Laboratory Measurement Methods and Apparatus for High-Temperature Nuclear Magnetic Resonance in Rock Cores

Abstract

This invention discloses a laboratory method and apparatus for high-temperature nuclear magnetic resonance (NMR) measurement of rock cores. The method involves wrapping a hydrophobic thin film material around a rock sample saturated with formation fluid; completely encasing the sample with the hydrophobic film material in a sealing colloid; heating the sealed rock sample to formation temperature; and then acquiring the first NMR T2 spectrum of the sample under specific test conditions. The colloid shell is then peeled off from the tested rock sample and reassembled to its original shape. The reassembled shell is then heated to the aforementioned formation temperature, and a second NMR T2 spectrum is acquired again under the same test conditions. Finally, based on the first and second NMR T2 spectra, the high-temperature NMR T2 spectrum of the rock core is successfully obtained. This method overcomes the fluid loss of the rock core under high-temperature conditions, making the measurement results more reflective of the NMR T2 spectrum characteristics of the actual formation rock core, thereby achieving accurate laboratory measurement of high-temperature NMR in rock cores.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration technology, and in particular to a laboratory measurement method and apparatus for high-temperature nuclear magnetic resonance in rock cores. Background Technology

[0002] With advancements in oil and gas technology and continuous increases in drilling depth, deep oil and gas reservoirs have become a crucial area for breakthroughs in onshore oil and gas exploration and large-scale reserve increases in my country. Due to their great depth, deep oil and gas reservoirs have vastly different in-situ environments compared to the surface, with temperatures typically exceeding 100°C.

[0003] Nuclear magnetic resonance (NMR) is currently the only geophysical technique that can simultaneously reflect porosity and fluid information. It has been widely used in rock physics experiments and well logging evaluation, achieving good results in reservoir property parameter calculation and fluid identification. Existing research shows that the NMR T2 spectra of fluids at different temperatures vary greatly, which also affects the NMR T2 spectral characteristics of formation rocks. This means that the NMR T2 spectra of cores measured under ambient surface conditions cannot reflect the true NMR T2 spectral characteristics of the formation.

[0004] Measuring high-temperature nuclear magnetic resonance (NMR) in rock cores in the laboratory presents challenges: under high-temperature conditions, the fluid (water or crude oil) in the pores of the rock core dissipates rapidly, leading to significantly lower measurement results. Therefore, it is necessary to design a laboratory method for measuring high-temperature NMR in rock cores that does not involve fluid loss during the measurement process. Summary of the Invention

[0005] The purpose of this invention is to provide a laboratory measurement method for high-temperature nuclear magnetic resonance of rock cores. This method overcomes the fluid loss of rock cores under high-temperature conditions, and makes the measurement results more reflective of the nuclear magnetic T2 spectrum characteristics of real strata rock cores, thereby achieving accurate determination of strata porosity and fluid information.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] A laboratory method for high-temperature nuclear magnetic resonance (NMR) measurement of rock cores, the method comprising:

[0008] A hydrophobic thin film material was wrapped around a rock sample saturated with formation fluid.

[0009] Completely cover the rock sample containing the hydrophobic film material with a sealing colloid.

[0010] The rock sample sealed in colloid was heated to the formation temperature, and then the first nuclear magnetic resonance T2 spectrum of the rock sample was collected under specific test conditions;

[0011] The gelatinous shell was peeled off from the tested rock sample and then reassembled to its original shape.

[0012] The assembled gel shell was heated to the formation temperature, and the second NMR T2 spectrum was reacquired under the same test conditions;

[0013] Based on the first and second NMR T2 spectra, the high-temperature NMR T2 spectra of the core were obtained.

[0014] As a further improvement of the present invention, obtaining the high-temperature nuclear magnetic resonance T2 spectrum of the core based on the first NMR T2 spectrum and the second NMR T2 spectrum includes:

[0015] The difference between the first NMR T2 spectrum and the second NMR T2 spectrum is obtained, and the difference is the high-temperature NMR T2 spectrum of the core.

[0016] As a further improvement of the present invention, the specific test conditions include:

[0017] The NMR test conditions were set as follows: measurement time ≤ 20s, sampling frequency SW 200KHz, resampling wait time TW 4000ms, echo time TE 0.2ms, and number of echoes NECH 5000.

[0018] As a further improvement of the present invention, the sealing colloid includes, but is not limited to, a mixture of epoxy resin and curing agent.

[0019] As a further improvement of the present invention, the complete sealing colloid coating outside the rock sample containing the hydrophobic film material includes:

[0020] A mixture of epoxy resin and curing agent is poured into the bottom of the mold;

[0021] After the bottom has solidified, place the rock sample wrapped with raw material tape, and continue to pour the mixture of epoxy resin and hardener until it covers the rock sample. After the colloid has completely solidified, the sealing colloid is completely wrapped around the rock sample.

[0022] As a further improvement of the present invention, the mold may include, but is not limited to, A4 paper.

[0023] As a further improvement of the present invention, the formation fluid includes:

[0024] Formation water or crude oil.

[0025] As a further improvement of the present invention, the step of peeling the gelatinous shell from the tested rock sample includes:

[0026] First, saw the rubber shell at both the top and bottom ends radially.

[0027] Then cut the remaining plastic shell along the axial direction to keep the shape of the plastic shell intact.

[0028] As a further improvement of the present invention, heating the rock sample sealed with the colloid or the assembled colloid shell to the formation temperature includes:

[0029] Place the rock sample sealed with colloid or the assembled colloid shell in a glass test tube;

[0030] Add fluorinated oil to the glass test tube until it submerges the rock sample or gel shell;

[0031] The rock sample or shell submerged in fluorinated oil is placed in an oven and heated to the formation temperature.

[0032] The present invention also provides a laboratory measurement device for high-temperature nuclear magnetic resonance in rock cores, the device comprising:

[0033] Hydrophobic thin film materials are used to encapsulate rock samples saturated with formation fluids.

[0034] Sealing colloid, used to completely encapsulate rock samples coated with hydrophobic film material;

[0035] The stripping unit is used to strip the gel shell from a rock sample sealed with colloid.

[0036] The assembly unit is used to assemble the peeled-off shells back to their original shape.

[0037] The heating unit is used to heat the rock sample sealed with colloid to the formation temperature, and also to heat the assembled colloid shell to the formation temperature;

[0038] The nuclear magnetic resonance (NMR) instrument is used to collect the first NMR T2 spectrum of a rock sample sealed in a colloid after heating under specific test conditions, and also to collect the second NMR T2 spectrum of a colloid shell assembled after heating under the same test conditions.

[0039] The acquisition unit is used to acquire the high-temperature nuclear magnetic resonance T2 spectrum of the rock core based on the first NMR T2 spectrum and the second NMR T2 spectrum.

[0040] As a further improvement of the present invention, the acquisition unit is used to acquire the difference between the first NMR T2 spectrum and the second NMR T2 spectrum.

[0041] As a further improvement of the present invention, the specific test conditions include:

[0042] The NMR test conditions were set as follows: measurement time ≤ 20s, sampling frequency SW 200KHz, resampling wait time TW 4000ms, echo time TE 0.2ms, and number of echoes NECH 5000.

[0043] As a further improvement of the present invention, the sealing colloid includes, but is not limited to, a mixture of epoxy resin and curing agent.

[0044] The beneficial effects of this invention are:

[0045] The present invention provides a laboratory method and apparatus for high-temperature nuclear magnetic resonance (NMR) measurement of rock cores. This involves: wrapping a hydrophobic thin film material around a rock sample saturated with formation fluid; completely encasing the sample with the hydrophobic film material in a sealing colloid; heating the sealed rock sample to formation temperature; and then acquiring the first NMR T2 spectrum of the sample under specific test conditions. The colloid shell is then peeled off from the tested rock sample and reassembled to its original shape. The reassembled shell is heated to the aforementioned formation temperature, and a second NMR T2 spectrum is acquired again under the same test conditions. Finally, based on the first and second NMR T2 spectra, the high-temperature NMR T2 spectrum of the rock core is successfully obtained. This method overcomes the fluid loss of the rock core under high-temperature conditions, making the measurement results more reflective of the NMR T2 spectrum characteristics of the actual formation rock core, thereby achieving accurate laboratory measurement of high-temperature NMR of rock cores.

[0046] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0047] Figure 1 This is a flowchart of the laboratory measurement method for high-temperature nuclear magnetic resonance in rock cores according to the present invention;

[0048] Figure 2 These are the nuclear magnetic resonance T2 spectra measured twice in Example 1 of this invention;

[0049] Figure 3 The high-temperature nuclear magnetic resonance T2 spectrum of the core in Example 1 of this invention;

[0050] Figure 4 This is the high-temperature nuclear magnetic resonance T2 spectrum of the core in Comparative Example 1 of this invention. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Please refer to Figure 1As shown, this invention involves wrapping a hydrophobic thin film material around a rock sample saturated with formation fluid; completely encasing the rock sample with the hydrophobic film material in a sealing colloid; heating the colloid-sealed rock sample to formation temperature; and then acquiring the first NMR T2 spectrum of the rock sample under specific testing conditions; peeling the colloid shell from the tested rock sample and reassembling the shell to its original shape; heating the reassembled shell to the aforementioned formation temperature and re-acquiring the second NMR T2 spectrum under the same testing conditions; finally, based on the first and second NMR T2 spectra, successfully obtaining the high-temperature NMR T2 spectrum of the rock core. This method overcomes the fluid loss of the rock core under high-temperature conditions, making the measurement results more reflective of the NMR T2 spectrum characteristics of the actual formation rock core, thereby achieving accurate laboratory measurement of high-temperature NMR of the rock core.

[0053] The method is explained in detail below:

[0054] (1) A columnar rock sample (core) can be prepared and the rock sample can be saturated with formation fluid; specifically, the formation fluid can be formation water or crude oil.

[0055] (2) Make a cylindrical mold with a diameter slightly larger than the rock sample and a height slightly higher than the rock sample; the material used to make the mold should be easy to shape and easy to peel off, for example, A4 paper can be used.

[0056] (3) Prepare a mixture of 10g epoxy resin and curing agent, pour it into a mold, and let it solidify for later use. It is worth noting that the sealant used here is a mixture of epoxy resin and curing agent. The purpose is to firmly encapsulate and seal the rock sample saturated with formation fluid within it, while also withstanding a certain degree of high temperature (formation temperature) to prevent the formation fluid in the rock sample from evaporating at high temperatures and affecting the accuracy of the measurement results. Those skilled in the art will readily realize that other types of sealants with similar functions can be substituted without departing from the inventive concept, and all such substitutions should fall within the scope of protection of this invention.

[0057] (4) Prepare 100g of epoxy resin and curing agent, and heat them in an oven for 30 minutes; the ratio of epoxy resin and curing agent is 1:1, and they should be heated separately in the oven at a temperature of 80℃.

[0058] (5) Take out the rock sample saturated with formation fluid, wipe off the surface fluid, wrap it with raw material tape (a hydrophobic film material, which is used to simply seal the rock sample saturated with formation fluid and isolate it from the outside) and place it in the mold. Quickly mix and stir the heated epoxy resin and curing agent evenly, pour it into the mold until it covers the rock sample, let it solidify naturally at room temperature for 60 minutes, peel off the mold and take out the rock sample sealed with colloid.

[0059] (6) Take out the sealed rock sample, put it into a glass test tube, pour in fluorinated oil until the rock sample is submerged, and then place it in an oven to heat to the formation temperature; the purpose of heating the rock sample in fluorinated oil here is to make it heat more evenly.

[0060] (7) Adjust the NMR instrument parameters as follows: sampling frequency SW 200 kHz, repetitive sampling wait time TW 4000 ms, echo time TE 0.2 ms, number of echoes NECH 5000, and set the measurement process to not exceed 20 seconds. Then, remove the heated glass test tube from the oven and quickly place it into the NMR measurement chamber to collect the NMR T2 spectrum. After the measurement is completed, remove the glass test tube and immerse it in cool water for rapid cooling.

[0061] (8) After cooling, take out the rock sample, peel off the rubber shell, and put the rubber shell back together to the original shape (the shape before peeling). Then put it into the peeling test tube and immerse it in fluorinated oil. Put it into the oven and reheat it to the formation temperature. During this period, when peeling off the rubber shell, you can first cut the two ends of the rubber shell along the radial direction, and then cut the remaining rubber shell along the axial direction to keep the shape of the rubber shell intact and facilitate the reassembly.

[0062] (9) Take out the glass test tube heated to the formation temperature and place it in the nuclear magnetic resonance measurement chamber. Collect the nuclear magnetic resonance T2 spectrum again with the same parameters as above. Note that when measuring the high temperature nuclear magnetic resonance T2 spectrum of the gel shell, the shape of the gel shell and the measurement environment should be the same as in step (7).

[0063] (10) Data processing: Export the nuclear magnetic resonance T2 spectrum data of the two measurements. The difference between the two is the high-temperature nuclear magnetic resonance T2 spectrum of the core.

[0064] The present invention also provides a laboratory measurement device for high-temperature nuclear magnetic resonance (NMR) of rock cores. The device includes a hydrophobic thin film material for encapsulating a rock sample saturated with formation fluid; a sealing colloid for completely encapsulating the rock sample encapsulated with the hydrophobic thin film material; a peeling unit for peeling the colloid shell from the rock sample sealed by the colloid; a splicing unit for assembling the peeled colloid shell back to its original shape; a heating unit for heating the rock sample sealed by the colloid to the formation temperature, and also for heating the spliced ​​colloid shell to the formation temperature; an NMR instrument for acquiring a first NMR T2 spectrum of the heated rock sample sealed by the colloid under specific test conditions, and also for acquiring a second NMR T2 spectrum of the heated spliced ​​colloid shell under the same test conditions; and an acquisition unit for acquiring a high-temperature NMR T2 spectrum of the rock core based on the first NMR T2 spectrum and the second NMR T2 spectrum.

[0065] Regarding the aforementioned high-temperature nuclear magnetic resonance laboratory measurement device for rock cores, the specific methods by which each unit performs its operation have been described in detail in the relevant implementation methods, and will not be elaborated upon here.

[0066] The following examples illustrate the laboratory measurement method for high-temperature nuclear magnetic resonance in rock cores according to the present invention.

[0067] Example 1

[0068] The method of this invention is used to measure the high-temperature nuclear magnetic resonance (T2) spectrum of rock cores. The operation method includes the following steps:

[0069] S1. Cut the rock into cylindrical rock samples with a diameter of 2.5cm and a length of 3cm, dry them, and then saturate them with formation water.

[0070] S2. Make a mold with a diameter of 3cm and a height of 4.5cm using A4 paper, and pour 10g of epoxy resin into the mold and let it solidify.

[0071] S3. Prepare 50g of epoxy resin and 50g of curing agent, and put them into an oven set to 80℃ and heat for 30 minutes.

[0072] S4. After wiping the surface of the rock sample dry, wrap it with raw material tape and place it in the mold. Take out the epoxy resin and hardener from the oven and quickly mix them evenly. Pour the mixture into the mold until it covers the rock sample. Let it solidify naturally for 60 minutes and then peel off the mold.

[0073] S5. Take out the sealed rock sample, put it into a glass test tube, pour in fluorinated oil until the rock sample is submerged, and place it in an oven to heat to the formation temperature.

[0074] S6. Adjust the NMR instrument parameters to SW 200 kHz, TW 4000 ms, TE 0.2 ms, NECH 5000. Remove the heated glass test tube from the oven and quickly place it into the NMR measurement chamber to acquire the NMR T2 spectrum. After the measurement is complete, remove the glass test tube and immerse it in cool water for rapid cooling.

[0075] S7. After cooling, take out the rock sample, peel off the gel shell, put the gel shell back together as the original sample, put it into the peeling test tube, immerse it in fluorinated oil, and put it into the oven to reheat to the formation temperature.

[0076] S8. Take out the glass test tube heated to the formation temperature and place it in the nuclear magnetic resonance measurement chamber to collect the nuclear magnetic T2 spectrum again with the same parameters.

[0077] S9. Data processing: Export the NMR T2 spectrum data from the two measurements, such as... Figure 2 As shown, the difference between the two is... Figure 3 The high-temperature nuclear magnetic resonance T2 spectrum of the core shown is obtained by... Figure 2 The curve data of the core + colloidal shell shown can be obtained by subtracting the curve data of the colloidal shell from the curve data of the core. Figure 3 The high-temperature nuclear magnetic resonance T2 spectrum of the core.

[0078] Comparative Example 1

[0079] Without using the method of this invention to seal the core, the core is directly heated and then its high-temperature nuclear magnetic resonance (T2) spectrum is measured. The operation method includes the following steps:

[0080] S1. After drying the rock sample, saturate it with formation water;

[0081] S2. After removing the rock sample and wiping off the surface water and raw material wrapping, place it in a glass test tube and pour in fluorinated oil until the rock sample is submerged. Then place it in an oven and heat it to the formation temperature.

[0082] S3. Adjust the NMR instrument parameters to SW 200 kHz, TW 4000 ms, TE 0.2 ms, NECH 5000. Remove the heated glass test tube from the oven and quickly place it into the NMR measurement chamber to acquire the NMR T2 spectrum.

[0083] S4. Export the acquired NMR T2 spectrum data (see...) Figure 4 ).

[0084] The results of comparing Example 1 and Comparative Example 1 ( Figure 3 and Figure 4 As can be seen, the amplitude of the high-temperature nuclear magnetic resonance T2 spectrum signal of the rock core measured by the method of the present invention (see vertical axis) is much higher than the measurement results of directly heating the rock sample without using the method of the present invention. This indicates that the method of the present invention overcomes the fluid loss of the rock core under high temperature environment and realizes accurate laboratory measurement of high-temperature nuclear magnetic resonance of the rock core.

[0085] In summary, the laboratory measurement method and apparatus for high-temperature nuclear magnetic resonance (NMR) of rock cores provided by this invention involves: wrapping a hydrophobic thin film material around a rock sample saturated with formation fluid; completely encasing the rock sample with the hydrophobic thin film material in a sealing colloid; heating the colloid-sealed rock sample to formation temperature; and then acquiring the first NMR T2 spectrum of the rock sample under specific test conditions; peeling the colloid shell from the tested rock sample and reassembling the shell to its original shape; heating the reassembled shell to the aforementioned formation temperature and re-acquiring the second NMR T2 spectrum under the same test conditions; and finally, successfully obtaining the high-temperature NMR T2 spectrum of the rock core based on the first and second NMR T2 spectra. This method overcomes the fluid loss of the rock core under high-temperature conditions, making the measurement results more reflective of the NMR T2 spectrum characteristics of the actual formation rock core, thereby achieving accurate laboratory measurement of high-temperature NMR of rock cores.

[0086] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laboratory method for high-temperature nuclear magnetic resonance (NMR) measurement of rock cores, the method comprising: A hydrophobic thin film material was wrapped around a rock sample saturated with formation fluid. Completely coating a rock sample with a sealing colloid, which is wrapped with a hydrophobic film material, includes: pouring a mixture of epoxy resin and curing agent into the bottom of a mold; after the bottom has cured, placing the rock sample wrapped with PTFE tape into the mold, and continuing to pour the mixture of epoxy resin and curing agent until it covers the rock sample; and waiting for the colloid to completely cure to complete the complete coating of the rock sample with a sealing colloid. The rock sample sealed in colloid was heated to the formation temperature, and then the first nuclear magnetic resonance T2 spectrum of the rock sample was collected under specific test conditions; The gelatinous shell was peeled off from the tested rock sample and then reassembled to its original shape. The assembled gel shell was heated to the formation temperature, and the second NMR T2 spectrum was re-acquired under the same test conditions; Based on the first and second NMR T2 spectra, the high-temperature NMR T2 spectra of the core were obtained.

2. The method of core high-temperature nuclear magnetic resonance laboratory measurement according to claim 1, wherein, The step of obtaining the high-temperature nuclear magnetic resonance (NMR) T2 spectrum of the core based on the first NMR T2 spectrum and the second NMR T2 spectrum includes: The difference between the first NMR T2 spectrum and the second NMR T2 spectrum is obtained, and the difference is the high-temperature NMR T2 spectrum of the core.

3. The laboratory measurement method for high-temperature nuclear magnetic resonance in rock cores according to claim 1 or 2, wherein, The specific test conditions include: The NMR test conditions were set as follows: measurement time ≤ 20s, sampling frequency 200KHz, resampling wait time 4000ms, echo time 0.2ms, and number of echoes 5000.

4. The laboratory measurement method for high-temperature nuclear magnetic resonance in rock cores according to claim 1, wherein, The sealant is a mixture of epoxy resin and curing agent.

5. The laboratory measurement method for high-temperature nuclear magnetic resonance in rock cores according to claim 1, wherein, The mold is made of A4 paper.

6. The laboratory measurement method for high-temperature nuclear magnetic resonance in rock cores according to claim 1, wherein, The formation fluids include: Formation water or crude oil.

7. The laboratory measurement method for high-temperature nuclear magnetic resonance in rock cores according to claim 1, wherein, The process of removing the gelatinous shell from the tested rock sample includes: First, saw the rubber shell open along the radial direction at both the top and bottom ends; Then saw the remaining plastic shell along the axial direction to keep the shape of the plastic shell intact.

8. The laboratory measurement method for high-temperature nuclear magnetic resonance in rock cores according to claim 1, wherein, Heating the rock sample sealed with colloid or the assembled colloid shell to formation temperature includes: Place the rock sample sealed with colloid or the assembled colloid shell in a glass test tube; Add fluorinated oil to the glass test tube until it submerges the rock sample or gel shell; The rock sample or shell submerged in fluorinated oil is placed in an oven and heated to the formation temperature.

9. A laboratory measuring device for high-temperature nuclear magnetic resonance in rock cores, the device comprising: Hydrophobic thin film materials are used to encapsulate rock samples saturated with formation fluids. A sealing colloid for completely covering a rock sample coated with a hydrophobic film material includes: pouring a mixture of epoxy resin and curing agent into the bottom of a mold; after the bottom has cured, placing the rock sample wrapped with PTFE tape into the mold, and continuing to pour the mixture of epoxy resin and curing agent until it covers the rock sample; and waiting for the colloid to completely cure to complete the complete coating of the rock sample with the sealing colloid. The stripping unit is used to strip the gel shell from a rock sample sealed with colloid. The assembly unit is used to assemble the peeled-off shells back to their original shape. The heating unit is used to heat the rock sample sealed with colloid to the formation temperature, and also to heat the assembled colloid shell to the formation temperature; The nuclear magnetic resonance (NMR) instrument is used to collect the first NMR T2 spectrum of a rock sample sealed in a colloid after heating under specific test conditions, and also to collect the second NMR T2 spectrum of a colloid shell assembled after heating under the same test conditions. The acquisition unit is used to acquire the high-temperature nuclear magnetic resonance T2 spectrum of the rock core based on the first NMR T2 spectrum and the second NMR T2 spectrum.

10. The high-temperature nuclear magnetic resonance laboratory measuring device for rock cores according to claim 9, wherein, The acquisition unit is used to acquire the difference between the first NMR T2 spectrum and the second NMR T2 spectrum.

11. The core high-temperature nuclear magnetic resonance laboratory measuring device according to claim 9 or 10, wherein, The specific test conditions include: The NMR test conditions were set as follows: measurement time ≤ 20s, sampling frequency 200KHz, resampling wait time 4000ms, echo time 0.2ms, and number of echoes 5000.

12. The high-temperature nuclear magnetic resonance laboratory measuring device for rock cores according to claim 9, wherein, The sealant is a mixture of epoxy resin and curing agent.

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