A complete knowledge of the drill bit direction and orientation during the drilling process is essential to guarantee accurate directional drilling procedure. Presently, three accelerometers and three magnetometers are typically used as a part of the Measurement-While-Drilling MWD equipment. In some cases, the use of magnetometers has deleterious effect on the accuracy of the surveying process. This is due to the magnetic interference of the drill string, downhole ore deposits and other geomagnetic effects. Recently, gyroscopes have been proposed to aid the magnetometers in environments of high magnetic interference. This paper describes the development of a reliable MWD surveying technique utilizing Inertial Navigation Systems (INS) as a replacement of magnetometers. Tactical grade INSconsisting of three gyroscopes and three accelerometers to be miniaturized inside the bottom-hole assembly is adopted in this study. The proposed system offers station-based surveying for monitoring of azimuth, inclination and tool face angles. Additionally, it provides continuous surveying by applying Kalman filtering to optimally integrate the sensor measurements and to provide both the drill bit position and orientation in realtime. This study also offers accurate modeling of INS long-term errors in order to achieve the desired accuracy for horizontal drilling applications. Pre-filtering using wavelet multi-resolution analysis is utilized in this study to improve the performance of both gyroscopes and accelerometers. This procedure removes most of the short-term and high frequency errors to separate the motion dynamics from the sources of vibration and shocks experienced downhole.The performance of the proposed system is examined using a special experimental setup that performs rotations similar to that experienced by the drill bit. The results showed that reliable MWD surveying performance can be achieved. The suggested INS-based MWD surveying technique eliminates the costly nonmagnetic drill collars for the magnetometers, survey the borehole continuously without interrupting the drilling process and improve the overall accuracy by utilizing real-time digital signal processing techniques.

GPS signals are refracted by the dispersive ionosphere, resulting in ranging errors dependent on both the given signal frequency and ionospheric total electron content. Such range errors translate into a degradation of positioning accuracies. While it is possible to mitigate the impact of ionospheric effects on GPS positioning applications through ionosphere modeling and/or differential techniques (DGPS), residual errors may persist in regions where steep gradients or localized irregularities in electron density exist, particularly during periods of high geomagnetic activity. Such effects are an issue for the reliable implementation of safety‐critical GPS systems. A solar maximum was observed in mid 2000 with associated degradations in GPS positioning accuracies. In this paper the impact of solar maximum on DGPS horizontal positioning applications is investigated. Analyses focus on determining limitations in horizontal positioning accuracies for operational marine DGPS systems. Long‐term analyses are conducted using data from permanent GPS reference networks in Canada, Brazil, and the United States. Several million observations are processed in this study during the years 1998–2000. Studies focus on large ionospheric gradients near the equatorial anomaly and at subauroral latitudes (associated with the main trough and storm‐enhanced densities). Results indicate that DGPS horizontal positioning accuracies are degraded by a factor of 2–5 relative to average values.

The small size of Micro-Electro-Mechanical-Systems (MEMS) gyroscope allows them to fit inside Measurement-While-Drilling (MWD) tool or Rotary Steerable System (RRS). However, the main cause of failure for MWD tools and the RSS is shock and vibration experienced downhole. This costs millions of dollars in repairs and nonproductive rig time [Akinniranye et al., 2007]. Investigation of the ability of MEMS gyroscope to perform under high shock and vibration motivated this research.MEMS gyroscopes are very challenged during the drilling operation due to the harsh environments they have to survive in. Yet, they are expected to perform efficiently and monitor the direction the drillbit penetrates the formation. We tested MEMS gyroscopes in the following ways. First, we exposed these sensors to harsh downhole conditions and checked if they continue to provide data throughout the experiments. Second, we analyzed the performance of the MEMS gyroscopes in severe shock and vibration environments. Finally, we evaluated the effects of the surrounding environment on the MEMS gyroscopes measurements. Additionally, we explored advanced signal processing techniques based on wavelet analysis to enhance sensor performance to provide accurate azimuth measurements while drilling.MEMS gyroscopes successfully passed the two shock and vibration qualification tests conducted at the testing facility in Houston, Texas. The first qualification test was conducted under shock forces of 1400 g at 3400 vpm for a period of 4 hours, while the second test was performed under vibrations ranging from 5 Hz to 400 Hz with a peak acceleration of 14 g. Additionally, sensors output signals were analyzed using PSD. Shock and vibration can damage high frequency components; the extent of damage depends on the magnitude of the applied shock or vibration. Background noise of a relatively high magnitude and broadband characteristics contaminated gyroscope measurements along the entire frequency spectrum; background noise increased with an increase in intensity of shock forces.This research qualified the MEMS gyroscopes for harsh drilling applications. The mechanical and electrical integrity and proper functioning of the MEMS gyroscopes were verified during both shock and vibration testing. MEMS gyroscopes performance was enhanced by reducing the induced short term error due to shock and vibration while drilling. Wavelet multi-resolution analysis was implemented to separate shock and vibration from the motion dynamic components and wavelet packet analysis was employed to analyze shock and vibration effects. The use of MEMS gyroscopes in this research aims to entirely replace the magnetometers while drilling. This overcomes the magnetic interference effects encountered by magnetometer based MWD tools.

The current method to compute the wellbore while drilling is based on stationary surveys at the desired station. This is done by measuring the inclination and the azimuth of the borehole between the current and the previously surveyed stations. Using a mathematical model based on assumptions of the shape of the drilled section, the coordinates of the borehole can be derived. This current method neglects the actual trajectory between the two surveying stations.Exploration and production companies demand cost effective drilling operations. Thus, demand has been rising for a continuous survey that captures the actual trajectory between the stationary surveying stations. This provides an actual estimate of the curvature "dogleg" along the well trajectory. In addition, this allows a better estimation of the casing and cementing of the borehole. Therefore, in this development the wellbore trajectory between the two surveying stations is continuously surveyed using three accelerometers and three MEMS gyroscopes. The computation algorithm is based on strap down Inertial Navigation System mechanization and Kalman filtering.The inputs to the continuous drilling survey system are the accelerometers and gyroscopes measurements, while the outputs are position, tool face, inclination and azimuth of the drill bit. This wellbore survey system will exhibit an unlimited growth of position, and azimuth errors if there are no external observations to update the surveying system. Two external update schemes can limit this error growth while drilling. The first is based on the continuous source of drilled pipe length measurements while the second is the zero velocity update. The Kalman filter continuous surveying system was successfully applied to drilling tests. External updates of the drill pipe length were utilized to reduce measurement error drift. When the drilling process was stopped to connect new drill pipe stands, zero velocity updates were employed by the Kalman filter.

The last two decades have witnessed an increasing trend in integrating different navigation sensors for the overall purpose of overcoming the limitation of stand-alone systems. An example of this integration is the fusion of the global positioning system (GPS) and inertial navigation system (INS) for several navigation and positioning applications. Both systems have their unique features and shortcomings. Therefore, their integration offers a robust navigation solution. This paper introduces a novel multi-sensor system integration using a recursive least-squares lattice (RLSL) filter. The proposed system has a similar structure to the widely used KF. However, it has the major advantage of working without the need of either dynamic or stochastic models. Furthermore, no prior information about the covariance information of INS and GPS is required. The proposed RLSL filter parameters, similar to Kalman gain, are tuned recursively in the update mode utilizing the GPS velocity components. The RLSL, in turn, can filter out the high frequency noise associated with the INS. To test the capabilities of the proposed architecture, a field test was conducted in a land vehicle using a tactical grade INS system (the Honeywell HG1700) integrated with differential GPS measurements collected by a NovAtel OEM4 GPS receiver. The proposed system is examined during the availability of the GPS signal and with intentionally introduced GPS signal outages. The results indicate that the proposed RLSL system is robust in providing a reliable modeless INS/GPS integration module.