#  > Petroleum Industry Zone >  > Reservoir >  >  >  Tuning  EOS parameters

## hoanglongbk88

I am learning to calibrate  cubic EOS for compositional simulation. Who can share me some experience to match between PVT of gas condensate calculated from EOS and observations by using PVTi in ECLIPSE solfware. How to quality check the PVT model after matching?


I am appriciated with your all kind help.See More: Tuning  EOS parameters

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## munqith

which cubic EOS's are you used?

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## hoanglongbk88

I use Peng-Robinson three parameters and volume shift is independent on critical properties.

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## Shakespear

hoanglongbk88
Check the tutorials for PVTi by opening the PVTi manual.

Also there is a PVT course by Whitson on egpet that may also help.

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## hoanglongbk88

I have read the PVTi manual , but I cannot match the PVT of gas condensate.

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## Shakespear

> I have read the PVTi manual



But did you do the Tutorials that are in that manual? 
None of this tuning work is easy and I think it very difficult to explain it through emails. That is why a course is the best way to go. However the tutorials are good way to go because they go step-by-step to show you the procedure.

The Whitson videos were the best that I have seen on the net regarding PVT analysis. However even in this case the problems they did were not available hence you only get half of the knowledge.

Look here and see if some useful info may be located

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Whitson's lecture stressed what is in this paper
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and he made it know that he thought that his program did a better job of controlling the tuning process than PVTi. You would need to listen to the lecture to try and understand this.

Also you would need to do a validation of your pVT data else your tuning will go nowhere.

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## hoanglongbk88

I know that it is very difficult to tune the EOS parameters. I read the tutorial of PVTi. As you see there are a lot of combinations of regression variables. I tried to do step by step as PVTi tutorial procedure. Firstly I split the C7+ into SCN45 by Whitson method , then I matched the dewpoint pressure based on the extended composition. Next, I group into 6 pseudo components ( N2C1, CO2+C2+C3, C4 to C6, MCN1,MCN2). I match dewpoint pressure again. Finally , I match other PVT properties. THe viscosity I match the last.
I dont know when we should set weight for dew point pressure to preserve this value in the regression. And which error is the PVT properties compared with the observations after tunning ?( maybe below 5%).
I  read the SPE as " New strategy to NEW STRATEGIC METHOD TO TUNE EQUATION-OF-STATE TO MATCH EXPERIMENTAL DATA FOR COMPOSITIONALSIMULATION" or " An effcient Tuning Strategy to calibrate Cubic EOS for Compositional simualtion" But I hardly do these strategies on PVTi. I  am really cuirous which solfware these authors use. WHo can help me tho answer above questions? THank you so much.

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## Shakespear

Have a look

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## hoanglongbk88

Thanks Shakespear, I have read all above documents that you posted here. But I really need some experimence how to realize which PVT properties ( dewpoint pressure, vapor density...) we should match firstly in PVTi? Can I contact with you by emails?my email is nguyenhoanglong2303@yahoo.com.

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## Shakespear

I would read carefully this paper

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This paper gives you a lot of hints how to do it. Also look up the references !!!
Again, listen to the Whitsen lectures as he talks about this and the regression process.

Yes, the weights needs to be used and the parameters used NEED TO BE constrained so as not to go out of the realistic range for the parameters. Again, this is in the paper and in the Whitson lecture.

Now this is a bonus, Prof. Whitson SHARES his lectures which he gives in Norway University

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This is education for FREE. I rarely see this done this well, even in places where you would think this should be the norm.

I will try to contact someone who may, I repeat may, help. No guarantee.

You are dealing with a near critical fluid which is not the norm for me and some of my friends. The one things I do know about Near Critical fluids is that it is very very easy to THINK you have matched the data when in fact you have not gotten it right at all.

When I have something I will share it here.

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## hoanglongbk88

I will try to read your papers you posted here carefully. Once again, I am really appreciated your kind help. Hope you can contact someone who used to match PVT model of gas condensate. Thank you very much.

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## Shakespear

Take a look at this also

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Now this paper deals with QC of the data BEFORE going to the tuning process

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This is something that Prof. Whitson spends some time explaining in the lectures.

This one is also on the NET. Use GOOGLE.





> New strategic method to tune equation-of-state to match experimental data for compositional simulation
> by Al-Meshari, Ali Abdallah, Ph.D., TEXAS A&M UNIVERSITY, 2004, 248 pages; 3156484
> 
> 
> Abstract:
> 
> Since the plus fraction of reservoir fluids has some uncertainty in its molecular weight and critical properties, equation-of-state, EOS, are generally not predictive without tuning its parameters to match experimental data. Tuning of the EOS is found to be the best method for improving the predictions of compositional reservoir simulators.
> 
> The proposed strategy for tuning EOS consists of seven steps: (1)?split the laboratory plus fraction to single carbon number groups, SCN, usually up to SCN 44; the last component will be C45+ , (2)?use set of correlations to calculate the critical properties and acentric factor for each SCN group, (3)?match the saturation pressure at reservoir temperature by altering the measured value of the molecular weight of the plus fraction using the extended composition, (4)?group SCN groups to multiple carbon number groups, MCN, (5)?assign critical properties and acentric factor for each MCN group, (6)?rematch the saturation pressure at reservoir temperature using the grouped composition, and (7)?match the volumetric data by regressing on volume shift parameters of all components in grouped composition.
> ...

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## hoanglongbk88

You sent to me the dissertation of Ph.D "New strategic method to tune equation-of-state to match experimental data for compositional simulation" 1 or 2 months ago.
I followed the strategy the Al-Meshari, Ali Abdallah, Ph.D proposed. There are 7 steps. I try to  do exactly as he wrote. But it is so hard to do on PVTi exactly.


do you have any gas condensate datta , such as components analysis, CVD test, CCE test that I can do on PVTi?See More: Tuning  EOS parameters

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## Shakespear

I would look through these papers

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and look in the text book

"Phase Behavior of Petroleum Reservoir Fluids"

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## Shakespear

Take a look on page 440

Ahmed-T-Equation-of-State-and-PVT-Analysis.pdf

Then go to references

Also a very good explanation of the tuning steps in the Petroleum Experts PVTP manual

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look at the Worked Examples





> If no other factors such as system integration influence the selection we would recommend PATH 1 to find a matched EoS. With integrated systems the surface facilities modeling package may not allow the changing of pure component properties. In this case select the approach outlined in PATH 2.
> 
> PATH 1
> 
> Start with all Tcs and Pcs selected (except for N2 and CO2).
> 
> If BI coefficients are available select the value between C1 and the heaviest component.
> 
> The reason AFs are not chosen initially is that they have a tendency to be pushed to extreme values which in turn lifts the low temperature end of the Phase Envelope to near vertical. Using Tcs and Pcs give a gentler and more controlled path to a solution.
> ...

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## hoanglongbk88

Shakespears, after you tune the PVT model, How can you validate whether your model is right or not?

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## Shakespear

If you are using PVTi, you will see how good things are through the Regression Report. Another way is through PLOT option for your different experiment data (CCE, DL etc.) which will show a plot of the regression results and the experimental data for different properties and parameters.

I have been going through the "WORKFLOW" example for PVTi and must say it is confusing. It was better described in a much older version of PVTi. Not sure why, but it seems that someone who knew it very well made one too many options of how a fresh user would interpret the written description.

However in the end this is a TRIAL-and-ERROR process.

The person who I thought might be the best source of info on the regression process has so far not responded :-(

Notice that Petroleum Experts PATH1 and PATH2 has lots of similarity to the "WORKFLOW" tutorial for PVTi.

Does anyone have access to this paper





> A systematic investigation into the most suitable data for the development of equations of state for petroleum reservoir fluids
> 
> Robert C. Merrill, Jr.a and Trevor M.J. Newleyb
> 
> aBP Research International, Sunbury Research Centre, Chertsey Road, Sunbury-on-Thames, Middle--- TW16 7LN Gt. Britain
> 
> bBP Exploration (Alaska), P.O. Box 196612, Anchorage, Alaska 99519 USA
> 
>  10 August 2001

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## hoanglongbk88

I have tried to match the PVT of gas condensate with observations from experiment by trial and error process. But I can't match all the observations exactly simultaneously. The errors of Liquid volume ( in CCE and CVD) and  vapor viscosity in CCE are very large. Can you take a look of my PVT file? I can send it to you. Can you give me your email? my email is nguyenhoanglong2303@yahoo.com.

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## Shakespear

A good paper

"How many components ... "
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## Shakespear

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hoanglongbk88 - Take a look at the graphs of the tuning results in this paper. Pay special attention to the Liq. Saturation CVD data. Tell me what you see.

Liq. Sat. experiment is IMPORTANT because it is the one that will model how much condensate will come out of the gas. Hence that will decide how much will be left in the reservoir if you pressure drops below Dew Point.

Dew Point is also important as it will effect the point on the Liq. Sat. curve at which condensate (Liq. Sat.) starts to drop out.

In you data these are the things that are the biggest problem from what I saw. The rest looked good.

I would suggest to carefully spend the time DOING tutorials "Regression" (R) and "Workflow" (W) to fully understand how PVTi works.  For instance you have "Superimpose" button. Do you know why? Then in "W" they tell you to CLOSE the project without saving. Do you know why? ....

Let me know here as this will help others.

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## hoanglongbk88

Superimpose button helps you plot the 2  different results in 1 diagram ( such as 2 phase envelopes, before and after you split the component). The phase diagram has not changed much at the reservoir temperature, which indicates a good splitting. In Workflow, they tell you to CLOSE the project without saving because the first splitting result is not good, the mole fraction of FRC2 is smaller than FRC1. WorkFLow advises us that We would rather have a splitting that has more of the mole fraction in the heaviest component. SO that we have to do another splitting.We don't accept the first splitting result , we  have to CLOSE the project without saving, and open again the initial component without splitting to do splitting again.

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## Shakespear

Yes, Super allows you to compare after you have changed the EOS parameter etc., to see what has changed. Now this can be used for ANY experiment results plot, not just  the Phase Diagram.

The "CLOSE" business is done this way because if you do a regression, splitting etc.  NEW parameters have been introduced into PVTi and you have MOVED FROM YOUR STARTING POINT. PVTi has no function that I am aware of moving you back to the START point once you except regression rsults. Hence if you change parameters after 2 cycles of tuning much worse YOU HAVE NO WAY to go back to the start. That is why they said to CLOSE the project without saving and leave the plots there. But recall that the PLOTS were still there which allows you to reload the START POINT, make changes, then make a new plot that is SUPERIMPOSED  on the old to see the effect.

Hope that is clear. If so then make a spreadsheet with CASES running down one column and various parameters across the sheet (as per suggestion in the "W" tutorial for the 3 Groupings. For each Grouping , each case of parameter permutation that you run see how your RMS Error has changed from either the ORIGINAL starting point (in the RESULTS report) or from a POINT that you chose that you think was your best tuned result that you want to make better. Then you will be able to plot case vs. error and see what set of parameters is helping and which is not.

What about the Dissertation? What did you notice here?

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## hoanglongbk88

I have a  PH.D dissertation you post here. the match of Liq saturation in CVD test is  also not good. In my project,  error of the liq saturation compared with experiment is 5% . I think it is not bad. What do you think about my project result?

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## Shakespear

I have looked over some cases of condensate fluid systems and from what I have seen it appears that Liq. Sat can be a problem. It is stated in some cases that the problem may be contamination. I have no idea if that is so in your case but do not forget that the lab data may have problems as well as the sample take.

Now your Liq. Sat is going in the right direction. However is not quite there and viscosity has gotten worst (Tune6.PVI).

I would recommend following the Regression and Workflow, and try the parameters groups suggested. The grouping in that dissertation above might also help. 

The grouping you have chosen is strange. How was this gone? CO2 should be by itself IMO, it is over 2% and is a unique none-HC component.

In Tune6 it looks like you were only tuning VcritV. Is that correct?

I think you can do better.

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## Shakespear

hoanglongbk88 - The Model that you are building. Is there gas injection or is it just a depletion process?

See More: Tuning  EOS parameters

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## hoanglongbk88

I have grouped CO2 +C2 into pseudo-component as PVTi advices. The viscosity I tuned the last, so that I only choose Vcrit to regress, others PVT I set weight equals 0. 
I will try to read the dissertation carefully.
Thanks Shakepears a lot.

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## hoanglongbk88

I have grouped CO2+C2 into 1 pseudo-component (X2 in Tune6). I tuned viscosity the last after other PVT properties were matched. therefore you see  that I only choose a Vcrit to regress. 
I will try to read the above  dissertation carefully.
thank you so much.

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## Shakespear

I would not group CO2.
N2+C1
C2
C3
IC4+NC4
IC5+NC5+C6
C7+

This is how I would have them grouped

Do the spreadsheet idea. Even if you did the basic procedure suggested in "Workflow" then graph the total error % for various key experimental data vs. case (1,2,3,4 ...) it would visually show you how changing the parameters of the EOS moves you from the start point.

What is your model modeling? Is there gas injection going on in the model?

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## hoanglongbk88

Why didn't you group CO2 into C2?

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## Shakespear

Observe how the groupings are done in various papers and as demonstrated in text books. They go sequentially so as to maintain monotonicity which is reflected in the components properties. CO2 is MUCH different then C2, so you do not group it. Better to go in sequence when making the groups.

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## hoanglongbk88

PVTi advises us to group CO2 to C2 because  when you plot the K value of component vs pressure, the CO2 line is next to C2 line. So that we group Co2+ C2. Although molcular weight of CO2 is different so far from C2.

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## itag

Hi
I've been following this thread and am most impressed with the list of quality references offered up by Shakespear here. Great job.
However - there are many question remaining unanswered.
a) Where do the samples come from - good down-hole samples vs recombined separator samples ?
b) If separator samples,  the the bubble point of the oil should match the separator P,T - you can often characterize & split this 'oil' first then treat the recombination as a separate step   ( BTW the bubble point gas should match your sep gas composition! - another good check.)
c) I'm always a little suspicious of recombination ratios - and would have no problem varying the recombination fractions a little to see how this affected the final (mixture) C5+. This means tuning 2 or 3 mixtures and keeping the 'best'
d) Matching dropout curve - and getting C5+ yields right  is probably more important than getting Pdew exactly right ( 5% error in Pdew may be OK) - 
e) If the field is undeveloped - then the RFT/MDT tool usually provides for a very accurate in-situ gas density .... this can help your C5+ matching. I'm very surprised when folk don't use this density  data when its available. ( I'm an RE and density is important in getting initial Pressures right!!)
    ( Its easy to include gas density in a PVTi experiment)
f) I prefer the Whitson Splitting ( over the simple mole splitting in PVTi) ... Split C7+ into 2 or 3 fractions out to C45 or C50
g) In my mind splitting only makes sense if subsequent lumping is going to use more than just C7+ ( in other words if you lump everything back to C7+ why bother splitting in the 1st place  !). Splitting should help you match experiments - if not stop and read the literature!

Key questions for me: Where do the samples come from ? and Shakespear's question: What is the development plan for this reservoir ? Gas cycling ? pure depletion ,  Strong aquifer ?

good thread
itag

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## Shakespear

itag - all good points. I did not want to get into the data QC as this is a big issue and not my specialty though I am aware of its significance.

From what I understand hoanglongbk88 is doing a dissertation and has limited time to do his work. So I though it would be best to keep things simple.

The reason I was asking about gas injection is that if there is none he would not need to run the model using E300 which is a Bear.

Please add any knowledge you have in this area as sooner or later someone may have a need for it.

I can not say enough about the Whitson course that is on the net. It is long but well worth the time to go through.

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## hoanglongbk88

Shakespear, I am trying to match my file I sent to you by PVTsim and compare the 2 results. What do you think about this idea?

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## Shakespear

I know you have limited time thus there is only so much that you can do. By referring you to the other dissertations and papers where EOS tuning was done I was trying to let you see what kind of results people get. Sometimes it looks good, sometimes some lab data just is not replicated well and they apparently stopped trying. The Liq. Sat. sometimes simply will be a pain in the butt and unless you are an expert you will have no clue how to fix it.

In such a situation you can only do this EOS tuning in a systematic way and try various permutations of parameters and see how it moves you around. In my opinion the best way to do this is through some form of plotting. Hence the idea of a spreadsheet.

So do your best, come as close as you can and then go on, because there is only 24 hr. in a day and you do need to rest  :Smile:   :Smile: 

I am trying to write a C program to summarize the regression report but after a day of monkeying around with Turboc C (running in DOS using DOSbox) I realized that errors I was seeing from the program were not mine but strange memory management issues of DOSbox. In a few words, "This was not the best route for me to take". 

However with each round of permutation of parameters a summarization needs to be done to get some summary stats to plot or analyze. Looking in those PVTi results panels is good if you have done this a zillion times and know PVT behavior like your girlfriend, otherwise key data needs to be extracted to allow you to compare to other results.

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## hoanglongbk88

I am trying my best to match the PVT of gas condensate on PVTsim, then compare the results from 2 software. But using PVTsim is a little bit more complicated than PVTi or Maybe I don't have enough time to learn how to use PVTsim as PVTi. It is close to deadline to submit my dissertation. Should I accept the result I tuned on PVTi although I know this result is not good?

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## hoanglongbk88

Shakepear, Do you have a spreadsheet to calculate the dewpoint pressure based on EOS? I am trying to write on excel to calculate DEwpoint pressure base on Peng-Robinson By visual basic application (VBA). but the algorithm of calculating the DEWPOINT is not clear as flash calculation ( vapor-liquid) that is written sucessful by EXcel.

See More: Tuning  EOS parameters

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## Shakespear

I would do the following. Take my best results and go to my dissertation adviser and say.

1) "I did my best to tune the data within the time I had"
2) "Here are the problems I see"
3) "Here is how they would effect my results"

In other words, you need to show that you understand the effect of the error on your simulation. Thus you don't just dump data in, get results and say I am done. In the future you will know what to do, send them to a PVT expert.

With your time constraint I would let it go. Trying to learn a PVT program is not easy as each has its own problem. I just found out some limitations that post 2007 version of PVTi has and anyone not knowing this will have lots of fun trying to get this particular option to give good results. I will not be specific, but if you have a legal copy JUST CALL Schlumberger for information about different version problems.

Regarding calculating the Dew Point, again, that one reference I gave before had a lot of good papers on Condensate Reservoirs and has what you need. But are you sure you want to do this? Tuning is the way to go in my opinion.

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## Shakespear

Predicting the dew point pressure for gas condensate reservoirs

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## hoanglongbk88

Thanks Shakespear for your useful advice. I feel a little bit more confident about my result I got. Can you explain more about the idea "how I  show the effect of the errors on my simulation" as you said? I dont know much about simulation because my name of disser is just to make PVT model.

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## hoanglongbk88

Thank you for your advice. I feel a lit bit more confident about my result I got. Can you explain more about the idea" How I show the effect of error on simulation" as you said? I don't know much about simulation because my name of disser is just to make PVT model.

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## Shakespear

"I don't know much about simulation because my name of disser is just to make PVT model. " :Confused: 
oooo, if that is the situation then I would make you work harder. In other words, as your adviser I would ask that you put in more effort to get the best results and graphically prove to me that you found the best fit  :Wink:  

I would not be easy on you, as no one does a dissertation in one month. :Stick Out Tongue: 

OK, in a very simple model, Darcy's Eq., if you knew that you viscosity could be off by +- 15 %, you would put this variation into the equation and see how much your flow would change. Hence, you could estimate how much off you would be in estimating the flow rate if your only error was in estimating the viscosity. With more parameters you could use Monte Carlo Simulation to quantify probabilities in your errors.

For a simulation this would something like this

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<![CDATA[[Only Registered And Activated Users Can See Links]  :Embarrassment: 

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## Shakespear

I do not as a matter of fact read manuals front to back, hence was not aware that this option exists in PVTi. PVTi has a batch mode option. Something like running ECLIPSE 100 for instance. 

There is a data deck that needs to be set up to run it which is explained in the manual. What does this option give you? It allows you to try different combinations of what ever you are trying to do in one shot, regression, experiments, etc.

However getting your head around the key words etc. may take a bit of time  :Wink:

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## hoanglongbk88

I have sent you the link 4shared to load the data I set up already, you just run file.DATA in E300. It takes about a half of hour to complete the running. After you see the results, can you answer my questions I sent yo you by email? I am waitting for your reply.

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## Shakespear

> When I plot FOPR, I see the the FOPR line with the case 1(dewpoint 8000psia)  is below the FOPR line of the case2( dewpoint 7150 psia). the reservior  pressure is 8100 psia. I can't explain why? I think in case 1,  reservior pressure will hit the dewpoint earlier than case 2. so that the percentage of liquid produces more. But in the plot it is inverse. what do you think?



First, what is flowing to the well through the reservoir rock as you being producing above the dew point (forget about the pressure drop close to the well bore)? What enters through the perf? What will you see at surface?

Next, what happens if the reservoir drops below dew point, what flows through the reservoir rock to the well ? What enters through the perf?  What shows up at the surface?

Do you see something here that would account for different flow rates.

Case 1                 Case 2
Pres = 8100            8100
Pdew= 8000            7150

 :Wink:

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## munqith

Dear friends
Please i need this paper
"Gao, G., A Simple Correlation to Evaluate Binary Interaction Parameters of the Peng-Robinson Equation of State, Fluid Phase Equil. 74, 85, (1992)"
Thank you

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## paolomaldini

Thanks

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## mirhossein

hello dear friends,
I am working on a field's pvt. for that, I use software of PVTi (Eclipse). I followed the steps of manual for getting a match between Observes and Calculated Data. However, It is too complicated. I was wondering to know whether there are any referrences that discuss its steps clearly or not.
thank you all,

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