The standard lab analytical report used in the U.S. natural gas measurement industry is commonly referred to as a "C6 plus" (C6+) analysis performed by gas chromatography. This breakdown contains a lot of useful information, including a determination of the primary components of the gas stream expressed as a percentage of the total composition (mole percent); the theoretical yield of liquid hydrocarbons, in gallons per thousand cubic feet (GPMs); heating capacity in British Thermal Units (BTUs); and relative density. Even more detailed information is available through an "extended analysis," but the values derived from a C6+ analysis are principally used in determining both volume and energy.
The term "C6+ analysis" indicates that the gas components are split and individually measured by the gas chromatograph for low molecular weight components, from methane (C1) through pentane (C5), and that higher molecular weight hydrocarbons are lumped into the C6+ component category based on generally accepted assumptions regarding the C6+ chromatographic peaks. For example, the standard split for the Gulf Coast region assumes approximately 48% normal hexane (n-C6), 35% normal heptane (n-C7) and 17% normal octane (n-C8) for the purpose of determining flow rate and heating value. Extended analyses, such as a C9+ analysis, may be performed to produce a more comprehensive identification of hydrocarbon compounds, but because this effort typically produces only a nominal change in the volume and energy determinations, it is usually not required.
For a more detailed description of the C6+
analysis of natural gas and a sample laboratory analysis report, click here
"All the world is a laboratory to the inquiring mind."
~ Martin H. Fischer, German-American physician and writer