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Clariant Oil Services' Innovative SCALETREAT FeS 13805 Creates Paradigm Shift for Inhibiting Iron Sulfide Scale

Benefits
• Economically prevents iron sulfide fouling in the water 
handling system
• Works at significantly less “active” dosage rate (50 ppm) 
than the benchmark THPS product (100 ppm)
• Saves operations significant sums of money in chemical costs 
and production interruptions
• Helps operations to maintain and increase oil production rates
Background
One of the most successful oil production fields in the contiguous United States first began operation at the turn of the 20th century. The complex field included production originating from multiple zones and from thousands of wells.
The operation’s water injection system included eight free water knockout (FWKO) vessels, operating at a total capacity of 300,000 bbl/day. Historically, the system was challenged with the deposition of iron sulfide, resulting in scale buildup in the Induced Static Flotation (ISF) and storage tanks, filter screens and injection system. This caused production interruptions and challenges as operators constantly had to intervene 
to ensure that the production water was going where it was needed.
The traditional FeS controlling method employed consisted of allowing scale buildup and removal by using a benchmark concentrated tetrakis hydroxymethyl phosphonium sulfate (THPS) chelating agent, which worked on the basis of stoichiometry with the amount of scale present.
Acid cleaning was another method of remediating FeS, but this practice typically required equipment to be taken offline for remediation, leading to deferred oil production costs and downtime. The use of the strong acids typically led to H2S generation and subsequent system corrosion. 
Clariant Oil Services worked with the oil producer to develop a true high-performance and cost-effective iron sulfide scale inhibitor that worked at threshold levels, much the same way traditional calcium carbonate and barium sulfate scale inhibitors function. The goal of the lab and field trials was to develop new chemistry that prevented scale buildup vs. the industry standard of allowing scale deposition and using production-robbing mechanical and chemical methods for removal.
Innovation and Value Delivered
Pulling from vast experience in developing best-in-class chemistry, Clariant Oil Services‘ scientists built on a known foundation of copolymer chemistries. Lab tests conducted in a purely aqueous media showed three proprietary copolymer blends worked well at inhibiting iron sulfide accumulation. Once these promising copolymers were identified in the lab, the true test of efficacy was conducted in the field. 
Field trials were conducted using a two-electrode Linear Polarization Resistivity (LPR) probe which was positioned at the center of the sidestream to study the direct proportional relationship between iron sulfide scale thickness and electrical signal on the electrodes. This gave scientists an online, inline and real-time method of determining iron sulfide deposition. Secondary measurements of buildup were conducted by using online measuring probes, strategically located upstream and downstream of the LPR probe.
Technicians began by establishing a blank baseline rate using no chemical. Within two weeks, deposition of 2 to 3 mm was noticed on the electrode, translating into complete blockage of the system in less than 3 months. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis showed iron sulfide dominated the scale make-up at 74%.

 
Figure 1: LPR plot showing FeS deposition trend of the blank test with no chemical, injection of the THPS based chemical at  100 ppm, and injection of  SCALETREAT FeS 13805 at 50 ppm
         
Figure 2: Blank baseline: FeS scale deposits on fouled LPR probe (l); cleaned LPR probe shows significant damage due to under deposit corrosion resulting from FeS deposition (r). 
Clariant Oil Services then established an inhibition baseline, employing the industry standard THPS chemistry used in this region..
Trials with new copolymer consisting of A & B components, SCALETREAT FeS 13805, outperformed all of the other chemistries tested during the field trials. Injection rates of 50 ppm or greater exhibited zero buildup 
on the inline LPR electrodes, half the dosage of the next best alternative.  Testing to failure utilizing a SCALETREAT FeS 13805 dosage of 30 ppm indicated a slow progression of scale build-up. Using SCALETREAT FeS 13805 results in a very small percent deposit from iron sulfide, whereas when not treated with SCALETREAT FeS 13805, the iron suflide deposits dominate the solids. 
                       
Figure 3: SCALETREAT FeS 13805 probe: LPR probes after deployment of SCALETREAT FeS 13805 with no FeS deposits (l); cleaned LPR probe after deployment of SCALETREAT FeS 13805 (r). No surface corrosion of the electrodes was observed. The electrodes were also significantly cleaner than the other tests noted. 
Trials of SCALETREAT FeS 13805 promise effective iron sulfide scale inhibition at doses as low as 50 ppm, which is half that of the industry standard THPS product. This offers a significant paradigm shift from 
the standard deposition and removal method to iron sulfide inhibition at threshold concentrations, providing significant chemical cost savings and maintaining/increasing production rates.