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Airborne Surface Gas Flux Mapping for Onshore Frontier Exploration

Hirst, Bill *1; Jonathan, Philip 4; Krayenbuhl, Thomas 2; Gonzalez Del Cueto, Fernando 3
(1) Projects & Tecnology, Shell Global Solutions International BV, Rijswijk, Netherlands.
(2) Upstream Americas, Shell International Exploration and Production, Houston, TX.
(3) Projects and Technology, Shell Global Solutions US, Houston, TX.
(4) Projects & Technology, Shell Global Solutions UK, Chester, United Kingdom.

We present early deployment results from a new airborne direct hydrocarbon detection technique that maps hydrocarbon gas fluxes at the ground’s surface to kilometer scale resolution over areas of up to ~5000 km2 per flight. A critical and distinguishing attribute of this method, called LightTouch, is that it maps gas flux at the ground’s surface -not concentration anomalies in the atmosphere. These surface gas flux results detect and locate seepages associated with hydrocarbon systems and promote early focus during the frontier exploration phase of projects: helping to reduce charge risk. We present results demonstrating the method can: detect live hydrocarbon systems, help interpret secondary and tertiary migration pathways, and provide useful information on seal integrity. The resulting gas flux maps also provide valuable, strong, additional constraints to those developing subsurface models. We demonstrate the method has been able to detect, locate, and correctly quantify the mass emission rate of a calibrated gas emission source; and show it correctly locates known man-made emission sources within the survey areas.

The LightTouch data can be acquired simultaneously with gravity and magnetic data: reducing costs and operational risk by limiting the total number of flights and time in the air. The method uses proprietary ultra-sensitive gas sensors to measure the atmospheric concentrations of gases that naturally seep from hydrocarbon systems. These traces are detected as small increases over the respective, local, natural atmospheric background concentrations of those species. Using extensive meteorological data and appropriate gas dispersion modelling we are able to detect, locate and quantify the gas emission rates of the sources responsible. Typical significant emission rates are detectable from a range of many kilometres, as the gases dilute and disperse downwind of their ground level sources.

A key attribute of the technique is that it directly measures what the explorationist seeks: hydrocarbon molecules. Furthermore, as we are mapping gas flux rates at the ground’s surface, the results can be related to subsurface conditions. We are now surveying in a broader variety of climate settings and including surveys for interested third parties as a way of accelerating our deployment experience.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California