The world doesn’t stand still, even in pipeline pigging operations and materials.

Pigging has been in existence for over 100 years, with first operations being the removal of deposits and to prove

lines were clear of restriction. Today, the variety of different types of pigging operations has increased, yet many of the original pipeline challenges remain and there continues to be a reportedly high incidence

of pipelines being in a vulnerable condition due to improper maintenance.

Many existing and new lines are difficult to pig using conventional pigging tools, due to significant diameter

changes, short radius bends, and a lack of pig launching and receiving facilities.

With the current pricing challenge, there is a growing need to investigate and utilise effective and innovative methods and materials to provide essential cost savings through both improved production and reduced service costs.

Amidst this, the development and refinement of pig technology has continued. Over the last five years,

Aubin has developed new materials and techniques in response to limitations in existing methods, equipment and

materials. These include the introduction of the EVO-Pig range of pipeline pigs, which shares some similarities with mechanical and foam pigs but have a number of additional beneficial features. Aubin has also developed and improved pipeline gel pig fluids, which are generally used in conjunction with a pig. This article will provide an introduction to these two related but different technologies, and includes short case history summaries.

Novel pigsAubin’s EVO-Pigs (Figure 1) have unique properties which evolved for applications outwith the capabilities of mechanical pigs.

They do not require conventional pig launching and receiving facilities. Although very flexible to accommodate short radius bends

BREAKING WITH

Neil Johnston, Aubin, UK, introduces

two non-traditional pigging technologies that bring significant

benefits to the customer.

and 50% diameter reductions, the material is essentially incompressible. With diameter reduction, foam pigs change their mechanical properties and compress and harden. In contrast, EVO-Pigs increase in length to maintain the same volume. By having ‘shape memory’, they return to their original diameter after exiting the restriction. There are variants, the most commonly used are EVO-Pig LG (formerly L-Gel) for standard temperatures, and EVO-Pig XT for extreme temperatures. Their features, (depending on variant*), are:

) Elastic, incompressible, negotiate diameter restriction and short radius bends.

) Used in flexible lines, non-damaging to internal linings.

) Provides good fluid separation, e.g. for product batching in multi-fluid lines.

) Variable density, e.g. for easy recovery.

) No need for pig launcher/receiver, supplied in launch canister.

) May be extruded through suitable port.

) In certain circumstances, may be formed in-situ, inside pipe.

) Chemically compatible with most pipeline fluids.*

) Non-hazardous materials.

) Wide temperature range, -20 to +90°C.*

) Slight surface swelling in contact with oil or water*, improves seal.

EVO-Pigs have many applications. As they conform readily to different diameters they have little scraping action, but may be used with pick-up gels to remove loose debris. This is also an advantage in applications where the deposit is dissolved, not scraped off. EVO-Pigs are used in pipe flooding and dewatering applications, and are particularly useful subsea and expelled through a check valve or similar. EVO-Pigs are useful in line proving, where there is risk of a mechanical pig blocking the line.

Despite their elasticity, some remarkable pieces of debris have been removed. Figure 2 shows a 4 x 4 in. fence post, 1.5 m long that was removed from a 17 km, 16 in. dia. oil pipeline (if anyone has lost a fence post that fits this description please let us know!). The line was described as being ‘in a vulnerable condition’, with barred tees and notable diameter restrictions making it too risky to pig conventionally. Figure 3 shows EVO-Pig after use. Due to the nature of the material, some damage to the pig may occur, but this does not usually affect performance.

Pipeline dewateringIn a recent subsea 10 in. production pipeline dewatering operation in the North Sea, the operator could not use conventional pigs as there was a 10 - 6 in. reduction at the manifold header – a novel solution was required. Aubin proposed a single EVO-Pig to push dyed glycol/water 12 km at 0.25 - 0.5 m/s, exiting via a 2 in. subsea check valve. The EVO-Pig was launched from a bespoke high pressure canister and driven with nitrogen. Dewatering was a complete success, despite the significant diameter change.

Gel pigging for pipeline cleaningThere have recently been articles describing the use of gelled fluids in pipelines as being an innovative application of downhole completions technology. However, pipeline gel cleaning dates back to the late 1970s. It would appear that, perhaps as a consequence of the ‘Big Crew Change’, many experienced pipeline engineers are retiring, taking their gel pigging knowledge with them. New commissioning and maintenance engineers are not always familiar with this valuable technique established by their predecessors.

The additional benefits of gel pig cleaning trains compared with conventional pigging are well established:

) Pick up, suspend and transport debris out of line.

) Greatly increase the amount of debris removed.

Figure 1. EVO-Pig traversing 50% diameter reduction.

Figure 2. Wooden post removed by EVO-Pig.

World Pipelines / REPRINTED FROM JULY 2015

) Cleaning in a single pass, saving time.

) Enhance mechanical pig performance, pig lubrication, reduced bulldozing of debris and less risk of pig sticking.

) Verifiable estimate of debris removed and remaining.

) Useful in critical applications such as black powder removal before inline inspection.

Versatile materialsTo provide the best performance, Aubin pipeline gels are based on a variety of fluids such as freshwater, seawater, hydrocarbon, finished product (e.g. diesel) organic solvent, alcohols and glycols. Aubin’s MEG Gel is particularly useful in spool filling during pipeline construction, where the reduction of ingress helps prevent problems after commissioning caused by water, chloride ion or debris contamination.

Aubin has recently developed both hydrocarbon-based and environmentally friendly water-based gels to provide improved performance in resistance to dilution and debris carrying performance in variable pigging speed scenarios. In the past, pipeline gels have occasionally failed to adequately suspend and carry heavy debris out of the line due to dilution, bypass, or picking up excess fluid in the debris. This can cause the theological properties of the gel to deteriorate until suspension of the debris is compromised. Similarly, there have been problems reported when the pig velocity falls below the optimal pigging speed of 0.5 - 2 m/s. This can provoke the sedimentation of debris in some gels where there is insufficient turbulence to keep the debris in suspension. The consequence is a debris concentration at the 6 o’clock position, which can then accumulates in front of a mechanical pig, to the extent that it may stick – very undesirable. In contrast, Aubin’s Pipeline Gel DP can suspend heavy solids at a wide variety of pig speeds, and can tolerate 50% dilution and complete flow shut down. Suspending debris for prolonged periods; the pipeline gel train may even be ‘parked’ for periods of hours, even days, without significant debris drop out. Aubin’s hydrocarbon-based petrogel fluids provides similar options when water-based fluids are undesirable. They normally utilise diesel as the base fluid, although other hydrocarbons and solvents can be used following testing. Figure 4 shows standard Petrogel DP next to an identical sample containing 10% of debris (sand). After 24 hours static, no sedimentation of debris has taken place.

De-oilingA Middle East offshore subsea pipeline system consisting of two 10 in. pipelines and 16 in. header was being repurposed to provide water for emergency firefighting, therefore it was necessary to maximise oil recovery from the line prior to use (Figure 5).

Aubin’s water-based separator gel, Pipeline Gel 33, was used

due to the high viscosity of the oil (up to 140 cSt at 50˚C). The gel was supplied in its concentrate form to aid transport; 6000 litres of gel was produced, cross-linked and injected through the 12 in. flexible riser and into the 16 in. header. Treated seawater pushed the slug into the two 10 in. lines and finally to onshore storage tanks. The line was successfully de-oiled and 344 m3 of residual crude oil recovered. The use of Aubin pipeline gel had other advantages: a reduction in the time required to meet oil in water specifications; reduced water and treating chemical consumption; and lower liquid processing

Figure 3. EVO-Pig after removing post.

Figure 4. Petrogel DP sand suspension, 24 hours static.

Figure 5. Gel assisted de-oiling, field diagram.

REPRINTED FROM JULY 2015 / World Pipelines

and disposal costs, with an associated environmental benefit. Figures 6 and 7 show the blending configuration.

SummaryAubin is a leading developer and distributer of chemical technology to the oil and gas industry. Its success in delivering solutions to global markets has been rewarded through the recent receipt of the Queen’s Award for International Trade, the highest accolade in the UK. In an industry where one size seldom fits all, Aubin responds to clients’ particular requirements, with materials and method selected or modified to suit individual requirements.

The description of methods and case histories included in this article demonstrate that substantial savings in infrastructure costs can be made through the utilisation of recently introduced, non-traditional, pigging methods. In certain cases, where permitted by pipeline design and operations, it may be possible to consider omission of traditional, expensive, permanent pigging launcher and receiver installations, and utilise the innovative pigging methods described here. The risks of pigging challenging lines, either due to extreme diameter and bend limitations, or poor physical pipeline condition, can be reduced by the use of less aggressive methods and materials such as Aubin’s EVO-Pigs. New pipeline gels and methods provide increased flexibility in repurposing operations such as de-oiling, with associated saving in cost and time. From the financial point of view, these effective and environmentally responsible technologies have been proven to provide significant benefits to the customer.

Figure 6. Gel mixing equipment.

Figure 7. Riser injection manifold.

World Pipelines / REPRINTED FROM JULY 2015