Publications

The following Technical Papers are available for download: -

1. Pipeline Flooding, Dewatering and Venting - Aidan O'Donoghue, PPSA Conference London, December 2004

Flooding, cleaning, gauging, dewatering and venting of offshore oil and gas pipelines during pre-commissioning involves pipeline pigging and expensive deployment vessel time. To aid in the planning of such operations, a number of analyses can be undertaken to determine the duration to perform each of these tasks. The mathematical models can also optimise the equipment required (hoses, pumps, compressors). Problems that could be encountered without a clear knowledge of how the operation will proceed can be avoided. The operation can be monitored by comparing recorded and predicted values, for example inlet pressure. This paper provides an overview of work performed to establish pig velocity, inlet pressure and pigging duration during various pre-commissioning tasks.

2. Pigging as a Flow Assurance Solution – Estimating Pigging Frequency for Dewaxing - Aidan O'Donoghue, Pipeline Pigging Conference, Amsterdam, May 2004

Pigging is used widely for removal of wax build-up on the internal wall of a pipeline. Much information is available on the prediction of wax deposition levels in such lines and pigs play an important role in the removal of this expected wax accumulation. Although these tools are generally much cheaper than chemicals for wax inhibition or suppression, there is very little guidance available for the selection of the correct pig, the sizing of bypass ports and the pigging frequency. Incorrect selection can be dangerous since a significant build-up of wax ahead of the pig can plug the pipeline. This can lead to extended downtime and an expensive pipeline repair. For subsea launching, extending the time between pigging is advantageous since this means that fewer interventions are required to load the subsea launcher. Correct selection of the pigging frequency is therefore very important. This paper aims to provide direction on this subject, using the output from wax prediction models and expected daily wax build-up in the pipeline. The method outline can be used to determine a pigging strategy for pipeline start-ups; pigging at low flow; cleaning normally unpigged lines; progressive cleaning of problem lines and regular pigging of lines with full information on wax deposition or merely an indication of wax percentage in the flow.

3. Why Pigs get Stuck, and how to avoid it - Aidan O'Donoghue, Pipeline Pigging Conference, Amsterdam, October 2002

Operators and contractors have been running pigs successfully for years. Every so often, a problem occurs and one becomes stuck, stalled or damaged in the pipeline. As the need for innovative one-off pigs for specialist applications arises, the risk of this occurring increases. Sufficient planning and analysis should be performed to allow the pigs to run successfully and perform their duty in the line effectively. This includes stringent testing, CAD work and analysis. This paper looks at the main reasons for pigs sticking and stalling in lines and examines what can be done about it. The paper looks at several different categories of failures, identifies the root cause of the problem and looks at how these scenarios might best be avoided. The figures at the back of the paper may be used as guidelines for consideration and avoidance of the problems discussed.

4. Latest Design Techniques for Dual and Multidiameter pigs - Aidan O'Donoghue, Pipeline Pigging Conference, Houston, January 2001

The aim of this work is to show how design and simulation techniques can provide a greater insight into the nature of pig motion and how pigs behave in pipelines. A number of such methods used to investigate and improve the reliability and efficiency of dual and multidiameter pipeline pigs are described. A case study is presented based on actual field examples. The problem of pig selection for a dual diameter application is investigated followed by an analysis of pig efficiency during a dewatering operation. The transient motion of the pig, because of the sudden change in friction when negotiating the reducer, is presented using the Piglab model. Conceptual and detailed design and simulation of pig performance can allow pigs to be built that will perform more satisfactorily in the line, help reduce fear of stalling, and lead to innovative design solutions.

5. Dynamic Simulation of the Norne Heidrun 10" x 16" Dewatering Pig - Aidan O'Donoghue, Pipes and Pipeline International, January/February 2001

The 10" x 16" Norne Heidrun pipeline presents a considerable challenge in terms of pig development for both pre-commissioning and operations. The RFO (Ready for Operation) Department at Statoil in Stavanger has developed the pre-commissioning concept which employs five 10" x 16" Dual Diameter pigs, Figure 1, for pipeline dewatering. The Åsgard 42" x 28" Dual Diameter pigs are the basis for this concept [1, 2]. These pigs employ a wheel suspension system for centralisation in the large pipeline. Buckle Inducers are used for efficiently folding the 16" seals into the 10" line. Correct selection of seal geometry and properties allows the seals to buckle when required and recover sufficiently from compression set. The dewatering pig train consists of four pigs run with a glycol batch between each and a trailing final pig run in dry air or nitrogen. As the final pig exits the 10" flexible and enters the 16" line, a potential problem arises. Due to the sudden drop in friction, the pig will accelerate suddenly to a relatively high velocity. Such acceleration can cause the pig to compress the gas in front of it, decelerate and finally reverse. Therefore, the final pig could potentially reverse into the 16" Y-piece thus damaging either the Y or the pig. This scenario must be avoided.

6. Multi diameter pigging for Åsgard, Commissioning and pigging the 710km 42" x 28" Åsgard Pipeline - Christian Falck, Aidan O'Donoghue, OPT Conference, Oslo, 2000

Statoil has designed and tested dual diameter pipeline pigs to perform various tasks during operations, precommissioning and commissioning of the 710km 42"x28" Åsgard pipeline. The concepts developed have been put through a major design and testing program to demonstrate that the various functional requirements have been met. The paper describes the development process as well as field experience from the initial pigging runs of the Åsgard Pipeline.

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