A lithium-doped oil well cement and a method of making the same

Abstract

The application relates to the technical field of cement, and discloses lithium-doped oil well cement and a preparation method thereof. Nitric acid is used to pressurize and leach lithium spodumene solid waste as raw material for sintering oil and gas well cement clinker. In the sintering process of the oil and gas well cement clinker, the growth of C3S crystals can be promoted, the C3S crystal grains are increased, the reaction activity is enhanced, and especially the early reaction activity of the lithium-doped oil well cement can be improved. Not only can the activation energy of C4AF reaction be reduced, the hydration reaction activity of C4AF be improved, and the formation of AFm-OH phase hydration product be promoted, but also the doping of AFm-OH phase on the surface and interlayer of C-S-H can improve the deformation ability of C-S-H, densify the interlayer structure, and further improve the strength and toughness of the cement stone; and the formation of C3A crystals can be inhibited, which helps to improve the sulfuric acid corrosion resistance of the oil well cement.

Description

Technical Field

[0001] This invention relates to the field of cement technology, specifically to a lithium-doped oil well cement and its preparation method. Background Technology

[0002] Shale gas resources, as an important component of national energy, have become a significant driving force for increasing reserves and production in the natural gas industry. Compared with conventional natural gas reservoirs, shale gas reservoirs are characterized by low porosity and permeability, large-area continuous accumulation of low-abundance resources, long production life, and long production cycles. Shale gas extraction currently widely employs a "horizontal well + large-scale segmented volumetric fracturing" development method. Fracturing operations involve high pressure (wellhead pressure 60–100 MPa), numerous operations, large fluid volumes, and significant temperature variations. Frequent changes in wellbore temperature and pressure generate alternating loads, making the casing and cement sheath highly susceptible to damage. The inability of the cement sheath's mechanical properties to withstand the fracturing loads, leading to breakage, is one of the main reasons for the failure of the cement sheath's mechanical integrity, inducing problems such as annular pressure and casing damage.

[0003] Currently, toughening and reducing brittleness in oil well cement systems using exogenous toughening materials such as particles, latex, fibers, and whiskers is a crucial measure to ensure the mechanical integrity of downhole cement sheaths. However, the compatibility between cementing materials and toughening materials is poor, surface modification processes are complex and costly, and there are significant issues such as uncoordinated development of strength and toughness, making it difficult to meet the service requirements of oil well cement under complex loads. Summary of the Invention

[0004] To address the above issues, this invention provides lithium-doped oil well cement and its preparation method. It uses nitric acid-pressurized spodumene solid waste as raw material for sintering oil and gas well cement clinker. During the sintering process of the oil and gas well cement clinker, it promotes the growth of C3S crystals, resulting in larger C3S grains and enhanced reactivity, particularly improving the early-stage reactivity of lithium-doped oil well cement. This not only lowers the activation energy of the C4AF reaction and increases the hydration reactivity of C4AF, promoting the formation of AFm-OH phase hydration products; the doping of the AFm-OH phase on the surface and between layers of CSH can improve the deformability of CSH, densify the interlayer structure, and thus improve the strength and toughness of the cement stone; it also inhibits the formation of C3A crystals, helping to improve the oil well cement's resistance to sulfuric acid attack.

[0005] To achieve the above-mentioned technical effects, the technical solution adopted by the present invention is as follows:

[0006] A lithium-doped oil well cement, by weight, comprises 95-97 parts of oil and gas well cement clinker and 3-5 parts of natural dihydrate gypsum; the oil and gas well cement clinker is obtained by sintering raw meal powder, the raw meal powder comprising 75%-80 parts of limestone, 2-5 parts of spodumene solid waste leached by nitric acid pressure, 5.5-8.5 parts of sandstone, 5.5-6.0 parts of aluminum ore waste and 2.5-3.5 parts of iron ore waste.

[0007] Furthermore, the nitric acid pressure leaching of spodumene solid waste comprises the following chemical composition by mass fraction:

[0008]

[0009] The impurity oxide is a composition of one or more oxides selected from Fe2O3, K2O, CaO, and MgO.

[0010] To achieve the above-mentioned technical effects, the present invention also provides a method for preparing lithium-doped oil well cement, comprising:

[0011] Limestone, spodumene solid waste leached under nitric acid pressure, sandstone, aluminum ore waste residue, and iron ore waste residue are ground together to obtain cement raw meal powder.

[0012] The raw meal powder is calcined to obtain cement clinker for oil and gas wells;

[0013] The obtained oil and gas well cement clinker is mixed with natural gypsum and ground in a mill to obtain lithium-doped oil well cement.

[0014] Further, the raw material powder includes 75% to 80 parts limestone, 2 to 5 parts nitric acid pressure leaching spodumene solid waste, 5.5 to 8.5 parts sandstone, 5.5 to 6.0 parts aluminum ore waste, and 2.5 to 3.5 parts iron ore waste.

[0015] Furthermore, during the co-grinding process of limestone, nitric acid pressure leaching spodumene solid waste, sandstone, aluminum ore waste residue, and iron ore waste residue, the particle size of the grinding process is controlled within the range of 75–105 μm.

[0016] Furthermore, the raw meal powder is calcined in a rotary kiln at a temperature of 1300–1380°C and a kiln speed of 0.8–1.2 rpm, and the vertical weight of the oil and gas well cement clinker is ≥1450 g / L.

[0017] Furthermore, during the mixing process of the obtained oil and gas well cement clinker and natural gypsum, the amount of oil and gas well cement clinker is 95-97 parts, and the amount of natural dihydrate gypsum is 3-5 parts; the specific surface area of ​​the powder mixed and ground with the oil and gas well cement clinker and natural gypsum is controlled to be 310-340 m². 2 / kg.

[0018] Compared with the prior art, the beneficial effects of the present invention are: the present invention uses nitric acid pressure leaching of spodumene solid waste as a raw material for sintering oil and gas well cement clinker. While providing silica and alumina, the nitric acid pressure leaching of spodumene solid waste contains trace amounts of Li2O. Because Li... + With its small ionic radius and relatively high field strength, Li3S plays a role in the accumulation of silicate networks during the sintering process of oil and gas well cement clinker, thereby promoting the growth of C3S crystals, increasing C3S grain size, and enhancing reactivity, especially improving the early-stage reactivity of lithium-doped oil well cement. Furthermore, in Li... + Under the strong migration ability, Fe atoms in C4AF can be further induced to replace aluminum atoms, resulting in the transformation of the Fe-O four-coordinate structure [FeO4] to the Fe-O six-coordinate structure [FeO6], and the transformation of [AlO6] to [AlO4]. On the one hand, since the Fe-O bond is longer and has a lower breaking energy than the Al-O bond, the activation energy of the C4AF reaction is reduced, the hydration reactivity of C4AF is increased, and the formation of AFm-OH phase hydration products is promoted. The doping of AFm-OH phase on the surface and between layers of CSH can improve the deformability of CSH, densify the interlayer structure, and thus improve the strength and toughness of cement stone. On the other hand, the transformation of [AlO6] to [AlO4] inhibits the formation of C3A crystals, which helps to improve the ability of oil well cement to resist sulfuric acid corrosion. Attached Figure Description

[0019] Figure 1 The image shows a comparison of the XRD patterns of lithium-doped oil well cement and Grade G oil well cement in Example 4.

[0020] Figure 2 The triaxial stress-strain curves of cement stone specimens from Examples 2-5 and the control example after curing at 150℃ and 20MPa for 7 days are shown. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0022] Example 1:

[0023] A lithium-doped oil well cement, by weight, comprises 95-97 parts of oil and gas well cement clinker and 3-5 parts of natural dihydrate gypsum; the oil and gas well cement clinker is obtained by sintering raw meal powder, the raw meal powder comprising 75%-80 parts of limestone, 2-5 parts of spodumene solid waste leached by nitric acid pressure, 5.5-8.5 parts of sandstone, 5.5-6.0 parts of aluminum ore waste and 2.5-3.5 parts of iron ore waste.

[0024] In this embodiment, the present invention uses nitric acid pressure leaching of spodumene solid waste as a raw material for sintering oil and gas well cement clinker. While providing silica and alumina, the nitric acid pressure leaching of spodumene solid waste contains trace amounts of Li₂O. Since Li... + With its small ionic radius and relatively high field strength, Li3S plays a role in the accumulation of silicate networks during the sintering process of oil and gas well cement clinker, thereby promoting the growth of C3S crystals, increasing C3S grain size, and enhancing reactivity, especially improving the early-stage reactivity of lithium-doped oil well cement. Furthermore, in Li... + Under the strong migration ability of lithium ions, Fe atoms in C4AF can be further induced to replace aluminum atoms, resulting in the transformation of the Fe-O four-coordinate structure [FeO4] to the Fe-O six-coordinate structure [FeO6], and the transformation of [AlO6] to [AlO4]. On the one hand, since the Fe-O bond is longer and has a lower breaking energy than the Al-O bond, the activation energy of the C4AF reaction is reduced, the hydration reactivity of C4AF is increased, and the formation of AFm-OH phase hydration products is promoted. The doping of AFm-OH phase on the surface and between layers of CSH can improve the deformability of CSH, densify the interlayer structure, and thus improve the strength and toughness of cement stone. On the other hand, the transformation of [AlO6] to [AlO4] inhibits the formation of C3A crystals, which helps to improve the ability of oil well cement to resist sulfuric acid corrosion. Under the migration of lithium ions, the Al ion migration during the sintering process is promoted. 3+ For Ca in C2S 2+ and Si 4+ The substitution effect of aluminum promotes the formation of aluminum-doped calcium silicate hydrate during the hydration reaction, thereby improving the high-temperature resistance of the hydration products.

[0025] Example 2

[0026] Step 1: Limestone, spodumene solid waste leached by nitric acid pressure, sandstone, aluminum ore waste, and iron ore waste are ground together in a weight percentage ratio of 79.7:4.2:7.2:5.7:3.2 to a particle size of 80μm to obtain cement raw materials.

[0027] Step 2: The cement raw meal obtained in Step 1 is calcined at a kiln speed of 1.0 rpm and a temperature of 1360℃ to obtain cement clinker with a mass of 1460 g / L.

[0028] Step 3: Mix the cement clinker obtained in Step 2 with natural gypsum at a weight ratio of 96:4, and grind it in a mill until the specific surface area is 320 m2 / kg to obtain lithium-doped oil well cement.

[0029] Step 4: Prepare cement slurry by mixing the obtained lithium-doped oil well cement with the cement according to the requirements of GB / T-19139 "Test Methods for Oil Well Cement", with a water-cement ratio of 0.44.

[0030] Step 5: Place the cement slurry obtained in Step 4 into a cubic mold with dimensions of 50.8*50.8*50.8mm, and cure the prepared sample in a high-temperature and high-pressure curing autoclave at 150℃ and 20MPa for 7 days in accordance with GB / T-19139 "Test Methods for Cement in Oil Wells".

[0031] Example 3

[0032] Step 1: Limestone, spodumene solid waste leached by nitric acid pressure, sandstone, aluminum ore waste, and iron ore waste are ground together in a weight ratio of 80:4.5:6.9:5.5:3.1 to a particle size of 86μm to obtain cement raw materials.

[0033] Step 2: The cement raw meal obtained in Step 1 is calcined at a kiln speed of 1.0 rpm and a temperature of 1355℃ to obtain cement clinker with a mass of 1455 g / L.

[0034] Step 3: Mix the cement clinker obtained in Step 2 with natural gypsum at a weight ratio of 97:3, and grind it in a mill until the specific surface area is 325 m2 / kg to obtain lithium-doped oil well cement.

[0035] Step 4: Prepare cement slurry by mixing the obtained lithium-doped oil well cement with the cement according to the requirements of GB / T-19139 "Test Methods for Oil Well Cement", with a water-cement ratio of 0.44.

[0036] Step 5: Place the cement slurry obtained in Step 4 into a cubic mold with dimensions of 50.8*50.8*50.8mm, and cure the prepared sample in a high-temperature and high-pressure curing autoclave at 150℃ and 20MPa for 7 days in accordance with GB / T-19139 "Test Methods for Cement in Oil Wells".

[0037] Example 4

[0038] Step 1: Limestone, spodumene solid waste leached by nitric acid pressure, sandstone, aluminum ore waste residue, and iron ore waste residue are ground together in a weight percentage ratio of 79.4:4.4:7.1:5.8:3.3 to a particle size of 83μm to obtain cement raw materials.

[0039] Step 2: The cement raw meal obtained in Step 1 is calcined at a kiln speed of 0.9 rpm and a temperature of 1365℃ to obtain cement clinker with a mass of 1460 g / L.

[0040] Step 3: Mix the cement clinker obtained in Step 2 with natural gypsum at a weight ratio of 95:5, and grind it in a mill until the specific surface area is 330 m2 / kg to obtain lithium-doped oil well cement.

[0041] Step 4: Prepare cement slurry by mixing the obtained lithium-doped oil well cement with the cement according to the requirements of GB / T-19139 "Test Methods for Oil Well Cement", with a water-cement ratio of 0.44.

[0042] Step 5: Place the cement slurry obtained in Step 4 into a cubic mold with dimensions of 50.8*50.8*50.8mm, and cure the prepared sample in a high-temperature and high-pressure curing autoclave at 150℃ and 20MPa for 7 days in accordance with GB / T-19139 "Test Methods for Cement in Oil Wells".

[0043] Example 5

[0044] Step 1: Limestone, spodumene solid waste leached by nitric acid pressure, sandstone, aluminum ore waste, and iron ore waste are ground together in a weight percentage ratio of 79.1:4.3:7.3:5.9:3.4 to a particle size of 90μm to obtain cement raw materials.

[0045] Step 2: The cement raw meal obtained in Step 1 is calcined at a kiln speed of 1.1 rpm and a temperature of 1360°C to obtain cement clinker with a mass of 1450 g / L.

[0046] Step 3: Mix the cement clinker obtained in Step 2 with natural gypsum at a weight ratio of 94:6, and grind it in a mill until the specific surface area is 325 m2 / kg to obtain lithium-doped oil well cement.

[0047] Step 4: Prepare cement slurry by mixing the obtained lithium-doped oil well cement with the cement according to the requirements of GB / T-19139 "Test Methods for Oil Well Cement", with a water-cement ratio of 0.44.

[0048] Step 5: Place the cement slurry obtained in Step 4 into a cubic mold with dimensions of 50.8*50.8*50.8mm, and cure the prepared sample in a high-temperature and high-pressure curing autoclave at 150℃ and 20MPa for 7 days in accordance with GB / T-19139 "Test Methods for Cement in Oil Wells".

[0049] Comparison Example

[0050] Step 1: Mix G-grade oil well cement clinker with natural gypsum at a weight ratio of 97:3, and grind them in a mill until the specific surface area is 320 m2 / kg to obtain G-grade oil well cement.

[0051] Step 2: Prepare cement slurry from the obtained Grade G oil well cement according to the requirements of GB / T-19139 "Test Methods for Oil Well Cement", with a water-cement ratio of 0.44.

[0052] Step 3: Place the cement slurry obtained in Step 2 into a cubic mold of 50.8*50.8*50.8mm, and cure the prepared sample in a high-temperature and high-pressure curing autoclave at 150℃ and 20MPa for 7 days in accordance with GB / T-19139 "Test Methods for Cement in Oil Wells".

[0053] Table 1 shows the mechanical properties of the samples prepared in Examples 2-5 and the control after curing in a high-temperature and high-pressure curing vessel at 150℃ and 20MPa for 7 days:

[0054] Table 1. Mechanical Properties of Cement Stone

[0055] Example Test block size Compressive strength (MPa) Tensile strength (MPa) Example 2 50.8*50.8*50.8mm 40.88 4.38 Example 3 50.8*50.8*50.8mm 39.62 4.41 Example 4 50.8*50.8*50.8mm 40.02 4.31 Example 5 50.8*50.8*50.8mm 39.15 4.26 Comparison Example 50.8*50.8*50.8mm 27.36 2.72

[0056] The lithium-doped oil well cement prepared in Example 4 was characterized by XRD. Figure 1 The image shows the XRD diffraction pattern of lithium-doped oil well cement in Example 4. The C3A diffraction peaks of the lithium-doped oil well cement in Example 4 are more diffuse, while the peak width of the C4AF diffraction peaks is reduced, indicating that the crystallization of C3A in Example 4 is suppressed, while the crystal structure of C4AF changes. Furthermore, the diffraction peaks between 50-52° in Example 4 are significantly enhanced, indicating that the C3S crystals have grown sufficiently and exhibit high reactivity.

[0057] Figure 2 The figures show the triaxial stress-strain curves of cement stone cured at 150℃ and 20MPa for 7 days. The test results show that the area enclosed by the triaxial stress-strain curves and the X-axis of all examples is larger than that of the control example, indicating that the examples increased the energy required for cement stone failure and simultaneously improved the strength and toughness of the cement stone.

[0058] This method uses lithium salt solid waste extracted under pressure with nitric acid as a raw material, achieving in-situ improvement of the mechanical properties of oil well cement. From a scientific perspective, this method solves the problem of uncoordinated development of strength and toughness in cement stone. From a process perspective, it overcomes the cumbersome chemical and physical surface modification processes required for "exogenous" toughening materials in cement. From an economic standpoint, the cost of the solid waste raw materials used is lower than that of natural mineral materials.

[0059] The above are embodiments of the present invention. The above embodiments and specific parameters are only for clearly illustrating the invention verification process and are not intended to limit the patent protection scope of the present invention. The patent protection scope of the present invention shall still be determined by its claims. Similarly, any equivalent structural changes made based on the description and drawings of the present invention shall also be included within the protection scope of the present invention.

Claims

1. A lithium-doped oil well cement, characterized in that, By weight, the lithium-doped oil well cement comprises 95-97 parts of oil and gas well cement clinker and 3-5 parts of natural dihydrate gypsum; the oil and gas well cement clinker is obtained by sintering raw meal powder, which is calcined in a rotary kiln at a temperature of 1300-1380℃, and the raw meal powder comprises 75-80 parts of limestone, 2-5 parts of nitric acid pressure leaching lithium spodumene solid waste, 5.5-8.5 parts of sandstone, 5.5-6.0 parts of aluminum ore waste residue, and 2.5-3.5 parts of iron ore waste residue; The nitric acid pressure leaching of spodumene solid waste comprises the following chemical composition by mass fraction: SiO2 75-80%; Al2O3 15-20%; Li2O 0.05~0.1%; Impurity oxides: 0.01%–4%; The impurity oxide is a composition of one or more oxides selected from Fe2O3, K2O, CaO, and MgO.

2. A method for preparing lithium-doped oil well cement, used to obtain the lithium-doped oil well cement of claim 1, characterized in that, include: Limestone, spodumene solid waste leached under pressure with nitric acid, sandstone, aluminum ore waste residue, and iron ore waste residue are ground together to obtain cement raw meal powder. The raw meal powder is calcined to obtain cement clinker for oil and gas wells; The obtained oil and gas well cement clinker was mixed with natural dihydrate gypsum and ground in a mill to obtain lithium-doped oil well cement.

3. The method for preparing lithium-doped oil well cement according to claim 2, characterized in that: In the process of grinding limestone, spodumene solid waste leached by nitric acid, sandstone, aluminum ore waste residue, and iron ore waste residue together, the particle size is controlled within the range of 75–105 μm.

4. The method for preparing lithium-doped oil well cement according to claim 2, characterized in that: The raw meal powder is calcined in a rotary kiln at a temperature of 1300–1380℃ and a kiln speed of 0.8–1.2 rpm. The vertical weight of the oil and gas well cement clinker is ≥1450 g / L.

5. The method for preparing lithium-doped oil well cement according to claim 2, characterized in that: During the mixing process of the obtained oil and gas well cement clinker and natural dihydrate gypsum, the amount of oil and gas well cement clinker is 95-97 parts, and the amount of natural dihydrate gypsum is 3-5 parts; the specific surface area of ​​the powder is controlled to be 310-340 m² during the mixing and grinding of the oil and gas well cement clinker and natural dihydrate gypsum. 2 / kg.

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