Some basic Log interpretation

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Some basic Log interpretation
Mastery Items What is the Archie Equation and
why is it important? Basic reservoir
characteristics? Basic source rock
characteristics? Lithology identification and
determination
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Archie Equation for Sw and Sxo Water saturation
(Sw) of reservoirs uninvaded zone is calculated
by the Archie (1942) formula.
Where Sw water saturation of the uninvaded
zone (Archie method) Rw resistivity of
formation water at formation temperature Rt
true resistivity of formation (i.e. RIld or RLLd
corrected for invasion) Ø  porosity a
tortuosity factor m cementation exponent n
saturation exponent which varies from 1.8 to
2.5 but is normally equal to 2.0
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Archie Equation for Sw and Sxo
Where Sw water saturation of the uninvaded
zone (Archie method) Rmf resistivity of the mud
filtrate at formation temperature Rxo shallow
resistivity from Laterolog-8, Micropherically
Focused Log, or Microlaterolog f       
porosity a tortuosity factor m
cementation exponent n saturation exponent
which varies from 1.8 to 2.5 but is normally
equal to 2.0 Water saturation of the flushed zone
(Sxo) can be used as an indicator of hydrocarbon
moveability
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Ratio Method The Ratio Method identifies
hydrocarbons from the difference between water
saturations in the flushed zone (Sxo) and the
uninvaded zone (Sw). when water saturation of the
uninvaded zone (Sw) is divided by water
saturation of the flushed zone (Sxo), the
following results
Where Sw water saturation uninvaded zone Sxo
water saturation flushed zone Rxo formations
shallow resistivity from Laterolog-8,
Microspherically Focused Log, or
Microlaterolog Rt formations true
resistivity (RIld or RLLd corrected for
invasion) Rmf resistivity of the mud filtrate
at formation temperature Rw resistivity of the
formation water at formation temperature
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Basic reservoir characteristics

• Porosity,f (Total, effective, primary, secondary
  and intercrystalline)
• Permeability (K) (Absolute, relative)
• Saturation (S) (Sw, Sxo, Sh, So, Sg, Shr, Shm)
  and their interrelationships.

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• POROUS MEDIUM
• STANDARD REALITY

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Various pore geometries with different effective
path length
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Water-Wet Hydrocarbon-Bearing Formation
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Basic source rock characteristics

• Determination of organic mattr content
• Determination of organic carbon content

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Basic source rock characteristics

• Determination of organic mattr content
• Determination of organic carbon content

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SOURCE ROCK EVALUATION
Organic matter content can he determined directly
from laboratory analyses of the source rock
samples (shale, limestone or marl), but indirect
methods based on wireline data offer the
advantages of economic, ready availability of
data and continuity of sampling of vertically
heterogeneous shale section.
A hydrocarbon source rock evaluation system is
preliminary revealed by showing the effect of the
implicated organic material on the responses of
some specific types of logs as gamma-ray,
resistivity, density and sonic logs.
The total organic matter content of the shale can
be calculated either from the gamma-ray or the
density logs.
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Discrimination of Source Rocks from Non-Source
Rocks
There is a simple classification rule for
separating source rocks from non-source rocks on
the basis of quantitative wireline log
parameters. Two equations have been used to
discriminate roughly the source rocks from the
non-source rocks, on the basis of log
combinations (Sonic-Resistivity) and
(Density-Resistivity) .
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Bulk Volume of Water The product of a
formations water saturation (Sw) and its
porosity (f) is the bulk volume of water (BVW).
BVW Sw x Ø
Where BVW bulk volume water Sw water
saturation of uninvaded zone (Archie equation)
Ø       porosity
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LITHOLOGY IDENTIFICATION AND DETERMINATION
In oil field logging applications, the prime
importance is directed to define the types and
amounts of fluids encountered in the formations.
These determinations require the calculation of
the formation porosity, consequently the
estimation of the shale volume. Thus, the shale
content is an important quantitative function of
log analysis.
VOLUME OF SHALE
Shale volume is needed for correcting the
porosity and water saturation results for the
biased effects of shale. It is considered as an
indicator for reservoir quality, in which the
lower shale content usually reveals a better
reservoir quality. In addition to the shale
volume, it is important to determine the types of
shale for choosing the appropriate shale model,
which can be utilized for selecting the suitable
water saturation model.
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DETERMINATION OF MATRIX COMPONENTS
The simultaneous equations are considered an
analytical way used normally for accomplishing
this target. Such equations have important
applications in the mathematical field. Their
uses are also extended to the geological fields,
in which they are utilized in the formation
evaluation to determine the lithologic contents
and the accompanied porosities in fractions . It
can be more easy through the use of the computer
system, due to the complexity of their solution
by manual treatment. There are four equations
reflecting the normal rock constituents (porosity
shale silica carbonate) for every type of
the porosity tools (sonic, density and neutron).
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DETERMINATION OF POROSITIES
Porosity is the volume of the non-solid portion
of the rock, that is filled with fluids divided
by the total volume of the rock .
Primary porosity is the porosity developed by the
original sedimentation process, by which the rock
was created. It is often referred to in terms of
percentage
Rock porosities are usually measured from well
logs and corrected using the porosity tools
(Density, Neutron and Sonic). These porosity
tools are largely responsive to porosity and,
also, affected by other geologic factors, e.g.
formation matrix lithology, type of fluid present
in the pores and the type of porosity. This has
allowed the use of these logs in combination for
the determination of the total porosity (?T), as
well as the secondary porosity (?sec) and
effective porosity (?E).