The gas stream as it comes from the reservoir depending on the purity may need to be properly processed. Some streams may only require minimal processing in the form of dehydration other streams with more complex compositions may need more sophisticated forms of processing.
Field processing removes undesirable components and separates the wellstream into salable gas and hydrocarbon fluids.
The aim of processing:
- To remove condensable and recoverable hydrocarbon vapours
- To remove condensable water vapour which depending on conditions may promote hydrate formation
- To remove undesirable compounds
It can be said that the fluid composition will determine the design criteria for the sizing and selection of the separator and treatment processes for the hydrocarbon stream.
Arguably one of the most important duties of gas processing: to separate the gas from free liquids. A properly designed separator will perform the following functions:
- Primary phase separation of liquid hydrocarbons
- Refine the primary separation by removing entrained liquid
- Further refine separation by removing entrained gas from liquid
- Dis-charge the separated fluid gas/liquid streams in such a manner the no re-entrainment occur
Principles of Separation
- Centrifugal inlet to provide primary separation of liquid and gas
- Adequate dimensions/volume characteristics to promote settling and provide surge room
- Mist extractor/eliminator to coalesce small particles of liquid
- Provides adequate level control and instrumentation to properly monitor and manipulate fluid volumes/levels within the device and allow for safe operation
Typically natural gas treatment involves the dehydration of the gas before compression or transportation. The primary reason for dehydration is to remove water vapour which if left in the gas stream may promote the formation of hydrates. In addition when the water is present in the gas stream carbon dioxide and hydrogen sulphide may become corrosive liquids, the water may also promote slugging flow regimes reducing the pipeline flow efficiency and lastly water content decreases the heating value of the natural gas. Dehydration can be accomplished by cooling, adsorption and or absorption.
This is used to increase the pressure of the stream for the purposes of transportation. Via pipeline. In general compression and compressors are use to increase the potential energy needed for the movement of the gas stream. Compressors are usually located at a centralized point, relative to the wells they are fed by, and are used to collect and compress the gas stream for further transportation. Typically they are sized based on the input pressure and the expected volume they will handle.