Wellbore structure passing through high-pressure layer and basalt collapse layer and construction method thereof

Abstract

The present invention provides a wellbore structure for passing through a high-pressure layer and a basalt collapse layer and a construction method thereof. The construction method includes: Step S10, lowering the first casing string and cementing; Step S20, lowering the second casing string and cementing; Step S30, drilling the third open hole section to the upper part of the high-pressure layer, lowering the third casing string and cementing; Step S40, drilling through the high-pressure layer in the fourth open hole section and drilling to the upper part of the basalt collapse layer, lowering the fourth casing string and cementing; Step S50, drilling through the basalt collapse layer in the fifth open hole section and drilling to the upper part of the oil and gas target layer, lowering the fifth casing string and cementing; Step S60, drilling the sixth open hole section to the oil and gas target layer, lowering the sixth liner string and cementing. Through the present invention, the technical problems of accidents and complexities such as overflow, lost circulation, wellbore collapse, and stuck pipe that are likely to occur during drilling under geological conditions with a high-pressure layer and a basalt collapse layer are alleviated.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration and development, and particularly relates to a wellbore structure passing through a high-pressure layer and a basalt collapse layer and a construction method thereof. Background Art

[0002] In oil and gas exploration and development, an oil and gas passage needs to be established between the ground and the underground oil and gas reservoirs, which is an oil and gas well. During the establishment of an oil and gas well, the formation is sealed off with casing, and the outer wall of the casing is fixed to the formation with cement, thereby forming a combination of casing and cement. This combination of casing and cement is the wellbore structure. As one of the key contents of oil and gas exploration, the wellbore structure needs to fully consider the pore pressure of the drilled formation and the particularity of geological conditions. Different casings are used to seal off different pressure and complex formations to eliminate or reduce the risks of accidents and complexities that may occur during drilling.

[0003] Currently, for the exploration and development of oil and gas resources in deep formations, the depth of ultra-deep oil and gas wells is generally 6000m - 9000m, and it has now exceeded 8000m. Due to the complex and changeable geological conditions during ultra-deep well drilling, complex formation pore pressure systems are often encountered, the formation lithology varies greatly, high-pressure layers, lost circulation zones and collapse layers appear alternately, and the geological conditions are relatively complex, posing a great challenge to the construction of the wellbore structure.

[0004] In the ultra-deep wells in the Sichuan Basin, complex formations such as high-pressure brine, mudstone formations and basalt layers are often encountered in deep formations. When using a conventional wellbore structure, accidents and complexities such as overflow, lost circulation, collapse and stuck pipe often occur during drilling. Handling these accidents and complexities will cause huge economic losses to oil and gas drilling, and even ultimately it is impossible to continue drilling to the oil and gas target layer, resulting in the abandonment of the wellbore. Summary of the Invention

[0005] The purpose of the present invention is to provide a wellbore structure passing through a high-pressure layer and a basalt collapse layer and a construction method thereof, so as to alleviate the technical problems of easily occurring accidents and complexities such as overflow, lost circulation, wellbore wall collapse and stuck pipe during drilling under the geological conditions with high-pressure layers and basalt collapse layers.

[0006] The above purpose of the present invention can be achieved by the following technical solutions:

[0007] The present invention provides a construction method for a wellbore structure passing through a high-pressure layer and a basalt collapse layer, including:

[0008] Step S10, drilling the first open-hole section, running in the first open-hole casing string, and cementing;

[0009] Step S20, drilling the second open-hole section, running in the second open-hole casing string, and cementing;

[0010] Step S30: Drill the third drilling interval until reaching the upper part of the high-pressure formation, run in the third casing string, and cement the well.

[0011] Step S40: Drill the fourth drilling interval to penetrate the high-pressure formation and reach the upper part of the basalt collapse formation, run in the fourth casing string, and cement the well.

[0012] Step S50: Drill the fifth drilling interval to penetrate the basalt collapse formation and reach the upper part of the oil and gas target formation, run in the fifth casing string, and cement the well.

[0013] Step S60: Drill the sixth drilling interval to reach the oil and gas target formation, run in the sixth liner string, and cement the well.

[0014] In a preferred embodiment, running in the fourth casing string includes: suspending the fourth casing string inside the third casing string.

[0015] In a preferred embodiment, the fifth casing string includes a fifth liner string, and the fifth liner string is suspended.

[0016] In a preferred embodiment, the fifth liner string is suspended inside the third casing string.

[0017] In a preferred embodiment, the construction method includes step S70 which is set after step S60. Step S70 includes: running in a fifth tie-back casing to the top of the fifth liner string and cementing the well.

[0018] In a preferred embodiment, running in the sixth liner string includes: suspending the sixth liner string inside the fifth casing string.

[0019] In a preferred embodiment, the first drilling interval penetrates the surface loose formation and the lost circulation formation, and the second drilling interval penetrates the upper shallow gas and low-pressure lost circulation formation.

[0020] In a preferred embodiment, the high-pressure formation includes a high-pressure brine formation.

[0021] The present invention provides a wellbore structure for passing through a high-pressure formation and a basalt collapse formation, including:

[0022] A first casing string;

[0023] A second casing string disposed inside the first casing string;

[0024] A third casing string, and the third casing string is run to the top of the high-pressure formation;

[0025] The fourth casing string; the fourth casing string penetrates through the high-pressure layer and is run to the upper part of the basalt collapse layer, and the fourth casing string seals off the high-pressure layer;

[0026] The fifth casing string, the fifth casing string penetrates through the basalt collapse layer and is run to the upper part of the oil and gas target layer, and the fifth casing string seals off the basalt collapse layer;

[0027] The sixth liner string, the sixth liner string is run into the oil and gas target layer.

[0028] In a preferred embodiment, the fourth casing string is suspended on the inner wall of the third casing string by a fourth liner hanger.

[0029] In a preferred embodiment, the fifth casing string includes a fifth liner string, and the fifth liner string is suspended.

[0030] In a preferred embodiment, the fifth liner string is suspended on the inner wall of the third casing string by a fifth liner hanger.

[0031] In a preferred embodiment, the wellbore structure includes a fifth tie-back casing, and the fifth tie-back casing is run to the top of the fifth liner string.

[0032] In a preferred embodiment, the sixth liner string is suspended on the inner wall of the fifth casing string by a sixth liner hanger.

[0033] In a preferred embodiment, the first casing string penetrates through the surface loose layer and the lost circulation formation, and the second casing string penetrates through the upper shallow gas and the low-pressure lost circulation layer.

[0034] The features and advantages of the present invention are:

[0035] The construction method of the wellbore structure passing through the high-pressure layer and the basalt collapse layer provided by the present invention, the first casing string seals the upper loose, unstable and lost circulation well sections, providing support for the next wellhead installation. The second casing string seals the shallow gas and the low-pressure lost circulation formation.

[0036] The third casing string is run to the upper part of the high-pressure layer, sealing off the upper formation with relatively low pore pressure, avoiding well leakage in the upper formation with relatively low pore pressure when drilling the lower interval encountering the high-pressure layer due to increasing the drilling fluid density.

[0037] After the high-pressure layer is drilled through in the fourth drilling interval, the fourth drilling interval casing string is run to seal the formation, instead of running the casing to seal the formation after drilling into the lower basalt collapse layer. The fourth drilling interval casing string seals the high-pressure layer that requires high-density drilling fluid to maintain wellbore stability, which can effectively avoid accidents such as overflow of the upper high-pressure saltwater layer and wellbore collapse caused by reducing the drilling fluid density when drilling into the basalt collapse layer. The fourth drilling interval casing string seals the upper high-pressure layer suitable for drilling with high-density drilling fluid, creating conditions for reducing the drilling fluid density in the next drilling interval.

[0038] The fifth drilling interval casing string seals the easily collapsible basalt collapse layer, creating conditions for further reducing the drilling fluid density in the next drilling interval to protect the reservoir. The sixth drilling interval liner string seals the oil and gas target layer.

[0039] Through the construction method of this wellbore structure, the conditions for drilling to the oil and gas target layer can be constructed, alleviating the accidents and complex technical problems such as overflow, lost circulation, wellbore collapse, and stuck pipe that are prone to occur during drilling under the geological conditions with high-pressure layers and basalt collapse layers. Brief Description of the Drawings

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0041] Figure 1 It is a schematic structural diagram of the wellbore structure passing through the high-pressure layer and the basalt collapse layer provided by the present invention;

[0042] Figure 2a It is a schematic diagram of the cooperation between the wellbore structure passing through the high-pressure layer and the basalt collapse layer provided by the present invention and each structural layer in the formation;

[0043] Figure 2b It is a relationship diagram between each structural layer in the formation and the formation pore pressure;

[0044] Figure 3 It is a schematic diagram of the construction method of the wellbore structure passing through the high-pressure layer and the basalt collapse layer provided by the present invention.

[0045] Explanation of the Reference Numerals in the Drawings:

[0046] 100, cement sheath;

[0047] 10, the first drilling interval casing string; 101, the first drilling interval;

[0048] 20, the second drilling interval casing string; 201, the second drilling interval;

[0049] 30. Third casing string; 301. Third well section;

[0050] 40. Fourth casing string; 401. Fourth well section; 402. Fourth liner hanger;

[0051] 50. Fifth casing string; 51. Fifth liner string; 52. Fifth tie-back casing; 501. Fifth well section; 502. Fifth liner hanger;

[0052] 60. Sixth liner string; 601. Sixth well section; 602. Sixth liner hanger;

[0053] 71. High-pressure layer; 711. High-pressure brine layer; 712. High-pressure mudstone formation; 72. Basalt collapse layer; 73. Oil and gas target layer;

[0054] 80. Formation; 81. Formation pore pressure profile. Detailed implementation manners

[0055] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0056] Facing a complex formation with a high-pressure layer 71 and a basalt collapse layer 72, due to reasons such as unreasonable wellbore structure and limitations of casing levels, in a conventional wellbore structure, there will be multiple formation pore pressure systems and complex formations with different properties in the same well section. The pore pressure and collapse pressure of the high-pressure brine layer 711 and the mudstone formation are relatively high. To avoid overflow and wellbore collapse accidents, high-density drilling fluid needs to be used for drilling; while the leakage pressure and formation fracture pressure of the basalt collapse layer 72 are relatively low. To avoid well leakage and wellbore collapse accidents, low-density drilling fluid needs to be used for drilling. If the upper high-pressure brine layer 711, the middle mudstone formation, and the lower basalt collapse layer 72 are drilled through and then casing is run for isolation, after drilling into the basalt collapse layer 72, the drilling fluid in the well section cannot simultaneously meet the high density requirements of the high-pressure brine layer 711 and the high-pressure mudstone formation 712, as well as the low density requirement of the basalt collapse layer 72, which is likely to cause accidents such as overflow of the high-pressure brine layer 711, collapse of the mudstone formation, well leakage of the basalt collapse layer 72, and stuck pipe.

[0057] Embodiment 1

[0058] The present invention provides a method for constructing a wellbore structure under geological conditions with a basalt collapse layer 72, as Figure 2a and Figure 3As shown in the figure, the construction method includes: Step S10, drilling the first open-hole section 101, running in the first open-hole casing string 10, and cementing; Step S20, drilling the second open-hole section 201, running in the second open-hole casing string 20, and cementing; Step S30, drilling the third open-hole section 301. The third open-hole section 301 is drilled to the upper part of the high-pressure layer 71, running in the third open-hole casing string 30, and cementing; Step S40, drilling the fourth open-hole section 401. The fourth open-hole section 401 drills through the high-pressure layer 71 and drills to the upper part of the basalt collapse layer 72, running in the fourth open-hole casing string 40, and cementing; Step S50, drilling the fifth open-hole section 501. The fifth open-hole section 501 drills through the basalt collapse layer 72 and drills to the upper part of the oil and gas target layer 73, running in the fifth open-hole casing string 50, and cementing; Step S60, drilling the sixth open-hole section 601. The sixth open-hole section 601 drills into the oil and gas target layer 73, running in the sixth liner string 60, and cementing.

[0059] In this construction method, the first open-hole casing string 10 seals the upper loose, unstable and easily lost circulation sections, providing support for the next wellhead installation. The second open-hole casing string 20 seals the shallow gas and low-pressure easily lost circulation formations.

[0060] The third open-hole casing string 30 is run to the upper part of the high-pressure layer 71 to seal off the upper formations with relatively low pore pressure, avoiding well leakage in the upper formations with relatively low pore pressure when drilling the lower open-hole section encountering the high-pressure layer 71 due to increasing the drilling fluid density.

[0061] After the fourth open-hole section 401 drills through the high-pressure layer 71, the fourth open-hole casing string 40 is run to seal the formation, rather than running in the casing to seal the formation after drilling into the lower basalt collapse layer 72. The fourth open-hole casing string 40 seals the high-pressure layer 71 that requires high-density drilling fluid to maintain wellbore stability, effectively avoiding accidents such as overflow and wellbore collapse of the upper high-pressure saltwater layer 711 when drilling into the basalt collapse layer 72 due to reducing the drilling fluid density. The fourth open-hole casing string 40 seals the upper high-pressure layer 71 suitable for drilling with high-density drilling fluid, creating conditions for reducing the drilling fluid density in the next open-hole section.

[0062] The fifth open-hole casing string 50 seals the easily collapsible basalt collapse layer 72, creating conditions for further reducing the drilling fluid density in the next open-hole section to protect the reservoir. The sixth liner string 60 seals the oil and gas target layer 73.

[0063] The construction method of this wellbore structure can be applied to ultra-deep wells. Through this construction method of the wellbore structure, conditions can be constructed to drill to the ultra-deep oil and gas target layer 73, alleviating technical problems such as overflow, well leakage, wellbore collapse, and stuck pipe that are prone to occur during drilling under geological conditions with high-pressure layers and basalt collapse layers 72.

[0064] The high-pressure layer 71 is a high-pore-pressure formation with a pore pressure coefficient greater than 1.6. For example, the high-pressure layer 71 includes a high-pressure brine layer 711, a high-pressure mudstone formation 712, or a high-pressure carbonate rock formation. Please refer to Figure 2a and Figure 2b , Figure 2b As shown, the high-pressure layer 71 includes a high-pressure brine layer 711 and a high-pressure mudstone formation 712, and the high-pressure brine layer 711 and the high-pressure mudstone formation 712 can be distributed in sequence from top to bottom. In some cases, the geological conditions applicable to this wellbore structure also include a non-high-pressure mudstone formation, and the high-pressure layer 71 and the non-high-pressure mudstone formation are distributed vertically, with the non-high-pressure mudstone formation located between the high-pressure layer 71 and the basalt collapse layer 72. Please refer to Figure 2b In the formation pore pressure profile 81 in

[0065] In step S10, a φ660.4mm roller cone bit can be used. After drilling through the surface loose layer and the lost circulation formation, the bit is pulled out, and a first-stage casing string 10 with a diameter of φ508mm is run in, and cement is injected into the annulus between the first-stage casing string 10 and the formation for cementing to seal the upper loose, unstable, and lost circulation intervals and provide support for the next wellhead installation. Specifically, using a φ660.4mm roller cone bit, after drilling to a well depth of 200m, circulate at a large displacement to carry the cuttings in the well clean to ensure the smooth running-in of the first-stage casing string 10; the first-stage casing string 10 is a casing string with a diameter of φ508mm, a wall thickness of 11.13mm, and buttress threads. The bit is pulled out, and the first-stage casing string 10 is run in. Cementing is carried out in the annulus between the first-stage casing string 10 and the formation by the method of injecting cement from the bottom up and backwashing from the top, and the cement returns to the wellhead. The injected cement slurry solidifies to form a cement sheath 100.

[0066] In step S20, a φ444.5mm roller cone bit or a PDC bit can be used. After drilling through the upper shallow gas and low-pressure lost circulation formation, the bit is pulled out, and a second-stage casing string 20 with a diameter of φ365.13mm is run in, and cement is injected into the annulus between the second-stage casing string 20 and the formation and the upper casing for cementing to seal the shallow gas and low-pressure lost circulation formation. Specifically, using a φ444.5mm roller cone bit or a PDC bit, after drilling to a well depth of 1500m, the bit is pulled out, and a reaming drill string assembly is replaced for sufficient reaming to ensure the smooth running-in of the second-stage casing string 20; the second-stage casing string 20 is a casing string with a diameter of φ365.13mm, a wall thickness of 13.88mm, and buttress threads. The second-stage casing string 20 is run in, and cementing is carried out in the annulus between this casing and the formation and the upper casing by the interpolation method, and the cement returns to the wellhead.

[0067] In step S30, a PDC bit with a diameter of φ333.4 mm can be used. After drilling to the top of the high-pressure layer 71, the bit is pulled out, and a third casing string 30 with a diameter of φ273.05 mm is run in. Cement is injected into the annulus between the third casing string 30, the formation, and the upper casing for cementing to seal the upper formation with relatively low pore pressure. Specifically, using a PDC bit with a diameter of φ333.4 mm, drill to a well depth of 4500 m and to the top of the high-pressure layer 71. Then, pull out the bit and replace it with a reaming drill string assembly for sufficient reaming to ensure the smooth running-in of the third casing string 30. The third casing string 30 uses a casing string with a diameter of φ273.05 mm, a wall thickness of 13.84 mm, and gas-tight connections. When running in the third casing string 30, a double-plug and double-density cement slurry system is used to inject cement into the annulus between the third casing string 30, the formation, and the upper casing for cementing, and the cement returns to the wellhead.

[0068] In an embodiment of the present invention, the fourth casing string 40 is suspended on the inner wall of the third casing string 30. By using the liner hanger technology, the one-time return height of cement injection into the casing annulus is effectively reduced, avoiding complex well leakage in the basalt formation caused by excessive surface pump pressure during cement injection into the casing annulus.

[0069] For drilling the fourth open hole section 401, a PDC bit with a diameter of φ241.3 mm can be used. After drilling through the upper high-pressure layer 71, the bit is pulled out, and a fourth casing string 40 with a diameter of φ219.08 mm is run to the bottom of the well. The top of the fourth casing string 40 is connected to a fourth open hole liner hanger 402. The fourth casing string 40 is suspended on the inner wall of the third casing string 30, and cement is injected into the annulus between the fourth casing string 40, the formation, and the upper casing for cementing to seal the formation that requires high-density drilling fluid for drilling, avoiding accidents and complexities such as overflow, collapse, well leakage, and pipe sticking caused by reducing the drilling fluid density. Specifically, when drilling the fourth open hole section 401, use a PDC bit with a diameter of φ241.3 mm, drill to a well depth of 6400 m and drill through the upper high-pressure layer 71. Then, pull out the bit and replace it with a reaming drill string assembly for sufficient reaming to ensure the smooth running-in of the fourth open hole section 401. The fourth casing string 40 can use a liner string with a diameter of φ219.08 mm, a wall thickness of 12.7 mm, and straight connections. Run the fourth casing string 40 to a well depth of 6398 m. The top of the fourth casing string 40 is connected to a fourth open hole liner hanger 402, and the fourth casing string 40 is suspended on the inner wall of the third casing string 30 at a well depth of 4300 m. A high-density salt-resistant cement slurry system is used to inject cement into the annulus between the fourth casing string 40, the formation, and the casing, and the cement returns to the position of the fourth open hole liner hanger 402 to seal the upper high-pressure saltwater layer 711 and high-pressure mudstone formation 712 suitable for high-density drilling fluid for drilling, creating conditions for reducing the drilling fluid density in the next open hole section. In this construction method, the fourth casing string 40 is not back-connected to the casing, which can reduce the casing consumption and save the drilling cost.

[0070] The fifth casing string 50 can be installed at the wellhead or can be set in a suspended manner. When the fifth casing string 50 is installed at the wellhead, the fifth casing string 50 can be a casing extending from the bottom of the fifth interval 501 to the wellhead. When the fifth casing string 50 is set in a suspended manner, the fifth casing string 50 includes a fifth liner string 51, and the fifth liner string 51 can be suspended on the inner wall of the third casing string 30.

[0071] The fifth casing string 50 is preferably set in a suspended manner. As Figure 2a shown, the fifth casing string 50 includes a fifth liner string 51, and the fifth liner string 51 is suspended. The fifth liner string 51 can be suspended on the third casing string 30 or can be suspended on the fourth casing string 40. More preferably, the fifth liner string 51 is suspended on the inner wall of the third casing string 30. During the drilling of the fifth interval 501, after drilling through the basalt formation, the liner hanging technology is adopted, which effectively reduces the one-time return height of the annular cement injection of the fifth liner string 51, and avoids well leakage in the basalt collapse layer 72 due to excessive surface pump pressure when injecting cement into the annulus of the fifth liner string 51. At the same time, the use of liner hanging can reduce the weight of the casing and increase the well depth of the casing run-in, so as to seal deeper complex formations.

[0072] A PDC bit with a diameter of φ190.5mm can be used. After drilling through the basalt collapse layer 72, the bit is retrieved, and a φ168.28mm fifth casing string 50 is run to the bottom of the well. The top of the fifth casing string 50 is connected with a fifth liner hanger 502, and the fifth casing string 50 is suspended on the inner wall of the third casing string 30, and cement is injected into the annulus between the fifth casing string 50, the formation and the upper casing for cementing. Specifically, using a φ190.5mm PDC bit, drilling to a well depth of 7000m and drilling through the basalt collapse layer 72, the bit is retrieved, replaced with a reaming drill string assembly, and reamed thoroughly to ensure the smooth running-in of the fifth casing string 50; the fifth casing string 50 adopts a φ168.28mm, wall thickness 12.07mm, straight connection coupling liner string, and the fifth casing string 50 is run to a well depth of 6998m; the top of the fifth casing string 50 is connected with a fifth liner hanger 502, and the fifth casing string 50 is suspended on the inner wall of the third casing string 30 at a well depth of 4000m. Cement is injected into the annulus between the fifth casing string 50, the formation and the upper casing for cementing, and the cement returns to the position of the fifth liner hanger 502, sealing the easily collapsible basalt collapse layer 72, creating conditions for further reducing the drilling fluid density for reservoir protection in the next interval.

[0073] Further, in the case where the fifth casing string 50 is set in a suspended manner, the construction method includes step S70 which is set after step S60. Step S70 includes: running in the fifth tie-back casing 52 to the top of the fifth liner string 51 and cementing. Run in the fifth tie-back casing 52. The running-in depth of the fifth tie-back casing 52 is at the position of the fifth liner hanger 502, and cement is injected into the annulus between the fifth tie-back casing 52 and the third casing string 30 for cementing. The fifth tie-back casing 52 can adopt a 168.28 mm casing string. Specifically, run in the fifth tie-back casing 52. The running-in depth of the fifth tie-back casing 52 is at the position of the fifth liner hanger 502, and cement is injected into the annulus between the fifth tie-back casing 52 and the third casing string 30 for cementing. After completing the casing tie-back operation, transfer to the perforating and completion operation of the sixth liner string 60.

[0074] After the fifth liner string 51 is suspended and cemented, no casing tie-back is carried out. After the sixth liner string 60 is suspended and cemented, the tie-back operation of the fifth tie-back casing 52 is carried out. This can increase the annular clearance of the drill string assembly above the fifth liner hanger 502 when drilling the sixth well section 601, reduce the equivalent density of the drilling fluid circulation when drilling the sixth well section 601, and thus reduce the risk of lost circulation and complexity in the target formation.

[0075] The sixth liner string 60 can be installed at the wellhead or can be set in a suspended manner. Preferably, the sixth liner string 60 is suspended on the inner wall of the fifth casing string 50. In step S60, a φ139.7 mm PDC bit can be used to drill to the target formation, pull out the bit, run in the sixth liner string 60 with a diameter of φ114.3 mm. The top of the sixth liner string 60 is connected to the sixth liner hanger 602. The sixth liner string 60 is suspended on the inner wall of the fifth liner string 51, and cement is injected into the annulus between the sixth liner string 60 and the formation and the upper casing for cementing to seal the oil and gas target formation 73. Specifically, use a φ139.7 mm PDC bit to drill to the oil and gas target formation 73. After the footage reaches 200 m, pull out the bit and replace it with a reaming drill string assembly for sufficient reaming to ensure the smooth running in of the casing. The sixth liner string 60 can adopt a φ114.3 mm, 8.56 mm wall thickness, long-round-thread liner string. Run in the sixth liner string 60 to a well depth of 7500 m. The top of the sixth liner string 60 is connected to the sixth liner hanger 602. The sixth liner string 60 is suspended on the inner wall of the fifth liner string 51. At a well depth of 6800 m, cement is injected into the annulus between the sixth liner string 60 and the formation and the upper casing, and the cement returns to the position of the sixth liner hanger 602 to seal the oil and gas target formation 73.

[0076] For the liner string 60 in the sixth drilling interval, the liner hanger cementing technology is adopted without tie-back casing, which reduces the one-time return height of cement injection in the casing annulus, avoids well leakage and complexity in the target formation due to excessive surface pump pressure during cement injection in the casing annulus, and at the same time, reduces the casing consumption and saves costs.

[0077] Embodiment 2

[0078] The present invention provides a wellbore structure under geological conditions with a basalt collapse layer 72, as Figure 1 and Figure 2a shown. The wellbore structure includes: the first drilling interval casing string 10, the second drilling interval casing string 20, the third drilling interval casing string 30, the fourth drilling interval casing string 40, the fifth drilling interval casing string 50, and the sixth drilling interval liner string 60; the second drilling interval casing string 20 is run into the first drilling interval casing string 10; the third drilling interval casing string 30 is run to the top of the high-pressure layer 71; the fourth drilling interval casing string 40 penetrates the high-pressure layer 71 and is run to the upper part of the basalt collapse layer 72, and the fourth drilling interval casing string seals off the high-pressure layer; the fifth drilling interval casing string 50 penetrates the basalt collapse layer 72 and is run to the upper part of the oil and gas target formation 73, and the fifth drilling interval casing string seals off the basalt collapse layer; the sixth drilling interval liner string 60 is run into the oil and gas target formation 73.

[0079] In this construction method, the first drilling interval casing string 10 seals and consolidates the upper loose, unstable and easily lost circulation well section, providing support for the next wellhead installation. The second drilling interval casing string 20 seals and consolidates the shallow gas and low-pressure easily lost circulation formations.

[0080] The third drilling interval casing string 30 is run to the upper part of the high-pressure layer 71 to seal off the formations with relatively low pore pressure in the upper part, avoiding well leakage in the formations with relatively low pore pressure in the upper part when drilling the next interval and encountering the high-pressure layer 71 due to increasing the drilling fluid density.

[0081] After the fourth drilling interval section 401 drills through the high-pressure layer 71, the fourth drilling interval casing string 40 is run to seal and consolidate the formation, rather than running the casing to seal and consolidate the formation after drilling into the lower basalt collapse layer 72. The fourth drilling interval casing string 40 seals off the high-pressure layer 71 that requires high-density drilling fluid to maintain wellbore stability, effectively avoiding accidents such as overflow and wellbore collapse of the upper high-pressure saltwater layer 711 due to reducing the drilling fluid density when drilling into the basalt collapse layer 72. The fourth drilling interval casing string 40 seals and consolidates the upper high-pressure layer 71 suitable for drilling with high-density drilling fluid, creating conditions for reducing the drilling fluid density in the next interval.

[0082] The fifth drilling interval casing string 50 seals and consolidates the easily collapsible basalt collapse layer 72, creating conditions for further reducing the drilling fluid density in the next interval to protect the reservoir. The sixth drilling interval liner string 60 seals and consolidates the oil and gas target formation 73.

[0083] This well structure can be applied to ultra-deep wells. By adopting this well structure, the conditions for drilling to the ultra-deep hydrocarbon target formation 73 can be constructed, and it can alleviate the technical problems of accidents and complexities such as overflow, lost circulation, wellbore collapse, and stuck pipe that are prone to occur during drilling under the geological conditions with high-pressure formations 71 and basalt collapse formations 72.

[0084] Specifically, this well structure further includes a cement sheath 100 for cementing the first casing string 10, the second casing string 20, the third casing string 30, the fourth casing string 40, the fifth casing string 50, and the sixth liner string 60.

[0085] In an embodiment of the present invention, the fourth casing string 40 is suspended from the inner wall of the third casing string 30 by a fourth liner hanger 402.

[0086] In an embodiment of the present invention, the fifth casing string 50 includes a fifth liner string, and the fifth liner string is suspended.

[0087] In an embodiment of the present invention, the fifth liner string is suspended from the inner wall of the third casing string 30 by a fifth liner hanger 502.

[0088] In an embodiment of the present invention, the well structure includes a fifth tie-back casing, and the fifth tie-back casing is run to the top of the fifth liner string.

[0089] In an embodiment of the present invention, the sixth liner string 60 is suspended from the inner wall of the fifth casing string 50 by a sixth liner hanger 602.

[0090] In an embodiment of the present invention, the first casing string 10 penetrates the surface loose layer and the lost circulation formation, and the second casing string 20 penetrates the upper shallow gas and low-pressure lost circulation formation.

[0091] The above are only several embodiments of the present invention. Those skilled in the art can make various changes or modifications to the embodiments of the present invention without departing from the spirit and scope of the present invention according to the content disclosed in the application documents.

Claims

1. A method for constructing a wellbore structure passing through a high-pressure layer and a basalt collapse layer, characterized in that, it includes: Step S10: Drill the first drilling interval, run in the first casing string, and cement; Step S20: Drill the second drilling interval, run in the second casing string, and cement; Step S30: Drill the third drilling interval, drill the third drilling interval to the upper part of the high-pressure layer, run in the third casing string, and cement; Step S40: Drill the fourth drilling interval, drill through the high-pressure layer in the fourth drilling interval, and drill to the upper part of the basalt collapse layer, run in the fourth casing string, and cement; Step S50: Drill the fifth drilling interval, drill through the basalt collapse layer in the fifth drilling interval, and drill to the upper part of the oil and gas target layer, run in the fifth casing string, and cement; Step S60: Drill the sixth drilling interval, drill to the oil and gas target layer in the sixth drilling interval, run in the sixth liner string, and cement; The running in of the fourth casing string includes: the fourth casing string is suspended on the inner wall of the third casing string; The running in of the sixth liner string includes: the sixth liner string is suspended on the inner wall of the fifth casing string.

2. The method for constructing a wellbore structure passing through a high-pressure layer and a basalt collapse layer according to claim 1, characterized in that, the fifth casing string includes a fifth liner string, and the fifth liner string is suspended.

3. The method for constructing a wellbore structure passing through a high-pressure layer and a basalt collapse layer according to claim 2, characterized in that, the fifth liner string is suspended on the inner wall of the third casing string.

4. The method for constructing a wellbore structure passing through a high-pressure layer and a basalt collapse layer according to claim 2, characterized in that, the construction method includes step S70 arranged after step S60, and step S70 includes: running in a fifth tie-back casing to the top of the fifth liner string and cementing.

5. The method for constructing a wellbore structure passing through a high-pressure layer and a basalt collapse layer according to claim 1, characterized in that, the first drilling interval drills through the surface loose layer and the lost circulation formation, and the second drilling interval drills through the upper shallow gas and the low-pressure lost circulation layer.

6. The method for constructing a wellbore structure passing through a high-pressure layer and a basalt collapse layer according to claim 1, characterized in that, the high-pressure layer includes a high-pressure brine layer, a high-pressure mudstone formation or a high-pressure carbonate rock formation.

7. A wellbore structure passing through a high-pressure layer and a basalt collapse layer, characterized in that, it includes: The first casing string; The second casing string arranged inside the first casing string; The third casing string, and the third casing string is run to the top of the high-pressure layer; The fourth casing string; The fourth casing string penetrates the high-pressure layer and is run to the upper part of the basalt collapse layer, and the fourth casing string seals off the high-pressure layer; The fifth casing string, the fifth casing string penetrates the basalt collapse layer and is run to the upper part of the oil and gas target layer, and the fifth casing string seals off the basalt collapse layer; The sixth liner string, and the sixth liner string is run into the oil and gas target layer; The fourth casing string is suspended on the inner wall of the third casing string through a fourth liner hanger; The sixth liner string is suspended on the inner wall of the fifth casing string through a sixth liner hanger.

8. The wellbore structure passing through the high-pressure layer and the basalt collapse layer according to claim 7, characterized in that the fifth casing string includes a fifth liner string, and the fifth liner string is suspended.

9. The wellbore structure passing through the high-pressure layer and the basalt collapse layer according to claim 8, characterized in that the fifth liner string is suspended on the inner wall of the third casing string through a fifth liner hanger.

10. The wellbore structure passing through the high-pressure layer and the basalt collapse layer according to claim 8, characterized in that the wellbore structure includes a fifth tie-back casing, and the fifth tie-back casing is run to the top of the fifth liner string.

11. The wellbore structure passing through the high-pressure layer and the basalt collapse layer according to claim 7, characterized in that the first casing string penetrates the surface loose layer and the lost circulation formation, and the second casing string penetrates the upper shallow gas and the low-pressure lost circulation layer.

Images