PLUNGER LIFT APPLICATION IN DEEP OIL WELLS

Abstract

The Patchawarra Central Oilfields 40 km to the north of Moomba are operated by Santos Ltd. Wells produce 52 API oil with a high gas/oil ratio from depths of about 2 956 m (9 700'). A number of wells, not influenced by pressure maintenance, require some form of vertical lift assistance in order to deplete the reservoir effectively.

Following a successful trial on a gas well, plunger lift was installed on the Moorari 6 oil well in early 1987 to assess the suitability of this artificial lift method. This installation was the first use of plunger lift in Australia to assist production in a well at this depth.

Plunger lift uses a free piston as an interface to prevent fallback of liquids. The plunger is propelled by pressure build-up in the annulus. Crucial to the operation of plunger lift is the gas/liquid ratio. Sufficient gas must be available to produce the liquid load. In suitable wells, no external energy source is required and it provides a very economical method of maintaining production.

The Moorari 6 installation was tested at 11.5 m3/d (72 BOPD) on a well previously producing approximately 7 m3/d (44 BOPD) and requiring significant operator involvement for frequent blowdown of the well to atmosphere.

As the reservoir depletes, the expected rise in producing GOR will serve to increase the efficiency of plunger lift operation. Currently under consideration is the introduction of extra gas to the casing, which will give a significant production increase in the early life of the installation.