The Essentials of Fiber-Optic Distributed Temperature Analysis

The Essentials of Fiber-Optic Distributed Temperature Analysis

Absheron Consulting Ltd. G. Brown, September 2019

LPS “Life after casing” seminar

Contents

• Basics of the DTS measurement

• Installation options

• Flow measurement

• Examples:

Steam-flood monitoring

Fiber outside casing

Gas breakthrough in a horizontal producer

Gas flow rate in velocity string completions

Water injector responses

Acid stimulation

Flow behind casing

Gas lift monitoring

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Measurement Basics

An industrial laser sends pulses of light down an optical fiber

The backscattered light returning to the measurement box is analyzed to produce a temperature measurement every meter down the fiber. The profile acquisition can be from every few seconds to several hours, depending on the box settings

The temperature measurement assumes a single loss characteristic along the fiber if only one laser is used and the fiber is “single ended”

A variable loss characteristic (and the effect of fiber darkening) can be corrected for by either employing a “double ended” measurement or two lasers of slightly different wavelength and a “single ended” installation

3

DTS measurement

1064nm wavelength

*Re Schlumberger “The Essentials of Fiber-Optic Distributed Temperature Analysis” 4

NTS and TTS data – double ended fiber measurement

WellheadWellhead

Bottom of well

Fiber Length (ft)


Single ended vs. double ended measurements


Incident

Raleigh

Light

Brillouin

Anti-Stokes

Raman Band

Stokes

Raman Band

Laser 1

2 Laser Single Ended DTS measurement (Schlumberger ASE)

DTS Box Fiber in WellReference

Coil (RCT)

Analyser

Incident

Raleigh

Light

Brillouin

Anti-Stokes

Raman Band

Stokes

Raman Band

Laser 2

1064 & 1015nm

wavelengths

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DTS fiber measurement type responses(note 8km DE is 4km well depth – similar to 4 km SE)


4km two laser response

4km single laser response

8km double ended response

Installation options

Permanent installations

Fiber pumped down oilfield control line with water

Fiber installed as part of a downhole gauge cable

Temporary installations

Fiber located inside a “slick line” wire

Fiber installed inside coiled tubing

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Permanent installation options


Electrical pressure gauge cable and slick-line wire

Electric gauge cable Slick-line wireSchlumberger “Neon” Schlumberger “OPTICall”


Fiber inside coiled tubing (Schlumberger “ACTive”)

4 fiber’s inside a 0.071 inch tube – inside the coiled tubing


Basics of DTS flow measurement

1. The temperature measured in the well-bore at a given point above a flowing zone is flow rate and time dependent

2. In addition to this the temperature of the liquid is influenced by Joule-Thomson heating or cooling caused by the drawdown pressure drop flowing into the well - and also the pressure drop of flow up the production tubing

In simple flow rate calculations 2. can be ignored and the flow rate at a zone above the bottom zone is just the fraction of the cooling experienced at the higher zone

In more complex cases you need a near well-bore thermal reservoir model that will calculate the increase/decrease in temperature of the flow coming out of the formation due to the Joule-Thomson effect as a function of the drawdown pressure drop and also the change in temperature caused by the pressure drop of the fluid flowing up the tubing

13

Simple multi-zone temperature flow calculation


Flow from the upper zone

Qupper = Qtotal.(Tl – Tt)

(Tl – Tg)

The Joule-Thomson effect – radial flow drawdown calculator


Joule-Thomson multi-zone temperature flow calculation


Joule-Thomson temperature model vs. measured temperature


Joule-Thomson temperature model vs. PLT spinner

DTS flow rate

DTS model

temperature

DTS flowing

temperature


Some examples of DTS temperature monitoring

• Steam-flood monitoring

• Fiber outside sand-screens

• Gas breakthrough in a horizontal producer

• Gas flow rate in velocity string completions

• Water injectors

• Acid stimulation

• Flow behind casing

• Gas lift monitoring

19

Previously

steamed zone

Steam fronts moving

through the reservoir

X

X+500

X+1000

X+1500

X+2000

Steam-flood tracking at a monitor well over 5 year period


DTS fiber located outside sand-screens


DTS fiber located outside sand-screens showing upper zone depletion


Gas breakthrough on a horizontal sand-screen well


Conventional Velocity string Velocity string + annular flow

Gas well velocity string completions


Geothermal

Thermal model fit

Flowing temperature

Calculated gas

rate

Spinner flow

rateX+200

X

X+400

X+600

X+800

Velocity string analysis compared to a spinner log


Injector warm-back – 100 days injection


Horizontal well shut-in after a long injection


Injection re-starts - injecting a hot slug down the reservoir


Wormholes

Wormholes

Side view Top view

Acid stimulation wormholes


Acid exothermal warm-back

Normal warm-back

X

X+200

X+400

X+600

Acid exothermal heating during shut-in warm-back


Acid exothermal response

X

X+200

X+400

X+600

Acid exothermal heating during shut-in warm-back – with normal warm-back removed


Cross-flow between permeable reservoirs outside the casing

Flow behind casing


Gas lift – leaks in tubing between GL valves


Conclusions

DTS fiber temperature measurements (particularly permanently installed) can facilitate continuous monitoring of well performance over years of production without the need for expensive and risky production log interventions

Under many scenarios accurate flow profiles can be determined by modelling the temperature profile with a thermal near well-bore model

Spinners have a low velocity limitation (threshold) and cannot measure fluids outside the reach of the spinner (i.e. outside casing) - temperature can do this

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Thank you for listening to my

presentationGeorge Brown

The Essentials of Fiber-Optic Distributed Temperature Analysis

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