Deepwater suction pile well construction experimental device and bearing capacity test method

Abstract

The present application provides a deep-water suction pile well construction experimental device and a bearing capacity test method, the experimental device includes: a kettle body, which is used to fill the soil layer and the brine of the predetermined density; a kettle cover; a lowering component, including: a suction pile and a drill rod, the suction pile is a hollow cylinder, the bottom end is an open end, and the top end is penetrated by the drill rod to form a closed end; an injection component, including: a first pressure sensor; an air storage tank, an air intake pipeline is arranged between the air storage tank and the hollow chamber, and a booster pump and an air intake control valve are arranged on the air intake pipeline; a suction component, including: a recovery box, a suction pipeline is arranged between the recovery box and the drill rod, and a suction pump and a suction control valve are arranged on the suction pipeline; an experimental frame, a tension mechanism and a displacement meter are arranged on the experimental frame, and a tension meter is arranged between the tension mechanism and the drill rod. The present application can accurately simulate the deep-water high-pressure environment and the lowering process of the suction pile, so as to reveal the changing law of relevant process parameters when using suction piles to construct deep-water surface wells.

Description

Technical Field

[0001] The invention relates to the technical field of deepwater oil and gas drilling, and in particular to a deepwater suction pile well construction experimental device and a bearing capacity testing method. Background Art

[0002] Currently, offshore oil exploration and development operations are gradually shifting from shallow offshore areas to deep offshore areas in order to increase the area of ​​offshore oil and gas exploration and development and seek more oil and gas discoveries.

[0003] The deepwater surface well construction mainly adopts the jetting down pipe construction, which has a single operation mode and high requirements for the geological environment. The deepwater surface has the characteristics of high geological risk, loose shallow soil, shallow abnormal geological phenomena (shallow faults, shallow gas, shallow flow, natural gas hydrate, etc.), which makes the conventional pipe jetting well construction process have low ability to deal with shallow geological risks. The jetting down pipe construction is to form a channel for the seabed mud to be lowered into the pipe by hydraulic jetting. During the lowering process, the pipe sinks with the wellbore drilled by the drill bit under the action of its own weight and squeezes the surrounding formations until the designed depth. After being lowered to the designed depth, after a certain "waiting time", the cementation stress is established between the pipe and the formation clay, and it is reinforced with time, thereby ensuring that the pipe is "suspended" and does not sink.

[0004] In order to make the conduit "suspended" and not sink, it is necessary to ensure that the conduit has sufficient bearing capacity in the seabed soil. The lateral friction between the conduit and the formation can make up for the lack of formation bearing capacity. In the process of using jet conduit to build a well, if the jet force is too small, it is easy to increase the friction between the conduit and the seabed soil, resulting in a long time for the conduit to be lowered or even not being lowered into place; if the jet force is too large, it will take a long time for the seabed clay to recover the cementation stress, and it will be difficult to control the backfill time of the seabed soil, causing the conduit to sink. In contrast, suction pile well construction has the following advantages: it can be lowered using an offshore engineering vessel. At the same time, because the suction pile is large in size and can be lowered using negative pressure, it is not easy to cause the suction pile to sink, and the suction pile can be recycled and reused. In view of the above advantages, suction piles are widely used in deepwater surface well construction.

[0005] However, environmental factors such as the high pressure environment of deep seabed water, the high temperature during deepwater development operations, and seabed soil parameters (the friction of sand, clay, and silt is different) can affect the time and process of lowering suction piles. In addition, the shape, gravity, and other inherent factors of the suction pile are also related to its bearing capacity in the formation. Therefore, it is necessary to optimize the deepwater surface suction pile well construction process, so as to effectively evaluate the factors affecting the deepwater development operation process. Summary of the invention

[0006] To achieve the above purpose, the present application provides a deepwater suction pile well construction experimental device and a bearing capacity test method, which can accurately simulate the deepwater high-pressure environment and the suction pile lowering process to reveal the change law of relevant process parameters when using suction piles to construct deepwater surface wells. The technical solution provided is as follows:

[0007] A deep-water suction pile well construction experimental device, the experimental device comprising:

[0008] A kettle body, the kettle body having a hollow chamber, the hollow chamber being used to be filled with a soil layer and salt water of a predetermined density;

[0009] A kettle cover, used to close the hollow chamber, the kettle cover is provided with a through hole;

[0010] The lowering assembly comprises: a suction pile and a drill rod, wherein the suction pile is a hollow cylinder having a top end and a bottom end opposite to each other, wherein the bottom end is an open end, the top end is penetrated by the drill rod to form a closed end, and the drill rod is penetrated out of the through hole;

[0011] The gas injection assembly comprises: a first pressure sensor for detecting the internal pressure of the hollow chamber; a gas storage tank, an air intake pipeline is arranged between the gas storage tank and the hollow chamber, and a booster pump and an air intake control valve are arranged on the air intake pipeline;

[0012] A suction assembly comprises: a recovery box, a suction pipeline is arranged between the recovery box and the drill pipe, and a suction pump and a suction control valve are arranged on the suction pipeline;

[0013] An experimental frame is provided with a tension mechanism and a displacement meter, the displacement meter is used to detect the lowering depth of the lowering assembly, and a tension meter for measuring tension is provided between the tension mechanism and the drill rod.

[0014] As a preferred implementation, a pressure controller, an emergency safety valve and a pressure reducing pump are sequentially arranged on the suction pipeline downstream of the suction pump.

[0015] As a preferred embodiment, a two-phase separator is arranged between the pressure reducing pump and the recovery tank, the two-phase separator is provided with an exhaust pipeline connected to the outside, and the exhaust pipeline is provided with an exhaust valve; the gas separated by the two-phase separator is discharged through the exhaust pipeline, and the separated liquid and solid flow into the recovery tank along the suction pipeline.

[0016] As a preferred embodiment, the experimental device is further provided with a discharge component, which includes: an exhaust port arranged on the kettle cover; a discharge pipeline connected to the exhaust port, and a second pressure sensor and an outlet control valve are arranged on the discharge pipeline.

[0017] As a preferred implementation manner, the tension mechanism comprises: a lift and a steel wire rope connected to the lift, and the tension measuring meter is connected between the steel wire rope and the drill rod.

[0018] As a preferred implementation, the displacement meter is a scale, and a displacement measuring pointer is provided on the drill rod, and the displacement measuring pointer is used to read the indication of the scale.

[0019] As a preferred embodiment, the density of the brine is 1.03 g / cm3.

[0020] A method for testing the bearing capacity of deep-water suction pile well construction using the experimental device, the testing method comprising:

[0021] Obtain the distance L0 between the bottom of the suction pile and the soil layer and the length L1 of the suction pile;

[0022] Record the position of the displacement measurement pointer as the initial position X0;

[0023] Opening the air intake control valve and the boost pump, and injecting gas into the hollow chamber through the air intake pipeline until the first pressure sensor reaches a predetermined pressure value;

[0024] Lowering the lowering assembly through the tension mechanism, making the reading of the tension meter equal to the gravity value of the drill pipe during the lowering process, and recording the position X1 of the displacement measurement pointer after the first predetermined time of lowering;

[0025] Open the suction pump and the suction control valve until the suction pile is lowered to the stop position;

[0026] After waiting for the second predetermined time, the lowering assembly is lifted by the tension mechanism until the suction pile is pulled out, and the reading of the tension meter is read, and the friction between the suction pile and the soil layer is calculated, which is the bearing capacity of the suction pile in the soil layer. The bearing capacity is calculated by the following formula:

[0027]

[0028] Where: P0 is the minimum suction force of the suction pile, m 3 / min; P is the average displacement of the suction pile during penetration, m 3 / min; t is the static time of the suction pile, h; F u is the maximum bearing capacity of the overall structure, N;

[0029] F u =N cv +N co +N ci+N sv +N so +N si +N sb ;in,

[0030] N cv =q c A c ;

[0031]

[0032] After the sinking is completed, when a soil plug is formed in the conduit, N ci =q cs A cs ;

[0033] N sv =q s A s ;

[0034]

[0035]

[0036] N sb =q sb A sb ;

[0037] N cv is the support force at the end of the conduit, N co is the friction resistance of the outer side of the catheter, N ci is the friction resistance of the inner surface of the catheter, N sv is the end support force of the suction pile, N so is the friction resistance of the outer side of the skirt plate of the suction pile, N si is the friction resistance of the inner side of the skirt of the suction pile, N sb is the bearing capacity of the base plate at the top of the suction pile.

[0038] As a preferred implementation, when the suction pile is located at the stop position, the following relationship is satisfied:

[0039] X2-X1=L0+L1

[0040] Wherein, X2 represents the position of the displacement measuring pointer when the suction pile is in the stop position, and the unit is cm.

[0041] As a preferred embodiment, a pressure controller, an emergency safety valve and a pressure reducing pump are sequentially arranged on the suction pipeline downstream of the suction pump. If the decreasing rate of the reading of the first pressure sensor exceeds a threshold value, the pressure controller, the emergency safety valve and the pressure reducing pump are opened.

[0042] Beneficial effects:

[0043] The deepwater suction pile well construction experimental device provided by the present application can simulate the high-pressure environment under deepwater conditions of marine drilling by filling the kettle with salt water and injecting high-pressure gas. The suction pile is suspended and lowered by the drill pipe to simulate the lowering process of the deepwater suction pile, which is used to study the change law of process parameters when the suction pile is used to construct a deepwater surface well, so as to master the deepwater surface well construction method.

[0044] In the test method for the bearing capacity of deep-water suction pile well construction provided in the present application, the gravity of the drill rod can be balanced by suspending the drill rod through a tension mechanism, so that the suction pile can be lowered only by its own gravity, and the suction pile can be lowered to the stop position in combination with the suction method. When the suction pile is completely lowered, the lowering assembly is lifted by the tension mechanism until the suction pile is pulled out, and the friction between the suction pile and the soil layer can be calculated by reading the reading of the tension meter, thereby accurately reflecting the bearing capacity of the deep-water suction pile in the well construction process, and providing a theoretical basis for the optimization of the deep-sea suction pile well construction process.

[0045] With reference to the following description and drawings, the specific embodiments of the present application are disclosed in detail, indicating the manner in which the principles of the present application can be adopted. It should be understood that the embodiments of the present application are not limited in scope.

[0046] Features described and / or illustrated with respect to one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0047] It should be emphasized that the term “include / comprises” when used herein refers to the presence of features, integers, steps or components, but does not exclude the presence or addition of one or more other features, integers, steps or components. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative labor.

[0049] Figure 1 A schematic diagram of the structure of a deep-water suction pile well construction experimental device provided in an embodiment of the present application;

[0050] Figure 2 A schematic flow chart of a method for testing the bearing capacity of deep-water suction piles for well construction provided in an embodiment of the present application;

[0051] Figure 3 A schematic diagram of the longitudinal bearing capacity of the composite conduit of the suction pile provided in the embodiment of the present application;

[0052] Figure 4 A schematic diagram of the frictional resistance of a soil plug provided in an embodiment of the present application.

[0053] Description of reference numerals:

[0054] 100, catheter; 1, recovery box; 2, two-phase separator; 3, exhaust valve; 4, pressure reducing pump; 5, emergency safety valve; 6, pressure controller; 7, suction pump; 8, air intake pipeline; 9, booster pump; 10, nitrogen injection control valve; 11, gas storage tank; 12, suction pipeline; 13, first pressure sensor; 14, air intake control valve; 15, experimental stand; 16, first conversion joint; 17, air inlet; 18, second conversion joint ; 19. Elevator; 20. Displacement meter; 21. Wire rope; 22. Tension meter; 23. Second pressure sensor; 24. Discharge pipeline; 25. Outlet control valve; 26. Third conversion joint; 27. Exhaust port; 28. Fixing bolt; 29. ​​Kettle cover; 30. Displacement measurement pointer; 31. Gas; 32. Drill rod; 33. Brine; 34. Suction pile; 35. Soil layer; 36. Kettle body; 37. Suction control valve. DETAILED DESCRIPTION

[0055] The technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation methods. It should be understood that these implementation methods are only used to illustrate the present invention and are not used to limit the scope. After reading the present invention, modifications of various equivalent forms of the present invention by those skilled in the art all fall within the scope defined by the present application.

[0056] It should be noted that when an element is referred to as being "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation method.

[0057] Specifically, Figure 1 The upward direction indicated in the figure is defined as “up”. Figure 1 The downward direction indicated in the specification is defined as "down". It is worth noting that the definitions of various directions in this specification are only for the convenience of explaining the technical solution of the present invention, and do not limit the directions of the deep-water suction pile well construction experimental device of the embodiment of the present invention in other scenarios including but not limited to use, testing, transportation and manufacturing, which may cause the device to be reversed or its position to be changed.

[0058] There are currently two methods for deepwater surface well construction: drilling and jetting down the conduit. The drilling method is affected by the nature of the seabed soil. If the seabed soil is backfilled too quickly, it is easy to lose the wellbore, and the casing cannot be lowered or is only lowered halfway. Secondly, due to the low temperature of the seabed, cementing cement is difficult to solidify, affecting the timeliness of the operation (the average daily cost of deepwater offshore drilling platforms is about 160,000 US dollars). The jetting down the conduit method is to use hydraulic jetting to form a channel for the seabed mud to be lowered into the conduit. In comparison, suction pile well construction has obvious advantages. It can be lowered using marine engineering vessels. Suction piles are large in size and can be embedded in the seabed mud using negative pressure, so they are not easy to sink.

[0059] Suction piles are a type of foundation that is closed at the top and open at the bottom, similar to an inverted "bucket". Suction piles are widely used as the foundation for mooring marine floating structures and offshore oil and gas platforms due to their advantages such as fast construction speed, low cost and recyclability. They are also gradually being planned to be used in deepwater surface well construction as a reserve method for traditional jetting guide pipes.

[0060] The deepwater suction pile well construction experimental device provided in the embodiment of the present application can be based on suction piles and used to simulate the suction pile well construction process under deepwater or ultra-deepwater drilling conditions. In the field of marine drilling, drilling with a water depth greater than 500m is called deepwater drilling, and drilling with a water depth greater than 1500m is called ultra-deepwater drilling. Under deepwater drilling conditions, the water pressure gradually increases with the depth of drilling. Under ultra-deepwater drilling conditions, the ultra-high water pressure can reach 15MPa.

[0061] like Figure 1 As shown, the experimental device includes: a kettle body 36, the kettle body 36 has a hollow chamber, the hollow chamber is used to fill a soil layer 35 and a brine 33 of a predetermined density; a kettle cover 29, used to close the hollow chamber, the kettle cover 29 is provided with a through hole; a lowering component, including: a suction pile 34 and a drill rod 32, the suction pile 34 is a hollow cylinder, the cylinder has a top end and a bottom end opposite to each other, the bottom end is an open end, the top end is penetrated by the drill rod 32 to form a closed end, and the drill rod 32 is penetrated out of the through hole; a gas injection component, including: a first pressure sensor 13 for detecting the internal pressure of the hollow chamber ; An air storage tank 11, an air intake pipeline 8 is arranged between the air storage tank 11 and the hollow chamber, and a boost pump 9 and an air intake control valve 14 are arranged on the air intake pipeline 8; a suction component, comprising: a recovery box 1, a suction pipeline 12 is arranged between the recovery box 1 and the drill rod 32, and a suction pump 7 and a suction control valve 37 are arranged on the suction pipeline 12; an experimental frame 15, a tension mechanism and a displacement meter 20 are arranged on the experimental frame 15, and the displacement meter 20 is used to detect the lowering depth of the lowering component, and a tension meter 22 for measuring tension is arranged between the tension mechanism and the drill rod 32.

[0062] The deepwater suction pile well construction experimental device provided by the present application can simulate the high-pressure environment under deepwater conditions of marine drilling by filling the kettle 36 with salt water and injecting high-pressure gas. The suction pile 34 is suspended and lowered by the drill rod 32, which can simulate the lowering process of the deepwater suction pile 34 and is used to study the change law of the process parameters when the suction pile 34 is used to construct a deepwater surface well, so as to master the deepwater surface well construction method.

[0063] The kettle 36 is used to simulate a deep-water environment and is made of a high-pressure resistant material. The hollow chamber in the kettle 36 is filled with a seabed soil layer 35 and salt water 33 configured in a certain proportion. The salt water 33 is used to simulate seawater. Preferably, the density of the salt water is 1.03 g / cm 3 The soil layer 35 can be replaced with soil of different properties during the experiment, such as sand, clay, and silt, so as to simulate the lowering process of the suction pile 34 in different soils. The hollow chamber of the kettle body 36 is sealed by the kettle cover 29. The kettle body 36 and the kettle cover 29 can be sealed by fixing bolts 28, so that the kettle cover 29 can be easily separated from the kettle body 36, which is convenient for cleaning and replacing the soil layer 35.

[0064] The lowering assembly includes a suction pile 34 and a drill rod 32. The suction pile 34 is a hollow cylinder having a top and a bottom opposite to each other. The bottom is an open end. The top is penetrated by the drill rod 32 to form a closed end. The top of the drill rod 32 is penetrated through the through hole. The suction pile 34 is connected to the bottom of the drill rod 32 to ensure accurate vertical lowering. The top of the drill rod 32 is suspended on the experimental frame 15 by a tension mechanism, so that the entire suction pile 34 and the drill rod 32 can be hoisted, lifted and lowered by the tension mechanism.

[0065] The injection assembly is used to inject high-pressure gas into the hollow chamber of the kettle body 36, so as to cooperate with the brine 33 in the kettle body 36 to create a deep-water seabed environment. The injection assembly includes a gas storage tank 11, which can be used to store nitrogen or other types of inert gases, which is not limited in the present application. An air intake pipeline 8 is arranged between the gas storage tank 11 and the hollow chamber of the kettle body 36, and a booster pump 9 and an air intake control valve 14 for pressurizing the gas are arranged on the air intake pipeline 8. The air intake control valve 14 can be arranged downstream of the booster pump 9 on the air intake pipeline 8 to control the injection of high-pressure gas. A nitrogen injection control valve 10 can be further arranged between the booster pump 9 and the gas storage tank 11 to control the pressurization process of the gas by the booster pump 9.

[0066] Furthermore, the kettle cover 29 may be provided with an air inlet 17, which is used to connect the air inlet pipeline 8. In order to ensure the airtightness when the air inlet 17 is connected to the air inlet pipeline 8, a first conversion joint 16 may be provided between the air inlet 17 and the air inlet pipeline 8. The first pressure sensor 13 is used to detect the internal pressure of the hollow chamber of the kettle body 36. The first pressure sensor 13 may be a pressure gauge, which may be provided separately on the kettle cover 29 or on the air inlet pipeline 8. Preferably, in order to ensure the air intake tightness, the first pressure sensor 13 is provided on the air inlet pipeline 8 and is located downstream of the air intake control valve 14.

[0067] The suction assembly is used to suck the fluid inside the suction pile 34, so that negative pressure is formed inside the suction pile 34, so that the suction pile 34 enters the soil layer 35 under the action of negative pressure. Specifically, when the suction pile 34 relies on its own weight to embed its lower end into the soil, the lower end of the cylinder forms a closed state. At this time, water is pumped outward through the suction pipeline 12 connected to the drill rod 32, causing the pressure inside the suction pile 34 to decrease. When the pressing force formed by the internal and external pressure difference of the suction pile 34 acts on the suction pile 34, and the vertical downward pressure exceeds the friction resistance formed between the seabed soil and the side wall of the suction pile 34, the suction pile 34 is continuously pressed into the seabed soil.

[0068] The suction assembly includes a recovery box 1, which is used to recover the back-discharged soil layer 35 and brine 33. A suction pump 7 and a suction control valve 37 are provided on the suction pipeline 12 between the recovery box 1 and the drill rod 32. The suction control valve 37 can be located upstream of the suction pump 7 on the suction pipeline 12, so as to control the suction of the liquid by the suction pump 7. In order to ensure the sealing when the suction pipeline 12 is connected to the drill rod 32, a second conversion joint 18 can be provided between the suction pipeline 12 and the drill rod 32.

[0069] Furthermore, a pressure controller 6, an emergency safety valve 5 and a pressure reducing pump 4 are sequentially arranged on the suction pipeline 12 downstream of the suction pump 7. The pressure controller 6 is used to prevent excessive pressure from causing damage to the equipment. When the pressure is too high, the emergency safety valve 5 can be opened and the pressure can be reduced by the pressure reducing pump 4. The criterion for judging excessive pressure is to read whether the decreasing rate of the reading of the first pressure sensor 13 is too fast. If the reading of the first pressure sensor 13 decreases too fast during the suction process, there is a safety hazard and the emergency safety valve 5 needs to be opened.

[0070] It should be noted that the “upstream” and “downstream” described in this specification refer to the “upstream” and “downstream” along the flow direction of the fluid. For example, on the air intake pipeline 8, along the flow direction of the fluid, the air intake control valve 14 is located downstream of the booster pump 9, and the air storage tank 11 is located upstream of the booster pump 9; on the suction pipeline, along the flow direction of the fluid, the suction control valve 37 is located upstream of the suction pump 7, and the recovery tank 1 is located downstream of the suction pump 7.

[0071] In one embodiment, a two-phase separator 2 is provided between the pressure reducing pump 4 and the recovery tank 1, and the two-phase separator 2 is provided with an exhaust pipeline connected to the outside, and an exhaust valve 3 is provided on the exhaust pipeline; the gas separated by the two-phase separator 2 is discharged through the exhaust pipeline, and the separated liquid and solid flow into the recovery tank 1 along the suction pipeline 12. In this embodiment, the two-phase separator 2 is a liquid-solid separator, and the separated liquid and solid are discharged back to the recovery tank 1 for recycling.

[0072] In this specification, the experimental device is also provided with a discharge assembly for discharging the gas in the hollow chamber of the kettle body 36. The discharge assembly includes: an exhaust port 27 provided on the kettle cover 29; a discharge pipeline 24 connected to the exhaust port 27, and a second pressure sensor 23 and an outlet control valve 25 are provided on the discharge pipeline 24. The second pressure sensor 23 is used to detect the outlet pressure and can be a pressure gauge. In order to ensure the sealing when the exhaust port 27 is connected to the discharge pipeline 24, the exhaust port 27 and the discharge pipeline 24 are connected through a third conversion joint 26.

[0073] In this specification, the tension mechanism includes: a lift 19 and a wire rope 21 connected to the lift 19, and the tension meter 22 is connected between the wire rope 21 and the drill rod 32. Specifically, the lift 19 is used to drive the lifting and lowering of the entire lowering assembly. The wire rope 21 is used to connect the drill rod 32 and the lift 19, and the wire rope 21 is specifically a non-rebound wire rope. A tension meter 22 is set between the wire rope 21 and the drill rod 32, and the tension meter 22 is used to display the tension of the lowering assembly.

[0074] In this specification, the displacement meter 20 is a scale, and the drill rod 32 is provided with a displacement measuring pointer 30, and the displacement measuring pointer 30 is used to read the indication of the scale. The displacement measuring pointer 30 on the drill rod 32 can be raised and lowered together with the drill rod 32, and can be used as a measurement reference. By reading the reading on the scale, the lowering depth of the lowering assembly can be accurately and conveniently reflected.

[0075] The present application also provides a method for testing the bearing capacity of deep-water suction pile well construction using the experimental device, the testing method comprising:

[0076] S10: Obtaining the distance L0 between the bottom of the suction pile 34 and the soil layer 35 and the length L1 of the suction pile 34;

[0077] S20: Record the position of the displacement measurement pointer 30 as the initial position X0;

[0078] S30: opening the air intake control valve 14 and the boost pump 9, and injecting gas into the hollow chamber through the air intake pipeline 8 until the first pressure sensor 13 reaches a predetermined pressure value;

[0079] S40: lowering the lowering assembly through the tension mechanism, making the reading of the tension measuring meter 22 equal to the gravity value of the drill rod 32 during the lowering process, and recording the position X1 of the displacement measuring pointer 30 after the first predetermined time of lowering;

[0080] S50: Open the suction pump 7 and the suction control valve 37 until the suction pile 34 is lowered to the stop position;

[0081] S60: After waiting for a second predetermined time, the lowering assembly is lifted by the tension mechanism until the suction pile 34 is pulled out, and the reading of the tension meter 22 is read, and the friction between the suction pile 34 and the soil layer 35 is calculated, which is the bearing capacity of the suction pile 34 in the soil layer 35. The bearing capacity is calculated by the following formula:

[0082]

[0083] Where: P0 is the minimum suction force of the suction pile 34, m 3 / min; P is the average displacement of the suction pile 34 during its penetration, m 3 / min; t is the static time of the suction pile 34, h; F u is the maximum bearing capacity of the overall structure, N.

[0084] The specific process of determining the bearing capacity is as follows:

[0085] Firstly, the longitudinal ultimate bearing capacity model of suction pile 34 is established;

[0086] During the penetration of the suction pile 34 , the friction between the inner and outer walls of the skirt of the suction pile 34 is an important component of its bearing capacity. Especially when the suction pile 34 is penetrated into the seabed soil, the effective stress of the soil inside the suction pile 34 and the seepage in the soil have a great influence on the friction of the suction pile 34 .

[0087] Please refer to Figure 3 , schematic diagram of the longitudinal bearing capacity of a suction pile composite conduit (Chen Guanzhong).

[0088] Due to the influence of seepage, the friction between the soil and the inner wall of the suction pile 34 is very different from the friction between the outer wall of the pile tube, which causes the soil outside the suction pile 34 to flow into the pile tube. After the suction pile 34 is sunk to the set position, the suction pile 34 relies on the soil in the pile tube to provide bearing capacity. At the same time, since the soil is destroyed when it is sunk into place, the bearing capacity outside the pile tube gradually recovers after it is sunk into place. In the longitudinal direction, the suction pile composite conduit is supported by the lateral friction inside and outside the skirt of the suction pile 34 and the lateral friction inside and outside the conduit 100, in addition to the deadweight of the conduit 100 and the suction pile 34, the support force of the top plate between the suction pile 34 and the conduit 100, and the support force of the top plate between the suction pile 34 and the conduit 100. Figure 3 shown.

[0089] After the suction pile 34 is sunk into the seabed mud surface, it maintains vertical stability, then:

[0090] F u =N cv +N co +N ci +N sv +N so +N si +N sb ≥Q c +Q b (1)

[0091] in, Figure 3 Medium cv is the end support force of the catheter 100, N co is the friction resistance of the outer surface of the catheter 100, N ci is the friction resistance of the inner surface of the catheter 100, N sv is the end support force of the suction pile 34, N so is the friction resistance of the outer side of the skirt plate of the suction pile 34, N si is the friction resistance of the inner side of the skirt of the suction pile 34, N sb is the bearing capacity of the bottom plate at the top of the suction pile 34, Q c The gravity of the catheter is 100, Q b is the gravity of the suction pile 34, F u It is the ultimate bearing capacity of the suction pile composite conduit as a whole in the soil layer.

[0092] Based on the pile-soil interaction theory, the ultimate bearing capacity models of the inner and outer sides of the suction pile 34 and the outer side of the conduit 100 can be obtained as follows:

[0093] The ultimate bearing capacity model of the outer side of the conduit 100:

[0094]

[0095] The outer ultimate bearing capacity model of suction pile 34:

[0096]

[0097] The inner side ultimate bearing capacity model of suction pile 34:

[0098]

[0099] Based on the pile-soil interaction theory, the ultimate bearing capacity models of the end of the guide tube 100, the end of the suction pile 34, and the bottom plate at the top of the suction pile 34 can be obtained as follows:

[0100] The ultimate bearing capacity model of the end of the conduit 100:

[0101] N cv =q c A c (5)

[0102] The ultimate bearing capacity model of suction pile 34 end:

[0103] N sv =q s A s (6)

[0104] Suction pile 34 bottom plate ultimate bearing capacity model:

[0105] N sb =q sb A sb (7)

[0106] According to the soil arch effect in the pile soil, when the soil in the conduit 100 is subjected to pressure, the soil will be compressed to form a soil plug as the load is pressed in. When the pressure is too large, the soil arch will be destroyed and a new soil arch will be formed. At this time, the resistance of the soil arch exceeds the upward pressure. The soil arch effect converts the resistance of the soil at the bottom of the pile into the normal squeezing force of the inner wall of the conduit 100, greatly enhancing the friction between the seabed soil and the inner wall of the conduit 100. During the penetration of the suction pile 34, the seabed soil pressed into the conduit 100 undergoes a cycle of arch formation and destruction. When the seabed soil in the conduit 100 does not form a soil plug, the bearing capacity is the friction of the seabed soil in the conduit 100. When an elastic soil plug is formed in the conduit 100, it is equivalent to forming a closed pile, and the resistance is the end resistance.

[0107] Assume that after the penetration is completed, the friction of the inner wall of the catheter 100 takes effect, such as Figure 4 shown. Figure 4 Schematic diagram of the frictional resistance of the soil plug.

[0108] When the soil enters the conduit 100, the depth is z=∑h iWhen the total ultimate bearing capacity is:

[0109]

[0110] Assuming that a soil plug is formed in the conduit 100 after the penetration, the ultimate bearing capacity model is:

[0111] N ci =q cs A cs (9)

[0112] The ultimate bearing capacity of the suction pile 34 (composite conduit) is obtained by superposition of several values:

[0113]

[0114] When a soil plug is formed during penetration, the ultimate bearing capacity calculation model of the suction pile 34 (composite conduit) is:

[0115]

[0116] Among them, F u is the maximum bearing capacity of the whole structure, N; L is the height of the skirt board of suction pile 34, m; d c is the radius of the catheter 100, m; d s is the radius of the suction pile 34, m; f co —Force per unit area of ​​the conduit 100 in the soil, Pa; f so — Friction force per unit area between the interior of the suction pile 34 and the soil contact surface, Pa; f si —lateral friction force per unit area of ​​suction pile 34, Pa; A c —Cross-sectional area of ​​the conduit 100, m 2 ; A s —Suction pile 34 cross-sectional area, m 2 ; A sb —Top plate area of ​​suction pile 34, m 2 ;q c —Resistance per unit area of ​​conduit 100, N / m 2 ;q s — Resistance of suction pile 34 per unit area, N / m 2 ;q sb —Resistance to the top plate of suction pile 34 per unit area, N / m 2 .

[0117] The friction force per unit area between the suction composite pipe and the seabed soil is an important factor in determining its bearing capacity.

[0118] (1) Friction force per unit area of ​​clay soil

[0119] In clay, the change of the frictional force combined with the undrained shear strength between the suction pile 34 and the guide tube 100 is:

[0120] f=αs u (12)

[0121] Where: α is the dimensionless viscosity, α≤1; s u represents the undrained shear strength, pa.

[0122] Its exact size is:

[0123]

[0124] Where: v The sum of the earth pressure above this position, Pa;

[0125] (2) End resistance per unit area

[0126] q=N c s u (14)

[0127] Where: N c It is the load-bearing capacity assessment value.

[0128] (3) Friction force of sand per unit area

[0129] f=Kσ v tanδ (15)

[0130] Where: K is the lateral pressure assessment value, which is 0.5-1. δ is the pipe-soil friction angle, which is is the internal friction angle of soil.

[0131] (4) Sand end resistance per unit area

[0132] q u =N p P0 (16)

[0133] Where: N p is the bearing capacity coefficient.

[0134] (5) Soil plug resistance inside the conduit 100

[0135] The friction force per unit area is proportional to the weight of the upper soil plug, that is:

[0136] f ci =μα∑γ i h i (17)

[0137] Where: f zis the radial friction resistance per unit area at depth z, is the friction coefficient between the soil plug and the pile, is the lateral pressure coefficient, is the weight of the i-th soil layer, and h i is the thickness of the i-th soil layer above the depth ( Figure 4 They are the first soil layer h1, the second soil layer h2 and the third soil layer h3).

[0138] Longitudinal real-time bearing capacity model of composite pipes with suction piles

[0139] In the process of the suction pile 34 gradually sinking into the seabed soil, the soil inside the suction pile 34 is disturbed and damaged under the action of negative pressure, the bearing capacity of the soil inside the suction pile 34 increases, and the bearing capacity of the soil outside the suction pile 34 decreases. After the suction pile 34 is installed in place, the bearing capacity gradually recovers. The calculation model is:

[0140] F ut =kF u (18)

[0141] Where: F ut is the real-time bearing capacity of the whole structure, N; k is the dimensionless bearing capacity change evaluation parameter.

[0142] According to the principle of mechanics, the negative pressure inside the suction pile 34 is proportional to the force between the soil and the suction pile 34, so the influence factor of suction on it can be expressed as:

[0143]

[0144] Where: P0 is the minimum suction force of the suction pile 34, m 3 / min; P is the average displacement of the suction pile 34 during its penetration, m 3 / min; t is the static time of the suction pile, h.

[0145] Taking into account the static time and negative pressure factors, the reduction coefficient of the penetration bearing capacity of the suction pile composite conduit can be represented as:

[0146]

[0147] The overall real-time carrying capacity is:

[0148]

[0149] Where: P0 is the minimum suction force of the suction pile 34, m 3 / min; P is the average displacement of the suction pile 34 during its penetration, m 3 / min; t is the static time of the suction pile 34, h; F u is the maximum bearing capacity of the overall structure of the suction pile composite conduit, N.

[0150] Determining the real-time bearing capacity through the above formula can accurately reflect the bearing capacity of deep-water suction piles during well construction, and provide a theoretical basis for optimizing the deep-sea suction pile well construction process.

[0151] Specifically, in step S30, high-pressure gas is injected into the hollow chamber of the kettle body 36 through the air inlet pipe 8 to simulate the deep-water high-pressure environment. The predetermined pressure value is determined according to the experimental requirements. During the lowering process, the tension mechanism is adjusted so that the reading of the tension meter 22 is equal to the gravity value of the drill rod 32, thereby balancing the gravity of the drill rod 32 to ensure that the suction pile 34 enters the soil layer 35 only under the action of its own gravity. After lowering for a period of time, the position of the lowering component at this time is recorded by the displacement measurement pointer 30, and the suction pump 7 and the suction control valve 37 are opened at the same time, so that the suction pile 34 is quickly lowered under the action of negative pressure until the suction pile 34 is lowered to the stop position.

[0152] In this specification, when the suction pile 34 is located at the stop position, the following relationship is satisfied:

[0153] X2-X1=L0+L1

[0154] Wherein, X2 represents the position of the displacement measuring pointer 30 when the suction pile 34 is at the stop position, and the unit is cm.

[0155] When the suction pile 34 is lowered to the stop position, the entire suction pile 34 is lowered into the soil layer 35, so that in the process of waiting for the backfill of the seabed soil, a bonding stress is formed between the suction pile 34 and the soil layer 35, ensuring that the suction pile 34 is "suspended" in the soil layer and does not sink. After waiting for the second predetermined time, that is, after the bonding stress is formed between the suction pile 34 and the soil layer 35, the lowering assembly is lifted by the tension mechanism until the suction pile 34 is pulled out, and the reading of the tension meter 22 is read, and the friction between the suction pile 34 and the soil layer 35 can be calculated. The friction can reflect the bearing capacity of the suction pile 34 in the soil layer 35, providing a theoretical basis for the optimization of the deep-sea suction pile well construction process. In the subsequent test process, the above test steps can be repeated by changing the size and shape of the suction pile 34 and changing the soil layer 35.

[0156] In order to better understand this application, Figure 1 and Figure 2 , the deep-water suction pile well construction experimental device and the bearing capacity testing method provided in the embodiments of the present application are further explained.

[0157] First, build a deep-water suction pile well construction experimental device. Specifically, put the soil layer 35 and the prepared brine 33 into the kettle 36. Then connect the drill rod 32 to the wire rope 21 and the elevator 19, and measure the distance L0 between the bottom of the suction pile 34 and the soil layer 35 and the length L1 of the suction pile 34. Cover the kettle cover 29, tighten the fixing bolts 28, and record the position of the displacement measurement pointer 30 as the initial position X0. Ensure that the outlet control valve 25 and the suction control valve 37 are closed, open the nitrogen injection control valve 10 and the air intake control valve 14, fill a certain amount of nitrogen, and then close the air intake control valve 14 and the nitrogen injection control valve 10 in turn, and test whether the kettle 36 and each pipeline joint are leaking by monitoring the indication of the first pressure sensor 13. If the indication of the first pressure sensor 13 remains stable for a period of time after gas injection, the sealing is good. If it slowly decreases, it can be detected at the first conversion joint 16, the second conversion joint 18 and the third conversion joint 26 by soapy water.

[0158] Then, the nitrogen injection control valve 10 and the air intake control valve 14 are opened in sequence, and the booster pump 9 is used to pump nitrogen into the kettle body 36. The volume of the pumped gas is determined according to the simulated water depth, and then the air intake control valve 14 and the nitrogen injection control valve 10 are closed. The drill rod 32 and the suction pile 34 are slowly lowered to make the reading of the tension meter 22 equal to the gravity of the drill rod 32. After a period of time, the position of the displacement measurement pointer 30 is recorded as the initial stop position X1.

[0159] Calculate the position of X2 so that the difference between X2 and X1 is equal to the sum of L0 and L1. Turn on the suction pump 7, slowly open the suction control valve 37, and control the lowering of the suction pile 34 by sucking the internal pressure of the suction pile 34. When the displacement measurement pointer 30 points to the position of X2, close the suction control valve 37. Among them, when the suction pile is lowered by the suction force of the suction pump 7, part of the soil layer 35 and the brine 33 will be discharged along the drill pipe 32 and the suction pipeline 12. If the rate of decrease of the reading of the first pressure sensor 13 exceeds the threshold, open the pressure controller 6 and the emergency safety valve 5 to avoid damage to the instrument, and reduce the pressure by the pressure reducing pump 4 to enter the two-phase separator 2. After separation, the gas is discharged from the exhaust valve 3, and the solid and liquid return to the recovery box 1. Wait for a period of time for the seabed soil to be backfilled, and measure the friction between the suction pile 34 and the soil layer 35, which can reflect the bearing capacity of the suction pile 34 in the seabed soil.

[0160] The above embodiments are only for illustrating the technical concept and features of the present application, and their purpose is to enable people familiar with the technology to understand the content of the present application and implement it accordingly, and they cannot be used to limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit of the present application should be included in the protection scope of the present application.

[0161] All articles and references disclosed, including patent applications and publications, are incorporated herein by reference for all purposes. The term "consisting essentially of..." to describe a combination should include the identified elements, ingredients, parts or steps and other elements, ingredients, parts or steps that do not substantially affect the basic novel characteristics of the combination. The use of the terms "comprising" or "including" to describe a combination of elements, ingredients, parts or steps herein also contemplates embodiments that consist essentially of these elements, ingredients, parts or steps. By using the term "may", it is intended to indicate that any attribute described that "may" include is optional.

[0162] Multiple elements, ingredients, parts or steps can be provided by a single integrated element, ingredient, part or step. Alternatively, a single integrated element, ingredient, part or step can be divided into separate multiple elements, ingredients, parts or steps. The disclosure "one" or "an" used to describe an element, ingredient, part or step is not intended to exclude other elements, ingredients, parts or steps.

[0163] It should be understood that the above description is for illustration and not for limitation. By reading the above description, many embodiments and many applications beyond the provided examples will be apparent to those skilled in the art. For comprehensive purposes, all articles and references, including the disclosures of patent applications and announcements, are incorporated herein by reference.

Claims

1. A method for testing the bearing capacity of deep-water suction pile well construction in a deep-water suction pile well construction experimental device, characterized in that: The deep-water suction pile well construction experimental device comprises: a kettle body, the kettle body having a hollow chamber, the hollow chamber being used to fill a soil layer and salt water of a predetermined density; A kettle cover, used to close the hollow chamber, the kettle cover is provided with a through hole; The lowering assembly comprises: a suction pile and a drill rod, wherein the suction pile is a hollow cylinder having a top end and a bottom end opposite to each other, wherein the bottom end is an open end, the top end is penetrated by the drill rod to form a closed end, and the drill rod is penetrated out of the through hole; The gas injection assembly comprises: a first pressure sensor for detecting the internal pressure of the hollow chamber; a gas storage tank, an air intake pipeline is arranged between the gas storage tank and the hollow chamber, and a booster pump and an air intake control valve are arranged on the air intake pipeline; A suction assembly comprises: a recovery box, a suction pipeline is arranged between the recovery box and the drill pipe, and a suction pump and a suction control valve are arranged on the suction pipeline; An experimental stand, wherein a tension mechanism and a displacement meter are arranged on the experimental stand, wherein the displacement meter is used to detect the lowering depth of the lowering assembly, and a tension meter for measuring tension is arranged between the tension mechanism and the drill rod. The displacement measuring meter is a scale, and a displacement measuring pointer is provided on the drill rod, and the displacement measuring pointer is used to read the indication of the scale; The test method includes: Obtain the distance L0 between the bottom of the suction pile and the soil layer and the length L1 of the suction pile; Record the position of the displacement measurement pointer as the initial position X0; Opening the air intake control valve and the boost pump, and injecting gas into the hollow chamber through the air intake pipeline until the first pressure sensor reaches a predetermined pressure value; Lowering the lowering assembly through the tension mechanism, making the reading of the tension meter equal to the gravity value of the drill pipe during the lowering process, and recording the position X1 of the displacement measurement pointer after the first predetermined time of lowering; Open the suction pump and the suction control valve until the suction pile is lowered to the stop position; After waiting for the second predetermined time, the lowering assembly is lifted by the tension mechanism until the suction pile is pulled out, and the reading of the tension meter is read, and the friction between the suction pile and the soil layer is calculated, which is the bearing capacity of the suction pile in the soil layer. The bearing capacity is calculated by the following formula: Where: P0 is the minimum suction force of the suction pile, m 3 / min; P is the average displacement of the suction pile during penetration, m 3 / min; t is the static time of the suction pile, h; F u is the maximum bearing capacity of the overall structure, N; F u =N cv +N co +N ci +N sv +N so +N si +N sb ;in, N cv =q c A c ; After the sinking is completed, when a soil plug is formed in the conduit, N ci =q cs A cs ; N sv =q s A s ; N sb =q sb A sb ; N cv is the support force at the end of the conduit, N co is the friction resistance of the outer side of the catheter, N ci is the friction resistance of the inner surface of the catheter, N sv is the end support force of the suction pile, N so is the friction resistance of the outer side of the skirt plate of the suction pile, N si is the friction resistance of the inner side of the skirt of the suction pile, N sb is the bearing capacity of the base plate at the top of the suction pile.

2. The method for testing the bearing capacity of deep-water suction piles for well construction as claimed in claim 1, characterized in that: When the suction pile is at the stop position, the following relationship is satisfied: X2-X1=L0+L1 Wherein, X2 represents the position of the displacement measuring pointer when the suction pile is in the stop position, and the unit is cm.

3. The method for testing the bearing capacity of deep-water suction piles for well construction as claimed in claim 1, characterized in that: A pressure controller, an emergency safety valve and a pressure reducing pump are sequentially arranged on the suction pipeline downstream of the suction pump. If the decreasing rate of the reading of the first pressure sensor exceeds a threshold, the pressure controller, the emergency safety valve and the pressure reducing pump are opened.

4. The method for testing the bearing capacity of deep-water suction piles for well construction as claimed in claim 3, characterized in that: A two-phase separator is arranged between the pressure reducing pump and the recovery tank, and the two-phase separator is provided with an exhaust pipeline connected to the outside, and an exhaust valve is arranged on the exhaust pipeline; the gas separated by the two-phase separator is discharged through the exhaust pipeline, and the separated liquid and solid flow into the recovery tank along the suction pipeline.

5. The method for testing the bearing capacity of deep-water suction piles for well construction as claimed in claim 1, characterized in that: The experimental device is also provided with a discharge component, which includes: an exhaust port arranged on the kettle cover; a discharge pipeline connected to the exhaust port, and a second pressure sensor and an outlet control valve are arranged on the discharge pipeline.

6. The method for testing the bearing capacity of deep-water suction piles for well construction as claimed in claim 1, characterized in that: The tension mechanism comprises: an elevator and a steel wire rope connected to the elevator, and the tension measuring meter is connected between the steel wire rope and the drill rod.

7. The method for testing the bearing capacity of deep-water suction piles for well construction as claimed in claim 1, characterized in that: The density of the brine is 1.03 g / cm 3 .

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