[BurnCalories]

Please excuse a mundane question but I am curious about the mechanics of pumping oil. When you see those oil well pumps going up and down, where is the oil being pumped to. Are all of the individual wells connected to some pipe or storage area?

[ReserveGrowthRulz]

$this->bbcode_second_pass_quote('BurnCalories', 'P')lease excuse a mundane question but I am curious about the mechanics of pumping oil. When you see those oil well pumps going up and down, where is the oil being pumped to. Are all of the individual wells connected to some pipe or storage area?

[grillzilla]

Nothing wrong with RGRs response above, I just thought I would go into a little more detail for those who are not familliar with how most oil wells work:

[align=justify]Conventional oil wells, like the ones you see bobbing up and down in any oil patch work like this:

Wells are usually "cased" , that is they have one or more steel alloy sleeves to keep the reservoir material from closing up
the hole (just falling in, or exploding in because of overburden pressure). The casing is perforated either by the use of shaped
charge explosives fired while the casing is in the ground, or in the case of older wells the casing has been perforated prior to
running it in the hole. In either case these holes are what allow reservoir fluids to flow into the well, while keeping sand and
debris out. In a very young well, in a newly discovered field, pressures may be great enough for oil to flow from the reservoir to
surface without the aid of artificial lift (a pump or gas/water injection). In some cases, if the drillers are not careful the reservoir
pressures can overwhelm the weight of the drilling mud and "blow out" the well. After a while (varies greatly) the well will require
some sort of artificial lift to produce oil. A common rod pump is set up like this:

Within the casing, a (usually) steel alloy tube is lowered. At the end of the tube is a long slender pump, usually the
same diameter as the tube. The tube and pump may be only 2 to 3 inches in diameter. The tube goes all the way to the surface.
The size of the tube and length of the pump varies with the need/ability to move more fluid and the diameter of the well casing.
Within the tube there is a long rod, this rod is attached to the pump plunger and goes all the way to the surface and ends with
the "polish" rod you see attached to the pumping unit. It is polished to allow it to pass through a packer. The oil is pushed up the
tube from the pump at the bottom, going around the rod and exiting the well at the packer where it enters a flow line destined for a
tank or processing facility. There are single long rods that go from the surface to the pump, but a great many wells have the rods in
segments, each segment screwed together at a rod "box".

The rods and tubing can go very deep, a mile deep is not unusual. Depending on reservoir conditions they can be deeper than the top
perforations in the casing (risky because it is easy to suck in sand and ruin the pump). A way to judge how deep the pump is set
in a conventional well is to look at the counter-weights on the back of the pumping unit. The bigger the weights, the deeper the pump.
In sandy reservoirs usually the pump is set just above the perforations in the casing. The idea is to pump fluid levels down until the
pressure in the reservoir is higher than the pressure in the well. This allows fluid to flow into the well. If the well is open to more than
one reservoir sand layer, it is necessary to reduce the pressure enough that Both sands have a higher pressure than the wellbore.
(If one is higher and the other lower you may end up with fluid from one sand entering your well and exiting out the well at the other sand...
NOT what you want).

The size of the pumping unit tells you how much fluid the operators can produce from the reservoir.
The bigger the pumping unit and the faster it goes up and down, the more fluid is being moved.
The big units can easily move 1000 bbl per day of fluid.

Examples: A tiny pumping unit with small weights and a slow 36 inch stroke is probably moving heavy oil from a shallow reservoir, or
the oil is not heavy but the reservoir is tight (poor permeability) and the operator cannot get fluid out quickly.

A very large pumping unit, with weights heavier than your pickup truck, and a stroke of over 110 inches, is probably producing
from a deep reservoir and lighter crude, possibly moving a lot of water. The operator needs to, and can, move a lot of fluid at a
high water cut to make a profit.

Note that I said fluid, not oil. Especially in the U.S. an ever-growning percentage of the fluid produced is water.

Water causes problems. When a well is new, and the reservoir is still flush with oil, nearly all the fluid produced is oil.
The whole pump system is bathed in oil. In this circumstance the pump, rods, and tubing can last for years without repair.
When water percentage starts to rise downhole mechanical gear starts to fail more rapidly.

Two particular problems apply.
First is simple friction. The rod you see going up and down at the top is rubbing somewhere down the hole against the tubing,
24/7/365 rubbing. Especially at the rod "box" where the rods are screwed together. Why does it rub? Simple, wells are not straight,
they curve, they snake around, especially older ones. Bends in the wellbore result in the rod touching the tubing. I have seen rod boxes
worn all the way to the threads, and tubing worn all the way through many many times.

The second problem is chemical. Where rod boxes come close to the tubing, there is a pressure drop as they move up
and down thru the fluid. This pressure drop causes a CO2 driven acid reaction. The steel literally gets eaten away.
Some wells can produce a couple pounds of dissolved iron Per DAY as this process takes place (yes we measure it).
Acid wear leaves a particular pattern in the steel, you can easily tell the difference between rubbing and acid wear.

There are partial solutions to these problems: continuous rod ("co-rod", no rod boxes, but takes special equipment to handle).
Coated tubing, either with a thick epoxy or an abrasive resistant plastic inner liner. Plastic "centralizers" to keep the rod boxes from
rubbing against the tubing. Not to mention probably hundreds of weird chemical concoctions to slicken up the works or prevent
corrosion.

When you see a work-over rig on a well usually it is to correct holes in the tubing, a "parted" rod, or pump wear.

With the need to move ever-more fluid efficiently in wells, many operators are turning to electric submersable pumps (ESP). One reason
for using such a pump is that the wellbore is highly curved or deviated, a rod pump just won't work in this case (think horizontal wells,
offshore wells, or MRC wells). Another plus is that unlike a rod pump ESPs do not produce rapid pressure fluctuations in the well rapid
acceleration of fluids can cause additional formation fines (very fine sand) to enter the well. A steady pressure can reduce this problem.
ESP pumps are placed at the bottom of the tubing but instead of having a rod going up and down, power is supplied to the electric pump
at the bottom.
These pumps are expensive but eliminate the problems of tubing and rod wear. ESPs have to overcome the problems of downhole
temperature and the pump must be chosen carefully to ensure a proper match with inflow rates. If you see a well that just has an
electrical box and wires going down where the wellhead is, you are likely looking at an ESP setup.
Modern wells almost all have electric motors to drive the pumping units. One of the ironic aspects about power outages in and around the
U.S. is that in some cases the oil producers, being heavy users, are asked, or even required by contract to shut down their operations
to conserve power for residential use. Shutting down energy production in order that more energy may be consumed..such a deal [/align]