Oil-Based Mud Vs. Water-Based Mud

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OBM Benefits WBM

In this article, we will talk about the benefits of using Oil Based Drilling Fluid in drilling operations, but first, please don’t forget to subscribe with us

The most common type of oil-based fluid system is the inverted emulsion fluid system, where a water-in-oil micro-emulsion is formed between a brine phase and the oil phase, including the continuous phase. Oil-based drilling fluid systems are easy to run and have several advantages over water-based systems. They have a high tolerance to solids and are stable at high temperatures, making them suitable for HPHT wells.

They were developed as an alternative to Water Based Mud (WBM) for improving drilling performance, especially when drilling water-sensitive shale or salt formations. Invert Emulsion fluid systems use mineral or synthetic oils as the continuous fluid phase, with extremely fine brine droplets present as an emulsion, which gives oil-based muds several advantages over water-based muds, as detailed below:

1 Shale Stability

The improved inhibition provided by oil-based muds makes them ideal for drilling water-sensitive shales. Oil forms the continuous phase of the drilling fluid, which protects the formation from direct contact with water. However, some emulsified brine phases in invert-emulsion systems will inevitably come into contact with the formation. To minimize the effects of shale hydration or dehydration due to the osmotic impacts, the salinity of the brine phase is adjusted to match the saltiness of the brine trapped in the formation pores. The result is eliminating Under gauge Holes problems and any wellbore stability problems.

2 Drilling Salt Formations

The continuous oil phase and the salinity of the emulsified brine phase minimize the amount of salt that is dissolved while drilling salt formations, resulting in a gauge hole. Saturated salt Water Based Mud may not guarantee a gauge hole because solubility increases with temperature. Hence, a salt system saturated on the surface may not be saturated at bottom-hole temperatures, producing washouts. The increased lubricity of oil-based muds also reduces the effects of salt creep

3 Drilling Performance

Oil-based fluid systems generally deliver higher Penetration Rates (ROP) and improved drilling performance with excellent shale stability compared to water-based fluid systems.

4 Lubricity

The enhanced lubricity provided by oil-based mud systems makes them ideal for drilling highly deviated and horizontal wells. The risk of differential pipe sticking is also reduced due to the combination of high lubricity with the fragile filter cakes reproduced by oil-based drilling fluid systems.

5 Temperature Stability

Oil-based mud systems can tolerate high temperatures for long periods. They have been used with bottom-hole temperatures approaching 550°F (290°C), so they are particularly suited for drilling high-temperature wells. In contrast, the polymers used in water-based mud systems start to degrade at elevated temperatures, resulting in a loss of viscosity and filtration control, which restricts the use of water-based mud in some high-temperature wells.

6 Corrosion Control

Oil-based drilling fluids offer exceptional corrosion protection due to the non-conductive nature of the continuous oil phase, which coats the exposed surfaces of the wellbore tubular sand and prevents corrosion cells from forming. The products used in oil-based fluids are also thermally stable, so they do not degrade to form corrosive effects, and bacteria do not thrive in oil-based fluids. As a result, corrosion of all tubulars used in well construction is suppressed, compared with some polymers in water-based mud systems that break down to produce a corrosive environment at prolonged elevated temperatures.

7 Coring Fluids

The lubricity and enhanced Shale Inhibition provided by oil-based mud systems make them ideal for coring fluid, especially as they can tolerate high temperatures. Another advantage is that oil-based coring fluids will not introduce water into core samples so that water saturation can be determined more accurately.

8 Packer Fluids

Oil-based fluid systems can tolerate high temperatures and are stable over long periods, which makes them suitable as packer fluids. Corrosion is usually insignificant because oil forms the continuous phase, which compares favorably with water-based mud systems when subjected to similar conditions. Oil-based packer fluids can suspend weighting material for extended periods when formulated correctly.

9 Oil-Based Mud Recycling

The oil-based fluid systems are very stable and can be stored for long periods for repeated use to drill several wells without concerns about bacterial growth. The oil-based mud can be conditioned before being used again simply by reducing the drilled solids content with mechanical removal equipment or by blending with fresh solids-free premix.

10 Low Pressured Formations

Oil-based mud systems can be formulated with densities ranging from 22.0 ppg (2.64 sg) to 7.5 ppg (0.90 sg), which gives them an advantage over water-based mud systems for drilling formations with low pore pressures.

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