Introduction to Cased-Hole Data

Acquisition and Interpretation

Permanent Temperature Profiling

Overview

1- Well Integrity

• Cementing: Cementing is a critical part of any well competition and subsequently

well integrity. Poor cementing is responsible for casing outer wall corrosion, leaks

and subsequently casing collapse.

• Corrosion: Corrosion is initiated immediately after placing the casing. The rate of

corrosion depends on many factors such as casing metallurgy, poor cementing and

casing stresses- to quote a few.

• Leaks: Leaks in casings and tubing will materialize in the long run. This again is a

function of the metallurgy, cementing and borehole environment.

2- Production Logging:

• Water, oil and gas production from every zone.

• Productivity index and pressure for each zone

• Detection of leaks behind and inside casings

• Estimation of cross-flow between zones caused by uneven depletion.

• Three phase production in horizontal wells.

3- Reservoir Monitoring:

• Estimating fluid saturations of water, oil and gas behind conductive and non-

conductive casings

• Applications of Pulsed neutron logging: capture mode (Σ) and Carbon/Oxygen

mode.

• Resistivity (Rt) measurements behind conductive and non-conductive casings.

• Evaluating stand-alone PNL logs in old wells.

Annulus bleed-off

Leak response

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Leak Detections- Temperature profiling:

There are many forms of logging that are used to detect leaks (temperature, noise,

oxygen activation, Injectivity). The most effective form is temperature profiling. The

examples above show:

Permanent Temperature sensors using fibre optics: This will become almost

standard in the future where the temperature profiles continuously monitored.

Standard E-Line temperature logging: The example on the right shows the

geothermal logs for 20 wells. 3 of the wells show a deviation from the geothermal.

An increase above geothermal means leak up behind the casing, and a decrease

below the geothermal mean leak down ward.

Well Integrity: Leak Detection/Temperature Profiling

Well Integrity: Corrosion Monitoring

Corrosion Mechanisms: There are many corrosion mechanisms that take place

downhole. These can be divided into 3 categories:

• Galvanic

• Chemical

• Mechanical (Stress)

Five set of tools are used to quantify inner wall corrosion, outer wall corrosion, pits and cathodic protection design and evaluation.

Well Integrity: Corrosion Monitoring

Corrosion Monitoring and Protection:

The example on the left shows a cathodic protection system evaluation giving

the lowermost level of protection.

The example on the right shows the combined log data from Cement,

Electromagnetic and Electrical logging data. Note the perfect correlations

between corrosion metal loss (middle tracks) with poor cementing (track on left)

and electrical current leaving casing- anodic points (track on the right)

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UltrasonicRotating

Flexural Wave

The introduction of the ultrasonic rotating tool, followed by the rotating flexural

wave measurement created a quantum jump in the quality of the cement

evaluations.

• Ultrasonic: Measures the acoustic impedance of the cement

• Flexural wave: measure the compressive strength of the cement.

The combination can define fluid (oil/water/gas) or solid (cement) circumferential coverage around the casing.

Well Integrity: Cementing

Spinner Calibrations

Running the spinner at different velocities, in the opposite direction to the flow,

provides the basis for spinner calibrations at any desired station, above perforations

(B and C above) and at any station within the perforations (e.g. X).

The slope of the straight line plot is the spinner sensitivity (velocity / rps which for a

given spinner depends on the fluid type) and the intercept on the y-axis which is the

rps due to the flow.

The intercept on the x-axis represents the threshold, which is the frictional force,

caused by mechanical and viscous friction, that represents the force needed to iniate

the spinner response.

Water Production

Water production is a serious

production limiter in most fields. One

common reason in high producers is

water coning.

Example shows how the water

production drops by 80% without

reducing (and often increasing) the oil

production when the choke is

decreased .

A change in the choke from 2 1/8 to 1

7/8 reduced the top of the water entry

level by 25 ft and increased the oil

production by 700 bl/d.

Coke: 2 1/8 Coke: 1 7/8

Production Logging in Horizontal Wells

Horizontal wells provide more challenges to

production logging. Variations of velocities and

hold-ups will span a wide range for little variations

in flow volumes.

This is caused mainly by small variations in the

well trajectory around 90 degrees.

New technology, like the FlowScanner Imager

(FSI) are effective in evaluating multi-phase flow in

horizontal wells.

Reservoir Monitoring

Pulsed Neutron Logging

Pulsed Neutron Logging (PNL) is the main tool that is used for reservoir

monitoring. This involves two data acquisition types:

Neutron Capture Mode (Σ). This is very effective where the water salinity is

known. .

Inelastic mode (Carbon/Oxygen). This relies .on spectroscopy and used

mainly in where water salinity is unknown or the water salinity is very low.

Capture Mode Inelastic Mode

Reservoir Monitoring

PNL Life Cycle

The minitron source fires around 20 million neutrons at speeds of 17 MeV. They

interact (bump) into the various atoms, slow down, then they get captured. The whole

life cycle of the neutron is approximately 200 m-sec (200 thousands of a second).

• The first 50 m-sec when the neutron are travelling fast is when spectroscopy

takes place and C/O is obtained.

• The last 50 m-sec of the neutron cycle is when the capture mode slope is

obtained.

C/O Σ

Reservoir Monitoring

PNL Capture Mode

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The Neutron Capture Mode (Σ) is the most practiced form of reservoir monitoring. It is

very effective where the water salinity is high (>50 kppm). It is most applied form is

time-lapse as shown above. The measured capture mode equation is the law of

superposition as shown above where the measured Σ for is the integral sum of the

fractional volume of each component multiplied by its unique Σ value.

Reservoir Monitoring

PNL C/O Mode

The Neutron High energy interaction can be used to obtain elemental evaluation of

Carbon and Oxygen. Empirically derived trapeziums for C/O ratios of different

detectors spaced at different distances can be used to obtain both values of Sw when

the salinity is low or unknown and when combined with the capture Σ is also used to

evaluate the fraction of the two waters sweeping across.

Introduction to Cased-Hole Data Acquisition and Interpretation

This is a 3-day course which is an introduction to cased hole data acquisition and

interpretations. The course covers three main cased hole topics:

Well integrity: This covers corrosion mechanism and corrosion monitoring, leak detection and

cement evaluation

Production logging: This covers production logging in vertical, deviated and horizontal wells and

also covers modern technology data acquisition tools to obtain holdups and velocities of the

three phases: Water/oil/gas.

Reservoir monitoring: This covers estimations of water and gas saturations behind conductive

and non-conductive casings. This includes Pulsed Neutron (PNL) logging and resistivity logging

behind conductive and non-conductive casings. .

This class is open to all technical domains in the oil and gas industry. No prior cased hole

experience is necessary. However, the course will also be beneficial to engineers with cased

hole experience as it covers modern high technology tools' physics and operations.

Agenda

Day-1:

Topic: Well Integrity

• Leak Detection using temperature and noise log profiling and oxygen activation to detect

water movements inside and behind single and multiple casings.

• Corrosion Mechanism and Corrosion Monitoring. This covers new high technology corrosion

monitoring tools and cathodic protection (CP) applications

• Cement Evaluation: New cement evaluations tools that give detailed circumferential

coverage of cementing around the inner casing.

Day-2:

Topic: Production Logging

• The various high technology tools that are used to estimate the 3-fluid phase velocities

• The various high technology tools that are used to estimate the 3-vertical/deviated/horizontal

wells. hold-ups.

• Production logging in vertical/deviated/horizontal wells.

Day-3:

Topic: Reservoir Monitoring

• Pulsed Neutron Logging (PNL): The physics and applications of PNL to estimate water

saturation and gas saturation behind casings.

• PNL applications for gravel pack quality control and for log-inject-log applications.

• Cased Hole resistivity measurement behind conductive casings to obtain formation resistivity

measurements.