The Application of Wax Dissolver in the Enhancement of Export Line Cleaning

Abstract

Paraffin deposition in oil export pipelines can prove problematic during "intelligent pigging" operations, when hydrocarbon deposits on pipe walls are not removed sufficiently during the cleaning phase. This gives rise to sensor clogging and lift-off causing inaccurate and in some cases complete loss of data from the inspection tool.In pipelines where paraffin deposition has caused problems, specific wax dissolvers in tailored treatments have been applied during pigging programmes to aid the removal of deposits from pipe walls and to prevent further wax deposition. This paper will discuss the selection and application of these wax dissolvers and the results obtained on applying the products in field. The laboratory methods used to evaluate and select a wax dissolver and the process of modifying the amount of chemical required will be discussed in this paper. The paper will also discuss the interaction of these dissolvers with specific hydrocarbon deposits. Furthermore, we will compare the characteristics of wax deposits retrieved from pigging programmes prior to and during dissolver application. This paper will demonstrate that in certain North Sea fields the physical characteristics of pig waxes altered when dissolver was applied, allowing hydrocarbon deposits to be removed more effectively from the export pipeline and enhancing the cleaning phase of the pigging programme. The application of wax dissolvers prior to and during export pipeline cleaning programmes, in preparation for intelligent pig runs, has proven beneficial where waxy crudes are being exported. The introduction of such chemical injection regimes has improved the removal of hydrocarbon wax deposits from export pipelines and has allowed meaningful data to be retrieved during intelligent pig runs. Introduction Paraffin waxes are a normal component of crude oil and should therefore be viewed as a valuable source of potential refined products, however their deposition can lead to many process problems1. The presence of paraffin waxes in crude oils can deliver a number of problems to the producer, transporter and refiner. These problems can vary from minor to severe depending on the nature and quantity of the wax deposited. Therefore the assessment of wax deposition is extremely important in the oil and gas industry. An application where wax deposition may cause problems is in the use of "intelligent pigging" for data collection in transport pipelines2, 3. Here, although the quantity of wax deposited may not be significant, the nature of the wax deposited and the location of wax deposition can lead to severe and frustrating problems in the collection of data and subsequent interpretation as to the internal condition of critical transportation lines. This occurs when insufficient mechanical cleaning (pigging)3 results in the remaining waxy hydrocarbons depositing on the intelligent pig sensors, which leads to incomplete collection of data from the inspection tool. In some cases wax deposition can even cause removal of the sensors from the inspection tool and therefore a total loss of data4, 5. It is estimated that the costs associated with an intelligent inspection run in the North Sea basin are on average $50,0006 and that to receive little and / or inconclusive data makes this an expensive and wasteful exercise. More importantly the internal condition of the transportation pipe is still unknown. We have proposed and shown that the selective use of specific wax dissolvers in tailored treatment programmes can minimise and completely eliminate this problem.

Development, Testing, and Field Application of a Heavy-Oil Pipeline-Cleaning Chemical: A Cradle-to-Grave Case History

“…Oil naturally contains paraffins, asphaltenes, and naphthenates. During transport in a pipeline, these can precipitate and adhere to the walls of the pipeline (Craddock et al 2007).…”