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Wyświetlanie 1-10 z 795
Tytuł:
Study of the performance of LCMs in fractured formations
Autorzy:
Galves, L.
Miska, S.
Ozbayoglu, E.
Ziaja, M.
Tematy:
lost circulation
LCMS
Pokaż więcej
Wydawca:
Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie. Wydawnictwo AGH
Powiązania:
https://bibliotekanauki.pl/articles/298811.pdf  Link otwiera się w nowym oknie
Opis:
This study focuses on modeling three phenomena that greatly affect the performance of lost circulation materials (LCMs) in sealing thief zones: the process of construction of the LCM seal, the final flow rate after its creation, and the fractability of this seal to the pressures inside the wellbore. To model them, concepts related to fluid mechanics, and geomechanics become of the utmost importance. To help the validation of the models presented in this work, an experimental facility to simulate lost circulation was constructed. The facility makes use of a real limestone core drilled with the Tulsa Drilling Research Projects (TUDRP) drilling rig. This experimental setup represents progress in the reproduction of overall field conditions in comparison with other setups found in the literature. Several tests were performed with walnut at different sizes and concentrations, as well as with distinct fracture openings, inclinations, and orientations. As a result, a D90 as large as the size of the fracture aperture ends up to being effective in the plugging process. In addition, a D50 the size of 1/3 of the fracture opening also provides of a good seal. Depending on the concentration, smaller sizes can be applied - the smaller the size is, the larger the concentration must be. Finally, a computer program has been developed. Estimations of particle size distribution (PSD), plug time, and flow rate after seal formation are outcomes. This method of LCM selection can be used to assess the performance of different LCMs in the field. Hence, cost, time, and energy can be saved in dealing with lost circulation.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The thermal state of the North Atlantic and macro-circulation conditions in the Atlantic-European sector, and changes in sunshine duration in Central Europe
Autorzy:
Styszyńska, Anna
Marsz, Andrzej A.
Matuszko, Dorota
Opis:
This article explains the reasons for the long-term variability in sunshine duration (SD) in Central Europe. It presents a recently discovered mechanism regulating changes in sunshine duration, not described so far in the literature. The periods of global dimming and global brightening were linked with changes in the annual frequency of the macrotypes of the middle-tropospheric circulation and the variability in the surface component of the thermohaline circulation in the North Atlantic (NA THC). On the basis of the totals of annual sunshine duration from the years 1951–2015 from 21 stations located in the Netherlands, Germany, Denmark, Poland, Switzerland, Austria, the Czech Republic and Slovakia, it was shown that changes in NA THC account for onethird of the variability in sunshine duration, while changes in the frequency of macrotypes W and E, forced by the changes in NA THC, each separately account for about 26 and 22% of the variability in the totals of annual sunshine duration in Central Europe.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Tytuł:
The long-term course of the annual total sunshine duration in Europe and changes in the phases of the thermohaline circulation in the North Atlantic (1901-2018)
Autorzy:
Marsz, Andrzej A.
Styszyńska, Anna
Matuszko, Dorota
Opis:
The current study was based on sunshine duration data from 13 European stations during 1901–2018. It was found that the variability in the annual total sunshine duration (SD) over Europe is related to the variability in the component of the surface thermohaline circulation in the North Atlantic (NA THC). Positive NA THC phases (the condition of the ‘warm’ North Atlantic) correspond to the periods of increased SD (brightening), while negative phases correspond to the periods of decreased SD (dimming). These relationships remain stable and statistically significant. The mechanism of these relationships is based on the influence of weakened or enhanced heat flow from the ocean to the atmosphere on the course of the mid-tropospheric circulation processes. In periods of positive thermohaline circulation in the North Atlantic (NA THC) phases, the share of long waves (macrotype W according to the Wangengejm–Girs classification) increases, with the occurrence of which the frequency of anticyclonic weather over Europe increases, whereas in the periods of negative NA THC phases, the share of shorter waves (macrotypes E and C) increases, with the occurrence of which the frequency of cyclonic (frontal) weather over Europe increases. It is characterised by increased layer cloud cover, limiting the SD. Thus, along with changes in the thermal condition of the North Atlantic, the structure of cloud cover over Europe changes and becomes a factor regulating long-term changes in the annual total SD.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Tytuł:
The Atlantic Meridional Overturning Circulation is not collapsing
Autorzy:
Parker, Albert
Ollier, Clifford
Tematy:
Atlantic Meridional Overturning Circulation
Pokaż więcej
Wydawca:
Uniwersytet im. Adama Mickiewicza w Poznaniu
Powiązania:
https://bibliotekanauki.pl/articles/2054998.pdf  Link otwiera się w nowym oknie
Opis:
Boers (2021) wrote that, in the last century, the Atlantic Meridional Overturning Circulation (AMOC) may have evolved from relatively stable conditions to a point close to a critical transition. The claim is based on different AMOC indices, based on observational sea-surface temperature and salinity data from across the Atlantic Ocean basin. Boers’ conclusions (2021) are not based on systematic observations spanning the last and this century, but on subjective reconstructions of sea surface temperature and salinity, as accurate sea-surface and temperature data are only available over the last few decades. Additionally, the AMOC strength does not only correlate to sea surface temperature and salinity data. His as-sumption that the strength of the AMOC depends on poorly described sea-surface temperature and salinity only is not substantiated. The difficulties of estimating the sea surface temperature (SST) are highlighted in Chan et al. (2019). Even more difficult are the estimations of salinity.
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-10 z 795

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