Geotechnical interlaced geology long-distance land-to-sea horizontal directional drilling submarine cable landing construction method

Abstract

The invention relates to a long-distance land-to-sea horizontal directional drilling submarine cable landing construction method for rock-soil staggered geology. The method comprises the following steps: (1) construction preparation; (2) preparing slurry; (3) rock section guide drilling; (4) forward pushing and reaming of the rock section; (5) guiding and drilling a soil layer; (6) mounting a bracket and connecting the bracket with a drill rod; (7) grading stretching and expanding of the rock sections; (8) mounting a steel sleeve on the rock section; (9) staged stretching and expanding of the remaining soil layer; and (10) the pipeline is dragged back in a segmented mode. According to the invention, the stability of a soil layer and the safety of drill rod equipment during directional drilling and reaming construction of a rock layer section are effectively ensured. The problems that follow-up pipelines are dragged back and stuck due to hole collapse and stepped holes easily caused by reaming under the rock-soil interlaced geological condition and breakage occurs during long-distance penetrating drill rod connection are solved, and guarantee is provided for high-precision green and safe construction of long-distance land-to-sea horizontal directional drilling submarine cable landing construction under the rock-soil interlaced geological condition.

Description

Technical Field

[0001] The present invention belongs to the technical field of offshore pipeline construction, is suitable for the construction of submarine cable landing projects, and mainly relates to a long-distance land-to-sea horizontal directional drilling submarine cable landing construction method with rock-soil interlaced geology. Background Art

[0002] The landing construction of long-distance submarine cables is a key process for laying submarine cables and an important prerequisite for transmitting marine power to land power grids. When crossing ecological protection areas or the geological environment of the landing section is complex, the conventional pre-trenching method is no longer used. Horizontal directional drilling technology, with its advantages of environmental friendliness, precision and efficiency, and construction safety, has become the preferred method for submarine cable landing construction when crossing complex geology or high requirements for surrounding environmental protection. In view of the increasingly complex land geological conditions faced by submarine cable landing construction, crossing extremely important areas for coastal biological or physical protection, and the proximity of landing points to residential breeding areas, the crossing distance of the land-sea directional drilling design curve is getting longer and longer to avoid ecological protection areas and residential protection areas, which brings about multiple problems such as increased risk of drill rod instability and damage, increasingly difficult drill rod control, increased phenomenon of hole expansion and collapse, and sharp increase in friction resistance of ultra-long pipelines. At present, most of the long-distance directional drilling construction technologies are land-to-road directional drilling, and there are few projects of land-to-sea directional drilling crossing ultra-long distances. In addition, most of the geology crossed by a few long-distance land-to-sea directional drillings is silt strata or rock and soil layers, which have little reference value when crossing the adverse geological environment of rock and soil interlacing.

[0003] Among them, China National Offshore Oil Corporation applied for "A method for landing a submarine pipeline during offshore oil engineering construction CN 109356527 A". The above related patents mainly focus on the detailed description of the construction steps of the submarine pipeline landing construction using only one type of hole expansion method, namely forward push expansion.

[0004] Compared with the conventional land-to-land horizontal directional drilling process, the land-to-sea horizontal directional drilling process faces a complex construction environment. It may involve ecological protection areas, channel crossings, scour pits, etc.; the depth of the stratum to be crossed is deep and the geology is complex, and multiple different geological layers need to be dealt with during the crossing process; in addition, land-to-sea directional drilling has higher requirements for equipment than land-to-land directional drilling. Not only does it require offshore support platforms and ships, but its equipment must also meet the drilling and backhauling capabilities required by the technical solution, and the operating accuracy must also meet the engineering requirements. In addition, the land-to-sea directional drilling excavation point is located on the seabed surface, which is very likely to pose a threat to the marine environment during construction. At present, most submarine cable landing construction uses the reverse expansion method, that is, installing an expander from the excavation point to the entry point to expand back. This method allows a large amount of mud to infiltrate the ocean, destroying the ecological environment. In addition, for directional drilling crossings involving rock layers in the landing section, expansion is very likely to cause hole collapse, leading to subsequent risks such as stuck pipes.

[0005] The submarine cable protection steel pipe is the protective armor of the submarine cable. Completing the overall underground pipeline traction of the submarine cable protection pipe is an important prerequisite for the submarine cable landing construction. At present, during the land-to-sea horizontal directional drilling submarine cable landing construction, the pipeline traction is mostly completed by the offshore pipe-laying ship in cooperation with the offshore drilling rig. This traditional pipeline traction method mainly relies on the pipe-laying ship to prefabricate the pipeline and then transfer it to the drilling rig for pipeline traction. The cross-operation of pipeline prefabrication and pipeline traction makes the construction period longer, and the offshore pipeline transportation also increases the labor cost. At the same time, the prefabrication of steel pipes at sea also increases the difficulty of the construction personnel's work, resulting in uncertainty in the quality of steel pipes, and also increases the risk of pipe jamming in the later pipeline traction. In addition, the rework of steel pipes not only increases the time cost, but is also likely to cause project failure due to long-term pipeline suspension.

[0006] For long-distance land-to-sea horizontal directional drilling and submarine cable landing construction in rock-soil interlaced geology, ensuring the quality of hole expansion and sufficient pipeline pullback force is the key. Through the graded hole expansion method combining forward hole expansion and pull expansion by the onshore drilling rig and the offshore drilling rig, the appropriate hole expansion method is adopted for different geology and the rock layer is protected with steel casing. It can not only effectively improve the hole expansion efficiency, but also avoid the risk of drill pipe damage. In addition, multiple graded hole expansion also reduces the grade difference to ensure that the hole expansion diameter meets the preset requirements. In addition, a special reserved hole expansion section construction process is also used for each graded hole expansion, which can also effectively prevent mud from seeping into the sea and protect the marine environment. After the hole expansion is completed, the onshore pipe pusher is used to assist the offshore pullback barge to complete the pipeline pullback, providing sufficient thrust and pullback force to reduce the risk of pipe jamming. The onshore prefabricated welded steel pipe also ensures the accuracy of pipeline welding and the continuity of pullback. At the same time, considering the large friction resistance of the super-long steel pipe, the pipeline pullback is completed in sections by five-to-one method, ensuring the safety and reliability of the pipeline pullback operation.

[0007] In order to solve the problems of step holes or collapsed holes, easy damage to drill rods, uneven hole formation, leakage of directional drilling fluid, insufficient pull-back force of long-distance pipelines, and easy pipe jams during the construction of long-distance land-to-sea horizontal directional drilling submarine cable landing in rock-soil interlaced geology. This construction method was implemented in the submarine cable landing section of the Shenneng Hainan CZ2 offshore wind power demonstration project, and the long-distance land-to-sea horizontal directional drilling crossing and pipeline pull-back were successfully carried out, and the submarine cable landing construction was successfully completed. The non-excavation directional drilling plane spacing of the landing section was 4.5m for a total of two times, the directional drilling crossing length was 1650m, the water depth at the excavation point was about 20m, and the crossing section mainly crossed the silt layer, clay layer and rock and soil layer. The crossing section not only has an extremely important coastal protection biological protection area, but also has aquaculture ponds, public welfare forests and houses and buildings, provincial roads on the land side of the landing point, and there is a coral protection area in the sea area near the coastline. Combined with the geological conditions of crossing and the ecological protection zone involved in the landing section, this project selected the expansion process according to different geology, and combined with auxiliary equipment, finally formed a long-distance land-to-sea horizontal directional drilling cable landing construction method in rock-soil interlaced geology. It effectively ensures the stability of the expanded rock strata during the construction of land-to-sea horizontal directional drilling in rock-soil interlaced geology, the high quality of the entire expansion, the eco-friendliness, and the safety and reliability of the pipeline pullback. The 1650m long-distance land-to-sea horizontal directional drilling crossing and pipeline pullback under rock-soil interlaced geological conditions were achieved on site. It solves the problems of poor expansion quality of long-distance land-to-sea horizontal directional drilling under rock-soil interlaced geological conditions, easy damage to drilling rigs, leakage pollution, insufficient pipeline pullback force, and long construction period, providing a guarantee for the safe, green, and efficient construction of long-distance land-to-sea horizontal directional drilling cable landing in rock-soil interlaced geology. Summary of the invention

[0008] To achieve the above-mentioned object, the present invention aims to provide a long-distance land-to-sea horizontal directional drilling submarine cable landing construction method in rock-soil interlaced geology.

[0009] The technical solution adopted by the present invention is: a long-distance land-to-sea horizontal directional drilling submarine cable landing construction method in rock-soil interlaced geology, comprising the following steps:

[0010] S1: Construction preparation:

[0011] Before the formal construction, the surveying and positioning, site leveling, barge anchoring, equipment installation and commissioning should be done well, the construction equipment parameters should be confirmed, the material quality inspection should be completed, the technical personnel should be briefed, and the emergency materials should be inspected. Before the pilot hole is drilled, the magnetic azimuth angle of the crossing center line should be measured as the original basis for the pilot hole control;

[0012] S2: Mud preparation:

[0013] Before drilling, a mud pool should be arranged and a mud laboratory should be set up on site. Different additives should be added according to different geological conditions. Water samples from the site should be used to make necessary corrections to the initial mud formula tested when using clean water in combination with the specific conditions of the strata being drilled.

[0014] Prepare mud according to the mud ratio determined by the mud laboratory and the water quality of the on-site water, and measure the mud parameters in time. The mud parameters should meet the following performance indicators: Marsh funnel viscosity should be 50-60s, plastic viscosity 8-12MPa·s, dynamic shear force 5-10Pa, apparent viscosity 12-20MPa·s, filtration loss 8-12ml, pH value 9-11;

[0015] Increase the mud discharge volume, save mud materials and meet the mud preparation cycle through the mud circulation system; use a vibrating screen to remove sand and a centrifuge to remove mud for mud recovery. The sand content of the recycled mud after treatment by the mud recovery system should not be greater than 0.5%;

[0016] S3: Rock section pilot drilling:

[0017] First, measure the direction control parameters: calibrate the guide hole through the Paratrack II direction control system, calibrate the direction control parameters, measure at different positions of the crossing center line, compare, and keep records, control the offset radius of the guide hole curve and the design curve, the longitudinal deviation of the excavation point along the design axis, and the lateral deviation is not greater than the specification requirements. Before drilling, prepare universal spreadsheets. After drilling, draw the ordinate curve and abscissa curve of the guide hole. The curves will be permanently preserved as completion data; according to the hard and soft geology of different land and sea areas, the guide hole drilling rig adopts different drilling tools to improve efficiency; the rock section drilling tool combination is: horizontal directional drilling rig → 6-5 / 8"S-135 drill pipe → non-magnetic drill collar → mud motor → 9-1 / 2″ three-cone tooth drill bit; the drill pipe entry angle is controlled to 13°, and the allowable steering angle α of two adjacent sections of drill pipe is generally 1.5°~3.0°; the maximum bending angle of each drill pipe is about 1°;

[0018] S4: Forward expansion of rock section:

[0019] In order to reduce the step phenomenon that may occur when soft and hard strata are interlaced, the following segmented expansion measures are taken. First, the reinforced roller rock reamer is used to carry out graded forward expansion of the 170m rock section on the soil side; expansion levels: φ350mm, φ450mm, φ550mm, φ650mm, φ750mm, φ850mm. The forward push drill pipe torque is controlled to be no more than 20000~30000N·m;

[0020] S5: Soil section guide drilling:

[0021] Pull back the reamer from the onshore drilling rig and replace the soil drilling tool assembly. The soil drilling tool assembly is: horizontal directional drilling rig → 6-5 / 8" S-135 drill pipe → non-magnetic drill collar → mud motor → 9-1 / 2" three-cone milling drill bit or change to a tooth plate drill bit according to the geological conditions;

[0022] S6: Bracket installation and drill pipe connection:

[0023] Observe the direction control system to ensure that the drill rod excavation angle is controlled at 8°; after the drill bit is excavated from the seabed near the excavation point, use an air compressor with a displacement of 30 cubic meters / minute to inject air into the drill rod to blow away the seabed mud and sand. After the diver finds the drill bit along the air bubble and determines the excavation location and marks and collects the coordinates, the ship begins to install the drill rod bracket on the deck and hoist it to fix it. The drill rod is towed to the deck and extended into the sea to the excavation point with the help of the drill rod bracket to connect with the drill rod that removed the drill bit at the excavation point. After removing the drill bit, the drill rod is connected to the drilling rig on the ship;

[0024] S7: Rock segment staged expansion:

[0025] After the offshore drilling rig is connected to the entire drill pipe, φ950mm, φ1150mm, and φ1250mm drill bits are installed on the shore. The offshore drilling rig is used to pull and expand the 170m rock layer from the land to the sea. Each time the drill bit is changed, the shore drilling rig is used to pull it back.

[0026] After the hole is expanded, use a φ1250mm hole expander to perform 1-2 hole washing operations according to the site conditions;

[0027] S8: Installation of steel casing in rock section:

[0028] After the last stage of φ1250mm hole expansion is completed, the drilling rig is used to install steel casing to support the rock crushing section. The steel casing is X70 series oil and gas standard pipeline steel, with a diameter of φ1200 and a wall thickness of 20mm. After the casing is installed in place, conventional pulling and expansion construction of the remaining soil layer begins;

[0029] S9: Gradual expansion of the remaining soil layers:

[0030] Conventional pulling and expanding methods are used for the clay and silt layers in the sea area. After the rock section is expanded and the protective casing is installed, a barrel expander is installed to carry out four-level conventional pulling and expanding expansion of φ550mm, φ850mm, φ1050mm, and φ1250mm. The torque of the reverse thrust drill pipe in the sea area is controlled to be no more than 70000~90000N·m;

[0031] After the hole is expanded, use a φ1250mm hole expander to perform 1-2 hole washing operations according to the site conditions;

[0032] S10: Pipeline pullback:

[0033] Before the pipeline is pulled back, the hole needs to be cleaned 1-2 times according to the actual situation on site. After the final inspection to determine that there is no abnormal change in the torque of the drill pipe during the hole cleaning, the preparation for pulling back is carried out. After the entire pipeline is prefabricated and tested, the pulling heads or blind plates on both sides are welded and sealed, and the pipeline is pulled back.

[0034] Furthermore, in step S5, during the guide hole crossing process, in order to ensure that the drill bit drills smoothly through the formation and avoid sticking or drill jamming caused by rock cuttings, an appropriate amount of additives should be added to the mud to disperse the formation particles, reduce the drilling resistance, and prevent the occurrence of sticking.

[0035] Furthermore, in step S5, a mud sensor is installed behind the drill bit of the pilot hole drill to monitor the mud pressure in the hole throughout the entire process. The maximum mud pressure does not exceed 6Mpa. If the mud pressure increases abnormally, the drill bit will be withdrawn, and the hole will be washed before drilling continues.

[0036] Furthermore, in step S9, in order to avoid mud leakage and environmental pollution, about 100m of each level of hole expansion is reserved on the excavation point side without expansion. After the hole is expanded to the predetermined position, the land drilling rig pulls out the reamer and replaces the next level reamer for expansion.

[0037] Furthermore, in step S10, the crossing pipeline is towed back using an offshore drilling rig, and a pipe pusher with a traction force of 600t is arranged at the point where the pipeline enters the ground to provide the required thrust during the pipeline towing back; a sea drilling rig + a land pipe pusher, that is, a push-pull combined towing back method is adopted; the pipeline is towed back in sections to reduce frictional resistance, each section of the steel pipe is 350m long, and the entire section of the steel pipe is completed in a five-to-one manner; during the towing back process, the drilling rig pulling force and the pipe pusher thrust data are monitored in real time to ensure smooth towing back of the pipeline.

[0038] The beneficial effects of the present invention are:

[0039] The present invention selects the hole expansion process according to different geological conditions, and combines auxiliary equipment to finally form a method for landing a submarine cable from land to sea in a rock-soil interlaced geological condition. It effectively ensures the stability of the rock strata in the expanded hole section during the construction of land-to-sea horizontal directional drilling in a rock-soil interlaced geological condition, the high quality of the entire expanded hole, the eco-friendliness, and the safety and reliability of the pipeline pullback. The 1650m long-distance land-to-sea horizontal directional drilling crossing and pipeline pullback under rock-soil interlaced geological conditions were achieved on site. It solves the problems of poor hole expansion quality, easy damage of drilling rigs, slurry leakage pollution, insufficient pipeline pullback force, and long construction period in long-distance land-to-sea horizontal directional drilling under rock-soil interlaced geological conditions, and provides a guarantee for the safe, green, and efficient construction of long-distance land-to-sea horizontal directional drilling and submarine cable landing in a rock-soil interlaced geological condition. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a process flow chart of the present invention;

[0041] Figure 2-1 It is the general cross-section of rock-oriented construction;

[0042] Figure 2-2 It is a partial cross-section of the rock-oriented construction;

[0043] Figure 3-1 It is the general cross-section of the forward expansion of the rock formation;

[0044] Figure 3-2 It is a local cross-section of the forward expansion of the rock formation;

[0045] Figure 4-1 It is the general cross-section diagram of the soil layer guide hole construction;

[0046] Figure 4-2 It is a partial cross-sectional view of the connection between the bracket and the drill pipe;

[0047] Figure 5-1 It is a general cross-section diagram of rock strata classification and expansion;

[0048] Figure 5-2 It is a local cross-section of the rock strata graded and expanded;

[0049] Figure 6-1 It is the general cross-section of the rock formation casing installation;

[0050] Figure 6-2 It is a partial cross-sectional view of the rock formation casing installation;

[0051] Figure 7-1 It is the general cross-section diagram of soil layer expansion;

[0052] Figure 7-2 It is a partial cross-section of the reserved section for soil layer expansion;

[0053] Figure 8 This is a schematic diagram of pipeline segment pullback. DETAILED DESCRIPTION

[0054] The present invention is further described below in conjunction with the accompanying drawings and specific implementations.

[0055] like Figures 1 to 8 As shown, a long-distance land-to-sea horizontal directional drilling submarine cable landing construction method for rock-soil interlaced geology of the present invention comprises the following steps:

[0056] S1: Construction preparation:

[0057] Before formal construction, complete the surveying and positioning, site leveling, barge anchoring, equipment installation and commissioning, confirm the construction equipment parameters, complete the material quality inspection, technical personnel briefing and emergency material inspection, etc. Before the pilot hole is drilled, the magnetic azimuth measurement of the center line is completed as the original basis for the pilot hole control.

[0058] S2: Mud preparation:

[0059] Before drilling, a mud pool should be arranged and a mud laboratory should be set up on site. Different additives should be added according to different geological conditions. The initial mud formula tested with clean water should be modified as necessary by using on-site water samples and combining them with the specific conditions of the strata being drilled.

[0060] Prepare mud according to the mud ratio determined by the mud laboratory and the water quality of the on-site water, measure various mud parameters in time, check the mud effect, and deal with problems immediately. Mud parameters should meet the following performance indicators: Marsh funnel viscosity should be 50-60s, plastic viscosity 8-12MPa·s, dynamic shear force 5-10Pa, apparent viscosity 12-20MPa·s, filtration loss 8-12ml, pH value 9-11.

[0061] Increase the mud discharge volume, save mud materials and meet the mud preparation cycle through the mud circulation system; use a vibrating screen to remove sand and a centrifuge to remove mud for mud recovery. The sand content of the recycled mud after treatment by the mud recovery system should not be greater than 0.5%.

[0062] S3: Rock section guide drilling: Figure 2-1 , Figure 2-2 As shown,

[0063] First, measure the steering parameters: calibrate the guide hole through the Paratrack II steering system, calibrate the steering parameters, measure at different positions across the center line, compare, and keep records. Control the offset radius of the guide hole curve and the design curve, the longitudinal deviation of the excavation point along the design axis, and the lateral deviation is not greater than the specification requirements. Before drilling, prepare universal spreadsheets. After drilling, draw the ordinate and abscissa curves of the guide hole. The curves (not to be altered) will be permanently preserved as completion data.

[0064] In combination with the hard and soft geology in different land and sea areas, the pilot hole drilling rig adopts different drilling tools to improve efficiency. The rock section drilling tool combination is: horizontal directional drilling rig → 6-5 / 8" S-135 drill pipe → non-magnetic drill collar (Ф178) → mud motor (Ф172) → 9-1 / 2″ three-cone tooth drill bit (tooth type 637).

[0065] The drilling rod entry angle is controlled at 13°, and the allowable turning angle α between two adjacent sections of drilling rod is generally between 1.5° and 3.0°; the maximum bending angle of each drilling rod is about 0.1°.

[0066] S4: Forward expansion of rock section: Figure 3-1 , Figure 3-2 As shown,

[0067] In order to reduce the step phenomenon that may occur when soft and hard strata are interlaced, the following segmented hole expansion measures are taken. First, the reinforced roller rock hole expander is used to carry out graded forward push hole expansion on the 170m rock section on the soil side. Hole expansion levels: φ350mm, φ450mm, φ550mm, φ650mm, φ750mm, φ850mm. The forward push drill pipe torque is controlled to be no more than 20000~30000N·m.

[0068] S5: Soil layer section guide drilling: Figure 4-1 As shown,

[0069] Pull back the reamer from the onshore drilling rig and replace the soil drilling tool assembly. The soil drilling tool assembly is: horizontal directional drilling rig → 6-5 / 8" S-135 drill pipe → non-magnetic drill collar (Ф178) → mud motor (Ф172) → 9-1 / 2″ three-cone milled tooth drill bit (tooth type 137) or change to a tooth plate drill bit according to the geological conditions.

[0070] During the guide hole crossing process, in order to ensure that the drill bit drills smoothly through the formation and avoid sticking or drill jamming caused by rock cuttings, an appropriate amount of additives should be added to the mud to disperse the formation particles, reduce drilling resistance, and prevent sticking.

[0071] The mud sensor installed behind the drill bit of the pilot hole drill will monitor the mud pressure in the hole throughout the process. The maximum mud pressure should not exceed 6MPa. If the mud pressure rises abnormally, the drill bit will be withdrawn and the hole will be washed before drilling continues.

[0072] S6: Bracket installation and drill pipe connection: Figure 4-2 As shown,

[0073] Observe the direction control system to ensure that the drill rod excavation angle is controlled at 8°. After the drill bit is excavated from the seabed near the excavation point, an air compressor with a displacement of 30 cubic meters / minute is used to inject air into the drill rod to blow away the seabed mud. After the diver finds the drill bit along the bubbles and determines the excavation location and marks and collects the coordinates, the ship begins to install the drill rod bracket on the deck and hoist it to fix it. The drill rod is towed to the deck and extended into the sea to the excavation point with the help of the drill rod bracket to connect with the drill rod that removed the drill bit at the excavation point. After removing the drill bit, the drill rod is connected to the drilling rig on the ship.

[0074] S7: Rock segment expansion: Figure 5-1 , Figure 5-2 As shown,

[0075] After the offshore drilling rig is connected to the entire drill pipe, φ950mm, φ1150mm, and φ1250mm drill bits are installed on shore. The offshore drilling rig is used to pull and expand the 170m rock layer from land to sea, and the shore drilling rig is used to tow back each time the drill bit is changed.

[0076] After the hole expansion is completed, use a φ1250mm hole expander to carry out 1-2 hole washing operations according to the site conditions.

[0077] S8: Installation of steel casing in rock section: Figure 6-1 , Figure 6-2 As shown,

[0078] After the last stage of φ1250mm hole expansion is completed, the drilling rig is used to install steel casing to support the rock crushing section. The steel casing is X70 series oil and gas standard pipeline steel, with a diameter of φ1200 and a wall thickness of 20mm. After the casing is installed in place, conventional pulling and expansion construction of the remaining soil layer begins.

[0079] S9: Gradual expansion of the remaining soil layers: Figure 7-1 , Figure 7-2 As shown,

[0080] Conventional pulling and expanding methods are used for the clay and silt layers in the sea area. After the rock section is expanded and the protective casing is installed, a barrel expander is installed to carry out four-level conventional pulling and expanding expansion of φ550mm, φ850mm, φ1050mm, and φ1250mm. The torque of the reverse thrust drill pipe in the sea area is controlled to be no more than 70,000 to 90,000 N·m.

[0081] In order to avoid mud leakage and environmental pollution, about 100m of each level of hole expansion is reserved on the excavation point side without expansion. After the hole is expanded to the predetermined position, the onshore drilling rig pulls out the reamer and replaces it with the next level reamer for expansion.

[0082] After the hole expansion is completed, use a φ1250mm hole expander to carry out 1-2 hole washing operations according to the site conditions.

[0083] S10: Pipeline pullback: Figure 8 As shown,

[0084] Before the pipeline is pulled back, it is necessary to wash the hole 1-2 times according to the actual situation on site. After the final inspection confirms that there is no abnormal change in the torque of the drill pipe during the hole cleaning, the preparation for pulling back is carried out. After the entire pipeline is prefabricated and tested, the welding pulling heads (or blind plates) on both sides are sealed and the pipeline is pulled back.

[0085] The pipeline is mainly pulled back by offshore drilling rigs. A pipe pusher with a traction force of 600t is arranged at the point where the pipeline enters the soil to provide the boost required during the pipeline pulling back. The offshore drilling rig (pulling) + land pipe pusher (boosting) is used, that is, a push-pull integrated pulling back method. The pipeline is pulled back in sections to reduce friction. Each section of the steel pipe is 350m long, and the entire section of the steel pipe is completed in a five-in-one manner. During the pulling back process, the pulling force of the drilling rig and the thrust data of the pipe pusher are monitored in real time to ensure the smooth pulling back of the pipeline.

Claims

1. A long-distance land-to-sea horizontal directional drilling submarine cable landing construction method in rock-soil interlaced geology, characterized in that: The following steps are involved: S1: Construction preparation: Before the formal construction, the surveying and positioning, site leveling, barge anchoring, equipment installation and commissioning should be done well, the construction equipment parameters should be confirmed, the material quality inspection should be completed, the technical personnel should be briefed, and the emergency materials should be inspected. Before the pilot hole is drilled, the magnetic azimuth angle of the crossing center line should be measured as the original basis for the pilot hole control; S2: Mud preparation: Before drilling, a mud pool should be arranged and a mud laboratory should be set up on site. Different additives should be added according to different geological conditions. Water samples from the site should be used to make necessary corrections to the initial mud formula tested when using clean water in combination with the specific conditions of the strata being drilled. Prepare mud according to the mud ratio determined by the mud laboratory and the water quality of the on-site water, and measure the mud parameters in time. The mud parameters should meet the following performance indicators: Marsh funnel viscosity should be 50-60s, plastic viscosity 8-12MPa·s, dynamic shear force 5-10Pa, apparent viscosity 12-20MPa·s, filtration loss 8-12ml, pH value 9-11; Increase the mud discharge volume, save mud materials and meet the mud preparation cycle through the mud circulation system; use a vibrating screen to remove sand and a centrifuge to remove mud for mud recovery. The sand content of the recycled mud after treatment by the mud recovery system is no more than 0.5%; S3: Rock section pilot drilling: First, measure the direction control parameters: calibrate the guide hole through the Paratrack II direction control system, calibrate the direction control parameters, measure at different positions of the crossing center line, compare, and keep records, control the offset radius of the guide hole curve and the design curve, the longitudinal deviation of the excavation point along the design axis, and the lateral deviation is not greater than the specification requirements. Before drilling, prepare universal spreadsheets. After drilling, draw the ordinate curve and abscissa curve of the guide hole. The curves will be permanently preserved as completion data; according to the hard and soft geology of different land and sea areas, the guide hole drilling rig adopts different drilling tools to improve efficiency; the rock section drilling tool combination is: horizontal directional drilling rig → 6-5 / 8"S-135 drill pipe → non-magnetic drill collar → mud motor → 9-1 / 2″ three-cone tooth drill bit; the drill pipe entry angle is controlled to 13°, and the allowable steering angle α of two adjacent sections of drill pipe is generally 1.5°~3.0°; the maximum bending angle of each drill pipe is about 1°; S4: Forward expansion of rock section: In order to reduce the step phenomenon that may occur when soft and hard strata are interlaced, the following segmented expansion measures are taken. First, the reinforced roller rock reamer is used to carry out graded forward expansion of the 170m rock section on the soil side; expansion levels: φ350mm, φ450mm, φ550mm, φ650mm, φ750mm, φ850mm. The forward push drill pipe torque is controlled to be no more than 20000~30000N·m; S5: Soil layer section guide drilling: Pull back the reamer from the onshore drilling rig and replace the soil drilling tool assembly. The soil drilling tool assembly is: horizontal directional drilling rig → 6-5 / 8" S-135 drill pipe → non-magnetic drill collar → mud motor → 9-1 / 2" three-cone milling drill bit or change to a tooth plate drill bit according to the geological conditions; S6: Bracket installation and drill pipe connection: Observe the direction control system to ensure that the drill rod excavation angle is controlled at 8°; after the drill bit is excavated from the seabed near the excavation point, use an air compressor with a displacement of 30 cubic meters / minute to inject air into the drill rod to blow away the seabed mud and sand. After the diver finds the drill bit along the air bubble and determines the excavation location and marks and collects the coordinates, the ship begins to install the drill rod bracket on the deck and hoist it to fix it. The drill rod is towed to the deck and extended into the sea to the excavation point with the help of the drill rod bracket to connect with the drill rod that removed the drill bit at the excavation point. After removing the drill bit, the drill rod is connected to the drilling rig on the ship; S7: Rock segment staged expansion: After the offshore drilling rig is connected to the entire drill pipe, φ950mm, φ1150mm, and φ1250mm drill bits are installed on the shore. The offshore drilling rig is used to pull and expand the 170m rock layer from the land to the sea. Each time the drill bit is changed, the shore drilling rig is used to pull it back. After the hole is expanded, use a φ1250mm hole expander to perform 1-2 hole washing operations according to the site conditions; S8: Installation of steel casing in rock section: After the last stage of φ1250mm hole expansion is completed, the drilling rig is used to install steel casing to support the rock crushing section. The steel casing is X70 series oil and gas standard pipeline steel, with a diameter of φ1200 and a wall thickness of 20mm. After the casing is installed in place, conventional pulling and expansion construction of the remaining soil layer begins; S9: Gradual expansion of the remaining soil layers: Conventional pulling and expanding methods are used for the clay and silt layers in the sea area. After the rock section is expanded and the protective casing is installed, a barrel expander is installed to carry out four-level conventional pulling and expanding expansion of φ550mm, φ850mm, φ1050mm, and φ1250mm. The torque of the reverse thrust drill pipe in the sea area is controlled to be no more than 70000~90000N·m; After the hole is expanded, use a φ1250mm hole expander to perform 1-2 hole washing operations according to the site conditions; S10: Pipeline pullback: Before the pipeline is pulled back, the hole needs to be cleaned 1-2 times according to the actual situation on site. After the final inspection to determine that there is no abnormal change in the torque of the drill pipe during the hole cleaning, the preparation for pulling back is carried out. After the entire pipeline is prefabricated and tested, the pulling heads or blind plates on both sides are welded and sealed, and the pipeline is pulled back.

2. The long-distance land-to-sea horizontal directional drilling submarine cable landing construction method for rock-soil interlaced geology according to claim 1 is characterized by: In step S5, during the guide hole crossing process, in order to ensure that the drill bit drills smoothly through the formation and avoid sticking or drill jamming caused by rock cuttings, an appropriate amount of additives should be added to the mud to disperse the formation particles, reduce the drilling resistance, and prevent the occurrence of sticking.

3. The long-distance land-to-sea horizontal directional drilling submarine cable landing construction method for rock-soil interlaced geology according to claim 1 is characterized by: In step S5, a mud sensor is installed behind the drill bit of the pilot hole drill to monitor the mud pressure in the hole throughout the process. The maximum mud pressure does not exceed 6Mpa. If the mud pressure increases abnormally, the drill bit will be withdrawn and the hole will be washed before drilling continues.

4. The long-distance land-to-sea horizontal directional drilling submarine cable landing construction method for rock-soil interlaced geology according to claim 1 is characterized by: In step S9, in order to avoid mud leakage and environmental pollution, about 100m of each level of hole expansion is reserved on the excavation point side without expansion. After the hole is expanded to the predetermined position, the land drilling rig pulls out the reamer and replaces the next level reamer for expansion.

5. The long-distance land-to-sea horizontal directional drilling submarine cable landing construction method for rock-soil interlaced geology according to claim 1 is characterized by: In step S10, the crossing pipeline is towed back using an offshore drilling rig, and a pipe pusher with a traction force of 600t is arranged at the point where the pipeline enters the ground to provide the required thrust during the pipeline towing back. A sea drilling rig + a land pipe pusher, that is, a push-pull combined towing method is used. The pipeline is towed back in sections to reduce frictional resistance. The length of each section of the steel pipe is 350m, and the entire section of the steel pipe is completed in a five-to-one manner. During the towing back, the drilling rig pulling force and the pipe pusher thrust data are monitored in real time to ensure smooth towing back of the pipeline.

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