Gas Content Testing

Fast and Slow Desorption

The Fast and Slow desorption methods both involve the determination of Q1 (lost gas), Q2 (desorbed gas) and Q3 (residual gas, i.e. gas released on crushing). The sum of these three components is the “Measured Gas Content,” also known as “Qm” as defined in AS 3980-1999.

A test is deemed to be Slow Desorption where the measurement of gas evolved (Q2) exceeds five days.

Q1 (lost gas) is the gas that cannot be measured while the core is being recovered. It is estimated based on field gas desorption measurements.


The term ‘Q1 readings’ is commonly used to distinguish between gas desorption measurements taken in the field and those taken in the laboratory. Though technically speaking, Q1 readings form part of the Q2 measurements.

Most customers prefer to use their own on-site staff or drilling contractors for Q1 readings. GeoGAS offers Q1 training before the drilling campaign or as a refresher to ensure the crew understands how to conduct the Q1 process and to prepare a sample for transport.

GeoGAS can provide training for Q1 testing at our laboratories or on-site. Pricing for this service is available on request.


Q2 readings are taken in our laboratory. GeoGAS customers can choose between the Fast or Slow desorption method, and we can advise you on which method best suits your testing needs.


Q3 readings are taken in our laboratory.  During this process, two 150g representative sub-samples are taken from the core and crushed for Q3 determination. GeoGAS uses high-quality Rocklab ring mills that have been specifically modified for our gas testing needs.


Find your nearest GeoGAS office

Scroll to Top