The mixture from the wellhead usually travels by flowline to a separator 

 where the gas and liquid phases are split. With \/ery high gas pressure, extra 

 "low- temperature" separators may be used to remove liquids with low vapor 

 pressures that are mixed with the natural gas. When high-pressure gas leaves 

 the wellhead, it expands and cools according to the Foule-Thompson effect. If 

 water is present in the gas, it may freeze, blocking pipes and gas flow. 

 Therefore, dehydrators may be used to remove the water chemically, raise 

 temperatures, or add "antifreeze" materials to the gas. After treatment, the 

 gas will be compressed and pumped through pipelines to users. 



Oil may go through several separation stages to remove salt water and 

 sediment. Often this simply consists of a series of settling tanks where 

 sediment falls out and oil separates, floating on the water. The liquids are 

 drawn off from different levels in the settling tanks, and occasionally the 

 tanks are drained to remove the sediment. Sometimes the oil and water form an 

 emulsion that does not readily separate. In this case a "heater-treater" is 

 used whereby heat and chemicals cause the emulsion to disperse. 



Separation of crude from water and sediment is an important process. 

 Pipeline companies, the portion of the industry that buys and transports 

 petroleum, and state regulatory agencies have standards of purity of crude 

 ^il. They do not allow pipeline transport of crude that does not meet the 

 standard. Thus the purchasers of crude are assured petroleum with a specified 

 quality. In addition, salt water and sediment cause considerable wear in 

 pipelines, valves, and pumps. Thus, low levels of these materials are impor- 

 tant in minimizing maintenance costs, maintenance time, and the possibility of 

 leaks or breaks. 



After treatment, the oil is stored in large tanks in a tank battery. 

 Periodically the lease operator and pipeline gauger will meet at the tank 

 battery to measure the amount of oil stored. After the measurement is made, 

 the pipeline gauger will send the oil to the pipeline either by truck, barge, 

 or by gathering lines from the tank battery to a pipeline gathering point. 



The salt water evolved must be removed. In marine areas in some states 

 it is permissible to dispose brine directly into tidal waters unfit for human 

 or agricultural use, if the brine quality meets certain standards. In many 

 places, brine is injected back into the ground either into old wells or into 

 specially drilled wells. The brine injection may be part of a secondary 

 system designed to enhance petroleum recovery. 



During the production phase, activities take place at the wellsite and 

 production equipment area nearly every day. Most activities are related to 

 inspection, gauging, record keeping, maintenance, and operation of production 

 equipment. Periodically, major maintenance is required at the wellsite. This 

 is usually due to the buildup of paraffin or sediment in the wellbore, pump 

 and casing maintenance, periodic "treatment" of the petroleum-bearing strata. 



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