Iraqi Journal of Chemical and Petroleum Engineering
Vol.16 No.1 (March 2015) 71- 78
ISSN: 1997-4884
Formation Evaluation for Nasiriyah Oil Field Based on The Non-
Conventional Techniques
*Ayad A. Alhaleem, Antwan M. Avedisian,and Haider Alwan Flayeh
*Petroleum Engineering, University of Baghdad
Abstract
The unconventional techniques called “the quick look techniques”, have been
developed to present well log data calculations, so that they may be scanned easily to
identify the zones that warrant a more detailed analysis, these techniques have been
generated by service companies at the well site which are among the useful, they
provide the elements of information needed for making decisions quickly when time
is of essence
.
The techniques used in this paper are:
Apparent resistivity Rwa technique.
Rxo /Rt method.
The above two methods had been used to evaluate Nasiriyah oil field formations
(well-NS-3) to discover the hydrocarbon bearing formations. A computer program
had used to represent CPI results for the two mentioned methods, the results of
interpretation indicate to hydrocarbon zones in.
Key words: Nasiriyah Oil Field, quick look techniques.
Introduction
Nasiriyah structure was discovered in
1975 through a seismic investigations
covered partially the southern part of
Iraq by Iraqi National Oil Company
(INOC).this structure had clearly
appeared at that time as a longitudinal
anticline
[1]
.Five oil wells had been
drilled to Sulaiy formation during the
period 1978-1987.
It is considered as giant oil field in
southern part of Iraq and located in
Nasiriyah area.Nasiriyah oil field is
located in the NW-SE oriented
mesopotamian zone extending across
the alluvial plains of the Euphrates-
Tigris valleys. The mesopotamian zone
is characterized by quaternary
molasses and absence of surface
relieves of folds
[2].
Apparent Resistivity Rwa Technique
The Rwa techniques also called the
quick look techniques which is useful
for detections of hydrocarbon pay
zones and estimation of water
saturation and formation water
resistivity, Rwa define as[3][4]:
Rwa = Rt / F ……………… (1)
Where: -Rtis the true formation
resistivity from well logs, and F = 0.62
Ø
-0.25
which is Humble equation
*
.
Iraqi Journal of Chemical and
Petroleum Engineering
University of Baghdad
College of Engineering
Formation Evaluation for Nasiriyah Oil Field Based on The Non-Conventional Techniques
72 IJCPE Vol.16 No.1 (March 2015) -Available online at: www.iasj.net
*: Humble equation has been used in
sandstone and carbonate formations,
which are the main lithological column
of the studied area.
Porosity had been calculated from
sonic or neutron logs, in clean water
bearing zones, the reading of deep
resistivity tool will approximate to Ro
and because:
Ro=F. Rw…………………….. (2)
So as:
Rwa =Rt / F = Ro / F = Rw……… (3)
It follow that, in hydrocarbon zones
Rt>Ro so that Rwa>Rw.
Simple rearrangements to Archie
equation (1) and substitute of equation
(3) will results in:
Swa= (Rw/ Rwa)
1/2
.…… …. (4)
The water saturation is related to as
apparent due to this method is
unconventional one, in practice Rwa
may be calculated or read it directly
from well logs in the section of
interest, Rw also may be calculated
from SP or from formation water
analysis. If Rwa/ Rw calculated the
hydrocarbon zones can be defined
according to equation (4).
Restrictions of Apparent Resistivity
Rwa Technique
The Rwa technique is still applicable
when water resistivity Rw is unknown.
However two conditions must be
fulfilled [3][4]:
1- Water zones must be present in the
section evaluated.
2- No abrupt salinity changes can
occur over the section of interest so
that the Rw can be considered as
constant, therefore the (Rwa) min
in water bearing zones is then
selected to define Rw.
Abnormally high Rwa values can be
displayed by zones other than
hydrocarbon. Relatively high-
resistivity shale will display a high
Rwa values. Shale zones can be
distinguished easily by shale indicators
such as gamma ray and SP logs. Cycle
skipping of the sonic log will also
cause high Rwa values [3][5].
The Rxo/Rt Method
To economically establish the
existence of producible hydrocarbon
reservoirs (oil & gas), well logs
contain key information about the
formation drilled in different
petrophysical measurements, among
these measurements are (SP and
Resistivity)
[3].
This method was introduced by
Dumanoir et al.
[6]
for well site
interpretation. This technique involves
computing log (Rxo/Rt)from either the
RLL8/RILd or the RSFL/RILd ratio and
recording it as a comparative curve
with the SP. Separation between the
properly scaled (Rxo/Rt)curve and the
SP provide a quick- look location for
the producible hydrocarbons [3].
The Rxo/Rt method is based on the
calculation of the parameter (Esp)QL
derived from the ratio Rxo/Rt,so
[1][6]
:
(Esp)QL= -K log (Rxo/Rt) ………… 6
Because Rxo= F .Rmf / Sxo
n
and Rt=
F. Rw / Sw
n
then: Rxo/Rt= (Sw/Sxo)
n
(Rmf / Rw)
Then equation (6) becomes:
(Esp)QL = -K log{(Sw/Sxo)
n
(Rmf / Rw)}
…… 7
After re-arrange the above equation,
then it will became;
(Esp)QL= -k{log(Rmf / Rw) +
log(Sw/Sxo)
n
} ….. 8
Ayad A. Alhaleem, Antwan M. Avedisian,and Haider Alwan Flayeh
-Available online at: www.iasj.net IJCPE Vol.16 No.1 (March 2015) 73
Fig. 1, Swa Results from Mishrif to Zubair formations
Formation Evaluation for Nasiriyah Oil Field Based on The Non-Conventional Techniques
74 IJCPE Vol.16 No.1 (March 2015) -Available online at: www.iasj.net
Fig. 2, Swa Results from Zubair to Sulaiy formations
Ayad A. Alhaleem, Antwan M. Avedisian,and Haider Alwan Flayeh
-Available online at: www.iasj.net IJCPE Vol.16 No.1 (March 2015) 75
The calculation of (Rxo/Rt)does not
require knowledge of porosity,
formation factor, or Rw. The technique
is most suitable for cases where
porosity is not available or cannot be
determine accurately owing to complex
lithology, or when F-Ø relationships
are in appropriate
[7].
The main advantage of this method is
to[7]
(provide a means for locating
hydrocarbons), because the proven
presence of hydrocarbons does not
necessarily mean commercial
production, this method is an
appropriate companion to techniques
that only indicate hydrocarbon
presence, such as the previous method.
But the measured Esp is (Esp) log
can be approximated by the term {-k
log (Rmf / Rw)}; therefore:
(Esp)QL= (Esp)log – k log(Sw/Sxo)n
… 9
In water bearing zones or in the
zones with no movable hydrocarbons
Sw= Sxo ,then (Esp)QL= (Esp)log
and the separation will be negligible
,otherwise in movable hydrocarbon
zones the (Esp)QL will separate from
(Esp)log and (Esp)QL< (Esp)log
this is due to (Sxo>Sw) and
log(Sw/Sxo) < 0, the results are shown
in the figures (3) and (4) respectively.
Finally it is more important to know
that the Rxo / Rt method is applicable
to fresh mud, (Rxo>Rt) in formations
where invasion falls within the limits
demanded by the (Rxo/Rt)
computation
[7].
Evaluation of the Unconventional
Methods
The results of these methods indicate
to presence of hydrocarbons in
Maudud, Nahar Umar and Zubair
formations respectively in addition to
the conventional reservoirs (Mishrif
and Yammama), table (1) show the
results of these methods in Nasiriyah
oil field which are contiguity to the
results of DST and flow test.
Table (1) Hydrocarbon zones by
nonconventional methods
Conclusions
The detected oil zones in this study
are compared with the results of
conventional interpretation with actual
Archies’ parameters (a, m and n ),DST,
flow test and daily drilling reports
,from which we can be sure that most
zones that interpreted as oil are correct
because of convergence between the
different interpretation methods and
the provided reports data.
N FM. Rwamethod SP(QL)
Top Botto
m
Top Bottom
1 Mishrif
2006
.8
2026 2007.4 2019.5
2029 2085 2026 2074
2 Maudud
2265
.1
2268.4
2281 2289
2296 2304
2321 2323 2319 2322
3
NahrUm
r
2416
.1
2422.4 2414.3 2422.8
2505 2517
4 Zubair
2937.8 2940.5
2984 2988.7
5
Yamma
ma
3185
.7
3218.2 3184.2 3221.5
3227
.5
3238 3248.4 3268
334
2
3363 3280 3285
3326 3333
3358 3363
Formation Evaluation for Nasiriyah Oil Field Based on The Non-Conventional Techniques
76 IJCPE Vol.16 No.1 (March 2015) -Available online at: www.iasj.net
Fig. 3, Rxo/Rt method results from Mishrif to Zubair formations
Ayad A. Alhaleem, Antwan M. Avedisian,and Haider Alwan Flayeh
-Available online at: www.iasj.net IJCPE Vol.16 No.1 (March 2015) 77
Fig.4, Rxo/Rt method results from Zubair to Sulaiy formations
Formation Evaluation for Nasiriyah Oil Field Based on The Non-Conventional Techniques
78 IJCPE Vol.16 No.1 (March 2015) -Available online at: www.iasj.net
References
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