Description
 The
geoVISION Resistivity Tool (GVR6) makes lateralog resistivity
measurements. As a formation evaluation tool, its application
is limited to conductive muds. It may be run in several configurations
and provides up to five resistivity measurements. The GVR6 contains a scintillation gamma ray detector which supplies a
total gamma ray measurement. An azimuthal positioning system
allows both gamma ray and various resistivity measurements
to be acquired around the borehole. Additional measurements are
chassis temperature and radial and longitudinal shocks.
The GVR6 has a nominal 6.75-in (17 cm) diameter; it is meant to
be run in 8.5-in (21.6 cm) holes. Designed to be a flexible component
of the bottom hole assembly, the GVR6 may be connected directly
behind the bit or further back in the bottom hole assembly.
 A 1.5-in (3.8 cm) tall cylindrical electrode, located
3 feet from the bottom of the tool, provides a focused lateral
resistivity measurement (RING) with a 2-in (5 cm) vertical resolution,
independent of the location of the RAB tool in the bottomhole
assembly. In addition, the RAB sub has three longitudinally
spaced button electrodes that provide staggered depths of investigation.
As the tool rotates, azimuthal measurements are acquired from
the button electrodes. When
connected directly to the bit, the GVR6 uses the lower portion
(8-in; 20.3 cm) of the tool and the bit as a measure electrode. In this
configuration, it provides a bit resistivity measurement (RBIT)
with a vertical resolution just a few inches longer than the
length of the bit.
The GVR6 measurements have a high vertical and azimuthal resolution.
To make the most of the vertical resolution, the optimal sampling
density is greater than one sample every inch. At the maximum
sampling interval of 10 sec, the optimal sampling density can
be achieved for rates of penetration up to 29.5 ft/hr (9 m/hr). Achieving
this vertical sampling is most important when imaging.
Applications
The GVR6 tool provides four depth of investigation measurements
to detect early invasion of borehole fluids into the formation,
a sensor at the bit to ensure minimum invasion, azimuthal resistivity
images of the borehole to detect resistivity heterogeneity, and
a gamma-ray sensor for lithology characterization.
The GVR6 tool can also provide a close look at structural information
within a fault zone or an active tectonic area with a resolution
of 6-12 in (15-30 cm). The GVR6 measures oriented resistivity images of the
borehole wall, similar to FMS and FMS images. Fracture orientations and distributions can be observed as resistivity
contrasts in the image logs and are critical to recognize the
extent of the deformation front along a tectonic front. Conversion
of GVR6 images into relative porosity using Archie’s equation
can be used in combination with density and porosity
data to help define the azimuthal distribution of porosity and
overpressurized zones which may contribute to fluid flow along
planes of structural weakness.
Environmental Effects
The button measurements have a shallow depth of investigation
by design, in order to be sensitive to shallow invasion. When
the GVR6 tool is centralized in a 8.5-in (21.5 cm) hole, the buttons are
0.1875 in (0.47 cm) from the formation. Controlling this standoff insures
correct measurements. Therefore, proper centralization is recommended.
The GVR6 processing automatically corrects the resistivity measurements
for frequency effects and the effects of the borehole.
Log Presentation
Tool Specifications
| Tool make-up length: |
10 ft (3.3 m) |
| Tool weight: |
1,200 lbs (545 kg) |
| API nominal collar outside diameter: |
6.75 in (17.1 cm) |
| Maximum outside diameter: |
7.5 to 8.5 in (19.6 to 21.6 cm) |
| Minimum bit size: |
8.5 in (21.6 cm) |
| Maximum bit size: |
9.875 in (32.5 cm) |
| Maximum Temperature: |
300° F (149° C) |
| Maximum pressure: |
18 kpsi (12.4 kPa) |
| Flow range: |
0-800 gpm |
| Pressure drop coeffecient (C)*: |
135,000 |
| Maximum curvature - sliding: |
16 deg/100 ft (16 deg/31 m) |
| Maximum rotary torque: |
16,000 ft-lbf (4.877 m-lbf) |
| Minimum operating RPM: |
30 rpm |
| Uphole connection: |
5-1/2 FH box |
| Downhole connection: |
5-1/2 Reg box |
| (*) pressure drop = [mudweight in ppg] x [flow in gpm]²/C |
Measurement Specifications
| Gamma Ray |
| |
Measurement range: |
0-250 GAPI |
| |
Accuracy: |
7% |
| |
Vertical resolution: |
6 in (15.24 cm) |
| Azimuthal resistivity |
| |
Measurement range: |
0.2-1,000 ohm-m |
| |
Accuracy: |
5% (0.2-200 ohm-m); 20% (>200 ohm-m) |
| |
Vertical resolution: |
2-3 in (5.08-7.62 cm) |
| Ring resistivity |
| |
Measurement range: |
0.2-200,000 ohm-m |
| |
Accuracy: |
5% (0.2-200 ohm-m); 20% (>200 ohm-m) |
| |
Vertical resolution: |
3-4 in (7.62-10.16 cm) |
| Bit resistivity |
| |
Measurement range: |
0.2-200,000 ohm-m |
| |
Accuracy: |
5% (0.2-200 ohm-m); 20% (>200 ohm-m) |
| |
Vertical resolution: |
12-24 in (30.48-60.96 cm) |
Major Outputs
| GR: |
Gamma ray average (API) |
| BDAV: |
Deep resistivity average (ohm-m) |
| BMAV: |
Medium resistivity average (ohm-m) |
| BSAV: |
Shallow resistivity average (ohm-m) |
| RBIT: |
Bit resistivity (ohm-m) |
| RING: |
Ring resistivity (ohm-m) |
| RTIM: |
Ring resistivity time after bit (s) |
| B1TM: |
Shallow resistivity time after bit (s) |
| B2TM: |
Medium resistivity time after bit (s) |
| B3TM: |
Deep resistivity time after bit (s) |
| GRTK: |
Gamma ray time after bit (s) |
| RBTM: |
Bit resistivity time after bit (s) |
| RPM: |
Rotational speed (rpm) |
| ROP5: |
Rate of penetration per 5 ft (m/hr) |
| RTAB: |
Ring time after bit (hr or min) |
| P1AZ: |
P1 azimuth |
| HAZI: |
Azimuth (deg) |
Static and dynamic images are output at 3 depths of investigation: medium, shallow, and deep
Deployment Notes
Along with the LWD collars, additional equipment such as jars
must be included. Responsibility for providing this equipment
is discussed at the pre-expedition meeting.
* ®trademark of Schlumberger
|
