Environmental issues have created ever-moving targets for drilling fluids, or muds. Environmental regulations are diverse, complex, and have a tremendous impact on drilling operations, economically as well as logistically. In order to successfslly meet these regulatory constraints, synthetic-based muds are beconiing increasingly popular as substitutes for conventional oil- based muds. Continual evolution of synthetic-based muds (SBM's) and the increasing diversity of synthetic base fluids (SBF's) have made the selection of environmentally acceptable synthetic fluids increasingly complex requiring knowledge of chemical composition and structure effects on toxicity, biodegradability, and performance.

Examination of the SBF's, the synthetic base fluids, provides insight into the environmental and performance issues that affect the selection and drilling performance of the SBM's, the mud. The toxicity, biodegradability, and bioaccumulation of SBM's depend on the molecular composition and structure of the base fluid. In general, the degree of branching affects the biodegradability and the molecular weight affects the toxicity of synthetics derived from similar chemistry. The thermal stability and performance characteristics of the SBM's depend on the chemical composition of the base fluid and emulsifiers used in the SBM's. The final choice of the SBF (and thereby the SBM) depends on the application and environmental requirements for a particular area; however, synthetic hydrocarbon-based fluids have shown to be overall best in cost vs performance.

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