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Puddingstone - final slice

Hertfordshire Puddingstone

Fig 14 Schematic cross-section of the regional setting of Forties oilfield, indicating migration of oil from the underlying Kimmeridge Clay Formation. (From BP report, May 1985.)

Part Three – Reservoirs to the rescue?

In the last of three instalments, Bryan Lovell* looks back over a life in sandstones and oil, ponders the significance of events that happened 55 million years ago and reveals that the proof in the puddingstone - is of the heating.

Read Part One

Read Part Two

Geoscientist 18.8. August 2008


Half-a-century ago, those with sufficient imagination projected away to the north and east the position of the carbon-rich mudstones exposed on the shores of Dorset and Yorkshire. To the north and east lies – of course - the North Sea. We now count Kimmeridge Clay Formation as one of the most valuable rocks on the planet, in dollars as well as in stratigraphy.

Oil from the Kimmeridge Clay Formation made its way up from below, migrating into the Forties Formation, where it was trapped under a gentle arch of rock and sealed by overlying mudstones (Figure 14). Source, reservoir, trap and seal - and four billion barrels of oil in place. But the rapture of at least some of those who discovered, and recovered, that spectacular wealth must now be tempered by the realisation that they are responsible for starting a piece of unfinished business with Earth's carbon cycle.

Although getting carbon out of the ground is expensive, the customer is happy to pay because the product is so useful. But the customer has not paid for another cost in that process, the sum of which has only recently been fully recognised. The combination of hard-won fossil carbon with atmospheric oxygen bears a heavy penalty in Earth Court, which cannot simply be discharged with payment of a single fine or a limited period of community service. We have greatly accelerated the rate of release of fossil carbon. The unfinished business is to control that rate of release to safe levels.

Figure 15: team of BP sedimentologists recovering core of Forties Formation reservoir on the deck of Forties Delta on 17 May 1982. Photograph by Chief Sedimentologist (the author). As we all cope with that demand, oil geologists themselves may not feel particularly in need of redemption, despite the obloquy dished out to them by many environmentalists. But if the oil gang does feel abashed, help may lie close at hand, in their very own reservoirs.

At a time of record oil prices in the early 1980s, BP ran an experiment in enhanced oil recovery using surfactants in Forties oilfield (Figures 15 and 16). Chris Sladen led the work on the fine details of reservoir geology, especially the post-depositional changes in porosity. (For the record, these include quartz overgrowths in places and books of kaolinite across the throats of some pores.) Other oil companies and universities were engaged in comparable studies and wanted to exchange information and ideas. So, in August 1982, Sladen and I flew first-class to Hawaii to present the Forties data at a Geological Society of America Penrose Conference on diagenesis. (Yes, the oil price was really high!) Among those we met there with common interests was one Yousif Kharaka of the United States Geological Survey.

Figure 16: BP's Chief Sedimentologist pictured relaxing during core-recovery on the deck of Forties Delta on 17th May 1982. Note the immaculate and mud-free protective clothing. Now, over a quarter of a century later, Yousif comes back into my story. A recent (2006) paper, of which he is senior author, concerns the effects on the rocks themselves of storing greenhouse gases in sedimentary basins and lies on my desk as I write this. Yousif is still looking at reservoirs, but now with a view to putting fossil carbon back. The oil business will consider this idea favourably if it can make a profit commensurate with the risks. As well as considering the future price of a barrel of oil, the prospective value of a tonne of carbon put safely back underground becomes crucial. At least some of the technical and commercial skills required to produce oil and gas are comparable to those needed to inject and store CO2.

Princeton University researchers Robert Socolow and Stephen Pacala, in a study sponsored by the oil industry, do their patrons no special favours (2004). They conclude that the concentration of atmospheric CO2 must be kept at a level not far above that already reached, requiring the application of technology on a heroic scale. The good news is that the technology is familiar: the issue is not one of innovation, but of scale and motivation.

The numbers suggest that we do not have the luxury of choice between consuming less fossil fuel on the one hand, or carbon capture and storage on the other. Socolow and Pacala tell us that we need to do a lot of both, to have any hope of holding levels of carbon dioxide in the atmosphere at 550ppm by the middle of this century (Figure 17). (Then their targets get still tougher to meet.) Current oil production stands at c. 80 million barrels a day. Depending on how much you compress CO2 before injecting it, you could achieve, say, 20% of the Princeton target by pumping 80 million barrels of it underground each day, into reservoirs like Forties.

But is a new, giant industry - equivalent in size to that currently devoted to oil extraction - really going to be created, to pump carbon back underground? The prospect becomes slightly less preposterous when we consider that the oil industry is really a water industry. About three-quarters of all production from the world's oil wells is not oil at all, but brine. Include this and the total flow is over 300 million barrels per day.

Figure 17. Figure by Robert Socolow and Stephen Pacala (2006), indicating the scale of the task involved in holding levels of carbon dioxide in the atmosphere to 550 parts per million by the middle of this century.

Pumping 300 million barrels of compressed CO2 into underground storage each day would achieve most of the Princeton target. But though the potential for a significant contribution clearly exists, 300 million barrels a day looks like an oil pipe-dream. We who buy the oil industry's most useful product do so to feed the engines of planes, ships and cars - which don’t lend themselves to easy CO2 capture. However, capturing fossil carbon at coal-fired power stations is a simpler matter. The storage of their CO2 probably provides the best prospect for using the oil industry’s skills to help meet those stringent targets.

Figure 18. The thrill of the chase: Dave Pighin, a characteristically restless frontier exploration geologist, panning for gold in the mountains of British Columbia. And why should the oil industry not seize this opportunity? True, pumping waste into long-term storage is not what we veteran frontier explorers are used to, with our techno-gambler culture of high risk and high reward (Figure 18). This would be a future service industry, with a price per tonne for all carbon safely stored. The dull psalm of duty would appear to replace the trill of pleasure - but that is to set the technical challenges too low. The reservoir geology and engineering involved are interesting enough to quicken the blood of skilled young people. The task could be tackled properly between now and 2050.

Closing circles


Geological evidence is implacable. Geological processes act over periods of time far removed from human experience. Messages from rocks, read correctly, should be heeded.

The Paleocene-Eocene Thermal Maximum (PETM) at 55Ma affected evolution to the point of defining the boundary of an Epoch. Though its significance appears reduced in comparison with the drama of the closely preceding Era-ending extinctions of dinosaurs and ammonites at 65 Ma, it was a time of major change in the evolution of mammals. There was another effect on mammals at the PETM, apart from the vicious change in climate. Thanks to uplift caused by the 55 Ma hot blob in the early Iceland hotspot, distant ancestors of the present-day thoroughbred racehorse were able to browse their way from one side of the nascent North Atlantic Ocean to the other over a land bridge (Hooker, 1996). So it seems appropriate that the headquarters of British racing is at Newmarket, where the gallops stretch out over the well-drained chalk downs, formed from ooze on the Cretaceous sea floor, and first lifted up to form Cambridgeshire and Suffolk as part of the development of the early Iceland hotspot.

Newmarket is less than an hour by internal combustion engine (rather than horse) from the Hertfordshire Puddingstone quarry where this tale began. The sediments that were eventually laid down on top of the puddingstone were muds – the London Clay, through which many of the capital’s tunnels are cut. From the hippo bones it contains we know that the climate of Bloomsbury was even steamier then than when the Woolfs lived there or geologists met to exchange North Sea secrets in 1974; yet it was already considerably cooler than during the warming of the PETM, 55 million years ago.

Is there a direct link between that intense heat, and that unusual rock, the Hertfordshire Puddingstone? We cannot be sure; we do not have in these rocks the stratigraphical precision achieved by Shackleton and others elsewhere. But silica is more soluble at higher temperatures (Pettijohn & others, 1987): one may speculate that the cement that bound pebble and sand together into the plough-smashing menace of Hertfordshire farmers was formed as a result of the PETM.

The circle closes. Heat from the Earth’s interior temporarily increased at the hotspot that marked the location of Iceland in the early North Atlantic. A pulse in mantle convection at 55Ma lifted Paleogene Scotland above the waves. Erosion poured sand onto its flanks. That sand, carried further offshore into the precursor of today’s North Sea, was finally covered and sealed by layers of mud. Later still it filled with oil from below. And there it waited until October 1970, when BP came along, and drilled exploration well 21/10-1.

On proto-Scotland’s west flank the same hot blob may have triggered the PETM. Thus the same event that gave us a famous oil reservoir may also be sending us a warning about what will happen if that oil is not used wisely.

How will the age of oil end? All around the puddingstone copse where we began, flints lie scattered with fragments of puddingstone, unworked. The old joke that says the Stone Age didn’t end because Homo sapiens ran out of stone, becomes real here. Like flint and puddingstone before, oil is mighty useful, and, like those rocks, much of it may remain unused. It would be great if we could with impunity produce and consume the remaining oil in our present insouciant style, but calculations suggest otherwise.

Rocks and their messages, like the proof in the puddingstone, may be implacable; but the man-made discipline of economics is not. Economics can be changed, in response to what rocks tell us. The subtitle of Fritz Schumacher's classic (1973) work Small is Beautiful runs: "a study of economics as if people mattered”.

Many might assume that we geologists must feel rather lofty and detached about climate change because we know that the planet has seen it all - and worse - before. I don't feel very lofty or detached. I am part of a large, tribal family and I have grandchildren. When our own children were young, I ran for Parliament – unsuccessfully - against a future Labour Prime Minister and a future member of a Conservative cabinet (Michael Ancram won). In the chilly church halls of Edinburgh South, I set out an earnest programme to deal with global as well as local concerns: hunger, thirst, pestilence, inequality and wickedness in high places. Were I to run for election again, I would add emphatically the warning that we can now read in those 55 million year old rocks. I reckon the undoubted evils against which I inveighed in the Seventies can only become even more pressing if, by our own hand, we create our own extreme warming event. The time in which we now live would then, sadly and justly, surely be known as the “Anthropocene”.

We have received an important message from a warm planet. We can understand it, and we should respond - as if people mattered.

Acknowledgements:


I am indebted to Ted Nield and Nicky White for their trenchant advice on the form of this extended essay. Bryan Lovell


References


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