Foam Course

Public

Craig Kelly & Victoria Shearer

24.09.2012

Innovation Assured.

Value Delivered.

CLARIANT OIL SERVICES

7TH European Gas Well Deliquification Conference

GAS WELL DELIQUIFICATION USING FOAMERS

Today’s Session2

� Liquid Loading� Foam Theory� Foamer Properties and Factors

Affecting Performance

� Candidate Well Selection� Foamer Chemistries� Testing of Foamers� Foamer Application� Summary

Public, Gas Well Deliquification Using Foamers

Liquid Loading

– Liquid loading is the inability of a gas well to produce liquids to surface

– All gas wells which produced formation or condensed fluids will suffer from liquid loading at some point in the lifetime

– The aim of successful gas well deliquification is to:

– predict when this will occur, and

– implement the most optimal technique(s) at the most appropriate time, to allow the well to flow at its true potential and maximize recoverable reserves

Public, Gas Well Deliquification Using Foamers3

Liquid Loading

4

– When upward drag force of gas equals droplet weight, gas velocity is said to be ‘critical’

– Accumulated liquids cause a back-pressure on the well, further reducing gas production

– Eventually the back pressure of the liquid will equal the reservoir pressure and the well will cease to flow

– If no action is taken, the well will ultimately require to be abandoned, with the associated lost reserves


Liquid Loading

– The Critical Velocity to lift a liquid can be calculated by the Turner equation (1969):

5 Public, Gas Well Deliquification Using Foamers

∪� 1.92��

�

�� ⁄

PlungerCompression

Downhole Pump Jet Pump

Velocity String

FoamerCycling

Gas Lift

Liquid Loading Mitigation

– A number of available deliquification techniques

- May utilise the well’s energy or add energy from an external source


Liquid Loading Mitigation with Foamers

– Foam works in a fundamentally different way to most mechanical techniques

- Decreases critical velocity. How?

- Critical Velocity is proportional to liquid surface tension and liquid density

- Decreasing either will reduce the critical velocity



– For mix of water and foamer, surface tension reduction from 72 dynes/cm to ~ 30 dynes/cm

– Density reduction from 1.0 g/cm3

to ~0.1 g/cm3(depending on gas fraction)

– Accordingly, density reduction has largest impact on reducing critical velocity

– Recent discoveries recognise mechanisms other than droplet flow reversal



– Simplified way to think about the effect of lifting with foamers:

- It takes a lot less energy to blow bubbles upwards than it does to blow raindrops upwards


Today’s Session10



� Candidate Well Selection

� Foamer Chemistries� Testing of Foamers� Foamer Application� Summary


What is Foam?

– Foam is a collection of bubbles....a collection of gas bubbles separated by thin liquid films

– Several different types of foam based on the interplay of the gas and liquid phases:

- Gas dispersed in liquid – foam

- Liquid dispersed in gas –aerosol

- Gas dispersed in solids – solid foam

- Solids dispersed in gas –smoke


Foam ApplicationsPublic, Gas Well Deliquification Using Foamers12

Governed by bubble size…and…foam stability

Foams are very common place in every day life...

DetergentsPublic, Gas Well Deliquification Using Foamers13

Personal Care



Flotation


Oilfield

Fire FightingPublic, Gas Well Deliquification Using Foamers17

What Causes Foam?

– Open a bottle of cola and pour it into a glass – the liquid will fizz and foam

– Releasing the pressure on the liquid will create many little gas bubbles

– After a minute or two however the bubbles disappear and the foam has gone

– The foam on a cola is unstable


What Causes Foam?

– Beer is different!

– The bubbles slowly rise to the top of the glass and then stay there

– The head on a smooth, ice cold beer is a stable foam – so why this difference compared to cola?


What Causes Foam?

– The foam bubbles are stabilized by the proteins in the beer

– The proteins gather around the gas bubble and prevent them from collapsing


What Causes Foam?

– Surface Active Agents (Surfactants) are foam stabilizers just like the proteins in beer

– Many types of surfactant are found in oilfield environment

– Components found naturally in crude oil as well as many chemical additives used in drilling, production, Enhanced Oil Recovery, etc


What Causes Foam?

– In order to generate a foam, generally three things are required:

1.Reduction of surface tension

Addition of foaming agents (surfactants) which decrease the amount of energy required to mechanically form foam

2.Agitation of the liquid (e.g. introduction of gas)

3.Lamellae must be able to form


Basic Foam Structure

– Foam

- Liquid polyhedral cells consisting of:

- Gas bubble

- Lamella

- Plateau border

- Liquid pressure in Plateau border lower than in lamella


Basic Foam Structure

– Foam Structure is stabilised by presence of surfactant molecules in the lamella


Factors Affecting Foam Stability

25

Foam Stability

Gravity Drainage

Bulk & Surface Viscosity

Electric Double Layer

Gas Volume Fraction

Surface Elasticity


Today’s Session26






Foamer Requirements (1)

– Lots of foam = Good Liquid Unloading?

– Dry Foam

- Shaving cream → carries very little fluid

– Wet Foam

- Semi-stable

- Carries fluids within structure

- Remove accumulated fluids from the well-bore

– Amount of liquid carried in the foam is referred to as the Foam Quality


Foamer Requirements (2)


– Ideally, an aqueous foamer should also:

– Exhibit tolerance for hydrocarbon condensate (acts as defoamer)

– Have no/minimal adverse impact on surface facilities

– Exhibit stability at bottom-hole temperatures

– Environmentally acceptable

– Be compatible with all wetted materials

– Offer required secondary functions such as scale inhibitor, corrosion inhibitor, biocide

Factors Affecting Foamer Performance

– A number of well-specific factors can affect the performance of foamers

– In addition, no two wells will exhibit completely identical conditions and fluid compositions

29

Brine Salinity

% Condensate

Condensate Chemistry

% below Critical Velocity

Temperature


Factors Affecting Foamer Performance


Today’s Session31






Candidate Well Selection

– When selecting candidate wells for deliquification, it is critical to gather as much data as possible

- Production history

- Well bore schematics

- Fluid rates and compositions

- Downhole and surface pressures

- Temperatures

- Intervention history

- Other flow assurance issues


Candidate Well Selection

– Understand if the well is loading, how severely and at which location(s) in the well-bore

– Assessment to understand if well is within envelope which can feasibly be treated with foamer

- Modelling

- Combination of mechanistic and empirical correlations from historical data

– Also understand economic considerations

- Required foamer volume is proportional to liquid rate

- Foamer generally excellent ROI for low to medium liquid rate wells


Today’s Session34






Foamer Chemistries

– As discussed earlier, foamers are surfactants

– Surfactants can be classed into 1 of 4 different groups

- Non-ionic

- Cationic

- Anionic

- Amphoteric

– Classified based on charge and causes them to have differing properties


Foamer Chemistries


Non-Ionic Surfactants

Alcohol Ethoxylates, etc

Perform best in low salinity brines

Compatible with range of surfactants

Solubility decreases with temperature

Solubility at high salinity improves by degree of ethoxylation

Cationic Surfactants

Quats, Imidazolines, etc

Perform best in mid-high salinity brines

May be incompatible with anionics

High emulsion tendency

Poor biodegradability and toxicity

Foamer Chemistries


Anionic Surfactants

Ether sulfates, etc

Perform best in low-mid salinity brines

Incompatible with cationics

Easy to winterise

Unstable at high temperature

Amphoteric Surfactants

Betaines, Sulfobetaines

Perform over range of brine salinities

Stable at high temperature

Low emulsion tendency

Localised corrosion risk

Foamer Chemistries - Condensate

– Aqueous foamers carry or emulsify hydrocarbon

– Above ~60% condensate, oil soluble foamers should be used

– Effectively foam condensate but performance decreases in presence of water

– Chemistries

- Fluorocarbon, Silicone, Amine

– Disadvantages

- Can be expensive and therefore uneconomical

- Environmental profile


Today’s Session39






Testing of Foamers in the Laboratory

– Which foamer should I use and how much?

– Number of different techniques available

– No one technique is fully representative of field conditions

– Possible to examine different aspects via different techniques

- Liquid unloaded

- Foam height / volume

- Foam build-up rate

- Foam quality and consistency

- Foam half life


What data is required before testing can begin?

– Customer Desired Criteria

– Water Salinity/Condensate Cut

– Bottom-Hole Temperature

– Viscosity Requirements

– Fluid Handling

– Environmental Restrictions


Importance of Field Fluids for Testing

42

– Wherever possible, it is recommended that field fluids are used for lab testing

– Synthetic fluids can be used, but very difficult to replicate, especially the condensate

– However, field fluids can age over time

– Not the same as live fluids when taken

– Minimize time between sampling and testing


Laboratory Test Methods


Method Advantages Disadvantages

Blender Fast and portable Unrepresentative

Good measure of foam stability Limited condensate cut

Sparge Simple and fast Only measures foam, not liquid

Gas used to generate foam No temperature control

Foam Test

Rig

Most representative test method No standard procedure

Liquid carry-over measured Atmospheric pressure

Foam Test Rig


– Main technique for selection

– Modified ASTM D-892

– Video clip

Blank Test.MPG Foamed Test.wmv

Defoamers

– What is defoamer?

- Chemical chemical

- Causes rapid collapse of foam

- Injected at surface

- Mitigates downstream process upsets

– Not always deployed but recommended if:

- First treatment (especially batch)

- All wells are being treated with foamer


Defoamers

– Mechanism:

- Defoamer droplet enters lamella

- Lamella thins stretching droplet

- Bubble breaks

Defoamer droplet enters lamella

Defoamer droplet bridges lamella

Defoamer droplet stretches

Bubble bursts


Emulsion Tendency

– Surfactants may hinder the effective separation of water and hydrocarbon condensate

– Need to understand any potential adverse effects

– Especially important where environmental limitations exists on produced water discharge

– May require deployment of water clarification products


Thermal Stability

– 12 hrs – 28 day tests

– Pressurised vessel

– Measure before/during/after

- Appearance

- Viscosity

- pH

- Performance


Thermal Stability


Material Compatibility

– Confirm that foamer will not adversely affect any metals & elastomers which it contacts

– Exposure of materials in neat solution at system temperature

– Examine metals for general and localized corrosion

– Elastomers for swelling / hardness / degradation

– Some foamers can be corrosive to low chrome stainless steels, which are susceptible to pitting corrosion


Combination Foamer Products

– Advantages:

- Treat multiple issues with a single product

- Salt / mineral scale deposits, corrosion, H2S

- Reduced chemical consumption costs

- Single chemical storage tank / injection pump

– Disadvantages:

- Potential for adverse interactions between foamer and other components

- Removal of corrosion inhibitor film

- Performance compromise


Today’s Session52






Foamer Application Assessment

53

– A number of different factors will determine which application methods are most favourable, including:

– Well configuration

– Labour intensiveness

– Geographical constraints

– CAPEX vs OPEX considerations


Batch Treatment – Solid Products

− Commonly referred to as ‘soap sticks’

− Applied into the top of the well normally during a shut-in situation

− Automated launcher for intrinsically safe application

− Density of soap stick ensure they fall through the liquid/gas column to the bottom of the well and contact water


Batch Treatment – Liquid Products

− Excellent diagnostic approach

− Batch application is a simple method to evaluate a well’s response to the addition of a foaming agent

− Bullhead foamer directly into production tubing

− NB foamer does not enter the formation

Advantages

• Low cost to implement

• Simple set-up• Minimal

equipment required

Disadvantages

• Labour intensive

• Increased chemical consumption compared to other techniques

• Gas production declines between treatments


Example of Batch Deployment


Well Test • Baseline production data

Shut-in

Foamer • 1,000 – 10,000 ppm, based on liquid volume in well

Overflush • Small volume of potable water / KCl brine / Gas

Shut-in • 1 hr/2000 ft MD + 2 hours

Flow back• Monitor flow rate,

FTHP, foam volume, water quality

Typical Batch Foamer Treatment Response


Continuous Injection - Annulus

− Injection at surface into tubing-casing annulus

− Only possible in wells without production packers

− Commonly used method in North America

Advantages

• No well-head modifications required

• Foamer continuously applied

Disadvantages

• Not possible in wells with packers

• May be challenging penetrating fluid column

• Generally higher consumption compared to capillary string






Mobile test trailer to assess well’s response to foamer treatment

Continuous Injection – Capillary String

− Concentric, through-tubing injection string

− Can be installed down to perforations

− May require modifications to the well-head and DHSV

Advantages

• Precise injection at required location

• Generally gives best response compared to other methods

• Can also be used to deploy other products if required

Disadvantages

• CAPEX• Retro-fit

challenge (DHSV & well-head)

• May be prone to blockage

• Must be retrieved before well intervention


Gas Lift Injection

− Injection of foamer into tubing-casing annulus in flowing stream for gas-lifted wells

− Not a commonly-used method for deploying foamers

− Well-known method for corrosion inhibitor deployment

Advantages

• Can work synergistically with gas lift

• Allows DH injection in wells with packers without need for cap string

Disadvantages

• Depending on GL injection valve, may not reach bottom of fluid column

• Products must be correctly formulated to prevent ‘gunking’ and blockages


Foam Squeeze

63

− Not a commonly-used method for deploying foamers

− Bullhead foamer into near wellbore area

− Foamer adsorbs to the formation and releases slowly over time

Advantages

• Longer treatment life compared to batch

• May provide stimulation effects

Disadvantages

• Potential for formation damage

• Limited knowledge or experiences of correct application technique


Troubleshooting Foamer Applications

– Foamer added and no / limited well response?

- Well wasn’t liquid loaded! (well modelling)

- Incorrect concentration applied for well conditions

- Insufficient

- Overdosing (‘foam lock’)

- Well too severely loaded for foamer treatment

- Insufficient agitation to generate foam

- Rocking, batch treatment, gas sticks

- Capillary string blockage


Troubleshooting Foamer Applications

– Excessive foam at surface

- Optimise frequency of batch treatment

- Optimize injection rate

- Select a less persistent foamer (reduced foam half-life)

- Implement defoamer injection

- Not preferred option

- However, may provide best ROI


Horizontal Wells

– Becoming more common with shale gas in North America and Europe

– Liquid loading generally less of a problem in lateral sections

– May cause issues depending on heel-toe profile

– Challenges

- Delivery of foamer to horizontal

- Capillary injection

- Adequate agitation in horizontal


Challenges of Foamer Deployment Offshore

– Environmental Regulations (eg. OSPAR)

– Effluent water restrictions (oil in water)

– Modifications required for capillary retro-fit

– Subsea wells

– Limited space available


Foamer Application Summary

– Number of different methods available

– Flexible technique with solutions to match many different well configurations

– Foamers can be an effective, low cost method to maintain production and increase recoverable reserves


Today’s Session69






Date post:	15-Jul-2016
Category:	Documents
Upload:	anonymous-gzjllvf1v
View:	19 times
Download:	5 times

Foam Course

Documents