CompuServe Messages

>>Did you snag any of the earlier posts on this thread?<< Nope. Sorry if I repeat. >>more precise details of how they came to that conclusion and how they rule out some potential confounders.<< Every organic "ooz" has a chemical "fingerprint" comprised of ratios of atoms which are found in various organic materials, and ratios of molecules of different types. What plants and animals were present during deposition, what fluids present, atmostpheric conditions, etc., all go into making the fingerprint. There is a further fingerprint as a result of what is called diagenesis, or chemical changes to the rocks after burial. Geochemistry is a well grounded and mature science. The rocks and fluids all interact during diagenesis in ways that are controlled by geochemical processes and understandable via that science. Everything is predictable. You got the original stuff, you got the energy and forces applied as a function of time, you got the washing action of subsurface migratory fluids …. add 'em all up in your organic chemistry equation and *presto* you have only one possible fingerprint of oils that can be "cracked" from the source rock. Lo *AND* behold, you look around near the organic source rock and *there it is*!! Some oil (or gas) with just the right fingerprint for it to have come from that particular source rock. Other possible sources? Nope. There are too many coincidental trace atoms (primarily vanadium and gadolinium, but others exist) that have nothing to do with oil, per se, in both the source and the product of that source. There can be no other source from which the observed mix of molecules in thier respective fingerprint encarnations could have been cooked up. Add to that the new papers published by a Louisiana U. Prof showing the re-charging of known, depleted reservoirs close to source rock, where the fingerprint of the source rock matches the fingerprint of the oils produced in the reservoirs up to initial depletion and now matches the oils produced today after recharging. Any other explanation for the source of the oils besides the most available one (the organic source rock) must thus be discarded as being overly "energetic" in its untold and most probably dubious mechanisms. >>how do you use nuclear sensing??<< Chemical and electrical sources attached to metal tubes (2 to 5 inches in diameter) filled with computer equipment, sealed against 20,000+psi pressure and 350 deg f temperature are lowered on miles-long cables down drilled holes (8 to 12 inches diameter). Chemical sources produce moderate energy (ca. 3 Mev) neutrons and gamma rays that leave the tool, bang around in the formation, and finally return to the tool detectors for measurement (energy, time, numbers). The measured signals are encoded and sent up the cable for recording and processing at the surface, or transmission via satellite to the "home" office for perusal and processing. Electrical sources use deuterium and tritium (charged particles) in high voltage, staged electrical discharge-like ramps to crash these atoms together and cause high energy (14 Mev) neutron production. The neutrons interact with tool, borehole, and formation materials, slowing down to thermal levels. They are then absordbed by various materials and produce gamma ray radiation time and energy spectra. From all of these measurments it is possible to compute elemental abundances of hdyrogen, carbon, oxygen, calcium, gadolinium, etc., void space in rocks (holes in which the oil and gas exit), mineral types and abundances, fluid types and abundances, fluid flow characteristics, and rock mechanical properties (these last two require electrical and acoustic measurments to really be performed properly). The radioactive sources used are extremely dangerous if you were to hold them in your hand, but proper shielding and operating proceedure reduces risk to very small indeed. Companies like the electrical sources better because if an accident occurrs and you loose a source in the hole or stick a tool in the hole then all you have to do to render the source inactive is pull the cable off the tool at what is called the weak-point (a specially designed connection which allows the engineer to break the link between tool and cable should the need arise. Don't worry about the chemical sources ….. there are extreme saftey measures required by the government to control and monitor source loss and recovery operations. It doesn't happen often, but when it does there are enough saftey proceedures and container-strength requirements that there has never been any real problem in all the years of use ….. and in the overall scheme of things, the sources may be dangerous to a person's hand, but the amounts of material in any one tool is pretty small. Even so, the government acts like its a 3 Mile Island when talking about this type of stuff. And I guess it is a good idea, really, because by over reacting they ensure that not one atom of unwanted material ever has a chance of harming anyone. So these technologies are quite useful and extremely safe. After a measurement is produced and evaluated, the data is merged with data from acoustic recodings of explosions set off on the surface (siesmic cross-sections or lines). The size of the reservoirs is able to be deduced from processing of many such lines. Also, the physcial properties of the rocks and fluids in those reservoirs can be estimated based upon many well measurement records, called logs, together with those lines. This is how you tell not only where any oil/gas might be in a well you just drilled, but you also can predict the economics of recovery based upon these measurments (nuclear and otherwise). Is that more than you ever wanted to know about petrophysical well logging and data processing?