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Introduction and Objectives

Sand Control Fundamentals

Learning Objectives

This section will cover the following learning objectives:

Review the topics covered in this module covers

Discuss the problems that can be encountered when sand isproduced

Identify which types of sandstones are most likely to producesand

Sand Control Fundamentals═════════════════════════════════════════════════════════════════════════

© PetroSkills, LLC. All rights reserved._____________________________________________________________________________________________

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Reasons to eliminate sand production

Why control sand production?1

Look at the major techniques used to control sand

How do we choose the best technique

Sand Control Completion Options and Designs2

Sand Control Fundamentals ═════════════════════════════════════════════════════════════════════════


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Advantages and disadvantages of different designs

Sand Screen Designs3

Mixed results?

Expandable Sand Screens4



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Cased hole gravel packs Open hole gravel packs

Gravel Pack Completions5

How and why we need to know the range of sand sizes

Formation Sand Size Distributions6



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Equipment and techniques used to place the gravel

Gravel Placement Technique7

Controlling sand production in horizontal wells

Horizontal Wells8



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What can go wrong!

Common Sand Control Problems9

How we frac pack a well Advantages and disadvantages

10 Frac Packing



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Problems Encountered when Sand is Produced

Best solution:

Stop the sand production

entirely!

Solution



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Why Control Sand Production?

What does Sand do to our Wells?

Plugs Wells+ Erodes Pumps+ Cuts Tubulars+ Erodes Rod Strings+ Erodes Blast Joints+ Erodes Perforations____________________

Expenses

Well Productivity



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What does it do to our Facilities?

Sand fill in separators, tanks, flow lines, etc

Requiring shutdown of facilities and cleanouts

On an offshore platform, this means all production must be halted

What does Sand do to our Economics?



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• Production interruptions, reducing the Return onInvestment (ROI)

• Bridges formed in flowlines which reduce or cutoff production

• Sand filling the wellbore, affecting production

Many detrimental effects can occur without sand control:


Often a complete well workover is the only way to restoreproductivity

Safety can also be compromised by too much sand

Sand Control – A Safety Issue

Especially true for high‐rate gas well

production



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Causes of Sand Production

– If the cementing agent is calcium carbonate, water flowingthough the reservoir may dissolve some of the cementingmaterial

– Relative permeability effects may increase the drag forceson the sand grains, further increasing sand production

– Acid jobs may remove some of the cementing materials

– Removing reservoir fluids may generate some compactionfrom the overburden, weakening the sandstone

– Cementation between the sand grains assist in keeping thesand in place

The forces induced by the flow or other factors are strongerthan the forces that hold the grain in place

The forces induced by the flow or other factors are strongerthan the forces that hold the grain in place

Intermittent Sand Production

Intermittent sand production• Often very temporary• Usually a reaction to a change in

well operations due to:– Flowrate– Drawdown

– Fluid saturation changes

# o

f sa

nd

per

bb

l

Time



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# o

f sa

nd

per

bb

l

Time

Catastrophic Failure

If sand production is continuous, atreatment or workover may berequired to reduce or eliminatesand production

• May simply require a change inproduction rate, or

• May require a major well workover

Catastrophic Failure

• Unconsolidated sand

Simple Method to Describe Sandstone Strength

• Highly consolidated sandstone

• Consolidated sandstones

• Weakly consolidated sandstones

• Very weakly consolidated sandstones

• Very, very weakly consolidated sandstones

Normally no sand control problemsNormally no sand control problems

Will produce sand at some

point

Will produce sand at some

point



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Classification of Weak and Unconsolidated Rock Strengths

Dry SandNo Strength

Wet SandVery, Very

Weak

Weakly CementedVery Weak

Stronger Cementing

Weak

Unconsolidated Sands

Usually shallow depth [< 8000 ft (2400 m)], young (Miocene to recent) deposits, but may be found much deeper

May be difficult to keep the hole open, and perforations collapse immediately

Sand grain production begins with any fluid movement

Strength given by cohesion forces (grain-to-grain friction), but easily washed away

Coring is difficult – complete cores are not possible

Must control pump rates, and use fiberglass or rubber core catcher tool

Open hole completions may be difficult or impossible



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Very, Very Weakly Consolidated Sandstone

Only the capillary strength of water bonds grains together• Very low compressive strengths (<10 psi or 68.9 kPa)

Continuous water production destroys the capillary forces• Perforations collapse immediately

Sand control should be installed during the initial completion

Very Weakly Consolidated Sandstones

Cementing materials are minimal, and perforation tunnels may collapse

Changing operating conditions will lead to sand production

We now have several options regarding what type of sand control to use

These may be applied later in the life of the well



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Weakly Consolidated Sands

Cementing Cementing is strongeris stronger,, but but can still can still be removbe removed byd by chemicals,chemicals, acidizing, etc.acidizing, etc.

Coring is Coring is still still difficult, difficult, and core catcher and core catcher tools tools may be required to recover cores

May not produce sand – or may make sand intermittently orcontinuously – especially later in the life of the well,depending on conditions

May not produce sand – or may make sand intermittently orcontinuously – especially later in the life of the well,depending on conditions

Potential Causes of Sand Movement

Start of water or gas production due to increase in drag forces

Cementing affected by acidizing, water production, etc.

Changes in pumping rate

Any injected chemical can help initiate sand production

Acid stimulation treatments• They may dissolve cementing materials

Solvents and Surfactants• Can release fines, alter wettability, change the drag forces, and

plug pore throats



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• Due to start/stop of fluid flow caused by movement of rod pumps

Changes in the overburden stress

Reservoir fluid flowrate and velocity changes, and increased drag forces

Anything else that changes the flow rate

Learning Objectives

This section has covered the following learning objectives:

Review the topics covered in this module covers

Discuss the problems that can be encountered when sand is produced

Identify which types of sandstones are most likely to produce sand



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Sand Control Completion Options and Design


Learning Objectives


Describe the types of sandface completions that will prevent sand production

Recognize completions with no direct downhole mechanical control devices

Identify equipment installed downhole to control the sand

Describe how using resins help cement the sand grains together



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Sand Control Options

1 No Direct Mechanical Control (but change production

parameters)

2 Installation of Mechanical Devices Downhole

3 Chemicals Injected Downhole

No Direct Mechanical Control

Living with Sand Production

Surface Sand Separation• Wellhead desanders• Wellstream desanders

Rate Reduction

Selective Completion Practices• Oriented perforations• High-density perforating• Phase-oriented perforating• Wellbore trajectory; e.g., horizontal• Cavity or wormhole formation• Other…



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Mechanical Methods of Sand Control

Slotted Liners or Screens without a GravelPack

• Open hole or cased hole (not recommended)

Slotted Liners or Screens with a Gravel Pack• Open hole or cased hole

Frac packing or Fracturing

Expandable Screens

Vent Screens

Chemical Methods of Sand Control

Chemical Consolidation of

the Formation

Resin-Coated Gravel



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the Formation

Resin-Coated Gravel

Assists in cementing the

sand grains together

Holds the sand grains in place

“Do nothing" and let sand be produced

No Sand Control

• Sand disposal – sand must be cleaned before discarding• Subsidence• Casing collapse or damage• Surface erosion or blockages• High well maintenance costs• High facilities maintenance including shut down

Risks

• Sand is either produced, or falls to the bottom of the well and must be removed

• Used in many depleted reservoirs



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No Sand Control

Typically used when sand production is minimal and has not caused expensive workovers

Often done onshore rather than on a platform

Often used toward the end of the life of the reservoir

Limiting Velocity

Underream

Larger wellbore

Larger / more perforations

Cavity completion

Reduce the rate

Flux Rate = Fluid Flow Rate/Unit Area

Slow down fluid movement rate at the sand face



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Cavity Formation

Three methods of lowering the flux rate of the sand face

Original hole

Becomes

Per

fora

te

Un

der

ream

Use

Hig

h

Flo

w R

ates

Are there any other detrimental effects?

No Control / Cavity Formation / Rate Restriction

How much production is lost?

Will the well be stable at this point?

How much sand must be produced to form the cavity?

Will rate reduction stop the sand?



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Establishing Acceptable Rate Restriction

Units in Plot Above: Gas or liquid production per unit cross section area, calculated as if the phase were the only phase flowing in the porous medium; the value is usually readily determinable from lab work.

Many studies report on the approach of limiting the production rate

In this plot, the curves represent speed limits to control the sand

The recommendations for some well productivities are an order of magnitude off, meaning many of these charts are inaccurate

20 ppm (0.002%, ~ 6# / 1000 bbls sand rate) (2.7 kg/159 m3)

0.0001

0.001

0.01

0.1

1

10

100

0.1 1 10 100 1000

Superficial Gas Velocity(ft/s at process conditions)

Superficial Liquid Velocity

(ft/s at pro

cess

conditions)

No Failure Reported

Failures - Low Sand Production

Failures - High Sand Production

Shell Limit for Current Case

API Limits

Superficial Gas Velocity[ft/s (m/s) at process conditions]

Su

per

fici

al L

iqu

id V

elo

city

[ft/

s (m

/s)

at p

roce

ss c

on

dit

ion

s]

(0.31)(3.1)

(31) (305)

(31)

(3.1)

(0.31)

(0.03)

(0.003)

(µs/m)

(21.3) (24.4) (27.4) (30.5)


There have been many attempts to predict the maximum sand-free production rate for various wells.

Most attempts are not accurate, and the rates usually change as the wells age.



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Adding More Perforations, with Larger Entry Holes

Add more perforations and use larger diameter perforations• Double the entry hole size• Triple the number of shots

Deep penetrating perforations can only be used if the well will not be gravel packed

It is nearly impossible to get gravel to the end of the perforation

Gravel will mix with formation material resulting in a high skin

Perforating Creates Perforation Tunnel Damage

It can be removed by underbalance perforating



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Should be performed only with tubing‐conveyed perforating guns

The wellbore pressure is lower than the reservoir pressure

UNDERBALANCED PERFORATING

Preventing Perforation Damage

Most Efficient Damage Removal

Deep Penetrating vs. Gravel Pack Charge

Sandstone cores perforated with deep penetrating (upper) and big hole shaped (lower) charges at underbalanced conditions

If the perforations are going to be gravel packed, only big hole (also called gravel pack charges) should be used.



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Mechanical Sand Control Methods – Open Hole

Screen and gravel must be sized properly• No penetration of gravel by formation particles• No formation sand should pass through the gravel• When gravel is not used, screen should be sized to

retain only the largest 10% of the gravel

Screen Alone without Gravel

Screen with Gravel

Gravel Packing

Gravel packing can be performed in either open hole or cased hole completions

Gravel prevents the sand from moving into the wellbore

Cased hole completions historically the most common sand control technique

However, open hole completions usually have higher productivity, because of less formation damage

Open Hole

Gravel Pack

Cased Hole

Gravel Pack



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Cased Hole Gravel Pack

Screen

Gravel Pack

Perforation

Formation Sand

TunnelCement

Casing

Internal gravel pack

recommended thickness of pack

or pre-pack is 0.75 in. (19.1 mm) to 1.25 in. (31.8 mm)

Open Hole Gravel Pack

Minimum gravel pack recommended

thickness is 0.75 in. to 1.25 in. (19.1 mm to 31.8 mm)



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Resin Consolidation

Case and perforate the wellCase and perforate the well

Overflush, designed to open poresOverflush, designed to open pores

• Resin pumped down as liquid and coats the nearwellbore formation material

• Leaves only a thin coating of resin around sand grains• Resin is designed to set at bottomhole temperature

with a catalyst

Creates stronger matrix by cementing grains together with synthetic plastics / chemicals

Creates stronger matrix by cementing grains together with synthetic plastics / chemicals

Resin-Coated Gravel, Placed in Perforations

Pre-coated Gravel is placed inperforations and wellbore

Allow the resin to first liquify,by wellbore temperatureincease, and then set

Drill out the wellbore

Also used for screenless frac packs



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Consolidation:Resin

Sand Control Principles: 3 Ways

Filtration:Stand-Alone

Screen

Bridging:Gravel Pack

Back to Work Suggestions


Leverage the skills you’ve learned by discussing the skill module objectives with your supervisor to develop a personalized plan to implement on the job. Some suggestions are provided.

Meet with completions engineering and with service company representatives to participate in planning a sand control completion.



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Learning Objectives


Describe the types of sandface completions that will prevent sand production

Recognize completions with no direct downhole mechanical control devices

Identify equipment installed downhole to control the sand

Describe how using resins help cement the sand grains together



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Sand Screen Designs

Learning Objectives


Discuss the many different types of screen designs used in sand control completions, with or without a gravel pack



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Types of Liners and Screens

Slotted Liners

Wire-Wrapped Screens

Prepacked Screens

Premium Screens

Alternate Path Screens

Expandable Screens

Screens to equalize inflow along the length• Variable Inlet flow resistance

Many New Screen Designs Available

(d) PRE‐PACKED SCREEN

Only used to prevent hole

collapseTend to

plug rapidly if not used with a gravel pack

Liner and Screen Examples: Not a Complete List

Does NOT control sand production

Block sand grains



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Common Wire-Wrapped Screen

Consists of base pipe with drilled holes and wire-wrapped screen jacket

Axial rods hold the wire wrapping away from the pipe and hold the wrapping in place

The gap between the wire wrapping describes the screen gauge in thousandths of an inch

The screen opening should be smaller than the smallest gravel size when used as a gravel pack

If the screen is to be used as a stand-alone screen, the gap is usually sized to retain only the largest 10 percent of the formation

Views of Common Sand

Screen and Mesh Construction



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Layer of resin-coated sand encased in the screen, between the outer and inner wraps

Pre-pack provides an additional layer of protection within the screen in order to stop the formation sand in case of damage to the wire wrapping

Offers improved abrasion resistance, but plugs easily

Pre-Packed Screens

Ported base pipe

Mesh

Support shroud

Mesh Design



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Vector Weave

Premium Screens

Screen designs that are both very efficient and very long-lasting in the wellbore

Sold at premium prices

Base Pipe

Bakerweld Inner Jacket

Vector WeaveMembrane

Vector Shroud

Baker’s Excluder 2000

Slotted liners and screens in a non-gravel pack are FILTRATION DEVICES

EXPANDABLE STAND-ALONE SCREENS are primarily retention devices holding the formation in place; they do not tend to plug as rapidly

Non-Gravel Pack Horizontal Well Completions (SAS)

Stand-Alone Screens

Open Hole with Slotted Liner

Open Hole with Screen or Pre-Packed Screen

Many operators prefer stand-alone screens in open hole applications

Usually exhibit high initial production• If formation is non-uniform, screen plugging may occur rapidly• Lifetime may be short before holes develop in the screens



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EXPANDABLE STAND-ALONE SCREENS are primarily retention devices holding the formation in place; they do not tend to plug as rapidly


Stand-Alone Screens


Open Hole with Screen or Pre-Packed Screen

Halliburton PetroGuard Screen

Initial Filtration Layer

Coarse Filtration Layer

Medium Filtration Layer

Final Filtration Layer

Drainage Filtration Layer

Layered Mesh Premium Stand-Alone Screen Design

The screen may have multiple layers, as shown

The openings must stop only the largest formation material

This results in higher permeability of the material near the screen

This may allow a small amount of smaller material to be produced initially

Usually has the longest lifetime without plugging or failing



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Learning Objectives


Discuss the many different types of screen designs used in sand control completions, with or without a gravel pack



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Expandable Sand Screens


Learning Objectives


Evaluate the use of expandable screens as a sandfacecompletion method

Discuss the limitations of expandable screens



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An Open Hole Alternative

Expandable screens

Open hole sand control without gravel pack

Screen is placed in hole and expanded to stress formation inplace

Several expandable systems now available from several differentservice companies

First commercial well was in 1999

Expandable Sand Screens

(216 mm)

(191 mm)

(216 mm)

(165 mm)

(125 mm)

Screen is run into the wellunexpanded

Expansion takes place byrunning an expansion devicethrough the screen to expand it

Eliminates annular space on theoutside of the screen

In open hole applications, thisprevents the formation from re-arranging and plugging thescreen

Expanded screen is a retentiondevice, not a filtration device

Works best in open holecompletions



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ESS – Expandable Sand Screens

The ESS joint is comprised of 3 layers: inner, middle and outer layers

• The inner and outer layers expand due to slots cut into a pipe

• The middle layer is a filter membrane

• This membrane has overlapping layers that slide over each other in the expansion process

From: Weatherford


This view illustrates the 3 layers of the design.

These screens yield a larger flow path compared to other types of sand control completions.

They can also be easily repaired by adding a new layer within a failed screen in many situations.

However, some of these screens have been crushed in wells where the stresses have surpassed the strength of the pipe. Example shown:

6 in. (152 mm) O.D. Pre-expanded8.5 in. (216 mm) O.D. Post Expansion



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3 Slots open upOuter Shroud1

Slots open upEST Base Pipe 2

Sheets slides over one another

Woven Filter Material

1

2

3

12

3

ESS® Construction Middle layer does NOTexpand the screen

Expandable Screen Video



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Learning Objectives


Evaluate the use of expandable screens as a sandfacecompletion method

Discuss the limitations of expandable screens



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Gravel Pack Completions, Options and Design Alternatives

Learning Objectives


Discuss the use of gravel packs in both open hole and cased hole completions

Determine formation sand size distribution and why it is required to perform a successful gravel pack



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• Gravel is placed between screen and casing, and inside perforations

Cased Hole vs. Open Hole Gravel Packs

Cased Hole

The trend is toward more open hole gravel packs being placed in horizontal wells, wherever possible

• Higher initial production

• Eliminates expenses, including:

− Casing, cementing, and perforating

− Associated rig costs

• Gravel is placed between the screen and the formation

Open Hole

1

2

Gravel Pack Design Objectives

Gravel retains the formation sand in place

Screen holds the gravel in place This technique functions as a retention device, which

slows screen plugging Can cause reduction in well productivity (a positive skin)

Objective #1

Establish a highly permeable pathway between formation and wellbore that formation sand cannot penetrate

Objective #2

Objective #3



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Gravel Pack Design Principles

Gravel Pack Completion Sand Control

Works as a two-part retainer:

Step 1: Gravel is sized to retain formation sand

Step 2: Screen sized to retain gravel in place

“Bridging” occurs at this interface

Importance of Good Bridging in a Gravel Pack Design


GOOD BRIDGING

Formation Sand is Restrained By Gravel Pack Gravel in a Good Design

POOR BRIDGINGFormation Sand Invades

Gravel Pack



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Permeability of the Invaded Formation?

What is the permeability of the invaded formation if the 20/40 mesh gravel has a permeability of 120,000 md and the formation has a permeability of 1,000 md?

a) About 50,000 md

b) About 10,000 md

c) About 1,000 md

e) Zero

d) Less than 200 md

Gravel Pack Design Principles – 3 Steps

Obtain a good description of the formation sand grainsize distribution1

Select gravel size based on the formation sandgrain size distribution (Saucier Method)2

Select screen based on smallest gravel range3

• 50% cumulative grain size x 6 for gravel pack• 50% cumulative grain size x 8 for frac pack

• 50% to 75% of smallest gravel range size



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Formation Sand Size Distribution(Two Methods)

How do we get a good description of the sand size Distribution?

Obtain representative sand samples for a sieve analysis

Perform a sieve analysis of the sample, or

Perform a laser beam particle-size analysis of the formation



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Sidewall Cores

All other samples can be altered by contaminants or sorting

Formation Sampling for Sieve Analysis

Obtained ONLY when the wells are drilled

The most representative samples are Conventional Cores

Conducting a Sieve Analysis in the Lab

20 40



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U.S. Mesh Definition of Grain Size

Mesh refers to the number of openings per linear inch

• The U.S. Mesh series specifies the mesh size and width of opening

• Based on a progression of the square root of 2

• The wire thickness changes for different screen sizes



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U.S. Mesh Sizes

Sieve Analysis Results Measure weight percent sample retained on each sieve size screen opening


Plot the size versus cumulative weight percent

on semi-log paper



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U.S. Mesh Size

Sieve Opening, In.

(mm)Sieve Weight

Before (Grams)Sieve Weight After (Grams)

Sand Weight (Grams)

Cumulative Sand Weight

(Grams)


(percent)

80 0.0070 (0.18) 35.83 36.19 0.36 0.36 5.40%

100 0.0059 (0.15) 35.24 35.51 0.27 0.63 9.45%

120 0.0049 (0.12) 34.88 35.68 0.80 1.43 21.44%

140 0.0041 (0.10) 33.91 35.57 1.66 3.09 46.33%

230 0.0024 (0.06) 35.13 37.95 2.82 5.91 88.61%

400 0.0015 (0.04) 30.17 30.63 0.86 6.37 95.50%

Pan 154.20 154.50 0.30 6.67 100.00%

Example Results from Sieve Analysis

1. Measure the weight of each sieve

2. Place the sample on the largest sieve, and shake the stack

3. Measure the weight of the sieves with the amount of sample caught on each

4. Plot the cumulative weight percent of samples vs. sieve size

(2.54) (0.0254) (0.00254)(0.254)

Cu

mu

lati

ve W

eig

ht

(%)

Grain Diameter (inches) (mm)

Determine Gravel Size for Gravel Pack

d50

0.004 in.(0.102 mm)

Step A: Plot the formation size distribution from sieve analysisStep B: Determine the 50% intercept grain size

Note: A very uniform formation will allow the use of a stand-alone screen with no gravel required.



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(2.54) (0.0254) (0.00254)(0.254)

Cu

mu

lati

ve W

eig

ht

(%)



d50

0.004 in.(0.102 mm)


Step C: Select median gravel size and gravel range

For a gravel pack: 6 x 0.004 in. = 0.024 in. (0.61 mm) Use 20/40 mesh

For a frac pack: 8 x = 0.004 in. = 0.032 in. (0.81 mm) Use 16/30 mesh

6

8

gravel pack

frac pack

Note: A very uniform formation will allow the use of a stand-alone screen with no gravel required.

Commonly Available Gravel Sizes

May be natural gravel quarried from high quality deposits, or

Artificial gravel• Stronger, more spherical, with higher permeabilities

Also, 30/50 now often available, size range 0.023 – 0.0117 inches (0.58 – 0.30 mm)

U.S. Mesh Size

Size Range, in. (mm)

Medium Gravel Diameter (inches)

Median Gravel Diameter (mm)

Permeability (Darcies)

6/10 0.1320-0.0787 (3.35-2.00)

0.1054 2.677 2703

8/12 0.0937-0.0661 (2.38-1.68)

0.0799 2.029 1969

10/20 0.0787-0.0331 (2.00-0.84)

0.0559 1.420 652

12/20 0.0661-0.0331 (0.84-1.68)

0.0496 1.260 668

16/30 0.0469-0.0232 (1.19-0.59)

0.0351 0.892 415

20/40 0.0331-0.0165 (0.84-0.42)

0.0248 0.630 225

40/60 0.0165-0.0098 (0.42-0.25)

0.0132 0.335 69

50/70 0.0117-0.0083 (0.30-0.21)

0.0100 0.254 45



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Sieve Analysis Indicates Whether Formation has Uniform or Non-Uniform Grain Size Distribution

Non-uniform

Poorly Sorted Sand

Well Sorted Sand

(2.54 mm) (0.254 mm) (0.0254 mm) (0.00254 mm)

Require gravel packs rather than stand‐alone screens

Tend to plug much more rapidly

Production falls off much more rapidly

Uniform

Selecting Gravel Based Upon Sand Grain Size

Lower case “d“ designates formation sand median diameter

Upper case “D” is the selected gravel median diameter

Definitions to Assist Sand Control Design (SPE 37437)

Uniformity Coefficient40

90

d=

dCu

Sorting Coefficient10

95

d=

dC s

Saucier Criteria50

50

Gravel

Formation sand

D=

d6

1

2

3



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Screen Selection Guide

Based on reservoir sand d50 size that varies up to 50%. Indicative only.For Wire Wrap SAS: If formation fines >5%, use Metal Mesh; >10%, use Gravel Pack.

Sorting Coefficient is defined as Cs = d10 / d95

Where: Cu = Uniformity Coefficient

d40 = Grain Diameter at 40% Cumulative Weight


1616

Uniformity Coefficient

Cu = d40 / d90

if Cu <

if 3 < Cu <

if Cu >

Uniform Sand Distribution=

Non-Uniform Sand Distribution=

Highly Non-Uniform Sand Distribution=



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Various Grain Size Distribution Design Points

Design Point = d40

Design Point = d90

Design Point = d70

Design Point = d50

Design Point = d10

(2.54 mm) (0.254 mm) (0.0254 mm) (0.00254 mm)

1818

Design Point Selection for Gravel Pack

Saucier – D50 6(d50)

Coberly and Wagner – D10 10(d10)

Stein – D85 4(d15)

Schwartz – D10 6(d10) for Cu < 5

D40 6(d40) for 5 < Cu < 10

D70 6(d70) for Cu > 10

These are the most common

gravel pack design methods

These are the most common

gravel pack design methods



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Saucier’s Experiment

Establish initial flow rate (qi) and stabilized pressure drop, calculate initial permeability (ki)

Increase flow rate and establish new stabilized pressure drop

Reduce flow rate to initial rate (qi) and establish stabilized pressure drop, calculate final permeability (kf)

Optimum sand control occurs when kf = ki

Formation Sand

Fluid FlowGravel Pack Sand

Gravel to Sand Size Ratio (Saucier Method)

Gravel‐pack perm

eab

ility ratio

(Eff. vs Initial)

Gravel‐sand size ratio

(D50 Gravel vs D50 Formation)



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U.S. Sieve Number

Other Examples: Grain Size Distribution Sieve Analyses

Bailed Sample

Core Barrel Sample

Produced Sample

(2.54 mm) (0.254 mm) (0.0254 mm)

Grain Size Comparison Analyses at Various Depths –Same Well

Grain Diameter (mm)

Grain Diameter US Mesh Size



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Obtain a good description of the formation sand grain sizedistribution

Select gravel size based on the formation sand grain sizedistribution

Select screen based on smallest gravel range

Summary Review: Gravel Pack Design – 3 Steps


• Design screen opening as:− 50-75% of the diameter of the smallest gravel range size

− This size retains gravel in place behind screen

1

2

3

Gravel Pack Rules of Thumb

Gravel to Sand Size Ratio• Use a gravel size as large as possible; the sand must be retained

at the outer edge of the pack• Use Saucier’s technique (or another acceptable method) to find the

correct gravel size– Usually 6 times the size of the formation sand at D50 or D40

– For frac packs, multiply the median by 8 instead of 6

• Pay more attention to smaller sand grain sizes with:– Non-uniform sands– Higher flow velocity

– High gas oil ratios

– Fluctuating flow rates

These often lead to the choice of a slightly

smaller gravel



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Gravel Pack Rules of Thumb (continued)

• Gravel-to-Sand G/S ratio is based on “tight pack”

• Gravel movement caused by a loose pack will lead torapid failure of the pack

Pack gravel tightly Pack gravel tightly

Three-inch pack thickness normally designed for open holecompletions (but not most horizontal wells)


Do not allow the formation sand to mix with gravel duringplacement


• Thicker pack allows higher flow rate. Many wells are underreamed to allow a thicker pack

Cs = d10 / d95

26© 2010 PetroSkills, LLC. All rights reserved. 26

Other Relevant Reservoir Criteria

Pay Attention to the Sorting Coefficient

If the ratio is high, smaller gravel should be used

Large amount of fines, smaller than 44 μm (0.00173 in.) –may be problematic

Sorting Coefficient Defined as d10 / d95




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Laser Particle Size Analysis

Determines size distribution through measurement of degree ofscatter of laser.

If samples are poorly cleaned, mud cake will be recorded andresults will be adversely affected.

Results often different from sieve results, but depend on theshape of the sand grain, as well as proper cleaning technique.

Advantage: Much faster to make the

measurements.




Review the lab measurements and computational methods used to obtain the description of the sand size distribution.



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Learning Objectives


Describe the use of gravel packs in both open hole and cased hole completions

Determine formation sand size distribution and why it is required to perform a successful gravel pack



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Gravel Placement Techniques (Fluids and Equipment)

Learning Objectives


Describe the completion equipment required to place a tight gravel pack in a well

Recognize the importance of using clean fluids to place the gravel



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Gravel Placement

Gravel can be placed with many types of fluids and equipment

These fluids can damage the formation

Fluids must be properly cleaned before pumping

If the job is done well, the result should produce a well with good productivity and a long life

The key to an undamaged well is following the recommendations to the letter

Gravel Placement Fluids, Brines and Gels

Gravel can be placed with brines or polymer fluids and other fluids such as VES, etc.

Super-clean fluid essential (especially for brines)• No solids• Most open hole and cased hole pack failures result from surface

solids (dirty fluid / brine / polymer tanks)

Large volumes of brines are required, because of the low proppant loading. Therefore there is a large amount of fluid lost to the formation.

Must filter brine fluids if they are not free of solids.

The KEY is achieving a tight pack with very low skins and good well productivity.



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Gravel Placement Fluids – Gels

• Shear properly; permit no “fisheyes”

Problems

Properly hydrate the polymer fluid

The KEY is achieving a tight pack and good well productivity

• Viscosity and fluid loss control• Building a “filter cake”• Unhydrated gels• Incomplete filtration• Density

Polymers as Carrying Fluid

Three different polymer concentrations providing a wide range of viscosities



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HEC – Hydroxy Ethyl Cellulose

Gel that is often used in gravel packing wells

Safe to use

Compatible with the formation

Non-damaging to the environment

CRITICAL that the gel be mixed properly to avoid damaging the well

Mixing the Polymer (HEC) Gel Properly is Critical

HEC – Hydroxy Ethyl Cellulose

Gel that is often used in gravel packing wells

Safe to use

Compatible with the formation

Non-damaging to the environment

CRITICAL that the gel be mixed properly to avoid damaging the well

1. Use fresh water or 2–5% KCl or NH4Cl in water

2. Lower the pH to 3-5 with citric acid [0.25–0.33 lbs (0.11–0.15 kg)]

3. Disperse 1.5–2.0 lbs (0.68–0.91 kg) polymer in agitated tank

4. Raise pH to 6-8 with caustic or soda ash

5. Mix at high shear rate, but avoid over-shearing• Monitor viscosity with Brookfield viscometer • And run sand suspension test• Monitor filterability – 1 quart (946 cm3) in 1–2 min

6. Filter to remove any unhydrated solids

7. Pre-hydrated polymers are also available

Mixing the Polymer (HEC) Gel Properly is Critical



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Gravel Packing Position

.

.

Circulate Position

Packer shifted to crossover position

Carrier fluid and gravel are pumped down tubing and through tool to be placed in the screen / perforated casing annulus at perforations

By job end, packer is shifted back to producing position

Gravel Pack Equipment – Packer Crossover Tool

Crossover open

Crossover open

Wire wrapped screen

Wire wrapped screen

GravelGravel

Port Collar, Open

Wash Pipe(Tail Pipe)

Cased Hole

Note that gravel also fills perfs

Typical Gravel Pack System with Crossover Tool

Model SC-1 Packer

Model S Gravel Pack Extension

Model GPR-6 Shear Out Safety Joint

Blank Pipe

Bakerweld Screen

Model S-22 Multiple Acting Indicator Seal Assembly

Model D Sump Packer

Model SC Hydraulic Setting Tool

Bypass PortsBall Seat for Setting Packer

Reversing Ball

Washpipe

From: Baker Oil Tools

Model S-2 Gravel Pack CrossoverGravel Pack Port



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Crossover Tool Function

Squeeze:Forces all of the fluid

pumped to flow though the perforations into

the formation. This will force gravel into the

perforations, and pack it tightly.

Circulating:After the perforations are filled, the tool is

shifted opening a flow path for fluid to flow up the tubing annulus back

to the surface.

Reverse:After filling the screen

annulus with gravel, the work string shifts the tools to the reverse circulate position to clean any remaining

gravel out of the work string.

The crossover tool generally has 3 positions that provide all of the flow paths required for successful gravel packing:


1 2 3

Crossover Tool – Squeeze Position

The Squeeze Position forces gravel into the perforations

Achieved by setting down weight on packer

Bypass ports are sealed in packer bore

All fluid pumped is forced into formation



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Crossover Tool – Circulating Position

To fill the annulus, the tool is shifted to the circulate position:

By picking up approximately one foot on the workstring

This opens the return ports in the crossover tool

The fluid then flows through the screen, up the washpipe, lifting the reversing ball, and out the ports into the annulus

Crossover Tool – Reversing Position

After the gravel packing is complete:

The workstring is picked up another foot

Opening up an additional set of ports so that the workstring can be cleaned by reversing out any remaining gravel.

Finally, the workstring will be pulled, and the completion string can be run into the packer.



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Plan to attend a sand control completion operation to observe the steps taken to ensure a successful completion.

Learning Objectives


Describe what completion equipment is required to place a tight gravel pack in a well

Recognize the importance of using clean fluids to place the gravel



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Virtual Instructor Led Session #1



Sand produced from the reservoir may result in:• Abrasive action: cuts out pumps, chokes, tubing, etc.• Fills in the casing across perforations, affecting production• Bridges formed which reduce or cut off production• Flowlines, separators, tanks fill up, which must be removed• Production interruptions, reducing the Return on Investment

(ROI)• Surface handling and disposal problems• Completion failures which often lead to costly workovers• Safety!



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What does it do to our Economics?

Causes of Sand Production

The formation components move when:• The forces induced by the flow or other factors are stronger

than the forces that hold the grain in place• This can result from:

– Compaction squeeze– Radial differential pressure

• Fluid inertia

• Fluid drag

– Relative permeability effects– Reduction of bonding strength

• Acidizing• Waterflooding

– Other



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Classification of Weak and Unconsolidated Rock Strengths

Dry Sand,

No Strength

Wet Sand

Very, Very Weak

Weakly Cemented

Very Weak

Stronger Cementing

Weak

Unconsolidated Sands

Usually shallow depth [< 8000 ft (2400 m)], young (Miocene to recent) deposits, but may be found much deeper

May be difficult to keep the hole open, and perforations collapse immediately

Sand grain production begins with any fluid movement

Strength given by cohesion forces (grain-to-grain friction), but easily washed away

Coring is difficult – complete cores are not possible

Must control pump rates, and use fiberglass or rubber core catcher tool

Open hole completions may be difficult or impossible



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Very, Very Weakly Consolidated Sandstone

Only the capillary strength of water bonds grains together

Very low compressive strengths (< 10 psi, or 68.9 kilopascals)

Coring recovery very difficult, must catch core in a core holder

Perforations collapse immediately

Very Weakly Consolidated Sandstones

Cementing materials are minimal, and perforation tunnels may collapse

Core recovery more likely, but core catcher tool is still required to obtain core

Uni-axial compressive strengths from 10 psi (68.9 kilopascals) to 1,000 psi, (6,890 kilopascals)

Sand Production likely at some point in time



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Weakly Consolidated Sands

Cementing is stronger, but can still be removed by chemicals, acidizing, etc.

Cementing is stronger, but can still be removed by chemicals, acidizing, etc.

Coring is still difficult, and core catcher tools may be required to recover cores

Coring is still difficult, and core catcher tools may be required to recover cores

May not produce sand – or may make sand intermittently or continuously – especially later in the life of the well, depending on conditions

May not produce sand – or may make sand intermittently or continuously – especially later in the life of the well, depending on conditions


Additional phases causing relative permeability problems

• Water cut increases

• Gas cut increases

Acidizing, water production, etc. can affect cementing

Changes in pumping rate can cause sand production to begin

Any injected chemical can help initiate sand production

Acid stimulation treatments

• They may dissolve cementing materials

Solvents and Surfactants

• Can release fines, alter wettability, change the drag forces, and plug pore throats



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Reservoir fluid flowrate and velocity changes, and increased drag forces

Changes in the overburden stress, increased as fluids are withdrawn

Shut-in and start-up changes which alter the sand packing arrangement near perforations

Other

Sand Control Options

1 No Direct Mechanical Control (but change production

parameters)

2 Installation of Mechanical Devices Downhole

3 Chemicals Injected Downhole



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No Direct Mechanical Control

Living with Sand Production

Surface Sand Separation• Wellhead desanders• Wellstream desanders

Rate Reduction

Selective Completion Practices• Oriented perforations• High-density perforating• Phase-oriented perforating• Wellbore trajectory; e.g., horizontal• Cavity or wormhole formation• Other…

“Do nothing" and let sand be produced

No Sand Control

• Sand disposal – sand must be cleaned before discarding• Subsidence• Casing collapse or damage• Surface erosion or blockages• High well maintenance costs• High facilities maintenance including shut down

Risks

• Not unrealistic as an approach• Used in many depleted reservoirs



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Mechanical Methods of Sand Control

Slotted Liners or Screens Without a GravelPack

• Open-hole or cased-hole (not recommended)

Slotted Liners or Screens with a Gravel Pack• Open hole or cased hole

Frac packing or Fracturing

Expandable Screens

Vent Screens



the Formation

Resin-Coated Gravel



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No Sand Control

Typically used when sand production is minimal and has not caused expensive workovers

Often done onshore rather than on a platform

Often used toward the end of the life of the reservoir

In this case, note minimal sand in

separator

Limiting Velocity

• Underream• Larger wellbore• Larger / more perforations• Cavity completion• Reduce the rate

Flux Rate = Fluid Flow Rate/Unit Area

Slow down fluid movement rate at the sand face



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Cavity Formation

Enlarging the wellbore, whether by perforating (tunnel extension), underreaming, wormhole formation or cavity creation, increases the area of contact with the formation and decreases the flowing fluid velocity at any set flowrate

Original hole Becomes

Are there any other detrimental effects?

No Control / Cavity Formation / Rate Restriction

How much production is lost?

Will the well be stable at this point?

How much sand must be produced to form the cavity?

Will rate reduction stop the sand?



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0.0001

0.001

0.01

0.1

1

10

100

0.1 1 10 100 1000

Superficial Gas Velocity(ft/s at process conditions)

Superficial Liquid Velocity

(ft/s at pro

cess

conditions)

No Failure Reported

Failures - Low Sand Production

Failures - High Sand Production

Shell Limit for Current Case

API Limits


This shows production from a moderately high rate well at relatively low surface pressure.

The red star is the current condition and the green line is the erosional limit (like a speed limit).

The well is making sand at the limit.

20 ppm (0.002%, ~ 6# / 1000 bbls sand rate) (2.7kg/159M3)

Units In Plot Above: Gas or liquid production per unit cross section area, calculated as if the phase were the only phase flowing in the porous medium; the value is usually readily determinable from lab work.

1 ft/s = 0.3 M/s

Adding More Perforations, with Larger Entry Holes



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Preventing Perforation Damage

Underbalance Perforating

Basic Problem• Removing the damage created during the perforating process

Most Efficient Damage Removal• Perforate underbalance• The wellbore pressure is lower than the reservoir pressure

Should be performed only with Tubing Conveyed Perforating Guns

Mechanical Sand Control Methods – Open hole

Screen Alone – or – Screen with Gravel

Basic Problem• Control sand without reducing productivity

Design Parameters• Optimum gravel-sand size ratio• Optimum slot width to retain gravel or sand• Effective Placement Technique



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Consolidation:Resin

Sand Control Principles: 3 Ways

Filtration:Standalone

Screen

Bridging:Gravel Pack

Cased-Hole Gravel Pack

Screen

Gravel Pack

Perforation

Formation Sand

TunnelCement

Casing

Internal gravel pack

recommended thickness of pack

or pre-pack is 0.75" (1.79 cm) to 1.25" (3.18 cm)



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Open-Hole Gravel Pack

Minimum gravel pack recommended

thickness is 0.75" to 1.25" (1.9 to 3.2 cm)



Except for Expandable Screens

Stand-Alone Screens

Open Hole With Slotted Liner

Open Hole With Screen or

Prepacked Screen



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Gravel retains the formation sand in place

Screen holds the gravel in place This technique functions as a retention device, which

slows screen plugging Can cause reduction in well productivity (a positive skin)

Gravel Pack Design Principle #1

Establish a highly permeable pathway between formation and wellbore that formation sand cannot penetrate



• Gravel is placed between screen and casing, and inside perforations

Cased Hole vs. Open Hole Gravel Packs

Cased Hole

The trend is toward more open-hole gravel packs being placed in horizontal wells

• Higher initial production

• Eliminates expenses, including:

− Casing, cementing, and perforating

− Associated rig costs

• Gravel is placed between the screen and the formation

Open Hole

1

2



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Importance of Good Bridging in a Gravel Pack Design


GOOD BRIDGING

Formation Sand is Restrained By Gravel Pack Gravel in a Good Design

POOR BRIDGINGFormation Sand Invades

Gravel Pack

Permeability of the Invaded Formation?

What is the permeability of the invaded formation if the 20/40 mesh gravel has a permeability of 120,000 md and the formation has a permeability of 1,000 md?

a) About 50,000 md

b) About 10,000 md

c) About 1,000 md

e) Zero

d) Less than 200 md



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Gravel Pack Design Principles – 3 Steps

Obtain a good description of the formation sand grainsize distribution1

Select gravel size based on the formation sandgrain size distribution (Saucier Method)2

Select screen based on smallest gravel range3


• 50% to 75% of smallest gravel range size

How do we get a good description of the sand size Distribution?

Obtainrepresentativesand samples fora sieve analysis

Perform a sieveanalysis of thesample, or

Perform a laserbeam particle-size analysis ofthe formation



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Formation Sampling for Sieve Analysis

Conventional Cores

Sidewall Cores

Produced Samples

• Avoid Composite Samples, whenever possible

Bailed Samples

Which of these is Best? Worst? Why?




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U.S. Mesh Definition of Grain Size

Mesh refers to the number of openings per linear inch

The width of the opening depends on the mesh and diameter of the wire

The U.S. Mesh series specifies the mesh size and width of opening

U.S. Mesh Sizes



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U.S. Mesh Size

Sieve Opening, In.

(mm)Sieve Weight

Before (Grams)Sieve Weight After (Grams)

Sand Weight (Grams)


(Grams)


(percent)

80 0.0070 (.18) 35.83 36.19 0.36 0.36 5.40%

100 0.0059 (.15) 35.24 35.51 0.27 0.63 9.45%

120 0.0049 (.12) 34.88 35.68 0.80 1.43 21.44%

140 0.0041 (.10) 33.91 35.57 1.66 3.09 46.33%

230 0.0024 (.06) 35.13 37.95 2.82 5.91 88.61%

400 0.0015 (.04) 30.17 30.63 0.86 6.37 95.50%

Pan 154.20 154.50 0.30 6.67 100.00%

Example Results from Sieve Analysis

1. Measure the weight of each sieve

2. Place the sample on the largest sieve, and shake the stack

3. Measure the weight of the sieves with the amount of samplecaught on each

4. Plot the cumulative weight percent of samples vs sieve size

(2.54) (0.0254) (0.00254)(0.254)

Cu

mu

lati

ve W

eig

ht

(%)


Step C: Select median gravel size and gravel rangeFor a gravel pack: 6 x 0.004 in = 0.024 in (0.61 mm) Use 20/40 mesh

For a frac pack: 8 x = 0.004 in = 0.032 in (0.81 mm) Use 16/30 mesh


d50


0.004 in.(0.102 mm)



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Commonly Available Gravel Sizes

Also, 30/50 now often available, size range 0.023 – 0.0117 inches (0.584 - 0.297 mm)

U.S. Mesh Size

Size Range, in. (mm)

Medium Gravel Diameter (inches)

Median Gravel Diameter (mm)

Permeability (Darcies)

6/100.1320-.0787 (3.35-2.00)

0.1054 2.677 2703

8/12.0937-.0661 (2.38-1.68)

0.0799 2.029 1969

10/20.0787-.0331 (2.00-0.84)

0.0559 1.420 652

12/20.0661-.0331 (0.84-1.68)

0.0496 1.260 668

16/30.0469-.0232 (1.19-0.59)

0.0351 0.892 415

20/40.0331-.0165 (0.84-0.42)

0.0248 0.630 225

40/60.0165-.0098 (0.42-0.25)

0.0132 0.335 69

50/70.0117-.0083 (0.30-0.21)

0.0100 0.254 45

Sieve Analysis Indicates Whether Formation has Uniform or Non-Uniform Grain Size Distribution

Non-uniformNon-uniform

Poorly Sorted Sand

Well Sorted Sand

(2.54 mm) (.254 mm) (.0254 mm) (.00254 mm)

UniformUniform



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Selecting Gravel Based Upon Sand Grain Size

Lower case “d“ designates formation sand median diameter

Upper case “D” is the selected gravel median diameter


Uniformity Coefficient40

90

d=

dCu

Sorting Coefficient10

95

d=

dC s

Saucier50

50

Gravel

Formation sand

D=

d6

1

2

3

Screen Selection Guide for Open Hole Completion

Based on reservoir sand d50 size that varies up to 50%. Indicative only.For Wire Wrap SAS: If formation fines >5%, use Metal Mesh; >10%, use Gravel Pack.



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Uniformity Coefficient

Cu = Uniformity Coefficient



Cu = d40 / d90

if Cu < 3

if 3 < Cu < 7

if Cu > 7

Sorting Coefficient is defined as Cs = d10 / d95

Uniform Sand Distribution=

Non-Uniform Sand Distribution=

Highly Non-Uniform Sand Dist.=

U.S. Sieve Number

Other Examples: Grain Size Distribution Sieve Analyses

Bailed Sample

Core Barrel Sample

Produced Sample

(2.54 mm) (.254 mm) (.0254 mm)



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Grain Size Comparison Analyses at Various Depths –Same Well

Grain Diameter (mm)

Grain Diameter US Mesh Size

Obtain a good description of the formation sand grain sizedistribution

Select gravel size based on the formation sand grain sizedistribution

Select screen based on smallest gravel range

Summary Review: Gravel Pack Design – 3 Steps


• Design screen opening as:− 50-75% of the diameter of the smallest gravel range size

− This size retains gravel in place behind screen

1

2

3



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Gravel Pack Rules of Thumb

Gravel to Sand Size Ratio• Use a gravel size as large as possible; the sand must be retained

at the outer edge of the pack• The size of the gravel is usually 6 times the size of the formation

sand at D50 or D40 (Saucier’s technique – many other sizingtechniques have been reported in the literature)

• For frac packs, multiply the median by 8 instead of 6• Pay more attention to smaller sand grain sizes with:

– Non-uniform sands

– Higher flow velocity– High gas oil ratios

– Fluctuating flow rates

Gravel Pack Rules of Thumb (continued)

• Gravel-to-Sand G/S ratio is based on “tight pack”

• Gravel movement caused by a loose pack will lead torapid failure of the pack

Pack gravel tightly Pack gravel tightly





• Thicker pack allows higher flow rate

• Many wells are underreamed to allow a thicker pack



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Cs = d10 / d95


Other Relevant Reservoir Criteria

How Does Degree of Sorting Affect Gravel Sizing?

May Require Smaller Gravel Size if Highly Non-Uniform

Fines % of particles smaller than 44 μm (0.00173 in) – may be problematic

Again – Sorting Coefficient Defined as


Laser Particle Size Analysis

Determines size distribution through measurement of degree of scatter of laser.

If samples are poorly cleaned, mud cake will be recorded and results will be adversely affected.

Results often different from sieve results, but depend on the shape of the sand grain, as well as proper cleaning technique



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Problem ISand Size Distribution


Formation Sand Size Distribution Problem

Problem 1 – Formation Sand Size Distribution

The following weights were obtained for a sieve analysis on a sandstone sample. Calculate the sand sample weight on each sieve size, and plot the Percent cumulative weight vs. sample size results on semi-log graph paper.

Determine d40, d50, d90, Uc, the percentage of fines, and the recommended gravel size for this sample.



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Problem 1: What Size Gravel is Required?

What is the Uniformity Coefficient (d40/d90) for this sand?

What is the Sorting Coefficient (d10/d95)?

What is the percentage of fines?

Gravel Placement

Gravel can be placed with many types of fluids and equipment

These fluids can damage the formation

Fluids must be properly cleaned before pumping

If the job is done by the book, the result should produce a well with good productivity and a long life

The key to an undamaged well is following the recommendations to the letter



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Gravel Placement Fluid

Gravel can be placed with brines or polymer fluids and other fluids such as VES, etc.

Super-clean fluid essential (especially for brines)• No solids• Most open-hole and cased-hole pack failures result from surface

solids (dirty fluid / brine / polymer tanks)

Large volumes of brines are required, because of the low proppant loading. Therefore there is a large amount of fluid lost to the formation.

Must filter brine fluids if they are not free of solids.

The KEY is achieving a tight pack with very low skins and good well productivity.

Gravel Packing Position

.

.

Circulate Position

Packer shifted to crossover position

Carrier fluid and gravel are pumped down tubing and through tool to be placed in the screen / perforated casing annulus at perforations

By job end, packer is shifted back to producing position

Gravel Pack Equipment – Packer Crossover Tool

Crossover open

Crossover open

Wire wrapped screen

Wire wrapped screen

GravelGravel

Port Collar, Open

Wash Pipe(Tail Pipe)

Cased Hole

Note that gravel also fills perfs



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Typical Gravel Pack System with Crossover Tool

Model SC-1 Packer

Model S Gravel Pack Extension

Model GPR-6 Shear Out Safety Joint

Blank Pipe

Bakerweld Screen

Model S-22 Multiple Acting Indicator Seal Assembly

Model D Sump Packer

Model SC Hydraulic Setting Tool

Bypass PortsBall Seat for Setting Packer

Reversing Ball

Washpipe

From: Baker Oil Tools

Model S-2 Gravel Pack CrossoverGravel Pack Port

Crossover Tool Function

Squeeze:Forces all of the fluid

pumped to flow though the perforations into

the formation. This will force gravel into the

perforations, and pack it tightly.

Circulating:After the perforations are filled, the tool is

shifted opening a flow path for fluid to flow up the tubing annulus back

to the surface.

Reverse:After filling the screen

annulus with gravel, the work string shifts the tools to the reverse circulate position to clean any remaining

gravel out of the work string.



1 2 3



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Crossover Tool – Squeeze Position

The Squeeze Position forces gravel into the perforations

Achieved by setting down weight on packer

Bypass ports are sealed in packer bore

All fluid pumped is forced into formation

Crossover Tool – Circulating Position

To fill the annulus, the tool is shifted to the circulate position:

By picking up approximately one foot on the workstring

This opens the return ports in the crossover tool

The fluid then flows through the screen, up the washpipe, lifting the reversing ball, and out the ports into the annulus



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Crossover Tool – Reversing Position

After the gravel packing is complete:

The workstring is picked up another foot

Opening up an additional set of ports so that the workstring can be cleaned by reversing out any remaining gravel.

Finally, the workstring will be pulled, and the completion string can be run into the packer.

End of Review 1

Further Questions?



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Horizontal Wells (Gravel Packed or Stand-Alone Screens)

Learning Objectives


Recognize the benefits of using horizontal wells to reduce sand production and improve well productivity

Describe how to gravel pack horizontal wells using brines or gels

Describe how alternate path technology can be used to ensure successful gravel packs when using gel carrier fluids



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Open Hole with Screen or Prepacked Screen

Non-Gravel Pack Applications

Slotted liners and screens in a non-gravel pack are

FILTRATION DEVICESExcept for Expandable Screens

(Which may also be a good option)

Horizontal Well Gravel Pack Completions

Horizontal wells allow significantly more reservoir access compared to vertical wells so many operators prefer to place gravel in horizontal wells

• Usually extends the life of the well and can result in significantly higher well productivity

• Sand production is normally decreased because of lower fluid flux rates

• Sand control if often required in horizontal wells

Skins for gravel-packed wells (open hole or cased hole) are often higher than for wells with stand-alone screen wells

• Stand-alone screens can be used in formations that are uniform

Gravel may be required if the uniformity coefficient is poor• In non-uniform formations, screens plug over time, and “hotspots”

lead to early screen failures



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Horizontal Well Gravel Packing

• Brine carrier fluids• Gel carrier fluids (with alternate path technology)• In Cased hole completions• In Open hole completions

Long horizontal wells can be successfully gravel packedusing:

Frac packs can also be successfully placed in Horizontal Well

Expandable Sand Screens (ESS) have been used tocontrol sand production

Stand-Alone Screens (SAS) can be used (no gravel pack)but only in uniform sands

Gravel Placement in Horizontal Wells with Brine

When using brines to gravel pack horizontal wells, it is necessary to have a large diameter wash pipe, and to pump at a high rate, in order to get the well tightly packed with gravel.

Heel Toe

Tailpipe



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Horizontal Open Hole Gravel Pack

Alpha and Beta Wave Principle

Open Hole

Wash Pipe

Increased Friction During Beta Wave

Screen



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When gravel packing with a gel in a horizontal well, to get a successful tight gravel pack, Alternate Path Technology must be used!

Gravel Placement in Horizontal Wells with Gels

gk14.ppt

Shunt Tube Tool• Alternate slurry path• Ports every 3 ft (0.9 m)

Alternate Path Shunt Tube Configuration



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Horizontal Well and Multi-Zone Gravel Pack

Alternate path technologies allow gravel packing of horizontal wells using gel carrier fluids

Zonal packing is also aided by shunt tubes

from: Schlumberger

Gravel Pack Equipment Tool String

Shunt Tubes

Used to mitigateincomplete annulusgravel packing

Two carrier tubes without nozzles to deliver slurry

Two packing shunts feed off each main shunt

Only the carrier tubes connect from joint to joint



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Learning Objectives


Recognize the benefits of using horizontal wells to reduce sand production and improve well productivity

Describe how to gravel pack horizontal wells using brines or gels

Describe how alternate path technology can be used to ensure successful gravel packs when using gel carrier fluids



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Common Sand Control Problems

Learning Objectives


Identify the common mistakes that reduce productivity in gravel packed wells

Describe how the use of fluid loss control materials can lead to positive skins for wells

Apply Darcy’s law calculations to determine the effects of a positive skin



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Sources of Gravel Packing Problems

Damage from drilling fluid invasion

Dirty gravel placement fluids

Improper gravel size

Insufficiently packed perforations plugged by formation particles

Gravel crushed or mixed with formation sand

Fluid tanks not clean

Gravel sized incorrectly

Gravel does not meet API Specifications

Fluid loss control materials placed in perforations when pulling guns

Solids InvasionSolids Invasion Filtrate invasionFiltrate

invasion

Improper perforation packing


Crushed zone

Crushed zone

Fluid Loss Control Material

Fluid Loss Control Material

Benefits of Prepacking with Perforating Guns in Hole

Eliminate possible need for placing fluid loss control material into empty perforations.

If fluid loss control is needed it can be placed inside casing, allowing easier cleanup.

Extra trip with packer/ tailpipe assembly is eliminated.

Dedicated prepacking operation is still possible.



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Darcy’s Law for Radial Flow (Oilfield Units)

q (rate) – barrels per day

k (permeability) – millidarcies

h (reservoir thickness) – feet

P (pressure drop) – lb/in2

(viscosity) – cP

re and rw (radius) – feet

S (skin factor) – dimensionless

Bo Formation Volume Factor

Steady State

r wf

oo o e w

0.00708 kh (P - P )q =

B (ln r /r + )S

) r wf

oo o e w

0.00708 kh (P - P )q =

B (ln r /r + )S - 0.75 + S

Semi-Steady State

0 or negative value for best well productivity

* In oilfield units

Importance of Clean Tubulars and GP Equipment

Clean tubing before setting packer (pickle tubing)• Acid

• Solvent

Apply pipe dope moderately on pin only

Check that gravel pack completion equipment is not painted

Check that equipment is free of rust, mill scale, acidizing and cementing materials

Check that fluids storage containment is thoroughly cleaned before mixing completion fluids



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Productivity of Sand Control Methods Lake Maracaibo, Venezuela

PI bpd/psi(m3/d/psi)

No. Wells

Perforated Casing (Reference wells) 36.0 (5.7) 20

Inside Casing Pack Without sand oil squeeze (A predecessor to frac packing)

4.0 (0.64) 14

Internal Gravel PackWith sand oil squeeze

12.0 (1.9) 2

Open Hole Pack 48.0 (7.6) 14

Lab Testing Set-Up for Sand Control Analysis

(1.5 m)

It is strongly recommended to review all lab testing that has been done to aid in selecting the best completion type for your wells.



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Lab Testing an Internal Gravel Pack Completion

(m3/d)

(1.6) (3.2) (5.6) (6.4)

(690)

(kPa)

(1379)

(2068)

(2758)

Example pressure drop for perf design and gravel selection

API RP 58 Gravel Quality Specifications

Sieve analysis• Less than 0.1% oversized and less than 2% undersized

Sphericity and Roundness• Average sphericity and roundness of 0.6

Acid solubility• Less than 1% soluble in 12/3 HF-HCl mud acid

Silt and Clay Content• Turbidity NTU reading lower than 250

Crush resistance• Less than 2% fines created by 2,000 psi (13.8 mPa) confining stress



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Gravel Pack Quality Control

Gravel Pack Quality Control



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Gravel-Packing Recommendations

• The lowest skin,• The best production, and• The fewest amount of workovers required

Each step must be done “By the Book”

This yields:




Review well files to identify sand control failures, and consult with completions engineers to see what steps could have eliminated these failures.



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Attend a well workover, where the purpose of the workover is eliminating sand production in that well.

Learning Objectives


Identify the common mistakes that reduce productivity in gravel packed wells

Describe how the use of fluid loss control materials can lead to positive skins for wells

Apply Darcy’s law calculations to determine the effects of a positive skin



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Frac Packing for Sand Control


Learning Objectives


Evaluate the option of frac packing wells as a sand control completion method

Estimate the expected productivity of your wells

Perform a frac pack completion

Explain the benefits and restrictions on the use of screenless frac packs

Evaluate the option of placing frac packs in horizontal wells



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Hydraulic Fracturing

This sand control technique is basically a combination offracturing the formation, and installing a sand control completion,all in the same operation.

Frac Pack Completions

Prepacking the perforations abovefrac pressure

Gravel pack screen completionequipment in place

Gravel / proppant pumped to fillfracture created

Enhanced rate, longer lifetime,and sand protection control



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Frac Pack for Sand Control

Top view of a well with a frac pack placed through the damaged zone.

Wellbore damaged zoneWell drainage radius

Frac Pack – Sand Control with Well Stimulation

• The fracture becomes a very high permeability flow path into thewellbore

Conventional cased hole gravel packs often result in low wellproductivity, i.e., a high skin.

Typical fracture wing lengths are from 30 ft to 150 ft (9 m to 46 m)

Typical fracture widths at the wellbore are 2 in. to 3 in. (51 mm to76 mm)



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FRAC PACKING WAS THE SUBJECT OF 1995-96 SPE DISTINGUISHED LECTURER SERIES

“AN IMPROVED SAND CONTROLCOMPLETION METHOD”

BY R. C. (Dick) Ellis


• Propped hydraulic fracture stimulation using tip screen-outfracturing techniques, conducted prior to or as part of gravelpacking

A combination frac job and gravel pack:

This is usually done with gravel pack screens and packer-crossover tool assembly in place

Allows gravel packing after frac job in a single, continuouspumping operation



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Cement

Casing

Screen

Gravel Filled Perf Tunnel

A Frac Pack Completion

Proppant Filled Fracture

Damaged Formation

Tip Screen-Out Fracture Concept

Completion process begins with equipment in the squeezeposition

• A pad of the fracturing fluid with no proppant is pumped into theformation above frac pressure

• As fracture is established, fluid will leak off into the formation, leavingsome of the polymer on the fracture walls

• This will lower the leakoff rate of the fluid going into the formation

Hydraulic fracture is created and

then grows as pad is pumped



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Start pumping in gravel at a low concentration into the fracture

Gravel will distribute itself throughout the fracture and the fracture growth will continue


As carrier fluid leaks into formation, immobilization of proppant (or screenout) at fracture tip arrests fracture extension



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Since proppant can’t move, continued pumping expands fracture width and increases proppant loading in fracture

At this point the tools are shifted to the “Circulate” position and the screen annulus is filled

Next is the “Reverse Circulate” position• Clean the tubing, pull the workstring, and run in the production tubing

Tip Screen-Out Fracture Design

Net Pressure Plot (Log Net P vs Log Time)Fracture is packed and

pumping stops

Net Pressure = Treating Pressure – Fracture Closing Pressure



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Frac Pack Objectives

• More reserves• Faster• Improved net present value

By-pass near wellbore formation damage

Obtain a tip screen-out

Low skin – improves productivity

Mitigate fines migration damage

Improve recovery efficiency

• Results in a wide, highly conductive fracture

• Typical average skin range is often in the range of +/- 20

• Skins > 50 are not unusual

• An average of 8, occasionally obtained, would be excellent,but cuts production by 50%

Cased Hole GP Completions Often Have High Skins

The Wellbore can be easily damaged when completing wells within a cased hole gravel pack.



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Frac Pack Results

Typical skin value for fracpacked well: -2 to +3

Frac packs often result in 3 to 4 times more production compared to a conventional cased hole gravel pack

Longevity / gravel pack well life often very good

Fines migration is often completely eliminated

SLURRY VOLUME, gal

(m3)

FLUIDVOLUME, gal

(m3)

PROPPANT CONCENTRATION,

lb/gal (kg/l)

PUMP RATE, BPM

(m3/min)PUMP TIME

(min)

3,000 (11.4) 3,000 (11.4) 0.0 15 (2.38) 4.76

6,140 (23.2) 6,000 (22.7) 0.5 (0.06) 15 (2.38) 9.74

4,180 (15.8) 4,000 (15.1) 1.0 (0.12) 15 (2.38) 6.64

4,365 (16.5) 4,000 (15.1) 2.0 (0.24) 15 (2.38) 6.93

3,410 (12.9) 3,000 (11.4) 3.0 (0.36) 15 (2.38) 5.41

2,960 (11.2) 2,500 (9.5) 4.0 (0.48) 15 (2.38) 4.69

3,180 (12.0) 2,500 (9.5) 6.0 (0.72) 15 (2.38) 5.05

2,730 (10.3) 2,000 (7.6) 8.0 (0.96) 15 (2.38) 4.33

2,180 (8.3) 1,500 (5.7) 10.0 (1.20) 15 (2.38) 3.47

__________32,140 (121.7)

___________28,500 (107.9)

________51.02

NOTE: JOB DESIGNED FOR 80,000 LBS (36,287 kg) OF 20/40 PROPPANT

Typical Pump Schedule for Frac Pack



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Screenless Frac Packs

Wells can also be fracpacked without screens

Usually resin-coated proppant will be used to hold theproppant inside the fracture (to prevent proppantflowback)

Alternatively, resin can be pumped into the proppant atthe end of the job

The resin is allowed to set up to hold the proppant inplace

Screenless Frac Pack (Resin-Coated Gravel)

Low Strength

Sand

Higher Strength

Sand

Performed with resin-coatedsand and the resin is allowedto set up

The wellbore is filled withresin-coated gravel

The wellbore is then drilledout at the end of the job andthe well is placed onproduction



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Frac Packing Horizontal Wells

Many operators are placing multiple frac packs in highly deviated and horizontal wells combining the two popular completion methods

Combining methods gives better production results thaneither method alone




Take part in the planning of a frac pack completion in your field, and to then attend the frac pack application, and review how closely the actual treatment matched the frac pack design.



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Learning Objectives


Evaluate the option of frac packing wells as a sand control completion method

Estimate the expected productivity of your wells

Perform a frac pack completion

Explain the benefits and restrictions on the use of screenless frac packs

Evaluate the option of placing frac packs in horizontal wells

PetroAcademyTM Production Operations

Production Principles Core Well Performance and Nodal Analysis Fundamentals Onshore Conventional Well Completion Core Onshore Unconventional Well Completion Core Primary and Remedial Cementing Core Perforating Core Rod, PCP, Jet Pump and Plunger Lift Core Reciprocating Rod Pump Fundamentals Gas Lift and ESP Pump Core Gas Lift Fundamentals ESP Fundamentals Formation Damage and Matrix Stimulation Core Formation Damage and Matrix Acidizing Fundamentals Flow Assurance and Production Chemistry Core Sand Control Core Sand Control Fundamentals Hydraulic Fracturing Core Production Problem Diagnosis Core Production Logging Core Production Logging Fundamentals



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Virtual Instructor LedSession #2


Open Hole with Screen or Prepacked Screen

Non-Gravel Pack Applications

Slotted liners and screens in a non-gravel pack are

FILTRATION DEVICESExcept for Expandable Screens

(but may also be a good option)



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Horizontal Well Gravel Pack Completions

Horizontal wells allow significantly more reservoir accesscompared to vertical wells

More access results in significantly higher well productivity

Sand production is normally decreased because of lowerfluid flux rates

However, sand control if often required in horizontal wells

Stand-alone screens can be used in formations that areuniform

However, in non-uniform formations, screens plug overtime, and “hotspots” lead to early screen failures

Horizontal Well Gravel Packing

• Brine carrier fluids• Gel carrier fluids (with alternate path technology)• In Cased-hole completions• In Open-hole completions

Long horizontal wells can be successfully gravel packedusing:

Frac packs can also be successfully placed in Horizontal Well

Expandable Sand Screens (ESS) have been used tocontrol sand production

Stand-Alone Screens (SAS) can be used (no gravel pack)but only in uniform sands



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Gravel Placement in Horizontal Wells with Brine

Can completion and tight packing of the whole section be achieved in long extended length holes?

With proper design and equipment, the answer is...Yes.

Heel Toe

Tailpipe

Horizontal Open Hole Gravel Pack

Alpha and Beta Wave Principle

Open Hole

Wash Pipe

Increased Friction During Beta Wave

Screen



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Can completion and tight packing of the whole section be achieved in long extended length holes? Not without additional equipment – Gels require the use of Alternate Path Technology

However, with proper design and equipment, the answer is… Yes

Gravel Placement in Horizontal Wells with Gels

gk14.ppt

Shunt Tube Tool• Alternate slurry path• Ports every 3 ft (.9 m)

Alternate Path Shunt Tube Configuration



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Sources of Gravel Packing Problems

Damage from drilling fluid invasion

Dirty gravel placement fluids

Improper gravel size

Insufficiently packed perforations plugged by formation particles

Gravel crushed or mixed with formation sand

Brine - Tanks - Not - Clean

Gravel sized incorrectly

Gravel does not meet API Specifications

Fluid loss control materials placed in perforations when pulling guns

Solids InvasionSolids InvasionFiltrate invasionFiltrate invasion



Crushed zoneCrushed zone

Benefits of Prepacking with Perforating Guns in Hole

Eliminate possible need for placing fluid-loss control material into empty perforations.

If fluid loss control is needed it can be placed inside casing, allowing easier cleanup.

Extra trip with packer/ tailpipe assembly is eliminated.

Dedicated prepacking operation is still possible.



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Darcy’s Law for Radial Flow (Oilfield Units)

q (rate) – barrels per day

k (permeability) – millidarcies

h (reservoir thickness) – feet

P (pressure drop) – lb/in2

(viscosity) – cP

re & rw (radius) – feet

S (skin factor) – dimensionless

Bo Formation Volume Factor

Steady State

r wf

oo o e w

0.00708 kh (P - P )q =

B (ln r /r + )S

) r wf

oo o e w

0.00708 kh (P - P )q =

B (ln r /r + )S - 0.75 + S

Semi-Steady State

0 or negative value for best well productivity

* In oilfield units

Importance of Clean Tubulars and GP Equipment

Clean tubing before setting packer (pickle tubing)• Acid

• Solvent

Apply pipe dope moderately on pin only

Check that gravel pack completion equipment is not painted

Check that equipment is free of rust, mill scale, acidizing and cementing materials

Check that fluids storage containment is thoroughly cleaned before mixing completion fluids



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API RP 58 Gravel Quality Specifications

Sieve analysis• Less than 0.1% oversized and less than 2% undersized

Sphericity and Roundness• Average sphericity and roundness of 0.6

Acid solubility• Less than 1% soluble in 12/3 HF-HCl mud acid

Silt and Clay Content• Turbidity NTU reading lower than 250

Crush resistance• Less than 2% fines created by 2,000 psi (13.8 mPa) confining stress

Gravel-Packing Recommendations

• The lowest skin,• The best production, and• The fewest amount of workovers

required

Each step must be done “By the Book”

This yields:



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Darcy’s Law CalculationProblem 2

What production rates would be predicted for a 7-inch (17.8 cm) diameter, gravel-packed cased-hole completion? The formation Permeability is 100 md, the reservoir height is 50 ft (15.2 m), a delta P of 1,000 psi (6895 kPa), a formation volume factor of 1, and fluid of 3 cp.

Calculate the expected flows for a skin of 0, and for a skin of 8. The wells are on 40 acre spacing, i.e., drainage radius = 660 ft (201.2 m).



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(21.6 cm)

(19.1 cm)

(21.6 cm)

(16.5 cm)

(12.5 cm)

Eliminates annular space of a conventional liner run in hole which is a possible erosion site

Virtually no annulus after expansion

Conventional liner completion with annulus

Now Available from several service companies


Remedial Sand Control capability - reduced workover costs

Optimized O.D. / I.D. ratios – maximized flow conduit, minimized well costs

Reduced erosion potential

Reduced ∆P – optimized productivity

Borehole stabilization

Sand Control for slimhole/ slender wells

Example shown:6" (15 cm) O.D. Pre-expanded8-½" (21.6 cm) O.D. Post Expansion



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Hydraulic Fracturing

This sand control technique is basically a combination offracturing the formation, and installing a sand control completion,all in the same operation.


Prepacking the perforations abovefrac pressure

Gravel pack screen completionequipment in place

Gravel / proppant pumped to fillfracture created

Enhanced rate, longer lifetime,and sand protection control



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Propped hydraulic fracture stimulation using tipscreen-out fracturing techniques, conducted prior toor as part of gravel packing

This is usually done with gravel pack screens andpacker-crossover tool assembly in place

Allows gravel packing after frac job in a single,continuous pumping operation

The proppant used must be strong enough towithstand the closure stress of the fracture. Thisoften requires manmade proppants.

Damaged Formation

Proppant FilledFracture

Cement

Casing

Screen

Gravel Filled Perf Tunnel

A Frac Pack Completion



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Hydraulic fracture is created and Then grows as pad is pumped


Start pumping in gravel, and it starts filling fracture



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As carrier fluid leaks into formation, immobilization of proppant (or screenout) at fracture tip arrests fracture extension


Since proppant can’t move, continued pumping expands frac width and increases proppant loading in frac



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Tip Screen-Out Fracture Design

Net Pressure Plot (Log Net P vs Log Time)Fracture is packed and

pumping stops

Net Pressure = Treating Pressure – Fracture Closing Pressure

Frac Pack Results

Typical skin value for fracpacked well: -2 to +3

Frac packs often result in 3 to 4 times more production compared to a conventional cased-hole gravel pack

Longevity / gravel pack well life often very good

Fines migration is often completely eliminated



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SLURRY VOLUME, gal

(m3)

FLUIDVOLUME, gal

(m3)

PROPPANT CONCENTRATION,

lb/gal (kg/l)

PUMP RATE, BPM

(m3/min)PUMP TIME

(min)

3,000 (11.4) 3,000 (11.4) 0 15 (2.38) 4.76

6,140 (23.2) 6,000 (22.7) 0.5 (0.06) 15 (2.38) 9.74

4,180 (15.8) 4,000 (15.1) 1.0 (0.12) 15 (2.38) 6.64

4,365 (16.5) 4,000 (15.1) 2.0 (0.24) 15 (2.38) 6.93

3,410 (12.9) 3,000 (11.4) 3.0 (0.36) 15 (2.38) 5.41

2,960 (11.2) 2,500 (9.5) 4.0 (0.48) 15 (2.38) 4.69

3,180 (12.0) 2,500 (9.5) 6.0 (0.72) 15 (2.38) 5.05

2,730 (10.3) 2,000 (7.6) 8.0 (0.96) 15 (2.38) 4.33

2,180 (8.3) 1,500 (5.7) 10.0 (1.20) 15 (2.38) 3.47

__________32,140 (121.7)

___________28,500 (107.9)

________51.02

NOTE: JOB DESIGNED FOR 80,000 LBS (36,287 kg) OF 20/40 PROPPANT

Typical Pump Schedule for Frac Pack



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Screenless Frac Packs

Wells can also be fracpacked without screens

Usually resin-coated proppant will be used to hold theproppant inside the fracture (to prevent proppantflowback)

Alternatively, resin can be pumped into the proppant atthe end of the job

One major advantage is that the wellbore is left fully openfor a larger flowpath

Screenless Frac Pack (Resin-Coated Gravel)

Resin-coated gravel placedabove frac pressure.

Gravel is allowed to set up(temperature plus catalyst),and then the wellbore isdrilled out.

All perfs must be filled withresin-coated proppant.

Cyclic loading can weakenproppant pack.

Risk of premature failure,due to proppant flowback.

Low Strength

Sand

Higher Strength

Sand



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Frac Packing Horizontal Wells

Many operators are placing frac packs in highly deviated and horizontal wells

Multiple frac packs may be placed in horizontal wells

With multiple frac packs, well productivities are very high

Sand Control Design Problem 3



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The well described in the next slide has been drilled and cased down to the top of the upper zone.

The rig is still on site

An Exploratory well was drilled into a new area, and the reservoir has the following characteristics:

• The top of the reservoir is at 4,550 ft (1,387 m), it is normally pressured. The reservoir has the lowest permeability at the top, where it is weakly consolidated. There is a sandy shale streak, about 15 feet (4.6 m) in thickness, and the extent of the shale is unknown. The oil is an API 30°, the uniformity coefficient for both formations is 3.5, and the bottom-hole temperature is 135°F (57.2°C). The median sand size for the top zone (d50) is 0.006 inches (0.0152 cm), and for the lower zone (d50) is 0.004 inches (0.0102 cm).

Select the best sand control method for these wells. • If you use a screen, select the screen type. • If you use gravel, select the size, type, and carrier fluid

to place the gravel.



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Oil/Water Interface

Exploratory Well - How Would You Complete?

Shale

Sand, 400 mD

Sand, 400 mD, Unconsolidated

Shale

Sandy Shale, Unstable, 2 mD

Sand, 200 mD, Unconsolidated

40'

15'

30'

20'

Top of Sand @ 4,550', 30o API, Strong Water Drive, UC = 3.59 5/8ths

BHT = 135 F

Kh/Kv = 2

Large Areal

Extent

Normally Pressured Reservoir

d50 = 0.004”

d50 = 0.006

QUESTIONS?



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