MDT * Modular Formation

Schlumberger
Dynamics Tester
Multiprobe
Permeability Determination

MDT Tool Configured for Three-Probe Pressure Measurement

Observation
probes
Sink
probe

Three-probe configuration of the MDT tool measures pressure response at two

locations in addition to the sink, or flowing, probe. These measurements, shown in
the plot below, allow accurate determination of near-wellbore horizontal and vertical
permeability characteristics.

Multiprobe Pressure Response

0 Vertical
observation
probe
Pressure Change (psi)

–5
Horizontal
–10 observation
probe
–15
–1,000
Quartz gauge
–1500 Strain gauge
–2000
Flowing probe
–2500
–25 0 25 50 75 100 125 150
Time (sec)

*Mark of Schlumberger SMP-5154-A (WTA 92)

10/95
MDT * Modular Formation
Schlumberger
Dynamics Tester
Resistivity Measurement

Resistivity Measurement Example

2 3⁄4-gal sample
13,000 32
Hydrocarbon
flowing

Sample
Sampling starts chamber full
12,000 24

Reservoir
pressure
11,000 16

Resistivity, ohm-m
Pressure, psi

10,000 8

9000 0

8000
1264 1272 1280 1288 1296 1304

Time, sec

Flowline resistivity measurement in the MDT probe module helps discriminate

between fluid contaminated by filtrate and pure formation fluid. Fluid removed from
the formation is excluded from the sample chambers until uncontaminated samples
can be recovered. Surface-controlled valves provide real-time control over testing
rate and volume as illustrated in the 3000-psi drawdown above.

*Mark of Schlumberger SMP-5154-B (WTA 92)

10/95
MDT * Modular Formation
Schlumberger
Dynamics Tester
Bottomhole Sampling

MDT Tool Configured for Bottomhole Sampling

Electric power
module

Sample modules

Hydraulic power
module

Probe module

This configuration of the modular MDT tool allows samples of

formation fluid to be taken within 18 in. of the bottom of the well,
so that critical formation pressure and samples can be obtained
in the event of minimal rathole. The number of sample modules is
limited only by cable strength and well conditions.

*Mark of Schlumberger SMP-5154-C (WTA 92)

10/95
MDT * Modular Formation
Schlumberger
Dynamics Tester
Pumpout Module

Typical MDT Tool Configuration

with Pumpout Module

Electric power
module

Hydraulic power
module

Probe module

Sample module

Sample module

Pumpout
module

When the MDT tool is equipped with the pumpout module,

it is possible to sample while monitoring the flowline resis-
tivity, using the pump to pump filtrate-contaminated fluid into
the mud column. When the engineer observes that the probe
is sampling uncontaminated formation fluid, pumping is
stopped and uncontaminated samples are obtained.
True formation fluid, previously masked behind filtrate,
may now be identified and retrieved for analysis.

*Mark of Schlumberger SMP-5154-D (WTA 92)

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MDT * Modular Formation
Schlumberger
Dynamics Tester
Pumpout Module

Pumpout Module Throughput, Pressure and Flowline Resistivity

POPV BFR1 BSG1

(gal) (ohm-m) (psi)
35 1.4 7000
23⁄4 gal
30 1.2 6000
BSG1 (probe pressure) 6 gal
25 1.0 5000

20 0.8 4000
BFR1 (flowline resistivity)
15 0.6 3000

10 0.4 2000

5 0.2 1000
POPV (cumulative volume pumped)
0 0.0 0
0 20 40 60 80 100 120 140 160
Time (min)

The sequence of pumpout module operations for operates, flowline resistivity starts to decline, indicat-
acquiring a representative water sample is illustrated ing that more formation fluid is entering the flowline.
in this chronograph. Hydrostatic pressure, BSG1 After 130 min, 25 gal of fluid have been pumped, and
curve, is approximately 5900 psi. After 1 min, the test flowline resistivity, 0.28 ohm-m, indicates that very
is initiated. The tool sets, and the pressure curve little filtrate is contaminating the sample.
starts displaying probe pressure, 5000 psi. The flow- At this time the engineer stops the pump, opens the
line resistivity curve, BFR1, peaks at 1.38 ohm-m, 6-gal sample chamber and monitors fluid pressure
indicating that the flowline is filled with relatively fresh and resistivity as it fills (about 7 min). At 140 min, the
mud filtrate. At approximately 7 min, the pumpout engineer opens and fills the 2 3⁄4-gal chamber (about
module is activated, and flowline fluid is pumped 3 min). At 150 min, the test is terminated and the tool
into the mud column. The POPV curve indicates the is retracted. Probe pressure and flowline resistivity
cumulative volume of pumped fluid. As the pump return to hydrostatic pressure and mud resistivity,
respectively.

*Mark of Schlumberger 10/95

MDT * Modular Formation
Schlumberger
Dynamics Tester
Collecting Multiple Samples

Many Small, PVT-Quality Samples

from One or More Locations Downhole

Electric power
module

Hydraulic power
module

Probe module

Multisample
module

Pumpout
module

In addition to modules collecting 6-, 2 3⁄4- and 1-gal samples, the

MDT tool can be equipped with a multisample module to collect
six 450-cm 3 samples. All samples may be taken during one tool
set, or one or more samples may be taken at various tool set-
tings. Bottles are easily detached from the carrier for safe trans-
port without disassembling the tool string when the multisample
module is returned to the surface.

*Mark of Schlumberger SMP-5154-E (WTA 92)

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MDT * Modular Formation
Schlumberger
Dynamics Tester
Interval Testing with Packers

MDT Packer Tool

The packer module employs two inflatable packers to
isolate a borehole interval for testing. The pumpout module,
using borehole fluid, inflates the packers to approximately
1000 psi above hydrostatic pressure. Packer spacing
varies, but the minimum distance of 4 ft (122 cm) provides
a borehole wall test area approximately 4000 times greater
than the cross-sectional area of the standard MDT probe.
The large area also provides a pressure buildup with a
radius of investigation of 50 to 80 ft and allows the with-
drawal of fluids at high flow rates without dropping below
the bubblepoint pressure—while limiting the fluid velocity
across the sandface.
The packer tool has demonstrated its usefulness in
low-permeability, fractured and vuggy formations where the
probe-type measurement has low success. Such cases
require a borehole televiewer or electrical borehole images
to determine packer placements.
The packer tool can pump into the formation after setting
the packers—leading to other possible applications.

*Mark of Schlumberger SMP-5154-F (WTA 92)

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MDT * Modular Formation
Schlumberger
Dynamics Tester
Vertical Permeability Measurements

MDT Packer-Probe Tool

Electric power
module

Hydraulic power
module

Probe module

Packer
module

Pumpout
module

Sample module

Similar to the MDT dual-probe configuration, the packer

module mounted below the single-probe module determines
vertical permeability—but at a longer spacing, since the
pressure pulse is much larger.

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MDT * Modular Formation
Schlumberger
Dynamics Tester
Tool Specifications

Hole Size Maximum Rating

Tool OD
Maximum
Minimum Maximum Pressure Temperature
with Kit

Single-probe tool 43⁄4 in. 6 in. 14 in. 19 in. 20 kpsi † 400°F†

(12.1 cm) (15.2 cm) (35.6 cm) (48.3 cm) (13.8 kPa) (205°C)

Multiprobe tool 6 in. 75⁄8 in. 13 in. 15 in. 20 kpsi † 400°F†

(15.2 cm) (19.4 cm) (33 cm) (38.1 cm) (13.8 kPa) (205°C)

Dual-packer tool 5 in. 61⁄4 in. 12 in.§ 20 kpsi † 300°F‡

(12.7 cm) (15.9 cm) (30.5 cm) (13.8 kPa) (150°C)

† 350°F (175°C) and 15 kpsi with the CQG* quartz gauge and/or the optical fluid analysis module
‡ 250°F (120°C) in oil-base mud
§ Maximum hole size depends on the packer installed. Larger packers are available for larger hole sizes.

Pressure Gauge Specifications

Specification Strain Gauge CQG* Quartz Gauge

Accuracy 0.10% full scale† 2.0 psi + 0.01% of reading

Repeatability 0.06% full scale† 1.0 psi

Resolution 0.001% full scale at 0.14-sec sampling 0.01 psi at 0.8-sec sampling
(0.1 psi for a 10-kpsi gauge)

Temperature rating 400°F (205°C) 350°F (175°C)

† 90% confidence limit

*Mark of Schlumberger SMP-5154-G (WTA 92)

10/95
MDT * Modular Formation
Schlumberger
Dynamics Tester
Module Specifications

*Mark of Schlumberger
10/95