Multi-functional chemical delivers production efficiencies

As oil and gas assets continue to mature, material such as iron sulphide (FeS), biomass and sand can accumulate in flowlines and water process systems. This build-up can result in loss of production due to issues such as plugging, corrosion, flow restriction and emulsions.

Once deposition has formed in a system, it can be removed by mechanical or chemical means. Most mechanical methods can be expensive, and some systems may have areas that are not accessible due to lack of pigging capability. As a result, chemical remediation can be the only option. It’s also a lower-cost option when downtime and the risk of potential exposure to cleanout debris is considered.

Chemical scale inhibitors, Tetrakishydroxymethylphosphonium sulfate (THPS) or acids have traditionally been used to remove FeS scale. However, their use can potentially lead to a variety of additional problems, such as hydrogen sulphide generation.

ChampionX Corporation, a global leader in chemistry solutions and highly engineered equipment and technologies that help companies drill for and produce oil and gas safely and efficiently, has developed a novel, multi-functional portfolio of products that act as cleaners, corrosion inhibitors, iron sulphide dissolvers and scale inhibitors. These products have very low corrosivity and have been proven effective not only in the laboratory but also in many different field applications, including saltwater disposal (SWD) operations.

Tackling costly scale build up
During a recent project, scale and solid deposits were causing operational challenges for a major public operator carrying out SWD operations in the Midland and Delaware Basins in the US. This included tank level monitor fouling, filter fouling and downtime related to mechanical removal of solid deposits.

The operator, who had relied on minimising solid build-up to maintain safe and economical produced water injection and disposal, was experiencing scale precipitation on their tank level monitoring probes at six of their saltwater injection facilities, causing major system issues.

Once the tank level monitors failed, the system would need to be shut down for manual cleaning, which was expensive and time consuming at the rate in which they were failing. Scale build-up was severe enough to require costly mechanical removal every 3-4 weeks. In addition, the filter pods located before the high-pressure injection pumps had to be cleaned frequently.

Solids collected from the probes were a combination of carbonate and iron sulphide scale with varying levels of organic proportions. While carbonate scaling tendencies from water analysis on the inlet were low, due to the large volume of water traveling through each facility, major scaling issues were still observed.

A treatment upstream of the SWD with one of the novel, multi-functional products at a 35 ppm continuous dose rate was proposed with an additional treatment at the inlet. This formulation was also recommended as a standalone treatment at a dose rate of 25 ppm on the lines feeding the smaller facilities.

Over a 4-month period, careful field observations were made to determine if the new treatment program was working. A visible reduction in turbidity and opaqueness of the water in the tanks can clearly be seen. Since the application of the multi-functional product, the tank level monitors have not failed due to FeS and calcite scaling.

Notably, significant variability in the water sent to public SWDs can make treatment validation difficult with varying throughput and total filtered solids data. A further complication arises from the fact that performing iron sulphide performance testing in the field is difficult due to the presence of oxygen once the sample is collected. To prove product and programme performance analytically, both soluble and insoluble iron measurements were taken.

Total and filtered iron were tracked during this new chemical application. Average soluble and insoluble iron collected at the largest SWD clearly showed an increasing trend in soluble iron and an overall decrease in the insoluble iron compared to the untreated sample.

The recommended treatment of the multi-functional formulation in this SWD application was a success and provided:

• Safer, more effective day-to-day operations.
• Unfailing tank level probes since the application was started.
• Significantly improved water quality.
• Reduced facility downtime by not having to clean tank probes.
• Calculated average reduction of 5,600 lbs. of insoluble iron per year.

Eradicating requirements for system shutdowns
Continuous application of the product containing the novel, non-corrosive iron sulphide dissolver eliminated the need for system shutdowns to clean the tank level monitors and reduced the frequency for filter changing. The water quality visibly improved, becoming clear and transparent. The soluble iron trends were reversed after the product was applied, indicating FeS was being dissolved. Overall, the method used to identify a multi-functional product to address iron sulphide and calcite scale was successful.