6 Perforating

Perforating is a critical part of any well completion process. The perforating process generates holes - perforation tunnels - in steel casing, surrounding cement and the formation. In the past, perforations were regarded simply as holes in steel casing made by different methods. Bur perforating is not just a simple hole drilling process. Perforations or perforated completions playa crucial role in economic oil and gas production, long-term well productivity and efficient hydrocarbon recovery. It also includes the reasons for considering specific formation, well and completion ments when selecting perforating techniques. Perforating

require-

is also covered in Volume 3 Part 1 Topic 4

While studying this Topic, you should focus on the following learning objectives: •

Basic physicsof perforating

•

New charges and manufacturing

•

Perforation damage mitigation

•

Optimised

•

Perforating practices for natural, stimulated

•

Safety and conveyance methods

perforation parameters or sand-management

completions

and

1

OPERATINGENVIRONMENT.

1.1

THE WELL COMPLETION AND IT'S SIGNIFICANCE IN PRODUCTIVITY

The significance of the well completion lies in the fact that it is the only productivity factor, amongst three, which can be influenced by man to increase productivity. The othet two productivity factors, namely reservoir boundary and reservoir properties are natural factors over which man has no control.

Reservoir boundary is the size of the reservoir, which is estimated during the temporary completion test.

Reservoir properties are properties such as porosity, permeability, fluid properties, and hydrocarbon saturation. Reservoir properties are measured through logging and testing methods. There are different ways to maximize productivity.

These include:

Creating a highly conductive path to the well bore by fracturing Reducing viscosity by employing

the formation.

methods such as steam injection.

Removing skin by employing methods such as acidising. Increasing well penetration

by perforating

deeper into the formation.

Reducing formation volume factor by choosing correct surface separator. Perforations in a well optimize the connection between the wellbore and the reservoir so as to enhance productivity.

In order to allow oil and gas to flow into the well, conduits need to be made into the formation. To do this, a gun is positioned across the producing formation and is detonated to create perforations through the casing and cement. The guns used for this purpose are known as perforating guns. Perforating

guns are divided into two primary categories.

Capsule guns Carrier guns TlbillJ casillJ

Retrig,':ille fnerjel Figure 10.2.133:

Stard<Jd Enerjet

E.>p(fl(lable Enerjet

ll1/n-in. 00 running

3.79-in.

00 dBplo'~-ed

Capsule Guns

In capsule guns, shaped charges are individually and the Pivot are the examples of capsule guns.

packaged in a pressure tight case. The Enerjet

G

Palentad charge pacl:ing

1.56·in. HSDg.m 4 spf 2((0 Jilasing

2,0·in. HSD g.m 6 spf. 60" spral phasi[lJ

2,25-in, HSo g.m 6 spf. 60" spral phasi[lJ

5.85-in, BiJshot 18 spf. 12ifl60" Jilasing

6 ',&- in, Bigshot 18 spf. 120';'60" JilasillJ

Carrier guns contain a group of shaped charges enclosed in a steel carrier. High Shot Density (HSD) guns are carrier guns designed to carry more number of shots per foor. The performance of the perforating cess of the well completion. 2.1

gun in the down hole environment

is critical to the suc-

GUN PERFORMANCE

Guns performance

is governed by several parameters.

These are:

Gun size

Shot density Gun phasing Perforating Temperature

length (penetration) rating

2.1.1 Gun size: The gun size is an important parameter that affects the guns performance. If a well is to be perforated before tubing is run, the casing ID becomes the limiting factor in specifying maximum gun size. Usually an operator will allow some clearance to permit fishing. Gun swell after fire, and burring are also important consideration that needs to be taken into account when choosing a gun size. If a well is to be perforated through tubing, then rubular accessories such as nipple-profile will limit gun size. 2.1.2 Clearance Clearance is the distance from the guns outer diameter to the inner diameter of the casing. Clearance is an important gun parameter from the perspective of performance. It helps in determining the length of perforating, which has a significant impact on well productivity. Gun clearance affects penetration and entrance hole diameter and these effects have a profound impact when perforating through rubing.

Low

clearance

Figure 10.2.135: ance on penetration diameter

Effect of gun clearand entrance

hole

The Pivot gun (see Figure 10.2.133 - Capsule Guns) which allows access through small ID tubing but allows the charge to swivel inside the casing before firing was designed to reduce clearance problems. 2.1.3 Entrancehole diameter The diameter of the hole made by the perforating jet depends on the strength of the materials being penetrated. Test results show that the hole in the cement and rock is usually larger than the hole in the casing. 2.1.4 Shot density The length of the perforating gun can be varied depending on the amount of interval that is to be perforated. Therefore, the number of shaped charges that is used in a gun is specified on a shot per foot bases. This is referred to as shot density. In engineering tables the shot density is designated as SPF. 2.1.5 Gun phasing Gun phasing is defined as the angle between charges and can vary considerably. Phasing has a critical impact on well productivity. Phasing also has a considerable effect on the remaining casing strength after perforating. Different phasing is available depending on completion objectives.

Scallop recess adjacent to charge

.--<

Shot phasing

2.1.6 Perforating length Perforating length, often called penetration is a key element to high productivity. Perforations beyond the damage zone increase effective well bore radius and intersect more natural fractures if these are present.

PowerJet charges are designed to yield maximum jet length and impact pressures that maximize penetration. PowerJet is proven to outperform other charges by 20 to 30%. It is highly recommended in perforating hard rock formations. 2.1.7 Temperature rating Temperature rating and duration of exposure have an effect on perforating guns performance. Exceeding temperature rating leads to reduced performance followed by burning (this applies to all explosives) and possible auto detonation in case of RDX and HMX charges. Seals, firing heads, detonating accessories, pressure and pressure cycles need to be given important consideration, especially in high temperature wells. The duration of wire line operation is 0-6 hours. Typical TCP operation ranges from 12 to 24 hours while Complete/Perforate operation may take several days. 2.2

DEBRIS

After firing the gun and while retrieving, unwanted solids enter into the well bore or formation through perforating tunnels. These are called the perforating debris. Perforating debris can create problems in highly deviated or horizontal well bores and can also create problems with the completion hardware. Sources of debris are not only gun system, but also from the casing, cement and formation. Gun hardwarecomponents

contributing

to debris are;

Gun body Shaped charge liner slug and jet Shaped charge case Shaped charge retaining system (that holds the charge inside the gun) 2.3

METHODS OF REDUCING PERFORATING DEBRIS AND FORMATION DAMAGE.

There are two main methods of reducing debris, using shaped charges with powdered metal liners and zinc cases or special guns that intentionally produce large size gun debris but the gun design prevents it from leaving the gun body after firing. 2.3.1 Shaped charge liner Shaped charges are designed to generate optimal combinations of hole size and penetration using a minimum of explosive material. Asymmetric or crooked jets reduce charge performance so perforating jets must form exactly according to design specs. Consequently shaped charge effectiveness depends on charge symmetry and jet characteristics. Penetration depends on consistently achieving long jets with optimal velocity profiles. A velocity profile must establish from tip to tail and perforating jets need to travel as fast as possible. Incorrect velocity profiles decrease penetration. Hole size is related to jet shape. Initially solid metal liners, often copper, were used to generate high density jets with big holes, but this created undesirable metal slugs or carrots, that plugged perforations. This plugging was believed to be offset by the large diameter holes and the high permeability of formations where big hole charges are used. Technology that eliminates slugs and maximises area open to flow (AOF) has revised this approach. Although solid copper liners are still used in some big hole charges, recent designs (using powdered metals) generate jets without producing a solid metal slug. Size of debris from the shaped charge case can be reduced by using Zinc instead of the traditional steel case.

2.3.2

Zinc casing method:

Schlumberger has developed a family of clean shot deep penetrating charges and clean packed big hole charges. Both charges have zinc instead of steel packing. The zinc casing breaks up into finely powdered material, which is acid soluble or can be circulated out. This method also has its disadvantages. More debris exits the gun in comparison with deep penetrating

charges or Bigshot guns

Zinc is only parcially acid soluble 15% debris remains in the well/formation Additional

cOSts with acid (trip, CT

&

after acidizing

acid)

Zinc deposits remain on hardware Charge performance

is reduced

Guns suffer more shock, i.e., Zinc reacts during detonation Zinc reacts with brines Precipitation

can form hard cement in well bore and formation

Precipitation

may cause formation damage

Figure 10.2.137: Zinc case and debris on the left, Traditional steel case and debris on the right

Detonating cord

Main explosive charge

Figure 10.2.138: Shaped charge in a carrier gun.

ExplosIVe

Steel target Metallic Ii er

II ed cavity effe.::t

Unlined

cavIty effect

D Figure 10.2.139:

SShaped-Charge Dynamics

Perforations are created in less than a second by shaped charges that use an explosive cavity effect, which is based on military weapons technology, with a metal liner to maximize penetratIOn. Perforating charges consist of a primer, outer case, high explosive and conical metal liner connected to a detOnating cord. Each component must be made to exact tOlerances. At the Schlumberger Reservoir Completions Centre (SRC) in Rosharon, Texas, USA, these charges are designed, manufactured and tested to meet strict quality standards. A detonating cord initiates the primer and detOnates the main explosive. The liner collapses to form a high-velocity jet of fluidized metal particles that is propelled along the charge axis. This high-energy jet consists of a faster tip and slower tail. The tip travels at about 4.4

miles/see [7 km/see}, but the tail moves more slowly, less than 0.6 miles/see [l km/sec}. This velocity gradient stretches the jet so that it penetrates casing, cement and formation. Perforating jets erode until all energy is expended at the end of a perforation tunnel. Perforating jets act like high-velocity, rapidly expanding rods. Rather than by blasting, burning, drilling or abrasive wearing, penetration is achieved by extremely high impact pressures 3 million psi [20 GPa} on casing and 300,000 psi [2 GPa} on formations. These enormous jet impact pressures cause steel, cement, rock and pore fluids to flow plastically outward. Elastic rebound leaves shock-damaged rock, pulverizedformation grains and debris in the newly created perforation tunnels.

Another technique to reduce debris associated with shaped charge case is to retain as much possible case metal inside the gun body. Either by using special packing arrangement or by using special shape charges cases that do not break up.

Figure 10.2.140:

Patented Packing

Method

To control debris, Schlumberger uses the patented packing method. It causes steel cases to fragment into large pieces that remain in the carrier and decrease the risk of debris exiting the gun. In this method, shaped charges are placed in the closest possible arrangement for a particular gun size and shot density so that they cannot expand. Tight confinement causes cases to break into large pieces that remain in the gun. Small carrier exit holes minimize the amount of debris that can escape. This system has proved extremely useful, when used for sand control, with big-shot-gun tems and is becoming the preferred method.

sys-

Perforating guns carry explosive charges to the borehole where they are detonated creating cylindrical holes in the casing and the cement. This allows oil and gas to flow from the formation into the well. The two critical parts of a perforating 2.6.1

gun are the detonator cord and the detonators.

Detonator cord:

The detonator cord is also referred to as primacord. The detonator cord runs through the length of the gun and provides the ballistic link from the detonator to each of the shaped charges. 2.6.2

Detonator:

A detonator is used to fire a perforating

gun. There are two primary detonator types.

Electrical detonators

Both electrical and percussion detonators contain the primary high explosive Lead Azide except for RF system detonators (SECURE or SAFE) that contain secondary high explosives only that are initiated by high voltage pulses instead of low voltage.

Electrical detonators are also known as blasting caps and are normally used in wirelinedeployed guns. Conventional electrical detonators are susceptible to accidental application power from electric potential differences (EPD), which constitute a safety hazard.

of

Electrical detonators come in two types: Pressure-tight detonators are used in guns exposed to well fluids and pressure, typically through-tubing. Fluid- desensitised detonators are used in carrier guns and are made in such a way that they deactivate if fluid leaks or enters into the gun.

Percussion detonators are normally used with tubing conveyed, coil tubing conveyed and nonelectric wireline systems. Percussion detonators that are used in TCP systems actuate mechanically when a firing pin strikes a pressure-sealed membrane and detonates a primary high explosive. 2.6.3

Safeguards.

There are numerous safeguards implemented in both the electrical and percussion detonation systems. However, these conventional systems may explode accidentally when exposed to electric magnetic fields or other voltages found around the field. The S.A.F.E Slapper-Actuated Firing Equipment system was developed to be immune from the potential differences created by the radio-frequency (RF) radiation, impressed current from corrosion cathodic protection, electric welding, high-tension power lines and induction motors such as topdrives on drilling rigs. S.A.F.E. equipment wireline.

is available for most types of perforating/explosive

assemblies run on

A major advantage of S.A.F.E. equipment tional electrical detonators. Disadvantages

is that wellsite assembly is quicker than for conven-

of the S.A.F.E. detonator are cost and size, which take up lubricator space.

The S.A.F.E system initiates a gun firing without

the use of any primary detonating

material.

The key components of the S.A.F.E. system are the EFI or Exploding Foil Initiator and the ESIC or the electrical secondary explosive initiating cartridge. The ESIC generates a unique signature of high voltage and current and rapidly discharges the pulse. The pulse is necessary to fire the EFI. The Secure detonator is a third-generation S.A.F.E.-type device that also uses an EFI. It does not contain primary high explosives or a down-hole electronic cartridge. A microcircuit performs the same function as the electronic cartridge and EFI together in a package. It is similar in size to a conventional electric detonator. The Secure system has all the technical advantages of S.A.F.E. detonators, bur is more reliable and fully expendable. It is also smaller in size and therefore allows the gun strings to be shorter. Both Secure and SAFE system fire using high voltage and current. There electronic circuits are protected and they do not fire accidentally in case of malfunction. 2.7

HIGH SHOT DENSITY(HSD) GUNS

HSD Guns (through tubing and casing type guns) both Wire line Deployed tubing if required. Note-

the larger sizes would not be wire line deployable as TTP guns.

The HSD guns is a type of carrier gun. They comprise of specific carriers, charges, detonating cords and boosters to provide maximum perforator performance. HSD guns provide increased shot density, optimum phasing patterns and the largest high-performance charges available for natural, stimulated or sand control completions. HSD are the most flexible guns in the field. They are expandable, retrievable carriers and can be tun on any type of conveyance (tubing, completion, slick line, TCP, wire line, coil tubing ... etc). 2.7.1

Features of HSD guns.

(All HSD guns can be used with the S.A.F.E. system.) Expendable carriers:

All HSD guns are expendable, eliminating the need for separate porthole plugs. All carrier sizes are available in 5-, 10- , 20- and 30-ft lengths. Shot density:

Shot densities range up to 27 SPF. Helical shot pattern:

The helical shot pattern available in all gun sizes provides the smallest vertical spacing between the shots and the optimum phasing pattern for productivity and remaining casing strength. Shot spacing can be customized on demand.

Schlumberger HSD guns feature self-aligning detonation transfer modules between guns and spacers for auromatic ballistic connection during makeup.

Borh borrom-up and rop-down firing modes are available: rop-down for TCP, which allows insrallarion of rhe firing head lasr, and borrom-up for wireline applicarions, providing fluid desensirisarion.

For TCP, Schlumberger HSD guns have modified API-rapered drill pipe connecrions incorporaring high-pressure a-ring seals. These connecrions provide fasr, safe verrical makeup on rig floor.

Loaded HSD guns contain only secondary high explosives (deronaring cord, boosrers and charges), allowing safe rransporr and handling when Schlumberger srandard safery procedures are observed. 2.7.2

Quality Assurance:

All HSD gun sysrems are manufacrured Schlumberger.

according ro rigorous qualiry assurance srandards of

HSD perforaring guns incorporare shaped charges, deronaring cord and deronarors. Srandard aperaring Procedures musr be followed when loading or running rhese gun sysrems. Loaded guns should be enclosed in prorecrive rubes during srorage ro prorecr rhe exposed explosives. Three crirical resrs are performed on HSD perforaring guns for reliabiliry resring. These are: Mechanical I Pressure I Temperarure

resr

Perforaring Gun Splir I Swell Tesr Drop Tesr To ensure rhar performance meers specificarions, charges are qualiry control-resred producrion in accual gun carriers. Mechanical/Pressure

during

/ Temperature test:

This resr is designed ro measure the performance of rhe gun in a well during deployment, under well conditions and during retrieval. The rest is performed in pressured vessels up ro 30,000-psi and 600 OF. Perforating Gun Split/ Swell Test:

This test is designed ro prove rhat the gun will survive deronation includes swell measurement with laser inspection.

in liquid and air. The test

Drop Test:

This test is designed ro ensure there is no damage ro the gun either during rransporration or if the gun is accidentally dropped. The test includes dropping rhe gun verrically and horizontally from 1, 2, 3 and 4 fr height. 2.8

EXAMPLE - 2

7/8

IN. HSD PERFORATINGGUN:

The 27 18-in. HSD guns (featuring PowerJet and HTX explosive) are for the slim-hole, 4 1/2_ in. ro 5 1/2-in. casing markets, bur have applications in any completion where downhole resrrictions limit gun size including the through-cubing, dual-completion, monobore and extended-reach markets.

2.8. 1 Natural Completions Natural completions require deep penetrating charges provided by PowerJet premium charges. For horizontal wells there is a low-debris CleanSHOT version of this charge. 2.8.2 Sand Control Sand control requires high shot density and big-hole charges to maximize area open to flow (AOF) and good phasing. To satisfy these conditions the 27/8-in. gun has 6 spf with 60° phasing and 38C CleanPACK charges. Sand prevention requires deep penetrating charges, high shot density and optimum phasing to prevent failure of the sand around the perforation tunnel and minimize perf-to-perf collapse. 2.8.3 Fracture Stimulation Fracture stimulation requires 120°-or 60°-phased guns wi th a large entrance hole or, if the gun can be aligned with the preferred fracture plane (PFP), 180° phasing. The standard 2 7 Is in. gun has a 60° spiral hole pattern and can be loaded with a choice of big-hole or deep-penetrating charges up to 6 spf. Also available is a 180° 4 spf gun. 2.8.4 Special Applications For special applications a low-side 1180°/60° phased gun using 38C CleanPACK charges is available for oriented perforating in highly deviated or horizontal wells. Other phasings and shot densities can be made upon request. Guns can be conveyed using wireline, slickline, tubing or coiled tubing. Multiple guns can be aligned using alignment inter-carriers. The diagrams and charts shown below are typical of the information available from the Perforating Contractors regarding their perforating gun specs and performances .

• .....L2 in.

.--X.-

.-.;-

.--.-

2h

•

34J CS.

34J CS.

PJ 2906 or 38C CP 6 spf. 60· phasing

PJ 2906 or 38C CP 4 spf, 180'

38C CP. 6spf. L180·/60·

Mech3nie" I Data Slml13IY Cltalge

Explosive maxillUll wei,hl (g)

ShOls pet 1001, phasing (0) 511

1011

lOll

30*

PJ2906

15.2,'150 15.2/15.0

6,6C!'

72

127

237

346

2.93/3.03

4.18)'>

372

239 232

3.:0

6.6C!'

119 129 125

221

19.0 155

68 73 71

180 180 3J:
PJ2906 34J CkunSHOT 38C CleanP.ACK

6.6C!'

t ~J,'eighliodude~ int€{(:arra 3~E~;Td (~. t Gun ~h01in 'A'Jter €':<~pt \\f1ere slated. S,,~1l9ighth" l3"!f.f In IItJid~ ·.•.ilh:) d?n~t"llilN-lh3n 'i GUll.~hol in air ~1 roro p~~SUM.

Weig~t

t

(Ill

MaXilllUlll diameter Iin.] Swell' Burl

:x'J

I

298/3.08 ' TeD TeD 3.09131') I

1 g'cr.

API S13tisrics Cllarge

Explosive rype,

S~ots pet

OlaxirlUll

1001.

wei,ht (gl

phasilg

HvpelJ"t 2906 UItl",let 2906

RDX.150 Ht,1:\ 15.0

6, Ell

Po\'!"fJ"t 2906 PoI,,."IJ,,t2906

Ht,1,\ 15.0 Hr;.~ ISO

6. Ell 6. IOU

POI""fJ"t 2906

H1X 195

6.m

34J ClronSH(iT 38C CleanP.ACK

RDX.151 RDX.155

6, t»

Entrance f ~ole Ii•. )

Bun aVetage! lllaxillUlU (il.j

0.38 0.36 0.36 0.32 0.33 0.27 ' 0.62

(OJ

6. Ell

6.m

AJea open tollow Ii•. 'Ill)

Pe.etllllioll (in.)

Targe{ Stretlgl~ Ips i)

Tesl dare

0':6;0.09

f\3

l"I3

15.3 214

34(\1240

0.•:>7/0.09

6>G4 5514

02-00

400/300

0.0510.08

n.1

27.7

40(\1300

6847

0.07/0.11

0051009

n.;

22.6

5001460

20.8

50(\/460

6518 65;:3

09·99

n.1

0')4/0.06 OCe/0.13

f\3

!"'" ,.1

340/240

7&31 58<»

04-97

1.81

8.4

t

Temperature' (OF)

340/240

12-99 (lH9 03-00

12-95

t API Rf\JJ,lhot in ~'/~in., II bib, l-80 ('3irg t tem~rJtur;;. rJlin9~ ,1ft' lor , hour and 100 t,:(JI'S. §1)1))ttiejjAHdaI3

Through tubing guns are used primarily for underbalanced initial or subsequent completions that have the tubing and bottomhole assembly already in place. Optimal underbalance can be applied to achieve clean, productive perforations while maintaining absolure well control. The through-tubing guns are designed as systems comprising of specific carriers, charges, detonating cords and boosters to provide maximum perforating performance Loaded through-tubing guns contain only secondary high explosives (detonating cords, boosters and charges), allowing safe transport and handling when Schlumberger standard safety procedures are being observed. Through-tubing

guns include:

The hollow carrier guns (HSD type). The exposed guns 2.9.1 Hollow Gun Carriers Schlumberger hollow carrier guns include the Scallop gun systems. These guns are fully retrievable and are the most rugged through-tubing guns, capable of withstanding the highest temperatures and pressures. The hollow carrier guns can be run at very high speeds. In these guns debris are confined within the gun, Example: 2

1/8 -

in. Scallop gun, 4spf, 600 phase

The 2 lis-in. Scallop gun is a retrievable 4-spf hollow carrier gun system suitable um-diameter bottomhole assemblies. It is a perforating gun with a recess profile forating gun body adjacent to the shaped charge. The scallop profile reduces the burrs created as the perforating jet exits the gun body, thereby reducing the risk or damage as the gun assembly is retrieved.

for mediin the perexternal of hang-up

HyperDome charges

and UltraJet

60 degree phasing

Scallop recess adjacent to charge

Retrievability Selectivity

Figure 10.2.144:

Hollow Carrier Gun (HSD Type) -

2 l/S - in. Scallop gun, 4spf, 600 phase

2.9.2

Exposed Guns

Schlumberger

exposed guns include Energet, HyperCap strip guns and Pivot guns.

Enerjet gun systems are wireline conveyed, capsule charge-type, perforating guns. In the Enerjet gun systems each shaped charge is encapsulated and loaded on a strip carrier rather than being enclosed in a hollow rube carrier. This permits larger charges for the same overall gun diameter. Also, due to the greater charge size, Enerjet guns outperform hollow carrier guns of the same diameter.

d~'-Q

Figure 10.2.145:

00

Enerjet Guns

Enerjet guns are available in 1.63 in., 1.69 in., 2.12 in. and 2.50-in. diameters and come in a variety of, phasing patterns and shor densities. Standard Enerjet was the first to be introduced two malO types.

in the field. Enerjet guns are now classified, in

With retrievable carriers With expendable carriers The retrievable system is designed for rugged conveyance while running down-hole. It provides shot verification. Any charge that does not fire will be retrieved from the well along with the carrier strip. As the carrier is retrieved there is less debris left in the well. Expendable systems are useful for applications where well components retrieval of the carrier strip difficult after the gun is shot.

or conditions make the

Expendible

Retrievable

API

27.3 in. PEN, 0.25 in. EH (2 liS-in. spiral, 4 spf, 45°, PowerJet)

22.9 in. PEN, 0.29 in. EH (2 liS-in., 6 spf, ±45°)

Temperature, Pressure, Maximum Length.

365°P HMX, 4500P HTX 15,000 psi. 35ft or 20 ft (spiral).

365°P HMX, 4500P HTX· 20,000 psi.

Sizes

I 11/16-in. (US in.), 2 liS-in. (2.25 in.), 2 lI2-in. (2.62 in.)

I 1l/16-in. (17S in), 2 liS-in. (2.25 in)

Shot density

4 or 6 spf, 00±45° (three phase), 45° spiral, 60° spiral

4 or 6 spf, ±45° (two phase)

Charges

DP, BH, HMX, HTX, PowerJet

DP, BH, HMX, HTX, PowerJet

35 ft

Enerjet systems have a long history of high reliability which exceeds any competitor's service rating. One reason for the high reliability of Enerjet is due to the closely controlled manufacturing process of sealing the charges. Each charge is individually checked for seal reliability before it is shipped. There have been virtually zero leaking charges in the past ten years since this comprehensive manufacturing process has been implemented. All Enerjet components are manufactured to strict ISO 9001 standards to insure the highest level of quality. There are certain limitations

of Enerjets:

Hostile environment Acid / H2S / C02 (special operating techniques Temperature

required)

(450°F with HTX, special operating techniques)

Debris (need rat hole for debris) Selectivity (limited to 2 guns with standard or retrievable) Length (recommended

max. 50 ft standard, less with others)

Wireline conveyed (CT conveyed not tecommended). Example: Exposed Guns: 2 1/ a-in. PowerSpiral Retrievable Enerjet

Description: The 21/8-in. PowerSpiral system is a retrievable capsule perforating gun designed for through-tubing wireline operations. The Power Spiral System uses the latest technology to attain optimum performance for maximum well productivity.

Uses PowerJet technology New charge design facilitates faster loading of the detonating

cord

Rugged, low profile strip allows for shot verification and easy retrievability Energy absorbing material virtually disappears after the gun detonates

Shock-absorbing material: A unique Power Spiral feature is the energy absorbing material that is positioned between the charges. This patent pending material reduces charge-tO-charge interference. It significantly reduces the energy of the pressure waves (sometimes called shock waves) in the well bore by absorbing the energy of the explosive detOnations. When an energy absorbing material is not present, primary pressure waves (generated by explosive detOnation) and reflected pressure waves (pressure waves reflected back from the inner surface of the casing) combine ro create regions of higher pressure in the wellbore.

Wire-line-conveyed perforating is an established, well-proven and reliable technique for perforating wells. It is often the most practical way of perforating because guns can be run in and our of the hole easily and quickly on electrical cable. Pre-job planning is the key to the success of a wire-line-perforating job. If the best results are to be achieved, selection and preparation of the perforating system must be based on a thorough understanding of reservoir parameters and the completion objectives. Once the perforating system has been chosen, there are various operational activities that need to be performed at the well-site. These are: Obtaining

a Cased-Hole Reference log

Surface Preparations Perforating

Depth Control

Gun Firing Gun Retrieval and Rig Down 3.1

OBTAINING A CASED-HOLE REFERENCELOG

The depths of intervals to be perforated in a well are usually described by referring to depths shown on an open hole reference log (e.g. 2060m to 2065m on GR log Run 3 dated 6/7 /2002). This is usually a gamma ray (GR) open hole log. The Base log is the log used as the reference for depths in the well. Each log may record formation features at slightly different depths due to their different response and the difficulty of aligning depths. It is therefore important to select one log to which the other logs are depth matched, and which is used as the reference for well-tO-well correlation and mechanical operations such as perforating. The gamma ray is most often used as the base log since it can be recorded in both open and cased holes. Depths on the GR openhole log are normally measured from the original drilling-rig table (or other reference datum).

rotary

Note; The Reference Depth is the point in a well from which depth is measured. Alternatively, the depth reference is the point at which the depth is defined as being zero. It is typically the tOP of the kelly bushing or the level of the rig floor on the rig used to drill the well. The depth measured from that point is the measured depth (MD) for the well. Even when the drilling rig has been removed, all subsequent measurements and operations in the well are still tied in to the same depth reference. However, for multiwell studies, the depths are normally shifted to the permanent datum. The depth reference and its elevation above the permanent datum are recorded on the log heading. After casing has been run and cemented, the standard method of controlling the depth of a perforating gun involves positioning it with reference to casing collars using a casing collar locatOr or CCl tOol. The use of the CCl tool for gun correlation and positioning is more reliable than using gamma ray tOols, which have fragile detectors that are easily damaged by perforating explosions. For accurate correlation, the CCl log is made near the perforated interval. The depth of the casing collars must be measured before the signature of the collars can be used to position the gun. To accomplish this, a cased-hole reference log is run, which is a record of gamma ray and casing collar locatOr tOols run in combination.

The first pass of the cased-hole reference log is usually recorded near the perforating interval, and could be off depth by few meters when compared to the GR open hole log. If for example the first pass log is found to be 3-m shallower in comparison to the open hole log a correction is made by adding 3 m to the odometer (i.e from 2010 m to 2013 m). After correcting the depth, it is important to record a second pass with the GR tool on depth over the whole interval. The tool then is pulled out of the hole, and a hard copy of the second pass becomes the cased-hole reference log. Note: If a cement bond log is available, it will usually include a record of both gamma ray and casing collar locatOrs run in combination. In this case, the cement bond log can be used as the cased-hole reference log. An additional GR-CCl run prior to perforation may not be needed. Once the cased-hole reference log has been made, with the depth of casing collars shown with respect to the GR open hole log, perforating guns can be accutately positioned using only a CCl tOol. 3.2

SURFACE PREPARATIONS

Rigorous planning and preparation are essential before beginning a wire line perforating operation. The following steps must be taken before any perforating gun is armed and run into the well. 1. Safety: All personnel involved in the operation should discuss the safety rules and procedures to be followed, and any potential hazards. If the perforating gun is to be loaded on a rig, additional safety precautions are required. 2. Hot check: This is an operational check of the perforating equipment performed by the engineer to verify the functionality and electrical circuitry of the gun and CCl tool. 3. Measure distance from CCl measure point to tOp shot: The distance from the CCl measure point to the top shot of each gun is measured and noted on the perforation worksheet for use during gun positioning. The distance is measured using a tape and noted. Several guns may be either run together and shot selectively in one descent, or run in multiple descents. When several guns are being run, each CCl-to-top-shot distance and gun length must be physically measured and noted. 4. Gun arming: Before arming the gun, the area must be safe for working with explosives. To ensure this, a series of precautionary measures needs to be performed. Gun arming is performed in two steps: a) Connect the detonatOr electric wires to the gun wires. The detOnator is a sensitive device that contains primary, high explosives and is, therefore, secured inside a safety loading rube while making the connection. b) Remove the detonator from the rube and crimp it to the detonator cord before the gun is sealed up and run into the well. 5. Zero the CCl measure point After rigging up the gun string the depth of the CCl measure point is set on the logging computer. If for example, the permanent darum is the old rig floor level located 5 m above the wellhead the engineer sets the computer depth to 0005 m with the CCl measure point at the wellhead.

The perforation-depth control log now shows the correct depth in relation to the GR open hole log datum. However, while running in hole it is very likely that some depth shift will occur. The correct depth of the CCl tool must be carefully checked and corrected once the perforating gun has reached the required depth before the guns are fired. 6. Run in hole: Mter verifying all the pressure control procedures, the gun is run into the well.

After the gun zero is set, run into the hole to below the perforation depth, taking certain precauoons. Once the perforation depth is reached, a correlation pass is logged coming up the well at a speed equal or close to the open hole reference logging. This pass must cover a sufficient interval to allow unambiguous correlation; in any case it must cover a minimum of six casing collars. If for example, the casing collars are shown 3-m deeper in the first correlation pass in comparison to the cased-hole reference log 3 m must be subtracted from the odometer (i.e it is changed from 1990 m to 1987 m) The engineer must correct the depth of the casing collars on the CCl log to within ±0.1 m of the cased-hole reference log. In addition, the depth of any distinctive features, such as short joints of casing or a cementing collar near the perforating interval, must be logged and checked. The CCl log is tied into the cased-hole reference log when the casing collars recorded on both logs are shown at the same depth. Once this has been achieved, a further correlation pass is made to confirm accurate tie in of the CCl log. A hard copy is made before continuing. This is called the perforating-depth control log, the tie-in CCl or the before-shooting correlation log. The hard copy of the perforating-depth control log is then used to check accurate correlation by comparing it with the hard copy of the cased-hole reference log. All casing collars should match depth within ±0.1 m. The engineer must also confirm that the perforating-depth control log is not off depth by the length of one or more whole collars. Unless all the casing joints are exactly of the same length, the technique of sliding the log one joint up and one joint down will quickly show whether the log is on depth. The presence of a shorr or long casing joint makes confirmation of the correlation easier. If any doubts exist in the correlation procedure DO NOT SHOOT until they are resolved. Remember that rectifying an incorrectly located perforation almost certainly involves rig intervention and is both time consuming and costly.

After ensuring guns proper positioning, val to be perforated.

run down three or four casing collars below the inter-

Preparations should now be made at surface to establish the required conditions for perforating. This may involve bleeding off pressure at surface or producing the well if perforations already exist. Note that any changes in well pressure or flowing conditions after tying in the perforating-depth control log may cause movement of the gun that will put the gun off depth. In this case, the log must be tied in again before perforating.

The depth of the CCl measure point with the guns at the required shooting depth should be checked again. This calculation must take into account the distance from the CCl to the tOp shot of the loaded gun section to be fired, measured at surface and noted in the perforating worksheet. After the company representative witnessing the operation has confirmed the calculation, the CCl is pulled up to the agreed depth. While coming up, ensure that casing collars remain on depth, and cable tension does not vary and stop the winch with the gun at the shooting depth. Once the witness confirms that shooting can proceed, the engineer sends the electric current to fire the gun. During and after firing, the engineer observes and notes changes, including cable tension, surface pressure and gun string weight. After a positive indication that the gun has fired, the engineer records the depth with the software by pressing the 'ENTER' key. For example, a pressure increase a shock felt at the wellhead indicates a successful detonation. Following this, the shifts one of the CCl curves to graphically show the depth of the CCl when the fired.

of the shot at surface or software gun was

The fired gun is picked up slowly while the cable tension is observed. The engineer should continue recording the log for three more collars. Note that the collars may appear slightly off depth due to the variation in gun weight after firing. While shooting multiple intervals, it is a common practice to perforate the lowest zone first, and work upwards to avoid exposure of the tool to gun debris. 3.5

GUN RETRIEVALAND RIG DOWN

The clearance between the gun and the casing or tubing, the size of restrictions in the well and the type of completion fluid all determine how fast the gun should be pulled from the well. Once the gun is at surface, all pressure-control procedures must be followed. The gun is treated as potentially unfired until the detonation of all the charges has been verified by inspection. All safety rules for running the gun into the well must therefore be observed when retrieving the fired gun from the well. Once the gun is out of the well, the engineer checks carefully that there is no high-pressure fluid trapped within the gun and that all of the charges have been fired. Trapped pressure should then be relieved before rigging down the gun. In the event of a misfire, the engineer must immediately disarm the gun using the proper disarming procedure described in the relevant operations manuals

Perforating is a critical part of any well completion process. Perforating is the only way to establish conductive tunnels that link oil and gas reservoirs to steel-cased well bores, which lead to surface. However, perforating also damages formation permeability around perforation tunnels. This damage and perforation parameters like formation penetration, hole size, number of shots and the angle between holes-have a significant impact on pressure drop near a well and, therefore, on production. Optimising the perforation parameters and mitigating induced damage are the vital aspects of perforating. Ongoing research confirms that under-balance perforating, where well bore pressure before perforating is less than the formation pressure is essential in removing damage and debris from perforations.

Optimising the perforation process is critical in order to maximise well productivity. To accomplish this, underbalance perforating is employed to remove crushed rock produced by perforating. Removing guns either by pulling them our of the well or by disconnecting them and dropping them to the bottom without killing the well is equally important since kill fluids often damage the formation. To achieve these aims several methods can be used. These are:

FlV WPAT CDAD Gun Stack 4.1.1

CIRP - Completion Insertion and Retrieval under pressure system.

Gate valves

I Deployment stack ~ Guide ram with rack_ No-go ram with lock /

Lock actuator ~CIRP

connector

If the gun length exceeds the length of the lubricator assembly and it is desired to run and pull the guns with the well still under pressure, then there are only few options. Shoot only the first run underbalanced Kill the well after perforating: the well productivity Drill additional

sump: Drilling

This operation risks damaging

the formation and limiting

extra holes is always an added cost

The CIRP system allows high shot density guns to be run into or our of a well, which is under pressure. With the introduction of the CIRP system, guns can be made into sections .. The CIRP

system showing WHE and the CIRP connector process.

4.1.2 X-Tools There are two types of gun release mechanisms. Mechanical release system offered by Schlumberger includes:

&

Automatic.

The automatic

gun

MXAR - Gun anchor

Upper Gun Adapter

Break Plug Assembly

1

Air Chamber __ Cushion

1-

Release Fingers

Lower Gun -Adapter

r.:7----GlJ" Figure 10.2.148:

adapter

MXAR, SXAR andWXAR

Schlumberger has developed a special perforating Monobore anchor explosive release referred to as gun anchor. The guns can be run into the well by either wire line or pipe and anchored into place using slips. The slips grip the inner wall of the liner or casing to prevent movement of the guns. Once anchored the guns are left behind in the well by the conveyance system. The cans can be fired using either the HDF or TCF style firing heads.

When detonation occurs, the detonating cord through the MAXR assembly shudders break plug. Once the break plug has disintegrated, the piston moves down due to the differential pressure. Note that the chamber around the break plug is at the atmospheric pressure. The movement of the piston shields the release pins and the slips are free to retraer. Once the slips disengage, the guns drop to the bottom leaving the pipe clear of any restrictions. By using the MAXR system, the benefits of Tubing Conveyed perforating be realised.

and Monobore can

The SXAR and the WXAR operate in a similar fashion to MXAR. Both allow guns to be dropped at the instance of detonation. Upon firing the break up element shedders allowing release fingers to collapse inwards to drop the guns. The SXAR disconnection leaves the wire line entry guide at the bottom of the tubing. WXAR is like an upside down SXAR. Most of the mechanism allows long run strings to be run on wire line.

is recovered. The WXAR

Perforation occurs under balanced and a small seer ion of gun is retrieved. This seer ion fits in the surface lubricator, so that the well does not kill to retrieve the guns. 4.1.3

Formation Isolation Valve (FIV)

The Formation Isolation Valve (FlV) is a mono-bore completion valve normally run below a permanent completion packer. The tool aers as a down hole lubricator valve, allowing long strings of guns to be run into and retrieved from the well isolating the perforated zone.

ii--- Knuckle joint

TUbing conveyed perforating (TCP) Guns

Long strings of guns can be perforated under-balanced prior to production. Snubbing

without having to kill the well

is not required once guns are pulled above the FlV and the valve is closed.

Tubing pressure reopen feature eliminates one intervention tIme.

trip thus reducing operation

Eliminates the need to apply kill fluids and lost circulation material across the perforated interval to retrieve the guns after perforating. The FlV is multi-cycle

and can be opened and closed as often as desired.

The ball valve is locked in the open position during production profile.

and has a smooth bore lD

The valve holds pressure from both directions to control the well and protect the formatIOn.

4.1.4 WPAT - Wireline Perforating Anchor Tool The Wire line Perforating Anchor Tool (WPAT) is designed for perforating wells with wire line under very high under balance. This method of anchoring wireline-conveyed guns is a practical, reliable and economical method of completing Monobore wells. The WPAT positively anchors guns from below using three circumferentially distributed slips. The slips are anchored in the casing prior to firing the gun via an electrical command from the surface. The profile of the slips is carefully crafted to prevent movement. After a pre-programmed time interval, which can extend up to one hour the slips are auromatically released and retracted. By removing the risk of gun movement during perforating, this tool makes perforating with very high under balance possible. Higher under balance improves the perforation cleanup resulting in higher well productivity 4.1.5

Electrica Initiation Section

Hydraulil Section

CDAD Gun Stack System

Features of the Gun Stack System include: Downhole assembly / disassembly of long gun strings Positive latch mechanism

to prevent guns being blown up hole

Mechanical latch allows disconnect even if guns have not shot Automatic time delay disconnect after the shot to prevent guns being blown up the hole Conveyed on slick line, E-line or CT Optional attachments

for auto-drop with MAXR

Slip Section

Perforating is the only way CO establish conductive tunnels that link oil and gas reservoirs co steel-cased wellbores, which lead co the surface. However, perforating also damages formation permeability around perforation tunnels. When flow is sufficiently high and there are unconsolidated or loose formation grains in and around the perforations, sand may be produced with oil, gas and water. Sand produced depends on formation strength,

formation stresses, flow rate and fluid type.

In addition, changes in flow rate related co pressure drawdown, increasing effective stress due co depletion and increasing water production with time are the main factors in sand production.

A microannulus formation.

is caused by the weakening of the hydraulic bond between cement and the

A microannulus

often gets created after:

Cementing Casing pressure-integrity

testing

Drilling Establishing

an underbalance

After perforating

and pumping

operations

A microannulus should be avoided because of the accompanying pressure and associated pinch points. 4.3. 1 Factors to be considered if Micro-annulus

flow restrictions,

increased

is present

If a micro-annulus is present or might be induced by perforating, various faccors need co be considered. To minimize pinch points and reduce flow-path cortuosity, Wells with inclinations less than 30° should be perforated with 180°-phased oriented within 10° of the preferred fracture plane (PFP).

carrier guns

When well inclination is greater than 30° and a well bore lies in or near the PFP, the recommendation is co use guns with 180° phasing oriented to shoot up and down. If PFP direction is not known or orientation mended.

is not possible, 60 or 120° phasing is recom-

Mi nimum hari zontal stress (S.)

•

Borehole CefT)3n1

CasiflJ Charg3s at 9'r phasing

Maximum horizontal ••. str ••ss (S,J f"eferred fracllIe planelPfP

Minimum horizontal stress (S,)

•

Unstat:le. ineffocti.e ~rforations

Maximum

•••••••••..

horizontal ..,..... stress (S,J

Unstable. inelfecti'i'9

pertoJ3ticns

Figure 10.2.151:

4.4

Factors to be considered if Micro -annulus is present

WIRELINE ORIENTED PERFORATING TOOL (WOPT)

The Wireline Oriented Perforating Tool (WoPT) is used to orient perforating guns conveyed on wireline in SO increments. Two runs are required to complete the operation. The first with a gyro to find the natural lie of the string in the well The second without the gyro to perforate

During the gyro run, deviation and relative bearing are recorded with the WPIT (Wireline Perforating Inclinometer Tool). The gyro finds the azimurh, so that at the surface the guns can be indexed around to poine in the desired perforating direction. On the second run, the gyro is removed from the string, as it would be damaged by perforation shock. The WPIT inclinometer remains in the string and is used to confirm position repeatability prior to shooting. Several other methods are also available to orient TCP guns. As well bores turn away from the PFP, perforated ineervals should be decreased, and 60° rather than 180° phasing should be more effective.

Initial GVroscope Run Relative Jearing, 0° Wireline swivel

Charges 'Nireline Perforatirg Inclinometer Tool (\'\ifll T) and casi ngcollar locator (CeL)

HSDgun

-Gyroscope carner UppenveightEd spring-positionirg devire (WSPD) Per10rating Run

Upp:r indexirg adapter

Relative Jearing, 0° -HSDHigh Srot Density gun, 180° phasing LO'N-erindexing adapter

Lov.rerweighta:! spring -positioning

device [\tVSPD)

HSD gun Casing

Runs on wireline (electric line) Used on wells with deviations greater than 20 Repeatability

is +-30

Indexing is provided at 50 increments Minimizes fracture pressure and eliminates multiple competing - phased guns within +- 100 of preferred fracture plane Minimize sand production direction Orient perforations

by aligning perforations

fractures by aligning

on either side of maximum

1800

stress

away from known mechanical obstacles.

Preferred phasing angles for available gun systems 0° for 180° HSD Guns 1.56-, 2-, 2.25-, 2 1/2-, 2 7/8, 3 3/8-,4

l/2-in.

HSD guns at 4 spf

± 10° for 2 7/8-in. HSD Gun at 6 spf Qualified with PowerJet charges ±14° 2 7/8-in. HSD Gun used at 4 spfwith ±25° for

UltraJet charges

3 3/8-in. HSD Gun at 4 spf

Qualified with UltraJet charges ± 10° for

3 3/8-in. HSD Gun at 5 spf

Qualified with PowerJet charges 20°, 160°, 200°, 340° for 4 l/2-in. Qualified with PowerJet 4.5

&

HSD Gun at 12 spf

UltraJet charges.

OTHER METHODS FOR ORIENTING Tep GUNS (FOR INTEREST).

Other methods for orienting TCP guns include: Orienting

by gravity

Orienting

by using Gyro Positioning

String

Orientation by gravity uses eccentering weighted spacers, ballistic swivels and tubing swivels. In this method, a directional survey is essential. In Gyro Positioning String, guns are positioned at a depth; gyro is seated in landing shoe, string is rotated to a desired direction, gyro removed and then the guns are fired.

In the past, theories and software were available to analyze perforation performance, bur completion decisions were often based on average formation properties or perforating limitations unrelated to productivity. Today, thinking in terms of what IS best for a reservoir is the predominant approach. Operators consider what a particular field development requires and then select the best completion techniques and hardware that are available.

Standard "off-the-shelf' equipment and services sometimes do not meet those needs. New tOols, procedures and services-shaped charges, completion equipment, conveyance alternatives and applications for under balance, overbalance or extreme overbalance-often need to be developed. The best perforation designs are based on specific well requirements to optimize production. This tOtal-systems approach-smart perforating- emphasizes on practices that maximize well productivity and help in overcoming dilemmas associated with perforated well completions. FactOrs that need to be taken into account for increasing well productivity

include:

Formation compressive strength and stress Reservoir pressure and temperature Zone thickness and lithology Porosity Permeability Anisotropy Damage Fluid type-gas or oil. Hard-high-strength-formations and reservoirs damaged by drilling fluids benefit the most from deep-penetrating perforations that extend beyond the formation damage and increase the effective well bore radius. Low-permeability reservoirs that need hydraulic-fracture spaced and oriented perforations.

stimulation

require appropriately

Unconsolidated formations that may produce sand need big holes, which reduce pressure drop and can be packed with gravel to keep the formation particles out of the perforation and the wellbore. Perforations can also be designed to prevent tunnel and formation failure associated with sand production.

Perforating is an integral part of sand control in cased hoes, fro frac-packing, gravel packing and screen-less completions. Proper design of the perforating process including gun type and stand-off, shot density and required under balance is critical to achieving a productive sand control completion. Perforated completions software Schlumberger

can be designed using the SPAN Schlumberger

Perforating

Analysis

Perforating Analysis Program (SPAN) consists of three modules:

Penetration - This module calculates the shot penetration based on the SPAN penetration database.

and entry hole diameter

Productivity - The efficiency of the completion is expressed as a Productivity Ratio (PR). It compares the expected production from the perforated completion, modified for the effects of damage, partial penetration, and well deviation, to the ideal openhole production under steady flow.

Underbalance - This module calculates the minimum under balance necessary for zero skin perforations based on the algorithms currently accepted as the best formulations for under balance criteria. SPAN software helps select gun systems based on: Specific well parameters Completion

geometry

U nderbalance

D Perforator cllaraeteristics GunichaflJil ~(pe: 4~~HSD n, 5 P,145(6 HMX Gun position: Positi oned Shot phasing: n dilgrees Gun rotatico offset 0 degrees

.03lllaglfdzone DCG<ment

P"rforation char aete ri&ics 144 Orientation (deg]: 0 72 29.694 Total penetration (in I: 2:3.24 30.888 28.48 Formation Penetration Jin): 28.037 2~.1)58 Entrance hole diameter, 1& csg tin): 0.44196 0.40014 0.33461

Job 10: File: O:\OOCUMENTS\SPANDATA\E,XAMPlf.SP"'IV

Figure 10.2.153:

Forn13tion

216

29.594 28.48 0.384'51

288 30.888

29.658 0.40014

SPAN Version 6.0 ®Cop'{rightI999 Schlumberger

SPAN Software

The SPAN program allows completion engineers to compare the impact different types of perforating guns will have on production prior to execuring the job.