The Experts below are selected from a list of 27 Experts worldwide ranked by ideXlab platform
Verga F. - One of the best experts on this subject based on the ideXlab platform.
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A semianalytic model for the productivity testing of multiple wells
2008Co-Authors: Fokker P.a., Verga F.Abstract:We present a semianalytic method for modeling the productivity testing of vertical, horizontal, slanted, or multilateral wells. The method is applicable to both oil and gas reservoirs and automatically accounts for well interference. The use of analytic expressions ensures that short-time transient behavior and long-time Semisteady-state behavior are handled appropriately, whether close to the well or further into the reservoir. Calculation times are still very limited - on the order of a few minutes to a few seconds when all wells are vertical. This makes the tool suitable for evaluating well testing and determining well productivity. We based the approach on an earlier derived productivity prediction tool, in which the steady-state equations were solved. It has now been extended to solve the time-dependent diffusion equation. In our current method, the equations have first been transformed using the Laplace transformation. The expressions for the producing wells are combined with auxiliary sources outside the reservoir. The crux of the semianalytic method involves an adjustment of the positions and strengths of these sources in order to approximate the boundary conditions at the reservoir boundaries. The solution obtained is transformed back into the time domain by use of a Stehfest algorithm. The new approach has been validated with numeric tools, including both reservoir simulators and well-test interpretation software. Validations were performed with artificial cases and with field production data, using both single-well and multiple-well production tests. The results of these tests were excellent. Copyright © 2008 Society of Petroleum Engineers
J. Gijs Kuenen - One of the best experts on this subject based on the ideXlab platform.
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nitrous oxide production by alcaligenes faecalis under transient and dynamic aerobic and anaerobic conditions
Applied and Environmental Microbiology, 1996Co-Authors: S. Otte, N G Grobben, Lesley A Robertson, J. Gijs KuenenAbstract:Nitrous oxide can be a harmful by-product in nitrogen removal from wastewater. Since wastewater treatment systems operate under different aeration regimens, the influence of different oxygen concentrations and oxygen fluctuations on denitrification was studied. Continuous cultures of Alcaligenes faecalis TUD produced N2O under anaerobic as well as aerobic conditions. Below a dissolved oxygen concentration of 5% air saturation, the relatively highest N2O production was observed. Under these conditions, significant activities of nitrite reductase could be measured. After transition from aerobic to anaerobic conditions, there was insufficient nitrite reductase present to sustain growth and the culture began to wash out. After 20 h, nitrite reductase became detectable and the culture started to recover. Nitrous oxide reductase became measurable only after 27 h, suggesting sequential induction of the denitrification reductases, causing the transient accumulation of N2O. After transition from anaerobic conditions to aerobic conditions, nitrite reduction continued (at a lower rate) for several hours. N2O reduction appeared to stop immediately after the switch, indicating inhibition of nitrous oxide reductase, resulting in high N2O emissions (maximum, 1.4 mmol liter-1 h-1). The nitrite reductase was not inactivated by oxygen, but its synthesis was repressed. A half-life of 16 to 22 h for nitrite reductase under these conditions was calculated. In a dynamic aerobic-anaerobic culture of A. faecalis, a Semisteady state in which most of the N2O production took place after the transition from anaerobic to aerobic conditions was obtained. The nitrite consumption rate in this culture was equal to that in an anaerobic culture (0.95 and 0.92 mmol liter-1 h-1, respectively), but the production of N2O was higher in the dynamic culture (28 and 26% of nitrite consumption, respectively).
Akira Fujii - One of the best experts on this subject based on the ideXlab platform.
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characteristics of radio frequency wave propagation in bounded plasma under the various magnetic field configurations
Physics of Plasmas, 2001Co-Authors: Shunjiro Shinohara, Akira FujiiAbstract:Detailed characteristics of radio frequency (rf) waves with pulsed modes in the whistler wave range were studied in a cylindrical rf-produced plasma, where the plasma boundary lay in the intermediate regime between infinite whistler wave propagation and bounded geometry helicon wave propagation. Excited magnetic field amplitudes and phases with three components in two-dimensional space were measured for different experimental conditions. Three magnetic field configurations were used and the diameter of the excitation loop antenna was also varied. Numerical calculation by the finite element method, which has been demonstrated to be a powerful means for this analysis, showed good agreement with the observed results, satisfying the dispersion relation and wave structures of helicons in the Semisteady state and also satisfying the dispersion of whistlers with a short pulsed mode. The excited waves propagated nearly along the magnetic field lines within a small angle of less than 10°. Furthermore, in the low (...
Fokker P.a. - One of the best experts on this subject based on the ideXlab platform.
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A semianalytic model for the productivity testing of multiple wells
2008Co-Authors: Fokker P.a., Verga F.Abstract:We present a semianalytic method for modeling the productivity testing of vertical, horizontal, slanted, or multilateral wells. The method is applicable to both oil and gas reservoirs and automatically accounts for well interference. The use of analytic expressions ensures that short-time transient behavior and long-time Semisteady-state behavior are handled appropriately, whether close to the well or further into the reservoir. Calculation times are still very limited - on the order of a few minutes to a few seconds when all wells are vertical. This makes the tool suitable for evaluating well testing and determining well productivity. We based the approach on an earlier derived productivity prediction tool, in which the steady-state equations were solved. It has now been extended to solve the time-dependent diffusion equation. In our current method, the equations have first been transformed using the Laplace transformation. The expressions for the producing wells are combined with auxiliary sources outside the reservoir. The crux of the semianalytic method involves an adjustment of the positions and strengths of these sources in order to approximate the boundary conditions at the reservoir boundaries. The solution obtained is transformed back into the time domain by use of a Stehfest algorithm. The new approach has been validated with numeric tools, including both reservoir simulators and well-test interpretation software. Validations were performed with artificial cases and with field production data, using both single-well and multiple-well production tests. The results of these tests were excellent. Copyright © 2008 Society of Petroleum Engineers
S. Otte - One of the best experts on this subject based on the ideXlab platform.
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nitrous oxide production by alcaligenes faecalis under transient and dynamic aerobic and anaerobic conditions
Applied and Environmental Microbiology, 1996Co-Authors: S. Otte, N G Grobben, Lesley A Robertson, J. Gijs KuenenAbstract:Nitrous oxide can be a harmful by-product in nitrogen removal from wastewater. Since wastewater treatment systems operate under different aeration regimens, the influence of different oxygen concentrations and oxygen fluctuations on denitrification was studied. Continuous cultures of Alcaligenes faecalis TUD produced N2O under anaerobic as well as aerobic conditions. Below a dissolved oxygen concentration of 5% air saturation, the relatively highest N2O production was observed. Under these conditions, significant activities of nitrite reductase could be measured. After transition from aerobic to anaerobic conditions, there was insufficient nitrite reductase present to sustain growth and the culture began to wash out. After 20 h, nitrite reductase became detectable and the culture started to recover. Nitrous oxide reductase became measurable only after 27 h, suggesting sequential induction of the denitrification reductases, causing the transient accumulation of N2O. After transition from anaerobic conditions to aerobic conditions, nitrite reduction continued (at a lower rate) for several hours. N2O reduction appeared to stop immediately after the switch, indicating inhibition of nitrous oxide reductase, resulting in high N2O emissions (maximum, 1.4 mmol liter-1 h-1). The nitrite reductase was not inactivated by oxygen, but its synthesis was repressed. A half-life of 16 to 22 h for nitrite reductase under these conditions was calculated. In a dynamic aerobic-anaerobic culture of A. faecalis, a Semisteady state in which most of the N2O production took place after the transition from anaerobic to aerobic conditions was obtained. The nitrite consumption rate in this culture was equal to that in an anaerobic culture (0.95 and 0.92 mmol liter-1 h-1, respectively), but the production of N2O was higher in the dynamic culture (28 and 26% of nitrite consumption, respectively).
