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Sand Control Systems

Gravel Pack Method

July 2012

By: MahbodKianmehr (Schlumberger Wireline Field Engineer)

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Gravel Pack Introduction

Potential sand producer formation:

Marine deposited sands, most oil and gas reservoir sands,

are often cemented with calcareous or siliceous minerals

and may be strongly consolidated. In contrast, Miocene or

younger sands are often unconsolidated or only partially

consolidated with soft clay or silt and are structurally

weak. These weak formations may not restrain grain

movement, and produce sand along with the fluids

especially at high rates.

Reasons, sands start producing:

Fluid movement causes stresses on the sand grains

because of the fluid pressure differences, fluid friction and

overburden pressures. If these stresses exceed the

formation-restraining forces, then the sand will move and

be produced.

Rapid changes in flow rates and fluid properties cause

unstable conditions which can result in increased sand

production.

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Consequences of Sand Production:

Production interruptions can be caused by sand plugging

the casing, tubing, flow lines and separators.

Casing collapse can be caused by changes in overburden

pressures and stresses in the formation.

Down hole and surface equipment can be destroyed,

downtime and replacement costs, spills and in extreme

cases a blowout.

Disposal of produced sands is costly.

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In Cased hole:

Reservoirs that produce sands:

Carbonate with particles and Non-Cemented Sand Stone

reservoirs produce sands.

After a while, lack of sands in their original spot in

formation shapes a cave or free space in the formation.

This space then allows an increase in fluid velocity toward

the set screen. Higher fluid velocity containing sands

results in erosion in the screen and decreases its working

life by passing thru screen surface.

This is also considered as gravel pack advantage vs.

standalone screen.

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In Open hole:

Since in open hole sands are non-homogeneous, finer

sands will pass the screens and come up to the surface.

These sands are filling up the vessels in production units

and reduce their performance.

Our suggestion is gravel pack to maintain high

production facilities’ performance for a longer period.

Steps in open hole:

Gravel pack system installation

Gravel pack the zone

Wash the mud 1- In order to increase the

production rate

2- Mud cake removal

In Open hole:

Results: 1- Blocking fine sands in the formation and

preventing them from movement

2- Avoid screen erosion

3- Preventing screen collapse

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Calculation

D = (5 or 6) D

D = the mean diameter of the gravel

D = the diameter of the formation grains at the

50 % weight

Volume of Gravel required:

Tot V = V of screen in casing + V of blank in casing + V of blank in tubing

= (ID Casing) 2 – (OD Screen) 2 (0.005454) cf / ft + ……

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Gravel Pack Assembly

Tool String from top to bottom:

Hydraulic setting tool Accessories

Packer Ball Seat

Sand Diverter Seal Tubes

Seal bore housing Centralizer

Shear joint

Blank pipe

Screen

Bull plug (Or wash down shoe)

See the figures on the next pages

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Hydraulic Setting Tool

Hydraulic setting tool Parts:

1. Working cylinder & piston to set the PKR

2. Seat & Ball Mechanism to maintain needed pressure to set

the PKR

3. Seal Tube Mechanism to Guide Carrier Fluid & Sand Gravels

behind the Screens

4. Contingency Release Mechanism

Note: The HST is being inserted in the packer in the shop.

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Packer

Objective:

1- To isolate the Annulus

2- Hang off the Sand Control Assembly

Caged Slip Packer Elements

Steps while packer is getting set:

Setting tool’s cylinders applies force on upper receptacle

Shear screws will shear and rubbers start swelling and blocking off

the way

At the same time slips come out and engaged to Casing

Packer is now set and is attached to Casing in two points by its robust rubbers

and slips.

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Seat Ball

Objective: In order to raise the pressure up to the PKR

setting and HST releasing points.

How many Seat ball is in an assembly:

1. Primary seat ball: Positioned below the window, to

guide the slurry out from the window.

2. Secondary seat ball: Positioned above the window,

for contingency release of HST

Seat ball is a narrowed portion on the assembly below and

above the window, so we can block off the way with a ball

dropped from surface.

Dump window and seat ball

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Sand Diverter

Objective: To provide pass for Circulation and reverse

circulation operation

By polling a little up, sand diverter moves and blocks the

window and opens another window above packer.

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Shear Joint

Objective: To disconnect the packer from the screen

assembly.

In case packer failed to set up properly we can disconnect

it from the screen assembly at shear joint.

Why not fish the whole tool string? Packer is not strong

enough to hold the rest, so the solution is to shear the

packer from the rest and do the fishing in two separate

parts as below.

1. Shear the packer from the rest at shear joint, fish the

setting tool and packer.

2. Fish the blank pipes and screens

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Blank Pipe and Screen

Blank pipe: To cover the non-productive zone

Screen: To be located in front of the perforation zone

(productive zone)

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Centralizer and Bull plug

Centralizer: Centralizes the screens inside the Production

Casing (Makes uniform Annulus for Gravels)

Bull Plug: Blocks the string end

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Job steps

• RIH with Sand Control Assembly to the desired depth

• Drop the ball to sit on seat ball

• Circulate to push the ball thru work string till it gets on

the Ball Seat, ( Fall time depends on depth )

• Pressure up the string

• Set the PKR by applying 2800 psi

• Rig up the Pump Lines on the Annulus, test the PKR

with 500 psi

• Release the HST by applying 3500 psi

• Continue Pressure Up the string to 4400 psi to open

the windows on the Sand Diverter

• Start pumping Slurry (Carrier Fluid +Gravel Sand) thru

the working string (Slurry will go out of the tool from

the window to the annular between the screen and

casing and fill it up till getting the screen out)

• POOH the working string