A three-opening well cementing anti-channeling method

Abstract

This invention discloses a three-section cementing anti-pressure channeling method, in which a horizontal well and a vertical well are connected; the vertical well is filled with sand, with the top of the sand above the connection point; a pressure gauge is installed at the inlet of the vertical well; the horizontal well casing is designed and the quantities of low-density cement slurry and high-density cement slurry are calculated before cementing; during the horizontal well casing cementing construction, low-density cement slurry is used first, followed by high-density cement slurry; the pressure gauge changes at the vertical wellhead are observed in real time during cementing; after setting, the vertical well is flushed with sand and the horizontal well is cleaned. This invention injects cementing slurry into the three-section casing, injecting both low-density and high-density cement slurry according to the designed quantities. The low-density cement slurry is located in the annulus between the second and third sections of the casing, while the high-density cement slurry is located in the annulus between the horizontal section of the L-shaped horizontal well and the open hole. The dual-density cement slurry effectively reduces the pressure of the cement slurry on the bottom of the well and effectively controls the pressure difference between the two ends, thereby improving the three-section cementing process for three-type wells.

Description

Technical Field

[0001] This invention relates to the field of three-section cementing technology, specifically to a three-section cementing anti-pressure channeling process for remotely connected U-shaped wells. Background Technology

[0002] The remote connecting well, also known as a "U"-shaped well, is formed by connecting an "L"-shaped directional horizontal well and a vertical drainage well. It combines the advantages of a horizontal well (effective communication with the coal seam) and a vertical well (strong drainage stability), making it widely used in coalbed methane development. Correspondingly, the construction difficulty of a "U"-shaped well is significantly higher than that of an "L"-shaped well. The completion stage involves multiple steps, including drilling and docking, running production casing and cementing, and secondary connection through wellbore drilling and cavity creation. The third-stage cementing of the horizontal well, ensuring the stability of the gas-water migration channel, is the most critical process in the entire U-shaped well construction. Improper cementing operations can easily lead to cement slurry from the horizontal well entering the vertical drainage well, preventing proper docking and connection.

[0003] In horizontal well cementing construction, traditional oil cementing techniques are used. High-density cement slurry of about 1.85 g / cm3 is selected for cementing the production casing. There is a risk that the cement slurry may be directly injected into the vertical well, resulting in abnormal connection between the horizontal and vertical wells after the well is completed.

[0004] For example, the existing literature with publication number CN114607318A, entitled "Collaborative Construction Method of Drilling and Fracturing for Multi-Layer Horizontal Well Co-production in Deep Coalbed Methane," records this method. Specifically, it discloses that "the horizontal well section adopts a two-stage large-diameter wellbore structure. In the first stage, drilling reaches 20m below the bedrock surface, and surface casing is run in, with cement slurry returning to the surface. In the second stage, the drill bit is drilled to the landing point of the A1 coal seam, and a second-stage technical casing is run in, using 1.7-1.8g / cm3 high-density cement slurry for cementing. The purpose is to improve the cementing quality of the second-stage casing in the engineering section, facilitate subsequent repeated side-drilling of the horizontal well, and reduce construction risks." This technology uses high-density cement slurry for casing cementing. However, this direct injection into the vertical well may cause abnormal connection between the horizontal and vertical wells after docking completion, and may also lead to pressure channeling. Furthermore, if pressure channeling occurs in the vertical well, drilling equipment needs to be reinstalled to create a cavity and perform a secondary docking, increasing costs and safety risks, and seriously affecting the construction period. Summary of the Invention

[0005] The technical problem to be solved by this invention is: how to solve the problems of abnormal connection between horizontal and vertical wells and pressure channeling caused by the current general use of high-density cement slurry in cementing.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A three-stage cementing method for preventing pressure channeling includes the following steps:

[0008] Step 1: The horizontal well and the vertical well are connected.

[0009] Step 2: Fill the vertical well with sand, with the top of the sand above the docking point;

[0010] Step 3: Install a pressure gauge at the inlet of the vertical well;

[0011] Step 4: Design before cementing of horizontal downhole casing, and calculate the amount of low-density cement slurry and high-density cement slurry;

[0012] Step 5: Horizontal well casing cementing construction. First, use low-density cement slurry for cementing, and then replace it with high-density cement slurry.

[0013] Step 6: During the cementing process, observe the changes in the pressure gauge at the wellhead of the vertical well in real time until the cementing is completed;

[0014] Step 7: Allow the well to set, and then flush the sand from the vertical well and clean the plug from the horizontal well.

[0015] This invention injects cement slurry into the three-section casing, injecting both low-density and high-density cement slurry according to the designed amount. The dual-density cement slurry can effectively reduce the pressure of the cement slurry on the bottom of the well and effectively control the pressure difference between the two ends. At the same time, this application fills the vertical well with sand and installs a pressure gauge at the inlet of the vertical well. The design of the diameter sand filling can block the cement slurry penetration and pressure transmission, while the design of the pressure gauge can monitor the pressure changes during the cementing process at all times. This achieves the perfection of the three-section cementing process of the three-type well, effectively prevents mud pressure channeling, and ensures normal communication between the horizontal well and the vertical well.

[0016] As a further aspect of the present invention: in step 2, the height of the sand top is 10-20m above the docking point.

[0017] As a further aspect of the present invention: in step 5, low-density cementing is performed twice, followed by high-density cementing three times.

[0018] As a further aspect of the present invention: the sand used in step 2 is quartz sand with a mesh size of 20 to 40.

[0019] As a further aspect of the present invention: the horizontal well is L-shaped, and the horizontal well and the vertical well form a U-shaped well.

[0020] As a further aspect of the present invention: the calculation formulas for the amount of low-density cement slurry and high-density cement slurry in step 4 are as follows:

[0021]

[0022] Where: r1—drilling radius;

[0023] r2—Sleeve radius;

[0024] k—wellbore enlargement rate;

[0025] L—Length of well section.

[0026] As a further aspect of the present invention: before cementing in step 4, a cement head is connected to the wellhead of the horizontal well. A grouting port one and a grouting port two are opened on the cement head. The grouting port one is close to the wellhead of the horizontal well, and a displacement rubber plug is installed inside the cement head, with the displacement rubber plug located between the two grouting ports. Then, the cement truck, ash tanker truck, and mud pump are connected by pipelines to prepare for cementing construction.

[0027] As a further aspect of the present invention, the grouting process in step 5 is as follows:

[0028] S1. Inject isolation fluid into the three-way sleeve from the cement head grouting port;

[0029] S2. Inject cement slurry into the three-section casing, i.e. inject low-density cement slurry according to the design amount, and then inject high-density cement slurry according to the design amount.

[0030] S3. Inject clean water displacement liquid into the cement head grouting port 2. Use the displacement rubber plug to replace the high-density cement grout and low-density cement grout into the outer annulus of the casing until the displacement rubber plug is pushed to the bottom of the casing floating hoop. The casing is then filled with clean water.

[0031] As a further aspect of the present invention: the displacement solution in step S3 is water.

[0032] As a further aspect of the present invention: after cementing in step 6, the high-density cement slurry is located in the annulus between the horizontal section of the casing and the open hole in the L-shaped horizontal well, and the low-density cement slurry is located in the annulus between the second and third casing sections.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] First, this invention injects cement slurry into the three-section casing, injecting both low-density and high-density cement slurry according to the designed amount. The low-density cement slurry is located in the annulus between the two-section and three-section casings, while the high-density cement slurry is located in the annulus between the horizontal section casing and the open hole in the L-shaped horizontal well. The dual-density cement slurry can effectively reduce the pressure of the cement slurry on the bottom of the well and effectively control the pressure difference between the two ends, thereby improving the three-section cementing process for the three-section well.

[0035] Secondly, this invention involves filling the vertical well with high-density quartz sand, specifically 20-40 mesh quartz sand. The sand is typically filled to a depth of 10-20m above the cavity section where the two wells meet. The diameter of the sand filling is designed to prevent cement slurry penetration and pressure transmission. Simultaneously, a pressure gauge is installed at the vertical well inlet. This pressure gauge allows for real-time monitoring of the wellhead pressure during cementing of the horizontal well, enabling control over pressure changes in both the horizontal and vertical wells. This further improves the three-stage cementing process for the three-well type.

[0036] Finally, after cementing, the present invention allows for a three-day settling period. After three days of settling, a small-diameter drill string is used to flush sand from the vertical well and clean the plugs from the L-shaped horizontal well. The L-shaped horizontal well is then flushed with clean water to flush out the quartz sand, thus achieving connectivity of the U-shaped well. The vertical wellhead returns water normally, and the connectivity is normal. The final plugging is then used to conduct a final completion test on the U-shaped well to ensure its normal use. Attached Figure Description

[0037] Figure 1 This is a schematic diagram illustrating the current situation of pressure channeling in cementing before improvements were made to the cementing process.

[0038] Figure 2 This is a schematic diagram of the improved cementing process according to an embodiment of the present invention;

[0039] Figure 3 This is a schematic diagram of pressure distribution according to an embodiment of the present invention;

[0040] Figure 4 This is a schematic diagram of the cementing equipment connection according to an embodiment of the present invention;

[0041] Figure 5 This is a schematic diagram of the cement head and displacement plug according to an embodiment of the present invention;

[0042] Figure 6 This is the cementing operation process for a U-shaped well according to an embodiment of the present invention.

[0043] Explanation of reference numerals in the attached diagram: 1. Cement head; 2. Grouting port one; 3. Wellhead connector; 4. Displacement plug; 5. Grouting port two; 6. Pressure gauge; 7. Horizontal section of horizontal well; 8. High-density cement slurry; 9. Low-density cement slurry. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Reference Figure 1 A three-section cementing method for preventing pressure channeling includes an L-shaped horizontal well and a vertical well, wherein the L-shaped horizontal well is drilled to the enlarged section (connection point) of the vertical well to form a U-shaped well (e.g., Figure 1 and Figure 2 As shown in the figure, the casing installation for the third section was completed, and the conditions for cementing construction were met. It also includes cementing the L-shaped horizontal well with dual-density cement slurry, filling the connection between the L-shaped horizontal well and the vertical well with sand, and installing a wellhead pressure gauge at the wellhead of the vertical well to monitor the pressure changes at the bottom of the well in real time.

[0046] Reference Figure 5 A cement head 1 is connected to the wellhead of an L-shaped horizontal well. A grouting port 1 2 and a grouting port 2 5 are opened on the cement head 1. The grouting port 1 2 is close to the wellhead of the L-shaped horizontal well. A displacement rubber plug 4 is installed inside the cement head 1 and the displacement rubber plug 4 is located between the two grouting ports. The grouting port 2 5 of the cement head is used to inject clean water displacement fluid, and the grouting port 1 2 is used to inject cement slurry.

[0047] Reference Figure 2 , Figure 4 and Figure 6 This application requires sand filling at the vertical well connection point before cementing, i.e. Figure 2 The sand filling is used to block the transmission of pressure during the cementing process. Specifically, the operation vehicle is used to fill the vertical well with sand. High-density quartz sand (20-40 mesh quartz sand) should be used to fill the sand to 10-20m above the cavity section where the two wells are connected. Only after the sand filling is completed can the cementing operation be carried out on the horizontal well. Then, the cement truck, ash tanker truck and mud pump are connected with pipelines to prepare for cementing construction.

[0048] Reference Figure 2 and Figure 6 Before cementing, this application requires the installation of a pressure gauge 6 at the vertical wellhead. This pressure gauge will be used to monitor the wellhead pressure in real time during the cementing process, allowing for the tracking of pressure changes in both the horizontal and vertical wells (e.g., ...). Figure 3 The pressure is displayed after real-time monitoring, and a pressure distribution map is drawn.

[0049] Reference Figure 2 and Figure 6 This application requires calculation of the usage of low-density cement slurry 9, high-density cement slurry 8, and displacement fluid during cementing. Specifically, the water-cement ratio of the low-density and high-density cement slurries is calculated before cementing, using the following formula:

[0050] ①

[0051] In formula ①: —The density of cement is generally taken as 3.1 g / cm3;

[0052] K – Water-cement ratio.

[0053] — The density of cement paste is generally 1.6 g / cm3 for low density and 1.89 g / cm3 for high density.

[0054] Ground tests were conducted on the properties of the two types of cement slurry to ensure that the performance parameters of the two densities of cement slurry met the design requirements.

[0055] Table 1 Properties of Cement Grout

[0056]

[0057] As can be seen from Table 1, the materials used in Formula 1 are Jiahua G-grade high-strength cement + dispersant + stabilizer + water loss reducer + anti-gas channeling agent; while the materials used in Formula 2 are Jiahua G-grade high-strength cement + fly ash + stabilizer + water loss reducer. Laboratory performance tests (the specific test procedures are not the technical points to be protected in this application) show that the density of Formula 1 is 1.89 g / cm³, which is the high-density cement slurry 8 proposed in this application; while the density of Formula 2 is 1.6 g / cm³, which is the low-density cement slurry 9 proposed in this application.

[0058] (2) The formula for calculating the amount of cement grout is as follows:

[0059] ②

[0060] In formula ②: r1—drilling radius;

[0061] r2—Sleeve radius;

[0062] k—well diameter enlargement rate, which is usually taken as 115% for the horizontal section 7 of an L-type horizontal well;

[0063] L – Well section length. In an L-shaped horizontal well, horizontal section 7 is a high-density well section, while the rest are low-density well sections.

[0064] (3) Dual-density cement slurry cementing reduces the pressure per kilometer of vertical depth by more than 3 MPa compared to conventional cementing methods. The bottom hole pressure is calculated as follows:

[0065] ③

[0066] In formula ③: — Cement grout density;

[0067] H – Vertical depth of the well section.

[0068] The specific operating principle of this application is as follows:

[0069] Step 1: Drill the L-shaped horizontal well to the enlarged section of the vertical well (connection point) to form a U-shaped well, complete the three-stage casing installation, and meet the conditions for cementing construction;

[0070] Step 2: Before cementing, fill the vertical well with sand, preferably 20-40 mesh quartz sand, up to 10-20m above the connection point;

[0071] Step 3: After completing the sand filling construction, close the vertical wellhead and install a pressure gauge at the vertical wellhead;

[0072] Step 4: Calculate the amount of dual-density cement slurry and displacement fluid before cementing: Calculate the amount of low-density cement slurry 9 using formula ②, where the length L of the low-density section is the depth of the second section; calculate the amount of high-density cement slurry 8 using formula ②, where the length L of the high-density section is the depth of the horizontal section; determine the amount of displacement fluid (clear water) by calculating the volume inside the third casing, where L is the depth of the third casing.

[0073] Step 5: Connect the cement head to the L-shaped horizontal wellhead and install the displacement rubber plug. Complete the connection of pipelines such as cement truck, ash tanker, and mud pump, and prepare for cementing construction.

[0074] Step 6: The cementing operation consists of three steps: ① First, inject 6 m³ (the volume of clean water) of isolation fluid (clean water) into the three-section casing through cement head injection port 2 to isolate the subsequent cement slurry from the mud in the well and avoid damaging the performance of the cement slurry; ② Inject cement slurry into the three-section casing: inject low-density cement slurry 9 according to the design amount, followed by high-density cement slurry 8 according to the design amount; the dual-density cement slurry can effectively reduce the pressure of the cement slurry on the bottom of the well; ③ Inject clean water displacement fluid through cement head injection port 25, and use the displacement rubber plug to displace the high and low density cement slurries to the outer annulus of the casing until the displacement rubber plug 4 is pushed to the bottom float collar of the casing, and the casing is filled with clean water;

[0075] Step 7: During the cementing process, observe the changes in the pressure gauge 6 at the wellhead of the vertical well in real time until the cementing is completed;

[0076] Step 8: Complete the cementing operation. At this time, the high-density cement slurry 8 is located in the annulus between the horizontal section 7 casing and the open hole, and the low-density cement slurry 9 is located in the annulus between the second and third casings.

[0077] Step 9: After three days of waiting for the sediment to settle, use a small-diameter drill string to flush sand from the vertical well and clean the plug from the L-shaped horizontal well.

[0078] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A three-stage cementing method for preventing pressure channeling, characterized in that, Includes the following steps: Step 1: The horizontal well and the vertical well are connected. Step 2: Fill the vertical well with sand, with the top of the sand above the docking point; Step 3: Install a pressure gauge at the inlet of the vertical well; Step 4: Design before cementing of horizontal downhole casing, and calculate the amount of low-density cement slurry and high-density cement slurry; The formulas for calculating the amount of low-density cement paste and high-density cement paste are as follows: Where: r1—drilling radius; r2—Sleeve radius; k—wellbore enlargement rate; L—Well section length; Before cementing, a cement head is connected to the wellhead of the horizontal well. A grouting port one and a grouting port two are opened on the cement head. The grouting port one is close to the wellhead of the horizontal well, and a displacement rubber plug is installed inside the cement head, with the displacement rubber plug located between the two grouting ports. Then, the cement truck, ash tanker truck, and mud pump were connected with pipelines to prepare for cementing operations; Step 5: Horizontal well casing cementing construction. First, use low-density cement slurry for cementing, and then replace it with high-density cement slurry. The grouting process is as follows: S1. Inject isolation fluid into the three-way sleeve from the cement head grouting port; S2. Inject cement slurry into the three-section casing, i.e. inject low-density cement slurry according to the design amount, and then inject high-density cement slurry according to the design amount. S3. Inject the displacement liquid from the cement head grouting port 2. Use the displacement rubber plug to replace the high-density cement grout and low-density cement grout to the outer annulus of the casing until the displacement rubber plug is pushed to the bottom of the casing floating hoop and the casing is filled with displacement liquid. Step 6: During the cementing process, observe the changes in the pressure gauge at the wellhead of the vertical well in real time until the cementing is completed; after the cementing is completed, the high-density cement slurry is located in the annulus between the horizontal section of the casing and the open hole in the horizontal well, and the low-density cement slurry is located in the annulus between the second and third casing sections. Step 7: Allow the well to set, and then flush the sand from the vertical well and clean the plug from the horizontal well.

2. The method for preventing pressure channeling in three-stage cementing as described in claim 1, characterized in that, In step 2, the height of the sand top is 10-20m above the docking point.

3. A three-stage cementing anti-pressure channeling method according to claim 1 or 2, characterized in that, In step 5, low-density cementing is performed twice, followed by high-density cementing three times.

4. The method for preventing pressure channeling in three-stage cementing as described in claim 1, characterized in that, The sand used in step 2 is quartz sand with a mesh size of 20 to 40.

5. The method for preventing pressure channeling in three-stage cementing as described in claim 1, characterized in that, The horizontal well is L-shaped, and the horizontal well and the vertical well form a U-shaped well.

6. The method for preventing pressure channeling in three-stage cementing as described in claim 1, characterized in that, The displacement fluid in step S3 is water.

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