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Non-excavation drilling guidance technology in rock strata

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The technology of laying underground pipeline in trenchless construction is widely used because of its low damage to surface structure, good environmental protection, high construction efficiency and low overall cost. Although China's development level in this field is more than ten years later than that of developed countries, with the continuous development of economic construction, the implementation of the strategy of western development and the acceleration of urbanization construction, the trenchless market is growing vigorously. Understanding and mastering the advanced technology of trenchless industry is helpful to the improvement of our country. This paper introduces the technique of non - excavation guided drilling in rock strata.
 
1. Drilling guiding mechanism in soil layer
 
In general, the construction of non-excavation guided drilling is mostly carried out under the condition of soil layer. At this time, the guide bit adopts the asymmetric structure with inclined plane. The mechanical mechanism of directional change of this kind of bit in the hole is that the thrust obtained from the drill pipe overcomes the formation resistance and pushes the bit forward. Taking the inclined drill bit as the analysis object, the drill thrust and formation resistance from the drill pipe act on the drill bit inclined surface together. The two forces are respectively decomposed into the component force perpendicular to the inclined surface and the component force parallel to the inclined surface. The two component forces parallel to the inclined plane are larger than the formation resistance component, and the final resultant force points in the direction of the inclined plane, making the drill bit advance along the inclined plane. The concrete operation is shown as follows: when the rotary action of the drill and the feeding action are carried out simultaneously, the drilling track presents a straight line; When the drilling machine only feeds without turning, the drilling track turns along the inclined surface of the drill bit to realize the direction change.
 
However, when the strata drilled are rock strata, the thrust of the drilling machine cannot effectively overcome the formation resistance, so it is impossible to achieve the function of only pushing without turning and changing direction. Even if drilling only in the pebble layer or the rock-bearing soil layer, the presence of hard rock will cause uneven force on the drill bit of the guide plate inside the hole, and it is difficult to achieve effective direction control.
 
2. Guiding technology in rock strata
 
2.1 traditional method 1
 
When I couldn't turn can't use only in strata method to change the drilling direction, in general, it is ordinary type cutting bevel grinding drill bit (guide plate) with eccentric or single cone bit, then if you want to change the direction of borehole trajectory, ejector and intermittent rotary function at the same time, the default is displayed on guidance instrument dial direction turning point on each side ejector and turning 60 degrees sector scope, implementation, eccentric grinding at each point of the rest of the dial indicator is idle in the past. For example, to change the direction of the drilling track toward the 12 o 'clock position indicated by the clock face (upward), the eccentric bit is idled to 10 o 'clock, thrust is applied, and pushed to 2 o 'clock to form a 120 degree fan face grinding. Then pull the drill bit back slightly to break away from the cutting surface, idling to 10 o 'clock position, applying thrust and pushing to 2 o 'clock position to achieve another grinding of the fan face of 120 degrees. In this way, push rotation and idle rotation are carried out repeatedly to make the drilling track deviate from the original axis and tilt upward by an Angle to realize the turning.
 
This kind of construction technology can only intermittently gram rock, and this kind of pushing and idling conversion operation needs to be manually carried out, so that the guidance efficiency is very low, change the direction of a few hours. Sometimes it is impossible to achieve effective direction control in fractured or pebble formations because of the inhomogeneity.
 
2.2 traditional method ii
 
Another traditional rock drilling technology is the hole bottom mud motors, this process under the condition of turning, drilling mud motor by drill pipe inner cavity transmission to drive the high pressure mud, provide the roller bit, take required torque, rock drill pipe don't need to turn, only provide thrust and drilling direction control, mud motor and a fitted between the drill pipe axis Angle, in order to realize the direction change; When drilling straight holes, the drill pipe and the mud motor rotate simultaneously. When using this process for construction, there are the following problems:
 
(1) the machine shall be equipped with high pressure and high flow mud pump to ensure that enough mud is pumped to drive the mud motor to work. Existing mud pumps of ordinary drilling RIGS are difficult to meet the requirements;
 
(2) the mud consumption is 2-3 times larger than that of ordinary drilling, which greatly increases the cost of mud material consumption;
 
(3) special high-power mud mixing system should be equipped to meet the needs of a large amount of mud;
 
(4) from the perspective of environmental protection, especially in urban construction, a large amount of waste slurry needs to be disposed of, which increases the construction cost;
 
(5) in order to make the mud power reach the mud motor parts effectively, the sealing requirements and high pressure scour resistance requirements of each connection of drill pipe string are further improved;
 
(6) more than 1m mud motor was added between the probe holding pipe and the guiding bit, which affected the directional accuracy of the drilling track.
 
The traditional method also USES the pneumatic subsurface hole hammer technology and the hydraulic impact integral drill pipe string method to carry out the construction of rock stratum guide hole. Although these methods have improved the efficiency of rock breaking, they can only be carried out in the way of partial grinding when drilling and turning, and the overall efficiency is still very low. In addition, air compressor with high pressure and large flow rate is required in the process of pneumatic submersible hole hammer, and a set of dust removal and dust removal device is required in dry drilling. The method of hydraulic impact on the whole drill pipe string increases the fatigue damage degree of the drill pipe and affects the construction safety and the service life of the drill pipe.
 
3. The latest construction technology -- double-wall drilling pipe technology
 
3.1 process principle
 
3.1.1 structure
 
The double wall drill pipe is a new undiggable patent from DITCH WITCH. This is a rod-in-rod structure, which is divided into two parts, the inner drill pipe and the outer drill pipe. In the working process, the domestic and foreign drill pipes are connected with each other through thread, and the internal drill pipes are connected with the male and female joint of hexagonal structure. Mud is transported to the bottom of the hole through the annular space between the inner and outer drill pipes. Within and is driven by double motor power head drill pipe and drill pipe can rotate relatively independent, rock drill with three roller guide drill bit and drill pipe connection, the probe to accommodate pipe and pipe connection at the back of the drill, and drill pipe column axis in 2 ° installation Angle.
 
3.1.2 guiding mechanism
 
During the construction process, when the inner and outer drill pipes rotate at the same time, the drilling track is in a straight state. When the inner drill pipe rotates and the outer drill pipe stops to advance in a certain fixed direction without rotation according to the installation Angle position of the probe holding pipe, the drilling track will turn in this direction, that is, the inner drill pipe supplies the bit torque, and the outer drill pipe supplies the bit thrust and direction control. For example, if you want the drill hole to turn upward, rotate the outer drill pipe so that it is at 12 o 'clock on the clock face of the ground tracker, indicating that the installation Angle is upward. When the outer drill pipe is fixed at 12 o 'clock and stops rotating, only thrust is applied, while the inner drill pipe drives the drill bit to rotate, making the drilling hole turn up quickly. After reaching the predetermined inclination Angle, the inner and outer tubes are rotated simultaneously to drill straight holes. In this way, no matter the straight hole segment or the turning hole segment, the drill bit can rotate continuously at high speed and steadily, effectively overcome the rock and achieve efficient construction.
 
3.1.3 guiding mechanism
 
Compared with the mud motor process, the dual-wall drill pipe process has the following characteristics:
 
(1) in double-wall drill pipe technology, the power of the drill bit is directly provided by the inner drill pipe, which is equivalent to a mechanical motor. Under the same main engine power condition, the mechanical transmission efficiency is much higher than the hydraulic transmission efficiency of the mud motor, so as to further ensure the efficiency of rock drilling;
 
(2) the double-wall drilling pipe process avoids the use of a large amount of mud required by the mud motor process in rock construction, and reduces the related mud power and mud material cost consumption and environmental pressure;
 
(3) under the condition of double-wall drill pipe, the receiver pipe of the probe follows the guide bit closely, and the directional accuracy is high, which avoids the directional accuracy error caused by the large distance between the probe and the guide bit in the mud motor process. Especially, it is more important in the construction of gravity pipelines with extremely high directional accuracy, such as sewage pipe.
 
3.1.4 supporting equipment
 
Double-wall drilling pipe construction technology can also be used for long-distance and efficient guidance in unusual strata such as gravel layer, pebble layer or soil-rock mixture layer. The universal JT2720AT and JT4020AT drilling RIGS matching this process are developed by DITCH WITCH company in the United States. In addition to the dual motor power head structure and the corresponding control system, the drilling RIGS also have unique electronic technology, which achieves a high degree of intelligence and automation, and can realize the automatic drilling function under uniform formation conditions. In addition, its automatic access drill pipe, automatic application of screw oil, drill pipe box side add drill pipe and other characteristics to ensure that reduce the consumption of auxiliary time in the construction, so that the high efficiency of this rock drilling process can be further fully developed. When the drilling machine changes from rock drilling mode (AT mode) to ordinary soil drilling mode (JT mode), it only needs to press the switch on the machine and change a set of drill pipe, and the machine itself does not need to make any changes.
 
3.2 usage
 
AT rock drilling system due to its high efficiency and practicability, the user's widely recognized, AT present, the domestic has this kind of drilling rig, a total of 10 units, have had communication pipeline construction, gas, water and other industries, has experienced the pebble bed of western sichuan plain cross, dalian, Qingdao area of weathered rock crossing through and other hard formation. As of July 2003, xi 'an bureau of China communications construction engineering co., ltd. had used JT2720AT drilling rig to carry out trenchless pipeline construction in a total of more than 30,000 meters in two years, including more than 5,000 meters in gravel and weathering layer. Now, together with four other JT2720AT drilling RIGS, the company is carrying out municipal engineering renovation and construction in the coastal city of dalian, many of which are carried out in weathered rocks with strong abrasion, fully demonstrating the unique advantages of AT technology. With the increasing popularity of trenchless technology in China, more hard and complex stratum construction will be encountered, and the high-efficiency rock drilling technology will have more extensive applications.

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