12.8 Sop Alfa Uht

ALFA – Acoustic Leak Flow Analyzer
Originator Alan Muhadjir Date 13 January 2023

Approver Revision B
Loss of annular integrity in a well can create loss of zonal isolation, which can
significantly impair the productive capability and efficiency of the well. Effective
remedial action must be based on a clear understanding of the underlying causes. It
has previously been difficult or near-impossible to locate and explain the undesired
fluid movements symptomatic of loss of annular integrity. Without this information,
repair or control is at best a matter of informed guesswork or trial-and-error.
INTRODUCTION
Achieving zonal isolation by cementing annulus space between casing and well bore wall is an important job
in many oil wells. Cementing of the annulus may take place during drilling stage of the well bore or completion
of the well. While cementing the annular space behind several casings strings or whole casings in the well may
be cemented properly in place to get a hydraulic seal.
The main purpose of cement over the production intervals is to provide isolation in the neighbouring zones.
Hydraulic isolation allows the well operator to selectively complete certain zones and assures that fluid will
not move into or from the neighbouring zones through the borehole behind casing. Failure of isolation can
cause myriad of problems such as (Smolen, JJ, 1996):
• Water production
• Depletion of gas drive mechanism
• Loss of production to the neighbouring zones
• Contamination of fresh water reservoir
Despite the efforts to get good zonal isolation, migration of formation fluid in the annulus takes place.
Migration implies here the entry of formation fluid from the formations pores into annulus behind casing due
to a pressure imbalance at the fluid-bearing formation face, followed by upwards migration of the fluid in the
annulus. The fluid flows to a lower pressure zone or possibly up to surface. Water/gas leakage in the
production casing annulus has been recognized as a major completion problem in the oil well. A successful
cement job results in complete zonal isolation on a permanent basis.
Conventional CBL tool is an “integrating” tool, it has monopole transducer which will read the average quality
of cement around the wellbore. It will give same response to following different conditions: 100% cemented
pipe with low compressive strength cement OR Partially cemented pipe with high compressive strength
cement (e.g. channels) OR – Micro-annulus. While newer segmented ultrasound Cement Evaluation only be
able to provide cement quality information right behind the casing. It has difficulty detecting formation bond,
may give false readings in high-viscosity mud and cannot distinguish between Micro-Annulus and absent
cement. Figure 2 is typical cementing problem may happen. Conventional CBL will only give the average
presence of the cement, while segmented ultrasound cement evaluation will not be able to detect cement
flaw type III, IV and some of type V which not directly in contact with casing.
Wellbore temperature profile data has been used to characterize down-hole fluid flow since at least 1918
(Van Orstrand), enhanced by additional simple acoustic energy levels to be correlated to fluid movement on
1955 (Enright). On simple case where the flow rate is quite high and temperature anomalies can be seen
obviously both data acquisition and the results may be treated as correspondingly simple. Most of the
occasions show that this is not the case.
 2016 GOWell International. All rights reserved. P a g e | 1/3

This document and the information contained herein are the sole property of GOWell International.
Any reproduction or distribution-in whole or in part-without written permission of GOWell International is prohibited.
Approver Revision B
CASE Example :
An oil well in offshore Java was logged with the conventional production logging suite (PLT) in order to identify
the water source affecting 100% of water cut production from a reservoir believed to contain oil. Nearby well
on same structure proven to produce 1800 bopd, which cutting log, petrophysical data, pressure test data
during drilling also suggest high confidence of oil in the reservoir. However the PLT survey failed to give an
answer. The PLT data suggest that 100% water is coming from perforated interval, which is contradictive to
the believed that the reservoir should produce oil.
GOWell’s Acoustic Leak Flow Analyser (ALFA) tool was deployed to identify the source of water being
produced from this oil well. The tool uses very sensitive acoustic sensors to be able to measure auible and
ultrasound produced downhole by either gas or liquid flow. Measurements are taken over a wide frequency
range, between 8 Hz and 60 KHz with very high frequency resolution, up to 512 channels, enabling a very
effective way of leak detection as well as detection of various kinds of gas, water, or oil flow, including flow
behind the pipe.
• Fluid movement thru media will produce noise. The noise comes from both fluid itself and vibrating
elements streamlined by fluid flows.
• The fluid noise is result of internal friction and normally audible in high speed turbulent flows.
• In wellbore, fluid flows generate noise through the vibration of various features of the geological
environment and wellbore components.
• Noise frequency spectrum depends on the type of channel through which fluid/gas moves.
• Noise intensity or volume increases with linear flow rate, as function of fluid type and pressure gradient.
Having very high frequency spectrum resolution enabling us to differentiate the flow type, whether laminar
flow inside wellbore, channeling flow behind casing, leaking thru jewelries and formation flow.
• To identify behind casing channeling, if there is.
• To identify the actual production zones.
• To identify the source of high water cut
The well was drilled on early 1980’s (Figure 2), well was workovered in
2016 to produce oil from a reservoir which is proven to produce 1800
3-1/2 SCSSV
3-1/2" GLM#1 (0.1875" GLV #530 psi)
3-1/2" GLM#2 (0.1875" GLV #520 psi)

bopd with very low water cut on same structure of nearby well. The zone
3-1/2" GLM#3 (0.1875" GLV #505 psi)
was perforated, the well can flow on gas lift arrangement with fluid rate
up to 1200 bfpd with flowing tubing Pressure 140 psi and A-annulus Gas
3-1/2" GLM#4 (0.25" SO)
3-1/2" SSD (2.813"), Down to open
lift injection Pressure 465 psi. Unfortunately fluid sample showed the
9-5/8 X 3-1/2 MRP (40-47)
well producing unexpected high water cut of more than 95%. The main
facilitating conditions for water production could be the unknown
3-1/2" SSD (2.813"), Down to open
3-1/2" EUE 'X' Nipple (2.812)

Target Reservoir
cement hydraulic isolation quality.

2954-3003'md 3-1/2" EUE WLEG (Full Shoe)
Top Of cement at 3097 ftmd
The driver of doing the wellbore flow surveillance are to get clear picture
cement lay in
Camco HSD-3-SP-LS
9-5/8" x 2-7/8" x 2-7/8"
Safety joint RHR
of wellbore flow problem for near future workover remediation plan.

Camco WB1-D SSD
Rubber coated blast joint
TOL @ 4576'
9-5/8" csg 43# K-55 BTC

1.338” OD Acoustic Spectral Based Annular Leak Flow Analyzer tool
(ALFA), High Resolution Temperature Tool (HRTT) and Casing Collar
9-5/8" Shoe @ 4785'
Locator (CCL) was ran to perform well flow diagnostic. A survey was
Camco WB1-D SSD
Camco HRP4-SP
7" x 2-7/8" Hydraulic packer
XN Nipple
undertaken from 3043 ft to surface inside production casing/tubing and
EOT
the result are shown in Figure 1,2 and 3.
PBTD @ 6455'

Approver Revision B
The ALFA are include temperature and CCL. The temperature sensors are critical to the effective interpretation
of an ALFA survey, so the first run into the well was a baseline log recorded while logging down. This pass was
recorded from surface to maximum logging depth.
Because the ALFA survey records a dynamic and unknown environment, almost the entire period in the well
are recorded (up, down and stationary). Survey design is highly dependent on the specific integrity
investigation (depth, leak rate, well structure). The following factors was considered:
• Annulus pressure. Consider varying annulus pressure as a means of perturbing any observed flow, or the
converse.
• The effect of tool movement –tool string configuration and/or logging speed adjusted to minimize ‘tool-
stick’, which will have a detrimental effect on log data, particularly temperature and to a lesser extent,
ALFA.
• Stationary measurements are a reference point for any ALFA dynamic log.
• ALFA survey was planned such that the well was logged under at least two different annular pressure
regimes (i.e. the annuli where flow is expected/suspected) should be ‘perturbed’ by varying the pressure
by intervention at surface. In this case, the survey was undertaken in 4 different condition, which are:
• Flowing 100% choke size on Gas Lift Operation
• Flowing 60% choke size on Gas Lift Operation
• Shut in
• Water injection to perforated zone (Since Gas Lift Mandrel flow activity creating dominant frequency
spectrum noise, injection pass is to evaluate flow path behind casing in area above the Gas Lift
Mandrel).
Result and Key outcomes
The data acquired in the well was of good quality. All the ALFA was run with a HRTT, which provided a good
benchmark to compare and qualify the flow problem in the well. CCL was run to give precise/accurate depth
correlation of the responses.
We are using a deep and thorough analysis which combines and cross-references several important data
sources and analysis techniques, which the processes are:
• Mapping of the audible and ultrasound noise energy map of the well bore which associated with fluid
movement activity (through-tubing Spectral Passive Noise ALFA log)
• A thermal profile of the well (through-tubing High Resolution Temperature Tool HRTT log).
• Manipulation of annuli or tubing at surface before or during logging, by the production or injection of
fluids in a planned program sequence.
• Measurement of hydrostatic pressure and fluid density in the well bore.
• Analysis and interpretation of other data as appropriate, including but not limited to cement bond logs,
pore-pressure data, lithology, drilling and cementing records, reservoir flow history and annular wellhead
pressure data
The analysis is open, transparent and logical, encouraging a teamwork response to problem-solving. The
method can often identify and differentiate flow in multiple annuli.

Approver Revision B
Effectiveness of evaluation
By gathering the result of Spectrum frequency Map and temperature data, flow behavior of the well can be
concluded:
• During 100% choke and 60% choke flow:

• Perforated reservoir is not actively producing fluid to wellbore (Figure 3). There is no high frequency
noise activity on that interval.
• The most active contributing reservoir is water zone right below perforated zone, and several
reservoir above it (Figure 2 and Figure 3). High frequency noise is detected, associated with a fluid
flow thru very tight pores, which is reservoir pores.
• There is indication of behind casing channeling flow from far below perforated zone to perforated
zone, high possibility contributing the water production as well (Figure 3). The source of fluid flow is
not recorded due to have been covered by a cement plug.
• Temperature data showing no heating effect at the top of perforation interval, associated with fluid
inflow from above zones through the channeling
• During Shut in condition:

• There is no frequency spectrum noise detected other than on surface which associated to surface
activity of sea wave and flow activity nearby well around their wellhead.
• During Water injection to perforated zone:

• Medium frequency spectrum is detected from perforated zone up to 250 ft. High possibility associated
with a channeling flow activity.
The essence of the final deliverable is a map of fluid flows in and between formations, annuli of the well
completion, and surface. The results have enabled the prioritization of the workover program for these wells.
With a high cost of each workover, by knowing the exact problem of the well, operator has ability to plan
effective and efficient remediation action.
Figure 1. ALFA-TEMP data, whole section of the well.

Approver Revision B
CONCLUSION
Annular integrity problems restrict the operational viability of a production well, and annular zonal isolation
surveillance can be successfully applied to provide clear identification of undesirable fluid movements in well
annuli. The qualitative and quantitative analysis provides effective support to justify the occurrence of these
movement for decision process in defining effective and efficient remediation solutions.
Production Logging tools are a great tool for inside wellbore flow profiling and passive spectral noise log
completing the surveillance by providing behind casing flow behavior.
With a diameter of 1.338" (34 mm), the tool can be run through most of the commonly used tubing sizes and
used to inspect well flow profile through the tubing. This allows for greatly reduced operating costs and time
to evaluate the well flow behavior without the need to pull-out the tubing string to evaluate the behind casing
flow behavior.
Approver Revision B
ALFA Operating Technique :

GOWell’s Acoustic Leak Flow Analyser (ALFA) is a memory tool used to carry out various well diagnostic
studies including Well Integrity Evaluation, Production Performance and Reservoir Monitoring. This device
measures Acoustic Spectrum within the range of 8 Hz to 60,000 kHz with very high frequency resolution. The
tool consists of Spectral Noise, Pressure, High Resolution Temperature and Casing Collar Locator sensors.
The tool uses very sensitive acoustic sensor to be able to measure sound produced downhole by either gas or
liquid flow. Measurements are taken over a wide frequency range, enabling a very effective way of leak
detection a well as detection of various kinds of gas, water, or oil flow, including flow behind the pipe.
The standard Acoustic Leak Flow Survey must include temperature and CCL log. Will be better if a complete
CCL/GR log is available from client. The temperature and pressure sensors are critical to the effective
interpretation of a survey.
Consideration should always be given to the deployment of two ALFA sensors – offering clients considerable
savings in logging time while ensuring repeatability of data.
Because the ALFA survey records a dynamic and unknown environment, as far as possible, almost the entire
period in the well should be recorded (up, down and stationary).
Temperature data is also critical to the interpretation of ALFA data, so the first run into the well should be a
baseline log recorded while logging down. This pass should be recorded from surface to maximum logging
depth at no more than 30ft/min (10 m/min).
Survey design is highly dependent on the specific integrity investigation (depth, leak rate, well structure). The
following factors should be considered:
• Annulus pressure, specifically in the case of a suspected micro-annular flow. High annulus pressure
may cause any microannulus to close or reduce flow. Consider varying annulus pressure as a means
of perturbing any observed flow, or the converse.
• The effect of tool movement – head tension should always be monitored, and toolstring configuration
and/or logging speed adjusted to minimise ‘tool-stick’, which will have a detrimental effect on log
data, particularly temperature and to a lesser extent, ALFA.
• In a well where a very low signal is to be expected (very low leak rates, high signal attenuation), or in
shallow wells (where RIH/POOH time is relatively short) the use of slickline deployment is
recommended, with data downloaded between runs. Slickline has a smaller perturbation effect on
both the acoustic profile and the temperature profile in the well, and is desirable for this reason.
However the slickline unit must be capable of steady logging speeds at 30 ft/min.
• Stationary measurements are a reference point for any dynamic log. Any programme must contain an
element of stationary logging.
• The content and history of the annuli in a well: an annulus know to have contained un-displaced drilling
mud will almost certainly have a solids-gradient, known as mud-sagging which will have a significant
and changing effect with depth on acoustic signals from that annulus or areas beyond.
A guideline operating programme (typical for a well with a low rate leak):
• Bring well to static condition a known time before logging - preferably at least 48 hours. (i.e. not
changing well status, which could mean steady bleeding of an annulus, for example)

Approver Revision B
• Run in hole recording baseline log at 30 ft/min. Logging up with 40 seconds station stops every certain
interval (i.e every 5 ft). An alternative strategy for deep wells/long survey interval that are time
constrained is to log on high density stops (i.e. every 5 – 10 ft) over the suspected leak/flow and less
density stops (i.e. every 25 – 50 ft) over the rest of survey. This approach produces the best possible
baseline acoustic and temperature log.
• Activate the well if applicable (i.e. vent/pressurize a well annulus or tubing as planned).
• Run in hole recording dynamic log at 30 ft/min. Logging up with 40 seconds station stops every certain
interval (i.e every 5 ft). An alternative strategy for deep wells/long survey interval that are time
constrained is to log on high density stops (i.e. every 5 – 10 ft) over the suspected leak/flow and less
density stops (i.e. every 25 – 50 ft) over the rest of survey. This approach produces the best possible
acoustic and temperature log.
• Where possible or appropriate, conduct at least one complete repeat of the Main Log. Running two
sensors removes the requirement for repeat logs like this and is very desirable.
• Where possible or appropriate, conduct temperature transient log by recording temperature right
after shutting off dynamic situation.
Maximum logging speed
The maximum logging speed for Temperature logging is 45 ft/min, but for optimum results a speed of 30
ft/min is required. The first down-log in the well is the most important for the temperature data.
Tool positioning
The ALFA tool is normally run with solid low-friction standoffs with the temperature tool at the most bottom
section in the tool string.
Recommended sensor configuration is:
• Rope Socket
• Roller Weight Bar
• CCL
• ALFA
• Temperature
• Bullnose
Repeatability
The ALFA Acoustic sensor is ultra-sensitive, and responds to dynamically changing stimuli on an instantaneous
basis. It is therefore not expected to produce identical repeat data, as conditions in the well may be changing
from second to second.
Potential sources of random mechanical noise or resonances must be taken into account when assessing the
repeatability of ALFA data.
The ALFA response is influenced by fluid media, so that a move from water to oil or oil to gas will reduce the
received signal due to changes in signal attenuation in the media.
Similarly, changes in casing/tubing structure, lithology, cement character and annular fluid can affect the ALFA
response.

Approver Revision B
Tool quality control log

A typical ALFA response will usually exhibit quiet areas where signal levels return to baseline. When the tool
string is moving it responds to all sources of frequency acoustic energy including those generated by the
movement of the tool itself.
All logging programs will include main element of stationary recording, which are the most reliable reference
as to whether recorded energy is created by the movement of the logging string or by some other source.
Other techniques
Where possible, the ALFA survey should be planned such that the well is logged under at least two different
annular pressure regimes (i.e. the annuli where flow is expected/suspected) should be ‘perturbed’ by varying
the pressure by intervention at surface. For example, a well with sustained A-annulus pressure could be logged
once with the annulus shut in, and once with the annulus bled down.
All annulus pressures must be recorded during logging – at a frequency of at least 30 minute intervals, but
preferably continuously/electronically.
Data quality checks
Because of the sensitive characteristics of the ALFA sensor, it is not easy to check data quality. Because sources
of acoustic energy are dynamic and variable, even the static level of signal can vary dramatically and
unpredictably with time due to uncontrolled downhole fluid movements.
The most effective way to confirm good data quality is to compare the response of the ALFA with that of the
Temperature tool. A valid energy peak over an interval of several feet is often correlated to a small (either
cooling or heating) local perturbation of the temperature.
However, the reverse is not true: the presence of a temperature perturbation does not automatically correlate
to an increase in acoustic energy. Temperature variations have a significant ‘remanence’ (i.e. once perturbed,
the effect dies away only slowly – in the case of temperature, exponentially) whereas acoustic signatures and
perturbations have negligible remanence.
Other environmental factors
The following external factors may influence ALFA response, and should be considered in assessing unusual
or unexpected data:
• The presence of scale, sand or other solid debris (moving or otherwise) in the well
• Production/flow in adjacent wells (especially immediately below an offshore platform)
• Mediators (interfere with how energy created arrives at the sensor)
o Pipe weight (wall thickness) and quality
o Completion ‘jewelries’
• Well geometry/structure:
o Well deviation (varying contact force to logging tool and cable, concentric tubular contact,
cement geometries)
o Micro annulus geometries
• Well media/environment:
o Wellbore, annular and formation fluid (density, viscosity, % solids, acoustic impedance)
o Emulsion in tubing (bubbles scatter ultrasound like solid particles)
o Cement (weight, type)
o Lithology (we do not currently fully understand the influence of lithology on frequencies)
• Fracture structures


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ALFA – Acoustic Leak Flow Analyzer

Originator Alan Muhadjir Date 13 January 2023

 2016 GOWell International. All rights reserved. P a g e | 1/3

3-1/2" GLM#1 (0.1875" GLV #530 psi)

3-1/2" GLM#2 (0.1875" GLV #520 psi)

3-1/2" SSD (2.813"), Down to open

3-1/2" EUE 'X' Nipple (2.812)

cement hydraulic isolation quality.

Top Of cement at 3097 ftmd

of wellbore flow problem for near future workover remediation plan.

Rubber coated blast joint

9-5/8" csg 43# K-55 BTC

 2016 GOWell International. All rights reserved. P a g e | 2/3

Result and Key outcomes

 2016 GOWell International. All rights reserved. P a g e | 3/3

• During 100% choke and 60% choke flow:

• During Shut in condition:

• During Water injection to perforated zone:

Figure 1. ALFA-TEMP data, whole section of the well.

 2016 GOWell International. All rights reserved. P a g e | 4/3

Figure 1. ALFA-TEMP data, whole section of the well.

Figure 1. ALFA-TEMP data, whole section of the well.

ALFA Operating Technique :

 2016 GOWell International. All rights reserved. P a g e | 6/3

 2016 GOWell International. All rights reserved. P a g e | 7/3

Tool quality control log

 2016 GOWell International. All rights reserved. P a g e | 8/3

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