Special wellhead device for large-diameter anti-flagpole cementing and cementing method thereof

Abstract

The present invention discloses a special wellhead device for large-caliber anti-flagpole cementing, including an end cover and a drill pipe fixedly connected to the middle of the end cover, the end cover is provided with a liquid inlet channel and an exhaust channel, and the liquid inlet channel and the exhaust channel are both connected with the casing; when the bottom of the end cover is connected with the top of the casing and placed together in a well filled with drilling fluid, liquid is injected into the annulus between the casing and the drill pipe through the liquid inlet channel, and due to the pressure difference between the inside and outside of the casing, the gas at the top of the casing is discharged through the exhaust channel. The present invention focuses on optimizing the end cover structure, making full use of the characteristics that gas can be compressed while liquid cannot be compressed, and by providing a liquid inlet channel and an exhaust channel on the end cover, liquid can be injected into the liquid inlet channel before injecting cement to empty the gas inside the casing, so that the cement injected from the drill pipe will not surge upward, and the bottom of the drill pipe will not be fixed, which can effectively prevent the occurrence of flagpole insertion accidents.

Description

Technical Field

[0001] The invention relates to the technical field of well cementing, and in particular to a special wellhead device for large-caliber anti-flagpole cementing and a well cementing method thereof. Background Art

[0002] In the construction of oil drilling, cementing is an important means to maintain the stability of the well wall. Cementing is to use cementing equipment to inject cement into the annular space between the casing and the wellbore in the oil and gas well where the casing is inserted, so as to effectively seal the casing and the formation. After the cementing construction, a complete cement ring is formed between the casing and the well wall, and a good bond is formed between the casing and the cement, and between the cement and the well wall, ensuring that the oil, gas and water layers do not communicate with each other, achieving effective isolation. However, due to the large size of the casing, the traditional cementing method of plugging cannot be used for large-diameter cementing construction. It is necessary to lower the cementing drill pipe into the casing so that the drill pipe is about 10-20m from the bottom of the casing, and use pressure to perform cementing operations.

[0003] When cementing a large-diameter well, drilling fluid must first be poured into the well, so that the top of the casing is fixedly connected to a cap, the middle of the cap is fixedly connected to a drill pipe, and the middle of the drill pipe is provided with a cement channel. Then the casing is set in the well, and cement is injected into the well at the bottom of the drill pipe through the cement channel at the top of the drill pipe. However, this traditional cementing method is prone to flagpole accidents, and the cause has not been found.

[0004] After continuous research and analysis, the inventors found that the cause of the flagpole inserting accident was that due to the seal on the top of the casing, when the casing penetrates into the well filled with drilling fluid, a large amount of air will remain at the top of the casing. Due to the compressible nature of air, the cement flowing out from the bottom of the drill pipe will surge upward and squeeze the air at the top of the inner wall of the casing, causing the cement at the bottom of the drill pipe to submerge the bottom of the drill pipe. The cement solidifies and fixes the bottom of the drill pipe, causing the flagpole inserting accident.

[0005] Therefore, providing a cementing method that can evacuate the gas in the casing during the cementing process and prevent the cement from surging upward and fixing the drill pipe has become an urgent problem to be solved by those skilled in the art.

[0006] In addition, it is of great significance to invent a wellhead device that can evacuate the gas in the casing during the cementing process to prevent flagpole accidents. Summary of the invention

[0007] The purpose of the present invention is to provide a special wellhead device for large-diameter anti-flagpole cementing and a cementing method thereof, so as to solve the technical problem that the cementing method and the wellhead device in the prior art cannot exhaust the gas in the casing during the cementing process, and cement easily surges upward to fix the drill pipe, causing a flagpole insertion accident.

[0008] In order to solve the above technical problems, the present invention specifically provides the following technical solutions:

[0009] In a first aspect of the present invention, a special wellhead device for large-caliber anti-flagpole cementing is provided, comprising an end cover and a drill pipe fixedly connected to the middle of the end cover, wherein the end cover is provided with a liquid inlet channel and an exhaust channel, and the liquid inlet channel and the exhaust channel are both connected to the inside of the casing;

[0010] When the bottom of the end cover is connected to the top of the casing and placed together in a well filled with drilling fluid, liquid is injected into the annulus between the casing and the drill pipe through the liquid inlet channel. Due to the pressure difference between the inside and outside of the casing, the gas at the top of the casing is discharged through the exhaust channel.

[0011] Further, the liquid inlet channel includes a first hole arranged on the end cover and a first tube arranged inside the first hole, and the exhaust channel includes an exhaust hole arranged on the end cover and an exhaust tube arranged inside the exhaust hole;

[0012] The first pipe is provided with a first valve, and the exhaust pipe is provided with a third valve;

[0013] When only liquid is discharged from the exhaust passage, the first valve and the third valve are closed to exhaust the gas inside the sleeve.

[0014] Furthermore, the third valve is a one-way check valve, so as to prevent external gas from entering the sleeve from the exhaust pipe when the internal gas of the sleeve is discharged through the exhaust pipe.

[0015] Furthermore, a pressure gauge for measuring the pressure difference between the drilling fluid inside the casing and the cement slurry outside the casing is provided on one side of the exhaust passage;

[0016] After cementing is completed, the cementing condition of the cement slurry is judged by comparing the pressure gauge value with the pre-calculated theoretical pressure difference value.

[0017] Furthermore, a liquid injection channel is provided inside the drill rod, a second tube connected to the liquid injection channel is connected to one side of the drill rod, a second valve is provided on the second tube, and the second tube is arranged on the top of the end cover;

[0018] The isolation fluid, cementing cement slurry and displacement fluid are injected into the well through the second pipe and the injection channel, and the isolation fluid, cementing cement slurry and displacement fluid flow into the solidification space between the casing and the well wall.

[0019] Further, the end cover comprises a sealing plate located at the top of the sleeve and an annular plate fixedly connected to the outer surface of the sealing plate, and the bottom of the annular plate is welded to the top of the sleeve;

[0020] The drill rod comprises a first rod located inside the end cap and a second rod located inside the casing, the first rod is fixedly connected to the end cap, and the bottom of the first rod is threadedly connected to the top of the second rod;

[0021] Wherein, the bottom surface height of the end cover is higher than the wellhead height.

[0022] In a second aspect of the present invention, a large-diameter anti-flagpole cementing method is provided, which uses the above-mentioned large-diameter anti-flagpole cementing dedicated wellhead device, including the following steps:

[0023] Step 100: Place the casing and fix the end cap on the top of the casing.

[0024] Step 200, injecting liquid, injecting exhaust liquid into the annulus between the casing and the drill pipe through the liquid inlet channel;

[0025] Step 300, exhausting the gas. With the injection of the exhaust liquid, the gas at the top of the casing is exhausted through the exhaust channel due to the pressure difference between the inside and outside of the casing;

[0026] Step 400: inject cement slurry into the well through the drill pipe to complete cementing.

[0027] Furthermore, in step 400, after the injection of cement slurry is completed, extrusion liquid is injected into the annulus between the casing and the drill pipe through the liquid inlet channel, so that the cement at the bottom of the drill pipe flows downward to the designed position as a whole, thereby keeping the bottom of the drill pipe away from the cement slurry.

[0028] Furthermore, the exhaust fluid and the squeeze fluid are both liquids with a density lower than that of the original drilling fluid, so that the injected exhaust fluid and the squeeze fluid are on the top of the original drilling fluid.

[0029] Furthermore, in step 400, before cement slurry is injected into the drill pipe, an isolation fluid is injected into the drill pipe to flush the casing wall and the well wall, and after cement slurry is injected, a displacement fluid is injected into the drill pipe to flush the inner wall of the drill pipe.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The cementing method provided by the present invention focuses on optimizing the grouting process. Before injecting cement slurry, the air at the top of the casing is emptied by injecting exhaust liquid into the annulus between the casing and the drill pipe, making full use of the characteristics that gas can be compressed while liquid cannot be compressed, thereby preventing cement at the bottom of the drill pipe from surging upward and backflowing, and preventing the flagpole insertion accident;

[0032] 2. The wellhead device provided by the present invention focuses on optimizing the end cover structure, making full use of the characteristics that gas can be compressed but liquid cannot be compressed. By providing a liquid inlet channel and an exhaust channel on the end cover, liquid can be injected into the liquid inlet channel before injecting cement to evacuate the gas inside the casing, so that the cement injected from the drill pipe will not surge upward, and the bottom of the drill pipe will not be fixed, which can effectively prevent the occurrence of flagpole insertion accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0034] Figure 1 A schematic diagram of the overall structure provided by an embodiment of the present invention;

[0035] Figure 2 This is a schematic structural diagram of the wellhead device provided by the present invention when in use.

[0036] The numbers in the figure represent the following:

[0037] 1-end cover; 2-drill rod; 3-liquid inlet channel; 4-exhaust channel; 5-first valve; 6-third valve; 7-pressure gauge; 8-liquid injection channel; 9-second tube; 10-second valve; 11-sealing plate; 12-annular plate; 13-first rod; 14-second rod; 15-first hole; 16-first tube; 17-exhaust hole; 18-exhaust pipe. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] When using the existing wellhead device in large-diameter cementing operations, flagpole insertion accidents are prone to occur, but the cause has not been found yet, resulting in extended cementing time and increased costs.

[0040] After continuous research and analysis, the inventor finally found out the cause of the flagpole inserting accident. Due to the sealing of the top of the casing, when the casing goes deep into the well filled with drilling fluid, a large amount of air will remain at the top of the casing. Due to the compressible nature of air, cement flowing out from the bottom of the drill pipe 2 will surge upward and squeeze the air at the top of the inner wall of the casing, so that the cement at the bottom of the drill pipe 2 submerges the bottom of the drill pipe 2. The cement solidifies and fixes the bottom of the drill pipe 2, causing the flagpole inserting accident.

[0041] This is the reason why the flagpole accident has not been solved in large-diameter cementing. After finding out the reason, the inventor took full advantage of the fact that gas can be compressed while liquid cannot be compressed, and developed a wellhead device that can discharge the gas at the top of the casing to prevent the flagpole accident.

[0042] like Figure 1 and Figure 2 As shown, the present invention provides a special wellhead device for large-caliber anti-flagpole cementing, which mainly discharges the top gas in the casing by providing a liquid inlet channel 3 and an exhaust channel 4 on the end cover 1.

[0043] The large-caliber anti-flagpole cementing special wellhead device comprises an end cover 1 and a drill pipe 2 fixedly connected to the middle of the end cover 1, and the end cover 1 is provided with a liquid inlet channel 3 and an exhaust channel 4, and the liquid inlet channel 3 and the exhaust channel 4 are both connected to the casing;

[0044] When the bottom of the end cover 1 is connected to the top of the casing and placed together in a well filled with drilling fluid, liquid is injected into the annulus between the casing and the drill pipe 2 through the liquid inlet channel 3. Due to the pressure difference between the inside and outside of the casing, the gas at the top of the casing is discharged through the exhaust channel 4.

[0045] This embodiment optimizes the structure of the end cap 1, makes full use of the characteristics that gas can be compressed but liquid cannot be compressed, and provides a liquid inlet channel 3 and an exhaust channel 4 on the end cap 1. Before injecting cement, liquid can be injected into the liquid inlet channel 3 to evacuate the gas inside the casing, so that the cement injected from the drill rod 2 will not surge upward, and will not fix the bottom of the drill rod 2, which can effectively prevent the flagpole insertion accident. Compared with the prior art, the air at the top of the casing can be easily discharged, solving the problem that the bottom of the drill rod 2 is fixed by cement slurry.

[0046] The specific steps are:

[0047] Step 1: Place the casing and fix the end cap 1 on the top of the casing.

[0048] Step 2: injecting liquid, injecting exhaust liquid into the annulus between the casing and the drill pipe 2 through the liquid inlet channel 3, the exhaust liquid is a liquid with a density lower than that of the original drilling fluid, preferably water;

[0049] Step 3: exhaust the gas. With the injection of exhaust liquid, due to the pressure difference between the inside and outside of the casing, the gas at the top of the casing is discharged through the exhaust channel 4 until all the liquid is discharged from the exhaust channel 4, which proves that the gas in the casing is completely exhausted. Then seal the exhaust channel 4 and the liquid inlet channel 3;

[0050] Step 4: Inject cement slurry. Inject spacer fluid, cementing cement slurry and displacement fluid into the well in sequence through drill pipe 2 to complete cementing.

[0051] By adopting this device, the gas at the top of the casing can be discharged, and after the cement slurry is injected, the cement at the bottom of the drill pipe 2 can flow downward to the designed position as a whole, so that the bottom of the drill pipe 2 is away from the cement slurry, further preventing the occurrence of flagpole insertion accidents.

[0052] The specific operation steps are: after completing the cement slurry injection, the extrusion liquid is injected into the annulus between the casing and the drill pipe 2 through the liquid inlet channel 3 again. The extrusion liquid is a liquid with a density lower than the original drilling fluid density, preferably water. The extrusion liquid squeezes the cement slurry, so that the cement at the bottom of the drill pipe 2 flows downward to the designed position as a whole, thereby keeping the bottom of the drill pipe 2 away from the cement slurry and preventing the bottom of the drill pipe 2 from being fixed by cement, thereby avoiding the flagpole insertion accident.

[0053] In a preferred embodiment, in order to control the opening and closing of the liquid inlet channel 3 and the liquid discharge channel, specifically, as Figure 1 As shown, the liquid inlet channel 3 includes a first hole 15 provided on the end cover 1 and a first tube 16 provided inside the first hole 15, and the exhaust channel 4 includes an exhaust hole 17 provided on the end cover 1 and an exhaust tube 18 provided inside the exhaust hole 17;

[0054] The first pipe 16 is provided with a first valve 5, and the exhaust pipe 18 is provided with a third valve 6;

[0055] When only liquid is discharged from the exhaust passage 4, the first valve 5 and the third valve 6 are closed to exhaust the gas inside the casing.

[0056] The opening and closing of the liquid inlet channel 3 is controlled by the first valve 5, and the opening and closing of the exhaust channel 4 is controlled by the third valve 6. After the air in the casing is emptied, the first valve 5 and the third valve 6 are closed to make the casing a closed space.

[0057] Preferably, the third valve 6 is a one-way check valve, so as to prevent external gas from entering the casing from the exhaust pipe 18 when the internal gas of the casing is discharged through the exhaust pipe 18. It can be achieved that when the gas in the casing is discharged, external gas is prevented from entering the casing from the exhaust pipe 18.

[0058] In the current large-diameter cementing operation, it is impossible to judge the injection status of cement slurry between the casing and the well wall, and after an accident occurs, it is impossible to find the cause. This is the difficulty of cementing. After analysis by the inventor, Figure 1 As shown, a pressure gauge 7 for measuring the pressure difference between the drilling fluid inside the casing and the cement slurry outside the casing is provided on one side of the exhaust passage 4;

[0059] After cementing is completed, the cementing condition of the cement slurry is judged by comparing the value of the pressure gauge 7 with the pre-calculated theoretical pressure difference value.

[0060] Before cementing, a theoretical pressure difference value will be calculated. Since the density of the drilling fluid in the casing is low and the density of the cement slurry outside the casing is relatively high, according to the principle of communicating vessels, there will be a pressure difference between the two due to the different densities. A pressure gauge 7 is provided on the end cover 1 to measure the pressure difference between the drilling fluid inside the casing and the cement slurry outside the casing. With the injection of cement slurry, the pressure measured by the pressure gauge 7 will gradually increase until the injection of cement slurry is completed. If the pressure difference value measured after the injection of cement slurry is completed is much smaller than the theoretical pressure difference value, it proves that there is a problem in the cementing process, for example, the casing is leaking, and the cement slurry is unevenly distributed in the space between the casing and the well wall. This can facilitate the judgment of the injection situation of the cement slurry between the casing and the well wall, and facilitate the identification of the cause, thereby improving the efficiency and quality of cementing.

[0061] In order to inject cement slurry into the bottom of the drill rod 2, specifically, a liquid injection channel 8 is provided inside the drill rod 2, a second pipe 9 connected to the liquid injection channel 8 is connected to one side of the drill rod 2, a second valve 10 is provided on the second pipe 9, and the second pipe 9 is arranged on the top of the end cover 1;

[0062] The isolation fluid, cementing slurry and displacement fluid are injected into the well through the second pipe 9 and the injection channel 8, and the isolation fluid, cementing slurry and displacement fluid flow into the solidification space between the casing and the well wall.

[0063] An isolation fluid is injected into the drill pipe 2 through the second pipe 9 to flush the casing wall and the well wall, and then cement slurry is injected into the drill pipe 2 through the second pipe 9. After the cement slurry is injected, a displacement fluid is injected into the drill pipe 2 to flush the inner wall of the drill pipe 2. After the cementing is completed, the second valve 10 is closed.

[0064] Specifically, in order to facilitate installation, the end cover 1 includes a sealing plate 11 located at the top of the casing and an annular plate 12 fixedly connected to the outer surface of the sealing plate 11, and the bottom of the annular plate 12 is welded to the top of the casing;

[0065] The drill pipe 2 includes a first rod 13 located inside the end cover 1 and a second rod 14 located inside the casing, the first rod 13 is fixedly connected to the end cover 1, and the bottom of the first rod 13 is threadedly connected to the top of the second rod 14;

[0066] Wherein, the bottom surface height of the end cover 1 is higher than the wellhead height.

[0067] In combination with the above-mentioned large-diameter anti-flagpole cementing special wellhead device, a large-diameter anti-flagpole cementing method is provided, comprising the following steps:

[0068] Step 100: Place the casing and fix the end cover 1 on the top of the casing.

[0069] Step 200, injecting liquid, injecting exhaust liquid into the annulus between the casing and the drill pipe 2 through the liquid inlet channel 3;

[0070] Step 300, exhausting the gas. With the injection of the exhaust liquid, the gas at the top of the casing is exhausted through the exhaust channel 4 due to the pressure difference between the inside and outside of the casing;

[0071] Step 400: inject cement slurry into the well through the drill pipe 2 to complete cementing.

[0072] In step 400 , before cement slurry is injected from the drill pipe 2 , an isolation fluid is injected into the drill pipe 2 to flush the casing wall and the well wall. After cement slurry is injected, a displacement fluid is injected into the drill pipe 2 to flush the inner wall of the drill pipe 2 .

[0073] The cementing method provided by the present invention focuses on optimizing the grouting process. Before injecting cement slurry, exhaust liquid is injected into the annulus between the casing and the drill pipe 2 to evacuate the air at the top of the casing, making full use of the fact that gas can be compressed while liquid cannot be compressed, thereby preventing cement at the bottom of the drill pipe 2 from surging upward and backflowing, thereby preventing flagpole insertion accidents.

[0074] In step 400, after the injection of cement slurry is completed, extrusion liquid is injected into the annulus between the casing and the drill pipe 2 through the liquid inlet channel 3, so that the cement at the bottom of the drill pipe 2 flows downward to the designed position as a whole, thereby keeping the bottom of the drill pipe 2 away from the cement slurry.

[0075] After the cement slurry is injected, the squeeze liquid is injected into the annulus between the casing and the drill pipe 2 through the liquid inlet channel 3, which can further prevent the drill pipe 2 from being fixed by the cement.

[0076] In order to prevent the exhaust fluid and the squeeze fluid from settling to the bottom of the original drilling fluid, the exhaust fluid and the squeeze fluid are both liquids with a density lower than that of the original drilling fluid, so that the injected exhaust fluid and the squeeze fluid are at the top of the original drilling fluid, which can more easily discharge the gas in the casing and squeeze the cement slurry downward.

[0077] The above embodiments are only exemplary embodiments of the present application and are not intended to limit the present application. The protection scope of the present application is defined by the claims. Those skilled in the art may make various modifications or equivalent substitutions to the present application within the essence and protection scope of the present application, and such modifications or equivalent substitutions shall also be deemed to fall within the protection scope of the present application.

Claims

1. A large-caliber anti-flagpole cementing special wellhead device, characterized in that: It comprises an end cover (1) and a drill rod (2) fixedly connected to the middle part of the end cover (1), the end cover (1) is provided with a liquid inlet channel (3) and an exhaust channel (4), and the liquid inlet channel (3) and the exhaust channel (4) are both connected to the inside of the casing; When the bottom of the end cover (1) is connected to the top of the casing and placed together in a well filled with drilling fluid, liquid is injected into the annulus between the casing and the drill pipe (2) through the liquid inlet channel (3), and due to the pressure difference between the inside and outside of the casing, the gas at the top of the casing is discharged through the exhaust channel (4).

2. The large-caliber anti-flagpole cementing special wellhead device according to claim 1 is characterized in that: The liquid inlet channel (3) comprises a first hole (15) arranged on the end cover (1) and a first tube (16) arranged inside the first hole (15); the exhaust channel (4) comprises an exhaust hole (17) arranged on the end cover (1) and an exhaust tube (18) arranged inside the exhaust hole (17); The first pipe (16) is provided with a first valve (5), and the exhaust pipe (18) is provided with a third valve (6); When only liquid is discharged from the exhaust passage (4), the first valve (5) and the third valve (6) are closed, thereby exhausting the gas inside the casing.

3. The large-caliber anti-flagpole cementing special wellhead device according to claim 2 is characterized in that: The third valve (6) is a one-way check valve, thereby preventing external gas from entering the casing through the exhaust pipe (18) when the gas inside the casing is discharged through the exhaust pipe (18).

4. The large-caliber anti-flagpole cementing special wellhead device according to claim 2 is characterized in that: A pressure gauge (7) for measuring the pressure difference between the drilling fluid inside the casing and the cement slurry outside the casing is provided on one side of the exhaust passage (4); After cementing is completed, the cementing condition of the cement slurry is determined by comparing the value of the pressure gauge (7) with the pre-calculated theoretical pressure difference value.

5. The large-caliber anti-flagpole cementing special wellhead device according to claim 2 is characterized in that: The drill rod (2) is provided with a liquid injection channel (8) inside, and a second tube (9) connected to the liquid injection channel (8) is connected to one side of the drill rod (2), a second valve (10) is provided on the second tube (9), and the second tube (9) is arranged on the top of the end cover (1); Isolation fluid, cementing slurry and displacement fluid are injected into the well through the second pipe (9) and the injection channel (8), and the isolation fluid, cementing slurry and displacement fluid flow into the solidification space between the casing and the well wall.

6. The large-caliber anti-flagpole cementing special wellhead device according to claim 5 is characterized in that: The end cover (1) comprises a sealing plate (11) located at the top of the casing and an annular plate (12) fixedly connected to the outer surface of the sealing plate (11), and the bottom of the annular plate (12) is threadedly connected to the top of the casing; The drill rod (2) comprises a first rod (13) located inside the end cover (1) and a second rod (14) located inside the casing, the first rod (13) being fixedly connected to the end cover (1), and the bottom of the first rod (13) being threadedly connected to the top of the second rod (14); Wherein, the bottom surface height of the end cover (1) is higher than the wellhead height.

7. A large-caliber anti-flagpole cementing method, characterized in that: The large-caliber anti-flagpole cementing special wellhead device according to any one of claims 1 to 6 comprises the following steps: Step 100, place the casing and fix the end cover (1) on the top of the casing; Step 200, injecting liquid, injecting exhaust liquid into the annulus between the casing and the drill pipe (2) through the liquid inlet channel (3); Step 300, exhausting the gas. With the injection of the exhaust liquid, the gas at the top of the casing is exhausted through the exhaust channel (4) due to the pressure difference between the inside and outside of the casing; Step 400: inject cement slurry into the well through the drill pipe (2) to complete cementing.

8. The large-diameter anti-flagpole cementing method according to claim 7 is characterized in that: In step 400, after the injection of cement slurry is completed, extrusion liquid is injected into the annulus between the casing and the drill pipe (2) through the liquid inlet channel (3), so that the cement at the bottom of the drill pipe (2) flows downward to the designed position as a whole, thereby keeping the bottom of the drill pipe (2) away from the cement slurry.

9. The large-diameter anti-flagpole cementing method according to claim 8, characterized in that: The exhaust fluid and the squeeze fluid are both liquids with a density lower than that of the original drilling fluid, so that the injected exhaust fluid and the squeeze fluid are on the top of the original drilling fluid.

10. The large-diameter anti-flagpole cementing method according to claim 9, characterized in that: In step 400, before cement slurry is injected into the drill pipe (2), an isolation fluid is injected into the drill pipe (2) to flush the casing wall and the well wall. After the cement slurry is injected, a displacement fluid is injected into the drill pipe (2) to flush the inner wall of the drill pipe (2).

Images