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Perforation Strategy for Sand Management

in

Lower Fars Unconsolidated Formation

Khalid Ahmed

Heavy Oil Group

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Outline

Concept Statement

Heavy Oil Fields in North Kuwait

Lower Fars Formation and its Rock Mechanics

Sand Production Potential

Perforation Strategy- Pre-Lab Test

Lab Test for Optimum Perforator Selection

Conclusions, Recommendations and Way Forward

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Concept Statement

Perforation Strategy has to be formation specific

Formation rock mechanics alongwith stress profile dictate perforation type (DP/ BH), spf and phase angle

For steam injector and producer, perforation strategy is essentially different

As soft formation essentially produces sand, critical drawdown pressure information shall help its containment

Sand containment through perforation strategy shall ultimately help in production enhancement by eliminating/ minimising sand control equipment

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Outline

Concept Statement

Heavy Oil Fields in North Kuwait

Lower Fars Formation and its Rock Mechanics

Sand Production Potential

Perforation Strategy- Pre-Lab Test

Lab Test for Optimum Perforator Selection

Conclusions, Recommendations and Way Forward

www.kockw.com

Heavy Oil Fields in North Kuwait

All major Fields of North Kuwait-South Ratqa, Mutriba, Raudhatain, Sabriyah, Bahrah and Umm Niqa have dedicated shallow-depth wells drilled in Lower Fars

MUTRIBA

SOUTH RATQA

RAUDHATAIN

SABRIYAH

BAHRAH

UMM NIQA

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South Ratqa & Umm Niqa- Two producing fields

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Outline

Concept Statement

Heavy Oil Fields in North Kuwait

Lower Fars Formation and its Rock Mechanics

Sand Production Potential

Perforation Strategy- Pre-Lab Test

Lab Test for Optimum Perforator Selection

Conclusions, Recommendations and Way Forward

www.kockw.com

Lower Fars FormationStacked Channel Sand

- Lower Fars is a shallow depth unconsolidated multi-stacked sand-shale sequence

- Porosity is in excess of 30 pu andpermeability for cleaner part is above4 to 5 Dacy

- Oil viscosities vary both laterally andvertically

Weak Rock

- Lower Fars is a weak, friable rock- Unconfined Compressive Strength

(UCS) is very low -225 psi for F1A and 350 psi for F1B

- Friction Angle is 25 deg for F1A and 27 deg for F1B

Grain Size Distribution

- Grain Size Analysis is a key input for Sanding risk analysis

- Finer particles have greater sanding potential

- F1A is relatively coarserthan F1B

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Lower Fars rock shows Plasticity• 7” casing is cemented with 15.8 ppg

thermal cement- without any loss

• ELOT and Minifrac suggest higher FracGradient (≥ 0.65 psi/ft), with Leak-off pressure in excess of 500 psi – against formation pressure of 230 – 250 psi

• Total Clay content in sand is ≤ 5%, majority being Illite- Smectite. Shale hydration can be controlled with higher % of KCl

The rock is friable.Under stress it behaves more plastic

than elastic

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Outline

Concept Statement

Heavy Oil Fields in North Kuwait

Lower Fars Formation and its Rock Mechanics

Sand Production Potential

Perforation Strategy- Pre-Lab Test

Lab Test for Optimum Perforator Selection

Conclusions, Recommendations and Way Forward

www.kockw.com

Sand Production Potential

Factors affecting sand production

- Rock Strength (UCS)- Pore Pressure and Depletion- In-Situ Stresses- Grain-size Distribution- Perforation Size and Orientation

Critical Drawdown Pressure

- Critical Drawdown Pressure defines “weak“ zones to start producing sand

- Typically, Perforation creates cylindrical cavity

- Expt. shows a spherical cavity to be more stable than cylindrical

- Drawdown determines stable shape of cavity, hence sand production

Sand-free Production

- It is possible to have sand free production in a well

- If there is no “Weak” zone interms of Critical DrawdownPressure

Green zones are sand freeRed zones produce sand

Co = Unconfined compressive strengthPc

d = Critical Drawdown pressure

Reference: Petroleum Related Rock MechanicsErling Fjar, R.M. Holt, A.M. Raaen, R. Risnes, P. Horsrud

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Outline

Concept Statement

Heavy Oil Fields in North Kuwait

Lower Fars Formation and its Rock Mechanics

Sand Production Potential

Perforation Strategy- Pre-Lab Test

Lab Test for Optimum Perforator Selection

Conclusions, Recommendations and Way Forward

www.kockw.com

Initial Experience with Perforators Geomechanics Study suggested to use Big Hole (BH) charge (Entry Hole diameter ≥0.8 in) for CSS

BH charges were used at 12 spf and later 9 spf

Initial 5 wells were completed as CHOPS (Cold Heavy Oil Production with Sand) with BH charge

Wells produced sand in early phase, later on no sand was produced

Under CSS, most wells produce large amount of sand with BH Charge

With small entry hole DP charge, sand production reduced appreciably

BH ChargeDP Charge

BH charge creates fracture that breaks down formation to produce sand

DP charge creates less fracture, hence less sand

Preferred is the charge that creates shallow perf tunnel, good enough to overcome the damage zone, without breaking the rock

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Limited Entry Perforation (LEP)- Analytical Approach For steam injection operations, G P Small suggested an analytical approach of LEP

LEP is based on the principle of critical steam flow through an orifice

At critical flow condition, steam is injected at sonic velocity

Under this condition, for a given hole diameter and bottom hole injection pressure :

– Flow is choked, thereby limiting maximum rate of injected steam per perforation

– No single perforation can act as a thief zone

Steam-Injection Profile Control using Limited Entry Perforations (SPE- 13607), 1985;

also Production Engineering September 1986

is = 4.07 FdD A p0.97 fs-0.5

is = steam injection rate per perforation at critical flow, B/D steam

FdD = dimensionless discharge factor, usually ranges between

0.6 and 0.7

A = perforation area, in.2

p = bottomhole injection pressure, psia

fs = steam quality, mass fraction

FdD = 0.65

A = various, calculated from perforation hole

diameters from different gun systems

p = 450 psia

fs = 60%

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Calculation with planned Gun SystemGun System

RP19B/43 Sec-1: Hole dia in 7" casing

is,, Flow rate per perf at critical flow

(B/D)

Max number of perforations allowed

for critical flow

Shot density over 150-ft interval

Total flow area over 150-ft interval (in2)

INJE

CTO

R

WEL

LS

2" DP 7g 0.24 58 17 1 shot/9 ft 0.774 1/2" DP 23g 0.3 90 11 1shot/14 ft 0.784 1/2" DP 39g 0.35 123 8 1shot/19 ft 0.774 1/2" DP 39g 0.4 161 6 1shot/25 ft 0.75

PR

OD

UC

ER

WEL

LS

4 1/2" BH 23g 0.65 12 SPF 5974 1/2" BH 28g 0.85 12 SPF 1021

4 1/2" BH 28g 0.96 12 SPF 1303

For commercial phase, it was decided not to perforate the full 150ft, rather only F1B is to be perforated, which is max

35ft per well

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Numerical Analysis and Simulation Numerical Analysis (Halliburton’s PerfPro) was

used to estimate Productivity index

Simulation (Halliburton’s PulsFrac) was used to predict formation Breakdown around the perforation tunnel and to optimize number of shots to avoid formation breakdown

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Analysis and RecommendationsGun Type spf EHD Formation breakdown (up to

10” hole)Formation breakdown (up to 15” hole)

4 ½” 5 spf SDP 5 0.37” No No

4 ½” 12 spf DP 12 0.38” Yes (Frac Length: 16.72 ft, fracwidth: 0.04” , conductivity: 55 md-ft)

No

4 ½” 12 spf BH 12 0.8” Yes (Frac Length: 12.6 ft, fracwidth: 0.04” , conductivity: 72 md-ft)

Not recommended as only 1” penetration inside formation

9 spf DP for hole size ≥15-in 9 spf BH for hole size ≤10-in If more production is desired and sand production can be tolerated, then 12 spf BH

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Outline

Concept Statement

Heavy Oil Fields in North Kuwait

Lower Fars Formation and its Rock Mechanics

Sand Production Potential

Perforation Strategy- Pre-Lab Test

Lab Test for Optimum Perforator Selection

Conclusions, Recommendations and Way Forward

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Experimentation with Core- Baker Hughes

Baker Hughes used 37gm charge in to the 3-ft long core barrel potted to 7-in dia from the original 4-in dia

Post perforation, the core was completely shattered

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Experimentation on Core - Halliburton

4”-dia 3ft long core removed carefully from aluminum tube

Removed core potted with hydrostone and low-strength Portland cement to make 7” dia Potted core encapsulated

in Viton sleeve

core was mounted in API RP 19B, Section 4 vessel confined at expected field stress

Single shots were fired on core target at

4 ½” gun sytem, 12 spf and 2” gun at 6 spf at room temp

with nominal pressure of 800 psi

and wellbore pressure of 600psi

OMS: Odourless Mineral Spirit

At a drawdown pressure of 50 psi,

crude oil in the core was displaced with

miscible OMS and both pre and post injection permeabilities were

measured

Reference: WHOC16-606

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Observations from the Experiment on Core Samples

3-ft Core Sample CT Scan Test-3 Perforation Event Pressure Plot

- 17.5 g DP charge- Depth of Penetration: 29 in- Entry Hole Dia: 0.35 in

Pressure-Temperature-Flow

Permeability Index= 1400 mD in production at a production ratio of 0.8 against baseline perm=1703mD

- 7 g DP charge After displacing with hot water

- 7 g DP charge- Depth of Penetration: 15.88 in- Entry Hole Dia: 0.19 in

Injection Production

Flow direction was reversed after 50 min of injection @100mL/min (≥3 pore volume) to

Production

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Observations from the Experiment on Core Samples

Hole Size Determination- OMS Hole Size Determination- Hot Water

- At 650 psi Overburden, 220 psi pore pressure, room temp (72°F) and max Drawdown of 180 psi

- OMS was flowed for perm determination- Pressure released, 6” long 1/8” hole

drilled and again pressurized- At 110 psi, failure occurred and sand was

produced

Hole Size Optimisation

- 650 psi Overburden and 220 psi pore pressure, 300°F, Drawdown of 180 psi

- Entry Hole diameter = 0.24 in

- 650 psi Overburden and 220 psi pore pressure, 300°F, Drawdown of 50 psi

- Water was flowed and Core was heated

For a 1” long and 1”dia hole, Sand started to

produce at a pressure of 10 psi only

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Outline

Concept Statement

Heavy Oil Fields in North Kuwait

Lower Fars Formation and its Rock Mechanics

Sand Production Potential

Perforation Strategy- Pre-Lab Test

Lab Test for Optimum Perforator Selection

Conclusions, Recommendations and Way Forward

www.kockw.com

Conclusions, Recommendations and Way Forward

Perforation Strategy- CSS & SF Overbalance and Drawdown Pressure

- Use 4 ½” gun DP charges at 6 spf and 60°phasing

- Entry Hole Diameter = 0.24”- Reduced sand production

Way Forward

- Under SF, Injector wells to be re-perforated with DP at 6 spf – to enhance injectivity

- Perforation is to be made with a minimum of 200 psi overbalance with water in wellbore

- No solvent to be added- Solvent can wash the crude oil off the

sand- This would reduce the cohesive strength

and resistance to sand movement

- Planned Injection rate = 1000 bcwe/d- Steam Injection pressure = 350 to 450 psi- Reservoir Pressure=230 psi- Differential Pressure= 120 to 220 psi

- Using LEP Concept, at 350 psi injection pressure for a 35ft interval, it would be at 23/35 = 0.66 spf and at 450 psi injection pressure for a 20ft interval, it would be at 18/20 = 0.9 spf

- Geomechanics Study suggests orienting perforation sub-parallel to minimum horizontal stress can enhance critical drawdown by 20 psi, reducing sand production

- Initial drawdown pressure should be 25% of expected maximum (which is 180psi)

- Just under 50 psi- This would avoid initial high-velocity

surging- Once flow is stabilized, drawdown can be

ramped up

- Under SF, Producer wells to be re-perforated with BH at 9 / 12 spf – to enhance productivity

- Entry Hole diameter = 0.8 in

- As it is difficult to orient in vertical well, shooting guns downward at 15°would reduce sanding and enhance steam contact with less disturbed formation

- Filling the void space inside the gun with Foam shall help to create Dynamic Underbalance, reducing sand production