oil

[ste v]

every year millions of gallons of oil are extracted from under the earths surface, this must leave massive empty pockets under the earth - do these stay empty - do the ones under the sea fill with sea water ???

[MargeB]

Hi,

This is a good question. A couple of points:

1. You never pull pure oil out of the ground, it's largely water with a bit of oil in it.

2. The cost of getting the oil out is mostly from lifting it UP. You can do this by just displacing it, which is often by pumping water into the reservoir so that the (lighter) oil comes up, where it can be pumped up a bit further.In doing this you do replete the reservoir.

3. The oil is held in pores between the rock, or in a big hole within some rock, or in a lot of sand/sandstone. You drill down through this rock etc and then you basically fit a tube in it, and blow a hole and then some chemicals sideways to create flow paths for the oil/water. The oil and water (and gas) have to move through the pores towards the lower pressure in your well. You need to do this with great care, if they move too fast then they can easily damage the reservoir. You can get round this by pumping oil into the reservoir to fill the gaps left by the water/oil.

4. The water pumped in is not actually sea water, it is too salty to do its job without damaging the reservoir. You need to pump sea water to your rig, desalinate it, then pump it back down.

There are various other factors (like gas) to watch out for too, but basically that's it.

[MargeB]

sorry 3. should read pumping water back into the reservoir.

[MargeB]

hi,

well, middle east wells have a higher proportion of oil than most places. Most have about 3-35 percent oil.

Water from the well is normally decontaminated anyway on the rig, for environmental/well flow reasons.

I did 6 years with that big ol blue company, good to see another oilman on here. My only ME experience was off Qatar, not very pleasant! Tiny jackup!