With increased concerns over the environmental issues regarding the use of oil-based mud (OBM)s, drilling companies in Iran are moving towards implementing less harmful water-based fluids. Due to low toxicity to the environment, effective shale inhibition and considerable cost savings, water-based glycol muds have the highest prospects as alternatives to OBMs in Iranian oilfields. However, designing water-based muds for drilling low-pressure shales may involve a compromise between mud weight optimization and overall environmental and economic advantages offered by these systems.

The present study will focus on optimizing the weight of a glycol mud by emulsifying oil in the system and comparing its performance, environmental compatibility and cost with OBMs used in drilling low-pressure zones in Iranian oilfields. Properties of glycol solutions in the presence of oil were also evaluated.

An emulsified glycol mud and an OBM with densities of 60 PCF were prepared and compared for their rheology and shale recovery. The shale recovery tests were conducted using shale samples from Maroon oilfield. Possible effects of contamination on the performance of the system were also studied. The glycol system was then treated to recover its diesel content.

Overall, the laboratory data were convincing. With very low filtration rates, the emulsified glycol system is a candidate to replace OBMs in reservoir sections. Shale recoveries were comparable to those of OBMs. Compared with a similar OBM, considerable cost savings can be made and the system is more environmentally friendly. However, rheology was more difficult to control and the system was susceptible to contamination.

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