Well cementation pipe string structure and large-size casing pipe well cementation method

Abstract

The invention belongs to the technical field of well cementation, and particularly relates to a well cementation pipe string structure and a large-size casing pipe well cementation method. The well cementation pipe string structure comprises a casing pipe arranged in a borehole and a drill rod string extending into the casing pipe. The drill rod string is used for injecting well cementation working fluid into a borehole; an annulus is formed between the sleeve and the well wall; a float shoe is arranged at the bottom of the casing pipe, a float collar is connected to the upper portion of the float shoe, an insertion seat is arranged in the center of the upper portion of the float collar, an insertion head matched with the insertion seat is arranged at the bottom of the drill rod string, and the insertion head is arranged in the insertion seat in a setting mode. The float shoe core part is provided with a float shoe channel, the float collar core part is provided with a float collar channel, and the float shoe channel, the float collar channel and the annulus are sequentially communicated. Due to the design of the pipe string structure, the situation that cement paste is mixed with drilling fluid in the casing pipe between the float shoe and the float collar is avoided, and the situation that mixed paste with poor performance pollutes an annulus between the casing pipe and the well wall after mixing, and consequently the well cementation quality is affected is prevented.

Description

Technical Field

[0001] This invention belongs to the field of cementing technology, specifically relating to a cementing string structure and a method for cementing large-size casing. Background Technology

[0002] Salt cavern energy storage is an important form of underground energy storage. It mainly utilizes freshwater to dissolve salt layers and form closed salt caverns to store various forms of energy on a large scale and efficiently. Converting old salt caverns into energy storage facilities can not only realize the reuse of abandoned and depleted salt cavern mines, but also meet the current and future demand for underground green energy storage, providing important support for the country to achieve its "dual carbon" goals as soon as possible.

[0003] Salt caverns are generally shallow, with the top well depth mostly around 500m. When constructing injection-production wells at the top of salt caverns, the injection-production wells generally adopt a two-section wellbore structure. The difference between them and oil and gas wells is that energy storage facilities need to face long-term cyclic injection-production operations. Therefore, energy storage injection-production wells mostly use different large-size casings of 473.08mm or more to complete the well construction.

[0004] Currently, cementing of large-diameter casing wells in oil and gas reservoirs typically employs the conventional insert cementing method. This method utilizes both bottom-hole insertion setting and wellhead setting, both requiring the insertion of inner casing within the casing. The casing string structure consists of a float shoe, casing, float collar, plug, and drill pipe. For conventional oil and gas wells using the insert cementing method, the casing size is generally less than 374.7 mm, while the casing size for energy storage injection-production wells is above 473.08 mm, with larger outer diameters reaching 762 mm. For shallow-depth energy storage injection-production wells, the inner annular volume of the large-diameter casing is 160–430 L / m, and the casing volume between the float shoe and float collar is 1.6–4.3 m³. 3 During cementing operations, the cement slurry will continuously come into contact with and mix with the drilling fluid inside the casing, producing cement slurry contaminated by the drilling fluid. When the cement slurry contaminated by the drilling fluid flows out from the float shoe channel into the annular space formed by the irregular large-sized wellbore and the large-sized casing, it is very easy to remain and adhere to the well wall. At the same time, the viscosity, rheological properties, thickening properties of the cement slurry contaminated by the drilling fluid deteriorate sharply, which will affect the safe and smooth progress of cementing operations, and even affect the cementing quality of the entire well section. In severe cases, it will lead to cementing failure and wellbore abandonment, greatly increasing construction costs and wasting resources.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a cementing string structure and a cementing method for large-size casing. The cementing string structure design avoids the mixing of cement slurry with drilling fluid in the casing between the float shoe and the float collar, and prevents the mixed slurry with deteriorated performance from contaminating the annulus between the casing and the well wall, thereby affecting the cementing quality.

[0007] To overcome the shortcomings of the prior art, the present invention provides the following technical solution:

[0008] A cementing string structure includes a casing disposed in a wellbore and a string of drill pipes extending into the casing; the drill pipe string is used to inject cementing fluid into the wellbore; an annulus is formed between the casing and the wellbore; a float shoe is provided at the bottom of the casing, a float collar is connected above the float shoe, an insertion seat is provided at the upper center of the float collar, and a plug matching the insertion seat is provided at the bottom of the drill pipe string, the plug being seated in the insertion seat; a float shoe channel is provided in the core of the float shoe, a float collar channel is provided in the core of the float collar, and the float shoe channel, the float collar channel, and the annulus are sequentially connected.

[0009] Furthermore, a one-way valve is installed at the top of the floating shoe channel; and / or, a flow-blocking ring is installed at the top of the floating hoop channel.

[0010] In addition, the present invention also provides a method for cementing large-size casing, using the above-mentioned cementing string structure, including the following steps:

[0011] S1. Use a cement truck to inject the pre-flush fluid and pilot cement slurry into the annulus in the designed amount through the drill pipe string.

[0012] S2. Then, the salt-resistant toughness cement slurry is injected into the annulus through the drill pipe string using a cement truck. After the fluid returns to the ground from the outlet of the elevated trench, a sample of the returned fluid is taken from the outlet of the elevated trench, and the fluid density is measured. When the fluid density is greater than the density of the pilot cement slurry but less than that of the salt-resistant toughness cement slurry, the injection of the salt-resistant toughness cement slurry is stopped.

[0013] S3. Use a cement truck to inject post-fluid. When the amount of post-fluid injected reaches 1 / 2 to 2 / 3 of the volume of the drill string, stop injecting post-fluid.

[0014] S4. Reduce the displacement of the cement truck and continue to inject post-flush fluid. Stop injecting post-flush fluid when the sum of the two injections reaches the design volume of post-flush fluid.

[0015] S5. Disconnect the bottom plug of the drill string from the insertion seat, remove the drill string, and wait for it to solidify.

[0016] Furthermore, the discharge rates of the pre-flush liquid, pilot cement slurry, and salt-resistant toughness cement slurry are all 0.8–1.0 m³. 3 / min.

[0017] Furthermore, the design dosage of the pre-fluid is calculated based on the pre-fluid flowing through the annulus for 20-25 minutes;

[0018] And / or, the design dosage of the pilot cement grout is calculated based on the annular volume from 10 to 25 meters into the upper casing to the ground.

[0019] And / or, the design dosage of the salt-resistant and tough cement slurry is calculated based on the annular volume of the entire well section;

[0020] And / or, the designed volume of the post-flush fluid is based on a difference in drill string volume of 0.1–0.2 m³. 3 Calculate the dosage.

[0021] Furthermore, in step S3, the displacement of the cement truck is set to 0.2–0.3 m³. 3 / min;

[0022] And / or, in step S4, the displacement of the cement truck is set to 0.1–0.2 m³ / h. 3 / min.

[0023] Further, the components and weight ratios of the pre-treatment liquid are as follows: 15 parts retarder, 10-15 parts suspending agent, 50-75 parts sodium chloride, 0-400 parts barite powder, 15-25 parts diluent, 10-15 parts water loss reducing agent, 0.05-0.1 parts defoamer, and 500 parts water.

[0024] Preferably, the preparation method of the pretreatment solution includes the following steps: weigh water according to the proportion and place it in a stirrer, turn on the stirrer, and slowly add the suspending agent to the water, stirring until the suspending agent is completely dissolved; then add the water loss reducing agent, retarder, sodium chloride, barite powder, diluent and defoamer in sequence, stir for 20 to 30 minutes and let stand to obtain the pretreatment solution.

[0025] Furthermore, the components and weight ratio of the pilot cement slurry are as follows: 700 parts of G-grade oil well cement, 7-12 parts of nano-early strength agent, 14-21 parts of microsilica powder, 30-45 parts of sodium chloride, 0.1-0.2 parts of retarder, 14-21 parts of water loss reducing agent, and 300-320 parts of water.

[0026] Preferably, the method for preparing the pilot cement slurry includes the following steps:

[0027] a) Weigh out G-grade oil well cement, nano-early strength agent and microsilica powder according to the proportion, mix them and stir evenly to obtain mixed dry powder;

[0028] b) Weigh out sodium chloride, retarder, and dehydration reducer according to the proportions, pour them into water and stir evenly to obtain a mixture;

[0029] c) Pour the mixed dry powder obtained in step a) into the mixed liquid obtained in step b), and stir evenly to obtain the pilot cement slurry.

[0030] Furthermore, the composition and weight ratio of the salt-resistant toughness cement slurry are as follows: 700 parts of G-grade oil well cement, 17.5-21 parts of nano-early strength agent, 14-21 parts of microsilica powder, 35-49 parts of toughening agent, 3.5 parts of dispersant, 30-45 parts of sodium chloride, 14-21 parts of water loss reducing agent, and 300-315 parts of water;

[0031] Preferably, the method for preparing the salt-resistant and tough cement slurry includes the following steps:

[0032] (1) Weigh out G-grade oil well cement, nano early strength agent, micro silica fume, toughening agent and dispersant according to the proportion, mix them and stir evenly to obtain mixed dry powder;

[0033] (2) Weigh out sodium chloride and dehydration reducer according to the proportion, pour them into water and stir evenly to obtain a mixture;

[0034] (3) Pour the mixed dry powder obtained in step (1) into the mixed liquid obtained in step (2) and stir evenly to obtain salt-resistant and tough cement slurry.

[0035] Furthermore, the composition and weight ratio of the post-treatment liquid are as follows: 10-15 parts of retarder, 20-25 parts of antifouling agent, 15-20 parts of sodium chloride and 100 parts of water;

[0036] Preferably, the preparation method of the post-treatment liquid includes the following steps: weighing the retarder, antifouling agent and sodium chloride in proportion, pouring them into water, and stirring evenly to obtain the post-treatment liquid.

[0037] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0038] I. This invention changes the conventional pipe string structure for cement slurry injection using the internal insertion method. It proposes for the first time a pipe string structure with a direct connection between the float shoe and the float collar for cementing. For casing cementing with a diameter greater than 473.08mm, the design of this pipe string structure avoids the mixing of cement slurry with drilling fluid in the casing between the float shoe and the float collar, and prevents the mixed slurry with deteriorated performance from contaminating the annulus between the casing and the well wall, thereby affecting the cementing quality.

[0039] II. The large-size casing cementing method of the present invention uses the specific pipe string structure of the present invention and a cementing working fluid system consisting of anti-salt pre-filling fluid + anti-salt pilot cement slurry + anti-salt tough cement slurry + anti-salt post-filling fluid to cement the well, which effectively avoids cement slurry contamination and ensures the sealing quality of the entire well section.

[0040] III. This invention changes the conventional single-displacement method of post-flush fluid and proposes a method of reducing the displacement in stages to achieve precise replacement and avoid the complex occurrence of emptying accidents.

[0041] IV. This invention, through the optimized configuration of a cementing working fluid with excellent salt resistance, effectively avoids the dissolution and collapse of the well wall in the salt-bearing formation of the salt cavern energy storage well, providing a solid guarantee for the long-term injection and production of the energy storage. Attached Figure Description

[0042] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0043] Figure 1 This is a schematic diagram of the cementing string structure of the present invention;

[0044] Figure 2 The acoustic amplitude diagram of cementing quality in Example 1;

[0045] Figure 3 This is the acoustic amplitude diagram of cementing quality in Example 2.

[0046] Explanation of reference numerals in the attached diagram: 1-Drill pipe string, 2-Casing, 3-Plug, 4-Insertion seat, 5-Blocking ring, 6-Float collar, 7-Float collar channel, 8-One-way valve, 9-Float shoe, 10-Float shoe channel, 11-Annulus. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0048] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0049] According to a first aspect of the present invention, a cementing string structure is provided, such as Figure 1As shown, the system specifically includes a casing 2 installed in the wellbore, with a drill pipe string 1 extending into the casing 2. The drill pipe string 1 is used to inject cementing fluid into the wellbore. An annulus 11 is formed between the casing 2 and the wellbore. A float shoe 9 is provided at the bottom of the casing 2, and a float collar 6 is connected above the float shoe 9. An insertion seat 4 is provided at the upper center of the float collar 6. A plug 3 matching the insertion seat 4 is provided at the bottom of the drill pipe string 1, and the plug 3 is seated in the insertion seat 4. A float shoe channel 10 is provided in the core of the float shoe 9, and a float collar channel 7 is provided in the core of the float collar 6. The float shoe channel 10, the float collar channel 7, and the annulus 11 are connected in sequence to ensure that the cementing fluid can enter the annulus 11. In addition, a one-way valve 8 is installed at the top of the float shoe channel 7, and a flow-blocking ring 5 is installed at the top of the float collar channel 7. The one-way valve 8 only allows fluid to flow from top to bottom, and can prevent the injected fluid from flowing backward from the one-way valve 8. The flow-blocking ring 5 has the same function as the one-way valve 8, providing double protection.

[0050] Existing cementing processes use a string structure consisting of float shoe + casing + float collar + plug + drill pipe. This invention, however, is the first to adopt a string structure with a direct connection between the float shoe and float collar for cementing. For casing cementing with a diameter greater than 473.08 mm, the string structure design of this invention avoids the mixing of cement slurry with drilling fluid in the casing between the float shoe and float collar, preventing the mixed slurry with deteriorated performance from contaminating the annulus between the casing and the wellbore, thereby affecting the cementing quality.

[0051] According to a second aspect of the present invention, a method for cementing large-size casing is provided, which uses the above-described cementing string structure and specifically includes the following steps:

[0052] S1. Use a cement truck to inject the pre-flush fluid and pilot cement slurry into the annulus in the designed amount through the drill pipe string.

[0053] S2. Then, the salt-resistant toughness cement slurry is injected into the annulus through the drill pipe string using a cement truck. After the fluid returns to the ground from the outlet of the elevated trench, a sample of the returned fluid is taken from the outlet of the elevated trench, and the fluid density is measured. When the fluid density is greater than the density of the pilot cement slurry but less than that of the salt-resistant toughness cement slurry, the injection of the salt-resistant toughness cement slurry is stopped.

[0054] S3. Use a cement truck to inject post-fluid. When the amount of post-fluid injected reaches 1 / 2 to 2 / 3 of the volume of the drill string, stop injecting post-fluid.

[0055] S4. Reduce the displacement of the cement truck and continue to inject post-flush fluid. Stop injecting post-flush fluid when the sum of the two injections reaches the design volume of post-flush fluid.

[0056] S5. Disconnect the bottom plug of the drill string from the insertion seat, remove the drill string, and wait for it to solidify.

[0057] In the aforementioned large-size casing cementing method, as a preferred embodiment, the discharge rates of the pre-flush fluid, pilot cement slurry, and salt-resistant toughness cement slurry are all 0.8–1.0 m³. 3 / min.

[0058] In the above-mentioned large-size casing cementing method, as a preferred embodiment, the design dosage of the pre-flush fluid is calculated based on the amount of pre-flush fluid that flows through the outer wall of the casing and the well wall for 20 to 25 minutes;

[0059] Optionally, the design dosage of the pilot cement grout is calculated based on the annular volume from 10 to 25 meters inside the upper casing to the ground.

[0060] Optionally, the design dosage of the salt-resistant and tough cement slurry is calculated based on the annulus volume of the entire well section;

[0061] Optionally, the designed volume of the post-flush fluid is based on a volume difference of 0.1 to 0.2 m³ within the drill string. 3 Calculate the dosage. The above cementing fluid dosage is designed based on cementing construction experience. Adopting this standard can ensure safe cementing construction and the quality of cement sealing of the annulus, thus guaranteeing subsequent drilling construction or oil and gas extraction.

[0062] In the above-described large-size casing cementing method, as a preferred embodiment, in step S3, the displacement of the cement truck is set to 0.2–0.3 m³ / h. 3 / min.

[0063] Optionally, in step S4, the displacement of the cement truck is set to 0.1–0.2 m³. 3 / min. The amount of post-fluid injected in the second stage is very small. If the discharge rate is set too high, it is very easy to cause a complex displacement accident. Therefore, it is necessary to reduce the discharge rate of the post-fluid.

[0064] Conventional cementing fluids lack salt resistance and are easily contaminated by drilling fluids, leading to flash-setting and severely impacting cementing safety. Contamination can also cause excessively slow cement slurry setting; slurry that fails to set for an extended period is difficult to effectively seal the formation, affecting subsequent drilling operations. This invention improves upon the formulation of conventional cementing fluids to ensure that the cementing fluid combination is suitable for cementing salt cavern energy storage facilities. The components and weight ratios of the pre-flush fluid are as follows: 15 parts retarder, 10-15 parts suspending agent, 50-75 parts sodium chloride, 0-400 parts barite powder, 15-25 parts diluent, 10-15 parts fluid loss reducer, 0.05-0.1 parts defoamer, and 500 parts water.

[0065] Preferably, the preparation method of the pretreatment solution includes the following steps: weigh water according to the proportion and place it in a stirrer, turn on the stirrer, and slowly add the suspending agent to the water, stirring until the suspending agent is completely dissolved; then add the water loss reducing agent, retarder, sodium chloride, barite powder, diluent and defoamer in sequence, stir for 20 to 30 minutes and let stand to obtain the pretreatment solution.

[0066] In the above-mentioned large-size casing cementing method, as a preferred embodiment, the components and weight ratio of the pilot cement slurry are as follows: 700 parts of G-grade oil well cement, 7-12 parts of nano-early strength agent, 14-21 parts of microsilica powder, 30-45 parts of sodium chloride, 0.1-0.2 parts of retarder, 14-21 parts of fluid loss reducing agent, and 300-320 parts of water;

[0067] Preferably, the method for preparing the pilot cement slurry includes the following steps:

[0068] a) Weigh out G-grade oil well cement, nano-early strength agent and microsilica powder according to the proportion, mix them and stir evenly to obtain mixed dry powder;

[0069] b) Weigh out sodium chloride, retarder, and dehydration reducer according to the proportions, pour them into water and stir evenly to obtain a mixture;

[0070] c) Pour the mixed dry powder obtained in step a) into the mixed liquid obtained in step b), and stir evenly to obtain the pilot cement slurry.

[0071] In the above-mentioned large-size casing cementing method, as a preferred embodiment, the composition and weight ratio of the salt-resistant toughness cement slurry are as follows: 700 parts of G-grade oil well cement, 17.5-21 parts of nano early strength agent, 14-21 parts of microsilica powder, 35-49 parts of toughening agent, 3.5 parts of dispersant, 30-45 parts of sodium chloride, 14-21 parts of fluid loss reducing agent, and 300-315 parts of water;

[0072] Preferably, the method for preparing the salt-resistant and tough cement slurry includes the following steps:

[0073] (1) Weigh out G-grade oil well cement, nano early strength agent, micro silica fume, toughening agent and dispersant according to the proportion, mix them and stir evenly to obtain mixed dry powder;

[0074] (2) Weigh out sodium chloride and dehydration reducer according to the proportion, pour them into water and stir evenly to obtain a mixture;

[0075] (3) Pour the mixed dry powder obtained in step (1) into the mixed liquid obtained in step (2) and stir evenly to obtain salt-resistant and tough cement slurry.

[0076] In the above-mentioned large-size casing cementing method, as a preferred embodiment, the composition and weight ratio of the post-filling fluid are as follows: 10-15 parts of retarder, 20-25 parts of anti-fouling agent, 15-20 parts of sodium chloride and 100 parts of water.

[0077] Preferably, the preparation method of the post-treatment liquid includes the following steps: weighing the retarder, antifouling agent and sodium chloride in proportion, pouring them into water, and stirring evenly to obtain the post-treatment liquid.

[0078] The present invention will now be described in detail with reference to embodiments thereof. These examples are provided by way of explanation and not by way of limitation. In fact, those skilled in the art will recognize that modifications and variations can be made to the present invention without departing from its scope or spirit. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the present invention encompass such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0079] In the embodiments of the present invention, unless otherwise specified, the experimental methods used are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0080] Example 1

[0081] See attached document Figure 1 The provided wellbore cementing string structure was used in the initial cementing of a well in a salt cavern energy storage facility in China. The method employed was a large-size casing cementing method to prevent cement slurry contamination. The initial well depth was 125m, the casing size was 609.6mm, the casing depth was 123m, the average wellbore diameter was 725.4mm, and the upper guide pipe depth was 24m. The specific cementing method included the following steps:

[0082] Cementing design and cementing preparation:

[0083] 1.1 Calculate the design dosage and density of the cementing fluid based on wellbore data: 20m³ of pre-flush fluid. 3 The density of the pre-fluid is 1.16 g / cm³. 3 14.8m of pilot cement grout 3 The density of the pilot cement slurry is 1.88 g / cm³. 3 Salt-resistant and tough cement grout 18.6m 3 Salt-resistant and tough cement grout: 1.91 g / cm³ 3 The first injection of post-filled fluid was 0.66m. 3 After the second injection, 0.48m of post-filled solution was added. 3 ;

[0084] 1.2 Determine the formulation of the cementing working fluid. The formulation of the pre-fill fluid is: 500 parts tap water + 15 parts retarder BH-R102L + 10 parts suspending agent BH-HS004S + 50 parts sodium chloride + 15 parts diluent BH-Q812L + 10 parts fluid loss reducer BH-F201L + 0.05 parts defoamer BZXP-1; The formulation of the pilot cement slurry is: 700 parts G-grade oil well cement + 7 parts nano early strength agent BHA-2S + 14 parts microsilica powder + 30 parts sodium chloride + 0.1 parts retarder BH-R102L + 14 parts fluid loss reducer BH-F201L + 300 parts tap water. The salt-resistant and tough cement slurry formula is: 700 parts of G-grade oil well cement + 21 parts of nano-early strength agent BHA-2S + 21 parts of microsilica powder + 35 parts of toughening agent BH-M1S + 3.5 parts of dispersant BZGF-1 + 30 parts of sodium chloride + 14 parts of water loss reducing agent BH-F201L + 315 parts of tap water; the post-treatment liquid formula is: 10 parts of retarder BH-R102L + 20 parts of anti-fouling agent + 15 parts of sodium chloride + 100 parts of tap water.

[0085] Cementing operations:

[0086] S1: After well cleaning, casing 3 is installed in the wellbore. Casing 3 has a float shoe 10 at its bottom and a float collar 7 connected above it. Float collar 7 has an insertion seat 5 in the middle of its upper part. A drill string 1 is installed above the insertion seat 5. A plug 4 is connected to the bottom of the drill string 1. The plug 4 is connected to the insertion seat 5 on the float collar 7. Float shoe 10 has a float shoe channel 11 in its core. A one-way valve 9 is installed at the top of float shoe channel 11. Float collar 7 has a float collar channel 8 in its core. A flow-blocking ring 6 is installed at the top of float collar channel 8. The drill string 1 and plug 4 are seated in the insertion seat 5.

[0087] S2: Use a cement truck to transport the prepared 20m 3 The pre-fluid is injected into the annulus 12 through drill pipe string 1 at a displacement of 0.8–1.0 m³. 3 / min;

[0088] S3: The injected pre-fluid reaches 20m 3 Then, the prepared 14.8m³ cement was delivered in sequence using a cement truck. 3 Pilot cement grout, 18.6m 3 Salt-resistant and tough cement grout is pushed by drill pipe string 1 to inject pre-fluid into annulus 12 at a displacement of 1.0 m³. 3 / min;

[0089] S4: Pre-fluid, pilot cement slurry, and salt-resistant toughening cement slurry sequentially enter annulus 12 and return to the ground from the elevated trench outlet. Samples of the returned cement slurry fluid were taken from the elevated trench outlet, and the fluid density was measured three times, showing a value of 1.80 g / cm³. 3 1.83g / cm 31.88g / cm 3 ;

[0090] S5: The measured fluid density is 1.88 g / cm³. 3 At that time, the cement truck stopped injecting salt-resistant and tough cement slurry;

[0091] S6: Use a cement truck to inject the post-flush liquid, with an injection displacement of 0.2–0.3 m³. 3 / min, 0.66m of post-filled solution injected. 3 Afterwards, the injection volume of the post-flush fluid is 0.529 times the internal volume of drill string 1, and the cement truck stops injecting the post-flush fluid.

[0092] S7: Reduce the displacement of cement trucks; set the displacement to 0.1–0.2 m³. 3 Continue injecting post-flush solution at a rate of 0.48 m³ / min. 3 Stop injecting post-filled fluid when the time comes;

[0093] S9: Disconnect the connection between the bottom plug 4 and the insertion seat 5 of drill pipe string 1, and remove drill pipe string 1. At this time, the cement slurry returns to the predetermined well section. After 72 hours of setting, measure the cementing acoustic amplitude quality. See the attached cementing acoustic amplitude quality diagram. Figure 2 .

[0094] Example 2

[0095] See attached document Figure 1 The provided wellbore cementing string structure was used in the second-stage cementing of a well in a salt cavern energy storage facility in China. The method employed was a large-size casing cementing method to prevent cement slurry contamination. The second-stage well was 520m deep, with a casing size of 473.08mm, a casing depth of 518m, an average wellbore diameter of 594.9mm, and an upper casing depth of 123m. The specific cementing method included the following steps:

[0096] Cementing design and cementing preparation:

[0097] 1.1 Calculate the design dosage and density of the cementing fluid based on wellbore data: 20m³ of pre-flush fluid. 3 The density of the pre-fluid is 1.31 g / cm³. 3 10.25m of pilot cement grout 3 The density of the pilot cement slurry is 1.88 g / cm³. 3 Salt-resistant and tough cement grout 52.5m 3 Salt-resistant and tough cement grout: 1.92 g / cm³ 3 The first injection of post-filled fluid was 3.2m. 3 The second injection of post-filled fluid was 2.21m. 3 ;

[0098] 1.2 Determine the formulation of the cementing working fluid. The formulation of the pre-flush fluid is: 500 parts tap water + 15 parts retarder BH-R102L + 15 parts suspending agent BH-HS004S + 75 parts sodium chloride + 25 parts diluent BH-Q812L + 15 parts fluid loss reducer BH-F201L + 0.1 parts defoamer BZXP-1; The formulation of the pilot cement slurry is: 700 parts G-grade oil well cement + 12 parts nano early strength agent BHA-2S + 21 parts microsilica powder + 45 parts sodium chloride + 0.2 parts retarder BH-R102L + 21 parts fluid loss reducer BH-F201L + 320 parts tap water. The salt-resistant and tough cement slurry formula is: 700 parts of G-grade oil well cement + 17.5 parts of nano early strength agent BHA-2S + 14 parts of microsilica powder + 35 parts of toughening agent BH-M1S + 3.5 parts of dispersant BZGF-1 + 30 parts of sodium chloride + 21 parts of water loss reducing agent BH-F201L + 300 parts of tap water; the post-treatment liquid formula is: 10 parts of retarder BH-R102L + 20 parts of anti-fouling agent + 15 parts of sodium chloride + 100 parts of tap water.

[0099] Cementing operations:

[0100] S1: After well cleaning, casing 3 is installed in the wellbore. Casing 3 has a float shoe 10 at its bottom and a float collar 7 connected above it. Float collar 7 has an insertion seat 5 in the middle of its upper part. Drill pipe string 1 is installed above the insertion seat 5. A plug 4 is connected to the bottom of drill pipe string 1. The plug 4 is connected to the insertion seat 5 on float collar 7. Float shoe 10 has a float shoe channel 11 in its core. A one-way valve 9 is installed at the top of float shoe channel 11. Float collar 7 has a float collar channel 8 in its core. A flow-blocking ring 6 is installed at the top of float collar channel 8. Drill pipe string 1 and plug 4 are seated in the insertion seat 5.

[0101] S2: Use a cement truck to transport the prepared 20m 3 The pre-fluid is injected into the annulus 12 through drill pipe string 1 at a displacement of 0.8–1.0 m³. 3 / min;

[0102] S3: The injected pre-fluid reaches 20m 3 Then, the prepared 10.25m³ cement was delivered in sequence using a cement truck. 3 Pilot cement grout, 52.5m 3 Salt-resistant and tough cement grout is pushed by drill pipe string 1 to inject pre-fluid into annulus 12 at a displacement of 0.8–1.0 m³. 3 / min;

[0103] S4: Pre-fluid, pilot cement slurry, and salt-resistant toughening cement slurry sequentially enter annulus 12 and return to the ground from the elevated trench outlet. Samples of the returned cement slurry fluid were taken from the elevated trench outlet, and the fluid density was measured three times, showing a value of 1.80 g / cm³. 3 1.85g / cm 3 1.89 g / cm3 ;

[0104] S5: The measured fluid density is 1.89 g / cm³. 3 At that time, the cement truck stopped injecting salt-resistant and tough cement slurry;

[0105] S6: Use a cement truck to inject the post-flush liquid, with an injection displacement of 0.2–0.3 m³. 3 / min, 3.2m of post-filled solution injected. 3 Afterwards, the injection volume of the post-flush fluid is 0.57 times the internal volume of drill string 1, and the cement truck stops injecting the post-flush fluid.

[0106] S7: Reduce the displacement of cement trucks; set the displacement to 0.1–0.2 m³. 3 The injection rate continued at 1000 m³ / min, with a total injection volume of 2.41 m³. 3 Stop injecting post-filled fluid when the time comes;

[0107] S9: Disconnect the connection between the bottom plug 4 and the insertion seat 5 of drill pipe string 1, and pull out drill pipe string 1. At this time, the cement slurry returns to the predetermined well section. After 72 hours of setting, measure the cementing acoustic amplitude quality. See the attached diagram for the cementing acoustic amplitude bottom hole quality. Figure 3 .

[0108] By examining the appendix Figure 2 and attached Figure 3 As can be seen, the use of the pipe string structure with direct connection between float shoe and float collar proposed for the first time in this invention, and the cementing working fluid system consisting of anti-salt pre-filling fluid + anti-salt pilot cement slurry + anti-salt tough cement slurry + anti-salt post-filling fluid, effectively avoids cement slurry contamination and ensures the sealing quality of the entire well section.

[0109] By applying the large-size casing cementing method of this invention to resist cement slurry contamination in the cementing of several wells in a salt cavern energy storage facility in China, the problem of drilling fluid contamination of cement slurry in the cementing section was effectively avoided, and the cementing success rate and cementing quality qualification rate reached 100%.

[0110] The foregoing has described and evaluated some embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. This does not affect the essential content of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, still fall within the protection scope of the present invention.

Claims

1. A cementing string structure, characterized in that, The system includes a casing installed in the wellbore and a string of drill pipes extending into the casing; the string of drill pipes is used to inject cementing fluid into the wellbore; an annulus is formed between the casing and the wellbore; a float shoe is provided at the bottom of the casing, a float collar is connected above the float shoe, an insertion seat is provided at the upper center of the float collar, and a plug matching the insertion seat is provided at the bottom of the drill pipe string, the plug being seated in the insertion seat; a float shoe channel is provided in the core of the float shoe, a float collar channel is provided in the core of the float collar, and the float shoe channel, float collar channel, and annulus are sequentially connected.

2. The cementing string structure according to claim 1, characterized in that, A one-way valve is installed at the top of the floating shoe channel; and / or, a flow-blocking ring is installed at the top of the floating hoop channel.

3. A method for cementing large-size casing, characterized in that, Using the cementing string structure according to claim 1 or 2 includes the following steps: S1. Use a cement truck to inject the pre-flush fluid and pilot cement slurry into the annulus in the designed amount through the drill pipe string. S2. Then, the salt-resistant toughness cement slurry is injected into the annulus through the drill pipe string using a cement truck. After the fluid returns to the ground from the outlet of the elevated trench, a sample of the returned fluid is taken from the outlet of the elevated trench, and the fluid density is measured. When the fluid density is greater than the density of the pilot cement slurry but less than that of the salt-resistant toughness cement slurry, the injection of the salt-resistant toughness cement slurry is stopped. S3. Use a cement truck to inject post-fluid. When the amount of post-fluid injected reaches 1 / 2 to 2 / 3 of the volume of the drill string, stop injecting post-fluid. S4. Reduce the displacement of the cement truck and continue to inject post-flush fluid. Stop injecting post-flush fluid when the sum of the two injections reaches the design volume of post-flush fluid. S5. Disconnect the bottom plug of the drill string from the insertion seat, remove the drill string, and wait for it to solidify.

4. The method for cementing large-size casing according to claim 3, characterized in that, The discharge rates of the pre-flushing liquid, pilot cement grout, and salt-resistant toughness cement grout are all 0.8–1.0 m³. 3 / min.

5. The method for cementing large-size casing according to claim 3, characterized in that, The design dosage of the pre-fluid is calculated based on the amount of pre-fluid flowing through the annulus for 20-25 minutes. And / or, the design dosage of the pilot cement grout is calculated based on the annular volume from 10 to 25 meters into the upper casing to the ground. And / or, the design dosage of the salt-resistant and tough cement slurry is calculated based on the annular volume of the entire well section; And / or, the designed volume of the post-flush fluid is based on a difference in drill string volume of 0.1–0.2 m³. 3 Calculate the dosage.

6. The method for cementing large-size casing according to claim 3, characterized in that, In step S3, the displacement of the cement truck is set to 0.2–0.3 m³. 3 / min; And / or, in step S4, the displacement of the cement truck is set to 0.1–0.2 m³ / h. 3 / min.

7. The method for cementing large-size casing according to any one of claims 3-6, characterized in that, The components and weight ratios of the pre-treatment liquid are as follows: 15 parts retarder, 10-15 parts suspending agent, 50-75 parts sodium chloride, 0-400 parts barite powder, 15-25 parts diluent, 10-15 parts water loss reducing agent, 0.05-0.1 parts defoamer, and 500 parts water. Preferably, the preparation method of the pretreatment solution includes the following steps: weigh water according to the proportion and place it in a stirrer, turn on the stirrer, and slowly add the suspending agent to the water, stirring until the suspending agent is completely dissolved; then add the water loss reducing agent, retarder, sodium chloride, barite powder, diluent and defoamer in sequence, stir for 20 to 30 minutes and let stand to obtain the pretreatment solution.

8. The method for cementing large-size casing according to any one of claims 3-6, characterized in that, The components and weight ratio of the pilot cement slurry are as follows: 700 parts of G-grade oil well cement, 7-12 parts of nano-early strength agent, 14-21 parts of microsilica powder, 30-45 parts of sodium chloride, 0.1-0.2 parts of retarder, 14-21 parts of water loss reducer, and 300-320 parts of water. Preferably, the method for preparing the pilot cement slurry includes the following steps: a) Weigh out G-grade oil well cement, nano-early strength agent and microsilica powder according to the proportion, mix them and stir evenly to obtain mixed dry powder; b) Weigh out sodium chloride, retarder, and dehydration reducer according to the proportions, pour them into water and stir evenly to obtain a mixture; c) Pour the mixed dry powder obtained in step a) into the mixed liquid obtained in step b), and stir evenly to obtain the pilot cement slurry.

9. The method for cementing large-size casing according to any one of claims 3-6, characterized in that, The composition and weight ratio of the salt-resistant and tough cement slurry are as follows: 700 parts of G-grade oil well cement, 17.5-21 parts of nano-early strength agent, 14-21 parts of microsilica powder, 35-49 parts of toughening agent, 3.5 parts of dispersant, 30-45 parts of sodium chloride, 14-21 parts of water loss reducing agent, and 300-315 parts of water. Preferably, the method for preparing the salt-resistant and tough cement slurry includes the following steps: (1) Weigh out G-grade oil well cement, nano early strength agent, micro silica fume, toughening agent and dispersant according to the proportion, mix them and stir evenly to obtain mixed dry powder; (2) Weigh out sodium chloride and dehydration reducer according to the proportion, pour them into water and stir evenly to obtain a mixture; (3) Pour the mixed dry powder obtained in step (1) into the mixed liquid obtained in step (2) and stir evenly to obtain salt-resistant and tough cement slurry.

10. The method for cementing large-size casing according to any one of claims 3-6, characterized in that, The composition and weight ratio of the post-treatment liquid are as follows: 10-15 parts of retarder, 20-25 parts of antifouling agent, 15-20 parts of sodium chloride and 100 parts of water; Preferably, the preparation method of the post-treatment liquid includes the following steps: weighing the retarder, antifouling agent and sodium chloride in proportion, pouring them into water, and stirring evenly to obtain the post-treatment liquid.

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