What Does Oil-Based Drilling Mud (OBM) Mean?
Oil-based drilling mud, also known as oil-based drilling fluid, is an emulsion whose continuous phase is oil. It was first developed and introduced in the 1960s to address drilling problems such as, clays in the formation that would react or swell when exposed to water-based drilling fluid, increasing downhole temperatures, torque, drag and stuck pipe. Drilling muds are either water-based or oil-based, mixed with appropriate additives.
The type to be used depends on the formation through which the bore will pass and also on fluid disposal post use. Environmentally sensitive locations have strict laws when it comes to drilling fluid disposal, and carelessness can attract heavy penalties to contractors and owners.
Trenchlesspedia Explains Oil-Based Drilling Mud (OBM)
An oil-based drilling mud can function well with an oil/water ratio ranging from 65/35 to 95/5, though the most commonly used range is 70/30 to 90/10. Oil-based drilling fluids that are used today are formulated using diesel, mineral oil and low-toxicity olefins and paraffin, also called synthetics. While some olefins and paraffin are derived from crude oil distillation, some are chemically synthesized from smaller molecules.
The primary agent that provides viscosity to oil-based systems is organophilic bentonite, and to increase the system density, barite is used. To ensure that particulate materials remain suspended, oil-wetting is essential.
To maintain elevated pH, enhance emulsion stability, and resist adverse effects of hydrogen sulfide (H2S) and carbon dioxide (CO2), lime is added to the emulsion.