1. technology and computing

SPWLA 55th Annual Logging Symposium, May 18-22, 2014
WHAT IS Rt? LOGGING-WHILE-DRILLING AND WIRELINE
RESISTIVITY MEASUREMENTS SPOTLIGHTED: AN OFFSHORE
CASE STUDY IN ABUDHABI
Amr M. Serry, Sultan A. Budebes, and Hassan Aboujmeih, ADMA OPCO;
Ahmet Aki and Michael Bittar, Halliburton
Copyright 2014, held jointly by the Society of Petrophysicists and Well Log Analysts
(SPWLA) and the submitting authors.
This paper was prepared for presentation at the SPWLA 55th Annual Logging
Symposium held in Abu Dhabi, United Arab Emirates, May 18-22, 2014.
practices for both well-placement and petrophysical
evaluation.
INTRODUCTION
ABSTRACT
Recent technology improvements in logging-whiledrilling (LWD) electromagnetic wave propagation
resistivity
devices
have
provided
dramatic
improvements
in
well-placement
applications.
Azimuthal, deep-sensing measurements, coupled with
other sensor measurements and significant software
enhancements, have facilitated enhanced geosteering
capabilities, which not only help maximize reservoir
exposure, but also provide real-time updates of the
local reservoir model.
However, LWD propagation resistivity measurements
in highly deviated and horizontal holes can also
present challenges to the analyst in answering
fundamental questions in relation to formation
evaluation. Typically, it is not only problematic to
correlate LWD resistivities to offset vertical and/or
pilot resistivity data, but it is also difficult to deduce
true resistivity (Rt) and the flushed zone resistivity
(Rxo), particularly in thin beds, from the numerous
multi-frequency and multi-spacing measurements
available.
This paper presents a case study from a thinly bedded
offshore carbonate reservoir in Abu Dhabi. Two
horizontal drains were drilled using LWD tools for the
purposes of geosteering and formation evaluation. The
available offset well data were from near-vertical
wells, which were logged using wireline tools. The
LWD
propagation
and
laterolog
resistivity
measurements are compared to the offset wireline
induction and laterolog resistivity measurements.
Comparisons are also made between LWD
propagation and laterolog resistivities acquired while
drilling and while wiping after drilling. Differences
between the various measurements are explored to
identify the most appropriate choice of measurement
in various circumstances. In light of the results,
recommendations are made for data selection in future
wells, with the intention of optimizing data acquisition
The formation evaluation of carbonate Reservoir-A,
located in one of the largest oil fields in offshore Abu
Dhabi, has been historically performed using a variety
of traditional logging tools. Beginning in the 1960s
and continuing to the present day, many wells are
cored and various formation evaluation techniques are
used. For example, elemental spectroscopy, nuclear
magnetic resonance (NMR), array sonic, dielectric,
and image log data are used for benchmarking against
core data analysis. However, some layers of ReservoirA have not yet been developed because of their lower
porosity and permeability compared to other layers
that have been major producers for many years. A
hydrocarbon
saturation
assessment
of
such
undeveloped carbonate layers is very critical. The
saturation computation model (Archie) is applied as
follows:
(
) =
Where,
∅
∗
................................................(1)
Sw = Water saturation in the uninvaded zone, %
a = Tortuosity factor
n = Saturation exponent
m = Cementation exponent
Rw = Formation water resistivity, Ohm-m
Rt = True formation resistivity, Ohm-m.
To obtain more control of the computed saturation
values, measurements of a, m, n, and Rw are
conducted at reservoir conditions at the core laboratory
and applied for each layer of Reservoir-A.
After calibrating the computed porosity with core
porosity for cored wells across the field, the remaining
element is to compute an accurate value of the Rt.
1
SPWLA 55th Annual Logging Symposium, May 18-22, 2014
Historically, this is achieved in the early phase of
development by combining the resistivity seeking
laterolog and the conductivity seeking induction array
deep-resistivity log using a unique software package
developed by service companies. To help minimize
acquisition costs and reduce the length of the
conventional logging string, while at the same time
staying coherent with the low-salinity-mud highformation-water salinity contrasts, laterolog-type tools
have been used later in the life of the field for modern
wells solely to acquire resistivity data. Then, a
resistivity inversion algorithm is applied to reconstruct
much more reasonable values for Rt after correcting
for invasion, shoulder beds, and sometimes for
formation dip, assuming a piston-like mud filtrate
invasion profile.
hydrocarbon in place, based on log saturation (Rt
driven) that must be to the highest possible accuracy,
while during drilling, openhole log data acquisition
must be performed with minimum operation time and
cost and cannot be compromised because the
estimation of hydrocarbons in place, based on log
saturation, must be very accurate.
WELL PLAN AND DESIGN
The original deviated pilot hole, shown as a black line
in Figure 2, was drilled at a 47° inclination. To
determine the resistivity profile of the well, the well
was logged with both wireline induction and laterolog
resistivity tools. After evaluating the pilot hole,
another sidetrack mother hole was drilled at a 63°
inclination. LWD tools were used in the evolution of
the sidetrack hole. Azimuthal deep resistivity (ADR)
and gamma data were acquired in real time, and
another wipe run was performed with ADR, gamma,
azimuthal litho-density (ALD), and compensated
thermal neutron (CTN) sensors, which are shown as a
blue line in Figure.2. After evaluation, two horizontal
drain wells were drilled. Drain 1 was drilled in
Reservoir-A, Layer 2 (shown as a green line in Figure
2), and Drain 2 was drilled in Reservoir-A, Layer 1
(shown as a red line in Figure.2).
To compensate for the limited vertical thickness and
low petrophysical properties of the undeveloped layers
in Reservoir-A, compared to other layers that have
been producing for years, ambitious development
plans include excessive drilling of horizontal and highangle wells into the undeveloped layers, which have a
porosity of up to 9% and permeability ranges between
1 to 10 md, as highlighted in the red envelope of the
crossplot of Figure.1.
Figure.2 Well plan and design showing original
deviated pilot and sidetrack mother holes together with
two horizontal drains.
Figure.1 Conventional Core Analysis (CCA) porositypermeability crossplot of Reservoir-A.
CHALLENGES
EVALUATION AND PLACEMENT OF DRAIN 1
IN LAYER 2
Consequently, there are many possible challenges to
consider, from geosteering operations to the start of
well production. Primarily Estimation of the
Pilot Hole Wireline Evaluation. The original pilot hole
drilled at a 47° inclination was logged with wireline
2
SPWLA 55th Annual Logging Symposium, May 18-22, 2014
gamma ray, density, neutron, and both induction and
laterolog wireline resistivity tools (Figure 3).
Reservoir-A, Layer 2 at a 47° inclination represented
in true vertical depth (TVD) scale.
Sidetrack Mother Hole LWD Evaluation. The sidetrack
mother hole was drilled at a 63° inclination. LWD
tools were used in the evaluation of the sidetrack.
Figure.5 displays the LWD logs obtained in drilling
and wiping mode. The gamma ray log is displayed in
Track 1. The ADR log obtained in drilling mode is
displayed in Track 2, and the ADR obtained during
wiping mode is displayed in Track 3. ALD and CTN
logs are displayed in Track 4. Both Track 2 and Track
3 display the 16-in., 32-in., and 48-in. phase
resistivities at 2 MHz and 500 KHz frequencies.
Figure.3 (A) Original deviated pilot hole wireline logs
and petrophysical interpretation. (B) Horizontal Drains
Logging While Drilling Data and Interpretation across
Reservoir-A, Layers 1 and 2.
The original deviated pilot hole wireline logs are
further illustrated in Figure.4, together with target
sublayers for Drain 1, Layer 2. The gamma ray log is
displayed on Track 1. The wireline resistivity laterolog
is displayed in red on Track 2, and the induction log is
displayed in Track 3. Both resistivity tools show good
resistivity readings across the target sublayers.
However, it is evident that the laterolog tool reads
higher than the induction tool. This is probably an
indication that the zone is highly anisotropic. In a low
angle and in the presence of anisotropy, laterolog tools
read higher than induction tools; in a low angle,
induction tools tend to read closer to the horizontal
resistivity (Rh).
Figure.5 Sidetrack mother hole LWD logs in drilling
and wiping mode at a 63° inclination.
The resistivity logs of Figure.5 show two important
features. The first is that the drilling mode resistivity
reads higher than the wiping mode across the target
zone (Layer 2). This shows that the wiping resistivity
log, which was obtained at a later time, is more
affected by invasion, and that the drilling resistivity
log reads higher because it is less affected by invasion.
Note the separation between the phase resistivity in
drilling mode, which indicates the presence of
anisotropy. Also, note that the ADR reads somewhat
higher than wireline induction because the inclination
increased to 63°, and that the ADR appears to be more
affected by anisotropy while the induction tool, at low
angle, basically reads Rh.
Figure.4
laterolog
Original deviated pilot hole wireline
and induction resistivity logs across
Well Placement of Drain 1. After evaluating the
original pilot and mother holes, the first lateral, Drain
3
SPWLA 55th Annual Logging Symposium, May 18-22, 2014
1 in Layer 2, was drilled. The well was geosteered
using the ADR tool and StrataSteer® 3D (SS3D)
steering software. A snapshot of the well placement,
along with the corresponding ADR and TVD logs, is
shown in Figure.6. From this figure, it is apparent that
the ADR resistivity values are closer to the pilot hole
wireline laterolog than the induction log, as the
inclination in this hole section is approximately 87 to
89°.
Again, it can be observed that the laterolog reads much
higher than the induction log. This is also an indication
that the target zone is highly anisotropic.
Sidetrack Mother Hole LWD Evaluation. Figure.8
shows the LWD logs obtained in drilling and wiping
mode. Good resistivity readings are observed across
the target sublayer of Layer 1. Again, the phase
resistivity separation in Track 2 obtained in drilling
mode indicates the anisotropic nature of the zone.
Figure.6 Well placement of Drain1 in Layer 2.
EVALUATION AND PLACEMENT OF DRAIN 2
IN LAYER 1
Pilot Hole Wireline Evaluation. Figure.7 displays the
wireline gamma ray log, the induction wireline
resistivity log, and the laterlog wireline resistivity logs,
together with the target sublayer for Drain 2.
Figure.8 Sidetrack mother hole LWD logs in drilling
and wiping mode at a 63° inclination.
WELL PLACEMENT OF DRAIN 2
After evaluation of the original pilot and mother holes,
the second lateral, Drain 2 in Layer 1, was drilled. This
time, the azimuthal focused resistivity (AFR) and
SS3D software were used to place the well. A snapshot
with the corresponding AFR TVD logs is shown in
Figure.9. The AFR (deep laterolog in red) is clearly
much closer to the wireline induction log from the
original deviated pilot hole. The inclination in this
drain is 88 to 90°. The AFR shows good promise in
these thin beds for well placement as well as for
determining Rt for formation evaluation.
Figure.7 Original deviated pilot hole wireline
laterolog and induction resistivity logs across
Reservoir-A, Layer 1 at a 47° inclination represented
in TVD scale.
4
SPWLA 55th Annual Logging Symposium, May 18-22, 2014
Figure.9 Well placement of Drain 2 in Layer 1.
Rt, Rxo, AND ADJACENT BED EFFECTS
Obviously, there are other issues to consider when
determining Rt, such as invasion and adjacent bed
effects. However, in horizontal wells, deep readings
that have a much greater diameter of investigation are
somewhat disadvantageous for formation evaluation
purposes. Much shallower measurements, such as
AFR, can be used as long as the deep laterolog is not
affected by invasion. It is also advantageous to be
close to Rh in horizontal holes because of the
robustness of Archie-based Sw algorithms.
Figure.10 Formation volumetrics and fluid analysis
from Drain 1 and Drain 2.
CONCLUSIONS
The Rxo result is an interesting comparison. Although
the invasion effects are evident in the wipe runs for
both the ADR and AFR, there seems to be more
control over Rxo with the AFR. For Drain 1, the
shallow phase 16-in. resistivity (RH16P) from drilling
was used as Rt, and the same RH16P was used as Rxo
from the wipe run. For Drain 2, the AFR deep was
used for Rt, and the AFR shallow from the wipe run
was used as Rxo (Figure 10). Therefore, combining the
ADR and AFR in both the drilling and wipe mode
proved beneficial for obtaining Rt and Rxo.
Determining Rt in horizontal or highly deviated wells
is challenging because of anisotropy effects and
adjacent bed boundaries effects. In vertical and lowangle wells, wireline induction and LWD propagation
tools tend to have no sensitivity to anisotropy and
instead read the Rh. On the other hand, wireline
laterolog and LWD toroidal resistivity tools have
sensitivity to formation anisotropy in both dipping and
non-dipping formations. Sensitivity to Rv increases
with a higher dipping angle but at a much slower rate
than with traditional induction and wave propagation
resistivity tools.
In horizontal wells, deep reading tools with a greater
depth of investigation are somewhat disadvantageous
for determining Rt because of adjacent bed effects.
Much shallower measurements from both wave
propagation and laterolog-type tools can be used as
long as they are not affected by invasion. This case
study emphasized that LWD laterolog- and LWD
propagation-type tools complement each other when
used for evaluation and for placing lateral wells, and
they help reduce uncertainty in the determination of Rt
in horizontal and highly deviated wells.
5
SPWLA 55th Annual Logging Symposium, May 18-22, 2014
Wu, P., Barber, T., Homan, D., Wang, G., Johnson, C.,
Heliot, D., et al. 2010. Determining Formation Dip
from a Fully Triaxial Induction Tool. Paper presented
at the SPWLA 51st Annual Logging Symposium,
Perth, Australia, 19–23 June.
ACKNOWLEDGEMENTS
The authors thank the management of ADNOC,
ADMA-OPCO, and Halliburton for their support,
encouragement to publish this work, and for reviewing
the manuscript and providing helpful comments and
suggestions.
REFERENCES
ABOUT THE AUTHORS
Bittar, M. and Rodney, P. 1996. The Effect of Rock
Anisotropy on MWD Electromagnetic Wave
Resistivity Sensor. Paper PP presented at the SPWLA
35th Annual Logging Symposium, Tulsa, Oklahoma,
USA, 19–22 June.
Amr Serry works as a petrophysicists
for Abu Dhabi Marine Operating
Company (ADMA-OPCO), Umm Shaif
field development division since 2010.
Bittar, M. 2000. Electromagnetic Wave Resistivity
Tool Having a Tilted Antenna for Determining The
Horizontal and Vertical Resistivities and Relative Dip
Angle in Anisotropic Earth Formations. US Patent No.
6,163,155.
Mr. Amr has acquired his BSc. Degree
of Petroleum Engineering at Cairo
University in 2004 before joining AlMansoura Oil Company, as a
petroleum engineer in the Gas
development operations division.
Bittar, M., Klein, J., Beste, R., Hu, G., Wu, M.,
Pitcher, J., et al. 2007. A New Azimuthal DeepReading Resistivity Tool for Geosteering and
Advanced Formation Evaluation. Paper SPE 109971
presented at the SPE Annual Technical Conference
and Exhibition, Anaheim, California, USA, 11–14
November.
He has joined Baker Atlas in 2005 as a petrophysical
engineer, conducting a variety of open and cased hole log
analyses, providing operations support and technical sales
for Egypt, UAE and various locations within the Middle East
Region. He is an active SPE Member since 2005 and a
member of SPWLA, Abu Dhabi local chapter.
Bootle, R., Waugh, M., Bittar, M., Hveding, F.,
Hendricks, W., and Pancham, S. 2009. Laminated
Sand-Shale Formation Evaluation Using Azimuthal
LWD Resistivity. Paper SPE 123890 presented at the
SPE Annual Technical Conference and Exhibition,
New Orleans, Louisiana, USA, 4–7 October.
Sultan Budebes works as a senior
petrophysicist for Abu Dhabi
Marine
Operating
Company
(ADMA-OPCO), Umm Shaif field
development since 2004.
Hu, G., Bittar, M., and Hou, J. 2006. Evaluation of
Horizontal Wells Using LWD Propagation Resistivity
and Laterolog-Type Resistivity Logs. Paper SPE
103150 presented at the SPE Annual Technical
Conference and Exhibition, San Antonio, Texas, USA,
24–27 September.
Mr. Sultan worked for Abu Dhabi
National Oil Company (ADNOC)
from 1995 to 2004 as a petrophysicist in the Umm Shaif
Khuff gas project providing petrophysical analysis.
Rodney, P., Mack, S., Bittar, M., and Bartel, R. 1991.
An MWD Multiple Depth of Investigation
Electromagnetic Wave Resistivity Sensor. Paper
presented at the SPWLA 32nd Annual Logging
Symposium, Midland, Texas, USA, 16–19 June.
Prior to that he worked as a wellsite geologist, for Al Ain
Ground water Research Project, a joint project of the
National Drilling Company (NDC) and the United States
Geological Survey(USGS).
Tabarovsky, L., Epov, M., and Rabinovich, M. 2001.
Measuring
Formation
Anisotropy
Using
Multifrequency Processing of Transverse Induction
Measurements. Paper SPE 71706 presented at the SPE
Annual Technical Conference and Exhibition, New
Orleans, Louisiana, USA, 30 September–3 October.
He graduated from the United Arab Emirates University of
Al Ain in 1990 with a BSc degree in Geology and Chemistry
and has a wide range of SPW/SPWLA publications.
6
SPWLA 55th Annual Logging Symposium, May 18-22, 2014
including Chief Technical Advisor, Halliburton Technology
Fellow, Director of Research and Senior Director of
Formation Evaluation.
Hassan
Aboujmeih
is
an
Operational
Petrophysicist
at
ADMA-OPCO, Managing the data
gathering operations and wireline
logging and perforation contracts.
Dr. Bittar received his BS, MS and PhD degrees in electrical
engineering from the University of Houston and has more
than 100 patents and publications. He is a long term
member of SPE and SPWLA and serves on King Abdullah
University of Science and technology (KAUST) Industry
Advisory Board. Dr. Bittar was as well the recipient of the
2006 SPWLA Technical Achievement Award and the 2009
Halliburton Outstanding Commercialized Invention of the
Year Award.
Mr. Hassan Aboujmeih holds a
Mechanical Engineering degree
from the University of Western
Ontario in Canada. He started his oil career with
Schlumberger Wireline and formation evaluation as a field
Engineer working in North America and the Middle East. He
also provided management and technical support in high
activity volume locations.
Ahmet Aki is the Regional
Technical Sales and Marketing
Manager with Halliburton Sperry
Drilling for Middle East and North
Africa.
Mr. Aki has obtained his B.Sc.
and
M.Sc.
degrees
from
University of Birmingham in the
UK in 1981. He has worked for Schlumberger and
Halliburton in field operations and management positions
in West and North Africa, North America, North Sea and
the Middle East, prior to moving into log analysis in 1994.
Mr. Aki has worked in petrophysical consulting and
technical support positions for both Wireline and LWD
since 1994 with numerous technical publications.
Mr. Aki has been a member of SPWLA and SPE since 1986,
and is currently serving on the board of SPWLA Abu Dhabi
Chapter.
Dr. Michael Bittar is a Senior
Director
of
Technology
for
Halliburton.
Dr. Bittar joined Halliburton in 1990
and since then has held various
technical and leadership roles,
7