True 3D measurements for
enhanced reservoir quantification
Rt Scanner measurements in three dimensions at multiple depths of
investigation (DOIs) quantify even low-resistivity laminated pay
zones to reduce uncertainty and refine your reservoir model
Rt Scanner* triaxial induction service calculates both vertical and
horizontal resistivity (Rv and Rh, respectively) from direct induction
measurements while simultaneously solving for formation dip at
any wel deviation. Making measurements at multiple DOIs in three
dimensions ensures that the derived resistivities are true 3D
measurements. The enhanced hydrocarbon and water saturation
estimates computed from these measurements result in more accurate
reservoir models and reserves estimates, especial y for formations with
laminations, anisotropy, or faults.
The compact, one-piece Rt Scanner tool has multiple triaxial arrays,
each containing three col ocated coils measuring at various depths into
the formation. Rv and Rh are calculated at each of the triaxial spacings.
A unique electrode sleeve with short single-axis and col ocated triaxial
The compact, one-piece Rt Scanner
receivers is used to ful y characterize the borehole signal and remove
tool has multiple triaxial arrays for
the borehole effect.
making true 3D measurements.
■ Quantification of laminated
or low-resistivity formations
■ Corrected resistivity for
shoulder beds at any angle
■ Determination of water
■ Geometric reservoir modeling
■ Structural analysis
■ Completion design and
In addition to advanced resistivity measurements, formation dip and
azimuth are available for structural interpretation. The Rt Scanner tool
also delivers standard AIT* array induction imager tool measurements
for correlation with existing field logs. The tool’s innovative single-piece
design requires the addition of only a caliper and the GPIT* general
purpose inclinometry tool to the toolstring to operate. Rt Scanner
service is also ful y combinable with most openhole services and the
Platform Express* platform—adding only 7 ft [2 m] to the length of a
Platform Express triple-combo when replacing the AIT resistivity tool.
The key to the unique measurement capabilities of Rt Scanner service
is proprietary col ocated coil technology. Inducing currents horizontal y
and vertical y into the formation from one depth point and then receiving
them at another mutual depth point provides measurement of the
formation properties in true 3D. The multiple col ocated receivers
also measure at progressively deeper radial depths. The resulting 3D
information contains structural dip, azimuth, and resistivity anisotropy
The col ocated transmitter and one of the several col ocated receivers (left) of the
information, which provides critical contrast in low-resistivity laminated Rt Scanner tool independently obtain tensor resistivity measurements (right) that
pay and other chal enging environments.
yield valuable information, especial y in laminated formations.
ACCURATE QUANTIFICATION OF LAMINATED SANDS
Conventional wireline induction tools measure mainly Rh. However,
this measurement bias results in low-resistivity readings in anisotropic
resistivity sequences, such as thinly laminated sands and shales. The
conductive shales dominate the resistivity, neutron, and several other
logs, masking pay zones in the sands and producing pessimistic interpre-
tations of hydrocarbon volume.
Rt Scanner service extends the basic AIT induction logs to include R
h. These additional measurements in combination with structural
dip and azimuth obtained by the tool provide valuable insight to the
resistivity of the sand portion (Rsand) of laminated formations. A 1D
inversion algorithm is used to determine Rh, Rv, and the bed boundaries
and dip azimuth. The dip-corrected measurements are used to populate
a reservoir model that can incorporate a shale anisotropy factor to
account for the intervening shales. The enhanced saturation estimates
computed with the model account for the geometry of the layers.
The 1D inversion of the Rt Scanner measurements obtained by
the col ocated coils produces both dip and resistivity information.
Rh runs paral el to the bedding plane, Rv is orthogonal to Rh.
Rv 101 Rshv = 3.2
h = 0.56
Sw(RvRh) = 0.4
Sw(Rh) = 0.87
The butterfly overlay on the crossplot of Rv and Rh (right) includes input for the shale content (left track). Data corresponding to shales, water zones, and pay zones are shown
in green, cyan, and magenta, respectively. As the horizontal bar is moved in the Sw track, the cumulative sand volume (∑Fsand), hydrocarbon volume from Rv and Rh (∑VhRvRh),
and hydrocarbon volume from Rh (∑VhRh) are displayed. The volume fraction of shale (Fshale) in the left log track is a good match to core from the interval at 850 to 950 ft (left).
FMI True DIP
FMI True DIP
AIT 90 in
AIT 90 in
ELAN* S Quality [4,12]
0.2 ohm.mohm.m 200 200
39-in Array R
39-in Array Rv
Triaxial AIT True DIP
0 Triaxial AIT True DIP
39-in Array R
39-in Array R
Flowmeter S Quality [12,120]
Low-resistivity laminated pay cannot be accurately logged with conventional tools. To the right of the log, a 20-ft [6-m] section of FMI* ful bore formation micro-
imager images shows the 60° relative dip and highly laminated formations in this US Northern Gulf Coast wel . The neutron log (Track 2) is so severely influenced
by the shale laminations that there is no density-neutron crossover. Resistivity is similarly dominated, with depressed measurements in Track 3. However,
laminated sand analysis based on Rt Scanner measurements accurately quantifies the hydrocarbon in place, including otherwise unidentified pay (Track 4).
In addition, the combination of dip measurements in Track 5 from Rt Scanner and imaging tools enhances structural understanding throughout the wel .
TRIAXIAL DIP FOR RESISTIVITY CORRECTION
AND ENHANCED UNDERSTANDING
Because Rt Scanner service continuously measures formation dip
0 20 40 60 80 X,500
1.0 10.0 100.0 1,000.0
and azimuth simultaneously with the resistivity measurements in 3D,
advanced corrections can be made for the effects of bed boundaries and
formation dip. The tool’s 3D measurement capabilities provide accurate
dip and azimuth measurements from a wide range of borehole conditions
and formation environments, including any wel angle up to paral el to the
formation layers and in air-fil ed boreholes.
54-in Rt Scanner Dip
AIT 10 in
AIT 90 in
Both the Rt Scanner and OBMI dip measurements show a distinct change
in dip at X,580 ft, indicating an unconformity. The change in dip is also
reflected in the shift of the classic AIT resistivity logs—they overlie the
Rt Scanner Rh curve in the low-dip interval above the change, but are between
the Rt Scanner Rh and Rv curves in the underlying interval of higher dip. The
overlay of Rv and Rh in the wet sands also provides a quicklook of the fluid type
in this case.
Seismic Section SW
Direction = 120°
Rt Scanner logging of this air-fil ed borehole revealed significant resistivity
Rt Scanner Dip
anisotropy. The structural dip matches the core information, even in the
lower zone, which has sections of rugose and washed-out borehole.
Layer dip is computed over 10- to 50-ft [3- to 15-m] intervals. Although
at a lower vertical resolution than dip from an imaging tool or dipmeter,
these measurements are suf iciently robust to provide critical structural
information and detect major events, such as bed boundaries and
unconformities or faults crossing the borehole. Additional stratigraphic
insight can be achieved from pairing Rt Scanner dip measurements with
OBMI* oil-base microimager data.
Stick plots of Rt Scanner triaxial dip measurements can also be used to
scale up from continuous structural content at a single-wel scale to the
Data Used for Cross Section
borehole or surface seismic section. Bridging the gap between image
logs and the seismic section with dip measurements greatly enhances
A stick plot was used to link Rt Scanner dip measurements in Wel s A and B in
South America. The stick plot was then used to scale up to the seismic section
geometric understanding of the reservoir.
to map the reservoirs between the two wel s.
ESTIMATING HYDROCARbON VOLUME
IN THINLY LAMINATED SANDS
Formation evaluation of conventional induction logs from a thinly
model that incorporated a shale anisotropy factor determined from
laminated gas-bearing sand calculated high values of Sw. These
the massive underlying shale. Instead of the nearly 100% Sw values
classic logs were essential y measuring a bulk value of Rh for the
obtained from classic induction resistivity measurements, the
interbedded sands, shales, and mudstones, which range from almost
Rt Scanner model calculated Sw between 20% and 50%.
a meter to less than a centimeter in thickness, with most of the layer
The Rt Scanner saturation values were a good match to nuclear mag-
thicknesses in the centimeter range, wel below the vertical resolution
netic resonance (NMR) logging and core measurements. Subsequent
of the classic induction tool. The low resistivity resulting from the low-
formation tester sampling downhole confirmed the presence of hydro-
conductivity anisotropic shale layers in turn depressed the hydrocarbon carbon, and producibility was demonstrated with a drilstem test. With-
out the revised Sw values possible with Rt Scanner 3D measurements,
To calculate correct Sw values, the dip-corrected Rt Scanner Rv and
the potential of this complex reservoir would have gone unrecognized.
Rh measurements were used in a laminated sand-shale
Bound Water Bound Water
P I 60
Anisotropic 0º 120º 240º 360º
Depth, Sand Fraction
Induction Resistivity 90 in
A P I 60
0 1.5 1.65 2.65
100 % 0
0 50 %
Compared with the analysis of classic induction logs, the Rt Scanner resistivity anisotropy measurements for the laminated sand indicate the presence of hydrocarbon
that otherwise would have been overlooked (Tracks 6 and 7 are the pay flags for the classic and Rt Scanner anisotropic interpretations, respectively). Gas is indicated
by the crossover between density and neutron at X,150–X,155 ft, X,188–X,192 ft, and X,268–X,271 ft.
RESOLVING bED bOUNDARY EFFECTS
IN HIGH-DIP, LOw-RESISTIVITY PAY
Induction logs are prone to bed boundary effects in thin-bedded sands.
the AIT 10-in [25-cm] resistivity at X,990 and Y,040 ft. The correctly identified
To better understand low-resistivity pay in a channel complex at a rela-
true resistivity (Rt) for the channel sands is greater by
tive dip of 60°, an operator ran Rt Scanner triaxial induction service. The a factor of 4 than the AIT 90-in [229-cm] resistivity value. If only conven-
Rt Scanner measurements identified the low-resistivity pay in the lower
tional logs had been used, the effects of the surrounding shale beds
half of the wel and resolved the bed boundary effects shown as horns in
would have resulted in an inaccurately low estimate of oil saturation
and consequently of reserves.
0 20 40 60 80
In Zone A, the conventional AIT 90-in resistivity
reads low in the thicker channel sands because of
the surrounding dipping shale beds. The AIT 10-in
resistivity also exhibits significant shoulder-bed
B horns. The Rt Scanner Rv and Rh measurements
correct for the dipping shale beds in Zone A. In
Zone B, the Rt Scanner measurements correctly
identify a low-resistivity pay zone that otherwise
would have been overlooked.
AIT 10 in
AIT 90 in
USING DIP INFORMATION TO FOLLOw TURbIDITE CHANNELS
An operator wanted to place additional wel s in a productive turbidite
Rt Scanner dip
sand in Mexico, but seismic information was lacking for fol owing the
sinuous channel body. However, Rt Scanner dip measurements were
obtained during the logging run. Stratigraphic interpretation of the
Lateral y accreted
Rt Scanner dip information in combination with imaging tool data
assumed a channel geometry with fine accretionary overbank
Channel reservoir facies
deposits resulting from the lateral and downstream migration of
relatively sinuous and confined subaqueous channels. In this scenario,
the strike of the bedding in the argil aceous channel base indicates the
Channel reservoir facies
direction the channel fol owed.
With the channel direction revealed, the next wel could be located
330 ft [~100 m]
northeast of the original wel . The wel trajectory was planned using
the dip information, and the same good-quality sands of the turbidite
As shown on the dip direction rose plots to the left, stratigraphic interpretation
channel were intersected.
of the Rt Scanner dip information identified the direction of the turbidite channel
from northeast to southwest.
DRILLING A SUCCESSFUL DEEPwATER SIDETRACk
IN THIN-bEDDED SANDS
Low-resistivity thin-bedded sands intercalated with shale layers were
The DCS analysis found that that as the DOI increases, the average
insufficiently characterized by conventional logs for placing a sidetrack
dip decreases. The same bedding nature was also observed in the
in turbidite deposits offshore West Africa. Additional complications
VSP data. Averaging the four sets of dip data achieved a more
were the possible deformation of bedding by nearby salt deposits and
realistic structural dip value that could be used to improve reservoir
that the seismic data was often doubtful because of the depth and
modeling. With this information, the operator was able to dril a
To better understand this chal enging situation, Schlumberger
recommended dip angle measurements at multiple DOIs around the
borehole wel . The OBMI2* integrated dual oil-base microimagers
New concept of
and Rt Scanner triaxial induction service were run because they can
computing structural dip
obtain accurate images and measurements of low-resistivity formations
dril ed with oil-base mud. The OBMI2 tool recorded dip data around the
borehole wal at a DOI of approximately 3.5 in [8.9 cm], and the Rt Scanner
tool obtained far-field, radial y variant dip measurements at DOIs of 39,
Borehole lled with drilling mud
54, and 72 in [0.99, 13.7, and 1.8 m]. The Rt Scanner 3D dip measure-
ment was also insensitive to any borehole irregularities, which were
expected in this heterogeneous depositional environment.
Schlumberger Data & Consulting Services (DCS) introduced a improved
The new DCS concept for structural dip computation integrates dip measurements
approach to structural dip computation that integrated the two dip
obtained at various DOIs. The green dots represent OBMI2 dips, and the red dots
represent Rt Scanner multiarray dips. The green dotted line is a horizontal plane
measurements. The first step was determining the level of confidence
fitting the four-dip measurement.
for the Rt Scanner dips with respect to borehole resistivity image dips
from a known formation. The structural dip values were also compared
with the vertical seismic profile to improve the view away from the
borehole and better display large-scale variations in the deposits. The
conventional averaging method was also used to compute another set
of dip values for comparison.