Dave Irvine-Halliday

Accuracy limitations of FOG-based continuous measurement-while-drilling surveying instruments for horizontal wells

Horizontal drilling processes in the oil industry utilize directional measurement-while-drilling (MWD) instruments to provide real-time monitoring of the position and the orientation of the bottom hole assembly (BHA). It has been reported that a single fiber optic gyroscope (FOG) can be incorporated with three-axis accelerometers to provide real-time MWD surveying of horizontal wells. However, the long-term performance and the accuracy limitations of this FOG-based instrumentation system have not been discussed. This article aims at describing a methodology for quantitative long-term analysis of the various surveying errors while drilling the near-vertical sections of the well. It also offers some techniques to enhance the long-term surveying accuracy in an experimental model of the FOG-based downhole-surveying instrument. The surveying errors are optimally estimated by the Kalman filtering techniques, and their long-term analysis is based on studying the corresponding mean square estimation errors. In order to limit the long-term growth of the surveying errors, we suggest improving the velocity computation provided by the FOG-based system either by continuous velocity update or by zero velocity update at some predetermined surveying stations. These techniques have significantly limited the long-term growth of the position errors (less than 100 m over a more than 2-h experiment). Moreover, the errors associated with the BHA orientation components were kept at less than 1/spl deg/. Suggested methodology significantly improved the surveying accuracy in an experimental model of the FOG-based MWD surveying system.

Measurement-while-drilling surveying of highly inclined and horizontal well sections utilizing single-axis gyro sensing system

In the oil industry, when developing a plan for drilling horizontal wells, measurement-while-drilling (MWD) surveying becomes one of the important prerequisites for the successful completion of the drilling process. MWD surveying of horizontal wells determines the position and the orientation of the bottom hole assembly (BHA) in real-time during the drilling operation. The BHA orientation is determined by its inclination from the vertical direction as well as its azimuth. The present MWD surveying system incorporates three-axis accelerometers and three-axis magnetometers mounted in three mutually orthogonal directions. This magnetic surveying system suffers from the deviation of the magnetic field measurements due to the massive amount of steel around the drilling rig. A new method utilizing the fibre optic gyroscopes (FOG) technology was suggested to replace the magnetic surveying system. It was reported that a single FOG mounted inside the bearing assembly with its sensitive axis along the tool spin axis could be incorporated with three-axis accelerometers to continuously survey the near-vertical well section. This study aims at suggesting a surveying methodology for highly inclined and horizontal well sections utilizing FOG sensors. At each surveying station, the intrinsic uncertainties of the surveying sensors and the other vibration-induced noise are reduced using a transversal finite impulse response filter. The inclination is then computed by processing the accelerometer measurements, while the gyro measurement is utilized to determine the azimuth. In addition, optimal estimation techniques based on Kalman filtering are used to improve the azimuth accuracy and to limit the effect of the drift of the surveying sensors over time. This study indicates that gyroscopic surveying utilizing the FOG technology can be a reliable solution for MWD surveying of horizontal wells.

New technique for reducing the angle random walk at the output of fiber optic gyroscopes during alignment processes of inertial navigation systems

Aboelmagd NoureldinDave Irvine-HallidayUniversity of CalgaryDepartment of Electrical and ComputerEngineeringAlberta, Canada T2N 1N4Herb TablerInternational Downhole Equipment, Ltd.Edmonton, Alberta, CanadaMartin P. MintchevUniversity of CalgaryDepartment of Electrical and ComputerEngineeringAlberta, Canada T2N 1N4E-mail: mintchev@enel.ucalgary.caAbstract. Angle random walk (ARW) is the noise component at the out-put of a fiber optic gyroscope (FOG) and it affects the FOG short-termaccuracy. Practical applications of FOGs inside an inertial navigationsystem necessitate monitoring the Earth’s rotation rate component alongthe FOG sensitive axis to determine the initial attitude of the movingobject. The ARW increases the measurement uncertainty, thus affectingthe overall accuracy. We introduce a new filtering approach that signifi-cantly reduces the ARW at the FOG output to a level that can ensure anaccurate measurement of the Earth rotation rate. The filtering approachemploys the forward linear prediction (FLP) technique to design a tapdelay line filter and a new criterion, based on controlling the step sizeparameter, is introduced to ensure the fastest possible convergence ofthe adaptive algorithm, while keeping the minimal possible mean squareerror. The proposed FLP filter of 300 tap weights is capable of reducingthe ARW from 4.66 to 0.0694deg/h(

Why the developing world is the perfect market place for solid state lighting

Much has been written about the daily challenge for survival faced by countless millions of developing world families and the overdeveloped world has offered a number of solutions by which those at the base of the economic pyramid (BOP) can help themselves. Light Up The World (LUTW), the global leader in bringing Renewable Energy (RE) based Solid State Lighting (SSL) to the developing world, offers yet another solution, and one that comes with a very high probability of success. In this paper we discuss: the critical role played by micro credit (banking for the poor); a typical example of a developing world community and their lighting needs and expenditures; how SSL can contribute positively to all eight of the Millennium Development Goals; the micro and macroeconomics of SSL at the BOP, its numerous societal benefits and its potential perverse outcomes; and thought there will always be a role for the donation based model, it is only through the market model that safe, healthy and affordable SSL will reach the majority of the BOP, such are the staggering numbers involved. LUTWs fundamental goal, through the facilitation of RE based SSL, is to improve the quality of life of those, who through no fault of their own, find themselves trapped in a cycle of poverty.

Computer modelling of microelectronic closed loop fiber optic gyroscope

Computer simulation of the Fiber Optic Gyroscope (FOG) has not been well elucidated in existing studies. In this paper, we present a comprehensive method for FOG modelling. Different parameters affecting the performance of the FOG and its stability and sensitivity are discussed and the performance of the FOG with respect to vibration and shock is analyzed. The simulation results show that: (1) both the sensitivity and the stability of the FOG are improved by increasing both the length of the fiber coil and the gain of the electronics signal processing system, (2) the modeled FOG can have immunity to vibration with resistance against shock up to 90g [N].

Testing the applicability of fiber optic gyroscopes for azimuth monitoring for measurement-while-drilling processes in the oil industry

Measurement-while-drilling (MWD) surveying is currently performed to provide the drill bit attitude at certain survey stations using three-axis accelerometers to determine the pitch and the roll and three-axis magnetometers to determine the azimuth. The magnetometers used in this process suffer from the deviation of the Earths magnetic field due to the presence of downhole ore deposits, and from drill string magnetic interferences. The aim of this study is to describe an experimental setup for replacing the magnetometers with a single fiber optic gyroscope (FOG). The experimental setup is designed to deliver rotations about three orthogonal axes and these rotations are performed using DC motors controlled by DC-servo amplifiers. Each amplifier compares the control signal from the operator with the feedback position signal from the motor and produces a command signal of certain angular change to the motor. In addition, optical encoders are installed on the shaft of each motor to monitor the speed and to send a feedback signal to the DC-servo amplifier. This feedback signal is used to control the motor speed. The FOG is installed in the horizontal plane of the setup together with three-axis accelerometers. The simulator provides precise angular changes about each axis as small as 0.5/spl deg/. The DC-servo amplifiers provide on-line tuning of the angular change corresponding to the variation in the command signal within /spl plusmn/10% error. The FOG can be oriented at near vertical and completely horizontal situations. Measurements from the FOG and the accelerometers are digitized using a data acquisition system and a laptop computer mounted inside the same setup. After integration, corresponding angular and velocity increments for processing by the developed navigation algorithms are provided. The experimental setup provides the flexibility to test the FOG at different orientations thus simulating various downhole situations.

Beat-length measurement of high-birefringence polarization-maintaining optical fiber using the dc Faraday magneto-optic effect

The polarization-maintaining (PM) capability of a high- birefringence (hi-bi) optical fiber can be described in terms of its modal birefringence or beat length. In the hi-bi (PM) fiber the beat length can be measured by changing the state of polarization of the light through an external means. One such technique is based on the Faraday magnetooptic effect. The technique is nondestructive, relatively simple, and efficient, and beat lengths of 2 mm and less have been measured accurately with it, thus fulfilling the measurement requirements for many of the currently available PM fibers. Utilizing optical sources with wavelengths of 633 and 814 nm, the beat lengths in a total of four hi-bi fibers have been successfully measured using the dc Faraday magneto-optic effect. The experimental results are comprehensive and very promising, and it has been demonstrated that this nondestructive technique has significant advantages over many others in simplicity, versatility, productivity, practicality, and accuracy.

A New Borehole Surveying Technique for Horizontal Drilling Processes Using One Fiber Optic Gyroscope and Three Accelerometers

This paper was selected for presentation by an IADC/SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the International Association of Drilling Contractors or the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the IADC or SPE, their officers, or members. Papers presented at the IADC/SPE meetings are subject to publication review by Editorial Committees of the IADC and SPE. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435.

The theoretical and experimental behavior of a thermooptic bulk deflector fiber-optic circuit switch

The temperature-dependent refractive index change of the dielectric, glass, has been utilized in the fabrication of a one-dimensional 1 × 2 thermooptic bulk deflector. A two-dimensional 1 × 4 thermooptic device utilizing the optical isotropy of glass, achieving enhanced switching capabilities, has also been successfully fabricated and tested. The theoretical analysis of the physical property dT/dx of the glass is confirmed to correspond closely with the optical behavior of the switch in terms of its deflection angle and transient response.

In-vitro measurements of light transmission parallel and perpendicular to the collagen orientation in tendons

Collimated light transmission studies of bovine tendon have been carried out to show the collagen waveguide effect. A monochromator/lamp apparatus was used to irradiate tissue samples and the transmitted light intensity was measured parallel and perpendicular to the collagen fiber orientation. The intensity parallel to the collagen fibers was at least twice that seen with perpendicular propagation. This indicates there is less scattering parallel to the fibers and light waveguiding is present for photon scattering. Also, absorption of light due to hemoglobin around 550 nm and due to water at 980nm was more prominent for parallel than perpendicular propagation. The light may travel either through the collagen fibril or fiber bundles or through the interstitial matrix. Sequential tests during tissue dehydration were performed and it was found that the transmitted light intensity increased with dehydration. This suggest that light may not be traveling through the interstitial matrix where water is the major component. Water may be acting as a reflection boundary for the light that is passing through the fibril or fiber bundles. Collagen waveguiding may be utilized to elucidate the collagen structure. Also, tissue water content could be measured from the transmission profiles. These may be of use in diagnosis and repair of connective tissues.