Methodological approach to optimal geological and technological characteristics determining when planning hydraulic fracturing at multilayer facilities

The paper considers the issue of increasing the hydraulic fracturing efficiency in a multilayer facility at the final stage of development with an uneven degree of reserves development along the section. Based on the results of the analysis, it was found that the upper layers, which have the worst filtration-reservoir properties, are less developed in comparison with the highly productive lower ones. When hydraulic fracturing was carried out in the upper formations, some of the operations had low success due to the breakthrough of hydraulic fractures into the lower depleted formations. On the basis of the revealed dependencies, the work determined the optimal specific loading of proppant per meter of effective power, depending on the geological conditions, and maps of the prospects for hydraulic fracturing are built. Keywords: oil fields development; hydraulic fracturing; hydraulic fracturing optimization; multilayer facilities.

Performance Analysis and Four-Objective Optimization of an Irreversible Rectangular Cycle

Based on the established model of the irreversible rectangular cycle in the previous literature, in this paper, finite time thermodynamics theory is applied to analyze the performance characteristics of an irreversible rectangular cycle by firstly taking power density and effective power as the objective functions. Then, four performance indicators of the cycle, that is, the thermal efficiency, dimensionless power output, dimensionless effective power, and dimensionless power density, are optimized with the cycle expansion ratio as the optimization variable by applying the nondominated sorting genetic algorithm II (NSGA-II) and considering four-objective, three-objective, and two-objective optimization combinations. Finally, optimal results are selected through three decision-making methods. The results show that although the efficiency of the irreversible rectangular cycle under the maximum power density point is less than that at the maximum power output point, the cycle under the maximum power density point can acquire a smaller size parameter. The efficiency at the maximum effective power point is always larger than that at the maximum power output point. When multi-objective optimization is performed on dimensionless power output, dimensionless effective power, and dimensionless power density, the deviation index obtained from the technique for order preference by similarity to an ideal solution (TOPSIS) decision-making method is the smallest value, which means the result is the best.

Investigations of Hydraulic Power Take-Off Unit Parameters Effects on the Performance of the WAB-WECs in the Different Irregular Sea States

Hydraulic power take-off (HPTO) is considered to be one of the most effective power take-off schemes for wave energy conversion systems (WECs). The HPTO unit can be constructed using standard hydraulic components that are readily available from the hydraulic industry market. However, the construction and operation of the HPTO unit are more complex rather than other types of power take-off, as many components parameters need to be considered during the optimization. Generator damping, hydraulic motor displacement, hydraulic cylinder and accumulator size are among the important parameters that influence the HPTO performance in generating usable electricity. Therefore, the influence of these parameters on the amount of generated electrical power from the HPTO unit was investigated in the present study. A simulation study was conducted using MATLAB/Simulink software, in which a complete model of WECs was developed using the Simscape fluids toolbox. During the simulation, each parameters study of the HPTO unit were separately manipulated to investigate its effects on the WECs performance in five different sea states. Finally, the simulated result of the effect of HPTO parameters on the amount of generated electrical power from the HPTO unit in different sea states is given and discussed.