Artificial rock core and preparation method and application thereof

Abstract

The invention provides an artificial rock core as well as a preparation method and application thereof, the preparation method comprises the following steps: taking water, cement and quartz sand, and sequentially carrying out stirring, pressurizing, steaming and soaking treatment to obtain the artificial rock core, wherein the quartz sand comprises quartz sand with the particle size of 6-8 meshes and quartz sand with the particle size of 70-140 meshes. By applying the technical scheme provided by the invention, the prepared artificial rock core has the advantages of larger size, lower permeability, better stability, simple preparation steps and mild preparation conditions, is suitable for large-scale production, and has wide industrial application prospects.

Description

Technical Field

[0001] This application relates to the technical field of oil and gas engineering, and particularly to an artificial core and its preparation method and application. Background Art

[0002] In the process of oil and gas development, core physical simulation experiments are the basic theory for reservoir evaluation and development. A large number of cores are required for repetitive experiments in physical simulation. Since natural cores have complex processes, high difficulty, and high costs, it is difficult to meet the needs of experimental research. Therefore, it is very necessary to find a model that can replace reservoir cores. In China, artificial cores are usually used for simulation experiments, and the control of the pore structure and size of artificial cores is very important.

[0003] The preparation methods of artificial cores in the prior art usually use raw materials such as epoxy resin, quartz sand, and aluminum phosphate cementing structure to make. For example, the patent (application number: CN 114371056 A) discloses a method for preparing a low-porosity and low-permeability dense sandstone artificial core. The main steps of this method are: (1) fully stirring and mixing the ingredients evenly; (2) filling the sand into the mold in multiple times; (3) placing the briquetting mold system on the pressing platform of a hydraulic press for pressing, and then putting it into a core baking oven for heating, heat preservation, and cooling to make a formed rock block; (4) cutting the formed rock block obtained in step (3) into a standard core. The permeability of the low-porosity and low-permeability dense sandstone artificial core prepared by this patent can reach 0.1 - 10 mD, and the porosity can reach 8 - 10%. This preparation method is limited to baking and heating with an oven for cementing, making it difficult to produce large-sized cores, and the conditions are harsh and have certain risks. At the same time, this method uses epoxy resin adhesives, and the pores of the artificial core produced have many non-connected "dead pores", which are quite different from real cores and have certain limitations.

[0004] Based on this, in the face of the technical problems of the artificial cores in the prior art, such as small size, high permeability, or cumbersome preparation steps, there is an urgent need to provide an artificial core and its preparation method to improve the above problems. Summary of the Invention

[0005] The main purpose of the present invention is to provide an artificial core and its preparation method and application to solve the technical problems of the artificial cores in the prior art, such as small size, high permeability, or cumbersome preparation steps.

[0006] To achieve the above object, according to one aspect of the present invention, a preparation method of an artificial core is provided. The preparation method includes: successively stirring, pressure molding, steam curing, and immersion curing of water, cement, and quartz sand to obtain an artificial core; wherein, the quartz sand includes quartz sand with a particle size of 6 - 8 mesh and quartz sand with a particle size of 70 - 140 mesh.

[0007] Further, steam curing specifically includes: taking the cored samples after pressure molding and performing steam curing in a sealed water tank at a treatment temperature of 30 - 70°C for a treatment time of 2 - 4 days; preferably, immersion curing specifically includes: taking the cored samples after steam curing and performing immersion treatment in water at 30 - 70°C for a treatment time of 2 - 4 days.

[0008] Further, by weight percentage, the addition amount of cement accounts for 17 - 35 wt% of the solid-phase raw materials; preferably, the addition amount of quartz sand accounts for 65 - 83 wt% of the weight of the solid-phase raw materials.

[0009] Further, the stirring treatment is carried out in a concrete mixer; preferably, the stirring treatment includes: taking cement and quartz sand for a first stirring treatment, and then adding water for a second stirring treatment to complete the stirring treatment; preferably, the rotation speed of the first stirring treatment is 30 - 60 rpm and the stirring time is 3 - 7 min; preferably, the rotation speed of the second stirring treatment is 30 - 60 rpm and the stirring time is 3 - 7 min.

[0010] Further, the pressure molding is carried out in a core press, the pressure for pressure molding is 10 - 60 MPa, and the pressure application time is 20 - 28 h.

[0011] Further, by weight percentage, the weight ratio of 6 - 8 mesh quartz sand to 70 - 140 mesh quartz sand is (2.5 - 3.5):1.

[0012] Further, after immersion curing, the cored samples after immersion also need to be dried, and the drying treatment is carried out under natural air-drying conditions.

[0013] To achieve the above object, according to one aspect of the present invention, there is provided an artificial core, which is obtained by the above artificial core preparation method.

[0014] Further, the size of the artificial core is: the diameter φ is 110 - 178 mm and the length is 600 - 800 mm; preferably, the porosity of the artificial core is 7 - 30%, and the permeability is 0.01 - 300 mD.

[0015] According to another aspect of the present invention, there is provided an application of the artificial core in the fields of core displacement, rock electricity testing or perforation target shooting.

[0016] The artificial core prepared by applying the technical solution of the present invention has a relatively large size, low permeability, good stability, simple preparation steps, mild preparation conditions, is suitable for large-scale production, and has broad industrial application prospects. Description of the Drawings

[0017] The accompanying drawings forming a part of this invention are used to provide a further understanding of the invention. The schematic embodiments of the invention and their descriptions are used to explain the invention and do not unduly limit the invention. In the drawings:

[0018] Figure 1 It is a schematic diagram of an artificial core prepared according to Embodiment 1 of the present invention. Detailed implementation manners

[0019] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0020] As described in the background art part of the present invention, the artificial cores in the prior art have technical problems such as small size, high permeability, or cumbersome preparation steps. Based on this, the present invention provides a method for preparing an artificial core, which includes: sequentially stirring, pressurizing, steaming, and soaking water, cement, and quartz sand to obtain an artificial core; wherein, the quartz sand includes quartz sand with a particle size of 6-8 mesh and quartz sand with a particle size of 70-140 mesh.

[0021] Based on the fact that the artificial cores in the prior art mostly use oven baking for heating and cementing, it is difficult to make large-sized cores, and the preparation steps are cumbersome and the preparation conditions are harsh, with certain risks. At the same time, the traditional preparation methods mostly use epoxy resin adhesives, and the pores of the artificial cores made have many unconnected "dead pores", which are quite different from real cores and have certain limitations. First of all, the present invention creatively adds steaming and soaking treatments in the preparation process of the artificial core. By using the above treatments, the porosity and permeability of the artificial core can be greatly reduced. Secondly, the preparation steps of the present invention include: sequentially stirring, pressurizing, steaming, and soaking water, cement, and quartz sand to obtain an artificial core; the present invention uses water, cement, and quartz sand as raw materials, which are easy to obtain and have low costs, and have the advantages of easy operation and environmental friendliness. Moreover, the preparation steps of the artificial core provided by the present invention are all controlled by machine equipment, reducing human interference, and having good formula stability. Among them, there is no need to use high-temperature baking in an oven, so that the size of the made core is not limited by the size of the oven. Therefore, the artificial core prepared by this method has a large size, low permeability, good stability, simple preparation steps, mild preparation conditions, is suitable for large-scale production, and has broad industrial application prospects.

[0022] In a preferred embodiment, the steam treatment includes: placing the pressurized material in a closed water tank for steam treatment, with the treatment temperature being 30 - 70°C and the treatment time being 2 - 4 days; further preferably, the soaking treatment includes: placing the post-steam material in water at 30 - 70°C for soaking treatment, with the treatment time being 2 - 4 days, so as to further significantly reduce the porosity and permeability of the artificial core.

[0023] To further control the principle cost and improve the structural stability of the artificial cement, by weight percentage, preferably the addition amount of cement accounts for 17 - 35 wt% of the solid-phase raw materials; by weight percentage, further preferably the addition amount of quartz sand accounts for 65 - 83 wt% of the weight of the solid-phase raw materials.

[0024] In a preferred embodiment, the stirring treatment is carried out in a professional concrete mixer; the stirring treatment includes: taking cement and quartz sand for a primary stirring treatment, and then adding water for a secondary stirring treatment to complete the stirring treatment; preferably, the rotation speed of the primary stirring treatment is 30 - 60 rpm and the stirring time is 3 - 7 min; the rotation speed of the secondary stirring treatment is 30 - 60 rpm and the stirring time is 3 - 7 min, so that the reaction raw materials are mixed more uniformly to obtain a more stable mixed solution.

[0025] To further press the artificial core into shape, preferably the pressing treatment is carried out in a core press, the pressure of the pressing treatment is 10 - 60 MPa, and the pressing time is 20 - 28 h; to further reduce the permeability of the artificial core, by weight percentage, preferably the weight ratio of 6 - 8 mesh quartz sand to 70 - 140 mesh quartz sand is (2.5 - 3.5):1.

[0026] To further remove the residual moisture impurities on the surface of the artificial core, preferably after the soaking treatment, the soaked material needs to be dried, and the drying treatment is carried out under natural air-drying conditions.

[0027] Another aspect of the present invention also provides an artificial core, which is an artificial core prepared by the above-mentioned artificial core preparation method. As described above, this artificial core has a relatively large size, a low permeability, and good stability.

[0028] In a preferred embodiment, the size of this artificial core is: the diameter φ is 110 - 178 mm and the length is 600 - 800 mm; preferably, the porosity of the artificial core is 7 - 30%, and the permeability is 0.01 - 300 m, so as to further improve the structural stability of the artificial core and make its performance better.

[0029] Another aspect of the present invention also provides an application of the artificial core in the fields of core displacement, rock electricity testing, or perforation shooting.

[0030] The following detailed descriptions are all exemplary descriptions, aiming to provide further detailed explanations for the present invention. Unless otherwise specified, all technical terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the present invention are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention.

[0031] Example 1

[0032] Take quartz sand of 6 - 8 mesh, quartz sand of 70 - 140 mesh and cement and mix them in a weight ratio of 1.6:0.5:1 to obtain a mixture. Then place it in a professional concrete mixer and stir for 5 minutes for the first time at a stirring speed of 48 rpm. Add 5500 mL of water and stir for another 5 minutes at a stirring speed of 48 rpm. Pour the stirred core raw material into a core press, turn on the press pump to apply pressure, with the pressure being 60 MPa and the pressurization time being 24 hours to form the core. Take out the core from the press, put it into a closed water tank for steam curing at 50 °C for 3 days, and then soak and cure it in water at 50 °C for 3 days. Dry it under natural air-drying conditions to obtain an artificial core. The artificial core has a diameter of φ178 mm, a length of 800 mm, a porosity of 7.1%, and a permeability of 0.05 mD.

[0033] Example 2

[0034] Take quartz sand of 6 - 8 mesh, quartz sand of 70 - 140 mesh and cement and mix them in a weight ratio of 2.6:1.4:1 to obtain a mixture. Then place it in a professional concrete mixer and stir for 5 minutes for the first time at a stirring speed of 48 rpm. Add 4100 mL of water and stir for another 5 minutes at a stirring speed of 48 rpm. Pour the stirred core raw material into a core press, turn on the press pump to apply pressure, with the pressure being 20 MPa and the pressurization time being 24 hours to form the core. Take out the core from the press, put it into a closed water tank for steam curing at 50 °C for 3 days, and then soak and cure it in water at 50 °C for 3 days. Dry it under natural air-drying conditions to obtain an artificial core. The artificial core has a diameter of φ178 mm, a length of 800 mm, a porosity of 29.5%, and a permeability of 255 mD.

[0035] Comparative Example 1

[0036] The difference from Example 1 is only that there is no steam and soaking treatment. Take quartz sand of 6-8 mesh, quartz sand of 70-140 mesh and cement and mix them according to the weight ratio of 1.6:0.5:1 to obtain a mixture. Then place it in a professional concrete mixer, stir for 5 minutes for the first time at a stirring speed of 48 rpm, add 5500 mL of water and stir for 5 minutes for the second time at a stirring speed of 48 rpm; pour the stirred core raw material into a core press, turn on the press pump to pressurize, the pressure is 60 MPa, and the pressurization time is 24 hours to form the core; take out the core in the press and carry out a consolidation reaction for 6 days under natural conditions. Dry it under natural air-drying conditions to obtain an artificial core. The artificial core has a diameter of φ178 mm, a length of 80 mm, a porosity of 10.5%, and a permeability of 16 mD.

[0037] Performance test:

[0038] 1) Porosity

[0039] The porosity was measured using an SCMS-E type high-temperature and high-pressure core multi-parameter test system under a confining pressure of 5 MPa in accordance with the standard SYT6385-2016 "Determination Method for Rock Porosity and Permeability under Overburden Pressure".

[0040] 2) Permeability

[0041] The permeability was measured using an SCMS-E type high-temperature and high-pressure core multi-parameter test system under a confining pressure of 5 MPa in accordance with the standard SYT6385-2016 "Determination Method for Rock Porosity and Permeability under Overburden Pressure".

[0042] Take the above-mentioned examples and comparative examples for the above performance tests, and the test results are shown in Table 1 below.

[0043] Table 1

[0044] Porosity (%) Permeability (mD) Example 1 7.1 0.05 Example 2 29.5 255 Comparative Example 1 10.5 16

[0045] From the test results of the above examples and comparative examples, the following technical effects can be obtained:

[0046] The artificial core prepared by the present invention has a large size, a low permeability, good stability, simple preparation steps, mild preparation conditions, is suitable for large-scale production, and has broad industrial application prospects.

[0047] It is known from common technical knowledge that the present invention can be implemented by other embodiments that do not depart from its spirit or essential features. Therefore, the above-disclosed embodiments are illustrative in all aspects and are not the only ones. All changes within the scope of the present invention or within the scope equivalent to the present invention are encompassed by the present invention.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent substitutions can still be made to the specific implementation manners of the present invention, and any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for preparing an artificial core, characterized in that, The preparation method includes: taking water, cement and quartz sand, and successively performing stirring, pressure forming, steam curing and immersion curing to obtain the artificial core; wherein, the quartz sand includes quartz sand with a particle size of 6-8 mesh and quartz sand with a particle size of 70-140 mesh.

2. The preparation method of the artificial core according to claim 1, characterized in that, The steam curing specifically includes: taking the pressure-formed core and performing steam curing in a closed water tank, with a treatment temperature of 30-70 °C and a treatment time of 2-4 days; Preferably, the immersion curing specifically includes: taking the steam-cured core and performing immersion treatment in water at 30-70 °C for a treatment time of 2-4 days.

3. The method for preparing an artificial core according to claim 1 or 2, characterized in that, By weight percentage, the addition amount of the cement accounts for 17-35 wt% of the solid-phase raw materials; Preferably, the addition amount of the quartz sand accounts for 65-83 wt% of the weight of the solid-phase raw materials.

4. The preparation method of the artificial core according to any one of claims 1 to 3, characterized in that, The stirring treatment is carried out in a concrete mixer; Preferably, the stirring treatment includes: taking the cement and the quartz sand and performing a primary stirring treatment, and then adding water for a secondary stirring treatment to complete the stirring treatment; Preferably, the rotation speed of the primary stirring treatment is 30-60 rpm, and the stirring time is 3-7 min; Preferably, the rotation speed of the secondary stirring treatment is 30-60 rpm, and the stirring time is 3-7 min.

5. The method for preparing an artificial core according to any one of claims 1 to 4, characterized in that, The pressure forming is carried out in a core press, and the pressure for the pressure forming is 10-60 MPa, and the pressure application time is 20-28 h.

6. The preparation method of the artificial core according to any one of claims 1 to 5, characterized in that, By weight percentage, the weight ratio of the 6-8 mesh quartz sand to the 70-140 mesh quartz sand is (2.5-3.5):

1.

7. The preparation method of the artificial core according to any one of claims 1 to 6, characterized in that, After the immersion curing, the soaked core needs to be dried, and the drying treatment is carried out under natural air-drying conditions.

8. An artificial core, characterized in that, The artificial core is prepared by the artificial core preparation method according to any one of claims 1 to 7.

9. The artificial core according to claim 8, characterized in that, The size of the artificial core is: the diameter φ is 110-178 mm, and the length is 600-800 mm; Preferably, the porosity of the artificial core is 7-30%, and the permeability is 0.01-300 mD.

10. An application of the artificial core according to claim 8 or 9 in the fields of core displacement, rock electricity test or perforation target shooting.

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