Clariant Shifts Market from Scale Removal to Scale Prevention
Innovative SCALETREAT FeS inhibits iron sulfide scale at low, continuous doses
Oil well producers are all-too-familiar with the flow assurance challenges associated with iron sulfide (FeS) scale build-up. Multiple system components, including the Induced Static Flotation (ISF) storage tanks, filter screens, and injection systems, can be affected by scale deposition and the resultant damage. This build-up can limit production, increase operating costs, contribute to equipment failure and decrease pumping rates.
Until recently, traditional methods to address iron sulfide formations included allowing the scale to build up and then remove it with chelating agents, such as tetrakis hydroxymethyl phosphonium sulfate (THPS), with dosage rates comparable to the amount of scale present. Producers also employ acid cleaning tactics, but these require the equipment to be taken offline and typically led to hydrogen sulfide generation and subsequent system corrosion.
“Iron sulfide scale formation is a significant and expensive challenge for oil and gas producers,” says Dr. Jonathan Wylde, global head of innovation for Clariant Oil Services. “It can lead to well failure and costly equipment repairs, resulting in lost revenue. In the past, chemical treatment alternatives required high doses of expensive chemistry to remove the scale. The industry simply could not afford to continue with the status-quo practice of scale build-up and removal.”
Clariant Oil Services partnered with a oil well producer operating in one of the most successful mature oil production fields in the United States, to develop a more effective and economic solution for Iron Sulfide scale. The complex field included production originating from multiple zones and thousands of wells.
The common problem experienced at the oil field: a high occurrence of iron sulfide scale formation. The specific partnership mission: develop a new high-performance scale inhibitor that shifts industry standard practice for resolving iron sulfide issues to scale prevention versus removal.
The focus of the field trial was centered on one particular water injection system operated by the producer. This target system was riddled with dense iron sulfide deposition throughout the water treatment plant, which caused production interruptions and uncertainty that the production water was going where it was needed.
Two forms of FeS-remediation methods were employed by the producer. “One included a THPS chelating agent dosed on the basis of stoichiometry equivalent to the amount of scale present,” explains Cyril Okocha, Ph.D., scale specialist, global innovation for Clariant Oil Services. “Acid cleaning was also employed, but this led to H2S generation and system corrosion. Both practices resulted in loss of production and equipment downtime.”
Pulling from vast experience in developing best-in-class chemistry, Clariant Oil Services’ scientists started their research on developing a true scale inhibitor, building on a known foundation of copolymer chemistries. Laboratory tests, conducted in a purely aqueous media, showed three copolymer blends worked well at inhibiting iron sulfide accumulation.
However, it is known throughout the industry that lab and field results do not always align. “The true test of a product’s efficacy rests on how it performs in the field,” mentions Scot Bodnar, head of flow assurance global innovation for Clariant Oil Services.
Field Value Established
Scientists first set out to devise a way to properly test and log the amount of iron sulfide deposition. They began by setting up a sidestream device with a turbine flow meter and chemical injection point on one of the FWKO vessels.
“We decided the best approach was to use a two-electrode Linear Polarization Resistivity (LPR) probe positioned at the center of the sidestream to allow us to study the direct proportional relationship between iron sulfide scale thickness and electrical signal on the electrodes,” adds Bodnar. This gave the scientists an online, inline and real-time method of determining iron sulfide formation.
Field trials began by establishing a blank baseline rate using no chemicals, and, within two weeks, deposition of 2 to 3 mm was observed on the LPR electrode. “We were amazed at how quickly the scale formed,” says Wylde. “At this rate, complete system blockage would have occurred in less than three months.” Iron sulfide dominated the scale composition, which also damaged the electrode.
An inhibition baseline was established using the industry standard THPS chemistry used in the region. On clean electrodes, a dosage of 50 ppm was enough to show no deposit build-up. “However, field systems are pre-fouled with iron sulfide deposits, and the injection rate to halt further deposits on such systems was double that dosage,” comments Okocha.
As trials progressed to the three different, lab-proven Clariant propriety copolymers, scientists documented performance field results much different than the lab findings. So they reformulated and optimized the chemistry using two new components. “This is precisely why we conduct field trials as part of our optimization process, so we get the right product that performs as needed for the customer in the field,” says Wylde.
The new two-copolymer formulation, SCALETREAT FeS 13805, went through extensive field study. The results showed that it outperformed all of the other chemistries tested during the trails, including the benchmark THPS product. At half the dosage of the next best alternative, SCALETREAT FeS 13805 provided true iron sulfide scale inhibition, as the inline LPR electrodes showed no build-up or damage.
Injected at threshold levels, the patented high-performance SCALETREAT FeS 13805 scale inhibitor offers a paradigm shift for the industry to scale inhibition, rather than the standard practice of scale deposition and removal.
“Our innovative SCALETREAT FeS 13805 requires significantly less product dosage than current alternatives on the market, and continuous application of the product allows companies to maximize oil production and lower operating costs,” concludes Wylde. “Our cost-effective method for continuous control of iron sulfide promises to keep wells producing for longer periods between remediation and at higher rates, so producers can realize more profit potential.”