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Pumping units are the familiar symbol of the oilpatch. Almost everyone in Alberta knows what they are and how they work. The jack is a familiar sight in Alberta and part of many a petroleum related company’s logo.

The jack has become an enduring symbol of our industry despite continued competition from other forms of artificial lift such as the screw pump, strap jack, hydraulic jack, and jet pumps, the pumpjack is the most familiar. They also tend to be the most enduring. It is not uncommon to have a jack built in the 50’s pumping away today.

The pumpjacks secret is few moving parts and slow operation speed. Key also is the proper sizing and design of a beam installation. The tried and true method for doing this thus far has been the API Recommended Practice 11L method. There are a number of programs out there such as RodStar and more that can help size pumping units.

Reliable DOS-based sizing programs are also available locally from K. Stuart Associates Ltd. in Calgary. These use methods based largely on API RP 11L, with the help from the Neely method. These programs help size the pumping unit and the driver. Based on target production rates, and given pump size, tubing diameter and oil gravity, recommendations are made in regards to gear box, structure size, stroke length and finally horsepower requirements.

One very comprehensive system is the NABLA method. This system is touted by Penta Completions as well as Lufkin Industries, and they have a steady clientele for sizing as well as optimizing beam pumping installations. The strength of this program is that it encompasses not only the typical pumping unit, but specific models from specific manufacturers. In practice, this means that the Mark II, Air Balanced as well as conventional pumping units are covered. You can give the Penta guys a specific brand and model, and they can tell you the actual loading stats on that unit.

The key is that arbitrary combinations of these jacks can be combined with arbitrary rod string designs, arbitrary drivers (prime movers), and arbitrary downhole conditions. This means that accommodations can be made for things like anchored or unanchored tubing, full liquid fillage, fluid pound, gas interference, and fluid inertia and friction effects. Additionally, different rod strings can be simulated to decide for example if a fiberglass rod string might be in order to optimize the pumping unit’s performance.

The bottom line is that you the producer, have a number of choices when it comes to sizing a pump jack. It is common to see one operator use a 320-213-120 in a field and have his competitor produce oil from the same depth and zone, and get a way with a 114-143-64 pumping unit. So what you ask? Let me put it in perspective. A reconditioned 320 pumping unit can sell in the range from $ 22,000.- for a less popular brand to as high as $29,000.- for a prime name. The same range of prices for a 114 pumping unit can range from $ 4,000.- to $ 12,000.-.

Your Mr. President will be very much more interested in buying the 114 of course. The savings alone will expedite the payout of the well by many months, and thus allows for perhaps another well to be drilled. Now how do you prove it?

The following are a few design parameters paramount in your search for the right jack:

This is the peak load imposed on the jack at the top of the rod string.

This number should be positive, or else there is slack in the bridle. This can also affect the fatigue life of sucker rods. (for example, fiberglass rods do not compress well)

This is merely the number of strokes per minute the unit makes.

This is a percentage of the structure’s rating. If you exceed this, the structure is overloaded. Interestingly enough there are a number of experienced engineers who are comfortable with a small percentage of overloading. The interesting thing is that the better manufacturers typically build in this type of abuse. This is why the better companies have the good name they have.

This is a direct measure of just how hard you’re making that slow speed gear work. This is usually a positive figure.

This is a measure of the amount of dead weight that’s suspended from the crank arms on the unit. Preferably the weights are in the right place and the unit is in balance. The closer the pumping unit is to being "in balance" the less wear you’re likely to incur on the gear train and structure of the pumping unit.

These calculations take into account the type of string you’re using, the amount of stress (compression and stretch)

Yes, tubing stretches as well, especially if it’s not anchored. This stretch can dtreact from useful pump stroke in lifting fluid to the surface.

These take into account the torque and horsepower your electric and gas driven engines can deliver at any point in the pumping cycle. This may be a factor in locations where power consumption carries a higher cost.

These refer to the bore size of the pump, the pump depth, and the fluid load on the pump. The fluid load can significantly affect the efficiency of the pump.

The above factors are all taken into consideration when sizing a pumping unit, and taking all, not just a few into account can save your company a great deal of money.

The task you’re faced is whether you’re going to make your company money by improving production or saving your company money by keeping down the repair bills, or both.

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