If the well is to be used for long term production, equipment which will allow the controlled fl ow of the hydrocarbons must be installed in the well. In most cases the first step in this operation is to run and cement production casing (9 5/8″ O.D.) across the oil producing zone. A string of pipe, known as tubing (4 1/2″ O.D.), through which the hydrocarbons will flow is then run inside this casing string. The production tubing, unlike the production casing, can be pulled from the well if it develops a leak or corrodes. The annulus between the production casing and the production tubing is sealed off by a device known as a packer. This device is run on the bottom of the tubing and is set in place by hydraulic pressure or mechanical manipulation of the tubing string.
When the packer is positioned just above the pay zone its rubber seals are expanded to seal off the annulus between the tubing and the 9 5/8″ casing (Figure 5). The BOP’s are then removed and a set of valves ( Christmas Tree ) is installed on the top of the wellhead. The Xmas tress is used to control the fl ow of oil once it reaches the surface. To initiate production, the production casing is “ perforated ” by explosive charges run down the tubing on wireline and positioned adjacent to the pay zone. Holes are then shot through the casing and cement into the formation. The hydrocarbons flow into the wellbore and up the tubing to the surface.
Institute of Petroleum Engineering, Heriot-Watt University