Oilfield heresy. Hydrocarbons are ubiquitous. They are found in space, out-gassing from volcanoes and Mid-Ocean ridge vents; in soils; in the atmospheres of several planets and at least one moon – Saturn’s Titan. They have been made in small quantities in laboratories, both by “cooking” organics, and by combining inorganic compounds under extreme heat and pressure. And of course, there are thermogenically produced hydrocarbons from organic-rich source rocks.
Inorganically derived hydrocarbons (abiogenesis) are well known phenomena. However, with the possible exception of a rare, oddball field or two, they have thus far not played a role in the business end of hydrocarbon exploration. For some, the subject of multiple hydrocarbon sources cannot even be broached, achieving the status of heresy.
In the last 25 years, the categories of life have been redefined, assigning our familiar Plants and Animals kingdoms to just one of three domains, the Eukarya; Bacteria and Archaea comprise the other two. The Archaea are extreme in many respects. For one, size. They are just barely large enough to harbor a DNA molecule, which makes them very difficult to locate, isolate and characterize. They also prefer to live in extreme environments of hot, cold and salinity that would kill other life forms. We know that they play a role in degrading oil, in moving sulfur in and out of oils, in producing methane and sulfuric acid, and they may have many other functions. But our knowledge of them is paltry. The fate of their corpses and/or their unique food and waste processes may reveal roles in hydrocarbon generation and migration no one has even guessed at.
When it comes to the Archaea and hydrocarbons, there’s much that we do not know. So, what does happen to dead Archaea?
The Hedberg research conferences are organized by the AAPG Research Committee, which selects a topic for critical examination. I was surprised to find that there was a Hedberg conference entitled, “Origin of Petroleum – Biogenic and/or Abiogenic and Its Significance in Hydrocarbon Exploration and Production.” Because abiogenesis is partly a cultural difference between Russia and the West, the conference needs to be held somewhere in between. It is scheduled for July 11 – 14, 2004, in Vienna, Austria. Perhaps due to malaise, cowardice, or lack of corporate backing, the conference is on thin ice and needs your support. In attendance will be Michel Halbouty, Peter Odell (Erasmus University), Barry Katz (ChevronTexaco), Ernest A. Mancini (University of Alabama) and other fearless individuals.
Because this is such a hot-button topic to say the least, perhaps even dangerous to one’s career, AAPG and the others deserve some accolade. It’s always good to remind ourselves of long-held beliefs that were extremely difficult to overturn, such as: the Earth does not revolve about the sun; there cannot be life without sunlight; continents do not pull apart; and the Earth is only 10,000 years old. Kudos to one and all for having the gumption and gall to promote these free-thinking forums. Without such effort and courage, we would never break free of the paradigms of past thinking, tradition, culture, and what is known. If you’d like to attend, speak or otherwise contribute, write Debbi Boonstra at: firstname.lastname@example.org.
New findings about petroleum systems. Five years ago, the Gas Research Institute (now GTI) funded a study through Cornell University about petroleum genesis, migration and capillary seals. The results showed some remarkable findings. At its core, the study involved chemical analysis of 138 non-biodegraded produced oil samples taken from four Gulf of Mexico fields, representing a 77-mi by 124-mi swath (from north to south: Tiger Shoals, South Marsh Island 9, South Eugene Island 330, and Jolliet). Although not the original focus of the study, it was discovered that the n-alkanes (C10) hydrocarbons varied in a regular manner through the area. They were intact at the southern end of the swath, but gradually disappeared toward the northern end, where they were 90% (by weight) depleted. The gas washing is occurring in high-permeability migration pathways.
Based on computer modeling of the geology and sedimentation and on geochemical work by Dr. Peter Meulbroek, which was his doctoral thesis at Cornell, the missing fractions are due to gas washing during migration. One outcome of this is further confirmation of the enormity of the hydrocarbon throughput required for this result.
I spoke with Cornell researcher Dr. Larry Cathles, one of the principal investigators in the study. He said 2.6 billion bbl of oil and 45 Tcf of gas has been discovered in the small study area, but its source rocks have the potential to generate 1,400 billion bbl of oil and 8,600 Tcf of gas – more than have been produced in the world throughout history. This area of the GOM is a highly active flow-through system, where more than 90% of the hydrocarbons generated are vented into the ocean, and reservoirs have been filled very recently, geologically speaking.
Other geochemical evidence points to two sources across the study area. One is Jurassic carbonate source rock that extends uniformly across the area and creates sulfur-rich oils. The other is silicate Eocene sources that create relatively sulfur-poor, oleanane-rich oils. Replacement of one oil type by another can help determine migration rates. Combining migration rates, gas-washing patterns and oil-replacement models can yield useful reconnaissance about where the next reservoir may lie.
Geochemists that I spoke with were not too critical of the study, rather, intrigued, wanting to know more. Although I do not want to overstate its significance, it is clear that this one has legs.
A brief article can be found at: www.gastechnology.org under publications, Spring ’03, Gas Tips. The report is available in a six-volume set, including stratigraphy, chemical analysis, and selected petroleum data in a GoCAD project, through GTI (GTI-03/0065).
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