Michael P. Smith
Advanced Hydrocarbon Stratigraphy, Inc.
3520 South Rolling Oaks Drive, Tulsa, OK 74107-4515 USA
email: AHStrat@AOL.COM, phone: 918/445-6111
For each sample, fluid inclusion volatiles are released into the mass spectrometer as several bursts of gas. Each burst results from squeezing each sample in a series of pressure steps. Only one sample is in the analytical chamber at a time. The samples were subjected to no heat prior to, or during analyses. Following inclusion volatiles analyses, the sample is transferred to another chamber and pyrolyzed. The gas evolved by pyrolysis is analyzed by another mass spectrometer. Several hundred samples can be analyzed in one day. This high analytical throughput allows fluid inclusion maps and well logs to be constructed.
Fluid Inclusion Volatile maps and well logs can be used in petroleum, minerals, and geothermal exploration, and to address some environmental issues.
In petroleum exploration, Fluid Inclusion Volatile Well Logs can be used to map migration, seals, and proximity to pay. Migration is documented as the presence of petroleum inclusions in a significant number of samples (care must be used to recognize possible recycled petroleum inclusions in clastics and self-generated petroleum inclusions in source rocks). Seals are documented at the stratigraphic boundary of petroleum bearing inclusions, versus petroleum barren inclusions, or at the boundary of strata containing different types of petroleum in inclusions. Proximity to pay may be recognized by elevated concentrations of water soluble hydrocarbons that can be present and trapped in the water legs of oil and gas accumulations. Information about product type is also provided by the mass spectra.
The Gravberg#1 Well drilled a fractured granite, cut by several mafic intrusions. The fluid inclusion volatiles well logs show several interesting features.
1) Air inclusions are ubiquitous shallow in the well, especially in the upper 4,000 feet. This air may have been trapped as a result of the meteorite impact, and samples from Meteorite Crater, Arizona are being collected to begin testing this idea. If this is correct, than this would be a unique method of sampling ancient atmosphere.
2) Helium-bearing inclusions are ubiquitous deep in the well, especially below 13,750 feet to TD (18,440). It is possible that He-bearing inclusions were ubiquitous throughout the granite before meteorite impact, and that the impact destroyed these inclusions down to this level.
3) Methane-bearing inclusions are ubiquitous below 5,000 feet to TD, i.e. this well sampled over 13,000 feet of methane-bearing inclusions. The top of the methane-bearing inclusions is a sill, which may be acting as a seal to migration. Although the methane bearing inclusions are particularly intense in the mafic sills, they are present in almost all granite samples below 5,000 feet. Samples below 13,750 feet are particularly methane-rich. From a petroleum exploration point of view, these data are encouraging.
Very preliminary interpretation of this ongoing work suggests that fluid inclusion volatile mapping may offer a unique method of mapping paleo-meteorite-impact shock waves (ambient fluids trapped near maximum shock, and ancient inclusions destroyed).
And although this author does not at this point endorse them, it may be necessary to reconsider some of Tommy Gold's ideas.
The loan of these samples from the Gas Research Institute is gratefully acknowledged.