Research On MWD Surveying Method And Locating Technique Of Horizontal Directional Drilling

With the development of trenchless technology, horizontal directional drilling (HDD) processes have gotten wide applications during the last decades. In order to realize orientation monitoring and accurate steering, the spatial attitude and three-dimensional position of the boring tool should be obtained beforehand. As the primary measuring issues, the method of measurement-while-drilling (MWD) and the technology of locating have already caused extensive concerns and become the subjects of intensive research. Supported by 863 National High Technology Research and Development Program"Advanced horizontal directional drilling pipelaying equipment"(2003AA430120) and Hunan Province Natural Science Foundation"Research on new method of locating and navigation in the trenchless horizontal directional drilling"(03JJY3083), the dissertation concentrates its attention on the research of the MWD methods, the locating techniques, and the development of locator equipment with own property right. The main contents and contributions of this dissertation are as follows:1. The MWD method utilizing three-axis accelerometers and three-axis magnetometers has been described. In order to eliminate the adverse effects of perturbing magnetic fields associated with magnetized sections of the drill collar, an azimuth correction method which relies on the knowledge of local geomagnetic field is proposed. Results show that the corrected azimuth is immune to perturbing magnetic fields. So, the method lowers the demand of costly non-magnetic drill collar and widens the application of the method with accelerometers and magnetometers.2. The MWD method utilizing three-axis accelerometers and three-axis gyroscopes, what is known as strapdown inertial navigation system (SINS), has been expatiated. Since the bottom hole assembly cannot accommodate a complete inertial measurement unit, this research considers some specific conditions in horizontal drilling operations to minimize the number of axes so that only one-axis or two-axis gyroscopes will be sufficient to provide full surveying of position, velocity and attitude. Corresponding measuring models are given respectively and the measuring errors are analyzed.3. Some engineering methods of determining the pitch and the roll have been discussed, and the practical sensors are demonstrated. Two photoelectric methods of determining the roll, which are based on photoelectric switch and optical position encoder respectively, are put forward for the first time. At the same time, the sensor prototypes have been designed. Results show that both of them are compact, simple, low-cost and solid, and they are especially well-suited for underground boring tool to perform MWD process.4. The electromagnetic method based on specific magnetic dipole has been described to realize locating and data communicating. An underground solenoid which carries very low frequency current can be equivalent to a typical magnetic dipole, and form a specific quasi-static electromagnetic field in the area less than a wavelength. Thus, according to the specific field, the dipole position can be determined and the measuring data can be transmitted by using a ground receiving antenna.5. The walk-over locating method and the depth measurement method have been proposed in detail. On the basis of detailed analysis of the dipole quasi-static field, the locating methods of single receiver, 45°dual receivers are respectively described. The concrete operating steps are denoted, too. Depth measurement can be realized after surface locating. Different depth measurement methods which utilize calibration, dual receivers, front and back locating points are proposed and the measurement errors among them are compared.6. The locator equipment with own property right has been developed. The entire equipment comprises of an underground MWD sonde, a surface locator and a bore path planning and monitoring software system. These systems constitute the HDD measuring platform for bore path monitoring and steering. The locator equipment fills the domestic blank in HDD locator equipment area, and its performance approaches international advanced level.