A heat-preservation cement material for upper well section of geothermal well and a preparation method thereof

Abstract

The application provides a geothermal well upper section heat preservation cement material and a preparation method thereof, and belongs to the technical field of oil well cement.The geothermal well upper section heat preservation cement material is composed of solid phase components and liquid phase components, wherein the solid phase components include a cement matrix, a reinforcing material, an early strength agent and a stabilizing agent; and the liquid phase component is a retarder.The heat preservation cement material has good high-temperature stability, and has no obvious sedimentation phenomenon, a free liquid content of 0%, and a filtration loss of less than 50ml.The thermal conductivity and the compressive strength of the heat preservation cement material at 110 DEG C are 0.1555 W / (m*K) and 20.47 MPa (2 days) respectively, and 0.1589 W / (m*K) and 20.56 MPa (14 days) respectively, and the strength is greater than 7 MPa.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oil well cement, and particularly relates to a heat preservation cement material for an upper well section of a geothermal well and a preparation method thereof. BACKGROUND

[0002] China is rich in geothermal energy reserves, of which the shallow geothermal energy reserves are 2.78 x 10 20 J, the geothermal reserves in sedimentary basins are 2.5 x 10 22 J, the heat release in hot spring areas is 1.32 x 10 17 J, and the dry hot rock heat reserves 3-5 km deep are 2.5 x 10 25 J. As early as the last century, China has developed and utilized geothermal energy, and established the first high-temperature geothermal power station, Yangbajing Geothermal Power Station, with a installed capacity of 26.18 MW. However, as of 2017, the exploitation rate of hydrothermal geothermal resources and shallow geothermal energy in China was only 0.2% and 2.3%, respectively, and the potential for geothermal exploitation is huge.

[0003] There are many research results on the development of geothermal energy at present, including geothermal well cementing materials, heat exchange process simulation, process monitoring technology, equipment research and development, water treatment, corrosion and scale prevention, drilling efficiency improvement, steam-water separation and intelligent control, etc. These research results are of great help to the development and utilization of geothermal energy, but are still not comprehensive in improving the outlet temperature of the heat transfer medium of the geothermal well.

[0004] Well bottom temperature, production capacity and heat loss along the way are important factors affecting the wellhead temperature. The heat transfer medium in the production well transfers heat to the low-temperature formation through the casing-cement ring during upward transportation. According to Fourier's law, the greater the absolute value of the temperature gradient, the greater the heat flux density, and the faster the heat transfer. From the well bottom to the ground, the formation temperature is decreasing, that is, the heat loss along the way is gradually increasing during the upward transportation of the heat transfer medium. Reducing the thermal conductivity of the cementing cement can reduce the heat loss of the heat transfer medium, thereby improving the wellhead temperature. Therefore, it is urgent to study the thermal conductivity of geothermal well cement and develop a heat preservation cement formula that can be applied to actual geothermal production.

[0005] And the current thermal insulation cement-based material compressive strength, thickening time and other performance indicators are difficult to meet the requirements of well cementing. The research on thermal insulation cement for geothermal is mostly concentrated in the discussion of insulation effect and analysis of influencing factors. Shen et al. (2022) obtained a thermal insulation cement formula suitable for 90℃ through experiments and evaluated its strength and thermal conductivity, but there is no complete thermal insulation cement formula suitable for geothermal exploitation at present (Author: Shen L, Tan H, Ye Y, et al. Year: 2022. Title: Using fumed silica to develop thermal insulation cement for medium–low temperature geothermal wells [J]. Journal name: Materials, Volume 15 Page 5087.).

[0006] The thermal conductivity of G-grade oil well cement is relatively low, and it will further decrease when the curing temperature exceeds 110℃. However, the upper well section of geothermal well loses heat the fastest due to the large temperature difference with the heat transfer medium. The upper well section is very long, and the temperature is mostly below 110℃, which is within the temperature range of increasing thermal conductivity. Therefore, it is necessary to conduct targeted research on thermal insulation cement materials for the upper well section of geothermal well.

[0007] Therefore, it is necessary to develop a thermal insulation cement formula that meets the actual requirements of geothermal well cementing, thereby improving the wellhead temperature of geothermal well and improving the utilization efficiency of geothermal resources, which has very important practical engineering significance and scientific value. SUMMARY

[0008] The purpose of the present application is to provide a thermal insulation cement material for the upper well section of geothermal well and a preparation method thereof.

[0009] The present application provides a thermal insulation cement material for the upper well section of geothermal well, characterized in that:

[0010] The thermal insulation cement material is composed of solid phase components and liquid phase components, wherein the solid phase components include cement matrix, reinforcing material, early strength agent and stabilizer; the liquid phase component is a retarder;

[0011] The cement matrix is composed of oil well cement and thermal insulation filler, wherein the percentage content of thermal insulation filler is (5-25)%;

[0012] The weight ratio of cement matrix, reinforcing material, early strength agent, stabilizer and retarder is (80-100):(2.5-12.5):(1-3.5):(0.01-2.5):(0.05-0.25).

[0013] The cement base: reinforcing material: early strength agent: stabilizer: retarder weight ratio is 100:(2.5-12.5):(1-3.5):(0.01-2.5):(0.05-0.25).

[0014] The oil well cement is G-grade oil well cement;

[0015] The thermal insulation filler is selected from one or more than two kinds of mixture of fly ash, silica fume, 100 mesh diatomite, 200 mesh diatomite, 100 mesh expanded vermiculite, 300 mesh expanded vermiculite, meerschaum powder, 50-100 mesh perlite powder, 100-200 mesh floating bead, HGB-1, 100 mesh-200 mesh perlite powder, HGB-2, HGB-3, HGB-4;

[0016] The reinforcing material is selected from I-SiO2, II-SiO2 and or III-SiO2;

[0017] The early strength agent is selected from ZQ-4, triethanolamine, anhydrous sodium sulfate, 7042F, 7100L;

[0018] The stabilizer is 3050F;

[0019] The retarder is MXSK-2.

[0020] The thermal insulation filler is HGB-4; the reinforcing material is II-SiO2; and the early strength agent is ZQ-4.

[0021] The cement base is composed of G-grade oil well cement and HGB-4, wherein the percentage content of HGB-4 is (17-23)%;

[0022] The cement base: II-SiO2: ZQ-4: 3050F: MXSK-2 weight percentage is 100:(5-10):2.5:0.02:(0.1-0.15).

[0023] The cement base is composed of G-grade oil well cement and HGB-4, wherein the percentage content of HGB-4 is 20%;

[0024] The cement base: II-SiO2: ZQ-4: 3050F: MXSK-2 weight percentage is 100:5:2.5:0.02:(0.1-0.15), preferably 100:5:2.5:0.02:0.1.

[0025] The cement base is composed of G-grade oil well cement and HGB-4, wherein the percentage content of HGB-4 is 22.6%;

[0026] The cement base: II-SiO2: ZQ-4: 3050F: MXSK-2 weight percentage is 100:5.1:2.5:0.02:0.1.

[0027] The present application also provides a thermal insulation cement slurry, which is prepared by mixing the thermal insulation cement material and water, wherein the water-solid ratio is 0.55-0.75.

[0028] The cement slurry is prepared by the following method:

[0029] (1) mixing and stirring cement, thermal insulation filler, reinforcing agent, early strength agent and stabilizer to obtain a solid phase mixture;

[0030] (2) mixing and stirring water and retarder to obtain a liquid phase mixture;

[0031] (3) mixing the solid phase mixture obtained in step (1) and the liquid phase mixture obtained in step (2) and stirring to obtain the cement slurry;

[0032] The water-solid ratio is 0.55-0.75, preferably 0.7-0.71.

[0033] The present application also provides a use of the thermal insulation cement material for thermal insulation of the upper well section of a geothermal well.

[0034] The experimental results show that the present application provides a thermal insulation cement material for the upper well section of a geothermal well and a preparation method thereof. The cement material has good high-temperature stability, no obvious sedimentation, free liquid content of 0%, filtration loss of <50 ml, thermal conductivity of 0.1555 W / (m·K) and compressive strength of 20.47 MPa (2 days) at 110℃, thermal conductivity of 0.1589 W / (m·K) and compressive strength of 20.56 MPa (14 days), and the strength is greater than 7 MPa. The comprehensive performance meets the design requirements.

[0035] Obviously, according to the above content of the present application, according to the ordinary technical knowledge and common means in the art, other various forms of modifications, replacements or changes can be made without departing from the above technical idea of the present application.

[0036] The above content of the present application is further described in detail through the following embodiment. However, it should not be understood that the above subject matter of the present application is limited to the following examples. Any technology realized based on the above content of the present application belongs to the scope of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 Cement slurry preparation and water bath curing process;

[0038] Figure 2 Cement high-temperature curing method;

[0039] Figure 3Thermal insulation filler screening results (0-control group, 1-fly ash, 2-silica ash, 3-100 mesh diatomite, 4-325 mesh diatomite, 5-100 mesh expanded vermiculite, 6-300 mesh expanded vermiculite, 7-sepiolite powder, 8-50-100 mesh perlite powder, 9-100-200 mesh floating beads, 10-HGB-1, 11-HGB-1, 12-100 mesh-200 mesh perlite powder, 13-HGB-2, 14-HGB-3, 15-HGB-4);

[0040] Figure 4 Thermal insulation filler dosage effect on cement performance trends;

[0041] Figure 5 Deviation value change under different 3050F dosages;

[0042] Figure 6 Actual value and predicted value relationship diagram: (a) compressive strength test, (b) thermal conductivity test;

[0043] Figure 7 Interaction analysis between compressive strength influencing factors;

[0044] Figure 8 Interaction analysis between thermal conductivity influencing factors;

[0045] Figure 9 Thickening time test results: (a) 0.1% MXSK-2, (b) 0.2% MXSK-2;

[0046] Figure 10 Free liquid and sedimentation test samples;

[0047] Figure 11 Compressive strength and thermal conductivity test results. DETAILED DESCRIPTION

[0048] The raw materials and equipment used in the present application are known products, which are obtained by purchasing commercially available products.

[0049] The following is the information of some raw materials:

[0050] Table 1 Raw material information

[0051]

[0052]

[0053] The G-grade high oil-resistant well cement of the present application: the G-grade high oil-resistant well cement produced by Sichuan Jiahua Cement Plant, which meets the requirements of GB / T10238-2015

[0054] Example 1, the nature of the thermal insulation cement of the present application

[0055] I. Performance index requirements of target thermal insulation cement

[0056] (1) The thermal insulation cement slurry should have good fluidity (18-22 cm) for easy mixing.

[0057] (2) The density of the thermal insulation cement slurry should be between 1.0-1.4 g / cm 3 .

[0058] (3) The initial consistency of the thermal insulation cement slurry is less than 30Bc, and the high-temperature thickening time can be adjusted according to different depths.

[0059] (4) The thermal insulation cement slurry has good stability at high temperature, the density difference between the upper and lower layers should not exceed 0.05 g / cm 3 , the filtration loss should be less than 100 ml, and the free liquid content should be less than 1.4%.

[0060] (5) The 48h compressive strength of the thermal insulation cement is not less than 7MPa.

[0061] II. Composition selection

[0062] (1) Thermal insulation filler

[0063] The thermal insulation filler used in the present application is hollow glass beads, i.e. hollow glass beads (HGB), the main component of which is soda lime borosilicate glass, the density of which is between 0.125-0.6 g / cm 3 , and the thermal conductivity is 0.003-0.01 BTU / in.hr. ℉. According to the particle size and strength, it is divided into HGB-1, HGB-2, HGB-3 and HGB-4, and the particle sizes are 70μm, 100μm, 110μm and 75μm respectively.

[0064] The thermal insulation filler used in the present application is HGB-4, which is a hollow structure with a particle size of 15-85μm. Among them, the volume fraction of 75μm beads is about 90%, and the existence of the remaining small particle size beads helps to reduce the pores between particles.

[0065] (2) Reinforcing material

[0066] Due to the high water-cement ratio of the formula and the nature of the thermal insulation filler, the compressive strength of the cured cement is severely reduced, which cannot meet the actual application requirements, so it is necessary to add a corresponding strength enhancing material to improve the strength, and the addition of silicon dioxide can effectively improve the strength of the cement.

[0067] (3) Admixture

[0068] Some additives need to be added to adjust the fluidity, structural stability, thickening time and other properties of the composite cement. The early strength agent used in the application includes ZQ-4, anhydrous sodium sulfate, triethanolamine and 7042F, wherein ZQ-4, anhydrous sodium sulfate and triethanolamine are purchased from the China National Pharmaceutical Group, and 7042F is purchased from BASF (China) Co., Ltd.; the stabilizer used is 3050F; and the retarder includes MXSK-1, MXSK-2 and FK-6, wherein the MXSK series is purchased from Mei Xi Material Co., Ltd., and FK-6 is purchased from Feike New Material Technology Co., Ltd.

[0069] III. Cement paste preparation and curing method

[0070] 1. Cement paste preparation method

[0071] The preparation process of the cement paste is as shown in Figure 1 , and the specific steps are as follows:

[0072] (1) Mix and stir cement, heat insulation filler, reinforcing agent, early strength agent and stabilizer to obtain a solid phase material mixture;

[0073] (2) Mix water and retarder to obtain a liquid phase mixture;

[0074] (3) Mix the solid phase material mixture obtained in step (1) and the liquid phase mixture obtained in step (2), and obtain a stable cement paste liquid by stirring.

[0075] 2. Standard curing and curing below 100 DEG C

[0076] Pour the prepared paste liquid into a 40x40x40mm steel mold, and place it in a SHBY-40B type standard curing box for standard curing. Other curing processes below 100 DEG C are completed in a water bath, and the three-union steel mold is placed in the water bath, and steaming is performed to the specified time.

[0077] 3. High temperature curing method

[0078] The early stage of the test mainly uses the method shown in Figure 2 . First, the cement paste liquid is heated to lose pumpability by high-temperature rolling, then poured into a three-union steel mold, and after fully oscillating to remove bubbles, the mold is placed in a water bath at 60 DEG C for 3h, and then taken out and placed in an aging kettle, and then the aging kettle is placed in an XGRL-4 type roller heating furnace produced by Qingdao Baileyda for high-temperature curing. The high-temperature roller furnace is an instrument for testing the high-temperature performance of drilling fluid, and the matching aging kettle is a closed container that can ensure that the water does not evaporate at a temperature greater than 100 DEG C. The internal pressure of this curing method is less than 20.7MPa specified in the standard.

[0079] After the optimal formula is obtained, the curing temperature is determined according to the relevant standards, the pressurized curing kettle is used for curing at 110 DEG C and 20.7 MPa, and then the compressive strength and the thermal conductivity are tested, so that the performance parameters of the accurate optimal formula are obtained.

[0080] Four, development of heat preservation cement for upper well section of geothermal well

[0081] (I) determination of curing temperature

[0082] The curing temperature of the present application is set at 110 DEG C. The temperature meets the actual downhole conditions and is also the critical temperature of the strength decline of cement at high temperature. When there is a demand for exploiting and utilizing higher temperature geothermal resources and the corresponding technical conditions are provided, the heat preservation cement material suitable for higher temperature can be developed more conveniently and quickly on the basis.

[0083] (II) selection of heat preservation cement heat insulation filler

[0084] 1. Heat insulation filler selection experiment

[0085] According to the performance requirements, environmental protection and workability of the heat preservation cement, 11 kinds of materials are selected, and the performance of the materials is compared under the same addition amount. The test scheme is shown in Table 2. According to the difference in water absorption of the materials, two kinds of water-solid ratio (the ratio of water to solid material, the solid material is cement and filler) schemes are set for the test. The water-solid ratio of test 0-10 is 0.55, and 10% heat insulation filler is internally mixed. The water-solid ratio of test 11-15 is 0.6, and 5% heat insulation filler is internally mixed. After the sample is cured at 110 DEG C for 2 days, the thermal conductivity and the compressive strength are tested, and the test results are shown in Table 3. Figure 3

[0086] Table 2: Filler selection test scheme

[0087]

[0088] From Figure 3 ​It can be seen that the addition of fillers has an adverse effect on the compressive strength of cement. (Zhang Tengteng et al., 2022; Zhang Tao et al., 2022) Research results show that the addition of fly ash and silica fume has a certain role in improving the compressive strength of cement under high temperature curing (Zhang Tao, Zhu Cheng. 2022. Research on strength, shrinkage performance and microstructure of cement-silica fume / fly ash system [J]. Bulletin of the Chinese Ceramic Society, 41(03): 903-912. Zhang Tengteng, Wang Chuanlin, Zhang Yuexuan, et al. 2022. Effect of fly ash content on performance of seawater and sea sand high-performance concrete [J]. Bulletin of the Chinese Ceramic Society, 41(05): 1677-1688.) However, in the test results this time, it is a weakening effect. The reason for analysis is that the addition of fillers indirectly reduces the amount of cement, which is the main reason for the decrease in compressive strength of cement. And other fillers are because the material itself is loose and porous, with low compressive strength, and the connection with cement is not firm, etc. which causes the strength to decrease.

[0089] At the same time, the addition of thermal insulation fillers reduces the thermal conductivity of cement to varying degrees. In the 0.55 water-solid ratio series test, the addition of HGB-1 has the most significant effect on reducing the thermal conductivity of cement, and the amount is changed to move it into the 0.6 water-solid ratio series for further screening. It can be seen that the thermal conductivity of HGB-3 and HGB-4 is about 0.38 W / (m·K), while that of HGB-1 is 0.4014 W / (m·K), which is not superior in terms of thermal insulation effect. HGB-3 and HGB-4 have almost the same thermal insulation effect, but HGB-3 has a greater impact on compressive strength, which is 45.4% lower than the control group of 25.63 MPa. At the same time, HGB-3 has strong water absorption, with a flow degree of only 11 cm under the condition of 5% internal addition and water-solid ratio of 0.6, which is very unfavorable for subsequent formula research. While the compressive strength and flow degree of HGB-4 are not as good as HGB-1, but the difference is within an acceptable range, and its lower thermal conductivity is also more conducive to the research of thermal insulation cement formula, so the invention chooses HGB-4 as the thermal insulation filler.

[0090] The experimental results show that under different conditions, the addition of different thermal insulation fillers reduces the thermal conductivity of cement to varying degrees, but also reduces the compressive strength of cement. Under the condition of 0.6 water-solid ratio, when the thermal insulation filler is 10%, the thermal conductivity of HGB-4 is the lowest, about 0.38 W / (m·K).

[0091] 2. Screening of thermal insulation filler HGB-4

[0092] After selecting HGB-4 as the thermal insulation filler, the influence of different HGB-4 addition amounts (Table 3) on the performance of cement was explored through experiments, and the experimental results are shown in Table 3. Since HGB-4 has strong water absorption, in order to maintain a certain fluidity under a larger addition amount and at the same time reserve a certain fluidity space for the subsequent addition of materials, the water-solid ratio is selected as 0.7, and the performance is tested after curing at 110 DEG C for 2 days, and the performance change trend is shown in Figure 4

[0093] Table 3 Test results of thermal insulation filler addition amount

[0094]

[0095] From Figure 4 and Table 3, it can be seen that with the increase of HGB-4 addition amount, the fluidity of the cement slurry decreases linearly, and when the addition amount reaches 25%, the fluidity is 12.6 cm (<14 cm), which has lost pumpability. HGB-4 material itself has small particle size and light mass, and under the same addition amount, the total volume will be larger than that of general materials, and the water absorption will be stronger. When the addition amount increases from 5% to 25%, the compressive strength decreases by 38.5%. In terms of thermal conductivity, HGB-4 can well reduce the thermal conductivity of cement, and the thermal conductivity decreases by 53.7% when the addition amount is 25% compared with that when the addition amount is 5%. The increase of addition amount enables HGB-4 to form more "thermal insulation nodes" in the cement matrix, thereby reducing the overall thermal conductivity of cement.

[0096] Considering the fluidity, compressive strength and thermal conductivity, although the thermal conductivity of cement with 25% addition amount is the lowest, its strength and fluidity are too low to meet the engineering requirements, and it is difficult to improve subsequently, therefore, 20% addition amount is selected as the basis for subsequent research.

[0097] (Three) Selection of reinforcing materials

[0098] 1. Experimental method

[0099] The present application selects three kinds of SiO2 powder with decreasing particle size, and the specific parameters are shown in Table 4. The water-solid ratio is set to 0.7, and the HGB-4 addition amount is 20%. The sample is cured at 110 DEG C for 2 days. The test scheme and results are shown in Table 5, wherein the percentage of reinforcing material is the percentage of the sum of the mass of cement and HGB-4.

[0100] Table 4 Partial parameters of SiO2 powder

[0101]

[0102] 2. Experimental results

[0103] The experimental results are shown in Table 5, and the analysis of the experimental results shows that: ​

[0104] Table 5 Intensity-enhancing material screening test scheme and results

[0105]

[0106] (1) With the increase of the amount, the flowability of the three different particle sizes of SiO2 all showed a downward trend, and the smaller the particle size, the stronger the water absorption. When the amount of III-SiO2 exceeded 0.6%, it lost pumpability, and the amount of the other two exceeded 7.5% to lose pumpability.

[0107] (2) The three different particle sizes of SiO2 can all improve the compressive strength of cement, among which II-SiO2 has the best improvement effect, which is 50% higher than that of the control group. With the increase of the amount of the three SiO2, the compressive strength first increases and then decreases. SiO2 can participate in the hydration reaction under high temperature conditions to generate more hydration products and improve the compressive strength of cement stone. If the amount is too high, the slurry flowability will decrease, the material cannot be effectively dispersed, and "micro defects" will be formed.

[0108] (3) The addition of SiO2 will make the thermal conductivity of cement stone increase, among which the improvement effect of I-SiO2 is the most obvious, which is increased by 26.5%, followed by II-SiO2, and III-SiO2 has the smallest improvement range. Preliminary analysis shows that the secondary hydration of SiO2 makes the cement stone more dense, the number of pores decreases, and the thermal conductivity increases accordingly. At the same time, SiO2 that does not participate in the secondary hydration is embedded in the cement matrix, and the thermal conductivity of crystalline SiO2 is higher than that of amorphous C-S-H gel, which promotes heat conduction.

[0109] Through the comparison of the improvement effect of the three particle sizes of SiO2 on the strength, the negative influence on the flowability and thermal conductivity, and the comprehensive consideration, II-SiO2 is selected as the reinforcing material, and the optimal amount range is about 5%. The SiO2 below is II-SiO2 unless otherwise specified.

[0110] The experimental results show that under the conditions of water-solid ratio of 0.7, HGB-4 amount of 20%, curing condition of 110°C, and curing time of 2 days, the application selects II-SiO2 as the reinforcing material by comparing the improvement effect of the three particle sizes of SiO2 on the strength, the negative influence on the flowability and thermal conductivity of cement, and the optimal amount range is about 5% of the sum of the mass of cement and HGB-4.

[0111] (Four) Selection of admixture

[0112] 1. Selection of early strength agent and its amount

[0113] Although the use of reinforcing materials improves the compressive strength of cement, further improvement is still needed. There are many types of early strength agents used in the field of concrete, which can be broadly classified into inorganic early strength agents (CaCl2, NaCl, Na2SO4, CaSO4, Ca(NO3)2, etc.) and organic early strength agents (ethylene glycol, propylene glycol, monoethanolamine, diethanolamine, sucrose, glucose, etc.). The performance of the cement formulation with the addition of early strength agent is tested after curing at 110℃ for 2 days, and the test scheme and results are shown in Table 6.

[0114] Table 6 Results of early strength agent screening test

[0115]

[0116] Through comparison, it can be seen that each early strength agent improves the compressive strength of the cement stone, among which ZQ-4 has the most obvious improvement effect, with an improvement of 31%. At the same time, it is found that it also has a certain improvement effect on the fluidity of the cement slurry during the test. Considering comprehensively, ZQ-4 is selected as the early strength agent. In order to make the amount more reasonable, it is necessary to find the optimal amount range through detailed amount test, and the test results are shown in Table 7, wherein the percentage of early strength agent is the percentage of the sum of the mass of cement and HGB-4.

[0117] Table 7 Influence of ZQ-4 early strength agent amount on the performance of cement

[0118]

[0119]

[0120] According to the analysis of the test results, with the increase of the amount of early strength agent ZQ-4, the compressive strength of the cement shows a trend of first increasing and then decreasing, and the turning point is 2.5%, which is increased by 34% compared with the control group. The fluidity also increases with the increase of the amount. In terms of thermal conductivity, the addition of ZQ-4 slightly increases the thermal conductivity of the cement stone, and the overall influence is small. Therefore, the optimal amount range of ZQ-4 should be around 2.5%.

[0121] The experimental results show that by selecting ZQ-4 of the National Pharmaceutical Group, the compressive strength of the cement of the present application is large, the increase of the thermal conductivity is small when the addition amount is 2.5%, the fluidity of the cement is increased, and the compressive strength is increased by nearly 34% compared with the cement with the addition of early strength agent.

[0122] 2. Screening of stabilizer and its addition amount

[0123] The application adds a large amount of HGB-4 to reduce the thermal conductivity of cement. Since HGB-4 has the characteristics of small particle size and light weight, its water absorption is also very obvious under such a large amount. In order to ensure that the cement slurry has a suitable fluidity to facilitate mixing, it is necessary to increase the water-solid ratio. However, too high water-solid ratio will lead to poor slurry stability and increased bleeding rate. At the same time, the density of cement clinker, HGB-4 and SiO2 powder in the formula is quite different, and sedimentation is easy to occur during the hydration of cement, which eventually leads to a certain difference in the upper and lower strength and thermal conductivity of the cement sheath.

[0124] Therefore, it is necessary to add a stabilizer. The stabilizers currently used in the field of cementing and drilling fluid mainly include ultra-fine calcium carbonate, natural polymer, synthetic polymer copolymer, clay, cellulose derivative, micro-silicon powder and biological polysaccharide. Since the amount of some stabilizers is small, it is difficult to weigh in small volume tests, and the influence on fluidity is also large.

[0125] The application selects 3050F as a stabilizer. 3050F is a light yellow high molecular polymer stabilizer, which has high anti-settling and anti-bleeding effects, and has water retention and filtration loss reduction effects. According to the characteristics of the stabilizer, a six-speed rotary viscometer is selected to test its effect under different amounts, and the influence on thermal conductivity and compressive strength is tested after curing at 110 DEG C for 2 days. The test results of the stabilizer amount test are shown in Tables 8 and 9, the deviation value is the difference between the speed ratio and 1, which represents the difference between the two viscometer readings, and the change trend is shown in Figure 1. Figure 5 Wherein the percentage of the stabilizer is the percentage of the sum of the mass of the cement and HGB-4.

[0126] Table 8 3050F amount test results

[0127]

[0128]

[0129] Table 9 Influence of 3050F amount on compressive strength and thermal conductivity

[0130]

[0131] Combining Tables 8, Figure 5 It can be seen that since 3050F itself has a certain thickening effect, with the increase of the amount, the viscosity of the cement slurry is gradually increased. At the same time, the deviation value also gradually approaches to 0 with the increase of the amount, which shows that the addition of 3050F helps to reduce the sedimentation in the cement slurry, and the more the amount, the better the water retention and anti-settling effect of the cement slurry.

[0132] From the analysis of Table 9, it can be seen that the addition of 3050F reduces the fluidity of the cement paste, and the fluidity is 14.2 cm when the addition amount is 0.025%, which is close to the loss of pumpable period. In terms of the thermal conductivity, the addition of 3050F can slightly reduce the thermal conductivity. The preliminary analysis shows that the addition of 3050F can make HGB-4 more uniformly dispersed in the cement stone, and the light density is not gathered to the upper part. In terms of the compressive strength, the addition of the stabilizer 3050F can reduce the strength, and when the addition amount is 0.025%, the strength is reduced by 7.5%.

[0133] In summary, the addition amount of 3050F is about 0.02%, which can meet the requirements of maintaining the stability of the cement slurry and ensure that the compressive strength and fluidity are in a reasonable range.

[0134] The experimental results show that the selection of 3050F as the stabilizer and the selection of the addition amount of 3050F as 0.02% can meet the requirements of maintaining the stability of the cement slurry, and also ensure that the compressive strength and fluidity are in a reasonable range.

[0135] 3. Selection of retarder and its addition amount

[0136] Unlike the building field, the geothermal well heat preservation cement has a longer pumping distance and a higher environmental temperature, and the requirement for the setting time is more stringent. The high temperature can accelerate the hydration of the cement, and in this case, the pumpable period of the cement is sharply shortened, causing pipe blockage. In order to improve the pumpable period of the heat preservation cement and meet the requirements of high-temperature downhole pumping, a retarder needs to be added to delay the hydration reaction.

[0137] At present, the retarder categories mainly include organic polymer, inorganic-organic polymer composite and compound. Too much addition of the retarder can inhibit the hydration reaction, affect the development of the compressive strength, and even not solidify. Therefore, the retarder with the best retarding effect and less influence on the compressive strength is selected by comparing the retarding effect of MXSK-1, MXSK-2 and FK-6 and their influence on the compressive strength under the same addition amount, and the test results are shown in Table 10.

[0138] Table 10: Retarder screening results

[0139]

[0140]

[0141] From Table 10, it can be seen that the three retarders all have a retarding effect, among which MXSK-1 has the best retarding effect, and FK-6 has the worst retarding effect. In terms of fluidity, MXSK-1 improves the fluidity most, but it causes slight bleeding of the slurry, which affects the stability of the cement slurry, so the fluidity is improved more, which indirectly causes the strength to decrease, and therefore MXSK-1 is not considered.

[0142] MXSK-2 can also improve the fluidity compared with FK-6, has less influence on the strength, and has no great difference in the thermal conductivity, and therefore MXSK-2 with better retarding effect is selected as the retarder. The cement slurry has different requirements for the pumpable period at different depths in the geothermal well, the setting time is too long, the cement slurry diffuses too much in the formation, the amount of the slurry is greatly increased, and the strength is formed more slowly. Meanwhile, the influence of different amounts of MXSK-2 on the thermal conductivity, fluidity and compressive strength of the cement is studied, and the test results of the cement cured at 110 DEG C for 2 days are shown in Table 11.

[0143] Table 11 Influence of MXSK-2 amount on the performance of the heat-preservation cement

[0144]

[0145] Note: In the table, “G-grade oil well cement + 20% HGB-4 + 5% SiO2 + 2.5% ZQ-4 + 0.02% 3050F + MXSK-2”, “G-grade oil well cement + 20% HGB-4” means that the amount of HGB-4 is 20% of the total amount of G-grade oil well cement and HGB-4; “5% SiO2 + 2.5% ZQ-4 + 0.02% 3050F” means that the amounts of SiO2, ZQ-4 and 3050F are 5%, 2.5% and 0.02% of the total amount of G-grade oil well cement and HGB-4 respectively, and “MXSK-2 amount” in the table means that the amount of MXSK-2 is 0.05% to 0.25% of the total amount of G-grade oil well cement and HGB-4.

[0146] From the data in Table 11, it can be seen that the pumpable period and the fluidity increase with the increase of the amount of MXSK-2, which indicates that the addition of MXSK-2 can better adjust the pumpable period, and the amount can be adjusted to adapt to the pumping requirements at different depths. The compressive strength slightly increases and then decreases, and the turning point is at the amount of 0.15%, which is increased by 3.3% compared with the control group. In terms of the thermal conductivity, the increase of the amount causes the thermal conductivity to fluctuate slightly, and the overall influence is small. From the change trend of the pumpable period, the compressive strength and other performances, it can be seen that MXSK-2 can adapt to the heat-preservation cement slurry system.

[0147] The experimental results show that MXSK-2 is selected as the stabilizer, and the amount is 0.1%.

[0148] (v) Optimization of the heat preservation cement formulation

[0149] The present application determines the type and amount range of each admixture and additive, and also knows the influence of the amount of each material on the thermal conductivity, compressive strength and other properties of the heat preservation cement. However, it is still lacking to conclude that the heat preservation cement formulation for geothermal wells is the optimal formulation. The present application uses a response surface method test scheme, constructs a multiple quadratic regression equation based on the test data to fit the relationship between the influence factors and the target value, and the user can obtain the optimal target value and the corresponding parameter value according to the needs. Compared with some traditional test methods, it considers random errors and reduces the number of tests, and has the advantages of precision, speed and easy implementation. Central composite design (CCD) and Box-Behnken Design (BBD) are the two most commonly used methods in response surface method. BBD has fewer test times and higher stability than CCD, so the Box-Behnken Design test design method is selected.

[0150] 1. Response surface test design

[0151] The BBD test method is the same as the orthogonal test method, and it needs to set the influence factors and the corresponding levels. The present application determines the influence factors and levels by referring to the design ideas in similar research results and combining with its own experience; uses single factor test to determine the influence of each factor on the target parameter, so as to determine the factors and levels. It is found that the water-solid ratio, HGB-4, II-SiO2 powder and early strength agent have great influence on the thermal conductivity and compressive strength of the cement stone. The early strength agent is a kind of additive, and its dosage is already limited. The level setting can only change in a small range, and it is difficult to reflect the performance difference in the test, and too much dosage will lead to strength decrease. Therefore, considering comprehensively, the water-solid ratio, HGB-4 and II-SiO2 powder are taken as the influence factors, and the corresponding level setting is shown in Table 12, and the test scheme and the corresponding test results designed by the Design-Expert software are shown in Table 13. Table 12 Factor level setting

[0152]

[0153] Table 13 BBD test scheme design

[0154]

[0155]

[0156] 2. Establishment of regression model and variance analysis

[0157] Based on the test results, the Design-Expert software is used for regression analysis, and the regression equations (codes) of the compressive strength and thermal conductivity are as follows:

[0158] Compressive strength = -42.64 + 201.26A + 58.1B + 36.28C + 161.67AB + 426AC - 353.33

[0159] BC - 208.6A 2 - 465.56B 2 - 1318.4C 2 (4-1)

[0160] Thermal conductivity = 0.4876 - 0.5095A - 1.2281B + 0.7750C - 1.20AB - 0.720AC + 0.2

[0161] 0BC + 0.520A 2 + 4.3889B 2 - 0.8800C 2 (4-2)

[0162] In the formula, A, B, and C represent water-solid ratio, HGB-4 addition amount, and SiO2 addition amount, respectively.

[0163] Significance test of error sources of the model can be performed using analysis of variance, and whether the model is accurate and reliable is evaluated. Table 14 and Table 15 are analysis results of compressive strength and thermal conductivity, respectively. F value and P value are commonly used to determine the significance of the model, and when P≤0.05, it is indicated that the influence factor has a significant effect on the response target. In Table 14 and Table 15, the P values corresponding to the regression models of compressive strength and thermal conductivity are both <0.0001, indicating that they have reached a significant level. Moreover, the P values corresponding to the lack-of-fit terms of the two are >0.05, which are not significant, indicating that the fitting degree of the model is high, and there is no case where the test data does not match the model.

[0164] Determination coefficient (R 2 ), adjusted determination coefficient (Adjusted R 2 ), and predicted determination coefficient (Predicted R 2 ) are commonly used to indicate the fitting degree of the model, and the greater the values of the two, the higher the fitting degree of the model, and the higher the values of the adjusted determination coefficient and the predicted determination coefficient are better, but the difference between the two should be less than 0.2, and the higher and closer the values of the two, the better the interpretability of the model. Precision (Adeq Precision) is used to reflect the anti-interference ability of the model, which is generally greater than 4. Coefficient of variation (CV) less than 10% indicates that the model has strong reliability. From Table 14 and Table 15, it can be seen that the corresponding indicators of compressive strength and thermal conductivity all meet the requirements, indicating that the established model is reasonable and can be used to analyze the changes of compressive strength and thermal conductivity with water-solid ratio, HGB-4, and SiO2.

[0165] Figure 6 For the actual value and predicted value relationship diagram of compressive strength and thermal conductivity coefficient, it can be seen that each point is distributed around the straight line, and there is no obvious deviation point, which shows that the dispersion is small, and also shows that the model fitting accuracy is high, and can be used for predicting the actual test.

[0166] Table 14 compressive strength variance analysis results

[0167]

[0168]

[0169] Table 15 thermal conductivity coefficient variance analysis results

[0170]

[0171]

[0172] 3、Response surface analysis

[0173] The size of the F value corresponding to each factor in Table 14 and Table 15 also indicates the degree of influence on the response target. For compressive strength, SiO2> water-solid ratio > HGB-4. For thermal conductivity, HGB-4> SiO2> water-solid ratio. The test results are completely consistent with the previous test results. In order to more intuitively show the influence trend of each factor on the response target, the corresponding response surface graph and contour graph are constructed as shown in Figure 7 , Figure 8 The influence of each factor on compressive strength and thermal conductivity can be directly reflected from the response surface and contour graph, and the strength of the interaction between factors can also be expressed through the image, that is, the steeper the surface, the closer the shape of the contour to the ellipse, the stronger the interaction between factors, and vice versa.

[0174] Figure 7 (a) is the influence of the interaction between water-solid ratio and HGB-4 on compressive strength, the compressive strength decreases with the increase of water-solid ratio and the increase of HGB-4 addition, and there is no optimal addition interval. The contour shape is close to a circle, indicating that the interaction between water-solid ratio and HGB-4 is not significant. From Figure 7 (b) it can be seen that when the HGB-4 addition is 23% and the water-solid ratio is constant, the compressive strength increases first and then decreases with the increase of SiO2 addition, and there is an optimal addition. The contour shape is elliptical, and the interaction between them is significant. Figure 7 (c) in the case of constant HGB-4 addition, the compressive strength also increases first and then decreases with the increase of SiO2 addition, and the contour is circular, and the interaction is not significant.

[0175] Figure 8In (a), the thermal conductivity decreases with the increase of water-solid ratio and HGB-4 content, and the effect of HGB-4 on the thermal conductivity is better than that of water-solid ratio. The contour is elliptical, and the interaction between water-solid ratio and HGB-4 is significant. Figure 8 In (b), the thermal conductivity increases with the increase of SiO2 content, and the contour is not elliptical, and the interaction between them is not significant. Figure 8 In (c), the influence of SiO2 and HGB-4 is the same as before, and the contour is close to a circle, and the interaction between them is not significant.

[0176] Through response surface analysis and variance analysis, the influence of the interaction between factors on the compressive strength and thermal conductivity of cement is determined. In terms of compressive strength, AC>BC>AB; in terms of thermal conductivity, AB>AC>BC.

[0177] 4. Derivation and verification of the optimal formula

[0178] The influence of water-solid ratio, HGB-4, SiO2 and the interaction between factors on the compressive strength and thermal conductivity has been determined, and the thermal insulation cement slurry system has been basically formed. In order to obtain a more accurate optimal formula, the optimization scheme is set by Design-Expert as shown in Table 16. Compared with the compressive strength, the thermal conductivity can only be adjusted by water-solid ratio and HGB-4, and the adjustment method is relatively simple. At the same time, low thermal conductivity is also the key indicator of thermal insulation cement, so the optimization scheme takes low thermal conductivity as the target and limits the strength within a fixed range. The optimal amount obtained by software solution is shown in Table 17, and the optimal formula of thermal insulation cement for the upper section of geothermal well (hereinafter referred to as the optimal formula) is:

[0179] G-grade oil well cement + 22.6% HGB-4 + 5.1% Ⅱ-SiO2 + 2.5% ZQ-4 + 0.02% 3050F + 0.1% MXSK-2

[0180] 0.1% MXSK-2, water-solid ratio is 0.71

[0181] Among "G-grade oil well cement + 22.6% HGB-4 + 5.1% SiO2 + 2.5% ZQ-4 + 0.02% 3050F + 0.1% MXSK-2", "G-grade oil well cement + 22.6% HGB-4" means that the amount of HGB-4 is 22.6% of the total amount of G-grade oil well cement and HGB-4; "5.1% SiO2 + 2.5% ZQ-4 + 0.02% 3050F + 0.1% MXSK-2" means that the amounts of SiO2, ZQ-4, 3050F and MXSK-2 are 5.1%, 2.5%, 0.02% and 0.1% of the total amount of G-grade oil well cement and HGB-4, respectively.

[0182] The performance test results of the optimal formula are shown in Table 18, the 2-day compressive strength is 19.64 MPa, only 0.27 MPa different from the predicted value 19.91 MPa. The thermal conductivity is 0.1515 W / (m·K), only 0.0035 W / (m·K) different from the predicted value. The difference of the two performances is within a reasonable range, indicating that the model is accurate and reliable. The 14-day compressive strength is 20.56 MPa, slightly higher than the 2-day strength, indicating that the hydration reaction continues after 2 days, and there is no obvious strength decay phenomenon. The addition of Ⅱ-SiO2 powder improves the strength and alleviates the problem of strength decay. The thermal conductivity is 0.1589 W / (m·K), still at a low level. In summary, the strength and thermal conductivity of the optimized formula at 110 DEG C meet the use requirements.

[0183] Table 16 Response surface optimization design

[0184]

[0185] Table 17 Optimal results of adding amount

[0186]

[0187] Table 18 Measured strength and thermal conductivity of the optimal formula

[0188]

[0189] The experimental results show that, in order to obtain the optimal formula, the Box-Behnken Design test design method in the response surface test is selected to establish a regression model of compressive strength and thermal conductivity, the accuracy, reliability of the model, and the influence of the interaction between each factor on the strength and thermal conductivity are analyzed. The optimal formula is obtained by software analysis, the optimal formula is: G-grade cement + 22.6% HGB-4 + 5.1% Ⅱ-SiO2 + 2.5% ZQ-4 + 0.02% 3050F + 0.1% MXSK-2, and the water-solid ratio is 0.71.

[0190] (5) The compressive strength and thermal conductivity of the optimal formula are verified, the 2-day compressive strength and thermal conductivity are 19.64 MPa and 0.1515 W / (m·K) respectively, which are not much different from the predicted results. The 14-day compressive strength and thermal conductivity are 20.56 MPa and 0.1589 W / (m·K) respectively, indicating the effectiveness and reliability of the long-term performance of the optimal formula.

[0191] The beneficial effects of the present application are demonstrated by the following experimental examples.

[0192] Experimental Example 1, the heat insulation characteristics of the thermal insulation cement of the present application

[0193] (1) High temperature thickening time

[0194] High temperature can accelerate the hydration of cement and shorten the setting time of cement. In the process of geothermal exploitation, the temperature at different depths in the well is different, and the closer to the bottom of the well, the higher the temperature. This requires that the cement slurry can maintain a certain fluidity during pumping, that is, its thickening time should meet the requirements of pumping the cement slurry to the specified depth. In addition, it should also have a shorter waiting time, reach the specified depth quickly, and prevent the cement slurry from losing stability while shortening the drilling waiting time, which is reflected in the "right angle thickening" in the thickening test result graph. Since the higher the temperature, the faster the thickening of the cement slurry, as long as the optimal formula under the condition of 110℃ can meet the test requirements, the thickening time requirements under other low temperature conditions can be met by reducing the amount of retarder. The test is based on the optimal formula, only the amount of retarder is changed for testing, and the results are shown in Figure 9

[0195] From Figure 9 it can be seen that the initial consistency of 0.1% MXSK-2 addition is 9Bc, and the initial consistency of 0.2% addition is 4Bc, and the initial consistency is less than 30Bc, which has good pumpability. At the same time, from Figure 9 (a) and 9(b), it can be seen that the consistency slowly increases with time, and after reaching a certain limit, the consistency sharply rises, showing the "right angle thickening" characteristics, which is more conducive to engineering construction. The thickening time of 0.1% addition is 110min, and the thickening time of 0.2% addition is 181min, which is different from the pumpable period test results, but the difference is not large and the addition law is the same.

[0196] The current development depth of geothermal resources in China is mostly 2000-3000m (such as Yangbajing ZK4001 well depth is only 1459m, 0.1% MXSK-2 addition can meet the requirements of cementing engineering. At the same time, the test results also show that the thickening time of the heat preservation cement is adjustable, which can be reasonably adjusted according to the requirements.

[0197] The experimental results show that the initial consistency of the heat preservation cement slurry is less than 30Bc, the high temperature thickening time is adjustable, and can be adjusted according to different depths to meet the target heat preservation cement index requirements.

[0198] (2) High temperature stability

[0199] ​The stability of cement slurry under high temperature condition has great influence on the smoothness of construction. If the stability of cement slurry is insufficient, the solid phase material in the slurry will quickly settle, and pump stopping during construction will easily cause pump blocking. Even if the cement slurry can reach the designated position, the problems of water separation and heavy particle settlement will cause large empty well section and uneven strength of cement in the upper and lower part of the cementing section, which will affect the cementing effect, especially when the formula contains light material HGB-4, the insufficient stability of cement slurry under high temperature will have greater influence. Therefore, the free liquid Figure 10 a), settling stability Figure 10 b) and API fluid loss of the optimal formula under different temperatures are tested, and the results are shown in Table 19.

[0200] Table 19 Stability test results

[0201]

[0202]

[0203] From the results in Table 19, it can be seen that:

[0204] (1) The relative density difference of the upper, middle and lower three sections of the cement stone under different temperatures is 0.009 at 90℃, which is less than 0.01, indicating that the settling phenomenon of the cement slurry is not obvious, and the stability of the cement slurry is good.

[0205] (2) The free liquid content of the cement slurry under different temperatures is 0, and the API fluid loss increases with the increase of temperature, but it is all less than 50ml, which meets the requirements of cementing construction. 3050F is a high molecular polymer material, which can be adsorbed on the surface of cement particles to form a hydration layer, enhance the binding of free water and reduce the generation of free liquid. In addition, the high molecular chain can also adsorb small cement particles, which will bridge and fill the pores between large particles during the formation of filter cake, thereby reducing the permeability.

[0206] In summary, the stabilizer 3050F has excellent performance and can adapt to different working environments under different temperatures to ensure the stability of the cement slurry, which is an indispensable component in the optimal formula.

[0207] The experimental results show that the heat preservation cement slurry needs to have good stability under high temperature, the density difference between the upper and lower layers should not be more than 0.05 (the density difference of the present application is less than 0.01 g / cm 3 ), the fluid loss should be less than 100ml (the present application is less than 50ml), the free liquid content is less than 1.4% (the present application is 0), which meets the target heat preservation cement index requirements, and the density should be between 1.0-1.4g / cm 3 (the present application is between 1-1.2g / cm 3 ).

[0208] Experimental Example 2: Compressive strength and thermal conductivity of the thermal insulation cement of the present invention

[0209] I. Compressive strength and thermal conductivity

[0210] To further determine the performance of the optimal formulation under actual geothermal conditions, cement samples were sent to Leshan Jiahua Cement Company. After curing in a standard high-temperature curing autoclave for two days, their compressive strength and thermal conductivity were tested. The results are as follows: Figure 11 As shown.

[0211] from Figure 11 It can be known that:

[0212] (1) The compressive strength first increases and then decreases with increasing temperature, with an inflection point at 70℃. This follows the same pattern as the results above. The 20.47 MPa measured by the standard method is slightly higher than the 19.64 MPa measured by the self-developed curing method, but the difference is not significant, indicating that the data obtained by the self-developed curing method has some reference value. The lowest compressive strength is at 20℃, at 17.58 MPa, far exceeding the 7 MPa required by the standard. Existing research results show that, to a certain extent, increasing the curing pressure can improve the compressive strength of cement, and the stability of the compressive strength of cement cured under actual well conditions is better than that under standard curing conditions.

[0213] (2) The thermal conductivity also increases first and then decreases with increasing temperature, with an inflection point at 70℃. This indicates that the hydration reaction of cement is faster and more complete at 70℃, and the large amount of hydration products fills the pores and microcracks inside the cement, resulting in an increase in both the thermal conductivity and compressive strength compared to other temperatures. The highest thermal conductivity is 0.1802 W / (m·K), which is still at a relatively low level, indicating that it has a heat insulation effect.

[0214] Experimental results show that the compressive strength of the thermal insulation cement grout of this invention after 48 hours should not be less than 7 MPa, while that of this invention is 17.58 MPa, which meets the target level requirements.

[0215] In conclusion, the application provides a heat preservation cement material for upper well section of geothermal well and a preparation method thereof, the performance of the optimal formula reaches the design target, can meet the requirements of actual geothermal exploitation, reduces the heat loss of heat transfer medium along the way, can meet the pumping requirements of 110 DEG C, and the thickening time of the application is adjustable, which can be adjusted according to different pumping depths, meanwhile, the heat preservation cement material has good high-temperature stability, the settlement phenomenon is not obvious, the free liquid content is 0%, and the filtration loss is less than 50ml. The thermal conductivity and compressive strength at 110 DEG C are 0.1555 W / (m*K), 20.47 MPa (2 days), 0.1589 W / (m*K), 20.56 MPa (14 days) respectively, the strength is greater than 7 MPa, and the comprehensive performance meets the design requirements.

Claims

1. A heat-insulating cement material for upper well section of geothermal well, characterized in that: the heat-insulating cement material is composed of solid phase component and liquid phase component, wherein the solid phase component comprises cement matrix, reinforcing material, early strength agent, stabilizer; the liquid phase component is retarder; the reinforcing material is II-SiO2; the early strength agent is ZQ-4, which is anhydrous calcium chloride; the stabilizer is 3050F; the retarder is MXSK-2; the cement matrix is composed of G-grade oil well cement and HGB-4, which is hollow glass microsphere, wherein the percentage content of HGB-4 is (17-23)%; the weight ratio of the cement matrix: II-SiO2: ZQ-4: 3050F: MXSK-2 is 100: (5-10): 2.5: 0.02: (0.1-0.15).

2. The heat-insulating cement material according to claim 1, characterized in that: the cement matrix is composed of G-grade oil well cement and HGB-4, wherein the percentage content of HGB-4 is 20%; the weight ratio of the cement matrix: II-SiO2: ZQ-4: 3050F: MXSK-2 is 100: 5: 2.5: 0.02: (0.1-0.15); the weight ratio of the cement matrix: II-SiO2: ZQ-4: 3050F: MXSK-2 is 100: 5: 2.5: 0.02: 0.

1.

4. The heat-insulating cement material according to claim 1, characterized in that: the cement matrix is composed of G-grade oil well cement and HGB-4, wherein the percentage content of HGB-4 is 22.6%; the weight ratio of the cement matrix: II-SiO2: ZQ-4: 3050F: MXSK-2 is 100: 5.1: 2.5: 0.02: 0.

1.

5. A heat-insulating cement slurry, which is prepared by mixing the heat-insulating cement material according to any one of claims 1-4 with water, wherein the water-solid ratio is 0.55-0.

75. The cement slurry is prepared by the following method: (1) mixing and stirring G-grade oil well cement, HGB-4, reinforcing material, early strength agent and stabilizer to obtain a solid phase mixture; (2) mixing and stirring water with retarder to obtain a liquid phase mixture; (3) mixing the solid phase mixture obtained in step (1) with the liquid phase mixture obtained in step (2) and stirring uniformly to obtain the cement slurry; 3. A thermal insulation cementitious material as claimed in claim 2, characterised in that: the water-solid ratio is 0.55-0.

75. the water-solid ratio is 0.7-0.

71.

8. Use of the heat-insulating cement material according to any one of claims 1-4 for heat insulation of upper well section of geothermal well. ​ ​ 6. The insulating cement slurry in accordance with claim 5, wherein: ​ ​ ​ ​ ​ 7. The insulating cement slurry in accordance with claim 6, wherein: ​ ​

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