Underbalanced Perforating

Underbalanced Perforating Early tests by Exxon showed that flow

patterns and perforation geometry prevent the cleaning out of an appreciable percentage of mud-or silt-plugged perforations by simple production from a well

Published studies of the flow rate necessary to remove damage observed that serious perforation plugging occurred whenever the pressure was higher in the wellbore than in the formation

Early tests by Exxon showed that flow patterns and perforation geometry prevent the cleaning out of an appreciable percentage of mud-or silt-plugged perforations by simple production from a well

Published studies of the flow rate necessary to remove damage observed that serious perforation plugging occurred whenever the pressure was higher in the wellbore than in the formation

Underbalanced Perforating

Plugs that formed when perforating in heavy mud were almost impossible to remove by reversing pressure.

"Permanent plugging of a high percentage of perforations may result from killing a well with mud or dirty fluid during well completion, servicing, or workover."

"When perforating in mud with a pressure differential into the formation, perforations are filled with mud solids, charge debris, and formation particles." Not easily removed.

Plugs that formed when perforating in heavy mud were almost impossible to remove by reversing pressure.

"Permanent plugging of a high percentage of perforations may result from killing a well with mud or dirty fluid during well completion, servicing, or workover."

"When perforating in mud with a pressure differential into the formation, perforations are filled with mud solids, charge debris, and formation particles." Not easily removed.

Underbalanced Perforating

Differential pressure required to initiate flow through each plugged perforation, varies.

When a few perforations requiring low differential pressures open up, flow into these perforations makes it difficult to create the higher pressure drawdown needed to open additional perforations.

“Crushed and compacted rock around the perforation has essentially zero permeability and further reduces the probability of perforation cleanout.”

Differential pressure required to initiate flow through each plugged perforation, varies.

When a few perforations requiring low differential pressures open up, flow into these perforations makes it difficult to create the higher pressure drawdown needed to open additional perforations.

“Crushed and compacted rock around the perforation has essentially zero permeability and further reduces the probability of perforation cleanout.”

Underbalanced Perforating

The post-shot flow into the wellbore (a function of the formation-wellbore pressure differential, the formation fluid viscosity and the formation permeability) helps remove the crushed formation from the perforation and provides improved flow channels.

High post-shot formation to wellbore flow generally provides optimum perforation cleanup and minimum skin.

The post-shot flow into the wellbore (a function of the formation-wellbore pressure differential, the formation fluid viscosity and the formation permeability) helps remove the crushed formation from the perforation and provides improved flow channels.

High post-shot formation to wellbore flow generally provides optimum perforation cleanup and minimum skin.

Underbalanced Perforating

Underbalance perforating followed by flow has been shown to be the best method for cleaning perforations and establishing high flow capacity from natural completions in moderate to high permeability core

Even when compared to surging and washing, underbalance perforating followed by flow can be superior

Underbalance perforating followed by flow has been shown to be the best method for cleaning perforations and establishing high flow capacity from natural completions in moderate to high permeability core

Even when compared to surging and washing, underbalance perforating followed by flow can be superior

The Level of Underbalance

Must balance perforation cleanup and well performance potential enhancement against the downside aspects of mechanical problems such as perforators or wireline sticking in the wellbore, near-wellbore rock formation disintegration, downhole tubulars and equipment damage, etc.

Must balance perforation cleanup and well performance potential enhancement against the downside aspects of mechanical problems such as perforators or wireline sticking in the wellbore, near-wellbore rock formation disintegration, downhole tubulars and equipment damage, etc.

The Level of Underbalance

The pressure differentials necessary to achieve the flow rates required to remove perforation and/formation-skin damage are affected by:

Formation pressure

Reservoir permeability

Perhaps limited by formation integrity

Usually range from approximately 500 psi to over 5000 psi

Have been established by trial and error in many fields

The pressure differentials necessary to achieve the flow rates required to remove perforation and/formation-skin damage are affected by:

Formation pressure

Reservoir permeability

Perhaps limited by formation integrity

Usually range from approximately 500 psi to over 5000 psi

Have been established by trial and error in many fields

Implementation

Downhole and surface mechanical equipment to achieve desired underbalance and maintain the integrity of the well

Control the well during deployment, perforating and retrieval,

Deploying the perforating device(s) to the proper downhole position,

Activating the perforating mechanisms, Monitoring the downhole perforating process, Retrieving the perforating system

Downhole and surface mechanical equipment to achieve desired underbalance and maintain the integrity of the well

Control the well during deployment, perforating and retrieval,

Deploying the perforating device(s) to the proper downhole position,

Activating the perforating mechanisms, Monitoring the downhole perforating process, Retrieving the perforating system

Precautions!

It is more costly to employ than conventional perforating.

Safety and well control is a primary issue. It requires the appropriate combination of

reservoir pressure, reservoir fluid properties and formation permeability to achieve the required underbalance for effective application.

Prospects must be thoroughly screened, and there are those that may not be, or are not, appropriate candidates.

It is more costly to employ than conventional perforating.

Safety and well control is a primary issue. It requires the appropriate combination of

reservoir pressure, reservoir fluid properties and formation permeability to achieve the required underbalance for effective application.

Prospects must be thoroughly screened, and there are those that may not be, or are not, appropriate candidates.

Jet PerforatingFormation Properties

Compressive strength, effective stress and specific rock characteristics can have significant impact

In unstressed rock, penetration decreases with increasing compressive strength

Pore fluid compressibility affects performance. Increasing liquid saturation improves

penetration Stress reduces penetration (other factors

being kept constant)

Compressive strength, effective stress and specific rock characteristics can have significant impact

In unstressed rock, penetration decreases with increasing compressive strength

Pore fluid compressibility affects performance. Increasing liquid saturation improves

penetration Stress reduces penetration (other factors

being kept constant)

Jet PerforatingFormation Properties

Effective Stress (ksi)

Pen

etr

ati

on

M

ult

iplie

r

Design

Perforator Type, Charge Strength and Gun Clearance

Conveyance Logistics, Surface and Downhole Equipment/Apparatus

Existing Wellbore Tubular/Cement-Sheath Limitations

Perforator Type, Charge Strength and Gun Clearance

Conveyance Logistics, Surface and Downhole Equipment/Apparatus

Existing Wellbore Tubular/Cement-Sheath Limitations

Design

Formation Mechanical Rock Properties and Characteristics

Reservoir Pressure and Fluid Flow Characteristics

Perforating Downhole Environment Conditions/Limitations

Formation Mechanical Rock Properties and Characteristics

Reservoir Pressure and Fluid Flow Characteristics

Perforating Downhole Environment Conditions/Limitations

Design (King’s Method)

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 500 1000 1500 2000 2500 3000 3500

Underbalance Pressure (psi)

Perf

ora

ting S

kin (

dim

ensi

onle

ss)

Gold SandstoneBerea Sandstone

Hsia and BehrmannHsia and Behrmann

1.0E-01

1.0E+00

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01

Reynolds' Number (dimensionless)

Fric

tion F

act

or

(dim

ensi

onle

ss)

Laminar FlowDarcy's Law ValidDrag Not Enough

for Cleanup

Non-linear Laminar FlowDarcy's Law Invalid

Drag Enough for Cleanup

Turbulent Flow

TariqTariq

Cleanup Criterion Based on Reynolds Number

perfc

2c

2o

7

perf

cc

cperfi r

1r1

rv10244.1rr

lnrkv

94815pp

vk1031735.1N 12

Re

cperfcRe

perf

c

o2

c

cRe216

r1

r1

rNrr

lnk

rN101974.7p

Design

Of the factors influencing the determination of correct underbalance

for cleanup the fluid properties, especially viscosity, are important but

the key factor is the formation permeability

Of the factors influencing the determination of correct underbalance

for cleanup the fluid properties, especially viscosity, are important but

the key factor is the formation permeability

Efficiency

The major factors affecting the efficiency of a perforation include shot density (spf), penetration depth into the formation, angular phasing, and diameter

Injectivity increases as shot density increases?

Injectivity increases with increases in perforation penetration?

The effect is greater at shallow depths.

The major factors affecting the efficiency of a perforation include shot density (spf), penetration depth into the formation, angular phasing, and diameter

Injectivity increases as shot density increases?

Injectivity increases with increases in perforation penetration?

The effect is greater at shallow depths.

EfficiencyAngular phasing other than 0° increases injectivity

by reducing the interference with flow resulting from the presence of the wellbore.

Perforation diameter plays a relatively minor role in determining injectivity?

The strength, in-situ stress conditions and lithology can effect the penetration length, the extent and severity of the damage zone around the perforation, and the cleanup characteristics.

Angular phasing other than 0° increases injectivity by reducing the interference with flow resulting from the presence of the wellbore.

Perforation diameter plays a relatively minor role in determining injectivity?

The strength, in-situ stress conditions and lithology can effect the penetration length, the extent and severity of the damage zone around the perforation, and the cleanup characteristics.

Modular Gun System

Deployment systems for multiple guns.

Guns are loaded at the surface, deployed downhole individually, and stacked on each other at the perforating zone, with the lower-most gun module being supported by the gun hanger.

Deployment systems for multiple guns.

Guns are loaded at the surface, deployed downhole individually, and stacked on each other at the perforating zone, with the lower-most gun module being supported by the gun hanger.

Modular Gun System

An entire interval can be perforated over- or underbalanced

Gun sizes from 2 to 7-inch OD can be run for casing from 3 ½ to 8 5/8 inches,

Zone can be perforated and tested with no downhole restrictions below or above the packer.

An entire interval can be perforated over- or underbalanced

Gun sizes from 2 to 7-inch OD can be run for casing from 3 ½ to 8 5/8 inches,

Zone can be perforated and tested with no downhole restrictions below or above the packer.