Pour point and gel properties 1

[MortenA]

As far as i understand a crude will form a stable gel when cooled below its pour point. I guess the name indicates that it "cant be poured". However: How stable is this gel? Can it still be moved in a pipeline if the differential pressure becomes large enough - or could a situation like plugging with hydrates occur?

Best regards

Morten

 

[ppata]

Hi,

If you go under the pour point the value of needed differential pressure will be huge. The source of your problems it will be the interfacial tension beetwen fluid and pipeline.
Interfacial Tension (IFT) is a measurement of the cohesive (excess) energy present at an interface arising from the imbalance of forces between molecules at an interface (gas/liquid, liquid/liquid, gas/solid, liquid/solid). It can be quantified as the force acting normal to the interface per unit length (force/unit length, mN/m).When two different phases (gas/liquid, liquid/liquid, gas/solid or liquid/solid) are in contact with each other the molecules at the interface experience an imbalance of forces. This will lead to an accumulation of free energy at the interface.
The excess energy is called surface free energy and can be quantified as a measurement of energy/area i.e. the energy required to increase the surface area of the interface by a unit amount. It is also possible to describe this situation as having a line tension or interfacial tension (IFT), which is quantified as a force/length measurement. This force tends to minimize the area of the surface, thus explaining why for example liquid drops and air bubbles are round. The common units for interfacial tension (IFT) are dynes/cm or mN/m. These units are equivalent.
This excess energy exists at any interface. If one of the phases is the gas phase of a liquid being tested the measurement is normally referred to as Surface Tension (ST). If the surface investigated is the interface of two immiscible liquids the measurement is normally referred to as interfacial tension (IFT). In either case the more dense fluid is referred to herein as the "heavy phase" and the less dense fluid is referred to as the "light phase". Solid surfaces also may be described to have an interfacial tension normally referred to as Surface Free Energy (SFE), but direct measurement of its value is not possible through techniques used for liquids.
A.


Best regards,
Andrei

 

[MortenA]

I was mostly thinking of multiphase pipeline with limited liquid hold up - allthough with terrain induced pockets etc. For an oil pipeline i allready guessed that cooling below pourpoit could cause one to "loose" the pipeline. But will this be the same for a multiphase?

 

[ppata]

I'm a reservoir engineer so I am not a specialist in pipelines. Generaly speaking, multiphase flow in reservoir is defined by diferent quantity of oil, gas & water. In your case gas is out of discusion so we talk just about oil&water flow. Try to remember the fact that reservoir water can "offer" you many corrosion problems.
I think that link will solve your problems:

http://www.bhrgroup.co.uk/confsite/hyd2home.htm

Contact me if you have reservoir related question.
A.

Best regards,
Andrei

 

[ppata]

me again,

search on IFP articles

http://www.ifp.fr/ifp/ifp_RechRevue.jsp?LANGUE=ANGLAIS

for that one: "Experimental Study of the Pipeline Lubrication for Heavy Oil Transport"

Best regards,
Andrei

 

[MortenA]

the ifp link seems very interesting - unfortunately my frech is too poor to do me any good :-(

Best regards

Morten

 

[MortenA]

mtna@ramboll.dk

Thank you for you help.

Best regrads

Morten