In the construction of long-distance horizontal directional drilling through pilot holes, due to the large frictional resistance between the drill string and the hole wall, the rotation of the drill bit obviously lags behind the rotation of the drilling rig power head, which makes it difficult to control the downhole tool face angle. , so that the steering accuracy is affected. To solve this problem, a docking technology is used. This paper mainly introduces the principle of docking technology and the combination method of downhole drilling tools during docking.
In trenchless pipeline construction technology, horizontal directional drilling technology is highly regarded for its advantages such as less damage and interference to traffic and environment, safe and efficient construction, and low comprehensive cost. With the application and development of this technology, a docking technology for long-distance directional drilling through construction has emerged. The horizontal directional drilling docking technology has the following advantages:
(1) Solve the difficult problem of directional control of long-distance horizontal directional drilling. In the process of directional drilling crossing, with the increase of drilling length, the frictional resistance of the drill string to the formation increases significantly, and the torsional deformation of the drill string increases, which leads to the failure of the drilling rig torque to be transmitted to the drill bit in time, and the drill bit is in a discontinuous state at the bottom of the hole. rotation state. In this case, it is difficult for the driller to control the direction of the downhole tool face angle, so that there is a certain deviation between the tool face angle displayed on the surface and the actual downhole tool face angle, resulting in out of control of the drilling direction. The docking technology, on the other hand, drills from the entry point and the excavation point of the design crossing the curve to the middle at the same time, thereby effectively shortening the drilling length of the one-way pilot hole, avoiding the directional control of the ultra-long distance, and making the azimuth and inclination of the drilling easier. Control to ensure smooth drilling curve.
(2) The entry point and the excavation point fully meet the design requirements. In the construction of directional drilling in medium and short distances, one-way directional control technology is generally used for pilot hole construction, and it is difficult for the actual excavation point to exactly match the designed excavation point. However, since the docking technology drills from the entry point and the excavation point to the middle at the same time, there is no problem of position error of the excavation point. The advantages of butt-joint technology are particularly obvious in the project where casings are used to isolate the pebble and gravel layers at both ends of the crossing curve.
The docking crossing technology has been successfully applied in many major construction projects at home and abroad. In China, there are long-distance or special geological pilot holes such as Qiantang River, Modaomen Waterway, Fujian LNG East-West Stream, Yinma River, and Heilongjiang Crossing Project of Sino-Russian Crude Oil Pipeline. Breaking the world record for directional drilling (see Table 1).
In foreign countries, the longest distance traversed by horizontal directional drilling is the 11 km crossing in Boston Bay in the United States. This crossing is divided into 4 sections, of which the longest section has a crossing distance of more than 4 km; NACAP company adopts this technology in Rhone, France. (Long River) Valley successfully crossed the thick gravel layers on both sides of the valley, and laid a steel natural gas pipeline with a total length of more than 1 036 m and a pipeline diameter of 609.6 mm;
In the Rhine River in northern Germany, the horizontal directional drilling rock traversal distance completed by this technology is up to 2500 m, and the maximum compressive strength of the rock reaches 160 MPa; in August 2005, the German LMR Drilling Company successfully adopted this technology in the Elbe River. Lay an oil PE pipeline with a length of 2 626 m and a diameter of 350 mm.
Downhole docking requires smooth drilling trajectory, which can lay a good foundation for subsequent reaming operations and successful pipe dragging. The smoothness of the drilling trajectory at the docking point largely depends on the pilot hole construction in the early stage.
The two drilling rigs drill from the entry point and the unearthed point to the middle horizontal section respectively. The well on the side of the entry point is called the main logging well, and the well on the side of the unearthed point is called the logging well. When docking, the main logging well is responsible for measuring the measured well The position of the downhole bit and the docking are realized, and the main logging axis is almost parallel to the logging axis.
The magnetic field generated by the axial magnet in the downhole BHA to be logged is decomposed into three mutually perpendicular magnetic field components, namely the axial component, the high-side component and the right-hand component; the sensor in the main logging downhole BHA The value of the downhole magnetic field component is measured, and the proximity of the two wells is judged by analyzing the value of the magnetic field component.
For the docking coordinate system established near the docking point, the vector ax is the axial unit vector of the main logging well, and the vector s is the axial unit vector of the logging well. [hs rs] to describe. The plane of the docking coordinate system [hs rs] is perpendicular to the vector ax and approximately perpendicular to the vector s. The origin of the docking coordinate system [hs rs], that is, the intersection of the vector ax and the plane [hsrs], is the position of the sensor in the main logging BHA, and the well depth value of this position in the main logging is mdtwt; The point (hstie, rstie) in the coordinate system [hs rs], that is, the intersection of the vector s and the plane [hs rs], is the position of the axial magnet in the downhole BHA to be logged. The well depth value in mdmwt. The values of hsconv and rsconv in the figure are used to characterize the parallelism between the axial vector s of the logging well and the axial vector ax of the main logging well. Among them, the main logging well depth mdtwt is obtained by accumulating the length of the drill pipe by the direction control personnel of the main logging side, and the logging well depth mdmwt, the relative distance of the docking (hstie, rstie) and the parallel measurement of the two wells (hsconv, rsconv) can all pass the main logging. Downhole sensor measured. According to the total length of the designed drilling curve and the actual drilling length of the main logging well and the logging well, the distance between the main logging well and the downhole bit of the logging well is calculated, and the docking is carried out when the distance is 5-10 m. When docking, the main logging downhole drilling tool remains stationary, and the downhole drilling tool assembly to be logged moves within a range of ten meters to several tens of meters (the specific range depends on the actual situation). Every time it moves 0.5 m, the main logging downhole sensor measures once, and a series of measured data are displayed on the main logging control software interface in the form of graphs and graphs. After measuring the above-mentioned set of data, move the main logging downhole drilling tool assembly to another well depth and keep it still, repeat the above actions for the logging well, and then measure another set of data from the main logging well. By analogy, the main logging downhole drilling tool assembly is placed in multiple well depths, and the logging actions are repeated. After measuring multiple sets of data, the longitudinal data is compared, and a set of data with high reliability is selected from them to determine the time of docking. Main logging well depth location. By analyzing the measured data, the relative distance (hstie, rstie) of the two wells in the docking coordinate system can be known, because this value represents the vertical, left, and right positions of the downhole axial magnet to be logged relative to the main logging downhole sensor. According to this value, the operator can adjust the tool face angle of the main logging or downhole directional control sub-sections to be logged and continue to drill to get closer to the opposite well. After drilling for a certain distance, repeat the measurement to obtain the relative distance between the two wells. , and then adjust the tool face angle of the downhole control sub joint to continue drilling until the docking is successful.
For the wired directional system, the downhole BHA is mainly composed of a drill bit, a screw motor with a curved casing, a mud pressure sensor, a directional probe (with centralizers at both ends) and a non-magnetic drill collar, where the directional probe is installed in the Non-magnetic drill collar inside. In the construction stage before the pilot hole is drilled to the docking point, the main logging is combined with the downhole drilling tool to be logged. After reaching the docking range, the logged well needs to be tripped out to replace the downhole drilling tool assembly. According to the actual situation, there are the following combinations:
(1) During the docking process, the main logging well is responsible for continuing drilling and completing the docking with the logging well. The logging well just moves back and forth in the original well within the docking range for the main logging well to measure the magnetic field data generated by its downhole axial magnet, and then the logging well moves back and forth in the original well within the docking range. The logging downhole assembly was replaced with a drill bit, axial magnet (sub with magnetic), mud pressure sensor, directional probe and non-magnetic drill collar.
(2) During the docking process, the logged well is responsible for continuing drilling and completing the docking with the main logging well. The main logging well only measures the magnetic field data of the downhole axial magnet of the logging well within the docking range, and then is replaced by the logging downhole BHA. For drill bits, axial magnets, screw motors with curved housings, mud pressure sensors, directional probes and non-magnetic drill collars.
The calibration and determination of the directional control parameters is the key procedure for the success of directional drilling and is an essential step in the construction of directional drilling. Before the single-penetration directional drilling construction is carried out, the accuracy of the direction control probe, the azimuth angle of the crossing curve, the gravity field, the magnetic field and the included angle of the geomagnetic field at the construction site must be measured. For the azimuth angle of crossing the site, refer to the values of the angle between the gravitational field, the magnetic field and the geomagnetism, and determine the measurement error of the steering probe, and use the error as a reference during construction. For the measurement and calibration methods of the above-mentioned related parameters, see the relevant literature. According to the changes of the magnetic field, the gravitational field and the included angle of the geomagnetism, the external interference can be judged, so that we can take other measures to eliminate the interference. Before implementing the docking traversal, the above parameters also need to be measured and calibrated in advance, in order to ensure that the pilot hole trajectory in the early stage conforms to the theoretical drilling trajectory designed for docking to the greatest extent. The axial magnet in the downhole BHA to be logged is an indispensable drilling tool in the docking construction. The measurement and calibration of the magnetic pole moment generated by the axial magnet and the parameters related to the magnetic field distribution around it is another necessary procedure to ensure the successful docking. .
5.1 Measurement and calibration of the magnetic dipole moment of the axial magnet
In order to reduce the measurement error and make the measurement data closer to the actual situation of the downhole docking, the axis of the steering probe should be coincident with the horizontal center line passing through the design curve, and there should be no external magnetic field (including high-voltage cables) within 10 m of the measurement position. , induced magnetic fields generated by communication cables, other metal objects, etc.). During measurement, the directional probe is placed on the centerline of the design curve, and is connected to a computer about 10 m away from it. The axial magnet is placed near the steering probe, and its axis is kept parallel to the axial direction of the steering probe, and the distance between them is 1 m, as shown in Figure 4. Use a computer to measure and record the magnetic field strength Bax of the axial magnet, then reverse the polarity of the axial magnet by 180°, and measure the magnetic field strength Bax (rev) of the axial magnet again. Then the magnetic pole moment of the axial magnet can be calculated by the following formula: M = (Bax-Bax (rev))/2. The M values calculated here are all absolute values, and the M values during docking are positive and negative due to the different magnetic pole orientations of the actual downhole axial magnets.
5.2 Measurement and calibration of the magnetic field components around the axial magnets After the measurement of the magnetic dipole moment of the axial magnets is completed, the direction-controlling probe is kept in place, and the drilling tool assembly with the axial magnet is placed at a distance of 1 ~ At a distance of 2 m, keep the axes parallel to each other, and then measure the exact vertical distance between them. During the measurement, the directional control probe is kept fixed, and the drilling tool assembly with the axial magnet moves forward step by step at a distance of 0.5 m each time along its axis. Length, the relative position between the two when measured.
Every time the drilling tool assembly moves 0.5 m, the equipment and personnel used for moving should be kept 10 m away from the measurement point to reduce external interference. The computer connected to the steering probe measures the data once, and completes the process from point A to point N in Figure 4. After all the measurements are completed, the measurement of a set of data is completed. After completing a set of data measurements, the vertical distance between the steering probe rod and the drilling tool assembly is used as the known initial condition, and the value range of the relevant parameters is input, and data processing is performed to obtain the component value of the magnetic field distribution around the axial magnet. , for use in downhole docking. In order to reduce the measurement error, several sets of data can be measured on site, and the average value can be taken.
