What's new in artificial lift: Part 1—twenty new systems are described for sucker rod and progressing-cavity pumping, plunger lift and gas lift

World Oil, April, 2006 by James F. Lea, Herald W. Winkler, Robert E. Snyder

Described here are 20 recent developments from 10 companies in four categories of artificial lift technology: sucker rod pumping (seven items); progressing-cavity pumping (PCP) (five); plunger lift (five) and gas lift (3) Part 2, coming in May, will present electrical submersible pumping (ESP), and other, miscellaneous artificial lift innovations.

Sucker rod pumping, now evolved from classic beam pumps to include tower type units, is the most widely used artificial lift, using the vertical rod motions, now also with cable, to operate a downhole reciprocating pump. PCP systems are based on a surface drive rotating a rod string, which drives a downhole pump rotor operating within an elastomeric stator. In plunger lift, a freely moving plunger falls through fluids in the tubing and is lifted back to surface with its slug of mostly liquids by higher-pressure, formation gas (or injected gas) from the tubing-casing annulus. Gas lift in valves injecting annulus gas under liquid columns or plungers in the tubing to drive to surface.

SUCKER ROD PUMPING

The seven new systems are recently applied by five companies, or are in the final test phase. They include: a larger tower type, longer stroke pumping unit; a hang-off tool to temporarily unseat and raise rods and pump; a gas-engine-driven power system to replace electric motors; two low-profile/low-cost rod pump units; a full-time, computerized downhole pump card; and a new tower type unit employing reciprocating downhole cable instead of sucker rods.

Larger Rotaflex * system available. The Rotaflex * is Weatherford's long-stroke pumping system for sucker rod pumps, Fig. 1. This system uses proven technology and design innovations to provide greater efficiency and cost-effectiveness for deep, troublesome and high-volume wells. With the unit, rod pumps can be used for applications where electric submersible or hydraulic subsurface pumps were once required. The larger unit has up to a 366-in. (30.5-ft) pump stroke.

[FIGURE 1 OMITTED]

The unit has virtually no minimum speed. Slower speeds and longer strokes result in more complete pump tillage and lower dynamic loading. Key benefits include efficient handling of high volumes, high loads and deviated wells; and reduced rod/tubing wear with fewer cycles and reversals. The mechanical reversing mechanism is field-proven in over 800 units.

The system's long-life, heavy-duty-load belt links power train and rods and acts as a shock absorber, reducing entire system stress. The short-radius torque arm reduces torque demand, allowing use of a smaller prime mover and gear reducer. To service a unit, after bridle and carrier bar are disconnected, the unit rolls away. When workover is completed, the unit is rolled back into place, and the carrier bar is reconnected.

Hang off tool. Harbison-Fischer, Ft. Worth, Texas, has finished testing and is offering a unique sucker rod hang off tool, Fig. 2. When a rod-produced well needs to have the rod pump unseated and hung in the tubing, the pump is lifted and the Hang Off Tool (HOT) is screwed onto the top rod at the surface, then lowered and screwed into the flow tee above the tubing string. The steel tool has a built-in sub for lifting the rod string and lowering it onto the flow tee. Some operators attach a hammer union, so the rod string does not need to be rotated when lowered.

[FIGURE 2 OMITTED]

This installation seals the wellbore and hangs off the rod string, providing safer installation than homemade hang-off tools. HOT conforms to NACE specifications for unhardened steel material service. It is available in several commonly used sizes.

Gas engine-driven power unit. DynaPump, Inc., Northridge, California, has announced the newest addition to its line of pumping systems, the Natural Gas DynaPump power unit, Fig. 3. It pumps liquids efficiently. Many oil and gas wells can be operated cost-effectively by using natural gas instead of electric power, freeing electricity for other needs. The unit provides one possible solution for producing maximum flow at the lowest lifting cost. Gas consumption is reportedly about 20% of conventional beam-pump power consumption, and the unit maintains all built-in controls, communications and feedback that the electrical unit may have.

[FIGURE 3 OMITTED]

The power unit control center can convert input power to hydraulic power, and control pump stroke as needed. The system allows for independent speed control, in both up and down directions, and for independent adjustments of top and bottom strokes. It also can adjust speed automatically to provide pump-off control. Major operators are using the new power unit in more than 50 wells, resulting in increased cash flow with many environmental benefits.

Low-cost rod pumping system. DynaPump has recently launched its new DynaSave a low-cost rod pumping system, stated to require low maintenance, Fig. 4. This very compact unit--one can be moved on a pickup truck--has flow-rates up to 640 of barrels fluid per day (bfpd) from less than 750 ft, and can pump 40 bfpd from 5,000 ft; maximum rod load capacity is 7,000 lb.