10 replies to this topic

[Naval]

Hi guys!

 

I am relatively in both the forum and petroleum community, however eager to learn!

 

I am currently working on project where the variation of several properties of crude oil (viscosity, specific heat,conductivity-especially specific heat  ) need to be known as function of temperature of the oil...

 

the problem is that I cannot find any correlation or points from tests around. Of course there is huge data on fractions etc but crude oil is what I need.

 

Any help where to look or how to treat this matter???

 

Thanks in advance!

[Erwin APRIANDI]

I'm quite confused to interpreting your problem here

 

1. I am relatively in both the forum and petroleum community, however eager to learn!

I believe what you want to say is, that you're relatively new in both ..., right?

 

2. I am currently working on project where the variation of several properties of crude oil (viscosity, specific heat,conductivity-especially specific heat) need to be known as function of temperature of the oil...

For any oil project since we cannot really know the real pure composition of crude oil, we do required to have this data in order to be able calculate several sizing later on for the sake of engineering design.

 

3. The problem is that I cannot find any correlation or points from tests around. Of course there is huge data on fractions etc but crude oil is what I need.

When you are making a correlation between one factor to another, make sure that you are using fix value of other factors. i.e Make sure that you are using the same crude sample at same water cut, when you are checking the sample properties at different temp. Or in other words, only the temp can be vary but you have to control other values. (Hope I understand this question correctly)

[Naval]

Thank you Erwin!

 

Probably  I need to clarify myself.

 

My problem is that of heating crude oil in a storage tank. To optimise the design, I need the variation of specific heat, conductivity, etc with temperature for this particular crude (e.g. arabian light). I am aware of the assays, but how can I find the viscosity at a temperature different than that of the assay?

[srfish]

The GPSA data book has a few properties of crude. A suggestion is 'Petroleum Refinery Engineering" by Nelson.

[Naval]

I already have these books  but the data are mainly for oil fractions which I guess have different properties from crude oil itself. (???)

 

Alternatively, I try to find sth like pseudocomponends modelling or a way to use data from API technical data book - petroleum refining.

[PingPong]

I need the variation of specific heat, conductivity, etc with temperature for this particular crude (e.g. arabian light). I am aware of the assays, but how can I find the viscosity at a temperature different than that of the assay?

 

Specific heat and thermal conductivity depend on the specific gravity (or API gravity) and Watson K (UOP K) of the crude. Graphs for that are available in books as mentioned above, or in API Technical Data Book. For specific heat and thermal conductivity there are nice graphs in the TEMA standards as well.

 

Viscosity depends very much on the crude itself. There is no real relation with gravity, and calculating it via pseudofractions usually gives wrong result.

Temperature dependence of viscosity can be estimated with Shell V50 formula. It will not post that formula here as it is considered proprietary.

 

1) In your Arab Light crude assay, exactly what specific gravity or API gravity is mentioned there?

2) What viscosity or viscosities are mentioned in that assay and at what temperature(s)?

3) At what temperatures do you need all properties?

Edited by PingPong, 06 September 2013 - 04:27 AM.

[Naval]

 PingPong, truly  thank you for your answer! It is very enlightening and exactly what I was expecting!

Thanks again!

1.

1) In your Arab Light crude assay, exactly what specific gravity or API gravity is mentioned there?

2) What viscosity or viscosities are mentioned in that assay and at what temperature(s)?

3) At what temperatures do you need all properties?

Here is the data from the assay:

API Gravity: 33.36  

RVP psig: 4.2,

Gas to C₄ %wt: 5.67,

Total Wax %wt: 4.1  

Pour Point °c: -54  

Cloud Point °c: -5  

Benzene %wt: 0.11             

Kinematic Viscosity cst :

V₁: 10.19 @  T₁°c: 20

V₂:   6.02 @  T₂°c: 40

 

I need the properties (specific heat, viscosity, density) at the range [cloud point temperature until 100 °c] approximately.

 

2.

Specific heat and thermal conductivity depend on the specific gravity (or API gravity) and Watson K (UOP K) of the crude

Thus, we can assume that it a has a fixed value for a specific crude (as API gravity and UOPK dont change with temperature)??

 

3. One more question: A lot of formulas etc are available for oil fractions etc. To what extend can these be used for crude oils?

Edited by Naval, 09 September 2013 - 05:27 AM.

[JMW]

If you go to http://www.cheresour...enu bar above).

 

The posted spreadsheet for viscosity requires you know the viscosity at tow temperature already and solves using ASTM D341 calculations.

But viscosity is always a problem area especially as there is no standard for lab viscosity for crudes, so far as I am aware, and the uncertainties quoted for ASTM D445 (Capillary) are quite wide. Moreover, sometimes it is not possible to obtain the viscosity at more than one temperature. However, viscosity at another temperature can often be estimated for simple hydrocarbons (i.e. not manipulated viscosity fluids like lubricants) using the multi-curve method which allows you to estimate the viscosity based on a single process or lab viscosity measurement. This method is used in a range of applications from fuel oils to crude oil (it is used for pipeline applications of Alberta crudes for example which are heavier and more vulnerable than Arabian light crude). I have a spreadsheet for the multi-curve solution which I will be pleased to let you have if you will contact me via the website address contacts page which you will find on my profile page.

[gegio1960]

Hi Naval.

I'd say that oil characterization is an art more than a science ;-)

The API gravity of your crude is 33.36, equivalent to SG 0.8583.

In the crude assay data you didn’t provide the characterization factor, k. In a similar crude assay you can easily find k = 11.6.

Moreover, your -5°C to 100°C temperature range is equivalent to 23 – 212°F; 20 and 40°C, reference temp.  for viscosity, are 68 and 104°F.

As a special welcome gift for you, I’ve made the exercise as follows ;-)

The first book mentioned in the answers is GPSA. From there you can find two useful graphs providing you with the curves for:

-          Specific gravity (my regression is SG = 0.8686-0.0007*t);

-          Thermal conductivity (k, W/m/°C = 0.1275-0.0005*t).

For the specific heat you can use TEMA chart, as stated above (Cp, kcal/kg/°C = 0.4352+0.001*t).

(t is always the temperature in °C; don't extrapolate, please)

Other than JMW advices above (JMW is a real expert of viscosities!), with viscosity at two different temperatures you can easily obtain the viscosity at any temperature by using the viscosity charts (by ASTM). In this case I’ve no time for the regression (log), so I report a string of data (other than the two assay points): 25, 20, 12, 4, 2.95, 2.4 cst @ -5, 0, 15, 60, 80, 100 °C.

The accuracies should be good enough for your scope

Good luck!

Edited by gegio1960, 09 September 2013 - 09:39 PM.

[PingPong]

I plotted the two given viscosities in an ASTM D341 chart and drew a straight line through them. See attachment.

 

ASTM D341 formula is: Log(Log(v + 0.7)) = A - B*Log(t + 273)

 

and therefor: v = 10^(10^(A - B*Log(t + 273))) - 0.7

 

v = kinematic viscosity, cStokes

t = temperature, ^oC

A = 8.45391 for Arab Light

B = 3.42058 for Arab Light

 

A and B are calculated from the two viscosities and temperatures in the Arab Light crude assay.

 

 

Thus, we can assume that it a has a fixed value for a specific crude (as API gravity and UOPK dont change with temperature)??

No, I meant that apart from temperature they also depend on gravity and UOP-K

 

 

 

 

3. One more question: A lot of formulas etc are available for oil fractions etc. To what extend can these be used for crude oils?

Strickly speaking al those formules and graphs that you find in the literature are only valid for narrow boiling petroleum fractions. But in the absence of more accurate data they are also used for wide boiling mixtures such as crude oil. As gegio already indicated: this is not an exact science.

Attached Files

•  Arab Light - Viscosity Temperature diagram.jpg   66.5KB   23 downloads

Edited by PingPong, 10 September 2013 - 02:04 AM.

[gegio1960]

Thank you pingpong.

You corrected my typo and completed the viscosity part (I had no time to look for the correlation).