Recently one of my friends asked whether or not there was a general trend towards improved safety in oil exploration. Coming from a mechanical engineering background, he noted that things like bridges and buildings have gotten safer over time through failures. Every new structure is built with the collective wisdom of the many failures before it. And with each failure, we learn how to avoid that specific kind of failure. Are the same principals at play in oil exploration?
I set about answering this question with data. I quickly found a list of oil spills on wikipedia. A quick pass through google spreadsheets and a few regexs later, and I’ve got the data in a form that it can be graphed with protovis, a wonderful web-based visualization package. An initial look shows some interesting trends. (Sorry IE users – modern browser required.)
First, it’s important to emphasize that this is a log-scale graph. Given the dynamic range of the input, it’s the only reasonable way to visualize what’s there, but if you’re not used to reading log-scale graphs, the data will be deceptive. In short, being a little higher on the graph means that the spill is a lot larger. In fact if would be very reasonable to only include the spills near the top of the graph when thinking about “big spills.” But I wanted to present the entire data set for completeness and analysis.
It’s interesting to note the general downward trend at the bottom of the graph. I believe this is not a real effect at all, but a result of selective memory. The smallest spill on this graph was only a couple months ago — the Great Barrier Reef spill in April. Are we to believe that in the preceeding 100 years of oil exploration there had never been a spill of less than 10 tons of oil, and only a single other spill of less than 100 tons? Of course not. I bet spills of this size have happened dozens if not hundreds of times, but 50 or 100 years ago nobody bothered writing them down. Or if they did write it down, the event has been filtered out of our collective historical memory before making it into wikipedia. The Lakeview gusher in 1909 is another interesting example of this effect. This certainly wasn’t the only oil production accident before 1930, but it was clearly an important major accident, and so has been remembered far better than others.
I’ve highlighted a few other spills because of their historical interest. The Gulf War oil spill (purple dot) of 1991 is exceptional in that it was not an accident, but a deliberate act of war. As such, it should not be considered in answering the question of whether oil exploration has been getting safer. The Exxon Valdez spill (light blue dot) in 1989 is large in our memory, but in context we can see that it was not at all a large spill by historic standards. But clearly the Deepwater Horizon spill (green dot) is huge, ranking as one of the largest spills ever and certainly the largest spill in quite some time. But aside from this current mess, there does seem to be a real trend towards increased safety in oil exploration.
Again, the log-scale graph makes this somewhat hard to read intuitively. Because the spills near the top are so much larger than the ones below them, a fair approximation of the sum of all spills can be found by simply considering the points along the top envelope, which is generally decreasing. Looking just at the last several decades on a linear scale, this trend becomes more clear: since about 1980, serious oil spills have been getting smaller / less frequent. Now we see visually that the majority of spills listed are tiny compared to the few big ones. I scaled the graph so only the bottom of the uncertainty bar for the gulf war oil spill. Also note that I’ve kept the middle dots at the geometric average of the low and high estimates, which works visually on the log-scale graph, and makes logical sense given the nature of the problem.
Another factor to consider is that the total amount of oil being produced during this time period has been generally increasing. I’ve overlaid data from the US Energy Information Administration on global oil production rate, scaled to the average amount produced each hour, to get it to show up on the same scale of this graph. Another interesting comparison which I haven’t included is the average size of each well, or the number of wells being drilled per unit time. My understanding is that oil exploration has been getting more difficult over time in that we’re having to drill deeper to get at relatively smaller oil deposits. Again, this reinforces the idea that we have been getting better and safer — we’re spilling less even though we’re drilling more holes. Except for the Deepwater Horizon.
Feel free to browse the javascript source code of the graphs for further details, inspiration, double-checking, or whatever.