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1. 1
The “Oil Patch” in a Nut Shell
Glenn Power: geologist Power Geological Services Inc.

2. Chapter
What makes up a …
good reservoir?
05

3. Chapter
What makes up a …
good reservoir?
05
…Size matters.

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What is a reservoir?

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A reservoir has to have ‘spaces’
where oil and gas can move into
and accumulate…
This is called “porosity.”

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There are various types of porosity…

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The amount of porosity and
permeability in reservoir rocks is often
a function of the ‘parent rocks’ that the
grains are eroded from.
The distance that those grains travel
before they are deposited will also affect
the grain size and shape and degree of
sorting; all are factors which affect the
porosity and permeability.
Additionally, sand grains that are
deposited in a beach environment will
likely be reworked over and over by
wave action and tides. This results in
angular grains becoming rounded, clays
are removed and the sorting is
increased.
Geologists need to study the source of
the sediment and the environments of
deposition in order help them predict
where the best reservoirs can be found.

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Oil comes out of the ground from microscopic holes in the rock
called “pores” or “pore spaces”. The measure of the amount of
pore space relative to the amount of solid rock is called
porosity and it is expressed as a percentage. Some estimate
of the porosity is essential to determine how much oil there
could be in a potential reservoir (the size of the resource).
The next essential component of a reservoir is how well
connected those pore spaces are and how well oil or gas can
flow through the rock. This is called permeability and is
typically measured in units of millidarceys. The higher the
permeability of the rock the better the flow rate and the more
oil or gas you can produce (the larger the reserves).
Key Reservoir Rock Properties

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13. This is a “screen capture” from a geology model software package. It depicts a “highly
deviated” wellbore that penetrates the reservoir rock layers across numerous fault blocks
(faults shown with red lines). Porosity values (low to high) are indicated by the color
changes.

14. This is a “screen capture” from a geology model software package. It depicts a “highly
deviated” wellbore that penetrates the reservoir rock layers across numerous fault blocks
(faults shown with red lines). Permeability values (low to high) are indicated by the color
changes.

15. Whiterose Hibernia
Terra Nova
‘Oil in Shale’ plays
require “fracking”
to enable the oil in
place to flow.

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20. The inset image is of a 0.5mm wide pencil lead;
it is equivalent to one Upper Medium grain or
eight Lower Very Fine sand grains (coarsest Silt).

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This photo shows a range of quartz Grain Sizes from left (orange = Fine; green = Medium
and the yellowish white grains = Coarse)..
There are two pencil-pens in the Coarse grained sand (one is .5mm the lowest range for the
classification of “Coarse grained” the other is .7mm about the width of a standard cuttings
probe. Either of these can be used to help determine grain size in cuttings.

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23. The pencil lead is for scale (0.5mm wide) the inset image on the pencil lead indicates the grain size measurements. The
width of the pencil lead is equivalent to the width of 1 Medium sand grain, 2 Upper Fine sand grains, 4 Upper Very Fine
sand grains, 8 Lower Very Fine sand grains. The Lower Very Fine grain size is equivalent to the Upper Coarse Silt grain size;
silt grains are even smaller than the yellow circle shown here in the inset image.

24. These images are cuttings samples from an oil bearing sandstone reservoir. The cuttings
samples on top are oil stained (very light tan) while the cuttings samples on the bottom are
heavily cemented with calcite cement and are not oil stained (dirty white to cream). The pencil
lead is for scale (0.5mm wide).

25. These images are cuttings samples from an oil bearing sandstone reservoir. The cuttings
samples on top are oil stained (very light tan) while the cuttings samples on the bottom are
heavily cemented with calcite cement and are not oil stained (dirty white to cream). The pencil
lead is for scale (0.5mm wide).

26. The pencil lead is 0.5mm wide. It is
the width of one Upper Medium
grain, two Upper Fine grains, four
Upper Very Fine grains and eight
Lower Very Fine grains (Upper Silt).
This cutting is ~6mm x 4mm. It is
clearly oil stained, it has bright
fluorescence under UV light which
indicates presence of oil.

27. Sandstone: Medium gray to grayish brown and occasionally tan, coarse silt to upper very
fine grained, trace lower fine grained, locally grading to sandy siltstone, rounded to sub
angular, well sorted, fair to moderate calcareous cement, good, grading to very good
intergranular porosity, estimated 15-20%, trace black carbonaceous material.
Note: what may appear to be a single grain (below the inset UF) is a cluster of grains.
Upper Very Fine

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We will ‘revisit’ this slide because now we are going to look at SHALE RESERVOIRS

30. These are ‘typical’ shales
which are being drilled and
completed in the “Shale Gas”
Plays around the globe.
The alternating ‘light’ and
‘dark’ layers are indicative of
the varying amounts of
organic matter and amounts
of very fine sand and/or silt
that were deposited with the
clay minerals that make up the
shales.

32. Early estimates of how much gas would be given up by the
Barnett Shale turned out to be far too low.
Lab experiments were repeated and it was realized that
shale would give up much more gas than was previously
thought.
Then it was realized, if you scale that up to the whole area
and then to the whole Basin, the whole county and the
whole world, the amounts of gas are really quite
astounding.
People became aware of that in 2002 and 2003 and that
really got the “Shale Gas” ball rolling.

34. North America

35. The World