TAILIEUCHUNG - PIPELINE PIGGING TECHNOLOGY- P10

PIPELINE PIGGING TECHNOLOGY- P10: Why pig a pipeline? This paper introduces a number of reasons for doing so, together with a discussion of the advantages and alternatives. In general terms, however, pigging is not an operation to be undertaken lightly. There are often technical problems to be resolved and the operation requires careful control and co-ordination. | Pipeline Pigging Technology 1. they are capable of withstanding a significant differential pressure 2. the system has to be reliable and repeatable with fail-safe systems to prevent failure 3. the barrier system has to be easily introduce into the pipeline 4. the barrier system should not cause any damage either to the pipe wall or to the integrity of the pipeline system 5. the system has to be easily removable following completion of the work. GEL ISOLATION Through its downhole applications Nowsco has developed a cross-linked aqueous-based gelling system which has been used for temporary abandonment of well bores. The properties of this particular gel are well known and in practise lengths of gel 15O-2OOft long placed inside 7-in internal diameter pipe have been able to withstand in excess of 250psi differential pressure. The major field problem with this particular system is that gellation takes place rapidly and the plug has to be displaced into location within a very short time for it to be able to form a coherent barrier. Gel technology has also been used extensively by Nowsco in the pipeline commissioning field where both aqueous and hydrocarbon systems were used to clean pig and lay down chemicals on pipelines at the time of commissioning and also subsequently during their operational life. Using this experience as a database it was decided to develop a gel system which could be pumped into place where the gel would have a controlled gellation time and an controlled viscosity enabling it temporarily to isolate a pipeline system. The design criteria also called for the life of the gel plug to be accurately determined this was carried out by chemically controlling the degradation of the gel after a predetermined time. To enable the testing to take place pipeline test loops were built and extensive research undertaken in the laboratory in the UK. The test loop design was slightly unusual in so much that air-actuated valves allowed the gel train to go round the

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