Rotary Drilling Fluids, Part III Oil Muds

Summary

This video provides an in-depth look at the process of drilling through various subsurface layers to reach petroleum-bearing formations. It focuses on the challenges and techniques involved in using oil-based drilling muds, which offer greater protection to the formation compared to water-based muds. Key aspects include the mixing and transportation of oil mud, testing for properties like viscosity and stability, and managing issues such as lost circulation and formation damage. The video emphasizes the careful monitoring and adjustments made to maintain efficient and safe drilling, especially when encountering complex formations like salt, shale, and dolomite.

Takeaways

• 😀 The rotary rig is drilling through layers of subsurface rocks to reach a petroleum-bearing formation, with the current operation involving cementing casing in a hole to isolate formations.
• 😀 The engineers designed the drilling program to avoid formation damage from drilling mud, particularly in sensitive areas like shale, salt, and anhydrite layers.
• 😀 A previous nearby well had formation damage due to water-based mud, which swelled clay particles and blocked oil flow, highlighting the need for careful mud selection.
• 😀 Oil-based muds (OBM) and invert oil muds (IOM) are used in drilling to minimize water-related formation damage, with OBM containing less than 5% water and IOM containing 10–50% water.
• 😀 Surfactants or soaps are used to emulsify water in oil, creating a stable oil mud mixture where the water remains dispersed as small droplets within the oil.
• 😀 Proper mixing of the oil mud is done at a liquid mud plant before being transported to the rig, ensuring a more stable and reliable mud composition.
• 😀 The oil mud contains components like emulsifiers and oil-wetting agents to improve viscosity, gel strength, and filtration control during drilling.
• 😀 Calcium chloride is crucial for ensuring the water in the oil mud is as salty as the water in the shale, preventing water transfer that could destabilize the mud or formation.
• 😀 Tests like viscosity measurements and electrical stability tests are essential to monitor the mud's performance, ensuring the emulsion remains stable and the mud behaves as needed.
• 😀 Special precautions are necessary when using oil mud, such as using oil-resistant rubber parts, installing fine mesh shaker screens, and employing mud-saving techniques to avoid wasting expensive mud.
• 😀 Oil mud is especially useful in drilling through challenging formations like salt and anhydrite, preventing dissolution and hole enlargement that could occur with water-based mud.
• 😀 Once the drilling is complete, the well is logged to determine the best part of the pay zone to complete, with oil mud's non-conductive properties requiring radioactive or sonic logging for accurate results.

Q & A

What type of casing is used to isolate the formation in the drilling process?

A 9 and 5/8-inch casing is cemented in a 12 and 1/4-inch hole to isolate the formation through which the hole has already passed.

Why were engineers concerned about drilling through shale, salt, and anhydrite layers?

Engineers were concerned because these layers could cause issues with drilling, such as affecting the stability of the well and damaging the producing formation. They wanted to use a drilling mud that would maintain a full gauge hole and protect the formation.

What is the potential problem caused by water-based mud in the formation?

Water-based mud can cause formation damage by allowing water filtrate to invade the formation, leading to clay swelling. This can block passageways between sand grains, preventing oil from flowing into the wellbore.

What are the two types of oil mud discussed in the script?

The two types of oil mud are oil-based mud and invert oil mud. Oil-based mud contains less than 5% water, while invert oil mud contains between 10% to 50% water.

How do emulsifiers play a role in the creation of oil mud?

Emulsifiers, or surfactants, are added to the oil and water mixture to break the water into small droplets and disperse it evenly within the oil, creating a stable emulsion.

Why is diesel oil preferred over crude oil for making oil mud?

Diesel oil is preferred because it minimizes the fire hazard posed by volatile components in crude oil and is less harmful to rubber components used on the rig due to its higher aniline point.

What is the importance of calcium chloride in oil mud?

Calcium chloride is important for preventing water transfer between the mud and the shale formation. The water in the mud should have the same salinity as the water in the shale to avoid water transfer, which can lead to formation damage.

What are some key precautions when using oil mud during drilling?

Precautions include ensuring all rubber components exposed to oil mud are oil-resistant, installing fine mesh shaker screens to prevent mud thickening, using pipe trays to catch draining mud, and keeping mud clean using pipe wipers and mud savers.

What is the role of spacers in the drilling process with oil mud?

Spacers, such as freshwater and oil spacers, are pumped into the well to prevent contamination between water-based mud and oil mud. They also help clean the hole as they are circulated.

How is the oil mud tested and monitored during drilling?

Oil mud is frequently tested for properties such as viscosity, density, stability, alkalinity, and chemical activity. Tests include measuring funnel viscosity, electrical stability, and filtration tests to ensure the mud is functioning properly and to identify any needed adjustments.