Clariant Oil Services Prevents Asphaltene Deposits in Subsea Flowlines

• Successful prevention of asphaltene deposits ensure flow assurance integrity
• Field optimization led to a 40% reduction of the chemical dose rate creating logistical cost savings
• Decrease in overall chemical cost spend as a result of injection optimization
• No application challenges or evidence of asphaltene deposits since treatment began

Background

A major producer in the UK sector of the North Sea was evaluating start-up requirements for a new offshore subsea field. All production was to flow via an 8” flowline to the host FPSO located 1.5 km away, in 100 m water depth with a reservoir temperature of 102oC and pressure of 5,000 psi.

In-depth assessments of the field characteristics were undertaken by independent third party laboratories and consultants to assess possible flow assurance challenges. An initial SARA analysis (tabled below) shows that this crude oil had the potential for unstable asphaltene deposition.

Further studies determined that, while the colloidal instability index and asphaltene/resin levels were low, the density and bubble point conditions were considered favorable for asphaltene deposition. As a result, deployment of an asphaltene inhibitor was recommended.

As the incumbent chemical solutions provider with more than 10 years of continuous support to the operator’s other North Sea assets, Clariant Oil Services was invited to evaluate and recommend a suitable product that would prevent any problems from occurring. Due to the subsea nature of the application, the product was required to meet stringent stability requirements, as well as compatibility with materials and cleanliness specification (<NAS-6) prior to injection down the subsea umbilical.

Clariant Oil Services Solutions and Value Delivered

After a thorough review and system analysis, Clariant Oil Services developed FLOTREAT DF 3167, an asphaltene inhibitor, to meet all of the operator’s requirements. Laboratory tests indicated an initial treatment of FLOTREAT DF 3167 to be 50 ppm, injected continuously from field start-up. See Figure 1 on page 3.

After two years of successful operation, a field optimization trial was undertaken to determine if a lower dose rate of FLOTREAT DF 3167 would maintain performance level, while also decreasing costs; results indicated a successful dose rate reduction of 40% (see Figure 2 on page 3). Additionally, since its application, no further problems or evidence of asphaltene deposits have been reported.

Figure 1: Performance of FLOTREAT DF 3167 vs. Blank in laboratory tests

Figure 2: Dose rate reduction during FLOTREAT DF 3167 field optimization trial

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