exploration, due to the need for perforating wells at the proper depth 

 for efficient pumping rates and the need to directionally drill some of 

 the wells to ensure as much coverage of the field as possible. 



The series of actions that are required to connect a well with the 

 valves and pipelines for transporting oil and gas to shore is termed 

 well "completion." As each well is drilled, it is lined with concrete 

 and then capped with a seal until the pipelines or other shipment methods 

 are in place and storage tanks are ready to receive the output. 



After the pipes, tanks, and processing facilities are installed, 

 sea water is pumped down the production casing of a well to flush out 

 any drilling mud which may have been left. A perforation gun is then 

 lowered into the casing. When it reaches a point opposite a stratum of 

 oil or gas-bearing rock, the gun fires explosive charges through the 

 casing and cement to establish a path for the oil or gas to flow from 

 the formation into the well bore. Another string of pipe termed pro- 

 duction tubing is put down the casing and serves as a conduit by which 

 the oil or gas come to the surface. Biocides are injected into the 

 formation to keep bacteria from clogging the flow. 



The final operation of completing a well involves the installation 

 of a series of wellhead valves termed a "Christmas tree" that are 

 bolted to the top of the production tubing. Christmas trees may be at 

 ocean floor or on platforms. The two purposes of the Christmas tree are 

 to control the rate oil and gas flows into the tubing and to direct the 

 oil and gas to the various items of platform-mounted processing facilities. 



Operations 



After the wells are completed, the drilling equipment and most of 

 the crew quarters are removed from the platform. All that remains 

 visible on a production platform is a maze of pipes, valves, coils, 

 tanks, compressors, and other pieces of equipment which serve the 

 following functions: 



1. to separate oil and gas from water which 



has been trapped along with the hydrocarbons in 

 the reservoir rock; 



2. in some cases, to separate the associated natural 

 gas from oil for separate flow into a pipeline 

 storage tank, or ship; 



3. in other cases, natural gas is pumped back into a 

 reservoir through a separate injection well to 

 help maintain reservoir pressure and thereby 

 maintain production. 



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