--> ABSTRACT: Worldwide Soil Gas Surveys Integrated with Seismic Surveys, by J. Sandy; #91021 (2010)
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Worldwide Previous HitSoilNext Hit Gas Surveys Integrated with Seismic Surveys

SANDY, JOHN

In recent years, regional Previous HitsoilNext Hit gas surveys are increasingly being integrated with seismic surveys, both 2-D and 3-D. Frontier projects benefit greatly from Previous HitsoilNext Hit gas surveys where the mere presence or absence of microseeping light hydrocarbon gas is critical information. Although semi-quantitative and somewhat subject to ground conditions, Previous HitsoilNext Hit gas patterns reveal much about trapped hydrocarbons. Interpretation models have been developed based on pattern recognition.

Previous HitSoilNext Hit gas surveys have been integrated with seismic worldwide. Examples of regional and detailed surveys are shown in North, Central, and South America, Africa, the Mid-East, and Australian Patterns are the same for similar geology, structure and type reservoir. The density of sampling is the greatest variable affecting interpretation, depending, of course, on the size and geometry of target reservoirs.

More than 10,000 regional interstitial Previous HitsoilNext Hit gas samples in ten prospective valleys in Nevada have revealed dozens of untested leads. Obvious, fault-controlled patterns are commonly seen along the faulted margins of the basins, and anomalous Previous HitsoilNext Hit gas clusters occur within the valleys. Previous HitSoilNext Hit gas microseepage values vary tremendously: Concentrations can reach tens of parts per million of the light alkane gases, methane, ethane, propane, and butane, in a background that ranges from 0.05 to 0.50 ppm.

Extensive surveys along seismic lines in several Australian basins show a remarkable correlation of anomalous Previous HitsoilNext Hit gas to well-defined seismic structures. One survey over 22 seismically-defined structures on the eastern edge of the Cooper-Eromanga Basin consisted of 2,800 samples. Only five of the seismic structures showed a strong geochem response. South of this survey, the positive Previous HitsoilNext Hit gas response over the Bodalla Oil Field stands in contrast to the negative Previous HitsoilNext Hit gas response over the Kyra dry hole only 4 km away, along the same fault, with the same type and size structural closure. Three Bodalla wells flowed more than 300 bpd each from a depth of 1,500 meters. The Kyra structure was apparently never charged with hydrocarbons.

A large reconnaissance Previous HitsoilNext Hit gas survey in a part of the Great Sandy Desert of Western Australia revealed essentially no significant Previous HitsoilNext Hit gas anomalies over an area of 3,000 square miles (7,770 square kilometers), even though significant seismic structures are present. The permit was relinquished.

There is no doubt that anomalous hydrocarbon microseepage is directly related to hydrocarbons at depth. Properly integrated with seismic, Previous HitsoilTop gas surveys are dramatic risk reducers.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.