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A Methodology to Investigate Factors Governing the Restart Pressure of a Malaysian Waxy Crude Oil Pipeline

Abstract : Waxy crude oils account for about 20% of world oil reserves. Wax gelation due to pipeline operating at low ambient temperature, especially in subsea environment, is a worst-case scenario that operators fear most since the gel can potentially block the entire pipeline, if it is not managed early. Restart pressure calculation is the first step to assess severity of gelation and subsequently used to plan for the mitigation strategies which are translated into project CAPEX (Capital Expenditure) and OPEX (Operating Expenditure). Gel characteristic (i.e. rheology behaviour and gel compressibility), operating conditions (oil temperature, ambient temperature and oil flow rate) and pipeline geometry (length and diameter) are known factors governing the restart pressure calculation for a gelled waxy pipeline. Malaysian waxy crude oils are unique and have distinctive rheology which differ from waxy crude oils from other regions mainly due to high gel yield stress of more than 500 Pa with potential failure to recovery from gelation. Hence, accurate restart pressure prediction that account for all the governing factors as well as the interplay between them, are crucial for safe operation and cost-effective mitigation strategies. A conservative approach where the entire gel is assumed to yield simultaneously is frequently used but this simple approach fails to take into account many factors, resulting in an overestimation of the restart pressure. Several improved restart pressure calculation methods have been proposed in literature. In this study, an original methodology developed by IFPEN, has been applied to predict the restart pressure of a Malaysian waxy crude oil pipeline at various conditions. The main benefit of this methodology comes from its ability to consider the conditions under which the gel has been formed, that produces a more realistic description where gel strength varies along a pipeline. The case study highlighted that Conservative laws, assuming a homogeneous gel structure everywhere in the pipe, can overestimate the restart pressure by a factor of up to 100 times than a heterogenous gel. Thanks to the 2D axisymmetric description of the pipeline gel, we showed that the shape and the location of the gel also impact the restart pressure.
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Submitted on : Tuesday, March 8, 2022 - 4:25:19 PM
Last modification on : Monday, March 14, 2022 - 12:44:48 PM
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Guillaume Vinay, Petrus Tri Bhaskoro, Isabelle Hénaut, Mior Zaiga Sariman, Astriyana Anuar, et al.. A Methodology to Investigate Factors Governing the Restart Pressure of a Malaysian Waxy Crude Oil Pipeline. Journal of Petroleum Science and Engineering, Elsevier, 2022, 208, pp.109785. ⟨10.1016/j.petrol.2021.109785⟩. ⟨hal-03601996⟩



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