Directional Drilling Reamers - Function and Advancements in Technology

Introduction to Directional Drilling Reamers

Directional drilling is a technique used to drill non-vertical wells. This drilling method allows operators to reach targets that are not directly beneath the surface location. Directional drilling enables access to reservoirs far from the drilling rig, drilling of multiple wells from one location, and drilling complex wells with multiple branches.

An essential component of directional drilling is the reamer. Reamers are critical tools that enlarge the diameter of the wellbore during drilling. As the drillstring progresses, reamers widen the path so that larger components like casings and liners can be installed.

What are Directional Drilling Reamers?

Directional drilling reamers are tubular tools with cutting structures on the outside. They are attached behind the drill bit on the drillstring. As the drillstring rotates and advances into the formation, the reamer enlarges the freshly drilled hole to the desired diameter.

Reamers have cutting blades made of steel with hardfacing. The hardmetal coating increases durability so the blades can regrind the hole repeatedly. Most reamers have three or four blades spaced evenly around the tool body. The blades may have tapered ridges or rows of cutting inserts like tungsten carbide to improve cutting efficiency.

Types of Directional Drilling Reamers

There are two main types of reamers used in directional drilling - straight reamers and tapered reamers.

Straight Reamers - These have a cylindrical body with consistent blade diameters over the reamer's full length. Straight reamers enlarge the wellbore to a uniform size. They are best suited for consolidated formations.

Tapered Reamers - Tapered reamers have blades that gradually increase in diameter from the back to the front. This design provides a tapered enlargement that eases the reaming action. The taper helps prevent sticking in unstable or uneven formations.

Key Features of Directional Drilling Reamers

Directional reamers have design elements that improve performance:

• Pilot Bit - A pilot bit at the front guides the reamer and initiates drilling. The pilot initiates directional changes.
• Stabilizers - Stabilizer fins center the reamer in the hole to ensure a uniform enlargement.
• FlexJoints - Flexible joints allow the reamer to steer more precisely through doglegs and lateral sections.
• Flow Ports - Strategic fluid ports optimize circulation and hydraulics across the cutting blades.
• Junk Slots - Junk slots in the body allow cuttings to flow away from the blades for efficient reaming.

Reaming Process in Directional Drilling

Reamers enlarge the wellbore in stages throughout the directional drilling process:

Pilot Hole Section

The first stage is drilling a small diameter pilot hole from the surface location along the desired well path. The pilot bit at the front of the reamer creates this initial hole. A mud motor provides rotation and steering control for directional precision.

Open Hole Section

Next, the reamer enlarges the pilot hole to the size needed for drilling ahead. This open hole section will be drilled until reaching the target zone. The reamer must enlarge the hole consistently as drilling progresses to ensure the drillstring can advance forward.

Casing Section

When the target zone is reached, the hole will be enlarged again. This time reaming to a sufficient size to install casing pipe. Cement is pumped down the casing to secure it in the wellbore. The cemented casing provides well control as drilling continues into the reservoir.

Completion Section

During the completion phase, liners and other equipment are installed deeper in the well. The reamer further enlarges the hole to accommodate these completion components.

Challenges of Reaming in Directional Wells

There are several challenges that reamers face when operating in directional wells:

• Bending Forces - Doglegs and lateral curves exert added bending forces on the reamer.
• Vibrations - Drilling directionally can cause damaging vibrations, shocks, and stick-slip.
• Hole Instability - Sections with shale or faults are prone to washouts and tight spots.
• Cuttings Removal - Cuttings can accumulate in inclined and horizontal sections.

Reamer engineers utilize various design elements like stabilization, vibration damping, and cuttings circulation to overcome these difficult drilling conditions.

Advancements in Directional Drilling Reamer Technology

Manufacturers continually innovate to improve reamer performance for directional drilling. Some key advancements include:

• More Robust Cutting Structures - Hardfacing, cutter inserts, and blade geometries optimized for durability.
• Enhanced Hydraulics - Strategic fluid ports and junk slots prevent clogging and improve borehole cleaning.
• Drilling Dynamics Sensors - Sensors provide downhole data to monitor and optimize drilling parameters in real-time.
• Hole Enlargement Control - Actuation systems allow controlled expansion of underreamer cutters.

With continuous improvements in reamer technology, operators can drill directionally to form wells with greater complexity, reach, and productivity.

Conclusion

Directional drilling reamers are essential tools that enlarge the wellbore to accommodate drilling of complex, non-vertical well paths. There are straight and tapered reamer designs optimized for various drilling conditions. Reamers enlarge the hole in stages throughout the directional drilling process. Advancements in reamer technology allow operators to overcome challenges when drilling directionally and construct more productive wells.

FAQs

What are the main types of reamers used in directional drilling?

The two main types are straight reamers and tapered reamers. Straight reamers enlarge the wellbore to a uniform diameter. Tapered reamers have a blade diameter that increases from back to front for a tapered enlargement.

When are reamers used during directional drilling?

Reamers enlarge the wellbore in stages - during drilling of the pilot hole, open hole section, casing section, and completion section.

What are some key features of directional drilling reamers?

Key features include a pilot bit, stabilizers, flex joints, optimized fluid ports and junk slots, and enlargement control systems.

What challenges do reamers face in directional wells?

Challenges include bending forces, vibrations, hole instability, and cuttings removal issues in inclined/horizontal sections.

How has reamer technology advanced for directional drilling?

Advancements include more robust cutting structures, improved hydraulics, drilling dynamics sensors, and controlled hole enlargement systems.