The pipeline crossing construction with horizontal directional drilling rig is generally divided into two stages: the first stage is to drill a pilot hole as accurately as possible according to the design curve; In the second stage, the pilot hole is enlarged, and the product pipeline (generally PE pipe, optical cable sleeve and steel pipe) is pulled back into the pilot hole along the enlarged pilot hole to complete the pipeline crossing work.
1. 1 drilling pilot hole:
According to the geological conditions of crossing, select the appropriate drill bit and guide plate or downhole mud motor, start the mud pump to drill at the penetration point, and the drill bit is driven to rotate by the drill under the thrust of the drill (or using mud motor belt).
Move the drill bit to rotate) to cut the formation and keep moving forward. Every time a drill pipe is drilled, the actual position of the drill bit should be measured, so as to adjust the drilling direction of the drill bit in time and ensure that the completed pilot hole curve meets the design requirements.
After that, drill the entire pilot hole until the drill bit is unearthed at the predetermined position. See figure 1: drilling pilot hole.
The drilling rig is installed at one side of the penetration point, and a curve from the penetration point to the excavation point is drilled along the design route from the penetration point as the guiding curve for pre-reaming and back-dragging the pipeline.
1.2 Pre-reaming and back-dragging product pipeline:
Generally, when using a small drilling rig, pre-reaming is needed when the diameter is greater than 200mm; When using a large drilling rig, pre-reaming is needed when the diameter of the product pipeline is greater than DN 350 mm.. The diameter and frequency of pre-reaming depend on the specific rig model and geological conditions.
When dragging the product pipeline back, first connect the reaming tool with the pipeline, and then start the dragging operation, and the drill pipe is driven by the rotary table of the drilling rig to rotate and retreat, so as to reaming and dragging back. The product pipeline will not rotate due to expansion in the process of dragging back.
The good hole is filled with mud, the product pipeline is hung in the enlarged hole, and the pipe wall and the periphery of the hole are lubricated with mud, which not only reduces the resistance, but also protects the pipeline anticorrosion layer, and is pre-drilled by the drilling machine for many times.
After reaming, the final aperture is generally 200mm larger than the pipe diameter, so it will not damage the anticorrosion layer. See Figure 2: Pre-reaming and Figure 3: Pulling back the pipeline.
In the pilot hole drilling stage, the hole drilled is usually smaller than the diameter of the tow-back pipeline. In order to make the borehole reach 1.3 ~ 1.5 times the diameter of the towed pipeline, it is necessary to enlarge the pilot hole from the excavation point to the buried point to the required diameter with an reamer.
After the pre-reaming of underground hole meets the requirements of back-dragging, connect the drill pipe, reamer, back-dragging joint and installed pipeline in turn, and drag the pipeline back to the buried point while reaming.
2, the characteristics of horizontal directional drilling construction:
2. 1 The directional drilling crossing construction will not hinder the traffic, destroy the green space and vegetation, affect the normal life and work order of shops, hospitals, schools and residents, and solve the interference of traditional excavation construction on the residents' life, the damage and adverse impact on the traffic, environment and surrounding building foundation.
2.2 Modern crossing equipment has high crossing precision, easy adjustment of laying direction and buried depth, and long arc laying distance of pipeline, which can completely meet the design requirements of buried depth and make the pipeline bypass underground obstacles.
2.3 The buried depth of urban pipe network is generally not more than three meters. When crossing a river, the buried depth is generally 9-18m below the river bed. Therefore, using the horizontal directional drilling rig to cross the river has no influence on the surrounding environment, does not destroy the landform and environment, and meets the requirements of environmental protection.
2.4 When the horizontal directional drilling rig crosses the river, there is no operation on or under water, which will not affect the navigation of the river, damage the dams and riverbed structures on both sides of the river, and the construction is not limited by seasons. It has the characteristics of short construction period, few personnel, high success rate and safe and reliable construction.
2.5 Compared with other construction methods, the access speed is fast, the construction site can be flexibly adjusted, especially in urban construction, which can fully display its advantages, and the construction area is small, the project cost is low, and the construction speed is fast.
2.6 When a large river crosses, because the pipeline is buried 9- 18 mm below the stratum, there are few corrosive substances such as oxygen in the stratum, which plays the role of natural anticorrosion and thermal insulation and can ensure the pipeline to run for a long time.
3. Introduction of horizontal directional drilling rig system;
Horizontal directional drilling rigs of various specifications are composed of drilling rig system, power system, directional control system, mud system, drilling tools and auxiliary machinery. Their structures and functions are described as follows:
3. 1 drilling rig system: it is the main body of drilling operation and towing operation through equipment, and consists of main engine and rotary table. The main rig is placed on the rig frame to complete drilling and towing operations. The turntable is installed at the front end of the main engine and connected with the drill pipe. By changing the rotating speed and torque of the turntable, the requirements of different working conditions can be met.
3.2 Power system: the power source consisting of hydraulic power source and generator provides high-pressure hydraulic oil for the drilling rig system as the power of the drilling rig, and the generator provides power for supporting electrical equipment and lighting on the construction site.
3.3 Direction control system: The direction control system is a directional tool to guide the drill bit to drill correctly by monitoring and controlling the specific position and other parameters of the drill bit in the well through a computer. Due to the control of the system, the drill bit can drill holes according to the design curve. At present, there are two commonly used directional control systems: portable wireless and wired.
3.4 Mud system: The mud system consists of a mud mixing and stirring tank, a mud pump and a mud pipeline to provide mud suitable for drilling conditions for the drilling rig system.
3.5 Drilling tools and auxiliary tools: various tools used for drilling and reaming. Drilling tools mainly include drill pipes, drill bits, mud motors, reamers, cutting knives and other tools suitable for various geology. Auxiliary tools include snap rings, rotary joints and traction heads with various diameters.
Layout plan of crossing construction site
1. The entry point is the main place for directional drilling construction, and the drilling rig is arranged on this side, so the construction area is relatively large. The minimum area of DD330 drilling rig is 30×30M, but it can be adjusted according to the actual situation. The areas of DD60 and DD-5 are much smaller.
2. One side of the excavation site is mainly used as the pipeline welding site, and the excavation site should be used for pre-reaming, back dragging, connecting drill pipes and installing other equipment; There is a pipeline welding operation area with the same crossing length behind the excavation point.
Cross example
Site Layout of Dagusha Crossing Drilling Rig
During the period from September of 1998 to September of 10, our company completed the crossing of two φ 2 19× 8 and 1 φ 426× 9 pipelines with a length of 960m in just 45 days.
Dagusha crosses the welding site (only two pipelines are shown)
Process flow chart of horizontal directional drilling crossing construction
The construction method of crossing rivers and other obstacles by using horizontal directional drilling technology has been widely used in the world. The Association of Horizontal Directional Drilling Crossing Contractors believes that horizontal directional drilling is adopted in the bidding process of engineering projects.
The contractor shall obtain as much relevant information as possible in order to make a complete and competitive quotation. The contractor shall obtain the following information before commencement to ensure the smooth progress of future work and complete the project under this condition.
Aim to construct, and at the same time, sufficient information before construction can ensure that the construction process is safer, reduce the damage to the surrounding environment and make the project go smoothly.
I. Overview
I. Development and use
Horizontal directional drilling technology first appeared in 1970s, which is a combination of traditional road drilling and oilfield directional drilling technology. At present, it has become a popular construction method, which can be used to transport oil, natural gas, petrochemical products,
The construction of water, sewage and other substances and various pipelines of power and optical cables is not only used to cross rivers and waterways, but also widely used in highways, railways, airports, coastal areas, islands and areas with dense buildings and pipelines.
Wait a minute.
B, technical restrictions
Directional drilling construction technology was first applied to alluvium crossing in coastal areas of the United States, and now it can be carried out under complex geological conditions such as coarse sand, pebbles, moraines and rock areas. The longest span construction reaches 6000 feet, and the pipe diameter is 18 inch.
C. advantages
Facts have proved that horizontal directional drilling crossing is the construction method with the least impact on the environment. This technology can also provide the largest protective layer for the pipeline and reduce the maintenance cost accordingly. At the same time, it will not affect the river transportation and shorten the construction period, which has been proved to be the most efficient and lowest cost crossing construction method at present.
D, construction process and technology
1. Pilot hole: a pilot hole is a hole drilled along a predetermined section at a predetermined angle in the horizontal direction, including a straight diagonal and a large radius arc. When drilling pilot holes, the contractor can choose and use a larger diameter.
Drill pipes (i.e. flushing pipes) are used to protect steering drill pipes. The flushing pipe can function like a catheter, and it can also facilitate the removal of the steering drill pipe and the replacement of the drill bit. The direction of the pilot hole is controlled by the drill pipe located at the back end of the drill bit.
The controller (called curved shell) is completed. During drilling, the drill pipe does not rotate. When the direction needs to be changed, if the curved shell is positioned on the right side, the drilling path will follow a smooth curve to the right. The drilling curve is drilled by placing it at the back end of the drill bit.
The electronic direction finder in the pole measures and transmits the measurement results to the receiver on the ground. After processing and calculation, these data are displayed in digital form on the display screen. The electronic device is mainly used to monitor drill pipes and the earth's magnetic field.
Field relationship and inclination angle (three-dimensional coordinates of the drill bit underground), compare the measured data with the design data, so as to determine the deviation between the actual position and the design position of the drill bit, and control the deviation value within the allowable range.
In this way, until the drill bit is unearthed at a predetermined position according to the predetermined pilot hole curve.
2. Pre-reaming:
After the pilot hole is completed, the hole should be enlarged to a suitable diameter to facilitate the installation of the finished pipeline. This process is called pre-reaming (reaming times are determined according to the final hole size). For example, if a 36-inch pipe needs to be installed, drill holes.
The hole must be enlarged to 48 inches or more. Usually, the reamer is connected to the drill pipe opposite to the drilling rig, and then the drilling rig rotates to pull it back into the guide hole to enlarge the guide hole. At the same time, a large amount of mud is pumped into the hole to ensure drilling.
The borehole is intact without collapse, and the cuttings are brought back to the surface.
3. Drag the pipeline back: After the pre-reaming is completed, the finished pipeline can be dragged into the borehole. The prefabrication of the pipeline shall be completed on the other side of the drilling rig. One end of the reamer is connected to the drill pipe, and the other end is connected to the finished product pipeline through the rotary joint. Rotary joint
The finished pipe can be prevented from rotating with the reamer to ensure that it can be dragged into the hole smoothly. Drag-back is completed by drilling rig, and this process also needs a lot of mud cooperation. The pulling back process should continue until the reamer and finished pipe are drilled by themselves.
One side of the plane broke through the ground.
Second, the website layout and design
I. Road
Heavy equipment is needed on both sides of the site. In order to reduce the cost, the roads leading to the construction sites on both sides should use the existing roads as much as possible to reduce the distance of new roads, or use the construction access roads of pipelines. All relevant road use right agreements shall be provided by the owner. It is too late to discuss these issues at the bidding stage.
B. Workplace
1. One side of the drilling rig-the area of the drilling rig construction site should be at least 30m (100ft) wide and 45m (150ft) long. This area should be at least within the designated area from the entry point.
3 meters (10 feet). At the same time, because many supporting equipment or accessories of the drilling rig have no designated storage place, the construction site on one side of the drilling rig can be composed of many irregular small pieces to save the floor space and make the site as large as possible.
Should be smooth, hard and clean, so as to facilitate the construction. Because a large amount of fresh water is needed to mix the mud during crossing construction, the construction site should be as close as possible to the water source or the place where it is convenient to connect the tap water pipeline.
2. One side of the pipeline-In order to facilitate the prefabrication of the finished pipeline, one side of the pipeline should have a sufficient length of construction site, which is also important to consider. The width of the site should meet the needs of pipeline construction (generally
12- 18m)。 Similarly, one side of the excavation site needs a construction site with a width of 30m (100ft) and a length of 45m (150ft). The total length is subject to the ability to place prefabricated pipes.
The total length of the ground is generally the length of the crossing pipeline plus 30 meters. Before towing back, the pipeline shall be prefabricated, including welding, ball passing, pressure testing and anticorrosion. During towing back, the pipeline can no longer be connected.
Because the dragging process is continuous, if the pipeline is connected at this time, it is likely to cause the underground hole to collapse and the whole project construction will fail.
C, the construction site investigation
Once the construction site is determined, it is necessary to survey the corresponding area and draw a detailed and accurate geological and geomorphological map. The final construction accuracy depends on the accuracy of this measurement result.
D, construction design parameters
1. Thickness of overburden-The factors to be considered include the characteristics of water flow across the river, the scouring depth of seasonal flood, the widening and deepening of the river in the future, the location of existing pipelines and cables, etc. Once the construction site is determined,
After the geological survey is completed, the thickness of the crossing layer will be determined. Generally speaking, the cover should be at least 6 meters (20 feet) thick. The above is only for crossing the river, and there will be others when crossing other obstacles.
Request.
2. Drilling Angle and Radius of Curvature-In most cross structures, the penetration angle is usually selected between 8- 12 degrees. In most constructions, an oblique straight line should be drilled first, and then a large radius curve should be drilled.
The velocity radius is determined by the bending characteristics of the finished pipe and increases with the increase of diameter. The rule of thumb for the curvature radius of steel pipes is 100FT/IN (generally, it is 1000- 1200 times of the pipe diameter). Inclined straight lines will guide.
The hole curve is guided to the design depth according to the predetermined trend, and then a long horizontal straight line is formed at this depth, and then it reaches the upward bending point, and then it reaches the excavation point. The excavation angle should be controlled between 5- 12 degrees, so that
Drag back the completed pipeline.
E, drilling construction
All direction finding and control tools include downhole measuring electronic equipment and ground receiving equipment, which can measure the magnetic azimuth (for left/right control) and inclination (for up/down control) of the drill bit and the drilling direction of the drill bit.
1. Accuracy: The accuracy of crossing construction depends largely on the change of magnetic field. For example, large steel structures (bridges, piles and other pipelines) and power lines will affect the reading of magnetic fields. The target deviation value of the guide hole crossing the excavation point should be controlled at 3m from left to right (10ft) and the length should be-3m to10m (-65438).
2. As-built drawing: Generally speaking, when drilling pilot holes, the measurement and control of pilot holes should be measured and calculated every drill pipe or every 9 meters (30 feet). The Contractor shall provide the construction drawings of pilot holes with the above measurement and calculation. Alternative methods such as gyroscope, ground penetrating radar and intelligent pig ball are also used for positioning.
Third, geological survey.
I. Number of exploration holes
The number of exploration holes depends on the stratum conditions and crossing length of the proposed crossing site. If the crossing length is 300 meters (1000 feet), it is enough to drill a hole at each crossing point on both sides. If the drilling results show that the crossing length is 300m (1000ft),
If the geological conditions in this area are relatively simple, there is no need for further drilling and sampling. If the exploration report shows that the geological conditions in this area are complex, or rocks or coarse sand layers are found, further detailed information is needed.
Geological survey. During the long-distance and large-diameter crossing construction, if coarse sand, pebbles, weathered rocks or hard rocks appear, samples shall be taken every 180m-240m (600-800FT). If there are obvious signs, see the table below.
The geological structure of Ming Dynasty is extremely complicated, so more geological exploration holes need to be drilled for more sampling work. All sampling exploration holes shall be along the direction of crossing section, and the sampling depth shall be subject to the planned crossing depth. If possible, sampling exploration should be carried out.
It is best to choose a place about 8 meters (25 feet) on one side of the center line. After the exploration task is completed, the exploration hole must be closed to prevent slurry leakage during construction.
B, detecting hole depth
The depth of all exploration holes shall be at least 12m (40FT) below the intersection or 6m (20FT) below the planned crossing depth, whichever is greater. Sometimes the crossing depth is set deeper or actually crosses.
The curve is deeper than the design position, which is beneficial to both the contractor and the owner. The key is to choose the crossing position in the stratum with consistent stratum structure, which is beneficial to the success of crossing.
C, standard classification of soil
Qualified geologists or geologists should be able to classify materials according to the unified soil classification system or ASTM design books D-2487 and D2488. He can ask the field technician or drilling company to submit a copy.
The field drilling records provided will be very useful for future construction. The record will include the visual classification of materials and the interpretation and evaluation of formation structure by the drilling company according to the sampling results.
D, standard puncture test
Standard penetration test In order to better determine the density of granular materials, geological engineers usually carry out standard penetration test SPT according to ASTM specification D 1586. This is a field test method, using a standard weight hammer to scoop.
Drive the V-type sampler into the soil to a certain depth, and record the number of blows when it enters the depth of 12 inch. The data obtained are standard puncture resistance values, which can be used to estimate the relative density of non-polymerized soil in the test site. Some drilling companies also use it.
Our company will choose to carry out this test in a small area of cohesive soil or rock area to confirm the consistency of dense soil and the hardness of rock.
E, coring sampling method
Most geological exploration companies prefer to use coring samplers to obtain underground core samples. These tests are usually carried out according to ASTM specification D- 1587. Except that the sampler is a thin wall with a sharp cutting edge and is driven by hydraulic pressure, there is no.
This test is similar to the standard puncture test mentioned above except for the cylinder. The required hydraulic values can be found in the field records. This method can obtain relatively complete samples for more detailed laboratory analysis. Samples can be found in the wild.
Field analysis was performed with a hand-held puncture instrument. For directional crossing, the above-mentioned cutting spoon sampler can usually meet the construction needs.
grading analysis
It is one of the most important experiments to analyze the particle size of the sample with a sieve, which is a mechanical test of the particle material obtained with a spoon sampler at the construction site. These samples are sent to the laboratory, and after passing through a series of sieves, the percentages of different particle sizes are obtained according to their particle sizes and weights.
G, rock conditions
If a rock stratum is found in the soil investigation, it is necessary to determine the rock stratum type, relative hardness and unconfined compressive strength, and a professional exploration company will use a diamond bit core barrel to take samples. Typical core sample diameters are
50 mm (2 inches). Geological experts classify rock types according to the relationship between core and total coring length. By comparing the rock with ten materials with known hardness, we can know the hardness of the rock. The compressive strength is fine.
The core is measured and then obtained by compression experiment. These data belong to the physical parameters of rock, so as to determine what type of crossing equipment and drill bit to use, and also to estimate the crossing footage.
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