Gas Lift Applications for Mature Fields

Objective:

Present a list of alternatives to prolong the economic life of the Gas Lift Method in Mature Fields before considering other types of Artificial Lift Methods

Contents:

• Introduction• 1st Stage Optimization (no Work Over required)• 2nd Stage (Alternative Completions)• Automation (Control and Data Acquisition)• Surface Facilities (Adapting to a New Reality)• Conclusions

Introduction

Accumulated Production (Bb)

Inje

ctio

n G

as

Liqu

id R

ati

o (

SC

F/B

b)

Liqu

id F

low

Rate

(B

b/D

)Max. Economical GLR

Accumulated Production (Bb)

Inje

ctio

n G

as

Liqu

id R

ati

o (

SC

F/B

b)

Liqu

id F

low

Rate

(B

b/D

)Max. Economical GLR

Compressors, pipe line gas distribution networks and current gas lift completions are by themselves expensive.

But it might be even more expensive (if not economically impossible) to invest in new electric generators and cables, pumps and new completions, training personnel… for mature fields.

….Can we extend the life of an old gas lift field?

1st Stage Optimization (no Work Over Required)

Trouble Shooting (System Approach)

o Find QL vs. Qgi (measure flowing bhp at different Qgi)

Do not take computer models as the indisputable truth!

o Identify where and why wells are not optimize

GAS INJECTION FLOW RATE

LIQ

UID

FLO

WR

ATE

Max Ql point

Opt. economic point

Assessment of current “best possible” Injection GLR

UNSTABLE WELLS

POINT OF INJ ECTION

COMPLETION INTEGRETY

OR

FORMATION DAMAGE, SAND...

GAS INJECTION FLOW RATE

LIQ

UID

FLO

WR

ATE

Max Ql point

Opt. economic point

Assessment of current “best possible” Injection GLR

UNSTABLE WELLS

POINT OF INJ ECTION

COMPLETION INTEGRETY

OR

FORMATION DAMAGE, SAND...

Shift from Continuous to Intermittent Gas Lift o Aim: to reduce Inj. GLR (not necessarily to increase liquid

production) o When?

There is no theoretical approachRule-of-thumb: static liquid level = 1/3 total depth

o Where?Avoid extreme tubing sizes (4-1/2 or < 2-3/8 in tubing)Avoid extreme annulus volume Surface facilities

o How?1-1/2 in vs. 1 in valvesSpring loaded or nitrogen charged valves / single element or pilot v.Surface controllers or choke control / Use plungers or notOptimum cycle time to maximize QL / Correct gas inj. per cycle

2nd Stage Optimization (Alternative Completions) Reduce Tubing size

Aim: prolong continuous gas lift while reducing Inj. GLR

Continuous GL is operationally always better than intermittent GL specially in small fields with few operating wells

Use other type of completionsLast resourceThe only way to extend GL to ultimate depletion

CHAMBER INSTALLATIONS

More liquid can be accumulated for a given flowing bottom hole pressure

Double Packer Chamber

• Can reduce IGLR• Might increase liquid

production (high P.I.)• Max. liquid capacity

than any other type of chamber

Attention to:

• Bleed valve port size• Gassy wells• Sand (difficulty to

pull the completion and wire line jobs)

• The completion is more complex. This increases the risk of any production inefficiency due to completion failure

Insert Chamber

• Can reduce IGLR

• Might increase liquid production (not necessarily high P.I.)• Max. Draw-down • Especially suitable for wells with long perf. Intervals.

Attention to:

• Bleed valve port size (chamber and outer annulus)• Gassy wells (but perform better than DPC)• Sand (difficulty to pull the completion and wire line jobs)• The completion is even more complex than double packer

chambers

ACUMULATORS

Compared with simple completion, more liquid can be accumulated for a given flowing bottom hole pressure but with less complex

completions

Simple Type Accumulator

• Can reduce IGLR• Might increase liquid

production (high P.I.)• Suitable for gassy

wells• Not as complex as

chamber

Attention to:

• Liquid capacity is always lower than any type of chambers

• I.D. of accumulator cannot be too large

UNLOADINGVALVE

OPERATINGVALVE

UNLOADINGVALVE

PACKER &STANDING VALVE

SIMPLE TYPEACCUMULATOR

Insert Type Accumulator

• Can reduce IGLR• Increases liquid

production (long perf. intervals) due to high draw-down

• Suitable for gassy wells

• Not as complex as chamber

Attention to:

• Gas lift valve should be at upper mandrel

• I.D. of accumulator cannot be too large

GAS LIFT GASMULTIPHASE FLOW

FORMATIONGAS INLET(Y-TOOL)

MANDREL

SPECIALPACKER

STANDING VALVE

INYECTION POINT

COILED TUBING

• Bleeb port should handle two-phase flow

Automation (Control and Data Acquisition)

An automation system can:• Help the gas-lift Operator to optimize each gas-lift well and

keep it optimized all of the time.• Help to optimize the performance of an entire gas-lift system:

by automatically coordinating injection cycles, it can reduce the occurrence of system upsets that may happen when two or more wells are injected at the same time

• Keep stable condition during a compressor trip or restart, a production station trip or restart, or the trip or restart of large wells on the system

• Continuously monitors all wells and the system to provide surveillance and troubleshooting information to the gas-lift Operators

Its major drawback is COST, but new technologies are reducing it

Surface Facility (Adapting to a New Reality)

• Lower well head pressure (use of low pressure booster might be necessary)

• Oversize tests separator (test accuracy)• Undersize separators (ability to handle gas for intermittent gas

lift, use chokes)• Gas handling (moisture[Dp], debris[old pipes] etc)• Well heads free of restrictions (streamlined wellhead free of

choke box)• Use of valves instead of orifices as the operating point to reduce

the impact of compressor shut-downs• Use abandoned wells to storage either high or low pressure gas

to increase the stability of the whole system

CONCLUSIONS

• The injection gas liquid rate can be kept within an economical level if proper steps are taken

• Long term planning for surface and subsurface equipment replacement can extend the Gas Lift Method up to ultimate depletion

• New technologies in automation equipment should make its implementation economically feasible even for low producing wells

• Training personnel for present and future operation requirements is essential for extending the life of the Gas Lift Method.

Stage Optimization (Alternative Completions)

Insert Chamber with Hanger Nipple

Insert Chamber with Combination Operating-Bleed Valve

Extremely long Insert Chamber

Insert Chamber for Tight Formations

Gas Chamber Pumps

• Increase liquid production by reducing fall back losses in wells with low API oil

• Can handle gassy wells and high temperatures (steam injection)

Attention to:

• Higher cost in surface controller equipment than in Gas Lift• For complex designs, parts are subject to wear and replacement• A High-Pressure gas source is required• Gas liquid ratios can be high for some designs due to venting of

high pressure gas

AdjChoke

Inj. Gas &vent string

AdjChoke

Vent motor valve

Pilot Control System

Inj. gas motor valve

Inj.Gas line

Flowline

Csg

InsertChamber

Perfs Intake check

valve

Discharge check valve

Chamber dip tube

Prod conduit