A method of suspended lateral drilling in a compacted formation

Abstract

The application provides a method for suspended sidetracking in compact strata, and belongs to the technical field of oil drilling and well completion. Before drilling a branch wellbore, a cement plug is first drilled in a bare hole main wellbore, and then the branch wellbore and the suspended window sidetracking are drilled by using the conventional method. The application is aimed at the problem that the compact strata such as carbonate rock and granite are difficult to be suspended and sidetracked, and the method of drilling a cement plug in the main wellbore is used to realize the suspended window sidetracking in the compact strata by using the high drillability of cement, so that the window sidetracking process is greatly simplified, and the construction difficulty is reduced.

Description

Technical Field

[0001] This invention belongs to the field of oil drilling and completion technology, specifically relating to a method for suspended sidetracking in tight formations. Background Technology

[0002] Common sidetracking methods for creating windows in branch wells or fishbone wells include directional drilling and suspended window drilling. Directional drilling is commonly used in cased wells because it is reliable, but requires specialized directional drilling tools, and the reliability of directional drilling tool retrieval is relatively low. Therefore, suspended sidetracking can be used for window creation in open-hole sections, which does not require specialized tools, leaves no tools in the wellbore, and ensures unobstructed wellbore flow.

[0003] When developing sandstone reservoirs and coalbed methane using branch wells or fishbone horizontal wells, the suspended window sidetracking method is often employed. First, the branch wellbore is drilled, with the tool face facing upwards. Figure 1a As shown), sliding drilling is used to move the branch wellbore trajectory away from the main wellbore, and then the azimuth is adjusted to complete the branch wellbore drilling. Figure 1b As shown), then continue drilling forward in the main wellbore. At this time, the suspended window side-drilling technique is commonly used, that is, the tool face downwards (as shown). Figure 1c As shown), relying on gravity, with low or even zero drilling pressure, grooves and pits are slowly made on the lower wellbore to form a support surface. Then, the drilling pressure is gradually increased to slide drilling, causing the wellbore trajectory to deviate downwards, forming a wall between the main wellbore and the branch wellbore. Gradually, the main wellbore and the branch wellbore are separated, completing the suspended window side drilling, followed by normal composite drilling. Figure 1d (As shown), the main wellbore is completed.

[0004] Chinese patent publication CN 111197461 A discloses a method and tool for suspended sidetracking of horizontal wells, which solves the problem of pressure buildup during suspended sidetracking of horizontal wells, allowing the sidetracking process to continue. The main technical solution of this invention is as follows: sliding sidetracking is performed during the first drilling period, stopping when the drilling pressure continues to rise without returning to normal; the location of the sidetracking point is selected; the sidetracking tool is selected; starting from the sidetracking point, a second drilling period is used for composite sidetracking; the composite sidetracking is configured such that the sidetracking tool and the drill bit rotate simultaneously during drilling.

[0005] The journal *Western Exploration Engineering*, 2010, Vol. 1, B2, disclosed a suspended side-drilling double-step horizontal well trajectory control technology. The side-drilling uses a 2.25° large screw. The operation steps are as follows: (1) Drill down to 1297m and ream to 1332m with a 50° tool face; (2) Run the drill string idle for 1 hour at 1332m; (3) Maintain a drill pressure of 0.2-0.5t in the 1323.5m section, with a tool face of 70° and a drilling speed of 3m / h, and start side-drilling; (4) After drilling a single section, apply a drill pressure of 80Kn. The reverse torque is large, the drilling speed is normal, and 80% of the new rock cuttings are returned, proving that a new wellbore has been drilled and the side-drilling is initially successful.

[0006] The journal "Natural Gas Exploration and Development" published in Volume 32, Issue 3, 2009, "Application Practice of Suspended Sidetracking Technology for Horizontal Wells in Abrasive Hard Formations of Moxi Gas Field". The suspended sidetracking technology measures are as follows: (1) Grooving: When the well depth is 3152m, the inclination is measured and the tool face is placed at 150°, and the tool face is kept relatively stable. The groove is repeatedly pulled up and down. (2) Controlling the drilling time: After drilling to a well depth of 3164m, the drilling speed is gradually increased. Drilling is done at 1m / h for 2m, and then the speed is increased to 1.5m / h. The gravity high-side tool face is gradually placed at 120, 90, 60 and other azimuths. The azimuth is twisted and the inclination is increased to completely separate the two wellbores. Normal pressure drilling can be carried out when the well inclination is significantly changed by more than 1° as seen on the MWD.

[0007] Sandstone and coalbed methane reservoirs have a high success rate for suspended side-drilling because the rock strata are relatively soft. However, for carbonate and granite reservoirs, the rock strata are dense and hard, making it difficult to create a hole on the well wall when drilling with zero drilling pressure. Increasing the drilling pressure often results in the well sliding into the branch wellbore, making it difficult to achieve the suspended window side-drilling process.

[0008] For dense and hard formations such as carbonate rocks and granites, with stable well walls, open-hole completion fishbone horizontal wells are an ideal development method. However, because it is impossible to perform suspended side-drilling, the only option is to use directional drilling, which greatly increases the difficulty and risk of developing branch wells. Summary of the Invention

[0009] The purpose of this invention is to solve the problems existing in the prior art and provide a method for suspended side drilling in dense formations. This method addresses the problem that it is impossible to make grooves and holes in hard and dense formations such as carbonate rocks. It utilizes the low hardness of cement plugs to achieve the function of making grooves and holes, thereby realizing suspended window side drilling in hard formations.

[0010] This invention is achieved through the following technical solution:

[0011] This invention provides a method for suspended side-drilling in tight formations. Before drilling the branch wellhead, a cement plug is first installed in the open main wellbore, and then the branch wellbore and suspended window side-drilling are performed.

[0012] A further feature of the present invention is:

[0013] The method specifically includes the following steps:

[0014] Step 1: Insert a cement plug into the main borehole.

[0015] Step 2, drill branch wells;

[0016] Step 3, drill from the side to create a suspended window.

[0017] A further feature of the present invention is:

[0018] In step 1, the length of the cement plug is greater than the length of the overlapping section between the branch wellbore and the main wellbore.

[0019] A further feature of the present invention is:

[0020] The length of the cement plug in step 1 is preferably 30-40m.

[0021] A further feature of the present invention is:

[0022] Step 2 involves drilling branch wells as follows:

[0023] With the tool facing upwards or sideways, first use a bent screw with a preset angle of 2-2.5 degrees to climb upwards on the cement plug at a build-up rate of 20° / 30m, quickly moving away from the main wellbore; then use a single bent screw with a preset angle of 1.5 degrees for directional and composite drilling.

[0024] A further feature of the present invention is:

[0025] Step 3, the side drilling for opening a window in mid-air, specifically involves:

[0026] After the branch well is drilled, the tool face is turned downwards, and the drill bit grooves and pits are made on the cement plug to form a drill bit support surface; then the drill bit pressure is increased, and normal compound drilling is carried out to complete the suspended window side drilling.

[0027] A further feature of the present invention is:

[0028] When drilling sideways with a suspended window, a single-bend screw with a preset angle of 2-2.5 degrees is used.

[0029] A further feature of the present invention is:

[0030] When grooving or creating a pit, the drill bit pressure should be 0-0.5t.

[0031] A further feature of the present invention is:

[0032] During normal composite drilling, the drill bit pressure is 0.5-1.5t.

[0033] A further feature of the present invention is:

[0034] For the first 10m of suspended window side drilling, side drilling is carried out using the time-controlled drilling method, with a drilling speed not exceeding 0.5m / h and a drill bit pressure of 0-0.5t; from 10m to 20m, the drill bit pressure is increased to 0.5-1.5t.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] This invention addresses the problem of difficult suspended window side-drilling in dense formations such as carbonate rocks and granites. It adopts a method of first inserting a cement plug into the main wellbore, and takes advantage of the high drillability of cement to achieve suspended window side-drilling in dense formations.

[0037] This invention enables suspended window drilling in dense and hard strata such as carbonate rocks, greatly simplifying the window drilling process and reducing construction difficulty. Attached Figure Description

[0038] Figure 1a This is a schematic diagram of existing suspended window side drilling with the tool face facing upwards;

[0039] Figure 1b This is a schematic diagram of existing suspended window side drilling with twisting azimuth;

[0040] Figure 1c This is a schematic diagram of existing suspended window side drilling with the tool face facing downwards;

[0041] Figure 1d This is a schematic diagram of composite drilling in existing suspended window side drilling;

[0042] Figure 2 This is a schematic diagram of cement plugging the main wellbore in a suspended side-drilling method for tight formations according to the present invention.

[0043] Figure 3 This is a schematic diagram of branch well drilling;

[0044] Figure 4 This is a schematic diagram of the suspended window side drilling of the present invention.

[0045] In the diagram, 1 is the main wellbore, 2 is the cement plug, and 3 is the branch wellbore. Detailed Implementation

[0046] The present invention will now be described in further detail with reference to the accompanying drawings:

[0047] The essence of this invention is to address the problem that it is impossible to groove and create pits in hard and dense strata such as carbonate rocks. By utilizing the low hardness of cement plugs, the grooving and pitting functions can be achieved, thereby enabling suspended window drilling in hard strata.

[0048] The cement plug is located in the main wellbore. Because the cement plug has a relatively low hardness, it is softer than hard and dense formations such as carbonate rocks. Therefore, the drill bit can groove and create a notch in the cement plug. Once the notch is created, the drill bit has a bearing surface, allowing for the application of drilling pressure and enabling lateral drilling. This allows for suspended side-drilling in hard formations. Without a cement plug, it would be difficult to create a notch in hard formations, leaving the drill bit without a bearing surface. Applying drilling pressure would cause the drill bit to slide directly into the branch wellbore.

[0049] The present invention provides a method for suspended side-drilling in tight formations. For tight and hard reservoirs such as carbonate rocks, before drilling the branch wellhead, a cement plug 2 is first installed in the open-hole main wellbore 1, and then the branch wellbore 3 and suspended window side-drilling are carried out in accordance with conventional methods.

[0050] An embodiment of the suspended side-drilling method for tight formations of the present invention is as follows:

[0051]

Example 1

[0052] The method specifically includes the following steps:

[0053] Step 1: Insert a section of cement plug 2 into the open-hole main wellbore 1, such as... Figure 2 As shown;

[0054] The construction process for cement plugging does not require any special techniques or cement hardness requirements, because the side-drilling process for cement plugging is a conventional and mature technique.

[0055] Furthermore, the length of the cement plug should be greater than the length of the overlapping section between the branch wellbore and the main wellbore, generally about 30-40m.

[0056] Step 2, drill branch well 3, such as Figure 3 As shown;

[0057] Drilling a branch well simply means moving the branch well off from the main wellbore. However, in order to drill the main wellbore from below after drilling the branch well, the branch well needs to be drilled upwards. This allows the drill string to utilize its weight during side-drilling, and it's easier to create grooves and recesses downwards. If the branch well is below the main wellbore, gravity cannot be utilized during side-drilling, making it even more difficult to create grooves and recesses.

[0058] Generally, when drilling branch wells, the tool face can be upward or sideways. A bent screw with a preset angle of 2-2.5 degrees can be used to climb up the cement plug at a build-up rate of 20° / 30m to quickly move away from the main wellbore. Then, a single bent screw with a preset angle of 1.5 degrees can be used to meet the requirements of directional and composite drilling.

[0059] Drilling branch wells is a single well, so there are no requirements for drilling pressure or time, but data such as well inclination and azimuth are usually determined by drilling-while-drilling (MWD) instruments.

[0060] Step 3, drill from the side to create a suspended window.

[0061] like Figure 4 As shown, after the branch wellbore 3 is drilled, the tool face is turned downwards to make grooves and holes on the cement plug 2. At this time, the drilling pressure is 0-0.5t. Because the hardness of cement is much less than that of carbonate rock, it is easy to make holes and grooves to form a drill bit support surface. Then the drilling pressure is increased to 0.5-1.5t, and normal composite drilling is carried out to form the main wellbore and complete the suspended window side drilling process in tight formation.

[0062] It should be noted that the tool face downwards can make the most of gravity. The angle of the tool is determined by the single-bend screw, and a single-bend screw with a preset angle of 2-2.5 degrees is generally sufficient.

[0063] Furthermore, in general, the first 10m of suspended side drilling is carried out using the time-controlled drilling method, with a drilling speed of no more than 0.5m / h and a drilling pressure of 0-0.5t; the drilling pressure can be increased to 0.5-1.5t from 10m to 20m.

[0064] In this invention, the side-drilling method and cement plugging do not require new tools; existing tools can be used.

[0065] The method of the present invention will be further explained below using the Ordovician carbonate reservoir in the Shunnan block of the Tarim Basin as an example.

[0066]

Example 2

[0067] The Ordovician carbonate reservoir in the Shunnan block of the Tarim Basin is a dense and stable carbonate formation, and open-hole completion is usually adopted.

[0068] Because it is a fractured-vuggy reservoir, branch well development is adopted. Connecting multiple fractured-vuggy reservoirs with a single well can significantly increase the production of a single well, increase the area of ​​reserve control per well, and reduce development costs. However, due to the dense reservoir and high confining pressure, it is difficult to form a tool face during suspended sidetracking. Methods such as directional drilling tools are required to sidetrack the reservoir. However, with directional drilling tools, the tool must be retrieved after sidetracking before drilling other branch wells can continue. The success rate of retrieving directional drilling tools in ultra-deep wells is low, which greatly increases the construction risk of branch wells.

[0069] According to the method of this invention, a cement plug is first injected into the horizontal section of the main wellbore. After it sets, the branch wellbore is drilled with the tool face facing upward. Then, the branch wellbore is completed. Since the drilling and completion of the branch wellbore has not yet been done by side-drilling with a window, there is no problem of wellbore re-entry.

[0070] After the branch well is completed, the tool face is facing downwards, and the drill is slid-drilled, slowly creating grooves and pits in the cement to form the tool face, i.e., the support face. Then, the drilling pressure is increased, and the drill is advanced. Since the branch well is above the main well at this point, the drill string or completion string is side-drilled along the bottom of the main well, preventing accidental entry into the branch well and thus avoiding the problem of re-entry.

[0071] This invention addresses the problem of difficult suspended window side-drilling in dense formations such as carbonate rocks and granites. It adopts a method of first inserting a cement plug into the main wellbore, and takes advantage of the high drillability of cement to achieve suspended window side-drilling in dense formations.

[0072] This invention enables suspended window drilling in dense and hard strata such as carbonate rocks, greatly simplifying the window drilling process and reducing construction difficulty.

[0073] Finally, it should be noted that the above technical solution is only one embodiment of the present invention. For those skilled in the art, based on the application methods and principles disclosed in the present invention, it is easy to make various types of improvements or modifications, and not limited to the methods described in the above specific embodiments of the present invention. Therefore, the methods described above are only preferred and have no limiting significance.

Claims

1. A method for suspended side-drilling in tight formations, characterized in that, Before drilling the branch well, a section of cement plug is first installed in the open-hole main wellbore, and then the branch wellbore and suspended window side drilling are performed. The method specifically includes the following steps: Step 1: Install a cement plug in the main open-hole well. The length of the cement plug should be greater than the length of the overlapping section between the branch well and the main well. Step 2, Drilling branch wells: With the tool face upward or sideways, first use a bent screw with a preset angle of 2-2.5 degrees to climb upward on the cement plug at a build-up rate of 20° / 30m, quickly moving away from the main wellbore; then use a single bent screw with a preset angle of 1.5 degrees for directional and combined drilling; Step 3, Suspended window side-drilling: After the branch well is drilled, the tool face is downward, and the drill bit grooves and pits are made on the cement plug to form a drill bit support surface; then the drill bit pressure is increased, and normal composite drilling is carried out in the tight formation to complete the suspended window side-drilling in the tight formation.

2. The method for suspended side-drilling in tight formations according to claim 1, characterized in that, The length of the cement plug in step 1 is 30-40m.

3. The method for suspended side-drilling in tight formations according to claim 1, characterized in that, When drilling sideways with a suspended window, a single-bend screw with a preset angle of 2-2.5 degrees is used.

4. The method for suspended side-drilling in tight formations according to claim 1, characterized in that, When the drill bit is grooving or creating a hole in the cement plug, the drilling pressure is 0-0.5t.

5. The method for suspended side-drilling in tight formations according to claim 1, characterized in that, During normal composite drilling in tight formations, the drill bit pressure is 0.5-1.5t.

6. A method for suspended side-drilling in tight formations according to any one of claims 3-5, characterized in that, When drilling sideways with a suspended window, the first 10m should be drilled using the time-controlled drilling method, with a drilling speed not exceeding 0.5m / h and a drill bit pressure of 0-0.5t; from 10m to 20m, the drill bit pressure should be increased to 0.5-1.5t.

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