrical; the core sample is dried to constant weight, and then cooled to room temperature, and then the length and diameter of the core sample are measured.

[0014] Preferably, in step S1, the test curve is drawn including the water saturation S i The relationship curve between the resistivity increase rate I and the porosity φ of the core in the same layer and the formation factor F.

[0015] The present invention provides a rock resistivity test system suitable for ultra-low permeability samples, comprising:

[0016] A core holder, which is used to hold a core sample;

[0017] a resistivity measuring device, the resistivity measuring device measuring the resistivity of the core sample in the core holder;

[0018] A vacuum system, wherein the vacuum system performs a vacuum process on the core sample in the core holder;

[0019] a brine injection system, the brine injection system pressurizing and injecting brine solution into the core sample in the core holder;

[0020] A nuclear magnetic resonance device is used to image the core sample in the core holder.

[0021] Preferably, the core holder comprises an outer cylinder and two insulating rods, both ends of the outer cylinder are provided with end caps with mounting holes in the middle, a rubber sleeve is provided inside the outer cylinder, and both ends of the rubber sleeve are respectively connected to the corresponding end caps;

[0022] The annular area enclosed by the end cover, the rubber sleeve and the outer cylinder is a confining pressure chamber, and the confining pressure chamber is connected to the confining pressure pump;

[0023] The two insulating rods are respectively inserted into the rubber sleeve from both ends of the rubber sleeve, the inner end of the insulating rod is provided with a rod head, the outer end of the insulating rod is provided with a rod head, the insulating rod is sleeved with an annular pad and an adjusting pressure cap, and the adjusting pressure cap is threadedly connected with the mounting hole in the middle of the end cover;

[0024] A metal pipeline is circumferentially arranged inside the insulating rod, with both ends of the metal pipeline exposed, the inner end of the metal pipeline is connected to a guide pad, the guide pad is provided with a seepage flow hole connected to the inner end of the metal pipeline, and the guide pad is provided with a plurality of radial guide grooves on a surface away from the rod head, and each of the guide grooves is connected to the seepage flow hole.

[0025] Preferably, the outer cylinder is provided with a confining pressure fluid injection port connected to the confining pressure pump.

[0026] Preferably, the resistivity measuring device comprises a digital bridge, and the digital bridge is electrically connected to the metal pipeline through an electrode wire.

[0027] Preferably, the evacuation system comprises a vacuum pump, the vacuum pump is connected to the metal pipeline via an exhaust pipe, and an air-water separator is provided on the exhaust pipe.

[0028] Preferably, the brine injection system comprises an intermediate container and a constant pressure pump, the lower part of the intermediate container is connected to the constant pressure pump, the upper part of the intermediate container is connected to the metal pipeline through an injection pipe, and a piston is provided in the intermediate container.

[0029] Compared with the prior art, the beneficial technical effects of the present invention are:

[0030] (1) Compared with the traditional rock resistivity test method, the present invention is applicable to all kinds of rock cores with extremely low permeability, especially low-permeability and ultra-low-permeability rock samples, which makes up for the shortcomings of the current rock resistivity test method; (2) The test process is simple to operate, eliminating the human error caused by the wet weight of the core, and the rock saturation is inverted by nuclear magnetic resonance, making the measurement more accurate; (3) Compared with the centrifugation method in the current standard, for low-permeability samples, extremely high centrifugal force is required to change the saturation, which has high requirements on equipment, and high centrifugal force can easily cause the core to crush. In the test process of this method, it is not necessary to remove the core , ensuring the integrity of the core before and after the test; (4) Compared with the centrifugation method, the core needs to be repeatedly taken out for centrifugation and then put back into the clamp, resulting in different forces at both ends of the core, affecting the test results. This method eliminates this influencing factor; (5) Compared with the displacement method, for low-permeability cores, the end of the clamp cannot effectively measure the displaced liquid, and thus cannot accurately calculate the water saturation. The present invention does not need to measure the displacement, and the test results are more accurate; (6) The present invention completes the test process during the saturation process, which greatly shortens the test time for low-permeability samples and improves the test efficiency.

[0031] In short, the present invention has a simple structure and is easy to connect and operate. The core does not need to be taken out during the test, which avoids the influence of human factors such as repeated loading and unloading and weighing of the core on the test results, and improves the accuracy of rock resistivity measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be further described below in conjunction with the accompanying drawings.

[0033] Figure 1 This is a schematic flow chart of a rock resistivity test method for ultra-low permeability samples in Embodiment 1 of the present invention;

[0034] Figure 2 This is a schematic structural diagram of a rock resistivity test system suitable for ultra-low permeability samples in Embodiment 2 of the present invention;

[0035] Figure 3 It is a structural schematic diagram of a core holder in the second embodiment of the present invention;

[0036] Figure 4 This is a schematic diagram of the structure of the guide pad in the second embodiment of the present invention;

[0037] Figure 5 is the water saturation S in Example 3 of the present invention i Relationship curve with resistance increase rate I;

[0038] Figure 6 The relationship table between the porosity φ and the formation factor F of the core at the same layer in the third embodiment of the present invention is shown;

[0039] Figure 7 is a relationship curve between the porosity φ and the formation factor F of the core at the same layer in Example 3 of the present invention;

[0040] Figure 8 This is the NMR T2 spectrum curve at different water saturations in Example 3 of the present invention.

[0041] Explanation of the reference numerals: 1. core holder; 101. outer cylinder; 102. insulating rod; 103. end cover; 104. rubber sleeve; 105. confining pressure chamber; 106. confining pressure pump; 107. rod head; 108. annular pad; 109. adjusting pressure cap; 110. metal pipeline; 111. guide pad; 112. seepage hole; 113. guide groove; 114. confining pressure fluid injection port; 115. nuclear magnetic resonance probe base; 116. sealing pressure cap; 117. high-precision pressure gauge; 2. core sample; 3. nuclear magnetic resonance device; 4. digital bridge; 5. electrode line; 6. vacuum pump; 7. exhaust pipe; 8. gas-water separator; 9. intermediate container; 10. constant pressure pump; 11. injection pipe; 12. six-way valve; 13. pressure sensor; 14. acquisition system. DETAILED DESCRIPTION

[0042] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0043] Embodiment 1

[0044] like Figure 1 As shown, this embodiment discloses a rock resistivity test method suitable for ultra-low permeability samples, comprising the following steps:

[0045] S1: Select the rock blocks required for the test and process them into standard core samples. The core samples are generally processed into cylindrical shapes. Dry the core samples to constant weight, then cool them to room temperature (generally 25°C), and measure the length and diameter of the core samples.

[0046] Prepare the salt solution required for the test according to the mineralization, and measure the resistivity R of the salt solution w The salt solution can be a sodium chloride solution. The solution prepared in the test is a solution prepared according to the formation water information or a salt solution with the same mineralization as the formation water. All liquids in the test are prepared fluids.

[0047] S2: vacuum the core sample. After vacuuming, measure the nuclear magnetic resonance T2 spectrum of the core sample as the base signal and record the spectrum area S0;

[0048] S3: Inject salt solution into the core sample under pressure, release the pressure after a period of time, measure the nuclear magnetic resonance T2 spectrum and rock resistivity of the core sample at this time, and record the spectrum area S1 and resistivity R 01 ;

[0049] S4: Repeat step 3 to measure the NMR T2 spectrum and rock resistivity at different times, and record the spectrum area S at that time. i and resistivity R 0i ;

[0050] S5: Repeat steps 3 and 4 until the nuclear magnetic resonance T2 spectrum of the core sample no longer changes, and the core sample reaches a fully saturated state. Measure the spectrum area S in this state. 饱 , resistivity R 0饱 ;

[0051] S6: Draw the test curve, including the water saturation S W The relationship curve between the resistivity increase rate I and the porosity φ of the core in the same layer and the formation factor F.

[0052] When the core sample is 100% saturated, its actual spectrum area is: S饱实际 =S 饱 -S0, if the actual spectrum area of ​​the core sample at other times is calculated: S i实际 =S i -S0.

[0053] Water saturation S of core samples w , the calculation formula is S w =100%×(S i实际 / S 饱 ).

[0054] Refer to SY / T6712-2023 standard and calculate the formation factor F of each core according to Archie formula. The calculation formula is F = R0 / R W =a / φ m Resistance increase rate I = R 0i / R0=b / S w n ,. Obtain the lithology coefficient related to lithology in Archie's formula: a; constant related to lithology; m; cementation index; n; saturation index; R w Formation water resistivity (i.e. brine resistivity in step 1); R0 is rock resistivity; Φ is porosity; I is resistivity increase rate. The calculation of NMR porosity is based on the rock sample NMR parameter laboratory measurement specifications.

[0055] Embodiment 2

[0056] like Figure 2 As shown, this embodiment discloses a rock resistivity test system suitable for ultra-low permeability samples, which is used to implement the method described in the first embodiment. The test device includes: a core holder 1, a resistivity measuring device, an evacuation system, a brine injection system and a nuclear magnetic resonance device 3. Among them, the core holder 1 is used to clamp the core sample 2; the resistivity measuring device measures the resistivity of the core sample 2 in the core holder 1; the evacuation system performs vacuum treatment on the core sample 2 in the core holder 1; the brine injection system pressurizes and injects salt solution into the core sample in the core holder 1; and the nuclear magnetic resonance device 3 performs imaging of the core sample 2 in the core holder 1.

[0057] like Figure 3As shown, the core holder 1 includes an outer cylinder 101 and two insulating rods 102, both ends of the outer cylinder 101 are provided with end caps 103 with mounting holes in the middle, and a rubber sleeve 104 is provided inside the outer cylinder 101, and both ends of the rubber sleeve 104 are respectively connected to the corresponding end caps 103. The annular area enclosed by the end cap 103, the rubber sleeve 104 and the outer cylinder 101 is a confining pressure chamber 105, and the confining pressure chamber 105 is connected to the confining pressure pump 106. The outer cylinder 101 is provided with a confining pressure fluid injection port 114 connected to the confining pressure pump 106. The confining pressure pump 106 can be a fluid pump, wherein the fluid injected into the confining pressure chamber 105 can be fluorine oil.

[0058] Two insulating rods 102 are respectively inserted into the rubber sleeve 104 from both ends of the rubber sleeve 104, the inner end of the insulating rod 102 is provided with a rod head 107, the outer end of the insulating rod 102 is provided with a rod head 107, the insulating rod 102 is provided with an annular gasket 108 and an adjusting pressure cap 109, and the adjusting pressure cap 109 is threadedly connected to the mounting hole in the middle of the end cover 103.

[0059] A metal pipeline 110 is circumferentially arranged inside the insulating rod 102, with both ends of the metal pipeline 110 exposed, and the inner end of the metal pipeline 110 is connected to a guide pad 111, on which a seepage flow hole 112 connected to the inner end of the metal pipeline 110 is arranged, and the guide pad 111 is provided with a plurality of radial guide grooves 113 on a surface facing away from the rod head 107, and each guide groove 113 is connected to the seepage flow hole 112.

[0060] In this embodiment, the end caps 103 are threadedly connected to the outer cylinder 101 , and the rubber sleeves 104 are inserted into the tapered ends of the end caps 103 on both sides.

[0061] In this embodiment, the outer cylinder 101, the guide pad 111, the annular pad 108, the internal pipeline 2, and the regulating pressure cap 109 are all made of aluminum alloy.

[0062] In this embodiment, a nuclear magnetic resonance probe base 115 is further installed on the outer cylinder 101 , and the core holder 1 is horizontally placed on the nuclear magnetic resonance device 3 through the nuclear magnetic resonance probe base 115 .

[0063] In this embodiment, a sealing cap 116 is provided at the connection position between the outer end of the insulating rod 102 and the metal pipeline 110. The sealing cap 116 forms a conical seal for the connection between the insulating rod 102 and the metal pipeline 110 to prevent air leakage.

[0064] In this embodiment, a high-precision pressure gauge 117 is also provided, and a signal line of the high-precision pressure gauge 117 is connected between the annular pad 108 and the rod head 107 to collect the forces acting on both ends of the core.

[0065] like Figure 1As shown, the resistivity measuring device includes a digital bridge 4, which is electrically connected to the metal pipeline 110 through an electrode line 5. The evacuation system includes a vacuum pump 6, which is equipped with a vacuum pressure gauge. The vacuum pump 6 is connected to the metal pipeline 110 through an exhaust pipe 7, and an air-water separator 8 is provided on the exhaust pipe 7. The brine injection system includes an intermediate container 9 and a constant pressure pump 10. A piston is provided in the intermediate container 9. The lower part of the intermediate container 9 is connected to the constant pressure pump 10, and the upper part of the intermediate container 9 is connected to the metal pipeline 110 through an injection pipe 11. The space above the piston of the intermediate container 9 is filled with brine. The constant pressure pump 10 pressurizes and injects water below the piston of the intermediate container 9, pushing the piston to inject the brine above into the metal pipeline 110.

[0066] In order to facilitate the connection of the metal pipeline 110 with the vacuum system and the brine injection system, the metal pipeline 110 is connected to the six-way valve 12 through a quick connector, and the vacuum pipeline 7 and the injection pipeline 11 are both connected to the six-way valve 12.

[0067] In this embodiment, a pressure sensor 13 is also installed on the six-way valve 12, and the force sensor 13, the nuclear magnetic resonance device 3 and the digital bridge 4 are all electrically connected to the acquisition system 14. The six valves of the six-way valve are interconnected, and it is a conventional valve component. The pressure sensor 13 can be installed on any valve interface. The six-way valve structure belongs to the prior art.

[0068] The operation process of the present invention is as follows:

[0069] The core sample 2 is placed in the rubber sleeve 104 in the core holder 1, and the pressure caps 109 at both ends are tightened so that the flow guide pads 111 on both sides clamp the core sample 2 in the middle. A certain confining pressure P is applied to the confining pressure chamber 105 through the confining pressure pump 106. 围低 (The confining pressure pump 106 has its own pressure sensor inside), so that the rubber sleeve 104 wraps and fixes the core sample 2.

[0070] Start the vacuum pump 6, open the corresponding valve on the six-way valve 12 connected to the evacuation system to evacuate the core sample 2, close the corresponding valve on the six-way valve 12 connected to the evacuation system after the evacuation is completed, and measure the nuclear magnetic resonance T2 spectrum of the core sample 2 as the base signal through the nuclear magnetic resonance device 3. The spectrum area is S 0。

[0071] Open the valve on the six-way valve 12 connected to the intermediate container 9, adjust the confining pressure pump 106, and increase the confining pressure to P 饱和围 , adjust the pressure of constant pressure pump 10 to P 饱和, the salt solution is injected into the guide pad 111 from the metal pipeline 110 at both ends of the core holder 1 under pressure, and the guide groove 113 distributed above the guide pad 111 guides the salt solution to the end of the core sample 2. After a period of time, the constant pressure pump 10 and the confining pressure pump 106 are adjusted, P 饱和 Drain to 0, P 饱和围 Drain to P 围低 .

[0072] Close and open the valve connected to the intermediate container 9 on the six-way valve 12, open the corresponding valve connected to the evacuation system on the six-way valve 12, and suck the residual brine in the pipelines at both ends of the clamp 7 into the gas-water separator 8, close the evacuation system, test the nuclear magnetic resonance T2 spectrum and rock resistance of the core sample 2 at this time, and calculate the spectrum area S1 and resistivity R under this state 01 .

[0073] Embodiment 3

[0074] Based on the specific structure of the rock resistivity test system for ultra-low permeability samples in Example 2, shale is selected as the test rock sample in this example to simulate its resistivity measurement test process. The specific operation steps are as follows:

[0075] S1: Select the shale rock blocks required for the test, and drill a core column with a size of 25*50mm. Dry the rock sample at 60℃ to constant weight, take out the core, place it in a cooler, cool it to room temperature, test the length and diameter of the core for later use, prepare sodium chloride solution with the same mineralization according to the formation water information of the well site, and measure the resistivity R of the solution w =0.2457Ω·m;

[0076] S2: Place the core to be tested into the core holder 1, tighten the pressure caps 109 at both ends so that the flow guide pads 111 on both sides clamp the core sample 2 in the middle, and adjust the confining pressure pump 106 to apply a certain confining pressure P to the core holder 1. 围低 =2MPa, start the vacuum pump 6, open the corresponding valve on the six-way valve 12 connected to the evacuation system to evacuate the core sample 2, close the corresponding valve on the six-way valve 12 connected to the evacuation system after the evacuation is completed, and measure the nuclear magnetic resonance T2 spectrum of the core sample 2 as the base signal through the nuclear magnetic resonance device 3, and the spectrum area is S0;

[0077] S3: Open the valve on the six-way valve 12 connected to the intermediate container 9, adjust the confining pressure pump 106, and increase the confining pressure to P 饱和围 =22MPa, adjust constant pressure pump 1 to P 饱和 = 20 MPa, and inject salt solution into the end of the core sample 2 from the metal pipeline 110 at both ends of the core holder 1. After 2 hours, adjust the constant pressure pump 10 and the confining pressure pump 106 to increase P 饱和 Discharge to 0MPa, P饱和围 Drain to P 围低 =2MPa, close the system valve, open the corresponding valve on the six-way valve 12 connected to the vacuum system and suck the residual brine in the pipelines at both ends of the core holder 1 into the gas-water separator 8. When the water volume in the gas-water separator 8 no longer increases, close the vacuum system, test the nuclear magnetic resonance T2 spectrum and rock resistance of the rock sample at this time, and calculate the spectrum area S1 and resistivity R in this state 01 ;

[0078] S4: Repeat step (3) to calculate the spectrum area S at different time states i and resistivity R 0i ;

[0079] S6: Water saturation S W The relationship curve with the resistance increase rate I is as follows Figure 5 The corresponding table of the relationship between the porosity φ of the core in the same layer and the formation factor F is shown in Figure 6 The relationship curve between the porosity φ of the core in the same layer and the formation factor F is shown in Figure 7 As shown in Figure 2, the NMR T2 spectrum curves at different water saturations are as follows: Figure 8 The calculation of nuclear magnetic porosity is based on the rock sample nuclear magnetic resonance parameter laboratory measurement specifications.

[0080] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A rock resistivity test method suitable for ultra-low permeability samples, characterized in that: The following steps are involved: S1: Select the rock blocks required for the test and process them into standard core samples; prepare the salt solution required for the test according to the mineralization, and measure the resistivity R of the salt solution w ; S2: vacuum the core sample. After vacuuming, measure the nuclear magnetic resonance T2 spectrum of the core sample as the base signal and record the spectrum area S0; S3: Inject salt solution into the core sample under pressure, release the pressure after a period of time, measure the nuclear magnetic resonance T2 spectrum and rock resistivity of the core sample at this time, and record the spectrum area S1 and resistivity R 01 ; S4: Repeat step (3) to measure the NMR T2 spectrum and rock resistivity at different times, and record the spectrum area S at that time. i and resistivity R 0i ; S5: Repeat steps (3) and (4) until the nuclear magnetic resonance T2 spectrum of the core sample no longer changes, and the core sample reaches a fully saturated state. Measure the spectrum area S in this state. 饱 and resistivity R 0饱 ; S6: Draw the test curve.

2. The rock resistivity test method applicable to ultra-low permeability samples according to claim 1 is characterized in that: In step S1, the salt solution is a sodium chloride solution.

3. The rock resistivity test method applicable to ultra-low permeability samples according to claim 1 is characterized in that: In step S1, the core sample is cylindrical; the core sample is dried to constant weight, and then cooled to room temperature, and the length and diameter of the core sample are measured.

4. The rock resistivity test method applicable to ultra-low permeability samples according to claim 1 is characterized in that: In step S1, a test curve is drawn including water saturation S i The relationship curve between the resistivity increase rate I and the porosity φ of the core in the same layer and the formation factor F.

5. A rock resistivity test system suitable for ultra-low permeability samples, used to implement the rock resistivity test method suitable for ultra-low permeability samples as claimed in claim 1, characterized in that: include: A core holder (1), the core holder (1) being used to hold a core sample (2); a resistivity measuring device for measuring the resistivity of the core sample (2) in the core holder (1); A vacuum system, wherein the vacuum system performs a vacuum process on the core sample (2) in the core holder (1); A salt water injection system, wherein the salt water injection system performs pressurized perfusion of salt solution into the core sample in the core holder (1); A nuclear magnetic resonance device (3) is used to image the core sample (2) in the core holder (1).

6. The rock resistivity test system suitable for ultra-low permeability samples according to claim 5 is characterized in that: The core holder (1) comprises an outer cylinder (101) and two insulating rods (102); both ends of the outer cylinder (101) are provided with end covers (103) with mounting holes in the middle; a rubber sleeve (104) is provided inside the outer cylinder (101); both ends of the rubber sleeve (104) are respectively connected to the corresponding end covers (103); The annular area enclosed by the end cover (103), the rubber sleeve (104) and the outer cylinder (101) is a confining pressure chamber (105), and the confining pressure chamber (105) is connected to a confining pressure pump (106); The two insulating rods (102) are respectively inserted into the rubber sleeve (104) from both ends of the rubber sleeve (104); the inner end of the insulating rod (102) is provided with a rod head (107); the outer end of the insulating rod (102) is provided with a rod head (107); an annular pad (108) and an adjusting pressure cap (109) are sleeved on the insulating rod (102); the adjusting pressure cap (109) is threadedly connected to the mounting hole in the middle of the end cover (103); A metal pipeline (110) is arranged in the circumferential direction inside the insulating rod (102), the two ends of the metal pipeline (110) are exposed, the inner end of the metal pipeline (110) is connected to a flow guide pad (111), the flow guide pad (111) is provided with a seepage flow hole (112) connected to the inner end of the metal pipeline (110), and the flow guide pad (111) is provided with a plurality of radial flow guide grooves (113) on a surface facing away from the rod head (107), and each of the flow guide grooves (113) is connected to the seepage flow hole (112).

7. The rock resistivity test system suitable for ultra-low permeability samples according to claim 6 is characterized in that: The outer cylinder (101) is provided with a confining pressure fluid injection port (114) connected to the confining pressure pump (106).

8. The rock resistivity test system suitable for ultra-low permeability samples according to claim 6 is characterized in that: The resistivity measuring device comprises a digital bridge (4), and the digital bridge (4) is electrically connected to the metal pipeline (110) via an electrode line (5).

9. The rock resistivity test system suitable for ultra-low permeability samples according to claim 6 is characterized in that: The vacuum system comprises a vacuum pump (6), the vacuum pump (6) is connected to the metal pipeline (110) via an air extraction pipeline (7), and an air-water separator (8) is provided on the air extraction pipeline (7).

10. The rock resistivity test system suitable for ultra-low permeability samples according to claim 6, characterized in that: The brine injection system comprises an intermediate container (9) and a constant pressure pump (10), the lower part of the intermediate container (9) is connected to the constant pressure pump (10), the upper part of the intermediate container (9) is connected to the metal pipeline (110) via an injection pipe (11), and a piston is provided in the intermediate container (9).

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