The construction process of horizontal directional drilling can generally be divided into three steps: pilot hole drilling, pre-expanding, and pipeline pulling back. The quality of the pilot hole trajectory directly affects the size of the pullback force, and the risk avoidance of directional crossing is largely reflected in the construction process of directional drilling. Therefore, only by mastering advanced steering technology can we reduce risks and ensure the safe completion of the crossing project with both quality and quantity.
Types of Steering Technology
Horizontal directional drilling control technology can be divided into two categories: one is wireless direction control technology, which is commonly used in medium and small directional crossing projects, and is characterized by simple operation, short operation time and low cost, but its detection depth is generally only If the maximum depth of the crossing project exceeds 15 m, it is necessary to adopt the second type of steering technology, that is, geomagnetic wire steering technology. As a kind of strong anti-interference ability and deep detection depth, the geomagnetic wired direction control technology is suitable for long distance and deep depth. It is often used in a series of large trenchless projects such as urban gas outer ring pipeline network and long-distance pipeline. .
Introduction to the Geomagnetic Control System
Taking the MGS directional system of Sharewell Company of the United States as an example, the system has five main components, namely: probe, driller display, interface instrument, computer and printer. Among them, the probe is installed in a set The non-magnetic components include 1 non-magnetic drill collar, 1 non-magnetic steering sub and 1 non-magnetic deflecting sub with jet drilling tool or mud motor bit.
Components of Sharewell Steering by Wire System
Its working principle is that the signal from the probe is transmitted to the ground through the steering wire, and after being processed by the interface instrument, it is transmitted to the driller’s display and computer to provide real-time information on drilling steering. The pilot can directly read various parameters from the computer, without having to track the drill bit along the drilling trajectory. The system can print guide records, which is more convenient for judging whether guide holes are available and collecting completion data.
Different from the electromagnetic wave transmission method of the wireless direction control signal, the geomagnetic wired direction control transmits the signal through the wire, so the signal is more stable and reliable. When used at deep drilling depths, its accuracy reaches ±2% of the vertical depth of the probe.
Practical Application of Geomagnetism Steering System
The Jiyang Road (Qiantan) natural gas pipeline project in Shanghai is a special pipeline for high and medium pressure regulator stations in Qiantan. The pipe material is D325mm×8mm high-pressure seamless steel pipe (20# steel). Yang River. There are two main difficulties in this project. First, the depth of direction control is about 27.0m, so the precision required for direction control is high; second, the channel width of Chuanyang River is about 70m, that is, there is a horizontal distance of nearly 70m It is drilling underwater, and it is impossible to track and measure with a conventional wireless steering system. The only steering method that can meet the construction requirements is the use of geomagnetic wired steering technology.
In the actual engineering construction, the drilling rig used is the American Wittmann D80mm×120mm small drilling rig. The drilling rig has a high degree of automation, the rotary torque of the drilling rig is 16270N·m, and the maximum pushing force is 36287kg (about 36t). The length of the drilling rig equipment does not exceed 10m, which is very suitable for city gas trenchless construction.
When connecting the Xuewei wired steering system with the drilling rig, it is necessary to consider that the length of the connecting wires should be minimized and the operation procedures should be simplified under the premise of ensuring the stability of the connection signal. After fully understanding the working principle of the system, first install the probe rod in a set of non-magnetic components, and the wire at the end of the probe rod passes through the central gap of the drill pipe to the rear power head of the drilling rig; The slip ring at the back of the head transmits the signal to the information processing interface instrument in the control room. The data obtained after processing is transmitted to two channels, one is transmitted to the computer control software in the control room, providing data for the control personnel to record and issue control instructions; the other channel is displayed to the driller to guide the driller’s work .
According to the actual situation of the crossing site, the entry site for the crossing is within the walls on both sides of the Shenjiang River, and the entire drilling site covers an area of 20m×30m. The drilling tools used in this crossing mainly include: 127mm S135 internally thickened drill pipe, 241mm inlaid tricone bit, and 168mm non-magnetic drill collar.
Construction process using geomagnetism steering system
Different from wireless steering, geomagnetic steering does not require the steering operator to follow up and measure directly above the drill bit in real time. Its working principle is to determine its own azimuth by calculating the angle between the probe and the earth’s magnetic field. Therefore, for geomagnetic steering technology, the accuracy of steering parameter (azimuth) measurement largely determines the accuracy of the final steering trajectory. In this construction measurement stage, we adopt the method of taking the average value of multiple measuring points along the center line at the entry point. Measurement.
The measured azimuth angle of the project is 176.7° at point A, 176.4° at point B, 176.5° at point C and 176.4° at point D, with an average of 176.5°. After the actual measurement obtains the best steering parameters, make original records and input them into the computer steering software.
In the whole technological process, steerable drilling is also a very critical process. In the steering stage, the steering officer and the driller cooperate closely, and the steering officer sends instructions to the driller to drill the pilot hole according to the design curve. Every time a drill pipe is drilled, the steering officer needs to monitor the inclination angle of each drill pipe in real time. The inclination angle can be calculated in the computer to obtain the real-time depth of the drill bit, and the next drill pipe can be adjusted at any time according to the depth required by the project. At the same time, every time a drill pipe is drilled, the steering operator needs to control the horizontal deviation of drilling according to the previously measured azimuth angle. If the return azimuth angle changes, it must be corrected in time. After comprehensive consideration, 1-311*910=2-9+7*3 inform the driller how to carry out the steering operation of the next drill pipe, and make a record of the steering construction truthfully and conscientiously.
The driller needs to operate the drilling route of the drill pipe according to the instructions of the steering officer, and judge the formation change and drilling resistance according to the change of the drilling parameters, and communicate with the steering officer in time, so that the steering officer can analyze and judge. Adjust the drilling trajectory.