--> Abstract: A Regional Micro-Seep Survey of the Wyoming-Utah Overthrust Belt, by R. G. Dickinson and M. D. Matthews; #91004 (1991)
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A Regional Micro-Seep Survey of the Wyoming-Utah Overthrust Belt

DICKINSON, ROGER G., Texaco USA, Denver, CO, and M. D. MATTHEWS,* Texaco E&P Technology, Houston, TX

A regional micro-seep survey of 1280 mi of the Wyoming-Utah overthrust belt clearly identified anomalously high surface occurrences of light hydrocarbons associated with Clear Creek, Ryckman Creek, and Whitney Canyon Carter Creek fields. The ethane to propane ratios of these anomalies are very similar to those of the hydrocarbons produced from the associated fields.

Ethane, propane, and butane were well correlated on a per-sample basis, suggesting that they came from a single subsurface source (Lower Cretaceous). The poor correlation of methane with the other light hydrocarbons suggests that multiple sources of methane exist (Upper Cretaceous, higher maturity Lower Cretaceous, Phosphoria, and perhaps recent biogenic activity).

Anomalies were identified by calculating the percentage of samples in sub areas, above the complete survey median for each light hydrocarbon, and stacking these values to create a composite map. This smooths the spatial information, transforming the data into a Previous HitbinomialTop distribution and permitting statistical tests of significance. The anomalies are both stronger and spatially more extensive than would be expected on a random basis.

This use of micro-seep data emphasizes the identification of broad areas of interest, rather than the direct identification of drilling locations often associated with surface geochemical surveys. These broad surface patterns must then be combined with available subsurface data to develop play possibilities.

This technique is one of the few tools that looks directly at hydrocarbons. It provides the explorationist unique information to help reduce risk. An example of this occurs in the Crawford thrust. Unexpectedly anomalous concentrations of ethane and propane in the micro-seep data along this thrust suggests the presence of a source of wet hydrocarbons.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)