Flushing fluid for well cementation and preparation method thereof

Abstract

The invention discloses a flushing fluid for well cementation and a preparation method thereof, and belongs to the technical field of flushing fluids for well cementation, the flushing fluid comprises an anionic surfactant, a nonionic surfactant, sodium carboxymethyl cellulose, a synergist and the like, the synergist is obtained by embedding organic acid with xanthan gum with stable properties, and the synergist is an anionic surfactant. After the flushing fluid is added, organic acid is continuously released within a short time, the released organic acid can be complexed with a large number of metal ions, then the influence of the metal ions on a surfactant in the flushing fluid is eliminated, meanwhile, an oil film on the well wall is efficiently dissolved, and the flushing efficiency is improved. In addition, sodium carboxymethyl cellulose is also added to improve the dispersibility of the synergist and the surfactant and the adhesiveness on the well wall, the synergist and the surfactant are ensured to fully play a role, all the components in the flushing fluid act jointly, the flushing efficiency is improved, the well cementation quality is ensured, and the flushing fluid has a good application prospect in well cementation.

Description

Technical Field

[0001] The invention relates to the technical field of flushing fluid for cementing, and in particular to a flushing fluid for cementing and a preparation method thereof. Background Art

[0002] In recent years, the number and scale of complex wells such as tight oil and shale oil have shown a rapid upward trend. Oil-based drilling fluids are widely used because they are of great help in improving drilling speed and dealing with complex underground conditions, and have good emulsification stability, excellent wetting ability, and high shale inhibition.

[0003] Flushing fluid is a pre-flushing fluid used before cementing. It is mainly used to clean the oil stains on the well wall and gel drilling fluid, improve the hydrophilicity of the cementing interface, increase the bonding strength between the interface and the cement ring, and improve the quality of cementing. During the cementing process, if the flushing fluid has a weak flushing ability and fails to completely wash the drilling fluid out of the wellhead, the oil film and oil slurry remaining on the interface will affect the bonding strength of the cement slurry, which will have a serious impact on the quality of cementing. Initially, clean water was used as the flushing fluid, but with the development of the drilling fluid system, the requirements for the performance of the flushing fluid have been continuously improved, and clean water can no longer meet the requirements. Adding components such as surfactants can greatly improve the flushing efficiency. However, metal ions such as calcium and magnesium in the drilling fluid are easy to react and combine with surfactants to reduce the effect of the surfactant. Conventional methods usually add inorganic salts such as sodium pyrophosphate to complex metal ions to eliminate their influence on the effect of surfactants. However, the complexing ability of inorganic salts such as sodium pyrophosphate is limited and the effect is not ideal. The large amount of residual metal ions is still easy to inhibit the surfactant and reduce the effect of the flushing fluid.

[0004] Therefore, there is a need to find a cementing flushing fluid with high flushing efficiency to solve the problem that traditional flushing fluids are easily affected by metal ions, resulting in poor flushing effects of the flushing fluids. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a flushing fluid for cementing and a preparation method thereof, so as to solve the problem that metal ions in conventional flushing fluids for cementing are easily reacted and combined with surfactants during flushing, resulting in reduced flushing effect of the flushing fluid.

[0006] The present invention solves the above technical problems by the following technical means:

[0007] A flushing fluid for cementing, the flushing fluid comprising the following raw materials:

[0008] Nonionic surfactant, anionic surfactant, sodium carboxymethyl cellulose, ethylene glycol monobutyl ether, tributyl phosphate, synergist, water.

[0009] Furthermore, the nonionic surfactant is any one of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, isomeric tridecanol polyoxyethylene ether, and coconut oil fatty acid diethanolamide;

[0010] Furthermore, the anionic surfactant is any one of sodium fatty alcohol polyoxyethylene ether sulfate, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate.

[0011] Further, the synergist comprises the following raw materials in parts by weight:

[0012] 0.2-0.5 parts of organic acid, 0.1-0.2 parts of xanthan gum, 0.005-0.01 parts of adipaldehyde, 0.01-0.02 parts of p-hydroxybenzenesulfonic acid, and 0.1-0.2 parts of cassava starch.

[0013] Furthermore, the organic acid is any one of citric acid, malic acid, tartaric acid and fumaric acid.

[0014] Furthermore, the flushing fluid is used at a downhole temperature of 80 to 150°C.

[0015] The present invention also discloses a method for preparing the flushing liquid, and the method for preparing the flushing liquid is specifically as follows:

[0016] (1) adding 10 times the mass of sodium carboxymethyl cellulose into water to dissolve it, leaving it to swell for 3 to 4 hours to obtain sodium carboxymethyl cellulose glue for later use;

[0017] (2) adding a nonionic surfactant, anionic surfactant, and tributyl phosphate into water, stirring and mixing evenly, and then adding ethylene glycol monobutyl ether, stirring and mixing evenly to obtain a base liquid;

[0018] (3) During flushing, sodium carboxymethyl cellulose glue and enhancer are added to the base liquid and mixed evenly to obtain a flushing liquid for flushing the well wall.

[0019] Furthermore, the mass ratio of water, nonionic surfactant, anionic surfactant, tributyl phosphate and ethylene glycol monobutyl ether in step (2) is 10:(3-4):(4-5):(0.07-0.14):(4-6).

[0020] Furthermore, in the step (3), the mass ratio of the base liquid, the sodium carboxymethyl cellulose glue and the synergist is 20:(1-2):(0.4-0.9).

[0021] Further, the preparation method of the synergist is as follows:

[0022] A: Add cassava starch into water and stir to disperse, then add organic acid and stir to mix thoroughly, then dry, and grind and crush through a 200 mesh sieve to obtain organic acid mixed particles;

[0023] B: Add xanthan gum to water and dissolve it to prepare a 10wt% xanthan gum solution, add p-hydroxybenzenesulfonic acid, react at 45-55°C with stirring for 30-60min, let stand for 4-8h after the reaction is completed, then add adipaldehyde and react with stirring for 20-40min, adjust the pH to 6-8 after the reaction is completed, heat to 80°C and react with stirring for 10-15min, quickly cool to room temperature, add organic acid mixed microparticles and mix well, let stand at room temperature for 20-30min, then dry at 45°C and granulate into particles with a particle size of 0.1-0.3mm to obtain a synergist.

[0024] Organic acids have excellent complexing ability for metal ions and can effectively reduce the influence of metal ions on surfactants. The present invention uses xanthan gum with good acid resistance, alkali resistance and high temperature resistance to embed organic acids into a sustained-release enhancer, which is added to the flushing liquid when used. This can prevent the organic acid from reacting with other components such as surfactants in the flushing liquid before the flushing liquid is injected to reduce their respective effects, thereby ensuring that the effects of each component in the flushing liquid are fully exerted and improving the flushing efficiency.

[0025] However, since flushing needs to be completed in a relatively short period of time, if the embedded organic acid cannot be released in a short period of time, the effect of the organic acid will be limited. Therefore, the present invention also uses p-hydroxybenzenesulfonic acid and adipic acid to treat xanthan gum. The p-hydroxybenzoic acid reacts with xanthan gum to change the charge properties of xanthan gum to reduce the cross-linking density, thereby improving the swelling performance of xanthan gum. When it is put into the base liquid of the flushing liquid and contacts water, it quickly absorbs water and swells, so that the embedded organic acid begins to dissolve and release. At the same time, since adipic acid reacts with xanthan gum to form a new molecular chain, the organic acid attacks the formed new molecular chain structure of xanthan gum during the release process, so that its gel structure quickly disintegrates, so that the remaining organic acid is continuously and efficiently released in a short period of time. On the one hand, it can efficiently complex metal ions such as calcium and magnesium, and inhibit the combination of metal ions and surfactants to ensure the flushing effect. On the other hand, the organic acid can also efficiently dissolve the oil film attached to the well wall, and work together with components such as surfactants to efficiently exert the cleaning effect.

[0026] In addition, the present invention further adds sodium carboxymethyl cellulose to the flushing liquid, so that the flushing liquid system is in a glue state with high viscosity, thereby enhancing the adhesion of each component in the flushing liquid to the well wall, and the synergist particles can be relatively evenly dispersed in the flushing liquid system and attached to the well wall to continuously release organic acid, and the residual drilling fluid, oil film, etc. adhered to the well wall are efficiently cleaned together with the surfactant that is better attached to the well wall, thereby improving the flushing efficiency and ensuring the cementing quality. Since sodium carboxymethyl cellulose may cause the hydrogen bonds and entangled structures between molecular chains to be destroyed when exposed to high temperature, when the flushing liquid is injected into the well wall at an environment with a downhole temperature of ≥80°C to flush the well wall, the viscosity of the flushing liquid system will gradually decrease due to the destruction of the hydrogen bonds and entangled structures between the sodium carboxymethyl cellulose molecular chains, and then the subsequent flushing liquid can flow out smoothly after the fluidity is enhanced, and the well wall cleaning efficiency is improved through the synergistic effect of each component in the flushing liquid to ensure the cementing quality.

[0027] Beneficial effects:

[0028] 1. The synergist prepared by the present invention is prepared by embedding organic acid with xanthan gum and added to the mud flushing fluid. The organic acid embedded with xanthan gum can be quickly released in a short time, and while complexing metal ions, it can better dissolve the oil film remaining attached to the drilling fluid, and work together with components such as surfactants to efficiently flush the mud and other components retained in the drilling fluid, thereby ensuring the quality of cementing. The synergist has good application prospects in the field of cementing.

[0029] 2. The present invention also adds sodium carboxymethyl cellulose to prepare the flushing liquid into a colloidal liquid with higher viscosity, which can effectively improve the dispersibility of each component in the flushing liquid and the adhesion on the well wall, so as to promote its better cleaning effect on the well wall and improve the cleaning efficiency. DETAILED DESCRIPTION

[0030] The present invention will be described in detail below with reference to specific embodiments:

[0031] Example 1: Preparation of Flushing Solution

[0032] Preparation of synergist:

[0033] A: Add 0.1kg of cassava starch to 0.5kg of water and stir to disperse, then add 0.35kg of citric acid and stir to mix thoroughly, then dry at 45℃, and grind to pass through a 200-mesh sieve to obtain organic acid mixed particles;

[0034] B: 0.15 kg of xanthan gum was added to water and dissolved to prepare a 10 wt% xanthan gum solution, 0.015 kg of p-hydroxybenzenesulfonic acid was added, and the mixture was stirred and reacted at 50° C. for 40 min. After the reaction was completed, the mixture was allowed to stand for 6 h. Then, 0.008 kg of adipaldehyde was added and stirred and reacted for 30 min. After the reaction was completed, the pH was adjusted to 7, and the mixture was heated to 80° C. and stirred and reacted for 12 min. After the mixture was quickly cooled to room temperature, organic acid mixed microparticles were added and mixed evenly, and the mixture was allowed to stand at room temperature for 25 min. After the mixture was dried at 45° C., the mixture was granulated to prepare a granular synergist with a particle size of about 0.2 mm.

[0035] Preparation of flushing solution:

[0036] (1) adding 10 times the mass of sodium carboxymethyl cellulose into water to dissolve it, leaving it to swell for 3 to 4 hours to obtain sodium carboxymethyl cellulose glue for later use;

[0037] (2) adding 3.5 kg of fatty alcohol polyoxyethylene ether, 4.5 kg of sodium dodecylbenzene sulfonate and 0.12 kg of tributyl phosphate to 10 kg of water, stirring and mixing evenly, and then adding 5 kg of ethylene glycol monobutyl ether and stirring and mixing evenly to obtain a base liquid;

[0038] (3) During flushing, add 1.5 kg of sodium carboxymethyl cellulose glue and 0.5 kg of enhancer to 20 kg of base liquid and mix well to obtain flushing liquid.

[0039] Example 2: Preparation of Flushing Solution II

[0040] Preparation of synergist:

[0041] A: Add 0.1kg of cassava starch to 0.5kg of water and stir to disperse, then add 0.2kg of tartaric acid and stir to mix thoroughly, then dry at 45℃, and grind to pass through a 200-mesh sieve to obtain organic acid mixed particles;

[0042] B: 0.1 kg of xanthan gum was added to water to dissolve to prepare a 10 wt% xanthan gum solution, 0.01 kg of p-hydroxybenzenesulfonic acid was added, and the mixture was stirred and reacted at 45°C for 35 minutes. After the reaction was completed, the mixture was allowed to stand for 5 hours, and then 0.005 kg of adipaldehyde was added and stirred and reacted for 25 minutes. After the reaction was completed, the pH was adjusted to 6, and then the mixture was heated to 80°C and stirred and reacted for 10 minutes. After rapid cooling to room temperature, the organic acid mixed microparticles were added and mixed evenly, and the mixture was allowed to stand at room temperature for 20 minutes. After drying at 45°C, the mixture was granulated to prepare a granular synergist with a particle size of 0.2 mm;

[0043] Preparation of flushing solution:

[0044] (1) adding 10 times the mass of sodium carboxymethyl cellulose into water to dissolve it, leaving it to swell for 3 to 4 hours to obtain sodium carboxymethyl cellulose glue for later use;

[0045] (2) adding 3 kg of alkylphenol polyoxyethylene ether, 4 kg of fatty alcohol polyoxyethylene ether sodium sulfate and 0.07 kg of tributyl phosphate to 10 kg of water, stirring and mixing evenly, and then adding 4 kg of ethylene glycol monobutyl ether and stirring and mixing evenly to obtain a base liquid;

[0046] (3) During flushing, add 1 kg of sodium carboxymethyl cellulose glue and 0.4 kg of enhancer to 20 kg of base liquid and mix well to obtain flushing liquid.

[0047] Example 3: Preparation of Flushing Solution III

[0048] Preparation of synergist:

[0049] A: Add 0.2kg of cassava starch to 1kg of water and stir to disperse, then add 0.5kg of malic acid and stir to mix thoroughly, then dry at 45℃, and grind to pass through a 200-mesh sieve to obtain organic acid mixed particles;

[0050] B: 0.2 kg of xanthan gum was added to water and dissolved to prepare a 10 wt% xanthan gum solution, 0.02 kg of p-hydroxybenzenesulfonic acid was added, and the mixture was stirred and reacted at 55°C for 60 min. After the reaction was completed, the mixture was allowed to stand for 8 h, and then 0.01 kg of adipaldehyde was added and stirred and reacted for 40 min. After the reaction was completed, the pH was adjusted to 8, and the mixture was heated to 80°C and stirred and reacted for 15 min. After the mixture was quickly cooled to room temperature, organic acid mixed particles were added and mixed evenly, and the mixture was allowed to stand at room temperature for 30 min. After the mixture was dried at 45°C, the mixture was granulated to prepare a granular synergist with a particle size of about 0.2 mm.

[0051] Preparation of flushing solution:

[0052] (1) adding 10 times the mass of sodium carboxymethyl cellulose into water to dissolve it, leaving it to swell for 3 to 4 hours to obtain sodium carboxymethyl cellulose glue for later use;

[0053] (2) adding 4 kg of coconut oil fatty acid diethanolamide, 5 kg of sodium dodecylbenzene sulfonate and 0.14 kg of tributyl phosphate to 10 kg of water, stirring and mixing evenly, and then adding 6 kg of ethylene glycol monobutyl ether and stirring and mixing evenly to obtain a base liquid;

[0054] (3) During flushing, add 2 kg of sodium carboxymethyl cellulose glue and 0.9 kg of enhancer to 20 kg of base liquid and mix well to obtain flushing liquid.

[0055] Comparative Example 1: Preparation of Flushing Solution

[0056] In contrast to Example 1, the only difference is that in the preparation of the flushing liquid in Comparative Example 1, p-hydroxybenzenesulfonic acid is not added to the synergist to treat the xanthan gum, as follows:

[0057] Preparation of synergist:

[0058] A: Same as Example 1;

[0059] B: 0.15 kg of xanthan gum was dissolved in water to prepare a 10 wt% xanthan gum solution, 0.008 kg of adipaldehyde was added and stirred for 30 min, after the reaction was completed, the pH was adjusted to 7, and then heated to 80°C and stirred for 12 min, and then quickly cooled to room temperature, organic acid mixed particles were added and mixed evenly, and then allowed to stand at room temperature for 25 min, and then dried at 45°C and granulated to prepare a granular synergist with a particle size of about 0.2 mm;

[0060] Preparation of flushing solution: same as in Example 1.

[0061] Comparative Example 2: Preparation of Flushing Solution

[0062] In contrast to Example 1, the only difference is that in Comparative Example 2, when preparing the flushing liquid, adipaldehyde is not added to the synergist to treat the xanthan gum, as follows:

[0063] Preparation of synergist:

[0064] A: Same as Example 1;

[0065] B: 0.15 kg of xanthan gum was dissolved in water to prepare a 10 wt% xanthan gum solution, 0.015 kg of p-hydroxybenzenesulfonic acid was added, and the mixture was stirred at 50° C. for 40 min. After the reaction was completed, the mixture was allowed to stand for 6 h, the pH was adjusted to 7, and the mixture was heated to 80° C. for 12 min. After the mixture was quickly cooled to room temperature, the organic acid mixed microparticles were added, the mixture was mixed evenly, and the mixture was allowed to stand at room temperature for 25 min. After the mixture was dried at 45° C., the mixture was granulated to prepare a granular synergist with a particle size of about 0.2 mm.

[0066] Preparation of flushing solution: same as in Example 1.

[0067] Comparative Example 3: Preparation of Flushing Solution

[0068] In contrast to Example 1, the only difference is that the pH of the synergist in the flushing liquid of Comparative Example 3 is not adjusted during preparation, and the remaining steps are the same as those of Example 1.

[0069] Comparative Example 4: Preparation of Flushing Solution

[0070] In contrast to Example 1, the only difference is that in Comparative Example 4, when preparing the flushing solution, the synergist is not embedded with xanthan gum, but the organic acid is directly added to the base liquid to mix and prepare the flushing solution.

[0071] Preparation of flushing solution:

[0072] (1) to (2) are the same as in Example 1;

[0073] (3) During flushing, add 1.5 kg of sodium carboxymethyl cellulose glue and 0.35 kg of citric acid into 20 kg of base liquid and mix well to obtain a flushing liquid.

[0074] Comparative Example 5: Preparation of Flushing Solution

[0075] In contrast to Example 1, the only difference is that in Comparative Example 5, when preparing the flushing liquid, p-hydroxybenzenesulfonic acid and adipaldehyde are not added as the synergist, as follows:

[0076] Preparation of synergist:

[0077] A: Same as Example 1;

[0078] B: 0.15 kg of xanthan gum was added to water and dissolved to prepare a 10 wt% xanthan gum solution, heated to 80°C and stirred for 12 minutes, quickly cooled to room temperature, added with organic acid mixed particles, mixed evenly, and allowed to stand at room temperature for 25 minutes, then dried at 45°C and granulated to prepare a granular synergist with a particle size of about 0.2 mm;

[0079] Preparation of flushing solution: same as in Example 1.

[0080] Comparative Example 6: Preparation of Flushing Solution

[0081] In contrast to Example 1, the only difference is that in Comparative Example 6, the xanthan gum in the enhancer is replaced with gelatin during the preparation of the flushing solution, and the remaining steps are the same as in Example 1.

[0082] Comparative Example 7: Preparation of Flushing Solution

[0083] In contrast to Example 1, the only difference is that in Comparative Example 7, the synergist is replaced with 0.35 kg of sodium pyrophosphate during the preparation of the flushing solution, and the remaining steps are the same as in Example 1.

[0084] Comparative Example 8: Preparation of Flushing Solution

[0085] In contrast to Example 1, the only difference is that in Comparative Example 8, sodium carboxymethyl cellulose glue is not added during the preparation of the flushing solution, but an equal amount of clean water is added, and the remaining steps are the same as in Example 1.

[0086] Experiment 1: Organic acid release experiment in synergist

[0087] The release performance of the organic acid in the synergists prepared in Example 1, Comparative Examples 1 to 3 and Comparative Examples 5 to 6 was tested, and the specific method was as follows:

[0088] Weigh 30g of the enhancer and put it into 1L of 90℃ constant temperature water. Stir it continuously at 100r / min. After a certain period of time, use acid-base titration to determine and calculate the citric acid content in the water.

[0089] According to the above method, the citric acid content of the synergists prepared in Example 1, Comparative Examples 1-3 and Comparative Examples 5-6 when added to water for 2 minutes and 8 minutes was detected respectively, and the obtained data are shown in Table 1.

[0090] Table 1

[0091]

[0092]

[0093] According to the data analysis in Table 1:

[0094] (1) The synergist prepared according to the method of the present invention is added to the flushing liquid, and the organic acid in the synergist can be efficiently released, which is beneficial to ensure the complexing effect of the organic acid on the metal ions and the removal effect on the oil film.

[0095] (2) In Comparative Example 1, the synergist did not add p-hydroxybenzenesulfonic acid to the xanthan gum, and the swelling performance of the xanthan gum was poor, so the amount of internal citric acid released by swelling in water was reduced; in Comparative Example 2, the synergist did not add adipaldehyde to the xanthan gum, and the structure of the xanthan gum molecular chain was relatively stable, the encapsulation of citric acid was good, and the release amount was reduced; in Comparative Example 6, the xanthan gum was replaced with gelatin during the preparation of the synergist, and the gelatin had poor thermal stability and quickly released the embedded citric acid at high temperature. In actual application, it is easy to cause the citric acid to be released too quickly, thereby reducing the effect of the citric acid, and having an adverse effect on the surfactant.

[0096] Experiment 2: Flushing efficiency test of flushing fluid

[0097] 1. The washing efficiency of the washing liquids prepared in Example 1 and Comparative Examples 1 to 8 was tested by a rotational viscometer method. The specific method is as follows:

[0098] The flushing liquid is placed in a slurry cup and placed in a constant temperature water bath at 95°C for 10 minutes; the rotary viscometer cylinder is cleaned and dried, and the mass of the cylinder itself is weighed and recorded as W0; the weighed cylinder is immersed in an oil-based drilling fluid for 20 minutes, and the drilling fluid is dripped until it stops dripping, and then the weight is recorded as W1. Then the cylinder is installed on a six-speed rotary viscometer, and the slurry cup is removed after flushing with the flushing liquid at a speed of 200r / min for a certain period of time. When the liquid stops dripping, the cylinder is removed and weighed and recorded as W3. Then the flushing efficiency is calculated: flushing efficiency = (w1-w2) / (w1-w0)×100%, and the flushing time is selected to be 4min and 8min respectively. The flushing efficiency of the flushing liquid prepared in Example 1 and Comparative Examples 1 to 8 is detected, and the average value is obtained by three parallel measurements. The data are shown in Table 2.

[0099] Table 2

[0100]

[0101]

[0102] According to the data analysis in Table 2:

[0103] (1) The flushing efficiency of the flushing fluid in Example 1 is better than that of Comparative Examples 1 to 8, and the flushing efficiencies of 4 min and 8 min are 86.88% and 98.72%, respectively, indicating that the flushing fluid prepared by the present invention has good flushing efficiency and has good application prospects in the field of cementing.

[0104] (2) The synergist in the flushing fluid of Comparative Example 1 does not contain p-hydroxybenzenesulfonic acid, the synergist in the flushing fluid of Comparative Example 2 does not contain adipic dialdehyde, and the synergist in the flushing fluid of Comparative Example 5 does not contain p-hydroxybenzenesulfonic acid and adipic dialdehyde. The release of organic acid in the synergist of the flushing fluids of Comparative Example 1, Comparative Example 2, and Comparative Example 5 is hindered, and the metal ions limit the effect of the surfactant. At the same time, the dissolution and removal effect of organic acid in the oil-based drilling fluid is also reduced, so the flushing efficiency is reduced to varying degrees.

[0105] (3) In the preparation of the rinsing liquid in Comparative Example 6, the synergist was replaced by gelatin, which had poor structural stability and thus affected the effect of the rinsing liquid. When the rinsing liquid was exposed to high temperature, a large amount of organic acid was released, which affected the effect of the surface activity. As a result, the metal ion complexing ability was weak and the effect of the surfactant was reduced during cleaning, resulting in a significant decrease in the rinsing efficiency. In Comparative Example 7, the synergist was replaced by sodium pyrophosphate. Although sodium pyrophosphate had a certain complexing effect on metal ions, its effect was lower than that of organic acid, so the rinsing efficiency was lower. In Comparative Example 8, no sodium carboxymethyl cellulose glue was added, and the dispersibility and adhesion of the synergist and surfactant were affected, thereby reducing the rinsing efficiency.

[0106] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention. The techniques, shapes, and structural parts not described in detail in the present invention are all known technologies.

Claims

1. A flushing fluid for cementing, characterized in that: The flushing solution comprises the following raw materials: Nonionic surfactant, anionic surfactant, sodium carboxymethyl cellulose, ethylene glycol monobutyl ether, tributyl phosphate, synergist, water.

2. A flushing fluid for cementing according to claim 1, characterized in that: The nonionic surfactant is any one of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, isomeric tridecanol polyoxyethylene ether, and coconut oil fatty acid diethanolamide.

3. A flushing fluid for cementing according to claim 2, characterized in that: The anionic surfactant is any one of sodium fatty alcohol polyoxyethylene ether sulfate, sodium dodecyl sulfate and sodium dodecylbenzene sulfonate.

4. A flushing fluid for cementing according to claim 3, characterized in that: The synergist comprises the following raw materials in parts by weight: 0.2-0.5 parts of organic acid, 0.1-0.2 parts of xanthan gum, 0.005-0.01 parts of adipaldehyde, 0.01-0.02 parts of p-hydroxybenzenesulfonic acid, and 0.1-0.2 parts of cassava starch.

5. A flushing fluid for cementing according to claim 4, characterized in that: The organic acid is any one of citric acid, malic acid, tartaric acid and fumaric acid.

6. A flushing fluid for cementing according to claim 5, characterized in that: The flushing fluid is used under the condition that the downhole temperature is 80-150°C.

7. A method for preparing a flushing fluid for cementing, characterized in that: The preparation method of the flushing solution is as follows: (1) adding 10 times the mass of sodium carboxymethyl cellulose into water to dissolve it, and allowing it to swell for 3 to 4 hours to obtain a sodium carboxymethyl cellulose gel; (2) adding a nonionic surfactant, anionic surfactant, and tributyl phosphate into water, stirring and mixing evenly, and then adding ethylene glycol monobutyl ether, stirring and mixing evenly to obtain a base liquid; (3) During flushing, sodium carboxymethyl cellulose glue and enhancer are added to the base liquid and mixed evenly to obtain a flushing liquid for flushing the well wall.

8. The method for preparing a flushing fluid for cementing according to claim 7, wherein the mass ratio of water, nonionic surfactant, anionic surfactant, tributyl phosphate and ethylene glycol monobutyl ether in step (2) is 10:(3-4):(4-5):(0.07-0.14):(4-6).

9. The method for preparing a flushing fluid for cementing according to claim 8, characterized in that: In the step (3), the mass ratio of the base liquid, sodium carboxymethyl cellulose glue and the synergist is 20:(1-2):(0.4-0.9).

10. The method for preparing a flushing fluid for cementing according to claim 9, characterized in that: The preparation method of the synergist is as follows: A: Add cassava starch into water and stir to disperse, then add organic acid and stir to mix thoroughly, then dry, and grind and crush through a 200 mesh sieve to obtain organic acid mixed particles; B: Add xanthan gum to water and dissolve it to prepare a 10wt% xanthan gum solution, add p-hydroxybenzenesulfonic acid, react at 45-55°C with stirring for 30-60min, let stand for 4-8h after the reaction is completed, then add adipaldehyde and react with stirring for 20-40min, adjust the pH to 6-8 after the reaction is completed, heat to 80°C and react with stirring for 10-15min, quickly cool to room temperature, add organic acid mixed microparticles and mix well, let stand at room temperature for 20-30min, then dry at 45°C and granulate into particles with a particle size of 0.1-0.3mm to obtain a synergist.

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