Formation of circularly polarized wave by impedance wire dipole located over square screen
For a radiating system consisting of a resonant half-wave impedance oblique wire dipole and a rectangular perfectly conducting screen the conditions guaranteeing formation of a circularly polarized wave with extremely achievable field amplitude in the set directions of the main observation planes are investigated. Computation of the far field components is based on the asymptotic solution of 3D vector problem of diffraction of the field of electric dipole on the ideally conducting rectangular screen, obtained by the method of uniform geometric diffraction theory. To define a wire dipole's slope angle guaranteeing equality of the amplitudes of the orthogonal field components, the technique with account of diffraction effects on edges of the finite size screen is developed. It is shown that in defined interval of the observation angles the circularly polarized wave with extremely achievable field amplitude may be formed by a choice of appropriate wire dipole's slope angle and removal from a screen.
Polarization of wave formed by impedance wire dipole with screen depending on screen sizes
For a resonant impedance wire dipole that is inclined at the angle over a square perfectly conducting screen the conditions guaranteeing formation of a circularly polarized wave with extremely achievable field amplitude in the set directions of the main observation planes depending on the screen sizes are investigated. The asymptotic solution of the 3D diffraction problem of the field of an arbitrarily oriented impedance wire dipole on the rectangular screen, obtained by the uniform geometric diffraction theory method was used. The detailed analysis of the dipole's slope angles, the dipole's removal from the screen, at which a circular polarized wave is formed with extremely achievable field amplitude depending on the screen sizes are given. It is shown that with increasing the screen sizes the interval of angles in the main observation planes at which can be formed the circular polarization considerably increases.
Prevention of Barite Sag in Oil-Based Drilling Fluids Using a Mixture of Barite and Ilmenite as Weighting Material
Drilling high-pressure high-temperature (HPHT) wells requires a special fluid formulation that is capable of controlling the high pressure and is stable under the high downhole temperature. Barite-weighted fluids are common for such purpose because of the good properties of barite, its low cost, and its availability. However, solids settlement is a major problem encountered with this type of fluids, especially at elevated downhole temperatures. This phenomenon is known as barite sag, and it is encountered in vertical and directional wells under static or dynamic conditions leading to serious well control issues. This study aims to evaluate the use of barite-ilmenite mixture as a weighting agent to prevent solids sag in oil-based muds at elevated temperatures. Sag test was conducted under static conditions (vertical and inclined) at 350 °F and under dynamic conditions at 120 °F to determine the optimum ilmenite concentration. Afterward, a complete evaluation of the drilling fluid was performed by monitoring density, electrical stability, rheological and viscoelastic properties, and filtration performance to study the impact of adding ilmenite on drilling fluid performance. The results of this study showed that adding ilmenite reduces sag tendency, and only 40 wt.% ilmenite (from the total weighting material) was adequate to eliminate barite sag under both static and dynamic conditions with a sag factor of around 0.51. Adding ilmenite enhanced the rheological and viscoelastic properties and the suspension of solid particles in the drilling fluid, which confirmed sag test results. Adding ilmenite slightly increased the density of the drilling fluid, with a slight decrease in the electrical stability within the acceptable range of field applications. Moreover, a minor improvement in the filtration performance of the drilling fluid and filter cake sealing properties was observed with the combined weighting agent. The findings of this study provide a practical solution to the barite sag issue in oil-based fluids using a combination of barite and ilmenite powder as a weighting agent to drill HPHT oil and gas wells safely and efficiently with such type of fluids.