Drilling Fluids: Making Peace With the Environment
Authors: Roger Bleier , Leuterman Arthur J.J. , Cheryl Stark 
Published: December 2007

Summary
Environmental problems, although nettlesome and often costly, have stimulated new developments in drilling-fluid technologies. Minimizing environmental impact involves reducing levels of toxic components in drilling fluids, waste minimization, and recycling. Significant progress is being made. This paper assesses the current state of technology and likely future directions. The constructive role of regulatory agencies in recognizing, fostering, and encouraging the use of emerging technologies, as opposed to blanket prohibitions, also is discussed.

Introduction
Mud companies have identified replacements for diesel and mineral oils in lubricants and spotting fluids that combine performance and environmental acceptability. Non-chloride potassium sources have replaced KCl in many water-based muds. New cationic polymer muds often are touted as replacements for oil-based muds, and preliminary field results are encouraging.
The trend to polymer muds, in general, has reduced consumption of traditional linosulfonate additives and other organometallic complexes. Weighting agents also have been affected. Barite ore sources are scrutinized carefully for their trace heavy metal content, particularly cadmium and mercury impurities.
Muds based on synthetic, low-toxicity, biodegradable, organic liquids are now available. These synthetic muds offer "designed-in" performance and environmental characteristics.
Processing of drilling-fluid waste is a rapidly growing industry. Commercially available technologies include dewatering, land farming, cuttings injection, fixation, and distillation. Bioremediation and solvent extraction have promise for the future. All of these affect the economics and the environmental acceptability of drilling operations. Tradeoffs between environmentally desired features (e.g., lower toxicity but larger waste volumes) also are addressed.

Background
Drilling-fluids companies supply and engineer the properties of fluids required in drilling of oil and gas wells. Although "mud" still describes the appearance of drilling fluids and is used freely in this paper, the term understates their complexity. Historically, as the performance demands on drilling fluids increased, chemicals were found that enhanced performance at relatively low concentrations. Oil-based muds were developed for situations where water-based muds were inadequate. By the mid-1970's, the technology had matured almost to self-satisfied complacency.
Drilling-fluids companies received an unmistakable environmental wake-up call in 1978. Oil companies wishing to drill exploratory wells off the U.S. mid-Atlantic coast had agreed, as a permit condition, to support a drilling-mud bioassay program.1 A testing protocol using the shrimp species Mysidopsis bahia (Mysid shrimp), worked out with the U.S. Environmental Protection Agency (EPA), became the basis for assessing toxicity of drilling fluids and additives. Also in 1978, the state of Alabama moved aggressively to enforce discharge regulations on oil companies drilling in Mobile Bay, signaling that local governments also would look more closely at drilling fluids. While environmental considerations had always been present, they surged to the foreground. Environmental acceptability now ranked with traditional cost and performance considerations in decisions on drilling fluids and additives.
This paper provides a snapshot of the current status of drilling fluids vis-à-vis the environment in the U.S. It describes progress made in improving environmental acceptability and suggests future directions. A deliberate attempt is made to present technical matters in a straightforward manner with enough background that environmentally concerned persons outside the industry can use it as a reference. At the same time, this paper touches on the most advanced fluids and technologies available today and those undergoing significant development. The interplay among environmental concerns, new technology, and the regulatory framework is an underlying theme.
Issues addressed in this paper include toxicity of water-based muds, heavy-metal impurities in barite, limitations of water-based muds, oil-based muds and alternatives, drilling-waste volumes, disposal options, and regulatory impact.
Biodegradability and bioaccumulation issues are in early stages of definition in terms of test protocols and interpretations2 and are more properly the subject of a separate paper.