Peer Review of Interim Report on Computational Fluid Dynamics Model for Predicting Wellhead Oil-Burning Efficiency at Bench and Intermediate Scales (2021) / Chapter Skim
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Appendix B: Anonymized Committee Responses to Charge Questions
Appendix B: Anonymized Committee Responses to Charge Questions
Pages 21-34
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From page 21... ...
Were the assumptions regarding wellhead conditions and two-phase wellbore flow (including film thickness and instability, liquid entrainment, and droplet diameter and its influence on wellhead ejection behavior) adequately characterized?
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From page 22... ...
amongst other data that can be used along with analog data and dynamic data as available, to build an independent WCD model to verify output or to cross-validate WCD output amongst different wellbore flow modeling methods to help characterize the wellhead conditions, and determine best method to do so given the problem at hand. At the very least impact of different wellbore models or flow regimes can be included.
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From page 23... ...
Errors: Perhaps a detailed uncertainty analysis is needed to assess the "safety limits" if the model is used for wellhead burning. The selection of n-heptane as the single component surrogate fuel for crude oil may be inaccurate in terms of predictions of preferential vaporization, and the resulting gas phase flow field and mixture formation.
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From page 24... ...
The more critical issue is that even the gas phase sooting effects were not well tested by experiments involving only n-heptane. Even in the simplest of laminar flames, a one-step soot formation model is unlikely to provide a reasonable representation of soot volume fraction and radiation effects.
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From page 25... ...
Errors: Perhaps a detailed uncertainty analysis is needed to assess the "safety limits" if the model is used for wellhead burning. The drop injection model may not adequately simulate particle mean diameter and size distributions in a two-phase high speed flow.
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From page 26... ...
with a gas phase flow of ethane and liquid injection of heptane. The BSSF flow conditions were configured such that the system was in the annular flow regime.
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From page 27... ...
for the droplet behavior measurements appropriately designed, clearly described, and adequate to capture droplet behavior for the Gas Phase and Two-Phase Spray Flame? Were there any apparent strengths, weaknesses, omissions, or errors?
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From page 28... ...
In a gas flow with significant temperature fluctuations due to turbulence, the temperature determined from an averaged CARS spectrum will be biased towards lower temperatures because CARS signals will be stronger from the higher density, lower temperature gases. In extreme cases with very significant temperature fluctuations it will not be possible to extract an average temperature from an averaged CARS spectrum because it will not be possible to fit a theoretical single-temperature spectrum to the averaged CARS spectrum.
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From page 29... ...
8.1 Do the results adequately characterize evidence of the droplet characteristics including droplet breakup, the droplet size (diameter) , droplet speed, and the duration of droplet in fire (bench- and intermediate-scales)
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From page 30... ...
9. Does the research product accurately characterize the impact of two-phase flow regimes (bubble, slug, and churn)
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From page 31... ...
While in bench and intermediate scale experiments, there was evidence that fallout of large droplets at the periphery of the plume, falls back to the surface, resulting in reduced burn efficiency, it is unclear if simulations actually captured this trend. The connection between pipe flow and ejected spray plume behavior is weak.
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From page 32... ...
While there may be several reasons for this mis-match, the reviewer believes that the two-phase flow mixture at the pipe flow exist needs to be better characterized to initialize the spray flame more accurately. The choice of turbulence model is also known to be important and the reviewer expects that LES would do a better job.
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From page 33... ...
However, one should also be careful in extending these results directly in wellhead conditions where the flow parameters, the fuel characteristics, well-hear pressure can be significantly different, leading to very different burn efficiency. The authors conclude that the annular fluid film that escapes the injection tube without being entrained into the main flow is the primary cause driving the burn efficiency.
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From page 34... ...
The scope of the validation is limited to temperature measurements, the modeled and measured droplet statistics are not compared, the gas velocity is not measured, the droplet velocities are partially measured, the plume scales are not compared. Given the objective of the report was to define burn efficiency of the wellhead flow, it seems imperative to include the details on the burn efficiency measurements in the body of the report, and not as an appendix.
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