Good old question about buoyancy and riser in oil industry

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SUMMARY

The discussion centers on the buoyancy effects experienced by a 3000 m steel riser when submerged in drilling mud, specifically water. When the riser is lowered and latched onto an existing riser, its apparent weight at the surface shifts from the weight in mud to the weight in air. The participants confirm that the buoyant force acting on the riser is determined by the volume of water displaced, which is calculated using the submerged portion of the riser and the weight density of water. Additionally, the potential for buckling under upforce before latching is acknowledged, impacting the overall buoyancy force.

PREREQUISITES
  • Understanding of buoyancy principles in fluid mechanics
  • Familiarity with drilling riser systems in the oil industry
  • Knowledge of weight density calculations for fluids
  • Basic concepts of structural integrity and buckling in long cylindrical structures
NEXT STEPS
  • Research the principles of buoyancy and Archimedes' principle in fluid mechanics
  • Study the design and function of drilling riser systems in offshore oil drilling
  • Learn about the calculations for buoyant force and weight density of various fluids
  • Explore the effects of buckling in long cylindrical pipes under axial loads
USEFUL FOR

Engineers, drilling specialists, and students in petroleum engineering who are involved in the design and analysis of riser systems in the oil industry.

mhl
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Hi
I've got a scenario and would like a confirmation or rejection on it's correctness.

If i lower a steel riser (for simplicity it is 3000 m and vertical, open ended, cylindrical steel pipe, completely flush) into drilling mud (assume water) the surface weight would be the steel weight in mud. When I set the riser down (say i latch it on to an existing riser that is already in place with top at ~3000m), the weight of the riser at surface immediately becomes the air weight of the riser when it latches.

Correct??

In reality the steel would buckle a bit by the upforce before beeing latched and even more so when it is latched and surface pulling reduced to zero so the whole string rests on itself (far fetched, but example purpose). How does this affect the buoyancy force on the steel pipe?? does it contribute to the buoyancy force acting on the riser??
 
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Honestly, I am not following the terminology that you are using. What do you have that is 3 km in length? What do you mean by "latching?" Can you do a diagram?

Anyways, the apparent weight is going to be the weight out of water - the weight of the displaced water. So, take the amount of the riser that is under water and calculate that volume. Use that volume and the weight density of water to calculate the buoyant force.
 
Hi. sorry for the oil terms. here's to simplify:

3000 m stell jointed tube, flush on outside and inside and open ended (no bottom, and might in real life be 9 5/8 inch in outside diameter, far fethced that it is vertical though) beeing lowered into a drilled hole and latched (screw onto an exciting in place pipe of same type about 3000 m into the hole.

because buoyancy upforce acts on casing from below, would this not stop to act on this area when it is set down (latched, or screw) on the steel tube already in place??

hope this is more clear...(?)
 

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