Weekly Petroleum Geoscience DigestANTICLINE: The Petroleum Geologist’s Rainbow! – 8 August 2017 - By Dr Livinus Nosike
On today’s digest, I introduce to you one of the most
important structure in petroleum geoscience.
An anticline is a curved layer of the
earth; it is like a curved bridge made of rocks (see the above picture of an
anticline). When it curves on all sides, like an inverted pan covering
what is underneath, it is called a dome. In petroleum
exploration you say it is a four-way closure. That is, it closes or
covers the oil and gas lying below on all sides. Anticline is perhaps the
most important structure in oil and gas exploration and production. That
is why I call it the petroleum geologist’s rainbow. Do you find anticlines
in a sure petroleum system under the ground? You must drill it for oil…
I still remember that first day in a field geology
class, and eventually in a structural geology lesson, when that shape was drawn
on the board – a simple inverted curve like a rainbow. That day I learnt
that it is even more important if it is broken and shifted, what is known
as faulting, as that further traps the oil below. I never
knew this will become the most important and sought out geologic feature I will
be looking for in oil and gas evaluation. Surprisingly anticlines are not
hard to find!
Have you been driving along a road and on the side you see curved earth,
curved rock or sedimentary layers? That is an anticline. Does it
look as if it is covering a sand body below? Are the earth layer
dark and the sand inside whitish? You may be looking at a trap structure
capable of holding in place oil and gas. In a sandstone-shale
sequence, common in Nigeria and most petroliferous regions of the world, the
sandstone holds the oil and gas while darker layer known as shale seals the oil
below. From now onwards, you
are an anticline hunter! I permit you to find one as
soon as possible.
In the picture above, my friend and I are standing
just beside one, along the road, during a geological field trip. Let me know if
you find one.
So why is anticline very important?
It is because oil floats above water, always rising
higher until it escapes. There is oil and water in pore spaces almost
everywhere under the ground in petroleum zones. Problem is that while the
water remains and is kept in place by gravity, the oil floats and escapes. All
we need is to find places where the oil overlying the water is not able to
escape. Anticlines do the job, it closes the oil and gas on the sides and have
them trapped on the central conical top of its structure.
For an anticline to be very useful, it has to be
deeply buried under the ground. Sorry, that anticline you found on the surface
along the road cannot retain the oil in it because they are cut or too close to
surface where the oil is able to leak out, is able to escape. Seismic
images are used to see anticlines under the ground. Also during geologic
field trip, you can use a compass, clinometers and other tools, to detect and
measure places where only a bit of the sides of the anticline, known as flank,
which usually looks like bent rocks, are exposed on the surface. They
suggest, and help you to predict, that the major part of the anticline is
buried deep under the ground.
That is our work as geoscientist. Are you
interested?
Join me again for next
week’s edition of petroleum geoscience digest or visit the news section of this
website for previous editions of the digest.
For more info, contact Dr
Livinus Nosike: contact@iesog.com
Dr
Livinus Nosike holds a PhD in
Sciences of the Universe - Tectonics and Petroleum Geology, from the University
of Nice-Sophia Antipolis, France, following a development of talent award to
study for his postgraduate education in Europe.
He worked in technical centres in different countries, onshore and
offshore, before returning to work in Nigeria. He is a Member of the Nigerian
Association of Petroleum Explorationists and the American Association of
Petroleum Geologists
Dr Nosike is the author of the book:
OVERVIEW OF THE OIL AND GAS
INDUSTRY – A New Perspective in the Saga of the Oil and Gas Struggle. The
book is now available in bookshops in every State of Nigeria www.iesog.com/bookshops
He is the Founder of IES Oil and Gas (iESog) www.iesog.com,
the first fully-integrated indigenous oil and gas training and services firm
with the aim of equipping every Nigerian with petroleum knowledge.
Twitter.com/DrLivinusNosike
Instagram.com/DrLivinusNosike
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