Framework for a comparative environmental assessment of drilling fluids

During the drilling of an oil or gas well, drilling fluid (or mud) is used to maintain well control and to remove drill cuttings from the hole. In response to effluent limitation guidelines promulgated by the US Environmental Protection Agency (EPA) for discharge of drilling wastes offshore, alternatives to water and oil-based muds have been developed. These synthetic-based muds (SBMs) are more efficient than water-based muds (WBMs) for drilling difficult and complex formation intervals and have lower toxicity and smaller environmental impacts than diesel or conventional mineral oil-based muds (OBMs). A third category of drilling fluids, derived from petroleum and called enhanced mineral oils (EMOs), also have these advantages over the traditionally used OBMs and WBMs. EPA recognizes that SBMs and EMOs are new classes of drilling fluids, but their regulatory status is unclear. To address this uncertainty, EPA is following an innovative presumptive rulemaking process that will develop final regulations for SBM discharges offshore in less than three years. This report develops a framework for a comparative risk assessment for the discharge of SBMs and EMOs, to help support a risk-based, integrated approach to regulatory decision making. The framework will help identify potential impacts and benefits associated with the use of SBMs, EMOs, WBMs, and OBMs; identify areas where additional data are needed; and support early decision-making in the absence of complete data. As additional data becomes available, the framework can support a full quantitative comparative assessment. Detailed data are provided to support a comparative assessment in the areas of occupational and public health impacts