Abstract

This paper describes the change of the chemical flow assurance mitigation strategy for a major deep water waxy crude oil pipeline in SE Asia. The case relates to an application of a Pour Point Depressant (PPD)/Wax Inhibitor (WI) chemical that is critical in maintaining subsea flow assurance due to cooling of a waxy crude oil over the length of the 210 km deep water subsea pipeline. The paper further describes how the injection strategy was successfully changed. New chemical key performance indicators (KPIs) were initially determined based on chemical performance and risk mitigation requirements. Results of the laboratory new chemical formulation, qualification and subsequent successful field trial are presented. Other significant benefits yields are also discussed.

KPI targets for the PPD/WI application were first determined based on field application performance and requirements. Candidate PPD/WI chemicals were selected based on the KPI requirements and initially screened to evaluate performance in reducing the crude oil pour point. Product development was then further refined once a definitive correlation between chemical structure and performance for the specific waxy crude oil was identified. Subsequently, more detailed laboratory testings were performed, including rheology measurements, coaxial shearing paraffin deposition and dynamic wax flow loop measurements. Field trial was later conducted to gradually obtain the optimum dosage while closely monitoring both onsite and in the lab to confirm the product effectiveness.

Key to the success of the change was the identification of the opportunity to switch the PPD injection from subsea to topsides. This decision enabled a much wider portfolio of PPD chemistries to be evaluated. New topside PPD was identified which was able to reduce the pour point of the crude oil from 18°C to 9°C using a low dose rate of ~100 ppm, which is a ~40% reduction in chemical consumption compared to the previous chemical used. The new chemical was piloted without any disruption to the facilities and/or production. Furthermore, the field trial created significant benefits by reducing OPEX through the reduction in waxy pigging debris and chemical logistics, improving HSE and reducing the risk of chemical non-deliverability due to umbilical blockages.

This paper demonstrates the re-evaluation of a field’s flow assurance strategy to realize significant benefits by challenging conventional wisdom regarding the need for subsea PPD/WI injection in waxy deep water fields. Understanding the gel strength of the crude through detailed evaluation and monitoring of the shear force needed to break the gel during a shutdown by using an optimized PPD/WI product/dosage is an important parameter to look at to ensure effective field optimization, rather than relying on the standard method of pour point monitoring.

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