J. M. Getliff and S. G. James, SPE, Dowell division of Schlumberger Evaluation and Production Services (UK) Ltd.
Alkyl-phenol ethoxylates (APEO) are a class of surfactants which have been used widely in the drilling fluid industry. The popularity of these surfactants is based on their cost effectiveness, availability and the range of hydrophilic-lipophilic balance values obtainable. Studies have shown that APEOs exhibit oestrogenic effects, and can cause sterility in some male aquatic species. This may have subsequent human consequences and such problems have lead to a banning of their use in some countries and agreements to phase out their use e.g. PARCOM recommendation 92/8.
The use of APEOs as additives in detergents, lubricants and stuck-pipe release agents for drilling fluid applications is discussed. The effectiveness of products formulated with APEOs are directly compared with alternative products which are nonpersistent and less damaging to aquatic species. Lubricity measurements using standard and in-house designed equipment and washing tests to compare the efficiency of surfactants are explained and product performance results presented.
The results show that alternatives to products containing APEOs are available and that in some cases they show a better technical performance. In addition to the improved environmental acceptability of the base chemicals, the better performance enables lower concentrations to be used, hence reducing the environmental impact even further.
Alkyl-phenol ethoxylate surfactants have been used for many years in a wide range of applications such as detergents, paints, herbicides and pesticides and they are also widely used in the oil industry. APEOs were first introduced into the UK in the 1940s and have become the 2nd largest group of non-ionic surfactants with worldwide production of 390,000 tonnes per annum.
Concern has increased recently about the widespread usage of APEOs because of their relatively stable biodegradation metabolites, especially the compounds nonylphenol and octylphenol, and their oestrogenic properties. This is part of a wider problem that includes other oestrogenic xenobiotics such as pthalates, bisphenol-A, PCBs and dioxins. This paper is particularly concerned with APEOs which are widely used in the oilfield but have several negative ecotoxicological characteristics that make their environmental acceptability questionable.
The microbial degradation, particularly during waste water treatment, of products containing APEOs results in refractory metabolites that are resistant to further biodegradation and are more toxic than their parent compounds. Nonylphenol has been demonstrated to be toxic to both marine and freshwater species, to induce oestrogenic responses in male trout, and may bioaccumulate in freshwater organisms. Concern over their possible environmental effects has led to the banning of NPEOs from cleaning products in Germany and Switzerland.
Norway has also banned their use offshore and APEOs are no longer used in household detergents in many European countries where usage is declining. A voluntary ban has been introduced on their domestic use in the UK and OSPARCOM (formerly known as PARCOM) has agreed that, as of January 1995, NPEOs and similar substances should no longer be used in domestic cleaning agents. Likewise OSPARCOM members have also agreed that they will no longer be used in industrial cleaning agents by the year 2000. In spite of this they are still widely used in many other large industrialized countries e.g. the US & Japan and are used in many other products and formulations where suitable replacement products have yet to be found. This paper attempts to describe in broad terms the environmental problems associated with APEOs and discusses how the environmental properties of drilling fluid additives and oil field chemicals can be improved by the removal of APEOs by direct omission, replacement with linear alcohol ethoxylates or the use of completely different chemistry.