A lightweight, core-shell structured ceramsite proppant and a method of making the same

Abstract

The application discloses a kind of light core-shell structure ceramsite proppant and its preparation method, belong to fracturing proppant technical field, solve the technical problem that the density of ceramsite proppant prepared by using coal gangue and dolomite is big, solution is as follows: the mass ratio of the core of light core-shell structure ceramsite proppant and the quality of coating shell is (0.5~2.5):1;The composition and mass fraction of the core are as follows: calcined coal gangue 70.5wt%, calcined dolomite 29.5wt%;The composition and mass fraction of the coating shell are as follows: bauxite 45.5wt%, kaolin 54.5wt%.Preparation method includes the following steps: S1, weighing raw materials;S2, core mixed powder, granulation;S3, core sintering;S4, sintered core coating;S5, semi-finished ceramsite proppant sintering forming, prepare light core-shell structure ceramsite proppant.The light low-density ceramsite proppant prepared by the application can greatly reduce the density of ceramsite proppant used for coalbed methane.

Description

Technical Field

[0001] This invention belongs to the field of fracturing proppant technology, specifically relating to a lightweight core-shell structure ceramic proppant and its preparation method. Background Technology

[0002] Currently, the world's proven coalbed methane reserves are approximately 270 trillion cubic meters. While the total amount of coalbed methane resources is abundant, a significant portion of these reserves are located in shallow to medium-depth formations with low extraction rates. Therefore, the remaining resource scale is considerable and urgently needs development. The main component of coalbed methane is methane (CH4). It is a clean energy source and a by-product of coal mining. It is an unconventional natural gas existing in an adsorbed state within coal seams or coal-bearing strata, characterized by low saturation, low pressure, and low permeability, which increases the difficulty of extraction.

[0003] Lightweight, low-density ceramic proppant can form a longer fracture support zone, optimizing the conductivity of oil and gas reservoirs. Simultaneously, low-density proppant is less prone to sedimentation, easier to extract, and reduces the viscosity requirements of fracturing fluids, effectively mitigating the risk of sand blockage. Therefore, when designing hydraulic fracturing proppant for coalbed methane wells, reducing its density parameter while meeting the fragmentation rate requirements is beneficial for efficient coalbed methane well production.

[0004] Coal gangue is a solid waste generated during coal mining and washing. It contains organic matter such as carbon and inorganic silicates and kaolinite minerals. If it is not comprehensively utilized and is directly discharged or used for backfilling in wells, it will not only occupy land but also cause air, water, and soil pollution. The current technological solution is to mix coal gangue with dolomite and then sinter it. Although this can solve the problem of comprehensive utilization of solid waste, the density of the ceramsite proppant is relatively high, which is not conducive to improving the extraction efficiency of coalbed methane wells.

[0005] Patent document "A Composite Ceramsite and Its Production Process" (Application Publication No.: CN 117185775 A) discloses a porous inner core prepared from a first ceramic raw material, rigid rubber waste, and flexible rubber waste, and a second ceramic raw material as a hard outer shell. The composite ceramsite is prepared from the porous inner core and the hard outer shell and applied to the field of oil and gas fracturing. However, in the technical solution disclosed in this document, the raw materials of the porous inner core—rigid and flexible rubber waste—decompose and generate gas during the high-temperature sintering process of the outer shell layer. The gas escape process damages the integrity of the outer shell layer. At the same time, the rigid and flexible rubber waste cannot form a matrix structure with a certain degree of support and stability with the first ceramic raw material at high temperature. During the cooling process, the first ceramic raw material is prone to accumulate at the bottom of the liquid rubber under the action of gravity, causing the ceramsite to agglomerate, which ultimately affects the material's resistance to breakage. Summary of the Invention

[0006] This invention provides a lightweight core-shell structured ceramsite proppant and its preparation method, primarily aiming to overcome the technical problems of high density and insufficient coalbed methane well extraction efficiency in existing ceramsite proppant technologies. Based on the comprehensive utilization of solid waste, this invention utilizes pre-calcination treatment to effectively eliminate ash in the raw materials, contributing to the uniformity of the material structure. Simultaneously, it forms microcrystalline nuclei in the raw materials, promoting nucleus growth and spatial support of the microcrystalline structure during sintering. In particular, utilizing calcined solid waste as the core of the core-shell ceramsite proppant allows for effective support of the outer shell through volume expansion at high temperatures, synergistically enhancing the matrix strength of the ceramsite proppant. Specifically, calcined coal gangue and dolomite are mixed to prepare the core of ceramsite pellets, while bauxite and kaolin form the outer shell, synthesizing a lightweight, low-density ceramsite proppant. Internal pore formation reduces density, while external coating increases strength. The desired lightweight ceramsite proppant for coalbed methane is prepared by controlling the sintering temperature and holding time during the manufacturing process.

[0007] This invention is achieved through the following technical solution: a lightweight core-shell structured ceramsite proppant, wherein the lightweight core-shell structured ceramsite proppant has a core-shell structure, and the mass ratio of the core to the outer shell is (0.5~2.5):1; the composition and mass fraction of the core are: 70.5wt% calcined coal gangue and 29.5wt% calcined dolomite; the composition and mass fraction of the outer shell are: 45.5wt% bauxite and 54.5wt% kaolin.

[0008] Furthermore, the bulk density of the lightweight core-shell structured ceramic proppant is 0.98 g / cm³. 3 ~1.04g / cm 3 The apparent density is 2.1 g / cm³. 3 ~2.55g / cm 3 The breakage rate under 21MPa conditions is less than 10%.

[0009] Furthermore, the calcined coal gangue contains: Al2O3 content of 31.372 wt% and SiO2 content of 40.285 wt%.

[0010] The calcined dolomite contained 68.05 wt% CaO and 20.658 wt% MgO.

[0011] The bauxite contains 78.225 wt% Al2O3, 10.991 wt% SiO2, and 7.675 wt% TiO2.

[0012] A method for preparing a lightweight core-shell structured ceramic support as described above includes the following steps:

[0013] S1. Weighing raw materials: Weigh calcined coal gangue, calcined dolomite, bauxite, and kaolin according to the composition and mass ratio of the core and the outer shell, grind them into powder with a particle size of less than 325 mesh, and then screen them through a standard sieve for later use.

[0014] S2. Core Mixing and Granulation: The calcined coal gangue and calcined dolomite weighed in step S1 are mixed evenly and placed in a granulator. Water is added for granulation, and granules with a particle size of 16-20 mesh are screened out to obtain core green bodies; wherein the mass of water accounts for 10wt%-15wt% of the weight of the core mixed powder.

[0015] S3. Core sintering: Dry the core green body prepared in step S2 for 4h~6h, and then put it into a heating furnace for high temperature sintering at normal pressure. The sintering temperature is 1200°C, the heating rate is 5°C / min, and the holding time is 1h to obtain the sintered core for later use.

[0016] S4. Sintered Core Coating: Add the sintered core prepared in step S3 to the sugar coating pot, then start the sugar coating pot and spray water and the mixed powder of bauxite and kaolin weighed in step S1 onto the surface of the sintered core. The volume of water sprayed is 1mL~2mL, so that the surface of the sintered core is evenly coated with a shell. After the coating is completed, put it into the oven to dry for 4h~6h to obtain the semi-finished ceramic support agent.

[0017] S5. Sintering of semi-finished ceramic proppant: The semi-finished ceramic proppant prepared in step S4 is placed in a rotating tube furnace and sintered at high temperature under normal pressure in an air atmosphere. The sintering temperature is 1200°C, the heating rate is 5°C / min, and the holding time is 1h to obtain a lightweight core-shell structure ceramic proppant.

[0018] The beneficial effects of this invention are as follows:

[0019] This invention uses calcined coal gangue and dolomite as the core and bauxite and kaolin as the outer shell. While meeting the pressure requirements of coalbed methane extraction, it can greatly reduce the density index of the ceramsite proppant used in coalbed methane, effectively improving sand carrying efficiency and avoiding blockage of gap channels. At the same time, the large-scale introduction of coal gangue (total mass percentage ≥ 50 wt%) effectively increases the total amount of solid waste coal gangue used, improving the current situation of large-scale coal gangue stockpiling to a certain extent, realizing its comprehensive utilization and reducing solid environmental pollution. Attached Figure Description

[0020] Figure 1 The XRD diffraction pattern of the sintered core prepared in Example 1;

[0021] Figure 2 The XRD diffraction pattern of the coating shell prepared in Example 1;

[0022] Figure 3Microscopic morphology of the lightweight core-shell structured ceramic support prepared in Example 1;

[0023] Figure 4 XRD diffraction patterns of lightweight core-shell structured ceramic particle proppant with different mass ratios prepared in Example 1;

[0024] Figure 5 The volume density performance curve of the lightweight core-shell structured ceramic proppant prepared in Example 1 is shown.

[0025] Figure 6 The apparent density performance curve of the lightweight core-shell structured ceramic proppant prepared in Example 1 is shown.

[0026] Figure 7 The graph shows the breakage rate performance of the lightweight core-shell structured ceramic proppant prepared in Example 1. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0028] In the following embodiments, the coal gangue, dolomite, bauxite, and kaolin were all purchased from Yangquan Changqing Petroleum Fracturing Proppant Co., Ltd., and the coal gangue and dolomite were calcined before being used as raw materials. Specifically, the calcined coal gangue contained 31.372 wt% Al2O3 and 40.285 wt% SiO2; the calcined dolomite contained 68.05 wt% CaO and 20.658 wt% MgO; and the bauxite contained 78.225 wt% Al2O3, 10.991 wt% SiO2, and 7.675 wt% TiO2. Example 1

[0029] A method for preparing a lightweight core-shell structured ceramic support includes the following steps:

[0030] S1. Weighing Raw Materials: According to the composition and mass ratio of the core and the outer shell, weigh calcined coal gangue, calcined dolomite, bauxite, and kaolin respectively, grind them to a particle size of less than 325 mesh, and screen them through a standard sieve for later use. The composition and mass fraction of the core are: calcined coal gangue 70.5 wt%, calcined dolomite 29.5 wt%; the composition and mass fraction of the outer shell are: bauxite 45.5 wt%, kaolin 54.5 wt%; in this embodiment 1, the mass ratio of the core to the outer shell is (0.5:1).

[0031] S2. Core Mixing and Granulation: The calcined coal gangue and calcined dolomite weighed in step S1 are mixed evenly and placed in a granulator. Water is added for granulation, and 16-mesh spherical particles are screened out to obtain the core green body; wherein, the mass of water accounts for 12 wt% of the weight of the core mixed powder.

[0032] S3. Core Sintering: The core green body prepared in step S2 is dried for 4 hours, then placed in a heating furnace for high-temperature sintering at atmospheric pressure. The sintering temperature is 1200°C, the heating rate is 5°C / min, and the holding time is 1 hour to obtain the sintered core for later use. The XRD diffraction pattern of the sintered core is shown below. Figure 1 As shown, it exhibits a variety of phase components, which is related to the composition of coal gangue solid waste;

[0033] S4. Sintered Core Coating: The sintered core prepared in step S3 is added to a coating pan. The pan is then started, and water is sprayed onto the surface of the sintered core while simultaneously spraying the mixed powder of bauxite and kaolin weighed in step S1. The volume of water sprayed is 1 mL, ensuring a uniform outer shell coating the surface of the sintered core. After coating, the core is dried in an oven for 4 hours to obtain a semi-finished ceramic support. The XRD diffraction pattern of the semi-finished ceramic support is shown below. Figure 2 As shown in the diagram, the material's phase is corundum.

[0034] S5. Sintering and forming of semi-finished ceramsite proppant: The semi-finished ceramsite proppant prepared in step S4 is placed in a rotary tube furnace and sintered at high temperature and atmospheric pressure in an air atmosphere. The sintering temperature is 1200°C, the heating rate is 5°C / min, and the holding time is 1h, to obtain a lightweight core-shell structured ceramsite proppant. The microstructure of the lightweight core-shell structured ceramsite proppant and its shell is as follows. Figure 3 As shown, combined with the above XRD analysis, the outer shell exhibits a typical granular corundum microstructure, and the fine particle state promotes the compactness and stability of the outer shell; the XRD diffraction patterns of the outer shell and the core coated with different mass ratios are shown below. Figure 4 As shown.

[0035] The performance curve of the lightweight core-shell structured ceramic proppant prepared in Example 1 is as follows: Figures 5-7 As shown, its average sphericity is 0.9, turbidity is less than 7 FTU, acid solubility is less than 4.7%, and bulk density is 1.04 g / cm³. 3 The apparent density is 2.55 g / cm³. 3 The breakage rate under 21 MPa conditions was 8.8%. Example 2

[0036] A method for preparing a lightweight core-shell structured ceramic support includes the following steps:

[0037] S1. Weighing Raw Materials: According to the composition and mass ratio of the core and the outer shell, weigh calcined coal gangue, calcined dolomite, bauxite, and kaolin respectively, grind them to a particle size of less than 325 mesh, and screen them through a standard sieve for later use. The composition and mass fraction of the core are: calcined coal gangue 70.5 wt%, calcined dolomite 29.5 wt%; the composition and mass fraction of the outer shell are: bauxite 45.5 wt%, kaolin 54.5 wt%; in this embodiment 2, the mass ratio of the core to the outer shell is (1:1).

[0038] S2. Core Mixing and Granulation: The calcined coal gangue and calcined dolomite weighed in step S1 are mixed evenly and placed in a granulator. Water is added for granulation, and granules with a particle size of 20 mesh are screened out to obtain the core green body; wherein, the mass of water accounts for 15 wt% of the weight of the core mixed powder.

[0039] S3. Core sintering: The core green blank prepared in step S2 is dried for 6 hours, and then placed in a heating furnace for high-temperature sintering at normal pressure. The sintering temperature is 1200°C, the heating rate is 5°C / min, and the holding time is 1 hour to obtain the sintered core for later use.

[0040] S4. Sintered Core Coating: Add the sintered core prepared in step S3 to the sugar coating pot, then start the sugar coating pot and spray water and the mixed powder of bauxite and kaolin weighed in step S1 onto the surface of the sintered core. The volume of water sprayed is 2 mL, so that the surface of the sintered core is evenly coated with a shell. After the coating is completed, put it into the oven to dry for 6 hours to obtain the semi-finished ceramic support agent.

[0041] S5. Sintering of semi-finished ceramic proppant: The semi-finished ceramic proppant prepared in step S4 is placed in a rotating tube furnace and sintered at high temperature under normal pressure in an air atmosphere. The sintering temperature is 1200°C, the heating rate is 5°C / min, and the holding time is 1h to obtain a lightweight core-shell structure ceramic proppant.

[0042] The lightweight core-shell structured ceramic proppant prepared in Example 2 has an average sphericity of 0.9, a turbidity of less than 10 FTU, an acid solubility of less than 4.7%, and a bulk density of 1.02 g / cm³. 3 The apparent density is 2.1 g / cm³. 3 The breakage rate at 21 MPa was 7.6%. Example 3

[0043] A method for preparing a lightweight core-shell structured ceramic support includes the following steps:

[0044] S1. Weighing Raw Materials: According to the composition and mass ratio of the core and the outer shell, weigh calcined coal gangue, calcined dolomite, bauxite, and kaolin respectively, grind them to a particle size of less than 325 mesh, and screen them through a standard sieve for later use. The composition and mass fraction of the core are: calcined coal gangue 70.5 wt%, calcined dolomite 29.5 wt%; the composition and mass fraction of the outer shell are: bauxite 45.5 wt%, kaolin 54.5 wt%; in this embodiment 3, the mass ratio of the core to the outer shell is (2:1).

[0045] S2. Core Mixing and Granulation: The calcined coal gangue and calcined dolomite weighed in step S1 are mixed evenly and placed in a granulator. Water is added for granulation, and 18-mesh spherical particles are screened out to obtain the core green body; wherein, the mass of water accounts for 13 wt% of the weight of the core mixed powder.

[0046] S3. Core sintering: The core green blank prepared in step S2 is dried for 5 hours, and then placed in a heating furnace for high-temperature sintering at normal pressure. The sintering temperature is 1200°C, the heating rate is 5°C / min, and the holding time is 1 hour to obtain the sintered core for later use.

[0047] S4. Sintered Core Coating: Add the sintered core prepared in step S3 to the sugar coating pot, then start the sugar coating pot and spray water and the mixed powder of bauxite and kaolin weighed in step S1 onto the surface of the sintered core. The volume of water sprayed is 1.5 mL, so that the surface of the sintered core is evenly coated with a shell. After the coating is completed, put it into the oven to dry for 5 hours to obtain the semi-finished ceramic support agent.

[0048] S5. Sintering of semi-finished ceramic proppant: The semi-finished ceramic proppant prepared in step S4 is placed in a rotating tube furnace and sintered at high temperature under normal pressure in an air atmosphere. The sintering temperature is 1200°C, the heating rate is 5°C / min, and the holding time is 1h to obtain a lightweight core-shell structure ceramic proppant.

[0049] The lightweight core-shell structured ceramic proppant prepared in Example 3 has an average sphericity of 0.9, a turbidity of less than 8 FTU, an acid solubility of less than 4.7%, and a bulk density of 0.98 g / cm³. 3 The apparent density is 2.14 g / cm³. 3 The breakage rate at 21 MPa was 7.8%. Example 4

[0050] A method for preparing a lightweight core-shell structured ceramic support includes the following steps:

[0051] S1. Weighing Raw Materials: According to the composition and mass ratio of the core and the outer shell, weigh calcined coal gangue, calcined dolomite, bauxite, and kaolin respectively, grind them to a particle size of less than 325 mesh, and screen them through a standard sieve for later use. The composition and mass fraction of the core are: calcined coal gangue 70.5 wt%, calcined dolomite 29.5 wt%; the composition and mass fraction of the outer shell are: bauxite 45.5 wt%, kaolin 54.5 wt%; in this embodiment 4, the mass ratio of the core to the outer shell is (2.5:1).

[0052] S2. Core Mixing and Granulation: The calcined coal gangue and calcined dolomite weighed in step S1 are mixed evenly and placed in a granulator. Water is added for granulation, and granules with a particle size of 20 mesh are screened out to obtain the core green body; wherein, the mass of water accounts for 15 wt% of the weight of the core mixed powder.

[0053] S3. Core sintering: The core green blank prepared in step S2 is dried for 6 hours, and then placed in a heating furnace for high-temperature sintering at normal pressure. The sintering temperature is 1200°C, the heating rate is 5°C / min, and the holding time is 1 hour to obtain the sintered core for later use.

[0054] S4. Sintered Core Coating: Add the sintered core prepared in step S3 to the sugar coating pot, then start the sugar coating pot and spray water and the mixed powder of bauxite and kaolin weighed in step S1 onto the surface of the sintered core. The volume of water sprayed is 2 mL, so that the surface of the sintered core is evenly coated with a shell. After the coating is completed, put it into the oven to dry for 6 hours to obtain the semi-finished ceramic support agent.

[0055] S5. Sintering of semi-finished ceramic proppant: The semi-finished ceramic proppant prepared in step S4 is placed in a rotating tube furnace and sintered at high temperature under normal pressure in an air atmosphere. The sintering temperature is 1200°C, the heating rate is 5°C / min, and the holding time is 1h to obtain a lightweight core-shell structure ceramic proppant.

[0056] The lightweight core-shell structured ceramic proppant prepared in Example 4 has an average sphericity of 0.9, a turbidity of less than 10 FTU, an acid solubility of less than 4.7%, and a bulk density of 1.01 g / cm³. 3 The apparent density is 2.37 g / cm³. 3 The breakage rate at 21 MPa was 9.1%.

[0057] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a lightweight core-shell structured ceramic support, characterized in that: Includes the following steps: S1. Weighing Raw Materials: Weigh calcined coal gangue, calcined dolomite, bauxite, and kaolin according to the composition and mass ratio of the core and outer shell. Grind them to a particle size of less than 325 mesh and sieve them through a standard sieve for later use. The mass ratio of the core to the outer shell is (0.5~2.5):

1. The composition and mass fraction of the core are: calcined coal gangue 70.5wt%, calcined dolomite 29.5wt%; the composition and mass fraction of the outer shell are: bauxite 45.5wt%, kaolin 54.5wt%. S2. Core Mixing and Granulation: The calcined coal gangue and calcined dolomite weighed in step S1 are mixed evenly and placed in a granulator. Water is added for granulation, and granules with a particle size of 16-20 mesh are screened out to obtain core green bodies; wherein the mass of water accounts for 10wt%-15wt% of the weight of the core mixed powder. S3. Core sintering: Dry the core green body prepared in step S2 for 4h~6h, and then put it into a heating furnace for high temperature sintering at normal pressure. The sintering temperature is 1200℃, the heating rate is 5℃ / min, and the holding time is 1h to obtain the sintered core for later use. S4. Sintered Core Coating: Add the sintered core prepared in step S3 to the sugar coating pot, then start the sugar coating pot and spray water and the mixed powder of bauxite and kaolin weighed in step S1 onto the surface of the sintered core. The volume of water sprayed is 1mL~2mL, so that the surface of the sintered core is evenly coated with a shell. After the coating is completed, put it into the oven to dry for 4h~6h to obtain the semi-finished ceramic support agent. S5. Sintering of semi-finished ceramic proppant: The semi-finished ceramic proppant prepared in step S4 is placed in a rotating tube furnace and sintered at high temperature under normal pressure in an air atmosphere. The sintering temperature is 1200℃, the heating rate is 5℃ / min, and the holding time is 1h to obtain a lightweight core-shell structure ceramic proppant.

2. The method for preparing a lightweight core-shell structured ceramic support according to claim 1, characterized in that: The bulk density of the lightweight core-shell structured ceramic proppant is 0.98 g / cm³. 3 ~1.04g / cm 3 The apparent density is 2.1 g / cm³. 3 ~2.55g / cm 3 The breakage rate under 21MPa conditions is less than 10%.

3. The method for preparing a lightweight core-shell structured ceramic support according to claim 1, characterized in that: The calcined coal gangue contained 31.372 wt% Al2O3 and 40.285 wt% SiO2. The calcined dolomite contained 68.05 wt% CaO and 20.658 wt% MgO. The bauxite contains 78.225 wt% Al2O3, 10.991 wt% SiO2, and 7.675 wt% TiO2.

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