batch chemical treatment

Status A second draft has been prepared and is shown below. It is ready for edit-

ing. Chair: Fenfen Huang, f [email protected] Team: Jose Macias, Ewout Biezen, Keith Mamot, Dan Sewatt, Sam

Toscano, Rick Hornsby, Clint Mason, Greg Shindler Comments: This draft is ready for editing by Dr. Tony Podio.

5.2 Batch Chemical Treatments

This section discusses the practical limits of batch chemical treatments in terms of liquid production rate, gas production rate, depth, pressure, temper-ature, etc. It presents rough guidelines on the relative costs of batch chemi-cal treatments. Obviously precise costs can not be given as they depend on many factors. It presents rough guidelines on the relative life expectancy of batch chemical treatments. Clearly, precise expectations can not be given as they depend on many factors.

Chemical foaming agents, also known as foamers, are one of the many artifi-cial lift methods available to deliquify the gas wells. With the addition of foamer to a wellbore where loading liquids are present, foam is generated with the agitation from the gas flow. The surface tension and fluid density of the foam are lower than the liquids so the lighter foam, whose bubble film holds the liquids, is lifted more easily by a low gas flow rate, often encoun-tered in the tail end production of mature gas wells. By removing the liquid column and associated hydrostatic pressure against the reservoir pressure, the inflow from the reservoir can be improved and ultimately, the production can be enhanced.

Foamers can be applied either by batch treatment or via continuous injec-tion. A batch treatment involves the application of a single volume of foamer to the well at one time, as opposed to a smaller volume applied continuously as in the case of continuous application. The next batch is applied after a period of time when the foamer dosage is reduced and performance starts to decline.

Foamer is a Very Cost-Effective Artificial Lift Method: Many forms of mechanical artificial lift are utilized to deliquify gas wells,

but there are scenarios where the application of chemical foamers is more favorable. This is especially the case for mature assets reaching their

Guidelines & Recommended PracticesSelection of Artificial Lift Systems

for Deliquifying Gas WellsPrepared by Artificial Lift R&D Council

mailto:[email protected]

Foamer Batch Treatment for Deliquifying Gas Wells

predicted lifetime, where any sort of Capital Expense (CAPEX) is unfavorable.

Cost-effectiveness of foamer is proven as the followings:• Low initial investment (CAPEX), requires one chemical pump, filter, valve

and one chemical storage tank, and a secondary containment for the chemical tank

• Low operating and maintenance cost (OPEX and R&M)• Versatility of treatment methods (batch vs. continuous), can be used alone

or in conjunction with other artificial lift methods such as a well-head compressor, plunger, gas-lift etc.

• Multi-functional foamer products are available to revolve corrosion, scale, paraffin, salt deposition etc. while the liquid is being removed from the wellbore. Multi-functional chemicals not only offer benefits in reducing CAPEX (single injection point, pump, tank etc.), it also helps drive the OPEX including logistics cost and man power etc.

• Fast response from the well (usually from 24 hrs to two days depending on the well depth) to confirm the foamer performance.

Applications for foamer:• For deliquifying gas wells as the primary artificial lift means or the

secondary artificial means that can be combined with gas lift, plungers, compressions etc.

• Can be used to remove liquid holdup in gas transport pipelines• Potential usage in conjunction with a gas-lift system to enhance oil

production• Potential application in pipeline liquid removal


Table of Contents

Practical Considerations..........................................................................4 Well Depth Limits Tubing Size Limits Pressures Limits Temperature Limits Flow Rate (gas and fluids) Limits with sand, corrosion, erosion, H2S, CO2, etc. Power Requirements Operating requirements Maintenance requirements

Cost Guidelines........................................................................................6 CAPEX OPEX R&M

Practical Limits for Batch Chemical Treatments……………………….. 7

Life Expectancy Guidelines for Batch Chemical Treatments………… 7

Best Operation Practices for Foamer Batch Treatment ……….……….7

Best Field Application Practices for Foamer Batch Treatment ……….8


Practical Considerations

- Well Depth limits

There are no practical depth limits for batch chemical treatments. The primary issues associated with depth include fall, soaking, and flow back times. Success is more dependent upon other factors such as loading types (partial loading vs. transient loading vs. full loading vs. depletion), fluids characteristics (pH, salinity, produced water vs. hydrocarbon ratio, hydrocarbon characteristics), fluid lev-els, inflow capability, foamer chemistries, foamer dosages, differen-tial pressure (downhole/surface), fluid rate and gas rate.

- Tubing Size Limits

There are no practical tubing size limits for batch chemical treat-ments. The primary issues include severity of the liquid loading and fluid level. Success is more dependent upon other factors men-tioned above.

- Pressure limits

Though there is no recognized pressure limits in batch foamer treatment, it is highly recommended that bottomhole pressure (both flowing and shut-in) and reservoir pressure be evaluated to access the likelihood of reservoir depletion and sufficient pressure buildup after shut-in. To ensure the success of the batch treatment or foamer application in general, maximized agitation (i.e. rock the well by extended period of shut in, allowing pressure build up fol-lowed by production to minimum pressure vessel or even atmos-phere) to maximize start up gas flow thus to generate mixing and foam is critical. Increased line pressures will adversely affect the ability of the well to adequately lift foamed fluids to the surface and produce in the system.

- Temperature limits

Thermal stability of chemical foamers under wellbore conditions (pH, temperature, compatibility with well fluids, and estimated re-tention time) needs to be taken into consideration in chemical batch treatment. Different foamer chemistries have different thermal sta-bility thresholds and solubility and compatibility with various fluid characteristics. Chemical foamers with thermal threshold above downhole temperature need to be used to avoid undesired degra-dation, loss of performance or adverse effect such as increased corrosivity in the wellbore.


- Flow rate limits (gas and fluids)

It is traditionally considered that low-rate gas wells with producing gas liquid ratios (GLRs) between 1,000 and 8,000 scf/bbl are among the better candidates for foamer treatment, though there are no limits of GLRs for batch treatment. Batch treatment of foamer has been carried out on fully loaded wells with encouraging produc-tion increases. Techniques such as “rocking”, “bull heading” are of-ten used to overcome the low gas rate at the beginning of the field application with the goal to unload the most fluids from wellbore and tubing.

When the inflow from the well is limited (i.e. in a severally loaded well with a high level of liquid column), N2 injection into the fluid col-umn via coil tubing can be conducted to help generate foam to re-move high level of fluid before the inflow from the reservoir can re-sume. Or gas sticks which can slowly release gas while dissolving in liquids can be utilized to help kick start the foam generation and liquid removal process.

To maximize the production enhancement, after a successful prove of concept trial with foamer batch treatment to confirm the effective-ness of chemistry in foaming the fluids and removing liquid reten-tion, continuous foamer injection is recommended to ensure smooth production.

- Limits with sand, corrosion, erosion, H2S, CO2, etc.

Chemical foamer, given its ease of customization, can have built-in corrosion inhibitor, H2S scavenger, and/or CO2 scavenger to be multifunctional. It also has tolerance for particulates and sand in the produced fluids. The foaming agent itself is surface active and pro-vides a limited corrosion protection to the production asset. If higher corrosion protection is desired, combinational foamer with the right type of corrosion inhibitor can be used. Foamer has good tolerance to H2S and CO2 as well and has been effective in deliquifying both sour wells and sweet wells.

- Power requirements

It depends on what kind of chemical pump is in use. Often times, a solar-driven chemical pump eliminates requirements for external power.

- Operating requirements


After the execution of a foamer batch treatment, on-going monitor-ing and optimization is crucial to maximize the value of the pro-gram. Close monitoring of the build-up pressure trend prior to re-opening the well, the characteristics of the flow back fluids, surface separation, and production uplift are highly recommended. Venting can be used to prompt the most agitation during the start-up process. If the foamer’s effectiveness starts declining due to deple-tion of chemical, a new treatment needs to be conducted.

- Maintenance requirements

Foamer batch treatment requires low maintenance since there is minimal new CAPEX investment. Chemical inventory management and dosage optimization to maintain the maximum production rate are major maintenance requirements.

Cost Guidelines

The chemical cost of a foamer batch treatment is usually low, starting from a few hundred dollars in total cost (for personnel training, chemical supply, and treatment executions). Of course, this depends on the kind of foamer that is needed, and the volume of foamer is needed to remove the retained liquid.

- CAPEX

CAPEX of foamer batch treatment is minimum, which usually only involves a chemical injection pump, a storage tank, and a sec-ondary containment for the tank. In application with short retention time of the surface separation (i.e. offshore application), contin-gency defoamer program is usually required to quickly break down potential residual foam on the surface. In rare cases, emulsion breaking and water clarification program may also need to be ad-justed to count for potential emulsion tendency when liquid hydro-carbon is present in the produced fluids.

- OPEX

OPEX of the foamer batch treatment is also minimum. Training for field operational personal is recommended and ongoing monitoring and optimization of the program based on well response is highly desired.

- R&M (Repair and Maintenance)


R&M cost of the foamer batch treatment is also minimum. Cost of repairing of chemical injection pump, lines and maintaining chemi-cal inventory is low.

Practical Limits for Batch Chemical Treatments

Foamer batch treatment requires the well to be shut-in to inject the foamer (for wells with a packer), thus there is loss of production during the injection, soaking periods. For wells without packer, foamer batch can be applied down the backside or via tubing and shut-in and soaking is still recommended to allow pressure build up to kick off the foam lift process.

It requires knowledge of the liquid level in the wellbore to estimate the foamer volume for treatment. It is recommended that liquid level within 3 days (preferably within 24 hrs) prior to the treatment is obtained with Echometer or similar technology for chemical batch volume estimation.

Water flush (or KCl substitute if clay swelling is an issue) is usually conducted to drive the chemical to mix with liquid in the wellbore to promote sufficient mixing.

Life Expectancy Guidelines for Batch Chemical Treatments

How long the foamer treatment effectiveness will last depends on the size of the treatment and amount of liquid that needs to be removed. Usually, the well can produce for one to two months before another batch treatment is needed. Lack of response post batch chemical can be caused by lower dosage of chemical than minimum effective dosage of chemical (i.e. encounter a larger volume of retained liquid than expected during field trial). In that case, another batch treatment with size half of previously injected volume can be administrated, followed by shutting in to allow soak and pressure buildup before reopen for production. These steps can be repeated a couple of times when deem necessary to aid the initial foam unloading given other potential root causes of lack of re-sponse such as reservoir depletion, formation damage, formation block-age etc. have been ruled out.

Best Operation Practices for Foamer Batch Treatment

o Train operators in liquid loading principles and chemical foamer batch treatment operation. Basic understanding of gas well liquid

loading Firm understanding of foamer and foamer

batch treatment Train and abide by safe operating principles


Establish key performance indicators (KPIs).

o Develop and implement a consistent optimization strategy.

o Communicate strategy with clearly defined division of responsibility.

o Foamer product recommendation and dosage based on laboratory or field bench top performance testing using fresh produced fluids need to be obtained and used as the base to design foamer batch treatment.

o Close monitoring the pressure build up and flow back fluids. If not successful, longer soaking time or higher dosage can be trialed. If overtreatment occurs, less foamer dosage needs to be applied in the next treatment.

o Always have a defoamer program in place as a start-up contingency in the pilot trial when short retention time in surface separation is expected.

o For offshore operation, topside squirt test to check foamer’s impact on the oil/water separation or MonoEthylene Glycol (MEG) regeneration unit is highly recommend before full scale trial. Foamer and/or anti-foam can be applied across the test separator in live well fluids and oil/water separation will be examined. Efficiency of MEG unit needs to be monitored.

Best Field Application Practices for Foamer Batch Treatment

1. Conduct a static fluid level shot 3 days or less (preferably 24 hrs) prior to batch treatment.

2. Verify valves were serviced less than 3 months prior.

3. Install injections systems (injection manifold with check valve, block valve, and pressure relief valve (PRV), etc.).

4. Slowly pressure up treatment equipment against closed block valve until safety shutdown switch kills engine at pre-set pressure settings.

5. Start pumping at low rate (i.e. 0.25 bpm) and gradually increase pump rate to its maximum capacity to slowly overcome the shut in wellhead pressure until the foamer dosage based on the laboratory testing and modeling is achieved.

6. Open upper and lower master valve, leave well shut in at the wing valve so tubing and casing pressures can be monitored.


7. Leave well shut in for overnight or (24 hours if needed) following batch treatment.

8. After sufficient pressure built up, bring well online with wide open choke setting to try to unload fluid column in tubing.

9. Once well is unloaded, monitor the flow back fluids and surface sepa-ration to determine the necessity of executing the defoamer injection (which is usually set up as a start-up contingency).

10. Monitor and report KPIs such as gas rate, fluid rate, pressures etc.

11. After depletion of foamer as indicated by decreasing production rates, conduct a new batch treatment.

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Rights to this information are owned by the Artificial Lift Research and Develop-ment Council (ALRDC). This material may be used by any member of ALRDC in any way they see fit as long as they refer to the ALRDC Artificial Lift Selection document where it is presented.

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