What's new in exploration

	Vol. 224 No. 3
PERRY A. FISCHER, EDITOR

 Slick data. In the years that I spent offshore, it wasn’t unusual to call MMS to report that “a slick is moving through our field.” This protected us from the potential bad luck of having an MMS-chartered helicopter, flying overhead at that moment, concluding that the slick must have originated from our operations. Although we often knew the source – either a neighbor or ourselves – as the distance from shore increased, many of those slicks were bona fide mysteries, and years later we would learn that these were caused by natural seafloor seeps.

 An editorial comment by MMS director Johnnie Burton said a recently released report from the US National Academy of Sciences – Oil in the Sea III – found that 1,700 barrels of oil per day enter US marine waters. This is “about 150 times the amount from oil and gas activities,” the editorial states, which translates to about 11 bopd.

 Considering the thousands of wells drilled offshore, in bays and in coastal marine environments, plus the thousands of producing wells and platforms, it is absurd to suggest that only 11 barrels of oil a day enter the marine environment from all E&P activity throughout the continental US and Alaska each year. This would mean that there was essentially 0.0-ppm oil in all produced water and drilling discharges, and would include oil from all leaks, drips, bilges, pipelines, tankers, supply boats, crew vessels, and so on.

 It’s bad enough when the environmentalists exaggerate the “damage” caused by the effects of oil and gas operations. Here, Burton is overdoing it on the other side and, in the process, damaging the credibility of her office. The last thing our industry needs is distortion to counter exaggeration. The greater points are that folks need to be aware of how much oil naturally seeps into the environment, that 1,700 bopd is a believable figure and that nature has evolved methods for handling it.

 AVO: a quantitative DHI. Recently, 90 members of the Geophysical Society of Houston woke up an hour or two early, braved a rare, cold winter morning, and drove the extra miles to Core Labs’ offices to hear a presentation on AVO from ExxonMobil’s Kurt Rudolph. This was a remarkable turnout for our little Society, considering the conditions. I mention these only to underscore the interest this topic continues to garner. 

 I recall that only four or five years ago, I was of the opinion that AVO was being over-hyped, that while it theoretically could distinguish rock properties and pore fluids, it was rife with problems. Numerous people that I had spoken with helped me form this opinion, and I’m sure that some are still of that mind.

 What seems to be happening in seismic is akin to what happens in computer technology: The hardware runs years ahead of the software. While the industry has been very good at acquiring high-quality seismic data at low cost, it takes longer to learn how to best apply a given processing/analysis algorithm in a particular geology. Such is the case with Amplitude Vs. Offset. And then the question arises: How much should a company share what it has learned? For ExxonMobil’s part, it’s allowing an overview of how it has learned to use AVO successfully. If you get a chance to see one of Mr. Rudolph’s presentations – go; you will not be disappointed. Although beyond the scope of this column, here are a few highlights of his presentation.

 ExxonMobil quantified what was otherwise a qualitative technique. They first determined when the technique is best applied. Then, in a systematic way, they assigned numeric confidence levels to each category of result. Integrating these, they arrived at an overall indicator as to the likelihood that the prospect contained commercial quantities of hydrocarbons, hence, a Direct Hydrocarbon Indicator (DHI). The bottom line is that the company says the method has boosted its exploration success rate by 20%. That’s a remarkable number, and it is likely to improve. That’s because, looking back, the method beat the experts in that, at above the 80% confidence level (i.e., drill here), the geoscientists were too pessimistic. Similarly, when the method fell to low levels, say, 20% (i.e., don’t drill), the explorationists were too optimistic. 

 One caveat: The method requires some additional man-hours. All the good geology and conventional hard work that would normally be done must come first. AVO analysis is not a substitute for these.

 Zircons from Hades. Living without surety is maddeningly difficult. The mind wants to believe. Yet certainty is a dangerous luxury for a scientist to indulge in – especially a geoscientist. If you thought you knew, well, almost anything, it would be best if you added, however subtly, a grain of doubt such as, “Of course, I could be completely wrong.”

 I hope that you didn’t too firmly believe that the Earth was 4.5 billion years old, or that life first appeared 3.5 billion years ago (Ga), or that the first rocks formed 3.8 Ga. Within the last decade, there has been increasing evidence that questions these long-held views.

 Zircon is a mineral containing a trace amount of uranium, and it preserves its original oxygen isotope values. Both of these characteristics make it particularly useful for determining geologic time, because it is virtually indestructible in the weathering process.

 The Hadean eon stretches from the Earth’s formation to 3.8 Ga. It is an environment characterized as so hot that neither rocks nor liquid water could exist. The problem is, zircons recently found in the Jack Hills in Western Australia test at 4  –  4.4 Ga. Worse yet, they appear to have been part of ordinary surface rocks such as granite. Furthermore, geochemistry indicates that the zircons clearly had contact with liquid water. What this means is that, at least as far as the geochemical analysis shows, Earth would appear to have either formed much earlier or cooled much quicker, and would have had liquid water – with its implications for oceans and life – 500 million years earlier than anyone had previously thought.

 To be sure, everyone agrees that it would be unwise to tear asunder the geologic foundations upon which the continents were built, all because of a few errant zircons. But, hey, it’s a start.