But that's totally the wrong way to look at it. First, the reserve
estimates you often hear quoted in the news are for estimates of
original oil in place (OOIP), the total amount of oil contained in the
reservoir. But, oil and gas aren't found in giant underground caves or
lakes but trapped in the pores of rocks.
Some of this oil is
stranded in sections of the field where the rock is impermeable, and
therefore, the oil can't reach the wellbore. And some of the oil will
simply be left behind during production; there’s no way to "pump" it
out as if it were in storage.
Typically, a producer won’t recover anything close to 100 percent of
the OOIP even after many decades of production. Some reservoirs with
lower permeability may only yield 15 percent of the OOIP. And even the
best, most permeable and most heavily developed fields in the world
rarely reach a 70 percent recovery factor.
And consider that the UK's two major fields, Brent and Forties, went
into production in 1975 and 1977, respectively. Neighboring Norway's
major fields started going into production in the early 1970s and
underwent major rehabilitation programs to boost production in the
’80s.
At any rate, not long after these giant fields entered production,
North Sea oil production began to soar. The initial growth in
production was rapid; the North Sea finally entered a sort of plateau
period in 1995. Production peaked early this decade and has since
fallen precipitously.
Although these fields will still be yielding oil (and gas) for many
years to come, the production rate will continue to fall. That's
despite the fact that some estimate that many North Sea oilfields still
contain 70 percent of their OOIP. What really matters isn’t how much
oil is in a reservoir but how quickly it can be produced.
Most fields follow some version of this "bell curve" production
profile. In other words, production ramps up quickly when a field is
first produced because underground pressures are high; natural geologic
forces drive production.
But at some point, as pressures fall, production hits a plateau. This
occurs long before all the OOIP is recovered. At this point, the
producer can use certain techniques--such as oil and/or gas
injection--to stabilize pressures and increase production. However,
these factors are unlikely to do much more than simply stabilize
production at relatively high levels.
To put this in the context of global supply, European energy giant
Total detailed some of their intermediate to long-term outlook for the
global energy markets. Total was careful to point out that the problem
is production, not reserves; the company estimates that there are about
1 trillion barrels of known reserves left worldwide. That is as much as
we have already produced since the dawn of the oil age.
Total estimates that an additional 200 billion barrels are left to be
found and new technology could allow us to bump up reserves by a
further 300 billion barrels. But due to geological and geopolitical
issues, Total sees total oil production globally peaking at 95 to 100
million barrels of oil per day.
