Onshore partial processing facilities may be established to process 

 natural gas and/or oil. A combined partial processing facility requires 

 approximately 15 acres of land per 100,000 barrels of oil and associated 

 gas processed [26]. A gas processing plant must be sited somewhere 

 between the gas pipeline landfall and the commercial gas transmission 

 line. The availability of land along this route is a primary determinant 

 in plant siting, as are local land-use patterns and regulations. Pipeline 

 transportation costs increase the farther inland the gas plant is sited, 

 but this increase is usually out-weighed by the high cost of coastal 

 land [26]. 



In a gas/oil mixture, heavier hydrocarbons are removed from the gas 

 as quickly as possible after separation of the gas from the oil to 

 minimize the possibility of plugging up the pipeline. Plugging, which 

 reduces line capacity, is due to the condensation of hydrocarbons or the 

 formation of hydrates on the inside of the pipe. As a result, gas 

 processing plants and tank farms are situated close to each other and to 

 the pipeline landfall. 



Cons tructi on/ 1 ns tal 1 ati on 



The construction of a gas plant handling a billion cf/d would 

 require about $85 million (1976 dollars) in capital investment. This 

 would include condensate receiving facilities and full fractionation and 

 storage for propane, butane, gasoline, and condensate. 



Environmental impacts vary with the site characteristics. If a 

 water front location is chosen, environmental disturbances may occur due 

 to dredging, filling, channel alteration, and spoil disposal. Inland 

 locations reduce these disturbances. Since no unique, heavy machinery 

 or processes are required on the site, site alteration and construction 

 are not expected to result in severe noise or air pollution. 



Operation 



The nature of onshore gas processing depends primarily on two 

 things: (1) the amount of ethane, propane, butane and other liquid 

 hydrocarbons present in the gas; and (2) the amount of water and hydrogen 

 sulfide (impurities) in the gas stream. An example process flow chart 

 is shown in Figure 42. In general, the gas is produced at an offshore 

 platform, partially processed to separate it from the oil and water in 

 the well stream, piped to shore, treated to remove impurities, processed 

 to recover valuable liquid hydrocarbons, and delivered to a commercial 

 gas transmission line [26]. 



If the gas produced offshore is associated with oil, the gas will 

 usually be separated from the oil and water on the platform by an oil- 

 gas separator. Water is removed from the bottom of the separator, 



206 



