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Tight Oil (and gas) are resources trapped in the pores of rock and sands
that do not have the permeability for it to migrate.
Conventional oil has typically migrated through a permeable rock until it
hits a barrier of dense rock that traps it in a pool - which allows it to
be cheaply drilled and extracted.
Hydraulic fracturing can be done on any rock brittle enough to shatter, and
the microscopic fractures increase the rocks permeability enough to allow
the oil to flow. These sort of wells drain quickly, with decline rates in
the order of 50% common, but because the rock is impermeable, you can move
the rig over and repeat the process in an untouched area a kilometer or two
away.
The issue for PO is that the wells are costly to drill, and take
considerable resources of energy and materials (embodied energy). So the
EROEI is much lower than traditional conventional oil.
Also, like traditional oil, drillers are targeting the best quality
reservoirs first, of course, and fanciful predictions of the USA becoming a
net oil exporter rely on being able to find and drill field after field
with results as good as the Barnett/Eagle Ford/Marcellus/Fayetteville
shales that are the current production drivers. This is desperately
unlikely, on a par with saying all we need to do is keep discovering new
Saudi Arabia's and our oil issues will be solved.
Anyway, tight sands are densely packed sands/sandstones that can be
fractured in a similar way to shales, but are not the "shale" rock type.
Since it was shale that was the starting point for unconventional hydraulic
fracturing, it is often used as a short hand for the process/resource, even
if the exact stone is not shale. This drives geologists crazy, of course,
so it is often in reports authored by them that you will see the tight
sands distinction (similarly happens with limestones).
Paul also mentioned the Oil Shale (kerogen) deposits that anti-PO people
love pointing to. This partially cooked hydro carbon hasn't been in the
ground long enough and/or at a high enough temperature to convert the
carbon from life forms remains into oil. To complete the process it must
literally be cooked at high temperature to make it usable, with the
associated energy costs. To my knowledge, this source of oil has never been
commercially produced after WW2, although plenty of shysters, er,
investment brokers claim it will be economical at $x+20 where x is today's
oil price. The trouble is that when the oil price goes up, so do the energy
costs to cook the kerogen, so it is never commercial.
The other end of this process geologically, is when the hydrocarbons are
overcooked for too long. This breaks the oil down further, leaving gas. You
can imagine that there are many more deposits that are to young or too old,
rather than the just-right middle which results in crude, and so it is that
the world has much more energy in gas than oil.
In Australia in particular, we have geology that favours older, hotter
deposits, which is why we have lots of gas and comparatively little crude.
And this is why geologists can be confident there is little likelihood of
finding more Saudi Arabia style crude sources - all the rocks in the right
age/temp range have been prospected. You can also see why there are often
oil and gas deposits together or near one and other, as the conditions for
forming one eventually form the second, and different deposits are just
different times along in the process.
The last comment I'll make is that 'fraccing' has gained some very bad
press lately, and deservedly so in some cases. But in the same way that the
Deep Water Horizon oil disaster is not an analog for an oil well drilled
on-shore, the issues with potential water table pollution etc. encountered
with fracking for CSG (Coal seam Gas, also called Coal Based Methane - CBM)
are different with fracturing in most shales, which are usually much
deeper, with less risk of problems.

Regards,
Michael Skeggs

On 25 March 2013 15:12, Paul Pollard <pollard at netspeed.com.au> wrote:

> Keith
>
> An early response, from my reading, is that 'tight oil' is actually a good
> description of oil that has to be 'fracked', or forced out of the shale in
> which it lies, by pumping in fracturing, or fracking, liquid. In other
> words
> it is pre-existing oil held tightly in the shale.
>
> On the other hand, there is oil shale. This is shale which has to be mined,
> then processed by heating in retorts, to manufacture oil. This is
> inherently
> more expensive than tight oil. (Oil shale was mined and processed
> marginally
> in Australia in the past, for instance at Newnes in the Blue Mountains up
> until the 1940s. You can see the overgrown ruins of the retorts there
> today).
>
> This manufactured product of oil shale is often called shale oil, which
> can be
> confused with the pre-existing oil from shale extracted through fracking.
> That
> is why tight oil is a useful term to distinguish the two.
>
> Paul
>
>
> On Sun, 24 Mar 2013 06:51:45 pm Keith wrote:
> > "Tight oil"? I don't know what tight oil is. Can someone enlighten me?
> >
> > I read the entry on Wikipedia, and am helped a little, as I read there
> that
> > it's oil extracted through the fracking process, but is not shale oil.
> >
> > I understand tar sands, conventional petroleum and shale oil. What is
> this
> > newcomer to the issue? What proportion of current US liquid petroleum
> > production is presently tight oil and what proportion will it expand to
> at
> > its peak?
> >
> > Since I first became aware of the term about 6 months ago I assumed it
> was
> > just a slick insider term for conventional liquid petroleum, but I can
> see
> > that I was way off beam. ------------------------------
> > Keith Thomas
> > myrmecia at gmail.com
> > +44 74 2929 4146
> > ------------------------------
> > On 24/03/2013, at 6:59 AM, Jenny Goldie wrote:
> >
> > http://www.huffingtonpost.com/daniel-davis/domestic-oil_b_2898256.html
> >
> > Awash in Misinformation: America's Domestic Tight Oil 'Bump'
> >
> > Daniel Davis, Huffington Post Blog, 22 March 2013
> > On March 4, David Frum, a former special assistant to President George W.
> > Bush, published an article on CNN.com titled "Peak Oil doomsayers proved
> > wrong"
> >
> > <snip>
> >
> >
> >
> >
> >
> >
> >
> >
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