Perforating Methods

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3. PERFORATING

METHODS

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



At the end of this chapter, students should be able

to:

– 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 a

completion 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 as

INTRODUCTION

we as o an gas recovery rom eac zone

Perforating…

• produce holes through the wall of the casing, the

cement 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 pressure

developed from gun detonation.

1993 : Tubing Conveyed Perforation (TCP), succeed in commercial

wells. 6TUNIO, May' 2011,,, Courtesy AP Aung



Causes for poor perforation

1. Lack of understanding of requirements for optimum

perforating

2. Inadequate gun clearance

INTRODUCTION

. e ect ng per orat ng guns or c arges on t e as s osurface penetration tests

4. Awarding perforating jobs on the basis of price rather

than job quality




Two(2) Types of Perforators

1. Bullet erforators

Types of Perforators

2. Jet perforators




1. Bullet perforators

• Bullet perforator is multi-barreled firearm designed for

bein lowered into a well


• Electrically fired from surface controls.

• Perforating of the casing, cement and formation is

accomplished 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

bullets

3. Simultaneously firing of all bullets




Availability:

• A number of bullet types


service 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 0.5

in. clearance


• When gun clearance = 2, penetration loss is 30 % than at

0.5 in. clearance

• When gun clearance = 0, penetration increases about 15%

over 0.5 in. clearance




TUNIO, May' 2011,,, Courtesy AP Aung 13



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

perforation tunnels. The explosive charge produces

an extremely high-pressure jet that penetrates the


formation.

• The shaped charges are contained in a perforating

gun assembly that can be conveyed on wireline,tubing or coiled tubing, depending on the

application and the wellbore conditions.14TUNIO, May' 2011,,, Courtesy AP Aung



Basic jet perforator consists of:

• A primacord / primer

Characteristics and Performance of Jet

Perforator

• 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 reaction

which successivel detonates


Perforator

• the primacord

• High velocity booster in the charge

• Finally, the main explosive




• High pressure generated by the explosive causes the

metal in the charge liner to flow, separating the inner and

outer layers of the liner.

Process of Jet Perforating

• Continued pressure buildup on the liner causes a needle

like high speed jet of fine particles to spew from the cone

at a speed of about 20,000 ft/sec at its tip with a pressure

this 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


Perforator

• 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 as

follows:

• Penetration len th


Perforator

• Perforation diameter

• Perforation hole volume

• Impact on casing integrity

• Perforation flow performance




Parameters which may influence the physical performance

of the jet perforator

• Gun Size Ex losive Char e Size


Perforator

– The size of the perforating gun will dictate the maximum

explosive load which can be accommodated in the charges.




Perforation Charge Arrangement

• The orientation of perforations defined as the angular

phasing can be:


Perforator

– 0° , 1800 or in-line firing which can provide the minimum

clearance for all perforations

– 45° to 120° phasing which provides the nearest approximation

to radial flow





Perforator





Perforator

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

Perforating Gun Systems

.

Whether perforating will be conducted prior to, or after

mechanical 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 multiple

casing strings.

Equipment Comparisons

. n mum urr ng o cas ng wa .

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.

Equipment Comparisons

. omp e e y se ec ve r ng ava a e.

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.

Candidate Selection

. uns an comp et on systems s ou e es gneto match given well conditions.

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

tubing-conveyed gun.




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

Candidate Selection

in 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.

Candidate Selection

. n mestone, c a , or o om te we s, t may edesirable 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 be

fractured.




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 satisfactory

Candidate Selection

.




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

a. It is impossible to remove mud of silt plugs

Candidate Selection

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 of the 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…


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Perforating Methods