Coiled Tubing Cleanout, Diagnosis, And Remediation of Sand Control Failures

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Through Tubing Cleanout, Diagnosis and

Remediation of Sand Control Failures

Prepared by:

Bryan Stamm

November 15, 2006



Introduction:

This document describes the Schlumberger technologies available for:

• Cleaning out sand control failures

•

Diagnosing the location of the failure • Repairing such failures

The described technologies are based on general sand control screen failures in both casedhole and open hole applications. Attached to this document are several brochures with the

descriptions of the available technology and also case histories.

Assumptions:

The screen types described in both well cases assume that the screen in composed of basepipe and screen jacket. The screen jacket can be premium (Dutch weave, sintered laminate,

etc.) or wirewrapped (including pre-packed).

Attached below are pictures representative of a premium and wire wrapped screen.

Premium Screen

Wire Wrapped Screen

Pre-packed Screen



Although Schlumberger does not manufacture expandable screens, the techniques

described in this document also apply.

Of more importance than the type of screen is access to the screens (minimum restriction

above). The ODs of the cleanout, diagnostic, and remediation tools are provided so that

their application different size wellbores is well defined.

Clean out:

Although not specified, the assumption is that a failed sand control well will have been shut

in or the production rate substantially reduced upon the detection of sand at the surfacedetector or production facility. This action was taken to prevent any damage to the

wellbore or production hardware.

For the purpose of this document, it is assumed that some fill may need to be removed inorder to gain access to the potential areas from which the sand was produced.

Schlumberger does not recommend attempting failure diagnostic work prior assuring the

wellbore is free of sand / gravel, as the risk of sticking the diagnostics tools is very high.

Prior to beginning any cleanout operations, a clear identification of the sand produced

should be provided to Schlumberger. The size and type of formation sand or gravel willallow for potential identification of the location of the failure, and may allow estimation as

to the amount of material potentially in the wellbore. The type and size of sand will also be

important in establishing the cleanout techniques (rates, fluids, etc).

The issue of bailing the sand with slickline while mobilizing additional equipment oftenarises. It is Schlumberger’s experience is that trying to remove sand from a failed gravel

pack with bailers can often lead to damage of the upper completion hardware if multipleruns are made. A few bailer runs to establish the depth of the fill may lead to a decision not

to rig up CT if complete access is possible (i.e. sufficient rat hole as in well type one).

Also identifying the fill depth will allow CT washing operations to commence at the filldepth rather than higher up the well, saving cleanout time.

The use of coiled tubing (CT) for through tubing remedial services after installed gravelpack completions fail is viable and efficient solution. The coiled tubing equipment is small

modular equipment and can be mobilized quickly.

For the purposes of this report, horizontal and vertical wells with 5 ½” production tubingand also 5 ½” screens were examined. However, well completions of any size can be a

challenge depending on the following.

- Maximum crane lift capacity offshore

- Deck space and deck loading capacity of the location

- Well depth



- The maximum inclination of the wellbore

- Bottom hole pressure and temperature

- Type and size of solids that fill the wellbore

Wellbore Solids RemovalWith the challenges described above in mind, Schlumberger can design an efficient

cleanout using their PowerCLEAN services. PowerCLEAN is the engineering approach toefficient wellbore cleanouts. The service is a combination of the following aspects.

- Software modeling program

- Special design cleanout wash nozzle

- Suite of cleanout fluids to fit the well conditions

- Solids monitoring device at surface

- Fluids and solids handling equipment for separation and re-cycling of fluids

Horizontal wellbore across the sandface:

This well is placed horizontally into the pay zone with a length of approximately 3,000

ft. cleaning out horizontal wells required high annular fluid velocities and goodcarrying capacity of the fluid used. The challenges in this wellbore profile are the long

horizontal section and the fairly large tubing ID. This well can be cleaned out using the

following coiled tubing string sizes.

1.75” OD Coiled Tubing

- Sweeping technique back up to 7,000 ft taking 50 ft bites

- Cleanout speed 5 ft/min

- Fluid rates 3.0 bpm

- Specialized cleanout fluid with high carrying capacity and low pump pressures


- Sweeping technique back up to 7,000 taking 100 ft bites


- Fluid rates 4.0 – 4.5 bpm


2.375” OD Coiled Tubing- Circulating wash technique 500 ft bites (Not POOH back to 7,000 ft for each bite

length)







- Circulating wash technique 500 ft bites (Not POOH back to 7,000 ft for each bite

length)



- No specialized fluids required. Fresh water or light brines can be used

Looking at the different available scenarios described above it will be possible to clean

the wellbore from solids. The PowerCLEAN approach will help to identify the most

efficient cleanout procedure within the limitations of the well and the location.

Vertical wellbore across the sandface (with exposed casing):

This wellbore is a vertical and is completed with 5 ½” production tubing. The

completion is placed in sections leaving voids back to casing ID. The challenges in this

type of wellbores are the already large ID of the tubing and the additional extreme largecasing ID between the different sections of the production tubing. After a brief review

of the well description and using the PowerCLEAN approach, this well can be cleanout

using the following coiled tubing sizes.


- Sweeping technique back up to 10,500 ft taking 200 ft bites




2.00” OD Coiled Tubing- Sweeping technique back up to 10,500 taking 500 ft bites





- Circulating wash technique 1000 ft bites (Not necessary to POOH back to 10,500

ft for each bite length)





- Circulating wash technique 1000 ft bites (Not necessary POOH back to 10,500 ftfor each bite length)





- No specialized fluids required. Fresh water or light brines can be used

Looking at the different available scenarios described above it will be possible to cleanthe wellbore from solids. The PowerCLEAN approach will help to identify the most

efficient cleanout procedure within the limitations of the well and the location. As

described the wellbore was simulated as a vertical drilled well. Changing the directionalpath of the wellbore will influence the cleanout efficiency of each coiled tubing size

described. Also increasing the length of the large ID voids in the completion will

complicate an efficient cleanout.

For both wellbore types, Schlumberger is able to supply the coiled tubing strings and fluids

required for the most efficient cleanout scenario. The specialized PowerCLEAN fluids that

we offer have the following technical parameters.

- Density range: 8.34 ppg – 15.5 ppg

- Temperature stable up to 300 F

- Compatible with high density brines

- Fluid recycling possible

To improve the cleanout procedures on location is real-time Schlumberger offers the DPS2

services, which enables engineer on location to adjust the cleanout schedule based on real-time recorded downhole data.

When the Coiled Tubing size able to be mobilized onto the location is limited due tologistical or location limitations, Schlumberger can offer reverse circulating techniques to

remove solids from the wellbore. This technique is a proven cleanout technique in several

parts of the world. To perform this cleanout technique the standard dual check valve

assembly can not be run to enable flow up the coiled tubing string. For well controlpurposes Schlumberger is currently looking into engineering solutions for reversible check

valves.

It is recommended that all CT cleaning operations be performed with the well in a slightly

overbalanced condition. This will minimize the amount of fluid lost to the formation

during washing operations (reducing damage) while preventing the well from flowingwhile will introduce more solids into the wellbore. Fluid losses should be controlled with a

solids free pill (VES, HEC, or X-linked HEC fluid loss control pills). Calcium carbonate

should be avoided as it may interfere with the subsequent diagnostic operations.

Attached are some case histories of CT cleanout operations utilizing the PowerCLEAN“integrated approach to fill removal” under similar of more demanding environments than

the two wellbore types given.

Also attached is information on CT TComp, which will allow for a safer and faster CT rig

up on all rig types, but provides active compensation when necessary on floating rigs andplatforms.



Also SPE 81729: Record Depth Coiled-Tubing Sand Cleanout and Gauge Retrieval should

be reviewed as it highlights the methodology, techniques, and design philosophy employed

by Schlumberger for CT cleanout operations of failed gravel packs.









































Diagnosing the Sand Control Failure:

Once the wellbore is deemed free of sand, diagnostic operations can begin. Traditional

methods and technologies as well as other potential methods to locate the sand controlfailure will be presented. Locating the source of the failure can be summarized using one

or more of the following techniques:

1.)

Gravel pack logs which may indicate voids in the gravel pack

2.)

Production log (spinner) to identify locations of anomalies in fluid flow. However,

it is recommended to not flow the well during the diagnostics to prevent thepossibility of sticking the diagnostic tools. Therefore, the spinner log is proposed

to be run while injecting into the well.

3.) Multi-arm caliper to detect anomalies which may be a result of erosion on the ID ofthe screen basepipe

4.)

Outside base pipe measurements (i.e.screen jacket) to detect anomalies which are a

result of screen jacket erosion.

Wireline tension modeling would need to be performed with the exact wellbore geometry

and trajectory to identify the type of cable required, as well as identify the need for a

wireline tractor.

• Gravel Pack and Production Log

The SLB PSP (Production Services Platform Tool) + RST (Reservoir Saturation Tool) is

used to measure the following log responses in gravel packed wells:

1.

GR/CCL is used for correlation2.

4 arm caliper + relative bearing is used to determine cross sectional area and also

for determining low side of the casing or screen. (pictured below)

• 4 arm caliper can be used to detect any unconformities in the gravel pack

• The advantage over multifinger is that it the arms are thicker. Less issues

getting stuck in a “split”

• Spinner response can also be used to identify voids.

3.

RST tool is deployed to measure the SIGMA of the formation for in-situ water

saturation monitoring. On the same descent, a gravel pack log is logged for

determining the quality of the gravel pack. The latter measurement is important for

two reasons:

• Qualifies the spinner response versus flow contribution. ie.. the spinnerresponse is in the base pipe, but how do you know its not a void or is itreally flow contribution? If the well is making sand, it may be better to run

the tools in “Injection” mode. This will minimize risks of “sanding up” the

tools.



2)

• The gravel pack log also gives the completion engineer assurance that thepack is good to minimize possible “Hot spots” or future erosion points. This

log is more representative of the gravel pack because the well has flowedand the pack has settled . The conventional memory tool run with the

washpipe is run immediately after the gravel placement and may not berepresentative of the gravel pack after things settled out. (see figure 2)

The PSP toolstring (minus RST) can also be run in memory mode deployed with either coil tubing

or slickline. The RST tool cannot be run in this mode because it requires surface power for theminitron operation. The primary log responses for identifying failed screens would be the 4 arm

caliper, temperature, and the spinner response.

Figure 1: PSP + RST Tool

4 arm cali er + s inner shown in detail



Figure 2:

Example of a

gravel of a gravelpack logging

procedure using

the PSP-RST

Explanation of the

RST siliconeactivation gravel

pack technique



Multi-arm Caliper

For initial measurement of screen damage the mechanical caliper (PMIT Tool) combined

with the Production Services Platform (PSP) is the most suitable option.

The PMIT is normally used to determine casing or tubing condition but can be used to

identify whether sand production has caused damage to the screen base pipe. There are twoversions of the Sonde available a 1-11/6” with 24 arms and a 2-3/4” with 40 arms. Both

Sonde’s can be used in horizontal or high deviated wells providing tools are centralised.

Screen base pipe perforation size and spacing must be examined with respect to the PMIT

arms to prevent sticking or damaging the PMIT tool.

Outside the Base Pipe Measurements (i.e. screen jacket)

• PSDT

This is the PSDT - an experimental sonic tool based on the SCMT (Slim CBL tool Segmented

Cement Mapping Tool). It uses a bandpass filter to differentiate fluid/sand flow.



• Image Behind Casing (IBC Tool)

The new Cement Evaluation Tool (IBC) Image Behind Casing is used to detect the “2 nd” interface.

(Figure 3). The example below is from a GoM well where the 9 5/8” casing and 13 5/8” casing

were logged with the IBC tool. The same principle could be used with a gravel pack screen using asmaller 3.56” OD tool. (See figure 4)

How do we prove the IBC could work to analyze failed screens?

1.

Sample screen could be placed in the vessel to analyze various anomalies.

2.

The IBC tool would be rotated inside the sample screen to determine if an accurate

image could be made to evaluate a failed screen. ie.. assume the base pipe is intact, butthe outer mesh is damaged.

3.

In the case of a base pipe failure, the tool would detect it with the inner diameter.

4. The IBC tool can detect imperfections as little as 1” and measures around the pipe

every 5 deg.

13 5/8” casing

9

5/8”

Figure 3: IBC tool showing the

inner casin and the outer casin



The test vessel shown here was used for evaluating deepwater cement jobs using

LiteCrete, heavy wall casing, and heavy SOBM. (SPE paper 83483). The vessel has been

used to evaluate many different type of casings + well bore fluids to assure log quality

signal to noise ratio.

Figure 4: Pressure Test vessel, theUSIT or IBC transducer requires

5000 psi for the transducer to

measure.

3.56” OD

SmallIBC tool

Sample

screen to

evaluatecould be

placed here



• Multifrequency Electronic Thickness Tool (METT)

The METT tool works on the principle of electromagnetism. It sends out a uniform

magnetic field. Any disruption to the field is caused by metal thickness or geometry

changes.

With this technique, the exact “as built” drawing of each screen joint would be required to

differentiate hardware changes from holes in the base pipe. The beginning and end of eachscreen joint, as well as centralizers and connections would show up as disruptions in the

electromagnetic field. However, disruptions in the middle of the screen joint where there is

only the screen jacket would indicate the potential failure location of the screen jacket.

The functionality for the METT tool has been replaced by a variety of other Schlumberger

logging tools





Remediation of the sand control failure:

Schlumberger can provide a number of through tubing mechanical and chemical repairsolutions. Schlumberger would also like to have the opportunity to discuss potential

changes to the initial wellbore design which would subsequently make repair of a failedgravel pack screen easier.

Chemical Repair

SandLOCK V is a gravel / epoxy resin system that sets up in the perforation tunnels andwellbore (internally catalyzed). In many cases, it needs to be drilled out of the casing or

repaired screen or at least a small pilot hole drilled to allow unrestricted flow up the

wellbore. Compression strength is very high (> 2000 psi). SandLOCK V resin has alsobeen used to fix failed gravel packs. Reference SPE 52192.

K300 is a furan resin that is injected into the matrix, consolidating the formation near thewellbore. It requires an HCl overflush to externally catalyze the resin. Many times an HCl

(or HCl followed by HF) is used ahead of the K300 in order to increase near wellbore

permeability and allow the resin to inject into all perforations. Reference SPE 39435.

The OrganoSEAL-R gel provides, in a single stage treatment, flexible formation

consolidation that eliminates formation failure due to reservoir depletion, repeated

drawdown cycles or fluid flow. The system works by forming a continuous rigid, butflexible, gel in the pore spaces of the formation; the gel network prevents the production of

formation sand. The pore filling nature of OrganoSEAL-R does not require bonding

between the gel and the formation sand thus eliminating a pre-flush stage. The simplicity

of the OrganoSEAL-R system and the ability to use a diverting agent, coupled with theflexibility of the crosslinked gel, gives effective consolidation with only 1 ft of penetration.

In the techniques mentioned above, the key is coverage across the failed screen area withundiluted chemical. Placement technique and procedure has much to do with the success

of the treatment.

Mechanical repair

Straddle Technology: Straddling is a method by where blank pipe are placed between two

packers that ‘straddle’ across a failure to prevent further sand production. The setting of astraddle system is accomplished by a number of runs. Firstly it requires the bottom packerto be set on either on wireline or coil tubing; then a composition of snap latch / screen or

blank and the top packer to be snapped into the bottom packer on a second run. Placing a

straddle assembly in the lower completion has the same effect as a choke ie production will

depend on the straddle length and exact location of production intervals. Schlumberger canprovide packers and assemblies to straddle 5” and 5-1/2” screens.



Insert Screens: Schlumberger can provide insert screens for all size screen failures in avariety of mesh configurations. Depending on the application, these can be used as “stand

alone” repairs or in conjunction with internal gravel packs.

Isolation plugs: In the even that the sand control screens failure was determined at thebottom of the well, a mechanical isolation plug could be set. It is recommended that this be

set across a screen coupling to allow complete isolation. Schlumberger can run 3rd

partyisolation plugs on e-line or CT.

PatchFlex:















Summary:

Please contact Schlumberger for additional details of clarification on any of the information

provided in this document. We look forward to developing a relationship to provide fit for

purpose cleanout, diagnostic, and repair services in the event of a sand control failure.

Sand Production Occurs

Log to locate andidentify failure

FailureLength short

( < 2 ft )

Set Isolation Plug When failure is situatedat a distance of up to

5 % of open hole lengthfrom shoe

Failure atToe of Well

Total FailureTop To Bottom Chemical Treatment

Placement with CoiledTubing and Inflatable

Packer

RepeatTreatment

Test Well forSand

Production

Insert Screens When failure is situatedat a distance between5 % - 20 % of open hole

length from shoe

Chemical TreatmentPlacement with CoiledTubing and Inflatable

Packer Failure at Topor Middle of

ScreenedSection

Chemical TreatmentPlacement with CoiledTubing and Inflatable

Packer Tubing Patch ConsiderTubing Patch

Straddle Abandon & Sidetrack Cut blank pipe above

screens and fish packerand blank pipe . Place

cement plug .

Failed Sand Control ScreenRepair Flow Chart

Yes

No

Yes No

Yes No

Yes

No Return well to production

Well Still Produces Sand

Coiled Tubing Cleanout, Diagnosis, And Remediation of Sand Control Failures

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