Special Report: Vegetable esters make drilling fluids more environmentally friendly

June 13, 2005
Vegetable ester-based drilling fluids may satisfy demanding technical criteria and strict environmental standards for offshore work.

Vegetable ester-based drilling fluids may satisfy demanding technical criteria and strict environmental standards for offshore work.

The rising world energy demand has led to exploration for oil and gas in increasingly challenging environments. Exploration has extended into sensitive regions, particularly offshore. Wells drilled in deep water that are increasingly deviated, extended wells encountering borehole instability, and challenging geological formations are some of the drilling obstacles. The trend to reduce environmental impact has steadily increased over the last decade. Vegetable ester-based drilling fluids, derived from palm oil or palm kernel oil, satisfy both technical drilling and environmental criteria.

Drilling in extreme conditions is under considerable time and cost pressures and new technologies are constantly being developed. Today’s drilling fluids have to satisfy higher and higher technical criteria and uphold safety standards and environmental protection.

Modern fluids

Drilling deeper, faster, and safer are the goals for modern drilling. This means that drilling fluids must resist low temperatures at extreme water depths. Despite the changing exterior conditions, they must also be mechanically stable, withstanding, for example, differences in pressure and temperatures at various depths. High stability against hydrolysis is another desirable attribute.

Drilling speed, measured by rate of penetration, has economic implications. Modern drilling fluids must rapidly discharge drill cuttings and help maintain borehole stability. Even at high drilling speeds, fluids must be able to cool and lubricate the drill bit. Lubricity is of great importance when drilling extended and deviated wells, more and more common in offshore exploration. Ester-based muds have generally better lubricating properties than other non-aqueous fluids, providing support in deviated and extended reach operations. Drilling with ester fluids results in exceptionally well-gauged boreholes. Esters protect the geological formation, preventing the swelling of reactive clay and shale formations. Their excellent lubricating properties add to these advantages, providing support in deviated and extended reach operations.

Oil-based drilling fluids have been used since the late 1960s, especially in technically demanding wells. They are usually based on diesel or mineral oil. These oil-based muds (OBMs) are invert emulsions with the oily phase forming the outer phase, incorporating the inner, brine phase, stabilized by emulsifiers and other conditioning additives. Oil-based mud systems perform much better than water-based muds in borehole stabilization and allow faster penetration rates. One of their most important features is their high lubricity.

Major drawbacks of OBMs include their poor biodegradability in both aerobic and anaerobic conditions and their toxic properties. Mineral oils and most petrochemical synthetic fluids can pollute the marine environment when cuttings are disposed overboard or accidentally spilled because of their:

  • Low biodegradability.
  • High toxicity of aromatic compounds.
  • Severe impact on the seafloor sediments, bottom feeders, and the food chain.
  • Tainting of marine life, affecting its edibility.

In many parts of the world, including the US, UK, the Netherlands, Norway, Nigeria, and Australia, use of diesel and mineral oil-based drilling fluids in offshore operations is already either severely restricted or banned because of their negative impact on the environment.

In direct response to the need for high performance and environmentally safe alternatives to petroleum-based drilling fluids, common vegetable and fish oils have been tested. None of them, however, as yet offers the necessary chemical stability nor the rheological properties required.

Notwithstanding this, after considerable research and extensive testing, a high performance and biodegradable vegetable ester has been produced from palm and palm kernel oils. This ester is derived from raw vegetable material and has been produced in Malaysia since 1995. It has found widespread acceptance and application in offshore regions where pressure from the local environmental authorities has been mounting.

The biodegradable ester is an alternative to petroleum-based muds. Petroleum muds are costly and troublesome to process (offshore cuttings drying and fluid recovery; onshore transport for treatment and disposal). Vegetable-ester drill cuttings, in contrast, can be safely discharged into the ocean without harming the ecosystem.

The impact of drilling on health and the environment is constantly gaining in importance. Drilling fluids must not have a negative effect on people or on the environment. They should not smell, be toxic upon inhalation, cause skin irritation or poisoning. Drilling fluids must be biodegradable under aerobic and anaerobic conditions. Even if particles should pass into the food chain, they must not have a toxic effect on living creatures.

Unique properties

The unique ecotoxicological properties of esters have dramatically reduced the impact of drilling fluids on the marine environment. Ester-based fluids meet the highest US Environmental Protection Agency standards, satisfying the EPA’s 275-day biodegradation test and Leptocheirus LC50 toxicity test (Fig. 1).

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Ecological testing, in particular for marine toxicity and anaerobic sediment biodegradation (275-day test) are performed by various certified institutes. Scotland’s ERT (Orkney) Ltd., wholly owned by Naremco Technology International Ltd. and based in the Orkney Water Technology Center (OWTC) at the Flotta Island Oil Terminal, provides testing for the North Sea. Louisiana-based Environmental Enterprises USA Inc. (EE-USA) is among the companies offering such testing services in the US.

Seafloor surveys in the North Sea, Gulf of Mexico, offshore Australia, and Brunei, as well as ongoing toxicity testing with various marine species have confirmed the esters’ environmentally benign properties. All seabed surveys have documented short-term recoveries after disposal of ester cuttings (Fig. 2).

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Since their introduction in 1990 in Norwegian waters, vegetable esters have surpassed expectations. Although the chemical and drilling industries have produced alternatives to esters (mostly based on synthetic petrochemicals), esters have thus consistently outperformed them by:

  • Showing excellent ecotoxicological properties (Table 1), in particular, high anaerobic biodegradibility and lowest toxicity to marine species.
  • Posing a much smaller risk to human health (no inhalation toxicity).
  • Having been used for more than 10 years without any epidemiological issues.
  • Not tainting marine life, not accumulating, and not having any negative effects on algal photosynthesis.
  • Being proven in the field in more than 400 wells.
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The “green” strategy decisively reduces contamination of the environment by eliminating the use of oil-based drilling muds. This minimizes long-lasting contamination and future liability arising from noxious waste deposits on the seafloor. This approach helps the oil and gas industry to improve its public image and oil companies enhance their corporate image, meeting the needs for sustainability, and avoiding long-term liability.


The cost of ester fluids is higher than the cost of mineral oil or synthetic petroleum-based drilling fluids (SBMs), reflecting the expense of producing esters from renewable resources such as palm kernel oil (as opposed to refining mineral oil pumped from the ground).

The higher cost is offset by the superior properties of vegetable ester-based fluids, in particular by increased rate of penetration, fewer drilling problems, lower cost of cuttings disposal, and reduced liabilities in the event of spillage. In the long run, ester carrier fluids offer a more economical solution.

New, low viscosity esters and new ester-based drilling fluids have been developed and certain blends with vegetable esters offer additional opportunities to satisfy requirements in several offshore regions. Continual improvements in process technology and increasingly strict regulatory rulings are enhancing the use of esters in drilling fluids worldwide.

Ester-based SBM drilling fluids have been and are being used mainly in the Gulf of Mexico, Southeast Asia (Malaysia, Brunei), Australia, and West Africa. Halliburton/Baroid is marketing these esters under the trade names Petrofree and Accolade. More than 600 wells have been drilled worldwide with the Petrofree ester system, and Accolade has been used over the last 4 years in more than 150 wells in the Gulf of Mexico. Other service companies in the US and overseas are using esters in various SBM formulations.

The author

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Stephan von Tapavicza ([email protected]) is international marketing and sales manager at Cognis Deutschland GmbH & Co. KG, Düsseldorf, Germany. He has also served as international marketing and sales manager at Henkel Oilfield Chemicals, a subsidiary of Henkel Corp., and sales manager at Oilfield Chemicals Stockhausen Gmbh & Co. KG. Tapavicza holds a diploma (MSc) and PhD (1974) in chemistry, physical chemistry, and chemical engineering from the Technical University Karlsruhe, Germany. He is member of the Society of Petroleum Engineers.