Nano tracer agent and shale matrix pore water content calculation method

Abstract

The invention relates to the technical field of shale, in particular to a nano tracer agent and a shale matrix pore water content calculation method, and the nano tracer agent comprises hexamethyl phosphonite triamide (HMPT) (boiling point is 233 DEG C), n-decane (C10H22) (boiling point is 233 DEG C) and radioactive reagent sodium iodide. Through a tracer experiment, the water content in the pores of the shale matrix can be calculated by utilizing the tracer concentrations of different pores, and the problem of water content calculation is solved from the microscopic distribution level.

Description

Technical Field

[0001] This invention relates to the field of shale technology, specifically to a nano-tracer and a method for calculating the pore water content of shale matrix. Background Technology

[0002] Shale gas is a relatively clean fossil energy source, often existing in adsorbed, free, and dissolved states within shale formations. It is a currently attracting significant attention as a clean energy source. However, current shale gas extraction processes often encounter problems such as unpredictable water production and abnormally high backflow rates, making the efficient development of shale gas in the future particularly crucial.

[0003] Previous studies have extensively investigated the distribution of water in shale. Currently, shale pores are generally classified into two main categories: organic pores and inorganic mineral pores. The gas and water content varies among different types of micropores. Korb (2014), through closed-core nuclear magnetic resonance (NMR) analysis of oil shale, concluded that shale oil is primarily found in kerogen pores, while water is mainly found in inorganic mineral pores (Korb et al., 2014). However, different scholars hold differing views on the gas-water distribution within organic pores. Hu et al., based on molecular simulation methods, found that the functional group properties, pore size, and morphological characteristics of organic pore surfaces may contribute to their hydrophilicity (Hu et al., 2014). Regarding inorganic mineral pores, scholars both domestically and internationally generally believe that inorganic mineral surfaces typically exhibit strong hydrophilicity. Taking clay minerals as an example, water molecules can be tightly bound to clay particles through electrostatic forces, hydrogen bonds, and intermolecular forces, forming a water film approximately 0.3-0.4 nm thick on the surface. Based on the state of existence, water can be classified into structural water, interlayer water, adsorbed water (bound water), and free water (Passey et al., 2010). For raw shale samples, some researchers have used TRA (Tight Rock Analysis) technology to measure and calculate that the bound water content in shale clay can reach 2.63%–7.19% of the total volume (Li Jing, 2017). The research team of Xiao Xianming, Tian Hui, and others proposed that the occurrence state of primary water includes three categories: mineral or organic matter bound water, surface adsorbed or capillary bound water, and free water in pores. Through experiments, they found that primary water in shale has a significant impact on in-situ gas content and gas content. However, current technologies lack methods for calculating the pore water content of the shale matrix. Summary of the Invention

[0004] The purpose of this invention is to provide a nano-tracer and a method for calculating the pore water content of shale matrix, thereby solving the technical problem that there is no method for calculating the pore water content of shale matrix in the prior art.

[0005] This invention discloses a nano-tracer comprising hexamethylphosphonotriamine (HMPT) (boiling point 233°C) and n-decane (C 10 H22 (boiling point 233℃) and radioactive sodium iodide, in a volume ratio of 10:30:1.

[0006] Furthermore, the hexamethylphosphonotriamine, n-decane, and radioactive sodium iodide are synthesized after extraction and purification using chloroalkyl extracts.

[0007] A method for calculating the pore water content of shale matrix with nano-tracers includes the following steps:

[0008] S1. Synthesis of radioactive nano-tracers;

[0009] S2. Obtain downhole temperature T1, pressure P1, and determine production pressure differential ΔP;

[0010] S3. Under high temperature and high pressure conditions, a saturated diffusion experiment was conducted on formation water containing nano-tracers;

[0011] S4. Reconstruct the three-dimensional spatial structure distribution of nanotracers through monitoring of nanotracers;

[0012] S5. Calculate the pore water content of the shale matrix using the formula.

[0013] Furthermore, the nano-tracer includes hexamethylphosphonic triamine, n-decane, and the radioactive reagent sodium iodide.

[0014] Furthermore, the downhole temperature T1, pressure P1, and production pressure differential ΔP are obtained through the fracturing construction diagnostic test (DFIT) method.

[0015] Furthermore, the specific steps of the saturated diffusion experiment in step S3 are as follows:

[0016] The shale sample was first cut into cubes, then degassed, and then brought to full saturation. The formation temperature (T=T1) and pressure (P=P1) were set, and the tracer diffusion time was set to 12 hours.

[0017] Furthermore, the reconstructing of the three-dimensional spatial structure distribution of the nano-tracer involves using single-photon emission computed tomography (SPECT) imaging equipment to scan the sample micro-area, recording the location, energy, and count information of the radioactive tracer. A computer system then uses a 3D Gaussian model to reconstruct the data and generate images based on the data recorded by the detector. Based on the distribution and flow channels of the tracer within the shale, images representing the fluid distribution and seepage channels are generated. These images can display information such as the distribution state of shale matrix water, its occurrence space, and flow channels.

[0018] Furthermore, the formula is C i =V o C0 / (V i +Vo )(Formula I)

[0019] V i =(V2C0-C i V2)(Form II)

[0020]

[0021] Qa=αVa

[0022] Ci represents the tracer concentration in any pore under experimental conditions, in mg / m³. 3 C0 represents the initial tracer concentration, in mg / m³. 3 V0 represents the original volume of formation water containing the tracer, in cm³. 3 Vi represents the water content in each pore, expressed in cm³. 3 Va represents the total water content in the shale matrix pores, in cm³. 3 α is the temperature and pressure correction coefficient, which is used to correct laboratory conditions to formation temperature and pressure conditions.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. By using a tracer experiment, the water content in the pores of the shale matrix can be calculated using tracer concentrations at different pore sizes, thus solving the problem of water content calculation at the microscopic distribution level;

[0025] 2. Taking into account the high temperature and high pressure environment of shale formations, the water content of the pores in the actual formations was obtained through temperature and pressure correction. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the process of the present invention.

[0028] Figure 2 This is a schematic diagram of the saturated diffusion experiment of high-temperature and high-pressure formation water containing tracers according to the present invention.

[0029] Figure 3 This is a schematic diagram of the three-dimensional spatial structure reconstruction and data generation of the nano-tracer of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0031] Example 1

[0032] This embodiment discloses a method for calculating the pore water content of shale matrix based on a nano-tracer. Data was collected from a key well (Well A) in Luzhou, Sichuan Province. Systematic sampling of various layers of shale in the Wufeng-Longmaxi Formation was conducted, avoiding fractured areas as much as possible. Tracer experiments and matrix pore water content calculations were performed. Figure 1-3 As shown, it includes the following steps:

[0033] S1. Nano-tracer materials were synthesized by mixing hexamethylphosphonotriamine (HMPT) (boiling point 233℃), n-decane (C10H22) (boiling point 233℃) and radioactive sodium iodide in a volume ratio of 10:30:1.

[0034] S2. Obtain downhole temperature T1 (25℃) and pressure P1 (5MPa) using the Fracturing Construction Diagnostic Test (DFIT) method;

[0035] S3. Shale samples were made into small cubes and saturated diffusion experiments were conducted on formation water containing nano-tracers to obtain the tracer concentration distribution results at different pore locations: C1, C2, C3, C4, Ci….

[0036] S4. Reconstruct the three-dimensional spatial structure distribution of nanotracers through monitoring of nanotracers;

[0037] Specifically, single-photon emission computed tomography (SPECT) imaging equipment is used to scan the micro-area of ​​the sample, recording the location, energy, and count information of the radioactive tracer. A computer system then uses a 3D Gaussian model to reconstruct the data and generate images based on the data recorded by the detector. Based on the distribution and flow channels of the tracer within the shale, images representing fluid distribution and seepage channels are generated. These images can display information such as the distribution, storage space, and flow channels of shale matrix water.

[0038] S5. Calculate the pore water content of the shale matrix using the formula:

[0039] Ci = VoC0 / (Vi + Vo) (Equation I)

[0040] Vi=(V2C0-CiV2)(Equation II)

[0041]

[0042] By comparing the concentration distribution results of different pores (C1, C2, C3, C4, Ci…) obtained from tracer concentration experiments with the original concentration, the water content of different pores can be obtained. Then, by cumulatively calculating the water content of all pores, the total water content of the sample is found to be 0.3638 cm³. 3 Dividing this by the sample mass (20.8g), the moisture content can be determined to be 16.62 cm³. 3 / kg.

[0043] Example 2

[0044] In this embodiment, which is a preferred embodiment of the present invention, the improvement on the basis of embodiment 1 is only to add a correction coefficient α that takes into account the high temperature and high pressure conditions downhole. This is because shale gas development is now mainly based on deep formations, and the temperature and pressure of the early correction coefficients are low and do not meet the deep formation conditions.

[0045] This embodiment employs a nano-tracer and a method for calculating the pore water content of shale matrix using the aforementioned device, such as... Figure 1-3 As shown, it includes the following steps:

[0046] S1. Nano-tracer materials were synthesized by mixing hexamethylphosphonotriamine (HMPT) (boiling point 233℃), n-decane (C10H22) (boiling point 233℃) and radioactive sodium iodide in a volume ratio of 10:30:1.

[0047] S2. Obtain downhole temperature T1 (95℃), pressure P1 (80MPa), and determine production pressure differential ΔP (40MPa) using the Fracturing Construction Diagnostic Test (DFIT) method;

[0048] By comparing the concentration distribution results of different pores (C1, C2, C3, C4, Ci…) obtained from tracer concentration experiments with the original concentration, the water content of different pores can be obtained. Then, by cumulatively calculating the water content of all pores, the total water content of the sample is found to be 0.3638 cm³. 3 Divide this by the sample mass (20.8g), and multiply by the correction factor α = 0.85 under normal temperature and pressure. The resulting moisture content is 14.87 cm³. 3 / kg.

[0049] In addition, pressure-controlled coring was performed on the same shale samples from this well. The cored shale samples were then rapidly sealed with wax and sent to the laboratory. The shale was then thoroughly crushed, and the water content was tested using distillation, yielding a water content of 15.64 cm³. 3 / kg, which is close to the pore water content calculated based on tracer experiments in this patent, proving the feasibility of this technical solution.

[0050] In summary, it can be seen that, among the two cases, Case 2, which considers temperature and pressure correction coefficients, has a more adaptable method and is better able to meet the actual situation of deep shale gas.

[0051] Comparative Example 1

[0052] In this embodiment, which serves as a comparative example of the present invention, the improvement on Example 1 is only in the tracer material. Trimethylamine is used instead of hexamethylphosphonotriamine (HMPT) as a reagent in the organic synthesis reaction. However, its boiling point is only about 2.9°C (37.2°F). At room temperature (25°C), its volatility is high, making it impossible to synthesize a stable organic tracer material. Furthermore, in the saturated diffusion experiment of formation water containing nano-tracers, the spatial distribution of the tracer cannot be clearly and accurately monitored, resulting in unsatisfactory application effects.

[0053] Comparative Example 2

[0054] In this embodiment, which serves as a comparative example of the present invention, the only improvement on Example 1 is the use of commonly used Wood's alloy nanomaterials as tracers. Under the same conditions, the same steps and the same testing methods are used, and Wood's alloy nanomaterials are used as geological probes to clarify the water content distribution in shale.

[0055] Wood's alloy (WU-DU alloy) is an unconventional nickel-based alloy developed by the First Nuclear Engineering Co., Ltd. of China National Nuclear Corporation. Its main components are nickel, molybdenum, cobalt, and iron, with a molybdenum content exceeding 20%, which significantly improves the material's corrosion resistance and high-temperature strength. It can also be fabricated into nanoprobes. Due to its excellent oxidation resistance and high-temperature strength, Wood's alloy maintains stable performance at high temperatures for extended periods, making it widely used in aerospace engines, underground oil and gas extraction, and other fields.

[0056] The specific method is as follows:

[0057] S1. Purchase readily available Wood's alloy and process it to synthesize nano-tracer materials;

[0058] S2. Obtain downhole temperature T1 (95℃), pressure P1 (80MPa), and determine production pressure differential ΔP (40MPa) using the Fracturing Construction Diagnostic Test (DFIT) method;

[0059] S3 injected Wood's alloy nanoprobes into shale under pressure to obtain the distribution of Wood's alloy.

[0060] However, since Wood's alloy is a metallic nanoprobe and is not hydrophilic, it cannot characterize the distribution of water within the micro- and nano-pores of shale, nor can it calculate the distribution of water in the shale matrix, ultimately making it impossible to measure the porosity within the micro- and nano-pores.

[0061] The above are the embodiments listed in this example. However, this example is not limited to the optional embodiments described above. Those skilled in the art can arbitrarily combine the above methods to obtain other various embodiments. Anyone can derive other various forms of embodiments based on the inspiration of this example. The above specific embodiments should not be construed as limiting the scope of protection of this example. The scope of protection of this example should be determined by the claims, and the specification can be used to interpret the claims.

Claims

1. A nano-tracer, characterized in that: It includes hexamethylphosphonic triamine, n-decane, and the radioactive reagent sodium iodide.

2. The nano-tracer according to claim 1, characterized in that: The hexamethylphosphonotriamine, n-decane, and radioactive sodium iodide were synthesized by extraction and purification with chloroalkyl.

3. A method for calculating the pore water content of shale matrix with nano-tracers, characterized in that: Includes the following steps: S1. Synthesis of radioactive nano-tracers; S2. Obtain downhole temperature T1, pressure P1, and determine production pressure differential ΔP; S3. Under high temperature and high pressure conditions, a saturated diffusion experiment was conducted on formation water containing nano-tracers; S4. Reconstruct the three-dimensional spatial structure distribution of nanotracers through monitoring of nanotracers; S5. Calculate the pore water content of the shale matrix using the formula.

4. The method for calculating the pore water content of shale matrix with nano-tracers according to claim 3, characterized in that: The nano-tracer comprises hexamethylphosphonic triamine, n-decane, and the radioactive reagent sodium iodide.

5. The method for calculating the pore water content of shale matrix with nano-tracers according to claim 3, characterized in that: The downhole temperature T1, pressure P1, and production pressure differential ΔP were obtained using the Fracturing Construction Diagnostic Test (DFIT) method.

6. The method for calculating the pore water content of shale matrix with nano-tracers according to claim 3, characterized in that: The specific steps of the saturated diffusion experiment in step S3 are as follows: The shale sample was first cut into cubes, then degassed, and then brought to full saturation. The formation temperature (T=T1) and pressure (P=P1) were set, and the tracer diffusion time was set to 12 hours.

7. The method for calculating the pore water content of shale matrix with nano-tracers according to claim 3, characterized in that: The reconstruction of the three-dimensional spatial structure distribution of the nanotracer involves using single-photon emission computed tomography (SPECT) imaging equipment to scan the sample micro-area, recording the location, energy, and count information of the radioactive tracer. A computer system then uses a 3D Gaussian model to reconstruct the data and generate images based on the data recorded by the detector. Based on the distribution and flow channels of the tracer within the shale, images representing the fluid distribution and seepage channels are generated. These images can display information such as the distribution state, storage space, and flow channels of the shale matrix water.

8. The method for calculating the pore water content of shale matrix with nano-tracers according to claim 6, characterized in that: The formula is C i =V o C0 / (V i +V o )(Formula I) V i =(V2C0-C i V2)(Form II) Qa=αVa Ci represents the tracer concentration in any pore under experimental conditions, in mg / m³. 3 C0 represents the initial tracer concentration, in mg / m³. 3 V0 represents the original volume of formation water containing the tracer, in cm³. 3 Vi represents the water content in each pore, expressed in cm³. 3 Va represents the total pore water content of the shale matrix, in cm³. 3 α is the temperature and pressure correction coefficient, which is used to correct laboratory conditions to formation temperature and pressure conditions.

9. An application of a method for calculating the pore water content of shale matrix with nano-tracers, characterized in that: Used for calculating the pore water content of shale matrix.

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