Clariant Oil Services Polymeric Halite Scale Inhibitor Proves Highly Efficient and Effective

• Polymeric inhibitor negates the requirement for copious fresh water injections, whilst still inhibiting halite formation
• Application of SCALETREAT HL 8430 led to a decrease in integrity risk caused by oxygen ingress
• The cost of the polymeric inhibitor was significantly outweighed by the lower fresh water requirement and the associated logistical cost savings
• Injection of SCALETREAT HL 8430 and the reduced water content resulted in a lower water cut and, therefore, a higher well PI

Background

The operator of a field in the South Timbalier area of the Gulf of Mexico, USA, was treating several wells for control of halite deposition by pumping fresh water down the annulus to dilute the produced water. Approximately 1,150 litres per day of fresh water was pumped down one particular well (Well B1), and when injection went offline, a differential pressure began to build on the flowline after only 10 minutes. The process trends of Well B1 and the water chemistry have been summarized in the table on page 2. 

Because every few weeks it was necessary to shut the well in and bullhead fresh water down the well tubing to remove the build-up of halite scale, Clariant Oil Services performed multiple modelling and laboratory experimentations. Results confirmed that in fact, 2,500 litres per day of fresh water injection was required to completely inhibit the halite deposition. Unfortunately, this was not possible due to restrictions in pump sizing and the risk to the annulus integrity that this would impose. Additionally, this would have a large impact on gas and condensate production.

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Modelling performed by the Application Development Group of Clariant Oil Services showed a high tendency for halite scale to form in the produced water in all parts of the tubing. The driving force was temperature; with decreasing temperature, precipitation potential increased exponentially.

Modelling the effect of 1,150 litres per day of fresh water showed that, while very much reduced, this was not enough dilution to completely prevent halite deposition; however, this was the operational maximum of fresh water that could be delivered to the well. Modelling showed that injection of 2,500 litres per day of fresh water would provide sufficient dilution to completely prevent halite deposition. 

Laboratory experimentations were then performed to confirm the modelling, as well as to evaluate alternative chemical inhibitor application for the prevention of halite deposition. Real produced water was used to determine the effect of dilution and chemical addition by cooling the water in a static jar test after heating to dissolve all the salt.

Results of the experimentation are shown in the photos below. The blank test had significant salt deposition that can be seen after cooling the produced water down from 92 to 37°C. The set of jars on the right show the effects of adding progressively increasing amounts of SCALETREAT HL 8430, a polymeric halite inhibitor chemistry.

A clear deposition on the bottom of the Blank jar can be seen after allowing settling to occur. The inhibited tests show some settling and high bulk precipitation (as a dispersion of halite) in the jars that had 100 and 200 ppm of SCALETREAT HL 8430 added to them. Only a slight haze of halite was seen with 300 ppm of SCALETREAT HL 8430, and deposition of halite was completely controlled with 400 and 500 ppm of SCALETREAT HL 8430.

The final field recommendation was to inject 500 ppm of SCALETREAT HL 8430 to the well (based on the produced water rate), coupled with the lowest amount of fresh water that the pump could deliver on the minimum turndown (approximately 120 litres per day).

Final optimization occurred in the field, as there was still a small dilution effect of the fresh water used to carry the SCALETREAT HL 8430. This, along with the dynamics of the system, showed that 300 ppm of SCALETREAT HL 8430 was sufficient to inhibit the formation of halite scale. This was determined by monitoring the differential pressure in the flowline along with the tubing head pressure and well flow rates. 

This successful application had a number of significant benefits, which included cost reductions due to the decreased amount of fresh water required to be injected, as well as associated costs of transporting this offshore. Well integrity was improved as less oxygenated fresh water was being injected, well production increased due to the halt of bull head treatments and a higher PI was realized due to less liquid loading. 

Inhibitor Evaluation of SCALETREAT HL 8430:

From left to right: Blank (notice the significant halite deposition in the bottom of the jar), with SCALETREAT HL 8430 at 100 ppm, 200 ppm, 300 ppm, 400 ppm and 500 ppm.

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