Anti-channeling tough cement paste system as well as preparation method and application thereof

Abstract

The invention relates to the technical field of oil and gas field well drilling and cementing, in particular to an anti-channeling tough cement paste system and a preparation method and application thereof, and aims at effectively relieving the problem that the sealing integrity of a cement sheath is damaged in the large-volume fracturing production process. According to the anti-channeling tough cement paste provided by the invention, the flexural strength is improved, meanwhile, the rapid decline of the compressive strength can be slowed down, and relatively high compressive strength is reserved. The invention provides an anti-channeling tough cement paste system which comprises the following components in parts by weight: 100 parts of oil well cement; 1-4 parts of a toughening agent; 0.7 to 2.5 parts of a fluid loss agent; 0 to 0.5 part of a drag reducer; 0-35 parts of a stabilizer; 1-4 parts of a suspending agent; 0 to 2.5 parts of a retarder; 0.1 to 0.3 part of a defoaming agent; and 42 to 54 parts of water.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas well drilling and cementing, and particularly relates to an anti-channeling tough cement slurry system, a preparation method thereof, and an application thereof. Background Art

[0002] With the long-term production of oil and gas wells and the increasing complexity of exploration and development targets, oil and gas well safety accidents caused by wellbore failure occur more frequently. As the downhole working conditions become more complex, downhole operations such as casing pressure testing, water injection, acid fracturing, and perforation during production will generate periodic alternating internal pressure and alternating temperature, which easily lead to fatigue damage of the cement sheath interface, forming micro-annuli and causing the failure of the casing-cement sheath seal integrity. The phenomena such as annulus pressure buildup, oil and gas and water channeling, and wellhead uplift seriously affect the safe and efficient production of oil and gas wells. In order to improve the brittleness of oil well cement stone and enhance its deformation ability and toughness, a tough cement slurry is formed by adding flexible materials. Therefore, it is of great significance to develop an anti-channeling tough cement slurry system to improve the cement sheath seal integrity. In view of the risk of the failure of the cement slurry sealing effect in the wellbore, research shows that an elastic and tough cement slurry system is the key to ensuring the cementing quality and the long-term sealing ability of the cement sheath. A latex cement slurry is a cement slurry system formed by adding latex polymer materials to a conventional cement slurry.

[0003] For example, in a Chinese patent with the publication number CN108046694A, an anti-channeling cement slurry system suitable for shale gas cementing and a preparation method thereof, and a Chinese patent with the publication number CN102618231 disclose a low-temperature shallow anti-channeling cement slurry. A certain amount of triisopropanolamine, calcium chloride, vinyl acetate emulsion, and styrene-butadiene latex are added to the anti-channeling cement slurry. The performance of the cement slurry system is optimized through the interaction of each component in the cement slurry system, and the interfacial orientation of the cement hydration products is changed, etc. This cement slurry has the advantages of low-temperature early strength, adjustable thickening time, and improved interfacial bonding performance. However, when the latex addition amount is too large, it will cause a loss of the compressive strength of the cement stone. A Chinese patent with the publication number CN113278106A discloses a well-dispersed pulverized latex toughening agent and a preparation method and application thereof. Using styrene-butadiene latex powder as a toughening agent, it is difficult to illustrate its excellent toughening performance only through a single characterization of the elastic modulus, and it can replace styrene-butadiene latex. At the same time, styrene-butadiene latex has instability and is prone to demulsification, resulting in product failure. Therefore, when considering improving the cement sheath seal integrity by preparing a latex cement slurry, we consider whether other types of latex can be used and develop high-performance latex additives. Therefore, eliminating the weak transition zone of interfacial bonding in cementing, improving the bonding strength of the first and second interfaces, improving the seal integrity of the cement sheath, developing a latex toughening agent and a high-performance anti-channeling tough cement slurry system are the problems that need to be solved urgently at present. Summary of the Invention

[0004] The object of the present invention is to provide a channeling prevention and toughness cement slurry system, its preparation method and its application, so as to effectively alleviate the problem of damaging the sealing integrity of the cement sheath during the large-scale volume fracturing production process. The channeling prevention and toughness cement slurry provided by the present invention can slow down the rapid decline of the compressive strength while increasing the flexural strength, and retain a relatively high compressive strength.

[0005] The channeling prevention and toughness cement slurry system provided by the present invention has the following characteristics: the density of the cement slurry system is 1.85 - 1.90 g / cm 3 , the thickening time is adjustable, with high flexural strength, low brittleness coefficient, low elastic modulus, low permeability, and the comprehensive performance meets the construction requirements.

[0006] In order to solve the above technical problems, the technical solution provided by the present invention lies in:

[0007] In the first aspect, the present invention provides a channeling prevention and toughness cement slurry system, and the channeling prevention and toughness cement slurry system comprises the following components in parts by weight:

[0008] Oil well cement, 100 parts;

[0009] Toughening agent, 1 - 4 parts;

[0010] Fluid loss reducer, 0.7 - 2.5 parts;

[0011] Friction reducer, 0 - 0.5 parts;

[0012] Stabilizer, 0 - 35 parts;

[0013] Suspending agent, 1 - 4 parts;

[0014] Retarder, 0 - 2.5 parts;

[0015] Defoamer, 0.1 - 0.3 parts;

[0016] Water, 42 - 54 parts.

[0017] Preferably, the oil well cement is of Grade G;

[0018] Preferably, the water is one or more of deionized water, fresh water, seawater, reclaimed water and mineralized water;

[0019] Preferably, the suspending agent is an inorganic material, and the suspending agent is one or more of ultrafine materials and clay substances;

[0020] More preferably, microsilica is one of the most commonly used ultrafine materials in the cement slurry. Clay substances include bentonite, attapulgite, sepiolite, vermiculite, clay-grade mica, expanded chlorite and imogolite, etc.

[0021] Preferably, the stabilizer is one or more of mineral powder, quartz sand, fly ash, magnesium aluminum silicate and Wenlun glue;

[0022] Preferably, the fluid loss additive is a mixture of one or two of 2-acrylamide-2-methylpropanesulfonic acid (AMPS), polyvinyl alcohol, amide or imide, and a multi-polymer modified by polymerization of 2-acrylamide-2-methylpropanesulfonic acid (AMPS), low molecular weight amide, and polyhydroxycarboxylic acid;

[0023] Preferably, the drag reducer is one or more of sulfonated ketone-aldehyde condensate, polynaphthalene sulfonate, and polycarboxylic acid series;

[0024] Preferably, the retarder is a phosphate or a polymer with acrylamide as the main chain;

[0025] Further preferably, the retarder is one or more of phosphates, such as hydroxyethylidene diphosphonic acid; polymers with acrylamide as the main chain, such as sodium borate and 2-acrylamido-2-methylpropanesulfonic acid / itaconic acid copolymer.

[0026] Preferably, the defoamer is at least one of an organic phosphate, an organic silicon, a siloxane copolymer, an organic siloxane, and a polyether-modified polysiloxane defoamer;

[0027] Preferably, the toughening agent is a redispersible latex powder, which is water-soluble and is a binary, ternary and quaternary copolymer powder formed by polymerization of vinyl acetate as the main monomer and one or more functional monomers added thereto, including one or more blends of ethylene-vinyl acetate copolymer (EVA), vinyl acetate-higher fatty acid vinyl ester copolymer powder, vinyl acetate-ethylene-higher fatty acid vinyl ester ternary copolymer powder, and vinyl acetate-acrylate-higher fatty acid vinyl ester ternary copolymer powder. The redispersible latex powder can be restored to the original emulsion state after being dispersed in water, and the basic properties and performance are consistent with the original emulsion. The redispersible latex powder can significantly reduce the permeability of cement stone, increase the interfacial bonding strength and improve the toughness of cement stone.

[0028] In a second aspect, the present invention provides a method for preparing the anti-channeling tough cement slurry system, comprising the following steps:

[0029] Step S1, dry-mixing 100 parts of oil well cement, 1-4 parts of toughening agent, 0.7-2.5 parts of fluid loss additive, 0-0.5 parts of drag reducer, 0-35 parts of stabilizer, and 1-4 parts of suspending agent to obtain a dry powder mixture;

[0030] Step S2, 0-2.5 parts of a retarder, 0.1-0.3 parts of a defoamer, and 42-54 parts of water are uniformly mixed to obtain a solution mixture;

[0031] Step S3: Using a constant-speed stirrer, add the above dry powder mixture completely into the solution mixture within 15 s at a low rotation speed of (4000 ± 200 r / min), and then mix at a high rotation speed of (12000 ± 500 r / min) for 35 s to mix evenly, ensuring that the cement slurry obtains 5.91 kJ / kg API mixing energy to obtain the anti-channeling tough cement slurry.

[0032] Furthermore, the toughening agent is prepared by the following method:

[0033] Synthesis includes the preparation of latex emulsion and the drying of latex emulsion to obtain redispersible latex powder, which is synthesized by the seed emulsion polymerization and continuous feeding method. The preparation process is to continuously add the reaction monomers into water under the action of an aqueous solution of protective colloid particles, emulsifier and pH buffer, and use an initiator to initiate polymerization under the required temperature and pressure conditions. After the polymerization reaction is completed, the latex emulsion is obtained, cooled to ambient temperature, and dried with a spray dryer to obtain latex powder.

[0034] In a third aspect, the present invention provides an application of the anti-channeling tough cement slurry system in oil well cementing.

[0035] Applying the cement slurry provided by the embodiments of the present invention to the cementing operation can effectively improve the bonding quality of the first and second interfaces, providing technical support for the long-term, safe and effective operation of oil and gas wells.

[0036] Integrating the above technical solutions, the technical effects that the present invention can achieve are as follows:

[0037] (1) In the anti-channeling tough cement slurry provided by the present invention, the toughening agent used is redispersible latex powder. The latex toughening agent is an oil well cement admixture that can effectively improve the toughness of oil well cement and avoid brittle fracture of the cement stone. When the cement hydrates and absorbs a large amount of water in the latex, the latex particles will penetrate between the hardened cement and cement, and between cement and polymer in the form of a polymer film, and finally form a dense three-dimensional network structure. This structure can fully absorb the fracture energy required for the expansion of defects and microcracks in the cement sheath, effectively delay the expansion speed of defects and microcracks, improve its tensile and flexural strength, and improve the toughness of the oil well cement stone. At the same time, this cross-linked network structure can greatly improve the gas invasion resistance of water and gas invading the cement slurry, effectively reducing the probability of channeling occurrence.

[0038] (2) The optimal addition amount of redispersible latex powder as a toughening agent is 2% to 3%, and the dosage is small. At the same time, latex powder has "one dose with multiple functions". In addition to being able to toughen cement stone, it also has a significant anti-channeling effect. It improves the fluidity of cement slurry by improving dispersibility, reduces cement water loss, and delays cement solidification. In order to meet the requirements of cementing, it is sometimes necessary to add a variety of admixtures, but there is a competitive adsorption effect between admixtures, which will cause the effects of each admixture to fail to varying degrees. Therefore, making one admixture have the functions of multiple admixtures can greatly weaken this effect. In addition, because it has multiple functions, the amount of other admixtures added can be reduced, which also plays a role in reducing costs, improving quality and increasing efficiency.

[0039] (3) Toughening agent is a redispersible latex powder, which is water-soluble and is based on vinyl acetate as the main monomer. On this basis, one or more functional monomers are added to form a binary, ternary or quaternary copolymer powder. By introducing functional monomers, the toughening agent has a variety of properties. Usually, these functional monomers have characteristic functional groups such as carboxylic acid, sulfonic acid, and amide groups, which change the properties of the toughening agent by affecting the cement hydration process.

[0040] (4) Compared with the traditional cement slurry system, the anti-channeling tough cement slurry system has a 61% increase in flexural strength, a 59% decrease in elastic modulus, and a cement stone compressive strength greater than 28MPa. While improving the flexural strength, it slows down the rapid decline of the compressive strength as much as possible and retains a high compressive strength. It has good construction performance, good mechanical properties and sufficient flexibility, which can effectively alleviate the problem of damaging the sealing integrity of the cement ring during large-scale volume fracturing production.

[0041] (5) The toughening agent used in this anti-channeling tough cement slurry system is redispersible latex powder based on ethylene-vinyl acetate, which is a hydrophilic solid powder. It solves the problems of poor storage performance stability of liquid products, resulting in shortened product performance validity period and irreversible environmental pollution usually caused by leakage during application and storage. Compared with liquid latex, this latex powder can be dry-mixed with cement powder, while liquid latex requires wet mixing and on-site water-mixing operations, which is more suitable for cementing construction conditions, reducing transportation costs, cementing process costs and labor costs, and having high economic benefits and broad application prospects. Compared with using the self-produced anti-channeling tough system and Boxin liquid latex system, it saves 8,666.74 yuan per well in small-diameter wells and 12,638.92 yuan per well in conventional wells. The self-produced anti-channeling tough system has excellent cost advantages. With the increasing national attention to environmental protection, white oily liquid latex will pollute the surface soil, while latex powder can reduce the pollution caused by latex and is environmentally friendly. And compared with styrene-butadiene rubber latex (SBR) and styrene-acrylic rubber latex (SAR), this latex powder has extremely strong hydrophilicity, does not require latex stabilizers and emulsifiers, and the raw materials are very easy to obtain with lower costs, being non-toxic, harmless and environmentally friendly.

[0042] (6) The anti-channeling tough cement slurry formed by the present invention does not add extra anti-channeling agents. The static gelation strength transition time of this cement slurry system is short and the anti-channeling performance is excellent. The excellent anti-channeling performance mainly comes from the latex. The latex film can effectively prevent substances such as oil and gas from invading the cement slurry column, and at the same time prevent the upwelling of oil and gas in the annulus gap, having a good anti-channeling effect.

[0043] (7) Applying the cement slurry provided by the embodiments of the present invention to cementing operations can effectively improve the cementing quality of the first and second interfaces, providing technical support for the long-term, safe and effective operation of oil and gas wells. So far, the cement slurry provided by the embodiments of the present invention has been widely promoted and used in the Changqing area. In 31 well tests in the Changqing area, the excellent cementing rate is as high as 100%. Among them, it is used 26 well times in the Wushenqi area, including 18 production wells, 1 natural gas evaluation well, and 7 plugging wells; it is used 5 well times in the Yanchi area, including 4 production wells and 1 natural gas evaluation well. The solid toughening agent for oil well cement forms a tough cement slurry system with conventional density, which is used to seal the target pay zone. The excellent cementing rate is 100%. The cement sheath has sufficient toughness, effectively seals the gas layer, can meet the requirements of large-scale volume fracturing technology for later exploitation, improves the sealing performance of the wellbore, and extends the life of the cement sheath. Description of the Drawings

[0044] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0045] Figure 1 (Left) Toughness enhancer for oil well cement; (Right) The toughness enhancer for oil well cement is dissolved in water to form a latex emulsion;

[0046] Figure 2 Thickening curve of the anti-channeling and tough cement slurry system with G301 as the fluid loss reducer in Example 1;

[0047] Figure 3 Thickening curve of the anti-channeling and tough cement slurry system with G31S as the fluid loss reducer in Example 2;

[0048] Figure 4 Thickening curve of the anti-channeling and tough cement slurry system with BZJS-2 as the fluid loss reducer in Example 3;

[0049] Figure 5 Thickening curve of the anti-channeling and tough cement slurry system with BH-F202S as the fluid loss reducer in Example 4;

[0050] Figure 6 Thickening curve of the anti-channeling and tough cement slurry system at a temperature of 120°C in Example 5;

[0051] Figure 7 Static gel strength development curve of the anti-channeling and tough cement slurry system with G301 as the fluid loss reducer in Example 1;

[0052] Figure 8 Acoustic amplitude map of Well Su 76-6-32X. Specific embodiments

[0053] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further details the present invention in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the described embodiments are only some embodiments of the present invention, rather than all embodiments.

[0054] Therefore, the following detailed description of the provided embodiments of the present invention is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0055] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents, materials, etc. used in the following examples can all be obtained from commercial sources unless otherwise specified.

[0056] In a first aspect, the object of the present invention is to provide an anti-channeling tough cement slurry system that can effectively alleviate the problem of damaging the sealing integrity of the cement sheath during the large-volume fracturing production process. The cement slurry system provided by the present invention is an anti-channeling tough cement slurry system for improving the sealing integrity of the cement sheath. The cement slurry includes the following components by weight: well cement, 100 parts; toughening agent, 1 - 4 parts; fluid loss reducer, 0.7 - 2.5 parts; friction reducer, 0 - 0.5 parts; stabilizer, 0 - 35 parts; suspending agent, 1 - 4 parts; retarder, 0 - 2.5 parts; defoamer, 0.1 - 0.3 parts; water, 42 - 54 parts.

[0057] In the present invention, unless otherwise specified, the raw materials used are all commercially available products in the art.

[0058] In the present invention, the well cement is Grade G. Specifically, it can be Shengwei Grade G, Yaowangshan Grade G, Jiahua Grade G, but it is not limited to these several specifically, and any commercially available Grade G well cement can be used.

[0059] In the present invention, the water can be deionized water, fresh water, seawater, recycled water, or water with salinity. The present invention has no special requirements for water. The anti-channeling tough cement slurry provided by the present invention exhibits excellent salt tolerance and performs well in three saturated salt solutions: saturated NaCl solution, MgCl2 solution, and saturated MgCl2 solution. Among them, there is no obvious change in the NaCl solution and MgCl2 solution, and it exists stably; in the CaCl2 solution, the viscosity increases and there is no flocculation. This is because the introduction of functional monomers and the insensitivity of latex particles to metal cations result in stable latex particle states, so its salt tolerance is relatively good. Due to its salt tolerance, when preparing this anti-channeling tough cement slurry, fresh water, seawater, recycled water, and water with salinity can be reasonably utilized according to the cementing construction conditions and economic costs to reduce costs and achieve the purpose of improving quality and efficiency for enterprises.

[0060] In the present invention, the friction reducer is one or more of sulfonated ketone aldehyde condensates, polynaphthalene sulfonates, and polycarboxylic acid systems. The friction reducer is not an essential component, and the addition amount of the friction reducer depends on the consistency and rheology of the cement slurry.

[0061] In the present invention, preferably, the defoamer is an organophosphate ester.

[0062] The anti-channeling tough cement slurry provided by the embodiments of the present invention, through the mutual cooperation and synergistic effect of each component, enables the cement stone formed after the anti-channeling tough cement slurry is cured to have good toughness while also having good compressive properties.

[0063] In the present invention, the toughening agent is redispersible latex powder, which is water-soluble and is a binary, ternary or quaternary copolymer powder formed by polymerizing vinyl acetate as the main monomer and adding one or more functional monomers on this basis, including one or a blend of ethylene-vinyl acetate copolymer (EVA), vinyl acetate - vinyl higher fatty acid ester copolymer powder, vinyl acetate - ethylene - vinyl higher fatty acid ester ternary copolymer powder, vinyl acetate - acrylate - vinyl higher fatty acid ester ternary copolymer powder. The redispersible latex powder can return to the original emulsion state after being dispersed in water (such as Figure 1 ), and its basic characteristics and properties are the same as those of the original emulsion. The redispersible latex powder can significantly reduce the permeability of the cement stone, improve the interfacial bonding strength and enhance the toughness of the cement stone. The preparation and synthesis of the toughening agent include the preparation of the latex emulsion and the drying of the latex emulsion to obtain redispersible latex powder. It is synthesized by using the seed emulsion polymerization and continuous feeding method. The preparation process is to continuously add the reaction monomers into water under the action of an aqueous solution of a protective colloid particle, an emulsifier and a pH buffer, and use an initiator to initiate polymerization under the required temperature and pressure conditions. After the polymerization reaction is completed, the latex emulsion is obtained, cooled to the ambient temperature, and dried with a spray dryer to obtain the latex powder.

[0064] For further detailed description, based on ethylene and vinyl acetate monomers, carboxylic acid functional monomers and sulfonic acid functional monomers are selected and optimized. The toughening agent for redispersible latex powder is formed by copolymerizing two functional monomers, sodium allylsulfonate (SA) and itaconic acid (IA), which are polar hydrophilic monomers. The preparation method of this toughening agent is as follows:

[0065] (1) Preparation of the protective colloid: Add 1 - 20 parts of polyvinyl alcohol (PVA) as the protective colloid particles into a high-pressure reactor with magnetic stirring, then add 80 - 100 parts of water, stir at room temperature for 30 min, heat up to 80 °C and stir for 2.5 h, and then cool to room temperature.

[0066] (2) Initial initiation reaction: At a low speed, add 57 - 64 parts of vinyl acetate, SA and IA initial monomers, heat up to 50 °C, degas the reactor, and displace with 10 - 20 parts of ethylene twice. Use ethylene to increase the pressure of the reactor to 4.0 - 6.0 MPa, and add 1% - 3% of the initiator hydrogen peroxide, potassium persulfate or ammonium persulfate based on the total mass of the monomers with a peristaltic pump to initiate the polymerization reaction. Since the addition of the IA system is acidic, the aqueous phase solution is adjusted to weakly alkaline with NaOH.

[0067] (3) Continuous polymerization reaction: Slowly raise the temperature to 80 °C, then set the pressure in the reactor to rise to 6.0 - 8.0 MPa. Add the remaining 23 - 26 parts of the continuous monomer vinyl acetate. Maintain the pressure in the reactor at 6.0 - 8.0 MPa, and adjust the water bath temperature to keep the reaction temperature at 80 °C.

[0068] (4) Polymerization termination reaction: After the continuous monomer is completely added dropwise, continue to add the initiator for a period of time while maintaining the reaction temperature at 80 °C. After the reaction ends, when the high-pressure reactor cools down to room temperature, slowly open the pressure relief valve of the reactor to discharge the unreacted ethylene gas, and obtain the latex emulsion produced by polymerization.

[0069] (4) The latex emulsion is used to prepare redispersible latex powder by spray drying.

[0070] In the present invention, there are no special limitations on the specific parameters of spray drying the latex emulsion, and the methods well-known to those skilled in the art can be adopted.

[0071] According to the principle of like dissolves like, this invention patent introduces two functional monomers, carboxylic acid functional monomer and sulfonic acid type, and uses a suitable drying method to prepare latex powder. In order to make the dried latex toughener have excellent redispersibility, the carboxylic acid functional monomer and the sulfonic acid type functional monomer are optimized, and the polar hydrophilic sodium allyl sulfonate (SA) and itaconic acid (IA) are selected. Sodium allyl sulfonate (SA) has polar functional groups, and -SO3H therein can not only improve the dispersibility of latex particles in the cement slurry system, but also provide certain salt resistance and hydrophilicity. At the same time, its molecular weight is 144.1, and the molecular weight of vinyl acetate is 86.089. Similar molecular weights are more likely to polymerize; Itaconic acid (IA) can provide stronger hydrophilic properties for the latex powder. Itaconic acid itself is a polar monomer, and -COOH forms -COO- in an alkaline environment, which is easy to form hydrogen bonds with H2O, increasing the hydrophilicity of latex particles.

[0072] In the present invention, the toughener is a redispersible latex powder, and its toughening mechanism is the polymer film formation mechanism. When the latex is added to the cement slurry system, the hydration of the cement slurry has already started, and then the latex particles agglomerate to form a polymer film. Then these polymer films cover the surface of the cement particles. When the hydration proceeds to a certain extent, the hydration products of the cement slurry and the polymer films interpenetrate each other to form a structurally dense three-dimensional network structure. Under the action of external stress, it can fully absorb the fracture energy required for the expansion of defects and microcracks in the cement ring, effectively delay the expansion speed of defects and microcracks, and improve its flexural and bending strength, thereby improving the toughness of the cement stone.

[0073] The toughening agent provided by the present invention also has the effect of reducing water loss. The redispersible latex powder is adsorbed on the surface of the cement to form a polymer film, which increases the bonding force between the hydration products, reduces the size of microcracks, and becomes a barrier layer for ion penetration and diffusion. Therefore, the latex powder has a certain filtration loss reduction performance. However, if the latex powder is used alone as a fluid loss reducer in well cementing, on the one hand, it will deteriorate the fluidity of the cement slurry, and on the other hand, it will increase the well cementing cost. Therefore, generally, a compound of latex powder and fluid loss reducer is used to jointly reduce the water loss of the cement slurry system.

[0074] The toughening agent provided by the present invention also has a retarding effect. The interfacial energy between calcium silicate hydrate (CSH) and the polymer phase is relatively high. A large number of latex particles are adsorbed on the surface of the cement particles to form a polymer film, which inhibits the nucleation reaction process of the hydration products by occupying the reaction sites of the hydration products, hinders the diffusion of ions, and delays the cement hydration process, but ultimately does not affect the hydration result of the cement.

[0075] In a second aspect, an embodiment of the present invention provides a method for preparing an anti-channeling toughened cement slurry, including the following steps:

[0076] Step S1: Dry-mix 100 parts of oil well cement, 1 - 4 parts of toughening agent, 0.7 - 2.5 parts of fluid loss reducer, 0 - 0.5 parts of drag reducer, 0 - 35 parts of stabilizer, and 1 - 4 parts of suspending agent to obtain a dry powder mixture;

[0077] Step S2: Mix 0 - 2.5 parts of retarder, 0.1 - 0.3 parts of defoamer, and 42 - 54 parts of water evenly to obtain a solution mixture;

[0078] Step S3: Using a constant-speed stirrer, add the above dry powder mixture completely into the solution mixture within 15 s at a low rotation speed of (4000 ± 200 r / min), and then mix at a high rotation speed of (12000 ± 500 r / min) for 35 s to mix evenly, ensuring that the cement slurry obtains 5.91 kJ / kg API mixing energy to obtain an anti-channeling toughened cement slurry.

[0079] The following examples and comparative examples are well cement slurries prepared according to the standard GB / T 19139 - 2012 "Test Methods for Oil Well Cements".

[0080] Preferably, the fluid loss reducer is preferably in powder form, which can be dry-mixed in the oil well cement. During the well cementing construction process, there is no need for the "water mixing" work, which greatly reduces the well cementing workload and well cementing cost.

[0081] Preferably, the anti-channeling toughened cement slurry system can be compatible with a variety of fluid loss reducers, so the fluid loss reducer is selected according to the principle of optimal economic applicability.

[0082] Preferably, the drag reducer is preferably in powder form. The powder drag reducer is dry-mixed to obtain a dry-mixed mixture; the liquid drag reducer is mixed into an aqueous solution to obtain a solution mixture.

[0083] In the present invention, the temperature application range of the anti-channeling tough cement slurry is 50-130 °C. Since the applicable temperature range of vinyl acetate is relatively low, a stabilizer needs to be added to ensure the stability of the cement slurry when the temperature is higher than 100 °C. Preferably, the stabilizer is selected as silica fume.

[0084] The anti-channeling tough cement slurry formed in the present invention does not add an additional anti-channeling agent. The excellent anti-channeling performance mainly comes from the latex. The principle is that under a certain pressure difference, a part of the latex particles dispersed in the cement slurry enter the micropores of the filter cake and accumulate between the cement particles, forming a cement filter cake that can reduce permeability, controlling the leakage rate of the liquid in the cement slurry to the permeable formation, and achieving the purpose of reducing the water loss of the cement slurry; at the same time, the tight three-dimensional network structure formed by the latex and cement particles enhances the bonding force between the hydration products. Under the action of the pressure difference, it effectively blocks the ion permeability and diffusivity, further reduces the permeability of the filter cake, reduces the volume shrinkage of the cement stone, improves the bonding strength of the first and second interfaces, and achieves an excellent anti-channeling effect. In addition, the latex is very positive for improving the anti-channeling performance, rheological properties and suspension stability of the cement slurry under high-temperature conditions.

[0085] In addition, the suspending agent in the anti-channeling tough cement slurry provided by the embodiments of the present invention can keep the cement slurry in good dynamic stability, coalescence stability and flocculation stability. At the same time, the suspending agent can make the toughening agent better dispersed in the cement slurry, and at the same time improve the rheological properties of the cement slurry to ensure the pumpability of the cement slurry during on-site construction. The stabilizer can effectively improve the compressive strength of the cement stone. The drag reducer can reduce the viscosity of the cement slurry and increase the fluidity. The retarder can adjust the thickening time of the cement slurry according to the on-site cementing construction requirements.

[0086] In summary, the cement slurry provided by the embodiments of the present invention has the characteristics of low water loss, good stability, short static gel transition time, strong gas channeling prevention ability, etc. The cement stone formed after the cement slurry solidifies has good compactness, low permeability, high strength and low elastic modulus, which can effectively improve the cementing quality, improve the sealing integrity of the cement sheath, and provide technical support for the long-term, safe and effective operation of oil and gas wells.

[0087] The present invention provides a tough cement slurry that can greatly improve toughness while slowing down the rapid decline of compressive strength and retaining a relatively high compressive strength.

[0088] When using redispersible latex powder as a toughening agent for oil well cement, the latex powder can significantly reduce the permeability of the cement stone and improve the bonding strength to enhance the toughness of the cement stone. By applying the theory of close packing of solid particle materials and particle size distribution, the suspending agent and stabilizer can slow down the rapid decline of the compressive strength. When combined, it greatly improves the toughness and gas channeling prevention performance of the cement stone, enhances the interfacial bonding strength, and at the same time has the effect of preventing the decline of the cement stone strength, retaining a relatively high compressive strength.

[0089] Fourthly, the present invention provides an application of an anti-channeling toughened cement slurry system for improving the sealing integrity of the cement sheath in oil well cementing.

[0090] Previously, the company used the liquid latex BCT-800L of Tianjin Zhongyou Boxin Engineering Technology Co., Ltd. in the Changqing area. After the successful self-production of the toughening agent by the company, during the cementing process in the Changqing area, the anti-channeling toughened cement slurry system provided by the present invention has completely replaced the products of Boxin Company, with a very obvious price advantage, greatly reducing the cementing cost and producing excellent effects for the company's quality improvement and efficiency increase. The comparison of the single-well costs between the self-produced anti-channeling toughened cement slurry system and the Boxin latex system is as follows:

[0091] 1. Comparison of the costs of the single-well cement slurry systems

[0092] Table 1 Composition of the price of the self-produced anti-channeling toughened cement slurry system

[0093] Table 2 Composition of the price of the Boxin latex system Formulation Unit price per ton (yuan) Increment per cubic meter (ton) Price per cubic meter (yuan) Jiahua G-class 469.03 1.33 623.81 BCT-800L 13970.27 0.0333 465.21 BXF-200L 13430.44 0.0399 535.87 D50 33465.84 0.005 167.32 Total 1.41 1792.21

[0094] Based on the system price, each cubic meter of the self-produced toughening system saves 662.03 yuan compared to each cubic meter of the Boxin latex system. Each small wellbore is expected to use 8 cubic meters of high-density cement, and using the self-produced toughening system saves 5296.24 yuan per well; each conventional well is expected to use 14 cubic meters of high-density cement, and using the self-produced toughening system saves 9268.42 yuan per well.

[0095] 2. Single-well labor and transportation costs

[0096] The self-produced anti-channeling toughened cement slurry system is dry-mixed, and the cement mixing is completed by Jiahua Cement Factory without additional costs; the Boxin latex system is wet-mixed and requires on-site water-mixing operations, and the related costs are as follows:

[0097] Table 3 Single-well labor and transportation costs Vehicle model Unit price per day (yuan) Number of trips Total (yuan) Crane truck 1217 2 2434 Pickup truck 286.5 1 286.5 Total 3 2720.5

[0098] The drug preparation and hoisting operations involve 4 person-times, with a labor cost of 440 yuan and a fuel cost of 210 yuan.

[0099] In summary, by using the self-produced anti-channeling toughened cement slurry system, 8,666.74 yuan can be saved per small-diameter well, and 12,638.92 yuan can be saved per conventional well. The self-produced toughening agent system has excellent cost advantages.

[0100] The following provides product information on some components used in the on-site application stage of the anti-channeling toughened cement slurry of the present invention. This information is only for discussion and illustration, and the components provided by the present invention are not limited to these products.

[0101] The fluid loss reducer G301 is produced by Weihui Chemical Industry Co., Ltd.; the fluid loss reducer polycarboxylate copolymer G31S is produced by Weihui Chemical Industry Co., Ltd.; the fluid loss reducer polyvinyl alcohol type BZJS-2 is produced by Bohai Drilling Engineering Co., Ltd. of China National Petroleum Corporation; the fluid loss reducer AMPS polymer BH-F202S is produced by Bohai Drilling Engineering Co., Ltd. of China National Petroleum Corporation.

[0102] The drag reducer sulfonated ketone aldehyde condensate BZJS-2 is produced by Bohai Drilling Engineering Co., Ltd. of China National Petroleum Corporation; the drag reducer polycarboxylate type BH-D301L is produced by Bohai Drilling Engineering Co., Ltd. of China National Petroleum Corporation; the drag reducer BH-D302L is produced by Bohai Drilling Engineering Co., Ltd. of China National Petroleum Corporation.

[0103] The stabilizer silica powder BH-B1S is produced by Bohai Drilling Engineering Co., Ltd. of China National Petroleum Corporation.

[0104] The retarder phosphate BH-R102L is produced by Bohai Drilling Engineering Co., Ltd. of China National Petroleum Corporation; the retarder vinyl acrylamide polymer HX-36L is produced by Chengdu Omek Petroleum Technology Co., Ltd., China.

[0105] The defoamer organic ester BZXP-1 is produced by Bohai Drilling Engineering Co., Ltd. of China National Petroleum Corporation.

[0106] Up to now, the solid toughening agent for oil well cement has been widely promoted and used in the Changqing area. The following provides the on-site test conditions of the anti-channeling toughened cement slurry of this patent invention in 31 well-times in the Changqing area (the results are shown in Table 4-5). The excellent well cementing rate is as high as 100%. Among them, it is used in 26 well-times in the Wushenqi area, including 18 well-times of production wells, 1 well-time of natural gas evaluation wells, and 7 well-times of plugging wells; it is used in 5 well-times in the Yanchi area, including 4 well-times of production wells and 1 well-time of natural gas evaluation wells. The solid toughening agent for oil well cement forms a toughened cement slurry system with conventional density, which is used for the pay zone. The excellent well cementing rate is 100%. The cement sheath has sufficient toughness, effectively seals the gas layer, can meet the requirements of the large-scale volume fracturing process for later exploitation, improves the sealing performance of the wellbore, and extends the life of the cement sheath. Through formula adjustment, the latex toughening agent can be compounded with a variety of fluid loss control agents and has good compatibility with other oil well cement additives; the toughened cement slurry is stable, the free water of the cement slurry and the density difference of the cement slurry are small, the rheology of the slurry is good, the compressive strength of the cement stone is high, and it has excellent well cementing engineering properties.

[0107] Table 4 Application situation of the toughening agent for oil well cement in the Wushenqi area of the Changqing market

[0108] Table 5 Application situation of the toughening agent for oil well cement in the Yanchi area of the Changqing market

[0109] The following further describes the technical solutions of the embodiments of the present invention in detail through specific data.

[0110] The following examples and comparative examples prepared well cement slurries according to the standard GB / T 19139-2012 "Test Methods for Oil Well Cements", and tested the performance of the well cement slurry system with reference to the standard SY / T 6544-2017 "Performance Requirements for Oil Well Cement Slurries". The G-grade oil well cement used is Shengwei cement from Weifang Shengwei Special Cement Co., Ltd.

[0111] Example 1

[0112] By weight, 100 parts of G-class oil well cement (Shandong Linqu Shengwei Special Cement Co., Ltd.), 2.5 parts of toughening agent redispersible latex powder (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation), 1.5 parts of suspending agent microsilica powder (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation), and 2.5 parts of fluid loss reducer G301 (Weihui Chemical Industry Co., Ltd.) are mixed to obtain a dry powder mixture. 0 - 0.5 parts of retarder BH-R102L (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation) or 0 - 0.6 parts of retarder HX-36L (Chengdu Omek Petroleum Technology Co., Ltd.), 0.3 parts of defoamer BZXP-1 (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation), and 42 - 45 parts of water are mixed to obtain a mixed solution. Using a constant speed stirrer, the above dry powder mixture is completely added to the solution mixture within 15 s at a low speed of (4000 ± 200 r / min), and then mixed at a high speed of (12000 ± 500 r / min) for 35 s to be evenly mixed, ensuring that the cement slurry obtains 5.91 kJ / kg API mixing energy to obtain an anti-channeling toughened cement slurry.

[0113] Example 2

[0114] By weight, 100 parts of G-class oil well cement (Shandong Linqu Shengwei Special Cement Co., Ltd.), 3 parts of toughening agent redispersible latex powder (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation), 2 parts of suspending agent microsilica powder (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation), and 0.8 parts of fluid loss reducer G31S (Weihui Chemical Industry Co., Ltd.) are mixed to obtain a dry powder mixture. 0 - 0.5 parts of retarder BH-R102L (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation) or 0 - 0.6 parts of retarder HX-36L (Chengdu Omek Petroleum Technology Co., Ltd.), 0.3 parts of defoamer BZXP-1 (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation), and 42 - 45 parts of water are mixed to obtain a mixed solution. Using a constant speed stirrer, the above dry powder mixture is completely added to the solution mixture within 15 s at a low speed of (4000 ± 200 r / min), and then mixed at a high speed of (12000 ± 500 r / min) for 35 s to be evenly mixed, ensuring that the cement slurry obtains 5.91 kJ / kg API mixing energy to obtain an anti-channeling toughened cement slurry.

[0115] Example 3

[0116] By weight, 100 parts of G-class oil well cement (Shandong Linqu Shengwei Special Cement Co., Ltd.), 2.5 parts of toughening agent redispersible latex powder (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation), 1.25 parts of suspending agent microsilica powder (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation), 1.8 parts of fluid loss reducer BZJS-2 (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation), and 0.3 part of friction reducer BZGF-1 (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation) are mixed to obtain a dry powder mixture. 0 - 0.5 part of retarder BH-R102L (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation) or 0 - 0.6 part of retarder HX-36L (Chengdu Omek Petroleum Technology Co., Ltd.), 0.3 part of defoamer BZXP-1 (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation), and 42 - 45 parts of water are mixed to obtain a mixed solution. Using a constant speed stirrer, the above dry powder mixture is completely added to the solution mixture within 15 s at a low speed of (4000 ± 200 r / min), and then mixed at a high speed of (12000 ± 500 r / min) for 35 s to be evenly mixed, ensuring that the cement slurry obtains 5.91 kJ / kg API mixing energy to obtain an anti-channeling tough cement slurry.

[0117] Example 4

[0118] By weight, 100 parts of G-class oil well cement (Shandong Linqu Shengwei Special Cement Co., Ltd.), 3 parts of toughening agent redispersible latex powder (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation), 1 part of suspending agent microsilica powder (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation), and 0.8 part of fluid loss reducer BH-F202S (Weihui Chemical Industry Co., Ltd.) are mixed to obtain a dry powder mixture. 0 - 0.5 part of retarder BH-R102L (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation) or 0 - 0.6 part of retarder HX-36L (Chengdu Omek Petroleum Technology Co., Ltd.), 0.3 part of defoamer BZXP-1 (Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation), and 42 - 45 parts of water are mixed to obtain a mixed solution. Using a constant speed stirrer, the above dry powder mixture is completely added to the solution mixture within 15 s at a low speed of (4000 ± 200 r / min), and then mixed at a high speed of (12000 ± 500 r / min) for 35 s to be evenly mixed, ensuring that the cement slurry obtains 5.91 kJ / kg API mixing energy to obtain an anti-channeling tough cement slurry.

[0119] Example 5

[0120] By weight, 100 parts of G-class oil well cement (Shandong Linqu Shengwei Special Cement Co., Ltd.), 3 parts of toughening agent redispersible latex powder (Bohai Drilling Engineering Co., Ltd., CNPC), 3 parts of suspending agent microsilica powder (Bohai Drilling Engineering Co., Ltd., CNPC), 35 parts of stabilizer silica powder BH-B1S (Bohai Drilling Engineering Co., Ltd., CNPC), and 0.8 part of fluid loss reducer G301S (Bohai Drilling Engineering Co., Ltd., CNPC) are mixed to obtain a dry powder mixture. 1.3 parts of retarder HX-36L (Chengdu Omek Petroleum Technology Co., Ltd.), 0.3 part of defoamer BZXP-1 (Bohai Drilling Engineering Co., Ltd., CNPC), and 53 parts of water are mixed to obtain a mixed solution. Using a constant speed stirrer, the above dry powder mixture is completely added to the solution mixture within 15 s at a low rotation speed of (4000 ± 200 r / min), and then mixed at a high rotation speed (12000 ± 500 r / min) for 35 s to mix evenly, ensuring that the cement slurry obtains 5.91 kJ / kg API mixing energy to obtain an anti-channeling toughened cement slurry.

[0121] Comparative Example 1

[0122] This comparative example is a blank original slurry of ordinary oil well G-class cement with a water-cement ratio of 0.44.

[0123] Comparative Example 2

[0124] The difference between this Comparative Example 2 and Example 1 is that no toughening agent is added.

[0125] Comparative Example 3

[0126] The difference between this Comparative Example 3 and Example 3 is that no toughening agent is added.

[0127] Test Example 1

[0128] Taking Examples 1-5 as test objects, conventional cement slurry performance tests are carried out, and the test results are shown in Table 6.

[0129] Table 6 Conventional performance evaluation results of anti-channeling toughened cement slurry

[0130] The comprehensive performance test results of the conventional density latex powder toughened cement slurry system are shown in Table 6. It can be seen from Table 6 that the comprehensive performance of the latex cement slurry is good, the free liquid content of the toughened cement slurry with different types of fluid loss reducers is 0, and the sedimentation density difference of BZJS-2, G301, and BH-F202S is 0.01 g / cm 3 , and the sedimentation density difference of G31S is 0.01 g / cm 3, indicating that the slurry has good stability; the flow index n of the tough cement slurry is greater than 0.77, and the consistency index K value is less than 0.32, indicating that the viscosity of the cement slurry system is low and the rheological properties are good. This is because the adsorbed latex particles have good dispersion and lubrication effects and can be stably dispersed and filled in the cement particles. The water loss of the tough cement slurry with different types of fluid loss additives is small, indicating that the fluid loss control effect of the cement slurry is good. The compound use of latex powder and fluid loss additives in cementing construction is the most economical and optimal working condition selection, and the compressive strength of the tough cement stone after 24 hours of curing is greater than 20 MPa (Table 7), meeting the technical requirements of cementing engineering.

[0131] From Figure 6 It can be seen that the thickening curve at 120 °C is a right-angle thickening. By adjusting the applicable temperature of the redispersible latex powder, it can range from 50 °C to 130 °C. When the temperature is higher than 100 °C, silica powder needs to be added to ensure the stability of the cement slurry, and at the same time, the type of fluid loss additive needs to be changed to G301. The thickening time of the tough cement slurry is adjustable, and the adjustability of the thickening time can be adjusted by the dosage of the redispersible latex powder (the redispersible latex powder has a weak retarding effect) and by adding a retarder, indicating that the application range of the redispersible latex powder is large and the market application prospect is broad.

[0132] Test Example 2

[0133] The compressive strength, flexural strength and elastic modulus of the oil well cement stone are the most important performance characterizations for characterizing the toughening performance of the solid latex powder toughening agent. Taking Example 1 and Comparative Example 2 as the test objects, the effects of different dosages of solid latex powder on the compressive strength, flexural strength and elastic modulus of the oil well cement stone under the condition of curing at 85 °C for 24 hours were explored. The test results are shown in Table 7.

[0134] Table 7 Toughness Performance Evaluation

[0135] With the increase in the dosage of solid latex powder, the flexural strength of the cement stone increases, and the strength values are all higher than those of pure cement. The reason may be that latex particles adsorb on the surface of cement to form a polymer film. When subjected to external forces, the polymer film with strong deformation ability can absorb most of the impact force, thus improving the toughness of the cement stone. From the perspective of the latex powder structural formula, the introduction of ethylene chain segments in the polyethylene main chain effectively reduces the internal rotation free energy and steric hindrance of the polymer chain, so it shows stronger flexibility compared with the polyethylene polymer chain. The ratio of compressive strength to flexural strength is called the brittleness coefficient, and its value can reflect the brittleness of the material. The larger the brittleness coefficient, the greater the brittleness of the material, and vice versa, it shows flexibility. Incorporating latex powder can significantly reduce the brittleness of the cement stone, and the greater the incorporation amount, the more obvious the reduction. However, considering the compressive strength of the cement stone, it can be seen that improving the flexural strength of the cement stone is at the cost of sacrificing part of the compressive strength. Therefore, on the premise of ensuring that the compressive strength of the cement stone meets the requirements of well cementing operations, the toughness of the cement stone should be maximally improved. With the increase in the content of solid latex powder, the elastic modulus decreases, but with the increase in the dosage of latex powder, it will seriously cause the thickening of the cement slurry. According to the compressive strength and flexural strength tests and combined with the construction conditions, it can be comprehensively shown that the optimal dosage of latex powder in the cement slurry is 2.0%-3.0%. In short, solid latex powder greatly enhances the toughness of the cement stone and improves the ability to resist extrusion and impact.

[0136] Test Example 3

[0137] Taking Examples 1-5 and Comparative Examples 1-3 as the test objects, the transition time of the static gel strength of the cement slurry system at 85°C and 23 MPa was tested, and the test results are shown in Table 8.

[0138] Table 8 Transition Time of Static Gel Strength of Different Cement Slurry Systems Cement slurry system Transition time for static gel strength of 48 - 240 Pa / (min) Example 1 24 Example 2 22 Example 3 23 Example 4 25 Example 4 24 Comparative example 1 67 Comparative example 2 42 Comparative example 3 40

[0139] It can be seen from Table 8 that the transition time of the static gel strength of the cement slurry systems in Experimental Examples 1-5 of the present invention is very short. The transition time of the blank cement slurry is 67 min, and the transition times of Comparative Examples 2-3 are slightly shorter. This shows that the latex has the performance of preventing gas channeling, and the latex cement slurry system has excellent gas channeling prevention performance and can effectively prevent the occurrence of annular gas channeling. The development curve of the static gel strength of Example 1 with G301 as the fluid loss additive is shown in Figure 7 .

[0140] Test Example 4

[0141] Field test application of the anti-channeling and tough cement slurry system.

[0142] So far, the solid toughening agent for oil well cement has been widely promoted and used in the Changqing area. The following provides the on-site test conditions of 31 well-times of the anti-channeling toughened cement slurry of this patent invention in the Changqing area (the results are shown in Table 4-5). The excellent well cementing rate is as high as 100%. Among them, it has been used 26 well-times in the Wushenqi area, including 18 well-times of production wells, 1 well-time of natural gas evaluation wells, and 7 well-times of plugging wells; it has been used 5 well-times in the Yanchi area, including 4 well-times of production wells and 1 well-time of natural gas evaluation wells. The solid toughening agent for oil well cement has formed a toughened cement slurry system with conventional density, which is used for the pay zone. The excellent well cementing rate is 100%. The cement sheath has sufficient toughness, effectively seals the gas layer, can meet the requirements of the large-scale volume fracturing process for later exploitation, improves the sealing performance of the wellbore, and extends the life of the cement sheath. Through formula adjustment, the latex toughening agent can be compounded with a variety of fluid loss control agents and has good compatibility with other oil well cement additives; the toughened cement slurry is stable, the difference between the free water and the density of the cement slurry is small, the rheology of the slurry is good, the compressive strength of the cement stone is relatively high, and it has excellent well cementing engineering properties.

[0143] Field application was carried out with the formulation of Example 3. Taking Well Su 76-6-32X as an example, its application situation is introduced below.

[0144] Well Su 76-6-32X is a two-opening directional well in the oil and gas cooperation block, with a total drilled depth of 3503 m and a casing setting depth of 3502.83 m. The gas layer well cementing construction of this well used the company's toughened cement slurry system, which was applied to the tail slurry from 2946.51 m to 3502.83 m to seal the target gas layer. During the entire well cementing construction, the density of the cement slurry was 1.88 g / cm 3 , with good fluidity. There was basically no thixotropic enhancement phenomenon in the whole process of the cement slurry. The density of the pumped cement slurry on site was stable, and the settlement stability was good. Acoustic amplitude logging was carried out on June 17, 2023. The well cementing quality of the first and second interfaces of the well section sealed by the self-produced anti-channeling toughened cement slurry was excellent ( Figure 8 ). The acoustic amplitude of Well Su 76-6-32X constructed by the Second Well Cementing Company of CNPC Bohai Drilling shows that the well cementing engineering quality is excellent, marking the successful first application of the self-developed anti-channeling toughened cement slurry system for improving the sealing integrity of the cement sheath.

[0145] In summary, the anti-channeling toughened cement slurry system provided by the present invention for improving the sealing integrity of the cement sheath has a 70% increase in flexural strength, a 30% decrease in elastic modulus, a compressive strength of the cement stone greater than 20 MPa, has good construction performance, good mechanical properties and sufficient flexibility, a short static gel strength transition time, excellent anti-channeling performance, can effectively alleviate the problem of the destruction of the sealing integrity of the cement sheath during the large-scale volume fracturing production process, is a technical reserve of the company, and has broad application prospects.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A kind of anti-channeling tough cement slurry system, characterized in that, The anti-channeling tough cement slurry system comprises the following components in parts by weight: Oil well cement, 100 parts; Toughening agent, 1 - 4 parts; Fluid loss reducer, 0.7 - 2.5 parts; Friction reducer, 0 - 0.5 parts; Stabilizer, 0 - 35 parts; Suspending agent, 1 - 4 parts; Retarder, 0 - 2.5 parts; Defoamer, 0.1 - 0.3 parts; Water, 42 - 54 parts.

2. The anti-channeling tough cement slurry system according to claim 1, wherein the oil well cement is of Grade G; the water is one or more of deionized water, fresh water, seawater, reclaimed water and mineralized water; the suspending agent is an inorganic material, and the suspending agent is one or more of ultrafine materials and clay substances; the stabilizer is one or more of mineral powder, quartz sand, fly ash, magnesium aluminum silicate and veegum; the fluid loss reducer is one or a mixture of two of 2-acrylamide-2-methylpropanesulfonic acid-based, polyvinyl alcohol-based, amide or imide-based, and a terpolymer obtained by polymerizing and modifying 2-acrylamide-2-methylpropanesulfonic acid, low molecular weight amide and polyhydroxycarboxylic acid; the friction reducer is one or more of sulfonated ketone aldehyde condensate, polynaphthalene sulfonate and polycarboxylate series; the retarder is phosphate-based or a polymer with acrylamide as the main chain; the defoamer is at least one of organophosphate ester, silicone-based, silicone ether copolymer-based, silicone oxygen alkane and polyether modified polysiloxane defoamers; the toughening agent is redispersible latex powder.

3. The anti-channeling tough cement slurry system according to claim 2, wherein the ultrafine material is microsilica.

4. The anti-channeling tough cement slurry system according to claim 2, wherein the clay substances are at least one of bentonite, attapulgite, sepiolite, vermiculite, clay-grade mica, expanded chlorite and allophane.

5. The anti-channeling tough cement slurry system according to claim 2, wherein the retarder is phosphate-based, and the retarder is hydroxyethylidene diphosphonic acid.

6. The anti-channeling tough cement slurry system according to claim 2, wherein the retarder is a polymer with acrylamide as the main chain, and the retarder is one or more of sodium borate and 2-acrylamido-2-methylpropanesulfonic acid / itaconic acid binary copolymer.

7. The anti-channeling tough cement slurry system according to claim 2, wherein the toughening agent is a blend of one or more of ethylene-vinyl acetate copolymer, vinyl acetate - higher fatty acid vinyl ester copolymer powder, vinyl acetate - ethylene - higher fatty acid vinyl ester terpolymer powder, and vinyl acetate - acrylate - higher fatty acid vinyl ester terpolymer powder.

8. A method for preparing an anti-channeling tough cement slurry system according to any one of claims 1-7, characterized in that, It includes the following steps: Step S1: Dry-mix 100 parts of oil well cement, 1 - 4 parts of toughening agent, 0.7 - 2.5 parts of fluid loss reducer, 0 - 0.5 parts of friction reducer, 0 - 35 parts of stabilizer, and 1 - 4 parts of suspending agent to obtain a dry powder mixture; Step S2: Mix 0 - 2.5 parts of retarder, 0.1 - 0.3 parts of defoamer, and 42 - 54 parts of water evenly to obtain a solution mixture; Step S3: Using a constant-speed stirrer, add the above dry powder mixture completely into the solution mixture within 15 s at a low rotation speed of (4000 ± 200 r / min), and then mix at a high rotation speed of (12000 ± 500 r / min) for 35 s to mix evenly, obtaining the anti-channeling tough cement slurry.

9. The preparation method of the anti-channeling tough cement slurry system according to claim 8, wherein the toughening agent is prepared by the following method: Under the action of an aqueous solution of a protective colloid particle, an emulsifier, and a pH buffer, continuously add the reaction monomer to water, initiate polymerization using an initiator, obtain a latex emulsion after the polymerization reaction ends, cool to the ambient temperature, and dry with a spray dryer to obtain latex powder.

10. Application of an anti-channeling tough cement slurry system according to any one of claims 1-7 in oil well cementing.

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