In this paper, hollow-core antiresonance sapphire waveguides were applied to guide the THz radiation emitted by the two-color laser air plasma, as well as to manage the THz source angular ...distribution. For this aim, three distinct waveguides were developed. Each of them is based on a cylindrical sapphire tube, either suspended in free space or coated by a polymer. The waveguides were first studied numerically, using the finite-difference eigenmode method, and experimentally, using the in-house THz pulsed spectrometer. The observed data uncovered the antiresonance regime of their operation, as well as their ability to guide broadband THz pulses over tens of centimeters with a high optical performance. The waveguides were then used to couple and guide (over the considerable distance) of THz radiation from the in-house two-color laser air plasma emitter, that exploits the mJ-energy-level femtosecond pulses of a Ti-sapphire laser. Small dispersion of a THz pulse and low-to-moderate propagation loss in the developed waveguide were observed, along with a considerable narrowing of the THz radiation angular distribution after passing the waveguide. Our findings revealed that such technologically-reliable hollow-core sapphire waveguides can boost the performance of laser air plasma-based THz emitters and make them more suitable for applications in the vigorously-explored THz sensing and exposure technologies.
We study angular and frequency-angular distributions of the terahertz (THz) emission of the low-frequency region (0.3-3 THz) from a two-color femtosecond plasma spark experimentally and in ...three-dimensional numerical simulations. We investigate the dependence of the angular shapes of the THz radiation on focusing conditions and pulse durations by using two laser facilities (pulse durations 35 and 150 fs) for different focusing geometries. Our experiments and simulations show that decrease in the numerical aperture from NA ≈0.2 to NA ≈0.02 results simultaneously in (I) squeezing of the THz angular distribution and (II) formation of the bright conical emission in the THz range. The moderate focusing NA ≈0.05, which forms the relatively narrow unimodal THz angular distribution, is identified as optimal in terms of angular divergence. Numerical simulations with carrier wave resolved show that bright THz ring structures appear at the frequencies ≥2 THz for longer focuses (NA ≈0.02), while for optimal focusing conditions NA ≈0.05 the conical emission develops at THz frequencies higher than 10 THz.
An anomalously strong (up to 13 times) reduction of the threshold of the stimulated Raman scattering of 15-ps laser pulses in liquid nitrogen has been found when moving the caustic of a pump beam ...from the bulk through the free surface. A nonmonotonic N-shaped dependence of the stimulated Raman scattering threshold on the distance of the beam waist to the surface has been recorded for the first time with a minimum reached when the plane front of the beam caustic coincides with the surface. The physical mechanism of the detected phenomenon has been discussed.
Today oil and gas complex in Bashkortostan is characterized by a deterioration in the quality of raw material base, which is associated with a significant degree of highly productive fields. It is a ...long-term operation, resource increment due to the discovery of fields unconventional oil, which are confined to low-permeable and weakly thick reservoirs oil deposits with extensive underwater gas and waterfowl zones. At the current stage of unconventional oil development of Bashkortostan oilfields, the urgent tasks are to study the experience of their development; identify peculiarities of the influence of geological and technological factors on the development efficiency of productive layers reserves; geological and commercial substantiation of various methods for enhanced oil recovery. The classification of development objects is based on the methods of mathematical statistics. Recommendations to improve the impact effectiveness on residual and unconventional oil reserves are based on the criteria-based analysis of enhanced oil recovery. The paper describes characteristics of reservoir systems and results of object grouping for oilfields development in Bashkortostan. Taking into account the established criteria for effective use of enhanced oil recovery and geological and field conditions of selected groups of objects with similar characteristics, there are some recommendations to increase the efficiency of oil recovery with targeted formation effects technologies.
Studies described in this paper were aimed at solving a set of problems related to selection, technological justification and design of enhanced oil recovery. Theoretical and laboratory studies of ...remaining reserves production were conducted, as well as prediction of their efficiency if applied to formation of Las Eganskoye oilfield.
The article presents the results of theoretical and experimental studies of insulation of absorbing intervals during penetration of rocks. The proposed systematic approach makes it possible to ...effectively apply insulation methods in various mining conditions of well construction. The methods for controlling the absorption of drilling fluids in the conditions of abnormally low layer pressures are combined in a systematic technology.
The article presents results of the improved technology for drilling and completion of oil and gas wells (Multi-technology Complex). The results are based on synchronization and consistency of ...thermodynamic processes of well bore strengthening and implementing system approaches and solutions. The authors discuss brief analytical generalizations on the quality and efficiency of well lining, factors that violate the well lining technology, and related problems. In addition, disadvantages of traditional technologies and the reason for their low efficiency in the construction of wells are mentioned. The authors give analytical generalizations of the results of well construction with the use of the Multi-technology Complex in various mining and engineering conditions of Russian fields. The method's advantages over traditional methods are noted. There are no occurrences of various complications in a well construction: fountains, emissions, gas-oil-water manifestations, absorption, instability and hydraulic fracturing of rocks. Furthermore, the complex allows improve well and filter structures reducing the metal intensity of the structure and the time frame.
Abstract
The article describes the results of improving the well construction completion technology. The factors and processes decreasing technological indicators of new exploration and production ...wells are analyzed. Research is based on systemic approaches to solving complex scientific and technical problems. The parameters of implementation of the improved technology are presented. The results of field trials intended to implement the technology in the construction of wells in Russian regions are analyzed.
A method for systematic improvement of the drilling technology in difficult mining conditions has been suggested. The study deals with unstable rocks of the sedimentary cover of the eastern edge of ...the Russian platform and conditions for well construction. Wells are directional with horizontal ends. Field tests have shown that technical and technological solutions can solve scientific and technical problems. It is recommended to test these solutions in the conditions of other Russian regions and abroad.
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