Designing the Perfect Drilling-Fluid Additive: Can It Be Done?

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 95196, “Designing the Perfect Drilling-Fluid Additive: Can It Be Done?,” by J. Hall, SPE, Halliburton, prepared for the 2005 SPE Asia Pacific Health, Safety, and Environment Conference and Exhibition, Kuala Lumpur, 19–20 September. The environmental effects and technical performance of drilling-fluid additives are important characteristics of these products, which at times seem to be at odds with each other. For example, materials that show good stability at high temperatures frequently do not biodegrade well. In addition to the paradox of performance vs. environmental acceptability, international drilling-fluid companies face diverse environmental regulations when operating in geographically distinct areas. The full-length paper discusses real-life examples of drilling chemicals that were designed to fit stringent environmental criteria, according to the areas where they were used. Introduction Use and discharge of drilling fluids and cut-tings during well-construction activities have occurred since the beginning of off-shore drilling. However, it was not until relatively recently that these discharges have been regulated. Some of the most active drilling regions in the world also contain important commercial fisheries. Where regulations have been established, government agencies have been charged with establishing a control system to ensure that long-term effects do not occur in areas where drilling and well-construction discharges take place. These control systems rely on a range of tools to predict, rank, or otherwise categorize the expected effect of discharged materials. There may be a heavy reliance on laboratory-based toxicity and biodegradation tests, or attempts to predict the potential for materials to bioaccumulate. For example, it is easy to demonstrate that many organic materials will almost completely biodegrade when tested by a commonly used test to assess biodegradation in seawater. However, this is not much help in predicting when a base fluid discharged on cuttings will no longer be detected on the seafloor, or when the effects of a drilling-fluid spill will no longer be detected. The reasons for this are two-fold. First, the marine environment is a dynamic place, and materials dispersal can be rapid. Also, to obtain test results in a useful time frame, the conditions of testing may be idealized. For example, in the biodegradation test, the water oxygen content, test temperature, and nutrient mixture available to the bacteria present are optimized to produce a result in 28 days. In the natural environment, seafloor temperature may be as low as 2°C, and if the material is buried in a pile of drill 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 provides the regulator an indication of the relative performance of a range of oilfield chemicals.