Maxoil Presentation on an Integrated Approach to Designing Systems for Handling Severe Naphthenates / Soaps Problems at the TEKNA OFCS 2014 Conference

9 Apr 2014

By Colin Smith, Production Chemistry Consultant, Maxoil Solutions.

As part of this 25th Oil Field Chemistry Symposium (OFCS) held in Geilo, Norway, Colin Smith was invited to give a talk about an integrated approach to designing systems for handling severe naphthenates/soaps problems. 

OFCS 2014

The idea of this conference was to address the upcoming challenges facing production chemistry and would specifically focus on corrosion, separation and deposition challenges faced in both current production environments as well as the new challenges facing production from unconventional reservoirs and in new frontiers. 

Production chemistry remains a significant challenge to oil and gas production both in mature/late life fields and also in the new green field and unconventional developments. Deposition (including inorganic scales and organic deposits), corrosion and separation remain key challenges requiring technical solutions to ensure continued production from ageing fields which are often producing way beyond their original design life.  The move towards more unconventional reservoirs such as heavy oils and shale gas and more challenging environments such as arctic production environments and the ongoing drive to subsea production ensures that production chemistry will remain an ongoing challenge where technological advances and experienced production chemists will continue to play a critical role in the future of oil and gas production. 

Naphthenates and Soap Emulsions

Calcium naphthenate and carboxylate soap type production problems have occurred in the oil and gas industry since the 1960s but have only been popularised since the year 2000.  Such operational problems have become a global phenomenon, from the North Sea to Africa, SE Asia, Australia and South America, with known ‘hot beds’ of these problems becoming evident, e.g. SE Asia for carboxylate soaps and west Africa for calcium naphthenates. 

What are Naphthenate Solids and Soap Emulsions?

It is the view of this author that naphthenate solids, commonly called Calcium Naphthenates, are formed from reactions between specific cyclic naphthenic acids, known as ARN acids (or Tetra Protic Acids, TPAs), along with certain other high molecular weight naphthenic acids from the oil phase and divalent cations (such as Ca, Mg and Fe) from the produced water phase, while carboxylate soaps form via a saponification type reaction between linear fatty (carboxylic acids) from the oil phase and monovalent cations such as Na and K from the water phase, with bicarbonate incorporated in the reaction.  Some authors have preferred to classify these two materials as Calcium and Sodium Naphthenates for ease of identification but this author retains the older more correct terminology.

Naphthenates tend to become fouling solids while carboxylates typically become major components in viscous forward emulsions and accumulate as oil – water interface sludges in topsides separation vessels.

How do these Materials Form?

As production fluids (produced oil and water) flow from oil and gas reservoirs to surface facilities, via production well tubing, they experience gradual drops in pressure.  Below the bubble point of the fluids, gases are lost from the hydro-carbon liquid phase to the gas phase.  Acidic gases such as carbon dioxide (CO2) are also lost to the gas phase which causes the pH of the water present to shift to more neutral values and this is the driving force for reactions between specific naphthenic or fatty acids in the oil (which become dissociated) to react with ions in the water phase, e.g. Ca, Mg, Fe.  At certain water pHs, the salts of certain organic acids then become insoluble and so precipitate out to form naphthenate or soap materials.  Dry oils do not form these precipitated solids.   

Where do these Naphthenates and Carboxylate Soap Emulsions Form?

Particles of naphthenates and carboxylates are found downhole in well streams when the fluids are below their bubble point but they tend not to form deposits in well tubing, on valves or in subsea flowlines, being carried through to the topsides process facility. Naphthenates have been found as part of deposits on downhole ElectroSubmersible Pumps (ESPs), where the hot surface attracts them.  In most cases the naphthenate and soap solids act as emulsifying agents, so in the presence of water droplets, they stay at droplet films and are carried through well streams to surface and only agglomerate after pressure drops across wellhead choke valves and on entry into separator vessels to form deposits (naphthenates) or oil-water interface emulsion pads (carboxylates).  From that point they can affect the performance of the oil dehydration and produced water treatment facilities detrimentally. 

Varieties of Naphthenates and Soaps

There are various types of naphthenates that can be found in oilfield fluids and the main types so far identified by this author include the following: 

  1. Calcium Naphthenates (fouling solids/scale)
  2. Sodium Carboxylates (Soap Emulsions)
  3. Calcium Carboxylates (Soap Emulsions)
  4. High Calcium Salt Crudes (oil-dispersable salts)
Solutions and Management

Since the late 1990s, operational problems caused by naphthenate and carboxylate soaps have occurred in production facilities, which then require remedial efforts and significant chemical treatment, both having to be developed under highly short term time periods to curb lost oil costs.  In other words, operators and service companies have been historically reactive to such problems. Nowadays, there are a number of different design schemes, operational strategies and chemical application control approaches published in the literature and in the author’s experience which can be included in facilities designs at the Concept Select stage of development projects, if the risk assessment for naphthenate foulants and/or carboxylate emulsion soaps is robust enough and indicative of major problems. In other words, more recent developments have been more proactive in designing out or mitigating the risk of these problems. 

As a result of ongoing research and development, operational experience, lessons learned and knowledge sharing a greater understanding of these issues has been gained within the oil industry.  In recent years it was not uncommon for an operator to tackle such issues with very little knowledge if any at all.  There is now enough knowledge to provide practical solutions to these issues at the oilfield development stage.  Additionally, production facilities hit with these issues, not previously risk assessed, can evaluate a solution more readily with the knowledge available; however planning at the design stage of a development is clearly preferable. 

Good design and preparation does not reduce effort required during production.  Not only do problems tend to be unique but constant monitoring and optimization is definitely required and as the fluids change over time, the nature of naphthenate scale and soap emulsion problems can vary over time also.  At the same time a good facility wide chemical management system must be in place that is compatible and integrated.  Attention must also be paid to additional issues that occur as a consequence of the deposit or emulsion or even the chemical treatment. 

No definitive solution has been identified for naphthenates or soaps but this talk by Maxoil Solutions provides a review of varying but proven strategies for control that if appreciated early or even later in production life, can result in successful management by application of an integrated approach.  As more knowledge is available, effort has been applied to the development stage through new innovative system designs. No particular approach is more effective but each one should be tailored to the particular development and how each specific production problem manifests itself.  Equally there is no ‘magic-bullet’ currently available to solve these problems. 

With prior knowledge of a naphthenate scale or a carboxylate soap risk then effective control and management is entirely possible and has now been done by a number of operators.  At the same time control and management is possible for a facility without prior knowledge of a risk; however the development of a holistic mitigation strategy will be complex and is likely to be unique.

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