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The main scope of this research was to develop and apply new methodology for energy prediction during a long-term period, based on the logarithmic relationship between electricity per capita and GDP per capita. This relationship was proven to be valid until 1989. It contains changeable energy and financial indicators and a dynamic rate of growth K, in the form of hyperbolic curves. With a range of slopes from 0.1 to 6, it enables a new economic classification of countries. Further research of this method, called IKoMet, has made the application of this relationship for future periods possible through the deduction of new energy and financial indicators. It was first applied to Italy, by the determination of indicators for a prediction after 1990. The results show that energy growth in the first period was more than ten times faster in comparison to the following period, while financial growth was almost twice as large in the first period. This procedure was also successfully applied for Switzerland, thus it can be concluded that IKoMet could generally be used for long-term energy prediction.

Prema objavljenim podacima o odabranom plinskom polju, predviđena je dinamika pridobivanja plina do 2025. godine. Pretpostavljajući ukupne količine proizvedenih fluida na pojedinim bušotinama, proračunat je i očekivani pad tlaka u ležištu. Temeljem ovih podataka izdvojena je tipska horizontalna bušotina, za postavljanje cjelokupnog proizvodnog modela bušotine u programu Prosper (Verzija 14.0, Sveučilišna licenca 4186). Na osnovu odgovarajućih ulaznih podataka, modeliranjem su određene proizvodne mogućnosti bušotine u podmorju. One prvenstveno uključuju proračun dinamičkog tlaka na dnu, odnosno indikatorsku krivulju, kao i proračun gradijenta pada tlaka u uzlaznim cijevima, čime je određena radna točka sustava. Cilj rada je usporediti točnost rezultata dobivenih temeljem dva različita modela za utok plina iz ležišta u horizontalnu bušotinu, prema autorima Goode i Kuchuk. Prvi slučaj proizvodnog modeliranja odnosi se općenito na ograničeno ležište (engl. Horizontal Well – No Flow Boundaries), a drugi uključuje i utjecaj trenja na dodatan pad tlaka (engl. Horizontal Well – dp Friction Loss in WellBore).

As the energy efficiency is at the heart of the integrated European Union energy policy, which aims to protect the environment through various research projects, the application of the Stirling engine for diffused electricity generation is one of the possible paths for low-carbon application. That is today particularly topical, just looking at the major interest paid at European level at the energy communities, also in terms of incentives and policies facilitating and supporting such initiatives. Although the tested engine V-160 runs on natural gas, its emissions can be neglected in comparison with the internal combustion engines, due to the much more favourable external combustion under the lower pressures and temperatures, as well as to the working medium, which is helium. Next step, becoming every day more and more relevant, will be using hydrogen as a clean (and green) fuel. A major advantage of the proposed engine for use in power generation is the constant speed under different loads. According to the thorough parametric analysis after 200 hours of operation of the engine at the University of Rome La Sapienza, new evidence of the possibilities of performance improvement was obtained. Compared to the Stirling engine with low temperature difference, it has a much lower Schmidt factor of about 21%, which means that a real thermodynamic efficiency of the cycle could be improved. The scope of the analysis was to determine the power that is changed due to the mass of helium and the power that is changed due to the temperature difference. Based on the experimental data, it is found that the temperature difference and the mass of the working medium have a reciprocal relationship. In such a working condition, the engine power is simultaneously increased due to the greater mass of helium, but at the same time decreased due to the decrease in the temperature difference, which is not valid for other types of Stirling engines. The resulting power can be optimized according to a new expression, presented in the paper.

The theory of Thermal Response Testing (TRT) is a well-known part of the sizing process of the geothermal exchange system. Multiple parameters influence the accuracy of effective ground thermal conductivity measurement; like testing time, variable power, climate interferences, groundwater effect, etc. To improve the accuracy of the TRT, we introduced a procedure to additionally analyze falloff temperature decline after the power test. The method is based on a premise of analogy between TRT and petroleum well testing, since the origin of both procedures lies in the diffusivity equation with solutions for heat conduction or pressure analysis during radial flow. Applying pressure build-up test interpretation techniques to borehole heat exchanger testing, greater accuracy could be achieved since ground conductivity could be obtained from this period. Analysis was conducted on a coaxial exchanger with five different power steps, and with both direct and reverse flow regimes. Each test was set with 96 h of classical TRT, followed by 96 h of temperature decline, making for almost 2000 h of cumulative borehole testing. Results showed that the ground conductivity value could vary by as much as 25%, depending on test time, seasonal period and power fluctuations, while the thermal conductivity obtained from the falloff period provided more stable values, with only a 10% value variation.

Analiza testa porasta tlaka za horizontalnu bušotinu temelji se na poznavanju protjecanja fluida u ležištu, koje je matematički opisano jednadžbom difuzije trodimenzionalnog protoka i njenim rješenjima. Prema modelu horizontalne bušotine u neograničenom ležištu za slučaj neustaljenog protoka mogu se pojaviti četiri režima protjecanja: rani radijalni protok, rani linearni, kasni pseudoradijalni i kasni linearni protok. Za svaki od navedenih protoka postoje odgovarajuća rješenja jednadžbe difuzije, koja se primjenjuju u analizi testa porasta tlaka, uz glavnu pretpostavku da je bušotina potpuno horizontalna i smještena u potpuno horizontalnom, homogenom ležištu, jednake debljine. Osim toga, ležište se uzima kao izotropno u horizontalnoj ravnini, ali da postoji vertikalna anizotropija, tj. da je vertikalna propusnost različita od horizontalne. Primjer analize testa porasta tlaka u računalnom programu Saphir prikazan je za horizontalnu bušotinu na plinskom ležištu Okoli. U analizi su korišteni podaci ispitivanja kao temelj za postavljanje odgovarajućeg modela bušotine. Primjena mjerenih podataka u modeliranju bušotine značajna je zbog točnosti i pouzdanosti, koju takvi modeli mogu dati u određivanju ključnih podataka za prognoziranje budućih promjena proizvodnog sustava, kao što su propusnost, skin faktor, početni ležišni tlak i sl., Build up test analysis for the horizontal well is based upon the theory of fluid flow in the reservoir, which is mathematically described by the diffusivity equation of the three dimensional flow and its solutions. According to the horizontal well model in the infinite reservoir for the case of the unsteady flow, four regimes can be developed: early radial flow, early linear, late pseudo-radial and late linear flow. Solutions of the diffusivity equation, that are used in the build up test analysis, are developed for each of the flow regime, supposing that the well is totally horizontal and placed in the totally homogeneous reservoir with equal formation thickness. In addition, it is considered that the reservoir is isotropic in the horizontal plane, but with the vertical anisotropy, meaning that the vertical permeability differs from the horizontal. Example of the build up test analysis in the computer program Saphir is shown for the horizontal well at the gas field Okoli. Well test data are used in the analysis as the basis for the corresponding well model design. Test data application in the well modelling is significant due to the accuracy that those models can obtain in the determination of the key parameters of the production system forecasting, such as permeability, skin factor, initial reservoir pressure etc.

Here is given the review of the book „Petroleum Production Engineering“ written by Marin Čikeš, Ph. D., a retired Full Professor of the Faculty of Mining, Geology and Petroleum Engineering of the University of Zagreb. The book was published in the year 2015, as a university textbook (Manualia universitatis studiorum Zagrabiensis).

Analiza proizvodnog sustava napravljena je za bušotinu Šandrovac-136, opremljenu neprekidnim plinskim liftom. U analizi su korišteni podaci ispitivanja kao temelj za postavljanje proizvodnog modela bušotine u računalnom programu ‘PROSPER’ (Verzija 10.3, Licenca 2681). Primjena mjerenih podataka u modeliranju bušotine značajna je zbog točnosti i pouzdanosti, koju takvi modeli mogu dati u prognoziranju budućih promjena u proizvodnom sustavu. Postavljanje modela može se podijeliti u šest koraka, od kojih su najvažniji: proračun indikatorske ili IPR krivulje, proračun sustava plinskog lifta, te ‘mečiranje’ VLP i IPR krivulja na osnovu ispitivanja bušotina. Cilj ‘mečiranja’ je odabrati odgovarajuću metodu za proračun gradijenata pada tlaka primjenom metode nelinearne regresije, što rezultira radnom točkom sustava koja u odnosu na mjerene podatke protoka i tlaka ima najmanja odstupanja. Tako postavljen model temelj je pouzdane analize osjetljivosti bušotine, u kojoj se odabirom triju ključnih varijabli prognozira njihov utjecaj na buduće promjene sustava, prvenstveno promjena protoka i dinamičkog tlaka na dnu., A production system analysis was made for the well Šandrovac-136 equipped with a continuous gas lift. The analysis was based on the test data which served as the foundation for creating a production well model in computer program ‘PROSPER’ (Version 10.3, License 2681). The importance of the measured data in well modeling is accuracy and reliability in predicting future developments of the production system. The model design can be divided in six steps among which the most important are: calculation of the IPR curve, calculation of the gas lift system and matching of VLP and IPR curves based on the well testing. The aim of the VLP/IPR matching is to choose an appropriate method for calculating the pressure drop gradient by applying the nonlinear regression method, which results in the system working point adjusted to the measured data. This model was applied in sensitivity analysis of the well, in which three key variables are selected to predict their effect on future system changes, primarily on changes of the production and bottom dynamic pressure.

This chapter focuses on risk to the environment from hydraulic fracturing operations, starting with transport of materials and ending when the well is routed to the production facilities. The initial assumption for the fracturing risk analysis is that the well is new and was constructed correctly so that all producible formations are securely isolated behind the barriers of casing and competent cement. The justification for this assumption is that the vast majority of fracturing is the first major stimulation in a well and occurs immediately after completing a new well. Although many well development problems are blamed on fracturing, there are only excluded problems that are real and worthy of the discussion to help define boundaries of the fracturing risk (King, 2012).

This work aims to determine the potential for energy efficiency improvement by means of minimizing fuel consumption in finished woven fabric manufacturing. Energy optimization in process with condensate and exhaust flue gases heat recovery is presented. Returning condensate makes many useful reasons like less make up water required, saving fuel and chemicals as well as treatment costs. The hot exhaust gases could be cooled by heating incoming combustion air and boiler feed water. In the process where an air preheater is applied for combustion air preheating together with condensate heat recovery the fuel i.e. natural gas savings becomes 13, 9%. At the same time the atmospheric thermal pollution is diminished because the exhaust flue gases temperature becomes 72, 7 0C instead of 232 0C.

Geothermal reservoir Velika Ciglena is placed 11 km south-east from the city Bjelovar. It is the high-temperature reservoir, according to the physical characteristics of rocks. So far, four wells have been made. Optimal production of the geothermal energy can be obtained on the well VC-1A, due to the production equipment and thermodynamic conditions of the reservoir. The well is 2881 m deep, with the static pressure of 247, 3 bar and the static temperature of 175°C. Production layer is located on the 2 543 m. The geothermal water production should flow through the annular space between the tubing and the casing, which are designed for the wellhead pressure of 20 bar. Calculations shows that the temperature of the geothermal water on the wellhead should be about 170°C, if the flow is 10 000 m3/h, based on the Duns-Ros methodology. In determination of the optimal temperature, the Joule-Thompson effect should be applied, as it strongly influences all gases and liquids, being important for geothermal water as well.

There are totally 28 geothermal reservoirs in Croatia, among which only 5 are high temperature resources. All reservoirs can be generally classified in two groups, according to the temperatures of geothermal water. The first group, having temperature less than 100oC, is suitable for the direct energy use. In the second group with temperature above the 100oC, except of the direct use, the electricity can be produced as well. Geothermal heat in Croatia is used only on 14 reservoirs, for direct purposes. The heat power amounts to 42 MWt, while the percentage of utilization of their available power is less than 50%. This condition can be improved on many geothermal locations by means of cascade processes. Excellent example for such a kind of energy usage is Heber Province in China, where geothermal heat is applied in textile industry as well. Geothermal well Gao4, at 3432 m depth, having wellhead temperature of 114oC and artesian flow of 2160 m3/d, has the highest well temperature in Northern China. Located in Gaoyang County, it has been used for drying wool. The drying equipment is a geothermal net conveyor belt drier. The moisture content by wet basis of the moist wool is 40% and the moisture content by wet basis of the dry wool is 15% the dry wool product capacity is 280 kg/h, the dehydrating capacity is 120 kg/h and the temperature of the hot air can reach about 95º ; ; C. The residual water leaving the geothermal drier is also used in geothermal greenhouses (7337 m2), district heating (1500 m2), fish ponds (3335 m2) and geothermal bathing.

Conservation option with 60% process condensate recovery shows 8% fuel saving. Whole condensate recovery drives Stirling engine with 13% electricity savings. The implementation of solar energy and condensate recovery rsults with 75% fuel reducing.

Downhole heat exchangers are comparatively low cost method of exploiting a geothermal resource. In addition they have certain advantages claimed for geothermal energy to a higher level than other methods of utilization. Environmental impact for example is usually very low when using downhole heat exchangers, as fluid is not normally removed from the reservoir. Downhole heat exchangers (DHE) allow very efficient use of the heat resource, and often provide a very low running cost (fuel cost) to the end user. However, the number of installations worldwide is relatively low because only under certain combinations of circumstances a DHE can be considered as a suitable method. It is at lower end of the temperature range, where the DHEs advantages are most easily realized. Moreover, it is important to recognize that in Croatia there are many more low temperature resources than high temperatures ones.