New oil mud passes environmental tests

In recent years there has been a substantial increase in the use of oil base drilling fluids. This paper discusses the performance characteristics of a new non-toxic oil mud system. This system employes a non-toxic mineral seal oil as the base fluid. The emulsifiers are formulated to give minimum toxicity while retaining the excellent temperature and contaminant stability normally associated with invert emulsion drilling fluids. Comparative studies were done on the toxicity of a conventional oil mud using diesel oil and the new non-toxic oil mud systems. All phases, liquid (LP) suspended particulate (SPP) and the solid phase (SP) of a 12 lb/gal mud were assayed. The indicator species used were the tidewater silverside (Menidia beryllina) and the grass shrimp (Palaemonetes pugio) for LP and SPP and a clam (Mercenaria mercenaria) for the SP. The results revealed that the new oil mud system was virtually non-toxic. LC/sub 50/ values were >100,000 mg/1 for LP and SPP, with a 90% survival rate for the SP. The development of non-toxic oil base drilling fluids raises the prospects for the direct disposal of drilled cuttings and spent muds offshore. The regulatory aspects of the off-shore disposal muds are discussed.