Construction device and construction method for surface open-circuit drilling of shallow gas wells for development wells

Abstract

The present invention relates to a construction device and a construction method for surface open-circuit drilling of shallow gas drilling in development wells. The construction device of the present invention comprises a conduit fixing frame fixed on the seabed, on which an underwater conduit deep into the seawater and an extension conduit extending out of the sea level are fixed, and the underwater conduit and the extension conduit are connected after the shallow gas is discharged; the construction method of the present invention comprises: firstly sinking the underwater conduit into the seawater; then drilling in the underwater conduit so that the shallow gas is discharged into the seawater through the underwater conduit, and then connecting the extension conduit on the top of the underwater conduit to form a waterproof conduit; finally, continuing drilling in the waterproof conduit. The construction device and the construction method for surface open-circuit drilling of shallow gas drilling in development wells provided by the present invention implement surface open-circuit drilling by establishing an underwater conduit, and the gas released from the shallow stratum during the drilling process overflows and is discharged into the seawater through the underwater conduit, so as to avoid the shallow gas returning to the drilling well or the production platform to cause a blowout and fire, thereby affecting the safety of the drilling operation.

Description

Technical Field

[0001] The invention relates to the technical field of offshore shallow gas drilling, in particular to a construction device and a construction method for surface open-circuit drilling of shallow gas drilling in a development well. Background Art

[0002] The existing offshore shallow gas drilling circuit is usually opened by lowering the first layer of drilling riser pipe. The bottom of the drilling riser pipe sinks to the seabed, and the top of the riser pipe is fixed at the altitude of different decks on the production platform. During the drilling process of shallow seabed formations, the drill pipe connected to the drilling platform rig passes through the riser pipe, and seawater is pumped into the drill pipe by a drilling pump. The seawater passes through the internal channel of the drill pipe to reach the drill bit at the bottom of the drill pipe. During the drilling process, the seawater carries the seabed shallow formation cuttings or shallow gas (natural gas dispersed or accumulated in the shallow formation) destroyed by the drill bit and water jet in the wellbore along the wellbore to the riser pipe, returns to the top of the riser pipe located above the platform deck through the annular space between the riser pipe and the drill pipe, and then overflows into the sea above the sea surface and falls into the seawater. The discharged shallow gas is prone to blowout and fire on the platform deck, affecting the safety of drilling operations.

[0003] In this drilling and opening method, since the watertight pipe goes directly from the wellbore to the operating wellhead, a diverter must be installed at the wellhead to prevent shallow gas blowouts. The quality and functional reliability of the diverter are the key to preventing and controlling the risk of shallow gas blowouts. Since the flow pipelines in the diverter system are easily eroded by the cuttings carried by the shallow gas under high pressure and high flow rate, it is very easy to cause the diverter system to fail, causing the risk of natural gas leakage and platform fire. In addition, the installation process of the diverter is relatively cumbersome. In the narrow wellhead area of ​​the offshore platform, it is difficult to safely arrange the nozzle on the diverter, and it is not convenient to temporarily fix it. It will affect the normal production operation of the adjacent producing wells and the safety of the wellhead. There are also certain risks in the simultaneous joint operation of drilling and production. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to provide a construction device and a construction method for surface open-circuit drilling of shallow gas drilling in development wells. There is no need to install a diverter. The surface open-circuit drilling is implemented by establishing an underwater conduit. During the drilling process, the shallow gas released from the shallow strata returns to the top of the conduit through the wellbore established by the underwater conduit and dissipates into the sea water, so as to avoid the shallow gas returning to the wellhead or the production platform to cause blowout and fire, affecting the safety of the drilling operation.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The construction device for surface open-circuit drilling of shallow gas drilling in development wells described in the present invention comprises a conductor pipe fixing frame and a watertight conductor pipe, the bottoms of the watertight conductor pipe and the conductor fixing frame both extend into the seabed; the conductor fixing frame comprises a plurality of conductor frame pile legs and a plurality of conductor frame platforms, the plurality of conductor frame platforms are horizontally arranged in sequence and arranged in parallel up and down, and the conductor frame platform of the topmost layer extends out of the sea level; a plurality of conductor frame pile legs are vertically arranged in sequence and distributed in an array around the plurality of conductor frame platforms and fixed to each layer of conductor frame platforms; the watertight conductor pipe is composed of an extension conductor and an underwater conductor connected up and down, and the top of the underwater conductor pipe is submerged in seawater; the underwater conductor pipe is vertically fixed on at least one conductor frame platform below the sea level, and after the shallow gas is discharged, the extension conductor is vertically fixed on at least one conductor frame platform located on the top of the underwater conductor pipe to be connected with the underwater conductor, and the top of the extension conductor extends out of the conductor frame platform of the topmost layer.

[0007] The construction device preferably comprises a plurality of water-blocking pipes, and the plurality of water-blocking pipes are fixed in parallel to each other on the plurality of pipe rack platforms.

[0008] The construction device is preferably provided with a plurality of conduit fixing holes on the conduit rack platform, and the corresponding conduit fixing holes on each layer of the conduit rack platform are coaxially arranged up and down, and each of the watertight conduits is sequentially fixed up and down in a conduit fixing hole on the same axis.

[0009] In the construction device, preferably, the jacket platform comprises at least two layers.

[0010] In the construction device, preferably, the top of the underwater conduit at least extends out of the lowest conduit rack platform.

[0011] In the construction device, preferably, the watertight conductor is sleeved with a surface casing, the bottom of the surface casing is close to the bottom of the wellbore, and the top of the surface casing is suspended at the wellhead.

[0012] The construction method of the construction device for surface open-circuit drilling of shallow gas wells for development wells of the present invention comprises the following steps:

[0013] The bottom of the conductor frame pile leg of the conductor fixing frame is fixed on the seabed, the uppermost conductor frame platform of the conductor fixing frame extends out of the sea level, the bottom of the underwater conductor is sunk into the seabed, the top of the underwater conductor is sunk into the seawater, and then the underwater conductor is fixed on the conductor frame platform through which it passes in sequence;

[0014] Drilling with a drill pipe in an underwater conduit causes shallow seabed gas to flow back through the underwater conduit to the top of the underwater conduit and overflow into the seawater;

[0015] When the drill pipe continues to drill to a depth of 300m to 600m below the seabed, the drill is pulled out after injecting thick slurry;

[0016] An extension conduit is connected to the top of the underwater conduit to form a watertight conduit, and a wellbore is established after the top of the extension conduit extends out of the uppermost conduit rack platform;

[0017] A surface casing is installed in the wellbore, the bottom of the surface casing is lowered to a position close to the bottom of the wellbore, and the top of the surface casing is suspended at the wellhead position;

[0018] Cement slurry is injected into the surface casing pipeline, and the injected cement slurry is displaced by drilling fluid and returned from the bottom of the surface casing into the annular space between the surface casing and the well wall. The cement slurry bonds and seals the surface casing and the well wall to complete the cementing operation.

[0019] In the construction method, preferably, the bottoms of the underwater conduit and the conduit fixing frame extend into the seabed to a depth of at least 30 m, and the bottom of the surface casing is 4-6 m away from the bottom of the wellbore.

[0020] The present invention adopts the above technical solution, which has the following advantages:

[0021] (1) The present invention implements surface open-circuit drilling by establishing an underwater conduit, the top of which is submerged in the seawater. During the drilling process, shallow gas released from the shallow strata on the seabed returns to the top of the conduit through the wellbore established by the underwater conduit and dissipates into the seawater. After the shallow gas is released, an extended conduit is connected to form a watertight conduit, thereby avoiding the risk of shallow gas returning to the drilling or production platform and causing leakage, blowout and fire.

[0022] (2) The present invention does not need to install a diverter at the wellhead to release shallow gas, which not only avoids the installation and use risks of the diverter, but also omits the process of assembling the diverter and pipelines, saves drilling time, and reduces drilling costs.

[0023] (3) Due to the existence of the conduit fixing frame, when drilling and discharging seabed cuttings, the top of the conduit is located on the conduit fixing frame of the seawater section of the conduit frame platform, at a higher position from the seabed. The fixing frame is provided with a guide groove to guide the drill cuttings returned from the top of the conduit out of the wellhead area, so as to avoid the accumulation of drill cuttings in the wellhead area and affect the drilling operation of adjacent wells. The guide groove of the fixing frame with a larger coverage in the seawater can drain the discharged cuttings. After drilling the shallow formation of a well, the watertight conduit in the seawater is connected back to the platform deck, and the wellhead is installed to carry out the drilling operation of the next well section, so as to prevent the cuttings returned from the top of the watertight conduit in the seawater from falling back into the drilled wellbore when drilling the shallow formation of the adjacent well, thereby protecting the wellbore. At the same time, the watertight conduit in the seawater has the function of supporting the drill rod to continue shallow drilling and inclining the well trajectory under the fixing and straightening action of the conduit fixing frame, which is also necessary to put the underwater watertight conduit in the seawater in advance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1It is a structural schematic diagram of the construction device of the present invention.

[0025] Figure 2 It is a schematic diagram of drilling operation of the construction method of the present invention.

[0026] The reference numerals in the figures are as follows:

[0027] 1-jacket platform; 2-jacket pile legs; 3-sea level; 4-underwater jacket; 5-jacket fixing hole; 6-drill pipe; 7-platform deck; 8-wellbore; 9-drill bit; 10-seabed; 11-shallow gas. DETAILED DESCRIPTION

[0028] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings so that the purpose, features and advantages of the present invention can be more clearly understood. It should be understood that the embodiments shown in the accompanying drawings are not intended to limit the scope of the present invention, but are only intended to illustrate the essential spirit of the technical solution of the present invention.

[0029] The present invention provides a construction device and a construction method for surface open-circuit drilling of shallow gas drilling in a development well. Surface open-circuit drilling is carried out by establishing an underwater conduit. During the drilling process, shallow gas released from shallow seabed strata returns to the top of the conduit through the wellbore established by the underwater conduit and dissipates into the seawater. After the shallow gas is released, the conduit is connected (reconnected) and extended to form a conventional shallow water oil and gas field development cluster well water-insulating conduit mode, thereby avoiding the risk of leakage, blowout and fire caused by shallow gas encountered during the drilling of shallow seabed strata returning to the drilling well or production platform, avoiding the cumbersome operation process of the existing diverter system installed at the wellhead, and avoiding the conventional reliance on installing a diverter at the wellhead to divert and release shallow gas, which affects the safety of platform personnel and the production safety of producing wells.

[0030] Embodiment 1:

[0031] like Figure 1 and Figure 2As shown, the present invention provides a construction device for surface open-circuit drilling of shallow gas drilling in development wells, including a conductor fixing frame and a watertight conductor, the bottoms of the watertight conductor and the conductor fixing frame are both extended into the seabed 10 at least tens of meters below by hammering or drilling, the conductor fixing frame includes a plurality of conductor frame pile legs 2 and a plurality of conductor frame platforms 1, the plurality of conductor frame platforms 1 are horizontally arranged in sequence and arranged in parallel up and down, and the conductor frame platform 1 of the topmost layer extends out of the sea level 3; a plurality of conductor frame pile legs 2 are vertically arranged in sequence and distributed in an array around the plurality of conductor frame platforms 1 and fixed to the conductor frame platforms of each layer; the watertight conductor is composed of an extension conductor and an underwater conductor 4 connected up and down, and the top of the underwater conductor 4 is submerged in the sea water; the underwater conductor 4 is vertically fixed on at least one conductor frame platform 1 located below the sea level, and after the shallow gas 11 is discharged, the extension conductor is vertically fixed on at least one conductor frame platform 1 located on the top of the underwater conductor 4 to be connected to the underwater conductor 4, and the top of the extension conductor extends out of the conductor frame platform 1 of the topmost layer.

[0032] Specifically, the bottom of the conductor frame pile leg 2 of the conductor fixing frame penetrates into the seabed 10 to a depth slightly deeper than the position of the bottom of the underwater conductor 4. The bottom of the underwater conductor 4 penetrates at least 30 meters below the seabed according to different underwater conductor diameter specifications (diameter specifications are 914mm, 762mm, 610mm, 508mm), and is preferably within the depth range of 40m-80m according to different underwater conductor diameter specifications. The depth range and diameter specifications are specifically selected according to the marine environmental conditions of the sea area and the bonding strength and bearing capacity of the seabed soil. The watertight conductor is vertically installed at least 30 meters below the seabed. The setting angle of the watertight conductor is determined according to the drilling form. When drilling vertically, the watertight conductor is set vertically to the seabed or sea level. When drilling an inclined well, the watertight conductor is set at a certain angle to the seabed or sea level. When it is set obliquely, the watertight conductor is also fixed at a certain angle to the conductor frame platform 1 of each layer.

[0033] In this embodiment, preferably, the catheter fixing frame is composed of four catheter frame pile legs 2 and five layers of catheter frame platforms 1 fixedly connected, and the five layers of catheter frame platforms 1 are parallel to the sea level 3 and evenly distributed up and down, and the lower four layers of the catheter frame platforms 1 are sunk into the sea water. The four catheter frame pile legs 2 are distributed in turn at the corners of all layers of the catheter frame platforms 1 and are arranged perpendicular to the sea level 3. The four catheter frame pile legs 2 are fixedly connected to the edges of the four layers of the catheter frame platforms 1 to ensure that the entire catheter fixing frame can stand stably on the seabed 10 to support the entire drilling operation platform and pipelines.

[0034] In this embodiment, before the shallow gas 11 is discharged after drilling, the top of the underwater conduit 4 is fixed at the center of the three-layer conduit frame platform 1 below, and the top extends out of the conduit frame platform table of the third layer from bottom to top. After the shallow gas 11 is discharged into the seawater after drilling, an extension conduit is connected to the top of the underwater conduit 4 by underwater welding or quick snap-on docking. The extension conduit has the same inner and outer diameters as the underwater conduit 4. The extension conduit is fixed at the center of the conduit frame platform 1 of the top two layers and is coaxially connected to the underwater conduit 4. The top of the extension conduit now extends out of the conduit frame platform table of the top layer. After the extension conduit and the underwater conduit 4 are connected and fixed, a watertight conduit is formed to support the wellhead. The watertight conduit pipe string separates the seawater and withstands marine environmental loads such as ocean wind, waves, currents or sea ice.

[0035] Furthermore, the watertight conductor includes a plurality of watertight conductors, and the plurality of watertight conductors are fixed in parallel to each other on several layers of conductor rack platforms.

[0036] Specifically, there are preferably 4-8 riser pipes, each of which is composed of an underwater pipe and an extension pipe. The multiple riser pipes are arranged in parallel and sequentially distributed at the center of the jacket platform 1 and connected to each layer of the jacket platform 1.

[0037] Optionally, for a wellhead with centralized risers, there may be up to 40 risers.

[0038] Furthermore, a plurality of catheter fixing holes 5 are provided on the catheter rack platform 1. The catheter fixing holes 5 on each layer of the catheter rack platform 1 are coaxially arranged up and down, and each watertight catheter is sequentially fixed up and down in the catheter fixing holes on the same axis.

[0039] Specifically, a plurality of catheter fixing holes 5 for accommodating the passage of a watertight catheter are arranged in an array on each layer of the catheter rack platform. The catheter fixing holes are through-hole structures. The inner diameter of the catheter fixing holes is slightly larger than the outer diameter of the underwater catheter and the extension catheter to ensure that the through-holes can accommodate the passage of the underwater catheter 4 and the extension catheter. The catheter fixing holes 5 at corresponding positions on each layer of the catheter rack platform 1 are coaxially arranged in the vertical direction. The watertight catheter composed of the underwater catheter and the extension catheter can be fixed in the catheter fixing holes 5 located on the same axis on all layers of the catheter rack platform 1.

[0040] Furthermore, the jacket platform includes at least two layers.

[0041] Specifically, the riser must be completely fixed on the jacket platform 1, and the jacket platform 1 has at least two layers. When the jacket platform 1 has two layers, the lower jacket platform fixes the underwater jacket 4, and the upper jacket platform fixes the extension jacket, and the underwater jacket 4 continues to extend from the lower jacket platform.

[0042] It can be selected that the number of layers of the catheter rack platform 1 on the catheter fixing frame is determined according to the seawater depth. The deeper the seawater depth, the more layers of the catheter rack platform 1.

[0043] Furthermore, the top of the underwater conductor at least extends out of the lowest conductor rack platform.

[0044] Specifically, when the jacket platform 1 is multi-layered, at least the jacket platform at the bottom layer fixes the underwater jacket 4, and the jacket platforms 1 at several layers above the underwater jacket 4 fix the extension jacket. Therefore, in order to ensure that the underwater jacket 4 and the extension jacket are fixedly connected, the underwater jacket 4 needs to extend out of the jacket platform 1 at the top layer that fixes all the jacket platforms at the bottom layer.

[0045] Furthermore, a surface casing is provided inside the watertight conductor, the bottom of the surface casing is close to the bottom of the wellbore, and the top of the surface casing is suspended at the wellhead.

[0046] Specifically, after the connection between the underwater conduit 4 and the extension conduit is completed, a watertight conduit supporting the wellhead is formed, and a wellbore 8 is established between the wellbore below the seabed 10 and the wellhead on the platform deck 7. A steel surface casing (the outer diameter of the surface casing is 508mm or 339mm) with a smaller inner diameter than the watertight conduit is lowered into the watertight conduit and the wellbore through the platform drilling rig. The bottom of the surface casing is lowered to close to the bottom of the wellbore, 4-6m away from the bottom of the wellbore, preferably 5m. The top of the surface casing is suspended at the designed wellhead position on the platform deck 7. After the drilling operation is completed, a well control blowout preventer is installed on the top of the surface casing.

[0047] Embodiment 2:

[0048] like Figure 2 As shown, the present invention also provides a construction method based on a surface open-circuit drilling construction device for shallow gas drilling in a development well, which is to first fix the bottom of the underwater conduit 4 on the seabed 10, and sink the top of the underwater conduit 4 into the seawater; then drill in the underwater conduit to allow the shallow gas 11 to overflow from bottom to top into the seawater through the underwater conduit 4, and then connect an extension conduit to the top of the underwater conduit to form a watertight conduit, and the top of the extension conduit extends out of the sea level 3; finally, continue drilling in the watertight conduit.

[0049] Further, the method comprises the following steps:

[0050] (1) The bottom of the conductor frame pile leg 2 of the conductor frame is fixed on the seabed, the uppermost conductor frame platform of the conductor frame extends out of the sea level 3, the bottom of the underwater conductor 4 is sunk into the seabed, the top of the underwater conductor is sunk into the seawater, and then the underwater conductor is fixed on the conductor frame platform through which it passes in sequence;

[0051] (2) Drilling a well with a drill pipe in the underwater conduit 4 causes the shallow seabed gas 11 to flow upward through the underwater conduit to the top of the underwater conduit and overflow into the seawater;

[0052] (3) When the drill pipe 6 continues to drill to a depth of 300 m to 600 m below the seabed, the thick slurry is injected and the drill is pulled out;

[0053] (4) An extension conduit is connected to the top of the underwater conduit 4 to form a watertight conduit, and the top of the extension conduit extends out of the uppermost conduit rack platform 1 to establish a wellbore 8;

[0054] (5) A surface casing is installed in the wellbore 8, the bottom of the surface casing is lowered to a position close to the bottom of the wellbore, and the top of the surface casing is suspended at the wellhead;

[0055] (6) Cement slurry is injected into the surface casing pipeline, and the injected cement slurry is displaced by the drilling fluid and returned from the bottom of the surface casing into the annular space between the surface casing and the well wall. The cement slurry bonds and seals the surface casing and the well wall, completing the cementing operation.

[0056] Specifically, in step (1), the conduit fixing frame is first fixed on the seabed, the top conduit frame platform of the conduit fixing frame is exposed above the sea level 3, and the conduit frame platforms of the remaining layers are sunk into the seawater, and the bottom of the conduit frame pile legs of the conduit fixing frame is extended into the seabed at a depth of about 30-100m by hammering or drilling, and a layer of pile pipe is driven into the seabed by hammering or drilling as the underwater conduit 4, and the bottom of the underwater conduit 4 enters the seabed at a depth of about 30-80m. The top of the underwater conduit 4 is sunk into the seawater, and the top of the underwater conduit 4 is about 10-20 meters away from the sea level. The top of the underwater conduit 4 extends out of at least the bottommost conduit frame platform 1, and the outer wall of the underwater conduit 4 is supported, connected and fixed by the conduit fixing hole 5 of the conduit frame platform;

[0057] In step (2), a drill pipe 6 is lowered from the uppermost conductor frame platform 3 into the underwater conductor 4, and reaches the bottom of the underwater conductor 4 through the underwater conductor 4 submerged in the seawater, and starts drilling the shallow strata of the seabed 10. The drilling pump on the platform deck 7 pumps seawater into the drill pipe 6, and the seawater reaches the bottom drill bit 9 through the drill pipe, and is ejected from the water hole on the drill bit 9, and cooperates with the rotation of the drill bit to break the shallow strata of the seabed. The seawater carries the broken rock debris or shallow gas along the wellbore to the underwater conductor 4, and passes through the annular space between the underwater conductor 4 and the drill pipe 6 to reach the top of the underwater conductor 4 submerged in the seawater, and is directly discharged into the seawater. The broken rock debris diffuses with the sea current and falls to the seabed around the conductor fixing frame. At this time, the conductor fixing frame submerged in the seawater can separate the discharged rock debris, prevent the rock debris from backfilling the wellbore formed by drilling on the seabed 10, and at the same time support the drill pipe 6 to continue shallow drilling and well trajectory deflection.

[0058] In step (3), after the surface drilling operation of the development well is completed, a thick slurry of a certain density is pumped into the drilled wellbore through the drill rod 6, and then the drill rod 6 is pulled out.

[0059] In step (4), a steel pipe with the same diameter as the underwater conduit 4 submerged in the seawater is inserted from the uppermost conductor frame platform 1 as an extension conduit, and the extension conduit is underwater welded or quickly fastened at the top of the underwater conduit 4 to form a watertight conduit supporting the wellhead, and a wellbore 8 is established between the wellbore below the seabed and the wellhead on the platform to form a channel for subsequent drilling operations.

[0060] In step (5), a steel casing with a smaller inner diameter than that of the underwater catheter 4 is lowered into the underwater catheter 4 and the wellbore by a platform drilling rig as a surface casing. The outer diameter of the surface casing is 508 mm or 339 mm. The bottom of the surface casing is lowered to a position close to the bottom of the wellbore, 4-6 m away from the bottom of the wellbore, preferably 5 m. The top of the surface casing is suspended at the designed wellhead position on the platform deck 7.

[0061] In step (6), a designed amount of cementing cement slurry is pumped into the surface casing by connecting the delivery string at the top of the surface casing, and then a displacement drilling fluid is pumped into the surface casing to displace the cementing cement slurry in the surface casing into the annular space gap between the surface casing and the wellbore. The cementing cement slurry bonds and seals the annular space formed by the surface casing and the well wall, fixes the surface casing and seals the gap between the outer wall of the surface casing and the formation, and completes the cementing operation.

[0062] The above steps (1) to (6) complete all operations in the surface well section of offshore drilling. Subsequent well section operations are all completed in the surface casing, and a well control blowout prevention device is installed on the top of the surface casing. Once the high-pressure fluid in the formation overflows upward along the wellbore 8 to the wellhead position of the platform deck 7, the blowout prevention device can be closed to control the overflow of the high-pressure flammable fluid in the wellbore 8 to prevent blowout and fire, which may cause an operation accident.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A construction device for surface open-circuit drilling of shallow gas wells, characterized in that: It comprises a conduit fixing frame and a watertight conduit, the bottoms of the watertight conduit and the conduit fixing frame both extend into the seabed; the conduit fixing frame comprises a number of conduit frame pile legs and a number of conduit frame platforms, the number of conduit frame platforms are horizontally arranged in sequence and arranged in parallel up and down, and the top conduit frame platform extends out of the sea level; a number of conduit frame pile legs are vertically arranged in sequence and distributed in an array around the number of conduit frame platforms and fixed to each layer of the conduit frame platform; the watertight conduit is composed of an extension conduit and an underwater conduit connected up and down, and the top of the underwater conduit is immersed in the seawater; the underwater conduit is vertically fixed on at least one conduit frame platform below the sea level, and after the shallow gas is discharged, the extension conduit is vertically fixed on at least one conduit frame platform located on the top of the underwater conduit to be connected with the underwater conduit, and the top of the extension conduit extends out of the topmost conduit frame platform.

2. The construction device according to claim 1, characterized in that: The watertight pipes include a plurality of watertight pipes, and the plurality of watertight pipes are fixed parallel to each other on the plurality of pipe rack platforms.

3. The construction device according to claim 1 or 2, characterized in that: The catheter rack platform is provided with a plurality of catheter fixing holes, and the corresponding catheter fixing holes on each layer of the catheter rack platform are coaxially arranged up and down, and each of the watertight catheters is sequentially fixed up and down in the catheter fixing holes on the same axis.

4. The construction device according to claim 3, characterized in that: The jacket platform comprises at least two layers.

5. The construction device according to claim 4, characterized in that: The top of the underwater conduit at least extends out of the lowest conduit rack platform.

6. The construction device according to claim 5, characterized in that: The water-proof pipe is sheathed with a surface casing, the bottom of the surface casing is close to the bottom of the wellbore, and the top of the surface casing is suspended at the wellhead.

7. A construction method for the construction device for surface open-circuit drilling of shallow gas wells for development wells based on any one of claims 1 to 6, characterized in that: The steps include: The bottom of the conductor frame pile leg of the conductor fixing frame is fixed on the seabed, the uppermost conductor frame platform of the conductor fixing frame extends out of the sea level, the bottom of the underwater conductor is sunk into the seabed, the top of the underwater conductor is sunk into the seawater, and then the underwater conductor is fixed on the conductor frame platform through which it passes in sequence; Drilling with a drill pipe in an underwater conduit causes shallow seabed gas to flow back through the underwater conduit to the top of the underwater conduit and overflow into the seawater; When the drill pipe continues to drill to a depth of 300m to 600m below the seabed, the drill is pulled out after injecting thick slurry; An extension conduit is connected to the top of the underwater conduit to form a watertight conduit, and a wellbore is established after the top of the extension conduit extends out of the uppermost conduit rack platform; A surface casing is installed in the wellbore, the bottom of the surface casing is lowered to a position close to the bottom of the wellbore, and the top of the surface casing is suspended at the wellhead position; Cement slurry is injected into the surface casing pipeline, and the injected cement slurry is displaced by drilling fluid and returned from the bottom of the surface casing into the annular space between the surface casing and the well wall. The cement slurry bonds and seals the surface casing and the well wall to complete the cementing operation.

8. The construction method according to claim 7, characterized in that: The bottoms of the underwater conduit and the conduit fixing frame extend into the seabed to a depth of at least 30 m, and the bottom of the surface casing is 4-6 m away from the bottom of the wellbore.

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