In these times of low oil and gas prices, the drive to provide 'more for less' has never been greater. One key component in achieving this is the ability to accurately monitor the production rates along a wellbore and across a reservoir. Ideally a range of different measurements should be available on-demand from all points in all wells. Clearly conventional sensors such as downhole pressure and temperature gauges, flow meters, geophone arrays and production logging tools can provide part of the solution but the cost of all these different sensors limits their widespread deployment. Fibre-optic Distributed Acoustic Sensing, or DAS for short, is changing that. Using an optical fibre deployed in a cable from surface to the toe of a well DAS, often in combination with fibre-optic Distributed Temperature Sensing (DTS), provides a means of acquiring high resolution seismic, acoustic and temperature data at all points in real-time. Since the first downhole demonstrations of DAS technology in 2009 there has been rapid progress in developing the technology and applications, to the point where today it is being used to monitor the efficiency of hydraulic fracture treatments, provides continuous flow profiling across the entire wellbore and is used as a uniquely capable tool for borehole seismic acquisition. With optical fibre installed in your wells and DAS acquiring data, there is now the ability to cost effectively and continuously monitor wells and reservoirs to manage them in real-time in order to optimise production.

1. 1
David Hill
Illuminating insights into well and
reservoir optimisation using fibre-optic
Distributed Acoustic Sensing
Society of Petroleum Engineers
Distinguished Lecturer Program
www.spe.org/dl

2. 2
Outline
• What is Distributed Acoustic Sensing?
• The value of DAS in:
– Completions monitoring
– Borehole seismic acquisition
– Microseismic monitoring
– Permanent production monitoring
• Summary and Conclusions

3. 3
The Principles of DAS
• Distributed Acoustic Sensing (DAS) provides continuous
acoustic measurements along the entire optical fibre:
The fibre is the sensor
The Fibre Is The Sensor
A single optical fibre can replace hundreds or
thousands of traditional single-point sensors
1. Light pulse
interrogates
fibre
3. Light pulse
with an acoustic
modulated signal
is backscattered
2. Acoustic signal
deforms fibre
DAS cable
(Full well coverage)
Depth
TD
Surface

4. 4
Fiber Optic Distributed Sensing
Types of scattering effect
Name Main measurand Scattering Effect Scattering type
Distributed Acoustic Sensing (DAS) Dynamic strain and temp Rayleigh Linear
Distributed Temperature Sensing (DTS) Temperature Raman Non-linear
Distributed Temperature and Strain Sensing (DTSS) Temperature and strain Brillouin Non-linear

5. 5
What is DAS
• Technology capable of turning regular optic fibre in a cable into an array of ‘acoustic’
sensors
• Uses a laser light pulse and the “Rayleigh scattering” effect to measure strains in the
proximity of the fiber
The Science Behind the Service
20 µs for 2 km
Optical
Amplifier
Optical
Detector
Pulse of coherent
light
Single Mode Optical Fibre (9µm core)
Acoustic SignalRayleigh scattering
~-80dB/m

6. 6
DAS implementation
Video showing how DAS acquired downhole signals are visualized

7. 7
Integrated Well Surveillance Using DAS
One fibre … multiple applications … applied over the life of the well
Construction Completion Production Abandonment
Vertical
Seismic
Profile
Passive
seismicity
Flow
Profiling
Hydraulic
Fracture
Profiling
Wellbore
Integrity
Monitoring
Microseismic Monitoring
Flow Assurance Permanent Flow Monitoring
Stim Profiling
Smart Well Monitoring
Casing Leak Detection
Repeat VSPBaseline VSP Repeat VSP
Cross Well Comms
Cement Cure
Assessment
CCS MMV VSP
Subsidence
Operational Issues

8. 8
Downhole fibre installation
Semi-Permanent:
Attached to
production tubing
Permanent:
Cemented behind
casing
Temporary:
Deployed via wireline
or coiled tubing
Vertical Seismic Profile
Passive seismicity
Flow Profiling
Hydraulic Fracture
Profiling
Wellbore Integrity Monitoring
• Robust fibre and cable
composition permits harsh
environment deployment:
– Temperature Rating: +570ºF
– Pressure Rating: 25,000 psi
• Modern fibres resilient to
hydrogen darkening
Different methods of fibre
cable deployment enable
monitoring of new and
existing wells

9. 9
Full life cycle measurement workflows
All acquired on a single permanently installed fibre using DAS
• Measurement of the input, effect
and output of a process enables
the petroleum engineer to
optimise production
‘Monitor it
to manage it’
Model
driven well
description
Data
driven well
description
Hydraulic
Fracture
Profiling
Passive
seismicity
Baseline
VSP
Repeat
VSP
Improved
Reservoir
Model
Permanent
Injection
Flow Profiling
Permanent
Production
Flow Profiling
Repeat
VSP

10. 10
Value of DAS in Completion Monitoring
Optimizing Your Completion
Hydraulic Fracture Profiling (HFP):
Getting The Most From Your Well
Mitigating Operational Issues:
Saving Completion Dollars
Identifying Cross Well Communication:
Mitigating Your Risk
Hydraulic
Fracture
Profiling
Passive
seismicity
Baseline VSP
Repeat
VSP
Improved
Reservoir
Model
Permanent
Injection
Flow Profiling
Permanent
Production
Flow Profiling
Repeat
VSP

11. 11
25% 25% 25% 25%
• Determine Distribution of Fluid
DAS flow monitoring during hydraulic fracturing
Traditional Fracture Fluid Distribution Challenge

12. 12
30%
40%
16% 14%
• Determine Distribution of Fluid
DAS flow monitoring during hydraulic fracturing
Traditional Fracture Fluid Distribution Challenge

13. 13
60%
30%
10%
0%
• Determine Distribution of Fluid
DAS flow monitoring during hydraulic fracturing
Traditional Fracture Fluid Distribution Challenge

14. 14
Optimizing Your Completion
Analysis of perforation efficiency and performance
High
resolution
DAS
Distributed
Temp
(DTS)
Pumping
data
Perf
Clusters
Perf
Clusters

15. 15
Hydraulic fracture profiling - Uptake Analysis
Real-time Fluid and Proppant % Uptake Calculations

16. 16
DAS flow monitoring during hydraulic fracturing
DAS can provide an accurate measure of flow at each perforation
• There is a strong correlation
relating acoustic response to flow
through an orifice with known
conditions
• Not all perforation can be treated
equally when measuring flow
through the orifice
• Symbolic regression gives
equation with 95% prediction
accuracy
Images courtesy of Halliburton | Stokely, SPE-179151-MS
The data and the model for different fluids and
geometric configurations for a single perforation cluster

17. 17
Cross Well Communication
Using very low frequency DAS data (<0.05Hz)
Jin and Roy, TLE, Dec 2017
• Hydraulic-fracture geometry characterizations using this method can be
used to evaluate completions and well spacing design and constrain
reservoir models
700ft

18. 18
Value of DAS in borehole seismic acquisition
Reliable, Repeatable, Low-Risk Seismic Acquisition
High Fidelity Seismic Recording:
Matching Geophone Performance
Repeatable Low-Cost Acquisition:
Decreased Wellbore Interventions
Cost Effective Time-Lapse Monitoring:
4D Reservoir Imaging
Hydraulic
Fracture
Profiling
Passive
seismicity
Baseline VSP
Repeat
VSP
Improved
Reservoir
Model
Permanent
Injection
Flow Profiling
Permanent
Production
Flow Profiling
Repeat
VSP

19. 19
DAS-VSP Detection of Subtle Reservoir Changes
Excellent repeatability enables time-lapse monitoring of reservoirs
• DAS-VSP – WAW images can reveal changes associated to the stimulation
• High receiver density DAS provides wide image coverage that can cover
the injection zone
• Time-lapse anomalies can be integrated along with other DAS studies
including Hydraulic Fracture Profiling and Cross Well Communication
Baseline Monitor Difference

20. 20
Offshore DAS-VSP
Low cost method of acquiring on-demand seismic for EOR
3D OBN survey 3D DAS-VSP (multiple image)
7X (km)0
1
8
Depth(km)
1
8
Depth(km)
7X (km)0
Zhan, SEGAM-2015-5876420.1
Wong, EAGE-BGW2015
Vs.

21. 21
Value of DAS for microseismic monitoring
Cost effective monitoring:
No need for an observation well
Permanent monitoring:
During completion and into production
Maximising value:
Events map to production profile
Hydraulic
Fracture
Profiling
Passive
seismicity
Baseline VSP
Repeat
VSP
Improved
Reservoir
Model
Permanent
Injection
Flow Profiling
Permanent
Production
Flow Profiling
Repeat
VSP

22. 22
Time (ms)
Vertical
partofwell
Healof
well
Horizontal
partofwell
• Detection of low frequency, high
magnitude (>-1.5) microseismic events
initiated at reactivated faults
• Geolocation using 1 component (1C)
sensor possible using shaped array
localization
S-wave:
3.29e+03 m/s
P-wave:
5.37e+03 m/s
Well head
Channel 300
Channel
400
Permanent detection of microseismic activity
Enabling automated detection, recording and reporting of events
Webster, SEG-2013-0182

23. 23
Microseismic acquired during hydraulic fracturing
DAS measurements of the microseismic activity from adjacent well
• Complex microseismic wave
field behaviour observed
• Apex of the event tells us
where along the fibre the
event occurred
• Separation in time between
the Pressure (P) and Shear (S)
waves tells us how far from
the fibre the event is located
DAS microseismic event locations for several stages plotted, with
colour indicating the magnitude of the event
Example DAS microseismic event
Time
(seconds)
Depth

24. 24
Value of DAS for permanent flow monitoring
Optimizing injection and production
Permanent Flow Profiling:
Logging ON DEMAND
Production / Injection Optimization:
Which Perfs / Zones Add Revenue?
Mitigating Production Risks:
Leak Detection
Maximizing Value:
Acquisition of Complementary Datasets
Hydraulic
Fracture
Profiling
Passive
seismicity
Baseline VSP
Repeat
VSP
Improved
Reservoir
Model
Permanent
Injection
Flow Profiling
Permanent
Production
Flow Profiling
Repeat
VSP

25. 25
• DAS enables the
characterization of wellbore
dynamics behaviour
• Production flow monitoring
acquired over short term or
long term using
permanently deployed on-
demand systems
Flow assurance
Examples of DAS data taken on unconventional gas producers
Van der Horst, IPTC-17528-MS
Hydrodynamic slugging & fall-back
Inflow
Restriction at the heel
3 failed start-ups
start-ups
Dynamic
interface
Inflow &
cross-flow
Horizontal well – fibre outside casing
Deviated well – fibre outside casing
PerfsPerfs
shut-in
Time

26. 26
Data Deliverables and Analysis
… for on-demand flow profiling – QUALITATIVE MEASURE
Tue Wed Thu Fri Sat SunMon
Perforation cluster efficiency
64% @ 12:00 Thu
88% @ 20:00 Sat
• Due to the natural variability in flow
intermittent measurements can produce
very different results
• Regular DAS measurements provides a
more accurate long term trend
Trend calculated from DAS
measurements
Richards, SPE-173440-MS
Perorations
Days
Mon Tue Wed Thu Fri Sat Sun
Waterfall of the acoustic signals produces at the perforations
• Historical waterfall date recorded
and processed
• Continuous measurement of the
perf cluster efficiency provided

27. 27
Long term trend
Waterfall showing decline in production over a two year period

28. 28
A single DAS measurement can
convey different information in
different frequencies:
• Low frequencies:
– Liquid transport
– Fluid interfaces
– Thermal disturbances
• Medium frequencies:
– Flow through ICVs
– Flow past obstacles
• High frequencies:
– Flow through GLVs
Information contained in different frequency bands
in ‘t Panhuis, SPE-170917-MS

29. 29
• Using DAS, gas-lift
performance can be
analyzed as a function of ICV
settings, down-hole
production & flow regime
High Frequencies
Low Frequencies
Setting - ICV A
Setting - ICV D
Gas-lift monitoring in smart wells
Providing real-time monitoring of dynamic behaviour
in ‘t Panhuis, SPE-170917-MS

30. 30
Time-lapse 3D visualization of flow
For quick review of dynamic behavior in well
• Visualization of slug formation and
movement (low frequency)
• Visualization of flow across ICV’s
and GLVs (high frequency)

31. 31
DTS DAS DAS - waterfall
DAS – waterfall Avg Diameter Reduct.
• Build-up of deposits can be picked up as a large peak in DAS
• Empirical DAS correlations used to quantify wax and scale build-up in time
and depth
Monitoring build-up of deposits in the wellbore
Identification of wax and scale location and effect on flow
in ‘t Panhuis, SPE-170917-MS

32. 32
Wellbore Integrity Monitoring
Casing leak detection
Gas
Water
Periodic
gas entry
Gas exit to
annulus
• Permanently deployed
fibre enables DAS to
continuously listen for
leaks
• Detection of both:
– Continuous leaks in casing
or tubing into annulus
– Intermittent injection of
gas from reservoir through
casing
Seconds
Minutes
Boone, et al, IPTC-17530

33. 33
Integrated Well Surveillance Using DAS
One sensor … multiple applications … over the life of the well
ProductionCompletions
DAS
Evaluation
Vertical
seismic
Profile
Micro-
seismic
Operation
monitoring
Frac
Profiling
Cross Well
Comms
Flow
assurance
Permanent
flow
monitoring
Smart well
monitoring

34. 34
Summary & Conclusion
 Permanent DAS systems deployed alongside DTS
MAXIMIZES ASSET VALUE by providing:
 low cost means of acquiring full wellbore measurements, with no
production deferment
 effective way of understanding the complexities and nuances of the
downhole production environment
 real-time visualization of production, enabling quicker response to the
changes in production behavior
 ability to acquire on demand borehole seismic data
 online asset condition and integrity monitoring
One sensor … multiple applications … over the life of the well

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