Lifting of heavy oil is currently carried out almost exclusively by rod pumps. Severe problems are often encountered, such as rod floating and overloading due to high fluid viscosity, pump sticking and erosion with high sand production, heavy crude plugging, and gas locking under steam flood conditions. Special rod pumps alleviate some of these problems but installation and maintenance expense typically remains high.
This paper describes an unconventional gas lift system which can replace rod pumping for shallow (<3,000 ft.) heavy oil production. It circumvents all of the aforementioned problems and in addition has advantages in adjusting to variable production rates, in steam injection and in ease of well cleanout.
The heart of this system is an insert chamber downhole, whose only moving parts are two standing valves. Produced fluid entering the chamber is periodically expelled into a production annulus by pressurized gas injected from the surface down a small injection string. Natural gas, inert gas, or even air can be used for pumping. This paper analyzes the operation of the chamber lifting system and shows how to optimize the system design and the operating variables to obtain maximum production at minimum cost.
With the close spacing of thermal wells (2-5 acres), the combination of a single inert gas generator and associated compressor to supply a large number of wells equipped with chamber pumps is feasible. Several types of inert gas generators are described. Capital and operating costs of chamber and rod pumping for a 170 well system are compared. The economic return is far greater for chamber pumps when bottomhole conditions are such that steam locking of rod pumps occurs.