Inhibiting hydrates

January 5, 2010

Hydrate formation in oil and gas operations has been a multi-billion dollar problem for many years. Nalco's Noah Morales discusses some of the chemicals his company has developed in answer to hydrate challenges and provides a case history about one of its new low dose hydrate inhibitors (LDHIs).

Traditional thermodynamic hydrate inhibitors such as methanol and ethylene glycol have been utilized to prevent hydrate formation, but more challenging production conditions such as deepwater pipelines and subsea tiebacks have required new hydrate inhibitor technology to be developed. Nalco has pioneered the development of LDHIs since the mid-1990s, starting with the introduction of its first LDHI in 1998. Since their debut in deepwater production, operators have used Nalco LDHI products in more than 100 projects worldwide.

A customer producing in the Gulf of Mexico was using Nalco's first generation anti-agglomerate (AA) for hydrate inhibition at a 2% dosage based on water produced for cold start-ups only. Historically, when pumping this product, the customer experienced water quality and vessel level issues. A specific well on the platform was a concern because when it begins producing water, continuous treatment would be required to inhibit hydrates. Nalco identified the need for an improved anti-agglomerate chemistry that could be injected continuously without causing water quality or process issues.

Nalco provided the customer with its third generation Freeflow AA, a new LDHI chemistry that Nalco formulated to dramatically improve water quality compared to the past LDHI chemistries while improving performance in higher water cut wells.

At the customer's facility, Freeflow AA was injected into the riser upstream of the topsides choke, thus only a single train's production vessels would be treated. Before the Freeflow AA trial, the low pressure separator water dump was shut in for water treating purposes. The first water separation was in the crude treater. Water samples were taken from the crude treater, hydrocyclone and float cell water dumps every hour during the six hour-trial.

The water production on the day of the trial was 5100 barrels. The injection rate was 900 gallons/day due to pump restrictions. While the injection rate was less than the 2% dosage required for treating, it was sufficient to test the impact of the product on water quality.

Before beginning the application, the overboard infrared was 22ppm and 23ppm oil in water. IRs during the trial averaged 21ppm. Note that the platform has water-soluble organics that Nalco is not treating. These water-soluble organics will interfere with the gravimetric until Nalco begins a continuous chemical or filtration treatment.

Nalco ran the trial for six hours without interruption or overboard water violations. The customer's system will be able to handle Freeflow AA injected on a continuous basis. Nalco and the customer consider the trial of Freeflow AA a success.

Chemical cut
Nalco's LDHIs offer dramatic advantages over their traditional counterparts, methanol and ethylene glycol in operation costs, safety and well life. Unlike commodity inhibitors, typical dose rates of LDHIs are 1-2% based on water production. One of the major advantages of LDHIs is that they substantially reduce hydrate inhibitor chemical consumption. Lower dose rates also equate to fewer deliveries and smaller pump and storage requirements offshore, which can lead to millions of dollars in savings each year.

Compared to methanol or glycols, Nalco's LDHI products have a substantially improved environmental profile. While methanol and ethylene glycol are toxic, are difficult to handle and store offshore and are potentially hazardous, using LDHI products virtually eliminates those concerns for operators. These products also extend well life because they can be applied beyond the treatment range for traditional commodity chemicals. Methanol and ethylene glycol reach their maximum pumping capacity down umbilicals when water cuts reach 20-30%, but LDHI products can increase well life by working up to 50% and beyond, depending on the chemistry used.

Addressing water cut
Nalco has developed two new antiagglomerate products that provide performance in higher water cut applications, improved low total dissolved solids tolerance, and step change improvement in water quality. Traditionally anti-agglomerates have been used on startup and shut in conditions only, due to the process upsets caused by poor water quality. Nalco's new anti-agglomerate technology provides customers with a product that can be used continuously without water quality problems.

Both new anti-agglomerate chemistries push the performance envelope with higher water cut performance, lower TDS requirements, and improved water quality. Nalco went a step beyond to offer one of the anti-agglomerates in a methanol-free package to help customers meet pipeline crude oil specifications. The methanol-free anti-agglomerate offers customers more operational freedom without the concern of costly fines resulting from breaking methanol specifications in delivered crude. OE

About the author

Noah Morales, Nalco's industry development manager, has been with the company for seven years and started his career in sales working in the Gulf of Mexico, and then Alaska. In the past year he has moved into the marketing group where he has responsibility for Nalco's hydrate inhibitor product line.

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