Benthic Geotech has developed a prototype Hydrocarbon Analysis System that enables real time methane sensing while drilling sub sea bed sediments. When used on Benthic Geotech’s PROD, the prototype Hydrocarbon Analysis System can produce a composite trace of hydrocarbon presence and relative abundance or absence can be produced concurrently with normal sampling and boring activities.

The System provides an early warning of potential shallow gas hazards and identifies the presence of methane hydrate concentrations.

The Benthic Geotech prototype Hydrocarbon Analysis System analyses drill returns as they pass through PROD before being vented on the sea bed.

The System, in its present form, includes two hydrocarbon sensors in line with the drill returns path. Drill returns, composed of seawater drawn from above PROD and pumped down the drill hole, mixed with cuttings created at the drill bit, also contain any gas or dissolved hydrocarbons that were held in the interstices between sediment particles. Using tool geometry, drill fluid flow rate, and borehole progression rate, the relative concentration of hydrocarbons sensed can be used to estimate the in situ hydrocarbon composition of the material being drilled.

Infiltration rate of gas into a borehole may also be estimated by water flushing and monitoring gas concentration over set time intervals. Gas origin, approximate concentration and approximate depth of intercept are logged versus borehole depth in real time and displayed on monitors in the control unit on board the surface vessel. Data is stored in digital format and can be combined with core logs and other in situ test data.

The System incorporates proven deepwater sensor technology

At present, two sensors are used; one for high range and the other for low range concentrations. These sensors, supplied to Benthic Geotech by Franatech Technologies, have been used in environmental and scientific studies in many locations to subsea depths greater than 2,000m and, like the PROD, have been proved robust and reliable.