Perforation in oil and gas wells

2

• Since the pay zone is sealed off by the production casing and cement, perforations must be made in order for oil or gas to flow into the wellbore.

• Perforating incorporates shaped-charge explosives which creating a jet of high-pressure, high-velocity gas.

• It can be overbalance or underbalance perforation, and wireline conveyed perforation (WCP) or tubing conveyed perforation (TCP).

PERFORATION

4

• Perforating gun (WCP type) is lowered into the hole at the depth where the oil or gas formation is found (A).

• After the gun is lined up properly, powerful explosive charges are fired (B) from the control panel at the surface. These explosives blast a hole in the steel casing and cement, up to several feet out into the rock.

• Finally, the oil and gas fluids flow into the holes and up the well to the surface (C).

Perforating History

•Mechanical, prior to 1932

•Bullet Gun, 1932 to present

•Hydraulic, 1958 to present

- Abrasive jetting

•Shaped Charge, 1946 to present- Most popular

Types of Perforators

• Bullet Perforators

• Hydraulic Perforators

• Mechanical Perforators

• Jet Perforators

• Perforation using laser technology

BULLET GUN PERFORATOR

GUN GUN

CEMENT

CASING

INWARD BULGING JUST

ABOVE AND BELOW

PERFORATION

(A)

SOFT ROCK

(B)

HARD ROCK

Bullet guns were the technique of choice until the jet (shaped

charge) perforator was developed in the 1950’s. Most bullet

guns were manufactured 3 1/4 inch outside diameter or larger

and were effective in penetrating materials with 600 psi

compressive strength and lower.

Bullet Perforation

• 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

(A) - HYDRAULIC (B) - MECHANICAL

Hydraulic: Sand laden

fluid is pumped

through a tubing

installed jet and holes

are horizontally cut

out of the formation

Mechanical Perforator:Mechanical perforators are circular cutters which

have been devised to cut through the casing into

the target material. The application of mechanical

cutters has been limited to the initiation of

horizontal fractures or other specific operations.

Wireline

Casing

Gun

Through-

Tubing Gun

Tubing-

Conveyed Gun

Perforating

Techniques

• Wireline

conveyed

perforating (WCP)- Wireline casing

perforating

- Thru Tubing

perforating (TTP)

• Tubing conveyed

perforating (TCP)

Perforating Techniques

Tubing-

Conveyed

Gun

Wireline

Casing Gun Through-

Tubing

Gun

Perforating Guns

• A device used to perforate oil and gas wells in preparation for production.

• It has different shapes of explosive charges.

• Different range of sizes and configurations.

• The diameter of the gun used is determined by the presence of wellbore restrictions or limitations imposed by the surface equipment.

WIRELINE

CASING

GUN

• Create holes in a casing string.

• Casing guns are typically 3 to 5-in. in diameter and carry up to four perforating charges per foot (shot per foot (spf))

• Allow perforation through production casing using larger diameter gun assembly.

Wireline Casing gun

Gun Classifications based on:

Retrievable

vs

Expendable & Semi-

Expendable Guns

• It is retrievable from the wellbore after firing.

• It generates minimal debris

• Minimum distortion of the gun body to help ensure easy retrieval.

Retrievable gun

THRU’ TUBING GUN• Expendable gun: A perforating gun

assembly that disintegrates upon firing, thereby reducing the volume and dimensions of retrieved components.

• Expendable guns are typically used

where wellbore restrictions allow only limited access, as in through-tubingapplications. The distortion caused to the gun assembly during firing would typically prevent recovery of a conventional gun design through the limited clearances.

• The expendable gun assembly breaks

into small pieces that drop to the bottom of

the well (?) , leaving only a relatively small

subassembly that is easily recovered to surface.

SUMP

Expendable gun

SEE

DETAILED

SECTION

PRODUCING

INTERVAL

WELL

REMOTE

CONTROLLED

WELL HEAD

GOOSENECK - 5ft

RADIUS

SEA SURFACE

FLOATING GATHERING

PLATFORM

TWO FLOW LINES

(UP T0 7000 - 8000 ft

IN GULF COAST)

SEA FLOOR

PRODUCTION

TUBING

BATTERY CARRIER

PACKER

"NO-GO" NIPPLE

CONTROL HEADS

7" CASING

GUN POSITIONER

PRODUCING INTERVAL

GUN

CIRCULATING PORT

CIRCULATING STRING

DETAILED SECTION

Semi and fully expendable guns are run through tubing due

their flexibility.

Retrievable

vs

Expendable ?

Casing gun?

Through-tubing

gun?

Tubing conveyed

perforating (TCP)?

TUBING CONVEYED PERFORATING (TCP)

The use of tubing, drillpipe or coiled tubingto convey perforating guns to the required depth.

TUBING CONVEYED PERFORATING (TCP)

28 Oct 05 32

Setting the packer

Packer

28 Oct 05 33

TCP Run

Sump Packer

A gravel pack looks something like this.

Top packer

Bottom packer

Liner

& Screens

Seal bore

Assuming we have 2 gravel packs in the well. It will look something like this

Top packer

Bottom packer

Screens

Seal bore

Top packer

Bottom packer

Liner &Screens

Seal bore

If we want to produce through the bottom zone, we will close the sliding side door so that hydrocarbons from the top zone does not enter the production string

Seal bore

Hydraulic packer

Sliding side door

Seals Assembly

No Go Nipple

Bullet Perforators

Hydraulic Perforators

Mechanical Perforators

Laser

Jet Perforators

(A) - HYDRAULIC (B) - MECHANICAL

GUN GUN

CEMENT

CASING

INWARD BULGING JUST

ABOVE AND BELOW

PERFORATION

(A)

SOFT ROCK

(B)

HARD ROCK

Perforating with Laser

• Conventional explosive charge perforation method reduces the rock permeability

• Laser perforation increase the rock permeability, hence, increase the oil or gas production rate of a well.

Perforating with Laser

Perforating with Laser

Jet Perforation

• It uses a shaped charges contained in a perforating gun assembly.

• Gun assembly is placed in wireline, tubing or coiled tubing, depending on the application and the wellbore conditions.

• High-pressure jet will penetrates the casing or liner to shoot into the reservoir formation to form channels.

43

47

High shot density

perforating gun

(TCP type)

Jet Perforation: Shaped Charge

MAIN EXPLOSIVE

CHARGE

PRIMER CHARGE

CASE or CONTAINER

LINER

DETONATION CORD

GROOVE - POINT OF

INITIATION

PORT PLUG

AIR CUSHION STEEL CARRIER ELECTRONIC DETONATOR

MAIN CHARGE PRIMER

SHAPED CHARGE

ASSEMBLYDETONATING CHORD

Jet Perforation

Shaped Charge Perforator ---Why Conical Liner ?

Cavity Effect

Jet Perforating Process

•High velocity -7,000 m/sec

•High Pressure -millions psi

•High speed -microseconds

•Particulated jet does the work

SHAPED CHARGE

SLUG

JET

V1

1"16

0.5"P1

PRESSURE ON TARGET P1 = 5 x 106 PSI

VELOCITY OF FORWARD JET V1 = 20,000 FT/SEC

Wireline

Casing

Gun

Through-

Tubing

Gun

Tubing-Conveyed

Gun

Perforating

Techniques

Gun System Design – Charge positioning

PARAMETERS AFFECTING SHAPED CHARGE PERFORMANCE

a d

a

b

PENETRATIONSTANDOFF

ENTRY

HOLE

TARGET

SHAPED CHARGE

p

DV

t

LC

c

VOLUME

Industry Testing of Perforating Systems

1000 PSI

CORE PRESSURE

1200 PSI

CORE PRESSURE

(KEROSENE FLOW)

CEMENT

BEREA SANDSTONESTAINLESS STEEL

CANISTER

DP = 500 PSI

DP = 200 PSI

SALT WATER

ESTABLISH:

1500-PSI WELL

PRESSURE

(9.6 PPG SALT WATER)

PERFORATE & INFILTER:

1500-PSI WELL PRESSURE

BACKFLOW TO STABILIZATION:

1000-PSI WELL PRESSURE

KEROSENE VISCOSITY mo

Lo

DPo

AREA , Ao

Qo

HASSLER UNITBEREA CORE

QP

DP = 200 PSI

CORE OF CROSS SECTIONAL AREA

"A" MOUNTED IN CANNISTER,

PERFORATED AND KEROSENE

FLOWED, VISCOSITY mPi

P

oi

oP

Po

PPPP

oo

oooo

k

k

kk

kkCFE

PA

LQk

PA

LQk

==

D

m=

D

m=

DETERMINE ORIGINAL ko:

CALCULATE PERFORATION

kP FROM TEST:

CALCULATE CORE FLOW

EFFICIENCY:

ki/k

o REPRESENTS THE RATIO OF THE EFFECTIVE

PERMEABILITY OF A TARGET CONTAINING AN IDEAL

(DRILLED) PERFORATION (OF THE SAME DEPTH &

DIAMETER AS THE PERFORATED ONE) TO THE ORIGINAL

TARGET PERMEABILITY ko

Industry Testing of Perforating Systems

• Major effects

– Gun clearance

– Casing and formation strength

– Effective formation stress

– Wellbore Fluid

– Temperature (selection of explosive)

Downhole Parameters That Affect Performance

Factors Affecting Performance –Gun Clearance

Typical Perforation Geometry

Shot Per Foot

(4spf) , (8 spf)

Problem with Perforation

• The main problem is the plugging after Perforation, these caused by:–Charge liner residue slugs

–Mud solids & crushed/compacted rock particles

• Solution to the problem: Cleanout of Plugged Perforations, these include:–Back surge perforations if consolidated

formations

–Use ‘wash tools’ if unconsolidated formations

–Breakdown with fluid or acid, and ball sealers

Factors Affecting Gun Perforating Results – Perforation

Plugging

Plugged Perforations Cleanout

Factors Affecting Performance ––Formation Compressive Strength

Gun Clearance

VARIABLE

CLEARANCE

1 11/16"

GUN

1 11/16"

GUN

CONTROLLED

CLEARANCE

7" DIAMETER CASING

MULTI DIRECTIONAL POSITIONED

Gun Clearance

Wireline

casing

gun

Through-

tubing gun

Tubing-conveyed

gun

Gun Clearance?

CONCLUSIONS

• Different perforation guns have specific application. Examples: casing gun, retrievable gun, high-shot density gun, & expendable gun.

• Methods of perforation, these include: Bullet, Jet, hydraulic, & laser.

• Problems from perforating operations should be overcome.

THANK YOU