Rock core lossless T2 cut-off value testing method and system

Abstract

The invention provides a rock core lossless T2 cut-off value test method and system, and the method comprises the steps: 1, enabling a rock core to be completely saturated with water through a vacuumizing method, and testing the T2 spectrum of the saturated water rock core; 2, sequentially displacing the rock core from low to high by adopting gas drive to remove movable water; 3, heavy water is adopted for sequentially displacing the rock core from low to high at different speeds; and 4, carrying out accumulation calculation on the saturated water T2 spectrum and the T2 spectrum after heavy water displacement, drawing an accumulation T2 curve and determining a T2 cutoff value. According to the method, the movable water is removed through gas drive and heavy water displacement, the problems that in an existing centrifugal method, a rock core is prone to being damaged, and the centrifugal rate is complex to determine are solved, the defect that manganese ions shield boundary movable water in manganese chloride solution displacement is overcome, and the purposes of true lossless effect and high precision are achieved.

Description

Technical Field

[0001] This invention relates to the field of T2 cutoff value testing technology, specifically to a non-destructive T2 cutoff value testing method and system for core samples. Background Technology

[0002] The T2 cutoff value is a key parameter for calculating bound water saturation and permeability in nuclear magnetic resonance logging. Current T2 cutoff value testing mainly uses centrifugation, which has limitations. Centrifugation for removing movable water has several drawbacks: First, determining a suitable centrifugation speed is difficult, requiring trial and error based on the core sample, a time-consuming and labor-intensive process. Second, existing standards cannot completely remove movable water due to differences in core permeability and structure. Third, excessive centrifugation speed can easily damage the core, especially high-permeability porous cores and ultra-low-permeability dense cores, leading to pore structure damage. Furthermore, high-speed centrifugation is also insufficient to effectively remove movable water from the pores of low-permeability dense cores. Therefore, this method negates the advantages of the T2 cutoff value being non-destructive and accurate.

[0003] Patent application CN118642188A discloses a method, apparatus, equipment, and medium for determining the T2 cutoff value using nuclear magnetic resonance (NMR). The method includes: acquiring a first T2 spectrum of a first saturated water rock sample and determining a first cumulative value S1; acquiring a second T2 spectrum of a second saturated water rock sample and determining a second cumulative value S2; determining whether the second cumulative value S2 meets preset conditions; if the second cumulative value S2 meets the preset conditions, acquiring a third T2 spectrum of a rock sample in a bound water state and determining a third cumulative value S3; and determining the T2 cutoff value based on the first T2 spectrum, the first cumulative value S1, the third T2 spectrum, and the third cumulative value S3. However, this patent cannot completely solve the existing technical problems, nor can it meet the needs of this invention. The use of manganese chloride solution for displacement has a shielding effect that is affected by concentration. High concentrations will shield the signal from the solid wall layer or immobile water in the pores, while low concentrations will result in poor shielding of mobile water, causing the T2 cutoff value to lose its accuracy. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a non-destructive T2 cutoff value testing method and system for core samples.

[0005] The non-destructive T2 cutoff value testing method for core samples provided by the present invention includes:

[0006] Step 1: Use the vacuum method to fully saturate the core with water and test the T2 spectrum of the water-saturated core;

[0007] Step 2: Use gas drive to sequentially displace the core from low to high pressure to remove movable water;

[0008] Step 3: Displace the core sample with heavy water at different rates from low to high.

[0009] Step 4: Perform cumulative calculations on the T2 spectrum of saturated water and the T2 spectrum after heavy water displacement, plot the cumulative T2 curve, and determine the T2 cutoff value.

[0010] Preferably, step 2 includes: using air or nitrogen to sequentially displace the core at preset low, medium and high flow rates in multiple stages; increasing the displacement rate when no water is produced; and then performing low-speed air displacement after no water is produced by high-flow-rate air displacement.

[0011] If the air drive still does not produce water after speed adjustment, then stop the air drive.

[0012] Preferably, step 3 includes: starting heavy water displacement when no water is produced after gas drive, using different speeds to displace the core in multiple stages from low to high, and determining the end of displacement by T2 testing during the process. If the T2 spectrum does not change or the change range is within a preset range, then heavy water displacement is stopped.

[0013] Preferably, step 4 includes: accumulating the saturated water T2 spectrum and the heavy water displacement T2 spectrum from the minimum relaxation time to obtain the saturated water accumulation curve and the bound water accumulation curve, respectively.

[0014] Using the maximum value of the accumulated curve of bound water as a reference, draw a straight line perpendicular to the vertical axis. The relaxation time corresponding to the intersection of this line and the accumulated curve of saturated water is the T2 cutoff value.

[0015] Preferably, nuclear magnetic resonance imaging (NMR) tests are performed after both gas-driven and heavy water-driven processes. Specifically, after shutting down the displacement process, the NMR imaging software is turned on, and imaging tests are performed according to preset test parameters.

[0016] The non-destructive T2 cutoff value testing system for core samples provided by the present invention includes:

[0017] Module M1: The core is fully saturated with water using a vacuum method, and the T2 spectrum of the water-saturated core is tested.

[0018] Module M2: Uses air drive to sequentially displace the core from low to high pressure to remove movable water;

[0019] Module M3: Heavy water is used to displace the core at different rates from low to high.

[0020] Module M4: Performs cumulative calculations on the T2 spectrum of saturated water and the T2 spectrum after heavy water displacement, plots the cumulative T2 curve, and determines the T2 cutoff value.

[0021] Preferably, the module M2 includes: using air or nitrogen to sequentially displace the core at preset low, medium and high flow rates in multiple stages; increasing the displacement rate when no water is produced; and then performing low-speed air displacement after no water is produced by high-flow-rate air displacement.

[0022] If the air drive still does not produce water after speed adjustment, then stop the air drive.

[0023] Preferably, the module M3 includes: starting heavy water displacement when no water is produced after gas drive, displacing the core at different speeds in multiple stages from low to high, determining the end of displacement by T2 testing during the process, and stopping heavy water displacement if the T2 spectrum does not change or the change range is within a preset range.

[0024] Preferably, module M4 includes: accumulating the saturated water T2 spectrum and the heavy water displacement T2 spectrum from the minimum relaxation time to obtain the saturated water accumulation curve and the bound water accumulation curve;

[0025] Using the maximum value of the accumulated curve of bound water as a reference, draw a straight line perpendicular to the vertical axis. The relaxation time corresponding to the intersection of this line and the accumulated curve of saturated water is the T2 cutoff value.

[0026] Preferably, nuclear magnetic resonance imaging (NMR) tests are performed after both gas-driven and heavy water-driven processes. Specifically, after shutting down the displacement process, the NMR imaging software is turned on, and imaging tests are performed according to preset test parameters.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) This invention utilizes nuclear magnetic resonance (NMR) technology to distinguish between mobile and bound fluids by obtaining the T2 cutoff value, and identifies the fluid type, estimates porosity and permeability, providing a basis for decision-making in oil and gas reservoir development;

[0029] (2) By using gas drive and heavy water drive to remove movable water, the problems of core damage and complex determination of centrifugation rate in the existing centrifugation method are solved. It also overcomes the shielding of boundary movable water by manganese ions in manganese chloride solution drive, achieving the goal of truly non-destructive and high precision. Attached Figure Description

[0030] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0031] Figure 1 Flowchart of the non-destructive T2 cutoff value test method for core samples;

[0032] Figure 2 This is a schematic diagram illustrating the calculation of the T2 cutoff value. Detailed Implementation

[0033] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0034] Example 1

[0035] like Figure 1 This invention provides a non-destructive T2 cutoff value testing method for core samples. During the T2 cutoff value testing process, after testing the T2 spectrum of saturated water, a combination of gas-driven and heavy water displacement is used to remove mobile water. This method is suitable for both high-permeability, porous cores and dense cores, achieving truly non-destructive and high-precision results. The gas-driven method employs sequential displacement from low to high permeability, with the end of displacement determined by observing the outflow. The heavy water displacement method employs 2-3 different rates (range 0.5 mL / min to 5 mL / min) to sequentially displace the core sample from low to high permeability, with the end of displacement determined by T2 testing.

[0036] If gas-driven pumping fails to remove liquid, switch to heavy water pumping and perform a T2 test. If the T2 spectrum remains largely unchanged, discontinue heavy water pumping. Gas-driven pumping is fast and prone to gas channeling, leaving behind a significant amount of water that is difficult to remove. Control the pumping speed; start with a low speed to facilitate the removal of water from medium and large pores, then increase the speed and pressure to drive out as much water as possible, including water from small pores. For heavy water pumping, start with a low speed to allow the heavy water to fill pores of all sizes, removing residual water from medium and large pores. Increase the pressure (speed) to further remove water from smaller pores.

[0037] It has the following beneficial effects:

[0038] This invention addresses the shortcomings of existing technologies by proposing a novel method for testing the T2 cutoff value using gas-driven and heavy water displacement. Gas-driven displacement removes most of the porous bulk water, followed by heavy water displacement to remove the remaining mobile water. Furthermore, heavy water does not produce detectable NMR signals and replaces the mobile water after displacement, resulting in a clear boundary between mobile and bound water. Since core centrifugation is unnecessary, damage to the core structure is avoided. Gas-driven displacement removes most of the mobile water, reducing the probability of miscibility between heavy and fresh water. This method is applicable not only to conventional cores but also to porous cores of any permeability, enabling truly non-destructive T2 cutoff value testing.

[0039] The heavy water displacement method demonstrates outstanding performance in T2 cutoff value testing experiments on loose sandstone and low-permeability tight cores. It overcomes the drawbacks of core loss, achieves better removal of movable water, and provides higher accuracy, more accurately reflecting reservoir permeability changes. By first testing the T2 cutoff value using gas-drive + heavy water displacement, and then re-saturating with water and performing T2 cutoff value testing using centrifugation, the results showed that the gas-drive + heavy water displacement method was more accurate than the centrifugation method. Imaging tests revealed concentrated movable water residue at the end of the centrifugation process, and core damage was also observed. The experiments demonstrate that the gas-drive + heavy water displacement T2 cutoff value method is feasible, more accurate, and achieves non-destructive and rapid testing of the T2 cutoff value.

[0040] Successful testing of T2 cutoff values ​​on multiple core samples demonstrates that this method has a clear experimental process, simple procedures and operations. By measuring and analyzing T2 spectral data at different stages, the T2 cutoff value can be tested. Furthermore, this method only uses a core displacement nuclear magnetic resonance imaging device, eliminating the need for a centrifuge, thus reducing costs and making it a truly non-destructive method for T2 cutoff value detection.

[0041] Specifically, the experiment was divided into three stages: core pretreatment, nuclear magnetic resonance (NMR) detection, and data processing. The main experimental steps are as follows:

[0042] 1) Use vacuum pumping to fully saturate the core with water. For low-permeability and dense cores, vacuum pumping pressurized water saturation can be used.

[0043] The core was loaded into the core holder of the core displacement nuclear magnetic resonance imaging device, and the T2 spectrum and imaging were tested.

[0044] Specifically: close the process, run the T2 test software, set the parameters, click test, and complete the T2 spectrum test; then open the imaging software, set the test parameters, and click the imaging test button to perform the test.

[0045] 2) Adjust the process: Displace the core with air or nitrogen at low, medium, and high flow rates in multiple stages. If no water is produced, increase the displacement rate. If no water is produced after high-rate displacement, switch to low-rate air displacement. If no water is produced after adjusting the rate, stop air displacement. Alternatively, test the T2 spectrum after no water is produced by air displacement. Stop air displacement if the area of ​​the T2 spectrum changes by no more than 3% in three consecutive tests.

[0046] 3) Displace the core with heavy water at a flow rate of 0.5 mL / m to 5 mL / min, gradually increasing (2 to 3 levels). After the water stops flowing, close the process and test the T2 spectrum. After three consecutive T2 spectra that show almost no change, perform the imaging test. Close the process, open the NMR imaging software, set the test parameters, and click the test button to perform the imaging test.

[0047] 4) Accumulate the T2 spectrum data of saturated water and the T2 spectrum data after heavy water displacement, plot two accumulated T2 curves, and then obtain the T2 cutoff value according to the cutoff value processing method.

[0048] The method involves first testing the spectrum of a core sample under saturated water conditions, and then testing the spectrum of a core sample after removing movable water. The two spectra are accumulated starting from the minimum relaxation time to obtain the accumulated spectrum curves for saturated water and bound water. A straight line perpendicular to the vertical axis is drawn from the maximum value of the accumulated spectrum curve, intersecting the accumulated spectrum curve for saturated water at a single point. The value corresponding to this point is the cutoff value. Figure 2 As shown, the relaxation time where the green line intersects the x-axis is the cutoff value.

[0049] Example 2

[0050] The present invention also provides a non-destructive T2 cutoff value testing system for core samples. The non-destructive T2 cutoff value testing system for core samples can be implemented by executing the process steps of the non-destructive T2 cutoff value testing method for core samples. That is, those skilled in the art can understand the non-destructive T2 cutoff value testing method for core samples as a preferred embodiment of the non-destructive T2 cutoff value testing system for core samples.

[0051] The system includes: Module M1: using vacuum method to fully saturate the core with water and test the T2 spectrum of the water-saturated core; Module M2: using gas drive to sequentially displace the core from low to high to remove movable water; Module M3: using heavy water to sequentially displace the core from low to high at different rates; Module M4: performing cumulative calculations on the T2 spectrum of saturated water and the T2 spectrum after heavy water displacement, plotting the cumulative T2 curve and determining the T2 cutoff value.

[0052] The module M2 includes: using air or nitrogen to sequentially displace the core at preset low, medium and high flow rates in multiple stages; increasing the displacement rate when no water is produced; and then performing low-speed air displacement after no water is produced by high-flow-rate air displacement.

[0053] If the air drive still does not produce water after speed adjustment, then stop the air drive.

[0054] The module M3 includes: starting heavy water displacement when no water is produced after gas drive, using different speeds to displace the core in multiple stages from low to high, determining the end of displacement through T2 testing during the process, and stopping heavy water displacement if the T2 spectrum does not change or the change range is within the preset range.

[0055] The module M4 includes: accumulating the T2 spectrum of saturated water and the T2 spectrum after heavy water displacement, respectively, starting from the minimum relaxation time, to obtain the saturated water accumulation curve and the bound water accumulation curve; drawing a straight line perpendicular to the vertical axis with the maximum value of the bound water accumulation curve as the reference, and the relaxation time corresponding to the intersection of this straight line and the saturated water accumulation curve is the T2 cutoff value.

[0056] Nuclear magnetic resonance imaging (NMR) tests were performed after both gas-driven and heavy-water-driven processes. Specifically, after shutting down the displacement process, the NMR software was turned on, and imaging tests were performed according to preset test parameters.

[0057] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0058] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A non-destructive method for testing the T2 cutoff value of rock cores, characterized in that, include: Step 1: Use the vacuum method to fully saturate the core with water and test the T2 spectrum of the water-saturated core; Step 2: Use gas drive to sequentially displace the core from low to high pressure to remove movable water; Step 3: Displace the core sample with heavy water at different rates from low to high. Step 4: Perform cumulative calculations on the T2 spectrum of saturated water and the T2 spectrum after heavy water displacement, plot the cumulative T2 curve, and determine the T2 cutoff value.

2. The non-destructive T2 cutoff value testing method for core samples according to claim 1, characterized in that, Step 2 includes: using air or nitrogen to sequentially displace the core at preset low, medium and high flow rates in multiple stages; increasing the displacement rate when no water is produced; and then performing low-speed air displacement after no water is produced by high-flow-rate air displacement. If the air drive still does not produce water after speed adjustment, then stop the air drive.

3. The non-destructive T2 cutoff value testing method for core samples according to claim 2, characterized in that, Step 3 includes: starting heavy water displacement when no water is produced after gas drive, using different speeds to displace the core in multiple stages from low to high, and determining the end of displacement by T2 testing during the process. If the T2 spectrum does not change or the change range is within the preset range, then heavy water displacement is stopped.

4. The method for non-destructive T2 cutoff value testing of core samples according to claim 1, characterized in that, Step 4 includes: accumulating the T2 spectrum of saturated water and the T2 spectrum after heavy water displacement, respectively, starting from the minimum relaxation time, to obtain the saturated water accumulation curve and the bound water accumulation curve; Using the maximum value of the accumulated curve of bound water as a reference, draw a straight line perpendicular to the vertical axis. The relaxation time corresponding to the intersection of this line and the accumulated curve of saturated water is the T2 cutoff value.

5. The method for non-destructive testing of T2 cutoff value in core samples according to claim 1, characterized in that, Nuclear magnetic resonance imaging (NMR) tests were performed after both gas-driven and heavy-water-driven processes. Specifically, after shutting down the displacement process, the NMR software was turned on, and imaging tests were performed according to the preset test parameters.

6. A non-destructive T2 cutoff value testing system for rock cores, characterized in that, include: Module M1: The core is fully saturated with water using a vacuum method, and the T2 spectrum of the water-saturated core is tested. Module M2: Uses air drive to sequentially displace the core from low to high pressure to remove movable water; Module M3: Heavy water is used to displace the core at different rates from low to high. Module M4: Performs cumulative calculations on the T2 spectrum of saturated water and the T2 spectrum after heavy water displacement, plots the cumulative T2 curve, and determines the T2 cutoff value.

7. The non-destructive T2 cutoff value testing system for core samples according to claim 6, characterized in that, The module M2 includes: using air or nitrogen to sequentially displace the core at preset low, medium and high flow rates in multiple stages; increasing the displacement rate when no water is produced; and then performing low-speed air displacement after no water is produced by high-flow-rate air displacement. If the air drive still does not produce water after speed adjustment, then stop the air drive.

8. The non-destructive T2 cutoff value testing system for core samples according to claim 7, characterized in that, Step 3 includes: starting heavy water displacement when no water is produced after gas drive, using different speeds to displace the core in multiple stages from low to high, and determining the end of displacement by T2 testing during the process. If the T2 spectrum does not change or the change range is within the preset range, then heavy water displacement is stopped.

9. The non-destructive T2 cutoff value testing system for core samples according to claim 6, characterized in that, The module M4 includes: accumulating the T2 spectrum of saturated water and the T2 spectrum after heavy water displacement, respectively, starting from the minimum relaxation time, to obtain the saturated water accumulation curve and the bound water accumulation curve; Using the maximum value of the accumulated curve of bound water as a reference, draw a straight line perpendicular to the vertical axis. The relaxation time corresponding to the intersection of this line and the accumulated curve of saturated water is the T2 cutoff value.

10. The non-destructive T2 cutoff value testing system for core samples according to claim 6, characterized in that, Nuclear magnetic resonance imaging (NMR) tests were performed after both gas-driven and heavy-water-driven processes. Specifically, after shutting down the displacement process, the NMR software was turned on, and imaging tests were performed according to preset test parameters.

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