Multi-fault analysis is an ExxonMobil stochastic tool for analysing the impact and sensitivities of stratigraphic uncertainty and variability on cross-fault leakage of hydrocarbons in faulted traps. This juxtaposition-based method provides quantitative prediction of hydrocarbon contact levels through a complex system of structural spills and juxtaposition leak points in traps with stacked reservoir systems and one or more faults. Validation of the Multi-fault analysis technology was carried out by comparing pre-drill predictions to post-drill results from 41 faulted exploration prospects drilled from 1994-2001. Of the 41 prospects, 29 were valid tests in which we made 22 successful predictions. Of the 22 successful outcomes, 11 were discoveries and 11 were dry wells. Some of the dry wells were drilled assuming the presence of sealing fault-zone material to trap hydrocarbons despite a Multi-fault analysis failure prediction. The seven Multifault failures comprise four predicted successes that were failures and three predicted failures that were successes. Most of the Multi-fault prediction failures can be attributed to data quality and uncertainty; however, some may be associated with sealing fault-zone material. Other considerations in fault seal analysis (i.e. dip leak along faults and sealing fault zone materials), model input uncertainties, and using drill-well learnings are also discussed.Fault seal analysis has been used since the 1960s to predict the impact of faults on the flow or storage of fluids in hydrocarbon reservoirs. Initial attempts at fault seal analysis concentrated on defining pressure or hydrocarbon column height differences across faults and using those observations to infer the sealing behaviour of faults (e.g. Smith 1966). Such studies used cross-sections constructed at high angles to the strikes of faults to understand the connections of permeable units across the faults. If disparate pressures or hydrocarbon fluid contacts were observed where a cross section provided evidence of a potential sand-to-sand juxtaposition, then it was assumed that the fault zone itself sealed in order to isolate the sands on each side of the fault from each other. However, the cross-section approach gives only a one-dimensional look at a fault (i.e. a single profile view along the fault), and the sand-to-sand juxtapositions across it, and as such, failed to define possible juxtapositions everywhere along the strike length of a fault. As well, early attempts at fault seal analysis were hampered by map quality and accuracy. In the 1960s and 1970s, depth-structure maps were constructed from variable quality two-dimensional seismic data and/or from well penetration data (formation or sequence tops), making derivative analyses, such as fault seal analysis, of suspect quality.With the development by Allan (1989) of a method for making fault plane profiles (so-called Allan diagrams), sand-to-sand juxtapositions along the length of faults could be defined in much better detail. Fault plane profiles are cross-sections ...
Unbalance of the three-phase currents in photovoltaic (PV) systems may depend on structural aspects of the installation, the effect of partial shading, or both. In this paper, a number of unbalance indicators are calculated starting from data that are measured during experimental analyses on a real building-integrated PV system that represents different types of unbalance. Detailed information is obtained from indices that identify the balance and unbalance components that are also in the presence of waveform distortion. These indices extend the current definitions of unbalance given in the power quality standards. The results show that the unbalance cannot be considered negligible, even with no singlephase inverters and is more significant if nonlinear loads add a contribution to both harmonic distortion and unbalance seen from the distribution transformer.
Several feed-in tariffs are now available for photovoltaic (PV) systems, and thus, the maximization of the productivity is very important; this goal can be achieved by solar cell technologies with high efficiency and low temperature losses, one axis or dual axis sun-tracking systems, proper cooling techniques for PV modules in building integrated applications, master-slave (M-S) control for the inverters in large grid-connected PV plants, etc. About the last item, this paper deals with the advisability of the master-slave concept versus the centralized inverter layout. Here, attention is focused on the influence of the installation site with its irradiation peculiarities, the tilt angle of the PV modules, the efficiency curve of the inverters, and the number of slaves. The simulated productions put into evidence energy gains up to 4% per year, considering the only cloudy-day contribution. On the basis of these comparisons, the M-S concept can be profitable if the number of cloudy days is sufficiently high, the tilt angle is adequate, and the dc-ac efficiency curve is "well shaped." Index Terms-DC-AC efficiency curve, energy performance, master-slave (M-S) inverter, photovoltaic (PV) system.
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