What is SGE?
SGE is a generic term for surface exploration methods and stands for Surface Geochemical Exploration.
The term is not strictly used for geochemical methods but also incorporates geophysical methods such as resistivity, radiometrics, magnetics etc. Direct Detection Methods is a term also frequently used for methods relating to signal information in near surface (onshore/offshore) environments on deeper (subsurface) oil and gas deposits.
SGE methods investigate and evaluate surface alterations or surface indications originating from past or present (active) seepage of subsurface hydrocarbons towards the surface. This way, a positive indication will aid the overall exploration effort for oil and gas and ultimately reduce the drilling risk involved in the search for hydrocarbon deposits. Since SGE is independent of any subsurface geologic data and seismic models, SGE would constitute an additional, independent exploration tool.
Since seepage usually involves the more mobile, gaseous fluid constituents of reservoir hydrocarbons at depth, many or most of these methods involve the direct measurement of gaseous or light hydrocarbons near the surface or their possible interactions, alterations or expressions in near surface environments.
Visible seeps have directly or indirectly played a major role in the discovery of many pools over the past century (Link, 1952). In contrast to these visible macro-seeps, micro-seeps are invisible, but detectable with modern analytical equipment and modern data processing. Micro-seep detection claims a similar role in exploration as did seep evaluation in the past, in that the information gained from SGE surveys contributes to better exploration assessment.
All these SGE methods rely on vertical or near-vertical migration of hydrocarbons to the surface unless known geologic conditions indicate lateral migration,, e.g. along major fault zones or highly permeable, dipping beds. They further rely on the premise that they record some form of paleo- or present seepage. And they rely on the premise that economic reservoirs have, in general, a more prominent seep response than subsurface hydrocarbons in non-reservoir sections.
Seepage of hydrocarbons to the surface is not a rare event, but appears to be embedded into the natural cycle of hydrocarbon generation / Hydrocarbon reservoir / reservoir destruction. Thus, leakage of Hydrocarbons from the reservoir body appears to be ubiquitous, with small-scale leakage probably far more frequent than large scale HC escape towards the surface.
The interest in SGE methods and the development of such methods goes back to the 1930's. Then, Germans and Russians were at the forefront of this new technology. In subsequent decades, numerous methods have been invented, developed and modified to a degree, which is difficult or impossible for the explorationist to keep track of these developments, not to mention to evaluate the merits or uselessness of various SGE methods.
Even after more than 50 years of their existence SGE is very controversial. Despite considerable industry efforts in the 1950 - 1970's and into the early 1980's none of these techniques had a landmark attention, in fact, the industry had and has taken a skeptical view on these methods alongside with outspoken critics such as, e.g. John Hunt of Woodshole Oceanography Institute and Martin Schoell, formerly with Chevron. This negative image was and is, in our opinion, to a considerable degree self inflicted by the "surface explorationists" from exaggerated claims, unscientific approaches, and occasionally point blank fraud. Some of these SGE methods have a "black box" image - and deserve it because they are built around smoke-screens and obscure procedures impossible or difficult to track for the outsider.
Yet, many companies routinely use and apply some or a number of these techniques to evaluate exploration areas or their prospect inventory. Also, there is a considerable body of sincere and objective literature and published data available that clearly indicate and prove the merits of at least some of these techniques.
In our opinion, a number of SGE methods have considerable merits for exploration when carefully applied and based on data of known origin and evaluated data structure. A major mistake in past SGE approaches has been a simplified approach from the transfer of prominent, major seepage patterns to the very subtle micro-seep environment. Along this conceptual transfer is the (previously) unrecognized dramatic decline of the S/N ratio for micro-seeps and false signal interpretation due to the fact, that surface phenomena and near-surface processes may mimic seep- or seep-related patterns. In 1991 Kate Weissenberger clearly demonstrated the many pitfalls and limitations of surface gas data. These pitfalls and limitations are equally valid for other, in particular indirect SGE methods.
At CTI we attempt to educate and train exploration personnel on SGE technology. This advice and training is far from the usual listing and demonstration of "successful" case studies. Our Education sessions investigate and assess the merits of various SGE applications, their strength and value as well as their limits, shortcomings and frequent errors in interpretations and their concepts, which, at times, do not even conform to chemical and/or physical principles.
CTI is a recognized leader in SGE with state of the art in-house lab facilities and data processing units for CTI's GEL technology. This technology is the most advanced and sensitive soil gas micro-seep system available today. It is based on a rigid, systematic, and logical scientific approach which the client can understand and follow step-by-step.
It is the purpose of these CTI web pages to provide data, information, knowledge, and expert advice to those explorationists with an interest in so-called "unconventional" exploration methods.
The reader is invited to browse through the related CTI web pages, search for more information on GEL (GEL-in-depth, GEL Track Record), turn to relevant questions on SGE (SGE FAQs), search for specific articles (SGE Literature), or the reader may Contact us directly.
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