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Abstract

The environmental and technical performance of drilling fluid additives is a key characteristic of such products. However, at times, the technical performance and environmental characteristics of materials used to make such additives seem to be at odds with each other. For example, materials that show good technical performance (stability) at high temperatures are frequently poor biodegraders, and those that are the most chemically active can show the highest toxicities.

In addition to the paradox of performance vs. environmental acceptability, international drilling fluids companies face diverse environmental regulations when operating in geographically distinct areas. Some of the most marked contrasts are observed when comparing regulations in the two most active offshore operating areas: the North Sea and the Gulf of Mexico. Regulatory discrepancies like these should be taken into consideration at the product design stage, when there is a potential for global technical performance to be sacrificed for environmental compliance in just one of the areas. One may be forced to ask which regional regulation should shape an additive’s design? Are there oilfield chemicals that have been rendered unusable by regulations in one area while showing excellent economic and technical performance in another, without any apparent degradation of the environment?

This paper will discuss and present real-life examples of drilling chemicals that have been designed and often redesigned to fit stringent environmental criteria, according to the areas in which they are used.

Introduction

The use and discharge of drilling fluids and cuttings during the course of well construction activities has occurred since the advent of offshore drilling. However, it is not until relatively recently that this discharge activity has been regulated. Some of the most active drilling regions of the world also contain important commercial fishery resources and may support indigenous fisheries or other marine based activities; it is clear that there is potential for conflict to arise between stakeholders. Where regulations have been established, government agencies have been charged with establishing a system of control to ensure that long-term impacts do not occur in areas where drilling and well construction discharges take place. These control systems may rely on a range of “tools” in order to attempt to predict, rank or otherwise categorise the expected impact of discharged materials. There may be heavy reliance on laboratory-based toxicity and biodegradation tests, or attempts to predict the potential for materials to bioaccumulate. It is important to recognize that these tests are useful in determining the potential for the tested materials to impact upon the environment, but that they are not direct predictors of actual environmental fate. 

For example, it is easy to demonstrate that many organic materials will almost completely biodegrade when tested in OECD 306[1], a commonly used test to assess biodegradation in seawater. However, this data is not a great deal of help in predicting when a base fluid discharged on cuttings will no longer be detected on the seafloor, or when the impacts of a spill of drilling fluid will no longer be detected. The reasons for this are twofold. First, the marine environment is a dynamic place, and dispersal of materials can be rapid. Also, in order to obtain the results of tests in a useful timeframe, the conditions of testing may be idealized. For example, in the OECD 306 biodegradation test, the water oxygen content, test temperature and nutrient mixture available to the bacteria present are optimized in order to get a result in a matter of 28 days. In the natural environment, the seafloor temperature may be as low as 2°C, and if the material is buried in a pile of drilled cuttings, influx of nutrient-containing, oxygenated seawater may be severely limited so that degradation of the same materials showing good laboratory results may be reduced. However, the laboratory test allows our industry to provide to the regulator an indication of the relative performance of a range of oilfield chemicals, so that regulation can take place.