Qilong Xue 1 Key Laboratory on Deep GeoDrilling Technology of the Ministry of Land and Resources, School of Engineering and Technology, China University of Geosciences, Beijing 100083, China e-mail: xqlfly@gmail.com Ruihe Wang College of Petroleum Engineering, China University of Petroleum, Qingdao 266580, China Baolin Liu Key Laboratory on Deep GeoDrilling Technology of the Ministry of Land and Resources, School of Engineering and Technology, China University of Geosciences, Beijing 100083, China Leilei Huang Sinopec International Petroleum Service Corporation, Beijing 100029, China Dynamic Measurement of Spatial Attitude at Bottom Rotating Drillstring: Simulation, Experimental, and Field Test In the oil and gas drilling engineering, measurement-while-drilling (MWD) system is usu- ally used to provide real-time monitoring of the position and orientation of the bottom hole. Particularly in the rotary steerable drilling technology and application, it is a chal- lenge to measure the spatial attitude of the bottom drillstring accurately in real time while the drillstring is rotating. A set of “strap-down” measurement system was devel- oped in this paper. The triaxial accelerometer and triaxial fluxgate were installed near the bit, and real-time inclination and azimuth can be measured while the drillstring is rotating. Furthermore, the mathematical model of the continuous measurement was established during drilling. The real-time signals of the accelerometer and the fluxgate sensors are processed and analyzed in a time window, and the movement patterns of the drilling bit will be observed, such as stationary, uniform rotation, and stick–slip. Differ- ent signal processing methods will be used for different movement patterns. Additionally, a scientific approach was put forward to improve the solver accuracy benefit from the use of stick–slip vibration phenomenon. We also developed the Kalman filter (KF) to improve the solver accuracy. The actual measurement data through drilling process verify that the algorithm proposed in this paper is reliable and effective and the dynamic measure- ment errors of inclination and azimuth are effectively reduced. [DOI: 10.1115/1.4031742] Keywords: strap-down, continuous MWD, rotary steerable, stick–slip vibration, spatial attitude 1 Introduction Directional drilling is the technology for directing a wellbore along a predefined trajectory, which is essential for many reasons, such as side tracking of an existing well, drilling multiple wells from the same offshore platform, multilateral drilling, and hori- zontal drilling. This dramatically reduces the cost and time of dril- ling operations. Thus, the development of directional drilling technologies has gained more attention in recent years. Besides the conventional drilling assembly, directional drilling operations require position sensors to provide estimations of the inclination (deviation from the vertical direction) and azimuth (deviation from the north direction in the horizontal plane) [1,2]. These sen- sors are part of the MWD tool, which is installed several feet behind the drill bit to monitor all physical parameters that affect the drilling operation. Current MWD survey is performed along the well path at sta- tionary survey stations. That is to say, the bottom drillstring atti- tude (inclination and azimuth) measurement is carried out in the case that the drillstring does not rotate. But with the development of drilling technology, continuous measurement of well trajectory becomes increasingly important. It also has become essential in rotary steerable system (RSS). As a booming technology catering the 21st century, rotary steerable drilling features extended the reach capacity, well trajec- tory control accuracy and flexibility, which can notably increase drilling efficiency and safety [3–6]. One of the technical difficul- ties in the rotary steerable drilling system is how to dynamically measure the spatial attitude accurately at the bottom rotating drill- string. The regular wellbore position calculations are typically performed by measuring azimuth and inclination with the MWD system in a stationary mode (the drillstring nonrotating). How- ever, the attitude of the bottom rotating drilling tool should be obtained in real time in both the RSS and automatic vertical dril- ling system. In this paper, we developed the methods of dynamic solving of azimuth and inclination when drillstring is rotating based on theoretical analysis and real data of the field test, with regard to the drillstring state of motion. The achievement can improve the attitude solving accuracy of bottom rotating drill- string and the trajectory guidance capability in automatic vertical or rotary steerable drilling. Mahmoud et al. [7], Noureldin et al. [8], and Pecht and Min- tchev [9] studied the continuous MWD under laboratory condi- tions using gyroscope-based system and proposed an advanced direction and inclination sensor package based on the inertial nav- igation system (INS). They verified the reliability of the algo- rithm, through simulation, which used INS to achieve the continuous MWD with high accuracy. They analyzed the influen- ces of vibration and temperature upon MWD and used KF to improve the system accuracy. However, they insufficiently con- sidered about the downhole complex situations [10–12]. The severe vibration of drillstring causes great challenges for the mea- surement accuracy and lifetime of the sensors, which will greatly affect the life of the gyroscope. Moreover, the increasing tempera- ture will give high-rise to the error drift of the gyroscope. Actually, in the control process, assume that the measured val- ues under stationary state remain unchanged during drilling, and could still achieve the closed-loop control of rotary steerable. However, the disadvantage is obvious. Figure 1 shows that the actual trajectory of drilling fluctuates with the design trajectory. This phenomenon cannot be avoided because of the hysteresis of 1 Corresponding author. Contributed by the Petroleum Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received February 27, 2015; final manuscript received September 1, 2015; published online October 29, 2015. Editor: Hameed Metghalchi. 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