The equilibrium phase densities and interfacial tensions of the binary mixture (ethane + n-pentane) have been measured simultaneously using the pendant drop method at 294.15 K. The experimental pressure was in the range of (6 to 30) bar. The measured phase densities are compared with calculated equilibrium densities by applying the GERG2004 equation. The deviations of the measured interfacial tension at each experimental condition are calculated on the basis of ISO combined standard uncertainty calculation recommendations. No open interfacial tension data for the system have been reported at any isothermal conditions. The measurement results extend the range of previous interfacial tension data of the hydrocarbon mixtures in the open literature.
An electrical measurement is non-linear when it is affected by the applied stimulus, i.e. when the measured phenomenon changes with amplitude. If pinched hysteresis loops can be observed in the voltage current representation, the underlying tissue can be classified as a memristor. Several biological memristors have been published, like human skin and apples. However, changes in the polarization impedance of electrodes may also cause pinched hysteresis loops. The question whether the reported biological memristors are real or whether the results just reflect changes in the polarization impedance arises. If the impedance of the measured object is close to or smaller than the polarization impedance of the used electrodes, the latter may dominate the measurement.
In this study, we investigated the non-linear electrical properties of silver/silver chloride electrodes in a sodium chloride solution that has a similar concentration as human sweat and compared these to results from human skin. First of all, we found that silver/silver chloride electrodes in sodium chloride solution can be classified as memristors. However, the currents obtained from the sodium chloride solution are much higher than the currents recorded from human skin and there is a qualitative difference in the pinched hysteresis loops in both cases. We can conclude that the non-linear electrical measurements with silver/silver chloride on human skin are actually dominated by the skin and we can confirm that the human skin memristor really exists.
The equilibrium phase densities, vapor phase compositions, and interfacial tensions of the ternary mixture (methane + ethane + n-pentane) have been measured simultaneously using the pendant drop technique at 294.15 K. The total mole compositions of the measured ternary mixtures are 50.61 % methane + 8.93 % ethane + 40.46 % n-pentane; 34.20 % methane + 6.04 % ethane + 59.76 % n-pentane; and 17.46 % methane + 3.08 % ethane + 79.40 % n-pentane, respectively. The measured phase densities and vapor phase compositions are compared with calculated equilibrium properties from the GERG2004 equation. No open interfacial tension data for these ternary systems have been reported at any isothermal conditions. The average experimental interfacial tension data can be described with the total deviations of about 3.2 %. The combined standard uncertainty at each experimental condition is calculated on the basis of ISO recommendations.
During drilling and well intervention (DWI) operations today operating limits are normally given as limiting wave height, and sometimes wave periods. The resulting diagrams are often not directly comparable with weather information received on the rig and the final decisions are often based on subjective assessment of wave height and period.
The paper will present how BP, on the newly developed Skarv field in the Norwegian Sea, through thorough planning in the engineering phase has implemented a system where operating limits are specified based on directly measurable parameters such as rig heave and upper and lower flexjoint angles. How weather forecasting can be translated to give the rig crew direct forecasting of the limiting vessel or riser responses (e.g. flexjoint angles or heave), will also be presented. It will be shown how this allows for improved operational planning and support from onshore.
Over the last years requirements for oil companies to be able to document the structural integrity of their subsea assets, including wells, has increased. On the Norwegian Continental Shelf (NCS) there has been a particular focus on fatigue loading in the wellhead structure, including the upper sections of casing and conductor, due to loads induced by the riser and BOP during DWI operations. There have been cases where the design fatigue life of a wellhead system limits the number of days one can perform operations with a rig on a given well. This in term affects future oil recovery rates as the well fatigue life may not be sufficient to allow for side step drilling or intervention work required to maintain an optimal production from the well.
The paper continues to present how BP on the Skarv field, stores and utilizes the measured lower flexjoint response to track and document well integrity. It will be demonstrated how the return on investment of a drilled well can be improved by documenting actual fatigue loading from each operation on a well compared to conservative design calculations.
BP has addressed the above issues in a way that is likely to set a new standard for drilling and intervention operations in the North Sea in the future.
4Subsea AS has provided the engineering and instrumentation services that formed the basis for this paper.
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