Page 401 - Compression Machinery for Oil and Gas

Upstream Compression Applications Chapter 8 379

Gas Lift/Reinjection
Gas lift and reinjection are two distinct processes for improving production at
oil wells. Gas lift focuses on improvement of well performance, and reinjection
focuses on improved yield from the reservoir.

Gas Lift
A gas lift compressor injects gas in to an oil well to aerate the crude oil, increas-
ing production [5]. The gas is introduced from the surface into the tubing-casing
annulus and introduced into the tubing at the desired depth. This gas injection
decreases the fluid density in the tubing, thereby increasing the well pressure at
the surface. An example gas lift system is shown in Fig. 8.4. The application
may be combined with a gas gathering operation, and some offshore operators
use the same compressor train to both feed a gas lift service and export com-
pression to feed gas into a pipeline.
The gas lift compressor is supplied with produced gas at the surface, typi-
cally at relatively low pressure (0.3–0.7MPa). This gas is compressed to a
higher pressure for injection, typically to pressures of 10–12MPa or even up
to 20MPa depending on reservoir requirements. Higher injection pressures
enable gas lift at deeper depths, maximizing the production increase. Thus,
gas lift compressors typically require high throughput and a high compression
ratio. The typical operating characteristics for gas lift compression are summa-
rized in Table 8.2.

FIG. 8.4 Gas lift system [6]. (Courtesy of Southwest Research Institute)