Cement slurry system for relieving casing deformation, and preparation method therefor and use thereof

Abstract

Provided in the present invention are a cement slurry system for relieving casing deformation, and a preparation method therefor and the use thereof. The raw materials of the cement slurry system comprise G-grade oil well cement and other raw materials with the following percentages (based on the mass of the G-grade oil well cement): 3-6% of micro-silicon, 15-50% of glass beads, 3-6% of a reinforcing material, 3-5% of a toughening material, 0-2% of a stabilizer, 0-2.5% of a dispersing agent, 3-6% of a fluid loss agent, 0-2.5% of a retarder, 0.2-0.5% of a defoaming agent, 0.2-0.5% of a foam inhibitor, and 70-95% of water, wherein the toughening material is formed by compounding fibers and a carbon material at a mass ratio of (2-4):1, and the compressive strength of the glass beads is 3000-5000 psi. The cement slurry system of the present invention has a good effect with regard to preventing and relieving casing deformation.

Description

A cement slurry system for alleviating casing deformation and its preparation method and application

[0001] Cross-reference information

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on June 30, 2023, with application number 202310795333.7 and invention name “A sleeve-change mitigation cement slurry system, its preparation method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present invention relates to the technical field of shale gas cementing, and in particular to a cement slurry system for alleviating casing deformation, and a preparation method and application thereof. Background Art

[0004] At present, in order to prevent casing deformation (casing change) in shale gas well cementing, methods such as increasing the cement sheath thickness or casing wall thickness and reducing the elastic modulus of cement stone are generally used to alleviate the casing change phenomenon. However, there is no cement slurry system specifically designed for preventing casing change in shale gas wells.

[0005] CN202210052442.5 discloses a high-density anti-channeling tough cement slurry system for shale gas cementing, its preparation method and application, which includes G-grade cement, water, composite weighting agent, nano anti-channeling agent, toughening agent, fluid loss reducer, retarder, dispersant and defoaming agent. Among them, the addition of nano anti-channeling agent not only has no negative impact on the construction performance of cement slurry, but also can promote the formation of early strength of cement, reduce the permeability of cement stone, make the structure of cement stone more uniform and dense, and effectively enhance the anti-channeling property of cement stone.

[0006] CN201910113067.9 discloses a cementing slurry system suitable for large-scale staged fracturing of shale gas horizontal wells, which mainly includes 100 parts of oil well cement, 43-46 parts of fresh water, 2-4 parts of elastic toughening agent, 1-2 parts of anti-channeling agent, 1-3 parts of fluid loss reducer, 0.4-0.6 parts of dispersant, 1-1.5 parts of expansion agent, 0.5-2.0 parts of retarder, and 0.1-0.5 parts of defoaming agent. The elastic toughening agent is a rubber fiber with a specific surface area ≥7m / g and a volume compression rate ≥5%, or a mixture of the rubber fiber and rubber particles. The cementing slurry system of this technology has excellent comprehensive properties such as thickening and anti-channeling performance, elasticity and toughness, which can effectively achieve synchronous deformation of the cement sheath and casing when the cement sheath is subjected to the alternating load of staged fracturing, ensuring the long-term integrity of the wellbore seal during the later reservoir transformation and gas test production operations of shale gas horizontal wells, effectively preventing the occurrence of casing annulus pressure, and providing effective guarantee for the long-term production and large-scale fracturing of shale gas horizontal wells.

[0007] CN201410471036.8 discloses a toughening and anti-channeling agent for cement and toughening cement for shale gas horizontal well cementing. The technology relates to a cement slurry used in shale gas horizontal well cementing and a toughening additive added thereto. The toughening and anti-channeling agent for cement is prepared by mixing styrene-butadiene rubber powder and redispersible latex powder in a mass ratio of 2:1, wherein the styrene-butadiene rubber powder is subjected to the following treatment before use: first preparing a silane coupling agent solution with a mass percentage of 1.5%, adding styrene-butadiene rubber powder thereto, letting it stand for 24 hours and then filtering, drying it to make cement slurry. After that, the system performance is stable, the thickening time is easy to adjust, the water loss is less than 30 ml, the free liquid at a 45-degree inclination angle and the upper and lower density differences are both 0.50°C, the compressive strength is greater than 30 MPa in 24 hours, the applicable temperature range is 50-120°C, and the thickening time is 110-240 min; the toughening and anti-channeling agent for cement is added to the toughening cement for shale gas horizontal well cementing. The cement slurry system produced therefrom has good stability and low water loss and separation, and can meet the requirements of shale gas horizontal well multi-stage fracturing for cement slurry systems.

[0008] While these existing technologies have achieved success in preventing casing deformation, they are still not universally applicable under complex casing deformation conditions. Therefore, research on shale gas cementing slurries to mitigate casing deformation is urgently needed to improve shale gas well cementing quality, ensure casing service safety, and ensure efficient shale gas development.

[0009] Summary of the Invention

[0010] In order to solve the above technical problems, the present invention provides a cement slurry system for alleviating casing deformation and a preparation method thereof. The cement slurry system has low finished product cost and is easy to prepare.

[0011] To achieve the above object, the present invention provides a cement slurry system for alleviating casing deformation, the raw materials of which include G-grade oil well cement and other raw materials in the following percentages based on the mass of the G-grade oil well cement: 3-6% microsilica, 15-50% glass microspheres, 3-6% reinforcing material, 3-5% toughening material, 0-2% stabilizer, 0-2.5% dispersant, 3-6% fluid loss additive, 0-2.5% retarder, 0.2-0.5% defoamer, 0.2-0.5% antifoaming agent, and 70-95% water;

[0012] The toughening material is formed by compounding fibers and carbon materials in a mass ratio of 2-4:1, wherein the fibers include one or a combination of two or more of basalt fibers, alumina fibers, and silicon carbide fibers, and the carbon materials include carbon nanotubes and / or expanded graphite.

[0013] The compressive strength of the glass microspheres is 3000-5000 psi.

[0014] According to a specific embodiment of the present invention, preferably, the raw materials of the cement slurry system for alleviating casing deformation include, by mass: 100 parts of G-grade oil well cement, 3-6 parts of microsilica, 15-50 parts of glass beads, 3-6 parts of reinforcing material, 3-5 parts of toughening material, 0-2 parts of stabilizer, 0-2.5 parts of dispersant, 3-6 parts of fluid loss additive, 0-2.5 parts of retarder, 0.2-0.5 parts of defoamer, 0.2-0.5 parts of antifoaming agent, and 70-95 parts of water;

[0015] The toughening material is composed of a compound of fiber and carbon material in a mass ratio of 2-4:1, the fiber includes one or a combination of two or more of basalt fiber, alumina fiber, and silicon carbide fiber, and the carbon material includes carbon nanotubes and / or expanded graphite; the compressive strength of the glass microbeads is 3000-5000psi.

[0016] In the above-mentioned cement slurry system for alleviating casing deformation, preferably, the compressive strength of the glass microspheres is 4000 psi.

[0017] The present invention reduces the elastic modulus of cement stone without affecting its compressive strength by adding glass microbeads with low compressive strength and a toughening material composed of fiber and carbon material. The internal glass microbeads are broken before the cement stone reaches its own compressive resistance limit and is destroyed, providing a certain buffer space for casing deformation, thereby gradually enhancing the cement stone's ability to alleviate casing deformation.

[0018] In the above-mentioned cement slurry system for alleviating casing deformation, preferably, the fiber length of the basalt fiber is 1.5-10 μm.

[0019] In the above-mentioned cement slurry system for alleviating casing deformation, preferably, the fiber length of the alumina fiber is 3-6 μm.

[0020] In the above-mentioned cement slurry system for alleviating casing deformation, preferably, the fiber length of the silicon carbide fiber is 10-15 μm.

[0021] In the above-mentioned cement slurry system for alleviating casing deformation, preferably, the length of the carbon nanotubes is 10-30 μm.

[0022] In the above-mentioned cement slurry system for alleviating casing deformation, preferably, the particle size of the expanded graphite is 40-50 μm.

[0023] In the above-mentioned cement slurry system for alleviating casing deformation, preferably, the average particle size of the microsilica is 4-10 μm, and the 45 μm sieve residue is ≤5%.

[0024] In the above-mentioned cement slurry system for alleviating casing deformation, preferably, the true density of the glass microspheres is 0.38-0.42 g / cm 3, more preferably 0.40 g / cm 3 The present invention optimizes the true density of the glass microspheres. When the true density of the glass microspheres is too high, the space they can provide after being broken is limited.

[0025] In the above-mentioned cement slurry system for alleviating casing deformation, preferably, the stabilizer is an ore powder stabilizer and / or a polymer stabilizer, more preferably an ore powder stabilizer.

[0026] In the above-mentioned cement slurry system for alleviating casing deformation, preferably, the dispersant is a condensation product of formaldehyde and acetone and / or a polystyrene sulfonate dispersant.

[0027] In the above-mentioned cement slurry system for alleviating casing deformation, preferably, the fluid loss additive is a polyacrylamide-based fluid loss additive.

[0028] In the above-mentioned cement slurry system for alleviating casing deformation, preferably, the retarder is an acrylamide retarder.

[0029] In the above-mentioned cement slurry system for alleviating casing deformation, preferably, the defoaming agent includes one or a combination of two or more of tributyl phosphate, polyoxypropylene glycerol, and polydimethylsiloxane.

[0030] According to a specific embodiment of the present invention, preferably, the 7-day compressive strength of the cement paste formed by the cement slurry system for alleviating casing deformation is greater than 20 MPa, and the elastic modulus is less than 5 GPa.

[0031] According to a specific embodiment of the present invention, preferably, the density of the cement slurry system for alleviating casing deformation is 1.30-1.60 g / cm 3 , the applicable temperature range is 30-150℃.

[0032] The present invention also provides a method for preparing the above-mentioned cement slurry system for alleviating casing deformation, which comprises: weighing raw materials in proportion, mixing them, and stirring them evenly at a speed of 11500-12500 r / min to obtain the cement slurry system for alleviating casing deformation.

[0033] According to a specific embodiment of the present invention, preferably, the method for preparing the cement slurry system for alleviating casing deformation comprises the following steps:

[0034] Weigh oil well cement, microsilica, glass microspheres, reinforcing material, toughening material, stabilizer, and dispersant in proportion, and evenly mix them to obtain a dry mix;

[0035] Weigh the fluid loss additive, retarder and defoamer in proportion and stir them evenly in water to obtain a wet mix solution;

[0036] At a rotation speed of 3800-4200 r / min, the dry mix is ​​evenly poured into the wet mix solution. After the dry mix is ​​completely added to the wet mix solution, the stirrer speed is adjusted to 11500-12500 r / min and stirring is continued to obtain the cement slurry system for alleviating casing deformation.

[0037] The present invention also provides an application of the above-mentioned cement slurry system for alleviating casing deformation in shale gas well cementing and preventing and / or alleviating casing deformation.

[0038] The technical solution provided by the present invention has the following beneficial effects:

[0039] The present invention provides a cement slurry system for mitigating casing deformation that meets cementing construction requirements. Furthermore, the cement paste has a low elastic modulus and can actively break up when there is significant formation slippage, creating space for casing deformation and effectively preventing and mitigating casing deformation. In some embodiments, the cement paste formed by the present invention's cement slurry system for mitigating casing deformation exhibits a 7-day compressive strength greater than 20 MPa and an elastic modulus less than 5 GPa. DETAILED DESCRIPTION

[0040] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0041] Description of the raw materials used in the examples of the present invention:

[0042] Grade G oil well cement is high sulfate resistance (HSR) Grade G oil well cement, produced by Dalian Cement Group Co., Ltd.;

[0043] The stabilizer is a mature product produced by China National Petroleum Corporation Engineering Technology Research Institute Co., Ltd., and its trade name is "DRB-1S, a reinforcing material ore powder for oil well cementing".

[0044] Basalt fibers are commercially available with a fiber length of 1.5–10 μm;

[0045] Alumina fibers are commercially available with a fiber length of 3–6 μm;

[0046] The length of silicon carbide fibers is 10-15 μm;

[0047] Carbon nanotubes, 95% purity, 10-30 μm in length;

[0048] Expanded graphite is commercially available with a purity of more than 95% and a particle size of 48 μm (mesh size 300);

[0049] Microsilica is commercially available with an average particle size of 5 μm and a 45 μm sieve residue of ≤5%;

[0050] The dispersant is a condensation product of formaldehyde and acetone or a polystyrene sulfonate dispersant;

[0051] Fluid loss additive is a type of polyacrylamide;

[0052] The defoaming agent is one of tributyl phosphate, polyoxypropylene glycerol and polydimethylsiloxane commonly used in the art.

[0053] Example 1

[0054] This embodiment provides a cement slurry system for alleviating casing deformation, and the preparation method thereof is as follows:

[0055] 1. Recipe

[0056] The cement slurry formula is as follows, by weight percentage: 100 parts of G-grade oil well cement, 5 parts of microsilica, 10 parts of reinforcing material, 4 parts of toughening material, 13 parts of glass microspheres, 1 part of stabilizer, 1.5 parts of dispersant, 3.5 parts of fluid loss additive, 0.8 parts of retarder, 0.5 parts of defoamer, 0.5 parts of antifoaming agent, and 70 parts of water; wherein the toughening material is prepared by uniformly mixing 2 parts of basalt fiber and 1 part of expanded graphite; the true density of the glass microspheres is 0.40 g / cm 3 , compressive strength is 4000psi.

[0057] 2. Preparation Method

[0058] Weigh oil well cement, microsilica, glass microbeads, reinforcing material, toughening material, stabilizer, and dispersant in proportion and mix evenly to obtain a dry mix. Weigh fluid loss additive, retarder, and defoamer in proportion and stir evenly in water to obtain a wet mix. Pour the dry mix evenly into the wet mix at a speed of 4000 r / min. After the dry mix is ​​completely added to the wet mix, cover the mixing cup, adjust the stirrer speed to 12000 r / min, and continue stirring for 35 seconds to obtain a cement slurry system that alleviates casing deformation. After testing, the density of the cement slurry is 1.6g / cm 3 .

[0059] Example 2

[0060] This embodiment provides a cement slurry system for alleviating casing deformation, and the preparation method thereof is as follows:

[0061] 1. Recipe

[0062] The cement slurry formula is as follows, by weight percentage: 100 parts of G-grade oil well cement, 5 parts of microsilica, 10 parts of reinforcing material, 4 parts of toughening material, 32 parts of glass microspheres, 1 part of stabilizer, 1.5 parts of dispersant, 3.5 parts of fluid loss additive, 0.8 parts of retarder, 0.5 parts of defoamer, 0.5 parts of antifoaming agent, and 75 parts of water; wherein the toughening material is prepared by uniformly mixing 3 parts of silicon carbide fiber and 1 part of expanded graphite; the true density of the glass microspheres is 0.40 g / cm 3 , compressive strength is 4000psi.

[0063] 2. The preparation method is the same as in Example 1. The density of the cement slurry is 1.45 g / cm 3 .

[0064] Example 3

[0065] This embodiment provides a cement slurry system for alleviating casing deformation, and the preparation method thereof is as follows:

[0066] 1. Recipe

[0067] The cement slurry formula is as follows, by weight percentage: 100 parts of G-grade oil well cement, 5 parts of microsilica, 10 parts of reinforcing material, 4 parts of toughening material, 50 parts of glass microspheres, 1 part of stabilizer, 1.5 parts of dispersant, 3.5 parts of fluid loss additive, 0.8 parts of retarder, 0.5 parts of defoamer, 0.5 parts of antifoaming agent, and 78 parts of water; wherein the toughening material is prepared by uniformly mixing 4 parts of alumina fiber and 1 part of carbon nanotube; the true density of the glass microspheres is 0.40 g / cm 3 , compressive strength is 4000psi.

[0068] 2. The preparation method is the same as in Example 1. The density of the cement slurry is 1.3 g / cm 3 .

[0069] Comparative Example 1

[0070] This comparative example provides a cement slurry system, the formulation and preparation method of which are the same as those of Example 1, except that no toughening material is added in this comparative example, and the true density of the glass microspheres used is 0.63 g / cm 3 , the compressive strength is 15000psi; at the same time, in order to keep the density of cement slurry unchanged, the weight proportion of water is changed to 68 parts.

[0071] Comparative Example 2

[0072] This comparative example provides a cement slurry system, the formula and preparation method of which are the same as those of Example 2, except that no toughening material is added in this comparative example, and the true density of the glass microspheres is 0.60 g / cm 3, the compressive strength is 12000psi; at the same time, in order to keep the density of cement slurry unchanged, the weight proportion of water is changed to 73 parts.

[0073] Comparative Example 3

[0074] This comparative example provides a cement slurry system, the formulation and preparation method of which are the same as those of Example 3, except that no toughening material is added in this comparative example, and the true density of the glass microspheres is 0.60 g / cm 3 , the compressive strength is 12000psi; at the same time, in order to keep the density of cement slurry unchanged, the weight proportion of water is changed to 76 parts.

[0075] Experimental example

[0076] The experiments were conducted in accordance with the national standard GB / T 19139-2012 "Test Methods for Oil Well Cement" to evaluate the conventional engineering properties (density, fluidity, API water loss) as well as the compressive strength and elastic modulus of the cement slurry system.

[0077] The main experimental instruments include: 30-60 type tile stirrer; TG7370D type pressurized curing kettle, Shenyang Tiger Petroleum Instrument Equipment Manufacturing Co., Ltd.; HH-420 type constant temperature digital display water tank, Changzhou Yineng Experimental Instrument Factory; YAW-300B hydraulic pressure testing machine, Jinan Xinshijin Testing Machine Co., Ltd.

[0078] This experimental example also uses the following method to test the breakage rate of glass beads under specified conditions:

[0079] 1. Measurement principle

[0080] The crushing rate is determined based on the change in density before and after compression of the sample under a specified pressure.

[0081] 2. Instruments and equipment

[0082] Strength tester, nitrogen (purity 99.9%), analytical balance.

[0083] 3. Experimental steps

[0084] (1) First, take (2-5) g of sample to measure the true density. The instrument used is the 3H-2000TD2 true density measuring instrument produced by Best Instrument Technology (Beijing) Co., Ltd. (or other instruments with the same true density measurement function);

[0085] (2) Take 2-5g of the same batch and put them into the sample chamber, put the sample chamber into the high-pressure chamber, and tighten the bolts of the high-pressure chamber;

[0086] (3) Open the nitrogen valve and fill with nitrogen until the nitrogen pressure reaches the required pressure. Keep the pressure constant for 5 minutes, release the pressure, take out the sample and measure the true density. The instrument used is the 3H-2000TD2 true density meter produced by Best Instrument Technology (Beijing) Co., Ltd. (or other instruments with the same true density measurement function).

[0087] 4. Calculation of crushing rate

[0088] The density of the sample before and after compression is calculated according to the following formula: R = ρ0 × (ρ2-ρ2) / ρ2 / (ρ0-ρ1) × 100

[0089] Where:

[0090] R—breakage rate under specified conditions, %;

[0091] ρ0—true density of the sample when it is completely crushed, g / cm 3 ;

[0092] ρ1—density of the sample before compression, g / cm 3 ;

[0093] ρ2—density of the sample after compression, g / cm 3 .

[0094] The test results of the cement slurry systems of the above examples and comparative examples are shown in Table 1.

[0095] Table 1 Cement slurry system performance test results

[0096] As can be seen from the data in Table 1, the fluidity of the cement slurry systems of Examples 1-3 is greater than 20 cm, and the API water loss is less than 50 mL, which meets the requirements of cementing construction. The cement stone formed by the cement slurry systems of Examples 1-3 has a 7-day compressive strength greater than 20 MPa and an elastic modulus less than 5 GPa, with good performance and meeting the cementing sealing requirements.

[0097] The test results of Comparative Examples 1-3 show that without adding toughening materials, the compressive strength of the cement stone formed is greater than 20 MPa, but the 7-day elastic modulus is high, and the cement stone has poor deformation ability during stratum slippage, which easily leads to stress concentration; in addition, when the stratum stress reaches the compressive strength limit of the cement stone, the cement stone breaks. At this time, the internal high-compression glass bead structure is basically intact and cannot provide space for sleeve deformation.

[0098] Comparing the results of Comparative Example 1 and Example 1, it can be seen that the conventional properties of the cement slurries, such as API water loss, fluidity, and compressive strength, show little change, both meeting construction requirements. Compared with Comparative Example 1, the addition of a toughening material and the replacement of glass microspheres with a compressive strength of 4000 pascals in Example 1 reduced the elastic modulus of the resulting cement paste from 7.94 GPa to 4.92 GPa, significantly reducing its brittleness. Before the cement paste reached its compressive capacity limit and failed, the internal glass microspheres shattered (with a crushing rate of 95.1%), providing a larger deformation space and providing a certain buffer for casing deformation.

[0099] Compared with Comparative Example 2, after adding toughening material and replacing glass microspheres with a compressive strength of 4000pasi in Example 2, the conventional properties of the cement slurry, such as API water loss, fluidity, and compressive strength, did not change much, and both met the construction requirements; however, the elastic modulus of Example 2 decreased by 2.95Gpa, and the elastic modulus of the cement stone was significantly reduced. When the local stratum slipped, the crushing of the glass microspheres (crushing rate was 96.6%) could provide a larger deformation space, thereby providing a certain buffer space for casing deformation.

[0100] Compared with Comparative Example 3, after adding toughening material and replacing glass microspheres with a compressive strength of 4000pasi in Example 3, the conventional properties of the cement slurry, such as API water loss, fluidity, and compressive strength, did not change much, and both met the construction requirements; however, the elastic modulus of Example 2 decreased by 2.91GPa, and the elastic modulus of the cement stone was significantly reduced. When the local stratum slipped, the crushing of the glass microspheres (crushing rate was 95.1%) could provide a larger deformation space, thereby providing a certain buffer space for casing deformation.

[0101] In summary, the cement slurry system for alleviating casing deformation provided by the present invention has a density of 1.30-1.60 g / cm 3 The applicable temperature range is 30-150℃, the 7-day compressive strength of cement stone is greater than 20MPa, and the elastic modulus is less than 5GPa. At the same time, the settlement stability and rheological properties are good, meeting the requirements of cementing construction.

[0102] The above-described embodiments are merely embodiments of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art may make various modifications, equivalent substitutions, and improvements without departing from the scope of the present invention, and these modifications fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be based on the appended claims.

Claims

1. A cement slurry system for relieving casing deformation, wherein the raw materials include G-grade oil well cement and other raw materials in the following percentages based on the mass of G-grade oil well cement: 3-6% microsilicon, 15-50% glass microspheres, 3-6% reinforcing material, 3-5% toughening material, 0-2% stabilizer, 0-2.5% dispersant, 3-6% fluid loss additive, 0-2.5% retarder, 0.2-0.5% defoamer, 0.2-0.5% antifoamer, and 70-95% water; in, The toughening material is compounded by fibers and carbon materials in a mass ratio of 2-4:1, the fibers include one or a combination of two or more of basalt fibers, alumina fibers, and silicon carbide fibers, and the carbon materials include carbon nanotubes and / or expanded graphite; The compressive strength of the glass microspheres is 3000-5000 psi.

2. The cement slurry system for alleviating casing deformation according to claim 1, wherein: The fiber length of the basalt fiber is 1.5-10 μm.

3. The cement slurry system for alleviating casing deformation according to claim 1, wherein: The fiber length of the alumina fiber is 3-6 μm.

4. The cement slurry system for alleviating casing deformation according to claim 1, wherein: The silicon carbide fiber has a fiber length of 10-15 μm.

5. The cement slurry system for alleviating casing deformation according to claim 1, wherein: The length of the carbon nanotubes is 10-30 μm.

6. The cement slurry system for alleviating casing deformation according to claim 1, wherein: The particle size of the expanded graphite is 40-50 μm.

7. The cement slurry system for alleviating casing deformation according to claim 1, wherein: The true density of the glass microspheres is 0.38-0.42 g / cm 3 .

8. The cement slurry system for alleviating casing deformation according to claim 1, wherein: The average particle size of the micro silicon is 4-10 μm, and the 45 μm sieve residue is ≤5%.

9. The cement slurry system for alleviating casing deformation according to claim 1, wherein: The stabilizer is an ore powder stabilizer and / or a polymer stabilizer.

10. The cement slurry system for alleviating casing deformation according to claim 1, wherein: The dispersant is a condensation product of formaldehyde and acetone and / or a polystyrene sulfonate dispersant.

11. The cement slurry system for alleviating casing deformation according to claim 1, wherein: The fluid loss reducer is a polyacrylamide fluid loss reducer.

12. The cement slurry system for alleviating casing deformation according to claim 1, wherein: The retarder is an acrylamide retarder.

13. The cement slurry system for alleviating casing deformation according to claim 1, wherein: The defoaming agent includes one or a combination of two or more of tributyl phosphate, polyoxypropylene glycerol and polydimethylsiloxane.

14. The cement slurry system for alleviating casing deformation according to any one of claims 1 to 13, wherein: The 7-day compressive strength of the cement paste formed by the cement slurry system for alleviating casing deformation is greater than 20 MPa, and the elastic modulus is less than 5 GPa.

15. The cement slurry system for alleviating casing deformation according to claim 14, wherein: The density of the cement slurry system for relieving casing deformation is 1.30-1.60 g / cm 3 , the applicable temperature range is 30-150℃.

16. A method for preparing a cement slurry system for alleviating casing deformation according to any one of claims 1 to 15, comprising: The raw materials are weighed in proportion and mixed, and stirred evenly at a rotation speed of 11500-12500 r / min to obtain the cement slurry system for alleviating casing deformation.

17. The method for preparing a cement slurry system for alleviating casing deformation according to claim 16, wherein: The steps include: Weigh oil well cement, microsilica, glass microspheres, reinforcing material, toughening material, stabilizer and dispersant in proportion, mix them evenly to obtain a dry mixed material; Weigh the fluid loss reducer, retarder and defoamer in proportion and stir them evenly in water to obtain a wet mix solution; At a rotation speed of 3800-4200 r / min, the dry mix is ​​evenly poured into the wet mix solution. After the dry mix is ​​completely added to the wet mix solution, the stirrer speed is adjusted to 11500-12500 r / min, and stirring is continued to obtain the cement slurry system for alleviating casing deformation.

18. Use of the cement slurry system for alleviating casing deformation according to any one of claims 1 to 15 in cementing shale gas wells and preventing and / or alleviating casing deformation.

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