Their most common primary metering device to measure gas

quantity is an orifice plate meter with a flow computer. The

orifice plate causes a pressure drop in the meter tube. The

flow computer senses the pressure drop and calculates the

volume based upon standard equations. Orifice plate meters

are simple, low-cost and installed on a very large percentage

of gas wells.

For gas quality, a gas chromatograph is required to provide a

gas composition from which the heating value is calculated.

However, most sites do not have enough gas volume to

justify purchasing a chromatograph. To alleviate this problem,

composite samplers were installed on measurement sites

where the flow was too low to justify a dedicated GC.

A composite sampler is a device containing a sample bottle.

On a periodic basis, either time or volume based, the sampler

will put an aliquot of gas in the sample bottle. The sample

bottles are collected either monthly or quarterly depending

upon the sales contract, and sent to a lab for analysis.

Problems with composite samplers