Fundamentals of Directional Drilling: Reasons for Drilling Deviated Wells

 

Introduction

"What would you do if the reservoir lies beneath a city or a river?" Directional drilling is the solution when traditional vertical drilling is not feasible due to surface obstructions, environmental constraints, or the need to access reservoirs that lie in hard-to-reach locations. This technique allows for controlled deviation of the wellbore, enabling access to reservoirs that are otherwise inaccessible, optimizing reservoir contact, and providing greater flexibility in drilling operations.

Accessing Inaccessible Reservoirs

1. Reaching Reservoirs Under Challenging Locations

One of the primary reasons for drilling deviated wells is to access reservoirs that are located beneath difficult terrain. Whether the reservoir is beneath a city, a river, or a protected environmental area, directional drilling offers the ability to reach these resources without disrupting surface activities. For example, drilling horizontally from a wellsite on one side of a river to access a reservoir on the other side eliminates the need for drilling through sensitive areas.

• Application: Directional drilling allows for accessing oil and gas reserves beneath urban developments, rivers, lakes, and other areas where surface drilling would be impossible.
• Benefit: Minimizes the environmental footprint and disruption of surface activities while still accessing valuable subsurface resources.

2. Reducing Surface Impact and Land Use

In areas where land availability is limited or restricted, directional drilling provides a way to drill from a central location and access multiple reservoirs spread out in various directions. This reduces the number of drilling sites needed and minimizes land usage, making it an ideal solution in densely populated or environmentally sensitive regions.

• Application: Offshore platforms can drill multiple wells in different directions from a single platform, optimizing reservoir access while minimizing the number of structures on the surface.
• Benefit: Reduces surface disturbance and maximizes the use of limited space.

Avoiding Surface Obstructions and Optimizing Reservoir Contact

1. Navigating Around Surface Obstacles

Surface obstacles such as buildings, roads, rivers, and infrastructure may obstruct direct access to an oil or gas reservoir. Directional drilling allows the drill bit to be steered around these obstacles and target the reservoir from an alternative location. This can be particularly useful in urban or industrial areas where drilling directly on top of the reservoir is not possible.

• Application: In urban oilfields or offshore platforms, directional drilling can be used to avoid environmental hazards, production facilities, or protected zones while still maintaining access to the reservoir.
• Benefit: Overcomes the challenges of surface obstructions while maximizing the reservoir’s drainage area.

2. Maximizing Reservoir Contact

By drilling at various angles, operators can increase the length of the wellbore within the reservoir, improving the ability to drain hydrocarbons more efficiently. In many cases, a deviated well will allow for a longer, more productive contact with the reservoir than a vertical well would, optimizing the extraction of oil or gas.

• Application: Multilateral wells, where multiple branches extend from a single main wellbore, can access larger sections of a reservoir, improving productivity.
• Benefit: Maximizes reservoir contact and increases the overall efficiency of well operations.

Applications in Offshore Platforms and Multilateral Wells

1. Offshore Platforms

Directional drilling is frequently used in offshore drilling to allow access to reservoirs that cannot be reached directly from the platform. Offshore platforms often have limited space for drilling rigs, and directional drilling allows them to target multiple reservoirs from a single location. This saves resources and reduces the need for additional platforms.

• Application: Offshore oil rigs can drill horizontally or at angles to access a wide array of subsea reservoirs, improving the overall efficiency and cost-effectiveness of offshore oil exploration and production.
• Benefit: Allows for greater flexibility in well placement and minimizes the need for new drilling locations.

2. Multilateral Wells

In multilateral wells, directional drilling techniques are used to drill multiple branches from a single main wellbore, allowing operators to access different parts of a reservoir that may be spread across a large area. This is particularly beneficial in reservoirs that are irregularly shaped or have multiple layers of hydrocarbons.

• Application: In reservoirs with complex geological formations, multilateral wells allow for better management of reservoir pressure and enhanced recovery techniques.
• Benefit: Increases well productivity and recovery rates by accessing multiple zones within a reservoir with fewer wellbores.

Conclusion

Directional drilling is a powerful technique that overcomes the limitations of vertical drilling by providing access to otherwise inaccessible reservoirs, navigating around surface obstacles, and optimizing reservoir contact. Its applications in offshore platforms and multilateral wells are crucial in maximizing production efficiency while minimizing surface impact. Whether drilling under a river, city, or industrial area, directional drilling is the key to unlocking the potential of hidden hydrocarbon reserves.