Chapter 3 - Perforating Methods

3. PERFORATINGMETHODS

1TUNIO, May' 2011,,, Courtesy AP Aung

At the end of this chapter, students should be ableto:– Describe the options, advantages and disadvantages for

perforating oil and gas wells.

LESSON OUTCOMES

– Describing an outline strategy to complete a well as part of acompletion operation.

– Understand the importance of charge design and factorsinfluencing performance.


• Perforation Techniques

• Candidate Selection

CHAPTER OUTLINE


Needs of perforating…

• To provide the communication path between the well-bore and all desired zones

• To evaluate and optimize production rate/injectivity aswell as oil and gas recovery from each zone

INTRODUCTION

well as oil and gas recovery from each zone

Perforating…

• produce holes through the wall of the casing, thecement sheath and penetrate into the formation


INTRODUCTION

• History:

1910 : Used mechanical perforators

Blade or wheel knife to open hole in the casing.

1948 : Through-tubing perforating (underbalanced perforating)

1975 : Tubing Conveyed perforating (TCP) 5TUNIO, May' 2011,,, Courtesy AP Aung

INTRODUCTION

1980 : Start to produce fractures from burst of pressuredeveloped from gun detonation.

1993 : Tubing Conveyed Perforation (TCP), succeed in commercialwells. 6TUNIO, May' 2011,,, Courtesy AP Aung

Causes for poor perforation

1. Lack of understanding of requirements for optimumperforating

2. Inadequate gun clearance

3. Selecting perforating guns or charges on the basis of

INTRODUCTION

3. Selecting perforating guns or charges on the basis ofsurface penetration tests

4. Awarding perforating jobs on the basis of price ratherthan job quality


Two(2) Types of Perforators

1. Bullet perforators

Types of Perforators


2. Jet perforators



• Bullet perforator is multi-barreled firearm designed forbeing lowered into a well


being lowered into a well

• Electrically fired from surface controls.

• Perforating of the casing, cement and formation isaccomplished by bullets or high velocity projectiles


THREE(3) ways of firing:

1. Selective firing of one bullet at a time

2. Selective firing of independent groups of


2. Selective firing of independent groups ofbullets

3. Simultaneously firing of all bullets


Availability:

• A number of bullet types

• Bullet guns for use in all sizes of casing from a number of


• Bullet guns for use in all sizes of casing from a number ofservice companies

• Velocity of bullet = 3300 ft/sec


• When gun clearance > 0.5 in, velocity and energy drop

• When clearance = 1 in., 25% penetration loss than at 0.5in. clearance


in. clearance

• When gun clearance = 2, penetration loss is 30 % than at0.5 in. clearance

• When gun clearance = 0, penetration increases about 15%over 0.5 in. clearance


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2. Jet perforators• The use of shaped explosive charges to create

perforation tunnels. The explosive charge producesan extremely high-pressure jet that penetrates thecasing or liner to shoot into the reservoir


casing or liner to shoot into the reservoirformation.

• The shaped charges are contained in a perforatinggun assembly that can be conveyed on wireline,tubing or coiled tubing, depending on theapplication and the wellbore conditions.


Basic jet perforator consists of:

• A primacord / primer

Characteristics and Performance of JetPerforator

• The main explosive charge

• A conical liner

• A charge case or container


Jet perforating process using a solid metal liner

16

Process of Jet Perforating

• An electrically fired detonator starts a chain reactionwhich successively detonates


which successively detonates

• the primacord

• High velocity booster in the charge

• Finally, the main explosive


• High pressure generated by the explosive causes themetal in the charge liner to flow, separating the inner andouter layers of the liner.

Process of Jet Perforating

• Continued pressure buildup on the liner causes a needlelike high speed jet of fine particles to spew from the coneat a speed of about 20,000 ft/sec at its tip with a pressurethis point estimated to be 10 million psi.


Factors on which Properties and extent of thecrushed zone depends:

• Size of perforation charge

• Casing wall thickness and strength

• Cement sheath thickness and strength


• Cement sheath thickness and strength

• Grain composition, size and shape of the formationrock

• Stress conditions in the near wellbore region

• Closeness of nearest perforations in the samevertical plane.


Factors Influencing Charge Performance are asfollows:

• Penetration length


• Penetration length

• Perforation diameter

• Perforation hole volume

• Impact on casing integrity

• Perforation flow performance


Parameters which may influence the physical performanceof the jet perforator

• Gun Size/Explosive Charge Size


• Gun Size/Explosive Charge Size

– The size of the perforating gun will dictate the maximumexplosive load which can be accommodated in the charges.


Perforation Charge Arrangement

• The orientation of perforations defined as the angularphasing can be:


– 0° , 1800 or in-line firing which can provide the minimumclearance for all perforations

– 45° to 120° phasing which provides the nearest approximationto radial flow





Perforation shot density: Example of 4 shots/foot in linefiring and 90o phasing


• Penetration prediction for formation rocks

Assessment of Jet Perforator Performance


Whether the gun will be run on:

– wire line

– or be conveyed on tubing or a drill string.

Perforating Gun Systems

– or be conveyed on tubing or a drill string.

Whether perforating will be conducted prior to, or aftermechanical completion of the well.


Optional technique for perforating27TUNIO, May' 2011,,, Courtesy AP Aung

Jet perforation is superior to bullets

• in dense formations

Comparison of the Bullet and Jet Perforators

• for penetration of multiple casing strings


In softer targets,


• Bullets lose velocity when gun clearance >0.5 in.• Often use in a unconsolidated formations• Cheaper to use, rarely been used today

• Bullets plug the end of the flow channel

29TUNIO, May' 2011

Bottom-hole temperature limitation

• Jet perforating .... Up to 400 °F


• Bullet perforating ..Less than 275°


Jet

1. Deeper penetration in hard rocks and multiplecasing strings.

2. Minimum burring of casing wall.

Equipment Comparisons

2. Minimum burring of casing wall.

3. Minimum cement shattering.

4. Available for use in permanent type completions

5. Higher temperature range.


Bullet

1. Deeper penetration in soft and medium.

2. Maximum fracturing of cement and soft rocks.

3. Completely selective firing available.

Equipment Comparisons

3. Completely selective firing available.

4. Controllable penetration available by using different

bullet.

5. High powered, large diameter gun available

6. Generally cheaper, due to lower cost per shot.32TUNIO, May' 2011,,, Courtesy AP Aung

1. Perforating Sandstone Wells

a. Perforate all wells in clean, non-damaging fluidsnormally NaCl, KCl, oil, or Nitrogen.

b. Guns and completion systems should be designed

Candidate Selection

b. Guns and completion systems should be designedto match given well conditions.

c. All sandstone wells should be perforated with astandard casing gun, through-tubing gun, or atubing-conveyed gun.


d. Sandstone wells should not be perforated in acidsbecause of severe emulsion problems andformation damage.

e. Selection of perforators should not be based alone

Candidate Selection

e. Selection of perforators should not be based alonein cement and/or sand stone. It may lead to poorquality penetrations. Ability to readily clean-out andflow through the formation and perforation tunnelmust be the basic criteria for perforator selection.


2. Perforating Carbonate Wells

a. Perforate in clean fluid, water or oil with a pressuredifferential into well bore.

b. In limestone, chalk, or dolomite wells, it may be

Candidate Selection

b. In limestone, chalk, or dolomite wells, it may bedesirable to perforate in HCl or Acetic acid with adifferential pressure of 200 t0 500 psi. Perforating inacid is especially beneficial if the well is to befractured.


c. If a carbonate well is perforated in Acetic acid, thisacid should remain under some differential pressureinto the formation for 8 to 12 hours to allow timefor dissolution of carbonates with Acetic acid.

2. Perforating Carbonate Wells


3. Perforating in oil, water, or acid belowa higher weight mud column is not satisfactoryand is not recommended.

Candidate Selection

and is not recommended.


4. When perforating in mud or other fluidscontaining fines, it should be recognized that:

a. It is impossible to remove mud of silt plugsfrom all perforations by back flowing or swabbing.

Candidate Selection

from all perforations by back flowing or swabbing.

b. Mud or silt plugs are not readily removedfrom perforations with acid or other chemicalsunless each perforation is fractured with ball

sealers.


5. Drilling mud and completion fluidcontaining appreciable fines should not beallowed to enter perforations through out the life ofthe well.

Candidate Selection

Water containing fines or dirty oil may be verydamaging due to perforation plugging and pluggingof formation pores with solids for a greater distancefrom the well bore.


Thank You…Thank You…Thank You…Thank You…


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Chapter 3 - Perforating Methods