Artificial shale core and preparation method thereof

Abstract

The invention belongs to the technical field of unconventional oil-gas field development, and particularly relates to an artificial shale core. The problems that the wettability of existing artificial shale cannot be adjusted and controlled according to the wettability of a natural shale core, and the physical property difference between the manufactured artificial shale core and the natural core is large are solved. The invention comprises the following components in percentage by weight: 20-55% of quartz particles; 20 to 35 percent of clay; 1-7% of graphite particles; 10 to 55 percent of epoxy asphalt; the sum of the weight percentages of the raw materials is 100%. The preparation method comprises the following steps: firstly, selecting standard quartz particles, then mixing the quartz particles with graphite particles, clay and epoxy asphalt in proportion to form a solid material, then putting the solid material into a forming mold, heating, demolding to prepare large shale, and finally cutting to prepare the shale core. The artificial shale core provided by the invention realizes wettability regulation and control, has a small physical property difference with a natural shale core, and can be used as a means for evaluating a shale recovery rate improving technology.

Description

Technical Field:

[0001] The present invention relates to the technical field of unconventional oil and gas field development, and particularly to an artificial shale core and a preparation method thereof. Background Art:

[0002] Shale oil has received increasing attention due to its rich reserves and huge development potential, and it has become a new hot spot for the exploration and development of unconventional oil and gas resources in China. Since the development of shale oil began in 2010, significant breakthroughs and remarkable progress have been made, but overall, it still faces development problems such as poor resource quality, low single-well production, and high investment costs. How to achieve significant cost reduction and efficiency improvement in shale oil development and promote the large-scale and efficient development of shale oil is of great significance for ensuring China's energy security.

[0003] Natural cores are the most intuitive and practical data for understanding underground reservoirs and the characteristics of the fluids contained therein. Due to the high cost, long cycle, and poor repeatability of natural core drilling, artificial cores are often used for experimental tests in the process of indoor physical simulation experiments to guide oilfield development. Shale reservoirs are characterized by low porosity, ultra-low permeability, and extensive development of nano-pores, which pose great limitations to the experimental research of shale oil. At present, artificial shale cores are mostly made by mixing, pouring, compressing, or sintering cement and quartz sand, or directly using cuttings to press on-site. The above two types of artificial shale cores are mainly used to evaluate the rock mechanics and hydration swelling properties during the fracturing process. However, in the experiment of improving the recovery rate of shale oil, a large number of parallel samples of shale cores are required as the basis for evaluating development technologies. The existing methods for making artificial shale cannot regulate the wettability of artificial shale according to the wettability of natural shale cores, and the physical properties of the made artificial shale cores are significantly different from those of natural cores, which has a great impact on the experimental results of ultimately improving the recovery rate. Therefore, it cannot be used as an effective technical means for evaluating the improvement of the recovery rate of shale.

[0004] Therefore, there is an urgent need to develop an artificial shale core and a preparation method thereof, and use the prepared artificial shale core for the research on improving the recovery rate of shale oil. Summary of the Invention:

[0005] The purpose of the present invention is to overcome the problems in the background art that the existing artificial shale does not consider the nano-micro pore structure, cannot regulate the wettability of artificial shale according to the wettability of natural shale cores, and the physical properties of the made artificial shale cores are significantly different from those of natural cores, and to provide an artificial shale core. This artificial shale core adopts a nano-micro pore structure, can regulate the wettability of artificial shale according to the wettability of natural shale cores, and the physical properties of the made artificial shale cores are slightly different from those of natural cores, and can be used as a means for evaluating the technology of improving the recovery rate of shale. The present invention also provides a preparation method of an artificial shale core.

[0006] To achieve the above object, a first aspect of the present invention provides an artificial shale core, and the components and their ratios are as follows by weight percentage:

[0007] Quartz particles 20 - 55%; clay 20 - 35%; graphite particles 1 - 7%; epoxy asphalt 10 - 55%; the sum of the weight percentages of the raw materials is 100%.

[0008] Preferably, the clay is composed of kaolinite, montmorillonite, illite, and chlorite.

[0009] Preferably, the mass ratio of kaolinite, montmorillonite, illite, and chlorite is 1:1:1:1.

[0010] Preferably, the composition of the epoxy asphalt and the mass fractions of its components are: 100 parts of petroleum asphalt, 16 parts of epoxy resin, 4 parts of diglycidyl dimerate, 8 parts of methyl acrylate, 9 parts of sodium dodecylbenzenesulfonate, 3 parts of dimethyl silicone oil, 12 parts of polyurethane, 5 parts of cinnamic acid, 10 parts of isobutyltriethoxysilane, 13 parts of montmorillonite, 12 parts of silicon dioxide, and 15 parts of boric anhydride.

[0011] Preferably, the epoxy resin is glycidylamine epoxy resin.

[0012] Another aspect of the present invention provides a preparation method of an artificial shale core, including the following steps:

[0013] Step 1: Test the average diameter of quartz sand particles in the shale formation and select standard quartz particles;

[0014] Step 2: According to the selected standard quartz particles, mix them with graphite particles, clay, and epoxy asphalt in different ratios to form a solid material;

[0015] Step 3: Put the solid material into a molding die, put the molding die into a muffle furnace, heat up and stir;

[0016] Step 4: Take out the molding die, naturally cool it to room temperature, then demold and take out to make a large - sized shale;

[0017] Step 5: Cut the large - sized shale obtained in Step 4 into standard cores to make shale cores.

[0018] Preferably, the diameter of the quartz particles is 0.1 - 10 um.

[0019] Preferably, the diameter of the graphite particles described in Step 2 is 0.05 - 20 um.

[0020] Preferably, the diameter of the graphite particles is 0.01 - 1 um.

[0021] Preferably, the molding die is placed in a muffle furnace and heated to 180 - 260°C; stir for 35 - 50 min.

[0022] The functions of the components of the artificial shale core of the present invention are as follows: quartz particles are used for simulating inorganic pores; clay is used for simulating clay minerals; graphite particles are used for simulating organic pores; and epoxy asphalt is used for simulating wettability regulation.

[0023] The present invention may have the following beneficial effects compared with the above background art:

[0024] (1) By adding micro-nano quartz particles, the micro-nano inorganic pore space in the natural shale reservoir is simulated, and by adding micro-nano graphite particles, the micro-nano organic pore space in the natural shale reservoir is simulated;

[0025] (2) Kaolinite, montmorillonite, illite, and chlorite are used to simulate the clay in the shale core, and by adjusting the clay composition, the chemical characteristics of the natural shale core's hydration upon encountering water are simulated;

[0026] (3) By adjusting the composition ratio of quartz particles and epoxy asphalt, the wettability of different natural shale cores is simulated;

[0027] (4) By adding epoxy asphalt, the pressure resistance and temperature resistance of the shale core are increased;

[0028] (5) By adjusting the proportion of quartz particles, the permeability of the shale core is adjusted.

[0029] The artificial shale core prepared by the formula of the present invention adopts a nano-micro pore structure, can regulate the wettability of the artificial shale according to the wettability of the natural shale core, and has small physical property differences from the natural core, and can be used as a means to evaluate the technology for improving the recovery rate of shale. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the preparation process of the artificial shale core provided by the embodiment of the present invention;

[0031] Figure 2 It is a diagram of the artificial shale core in the embodiment of the present invention;

[0032] Figure 3 It is a photograph of the surface wettability of the artificial shale core in the embodiment of the present invention; (where: Figure 3 -a shows the water phase wetting angle of 60°; Figure 3 -b shows the water phase wetting angle of 115°);

[0033] Figure 4 It is a scanning electron microscope image of the artificial core in the embodiment of the present invention;

[0034] Figure 5The relationship between the amount of quartz sand added and the permeability of the artificial shale core in the embodiment of the present invention;

[0035] Figure 6 This is a comparison chart of the core imbibition curves of artificial shale cores with the same permeability in the embodiment of the present invention. Specific implementation method:

[0036] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0037] The materials and reagents used in the following examples, unless otherwise specified, can be obtained from commercial sources.

[0038] The present invention provides an artificial shale core, the components and proportions of which are as follows by mass percentage: quartz particles 20-55%; clay 20-35%; graphite particles 1-7%; epoxy asphalt 10-55%; the sum of the weight percentages of the raw materials is 100%.

[0039] Clay is composed of kaolinite, montmorillonite, illite and chlorite. The mass ratio of kaolinite, montmorillonite, illite and chlorite is 1:1:1:1.

[0040] The composition of epoxy asphalt and the mass fraction of each component are: 100 parts of petroleum asphalt, 16 parts of glycidylamine epoxy resin, 4 parts of dimer acid diglycidyl ester, 8 parts of methyl acrylate, 9 parts of sodium dodecylbenzene sulfonate, 3 parts of dimethyl silicone oil, 12 parts of polyurethane, 5 parts of phenyl acrylic acid, 10 parts of isobutyl triethoxy silane, 13 parts of montmorillonite, 12 parts of silicon dioxide, and 15 parts of boric anhydride;

[0041] The preparation method comprises the following steps:

[0042] 1.1) Weigh each component by weight and set aside;

[0043] 1.2) Mix petroleum asphalt, glycidylamine epoxy resin, montmorillonite, silicon dioxide and boric anhydride evenly through a colloid mill;

[0044] 1.3) Add the remaining components, mix and stir at room temperature for 2.5 hours, and cure at room temperature for 6 hours to obtain a high temperature resistant epoxy asphalt material. The composition and preparation method of the epoxy asphalt can be found in CN 105924991 B.

[0045] See Figure 1 As shown, the method for preparing an artificial shale core provided by the present invention comprises the following steps:

[0046] Step 1: Test the average diameter of quartz sand particles in shale formations and select standard quartz particles; the diameter of standard quartz particles shown is 0.1-10um;

[0047] ​Step 2: According to the selected standard quartz particles, mix them with graphite particles, clay and epoxy asphalt in different proportions to form a solid material; the diameter of the graphite particles is 0.05 - 20 um.

[0048] Step 3: Put the solid material into a forming mold, put the forming mold into a muffle furnace, heat it up to 180 - 260 °C and stir for 35 - 50 min;

[0049] Step 4: Take out the forming mold, let it cool naturally to room temperature, then demold it to obtain a large shale block;

[0050] Step 5: Cut the large shale block obtained in Step 4 into standard cores to make shale cores.

[0051] The following further illustrates the present invention with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0052] Embodiment 1

[0053]

[0054] Preparation method of artificial shale core:

[0055] (1) Test the average diameter of quartz sand particles in the shale formation, and select the standard quartz sand with an average diameter of 3 um;

[0056] (2) The composition and mass fraction of each component of the epoxy asphalt are: 100 parts of petroleum asphalt, 16 parts of glycidylamine epoxy resin, 4 parts of diglycidyl dimerate, 8 parts of methyl acrylate, 9 parts of sodium dodecylbenzenesulfonate, 3 parts of dimethyl silicone oil, 12 parts of polyurethane, 5 parts of phenylacrylic acid, 10 parts of isobutyltriethoxysilane, 13 parts of montmorillonite, 12 parts of silica, and 15 parts of boric anhydride.

[0057] Its preparation method:

[0058] 2.1) Weigh each component by weight and set aside;

[0059] 2.2) Stir petroleum asphalt, glycidylamine epoxy resin, montmorillonite, silica and boric anhydride evenly through a colloid mill;

[0060] 2.3) Add the remaining components, mix and stir at room temperature for 2.5 h, and cure at room temperature for 6 h to obtain a high-temperature resistant epoxy asphalt material.

[0061] (3) According to the selected standard quartz sand, mix it with graphite, clay and epoxy asphalt in proportion to form a solid material;

[0062] (4) Put the solid material into a forming mold, put the forming mold into a muffle furnace, heat it up to 220 °C and stir for 40 min;

[0063] (5) Take out the forming mold. After naturally cooling it to room temperature, demold it to obtain large shale blocks (see Figure 2 ), and the size of the large shale blocks is length × width × height = 10 cm × 10 cm × 10 cm;

[0064] (6) Cut the large shale blocks obtained in step (5) into standard cores to make shale cores;

[0065] (7) The composition ratio of kaolinite, montmorillonite, illite, and chlorite is 1:1:1:1;

[0066] (8) The average diameter of graphite particles is 1 μm.

[0067] The permeability of the made shale core is 0.009 mD, the wettability of the rock surface is water-wet, and the water-phase wetting angle is 60° (see Figure 3 -a). After polishing the made shale core, perform a scanning electron microscope test on it, and the test results are shown in Figure 4 . The scanning electron microscope image of the artificial shale core shows that both inorganic pores and organic pores exist in the made shale core.

[0068] Example 2:

[0069]

[0070] Preparation method of artificial shale core:

[0071] (1) Test the average diameter of quartz sand particles in the shale formation, and select the standard quartz sand with an average diameter of 3 μm;

[0072] (2) The same as Example 1.

[0073] (3) According to the selected standard quartz sand, mix it with graphite, clay, and epoxy asphalt in proportion to form a solid material;

[0074] (4) Put the solid material into the forming mold, put the forming mold into the muffle furnace, heat it to 220 °C and stir for 40 min;

[0075] (5) Take out the forming mold. After naturally cooling it to room temperature, demold it to obtain large shale blocks;

[0076] (6) Cut the large shale blocks obtained in step (5) into standard cores to make shale cores.

[0077] (7) The composition ratio of kaolinite, montmorillonite, illite, and chlorite is 1:1:1:1.

[0078] (8) The average diameter of graphite particles is 1 μm.

[0079] The permeability of the produced shale core is 0.003 mD, the wettability of the rock surface is oil-wet, and the water wetting angle is 115°( Figure 3 -b)

[0080] Example 3:

[0081] When the epoxy asphalt content is 35% and the graphite content is 5%, by changing the ratio of different quartz sand particles to clay, the permeabilities of artificial shale were measured when the quartz sand contents were 25%, 28%, 31%, 34%, 37%, and 40%, and the corresponding test curves were fitted, as shown in Figure 5 . As the proportion of quartz sand increases, the permeability of the artificial shale increases. According to the fitted curve formula, shale cores with different permeabilities meeting the corresponding requirements were made.

[0082] Example 4:

[0083] The shale core obtained in Example 1 was used.

[0084] (1) The obtained shale core was wire-cut into a cylindrical core No. 1 with a specification of diameter × length = 2.5 cm × 3 cm;

[0085] (2) The cylindrical core was placed in kerosene and evacuated for 48 hours under a vacuum of -0.98 MPa, and the masses M 1 、M 2 of the shale core before and after evacuation were weighed;

[0086] (3) Then the volume V 1 of kerosene in the core was calculated using the following formula:

[0087]

[0088] In the formula: ρ—the density of kerosene, g / cm 3 .

[0089] (4) The core was placed in an imbibition bottle filled with water for an imbibition experiment, and the volume V 2 of the imbibed kerosene was read;

[0090] (5) The imbibition recovery curve of the shale core was calculated. The imbibition recovery of the shale core was calculated using the following formula:

[0091]

[0092] (6) The above steps were repeated to make the No. 2 shale core and conduct an imbibition experiment.

[0093] The comparison results of the imbibition curves of the No. 1 shale core and the No. 2 shale core with the same permeability are shown in Figure 6; As can be seen from the figure, the imbibition recovery rate error of the two cylindrical shale cores is less than 12%, indicating that the repeatedly produced shale cores have high repeatability and can be used as parallel samples for different shale imbibition evaluation experiments.

[0094] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are 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 perform equivalent replacements for some of them. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. Although the specific implementation manners of the present invention have been described above, it is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications or deformations that can be made without creative labor on the basis of the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. An artificial shale core, characterized in that: The components and proportions are as follows by weight percentage: Quartz particles 20-55%; clay 20-35%; graphite particles 1-7%; epoxy asphalt 10-55%; the sum of the weight percentages of the raw materials is 100%.

2. The artificial shale core according to claim 1, characterized in that: The clay consists of kaolinite, montmorillonite, illite and chlorite.

3. The artificial shale core according to claim 1, characterized in that: The mass ratio of kaolinite, montmorillonite, illite and chlorite is 1:1:1:

1.

4. The artificial shale core according to claim 1, characterized in that: The epoxy asphalt composition and the mass proportion of each component are: 100 parts of petroleum asphalt, 16 parts of epoxy resin, 4 parts of dimer acid diglycidyl ester, 8 parts of methyl acrylate, 9 parts of sodium dodecylbenzene sulfonate, 3 parts of dimethyl silicone oil, 12 parts of polyurethane, 5 parts of phenyl acrylic acid, 10 parts of isobutyl triethoxy silane, 13 parts of montmorillonite, 12 parts of silicon dioxide, and 15 parts of boric anhydride.

5. The artificial shale core according to claim 4, characterized in that: The epoxy resin is glycidylamine epoxy resin.

6. A method for preparing the artificial shale core according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1, testing the average diameter of quartz sand particles in the shale formation and selecting standard quartz particles; Step 2: According to the selected standard quartz particles, the selected standard quartz particles are mixed with graphite particles, clay and epoxy asphalt in different proportions to form a solid material; Step 3, placing the solid material into a forming mold, placing the forming mold into a muffle furnace, heating and stirring; Step 4: Take out the forming mold, cool it down naturally to room temperature, and then demould it to make a large piece of shale; Step 5: Cut the large block of shale obtained in step 4 into standard cores to make shale cores.

7. The preparation method according to claim 6, characterized in that: The diameter of the quartz particles is 0.1-10 um.

8. The preparation method according to claim 6, characterized in that: The diameter of the graphite particles in step 2 is 0.05 to 20 um.

9. The preparation method according to claim 8, characterized in that: The particle diameter of the graphite is 0.01-1 um.

10. The preparation method according to claim 6, characterized in that: Place the molding mold in a muffle furnace, heat to 180-260°C, and stir for 35-50 minutes.

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