Directional Drilling: Everything You Ever Wanted To Know

Directional drilling has revolutionized the way we extract oil and gas, enabling advancements such as multi-directional boring. As we've discovered through extensive research, directional drilling allows wells to be drilled at varied angles rather than strictly vertically, maximizing resource extraction while minimizing environmental impact.

What is directional drilling?

Directional drilling refers to any drilling activity that does not take a straightforward vertical path. In some cases, adjustments may be necessary even when drilling a vertical well, either to navigate around geological formations or to address a previously stuck pipe. This involves sidetracking techniques to return to the main drilling path.

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Unlike conventional drilling, where the drill bit, drillstring, pipe, and casing descend directly downwards, directional drilling allows for planned turns and deviations along the well trajectory. The development of advanced technology has drastically improved the precision and distance achievable in these drilling methods.

Directional drilling has been in practice for nearly a century, but it has seen significant advancements in engineering and technology in recent decades. Techniques like multilateral drilling, horizontal drilling, and extended reach drilling (ERD) can dramatically enhance oil recovery efforts, enabling drilling specialists to reach depths exceeding 10 kilometers (6.2 miles). Imagine a tree; the main rig as the trunk, and the numerous directional possibilities are the expansive roots, offering incredible potential for resource extraction.

Why is the technique so valuable?

This technique allows for multiple boreholes to be drilled from a single rig, significantly decreasing surface disruption and environmental footprint. Boreholes can extend vertically for a mile and horizontally for over five miles. This efficiency is particularly advantageous in oilfields with dispersed deposits, minimizing costs by maximizing the use of expensive rig assets which can command day rates in the hundreds of thousands of dollars.

Geologists and engineers often refer to underground resources using terms like 'oil reservoir' or 'hydrocarbon reservoir.' Though these terms are helpful for communication, the actual arrangement of resources is highly unpredictable, leading to the necessity of directional drilling.

Professionals in seismic geology, geoscience, and exploration engineering collaborate to determine the likely locations of oil and gas deposits through various surveys and historical data. However, pinpointing the most lucrative locations remains elusive.

For illustration, consider a reservoir of water—imagining a straw attempting to extract all the water does not accurately represent the complexity of underground resources. If the straw encounters an obstruction such as a gravel bar, the extraction will only yield a fraction of the water available.

This randomness in reservoir structure gives rise to several challenges:

• Drilling at angles can explore more of a reservoir since they generally form horizontally, not vertically.
• Deposits may not resemble typical reservoirs; for example, they can exist within oil-saturated sand or shale. Directional drilling is particularly beneficial in shale formations.
• A tough layer like granite may obstruct access to valuable hydrocarbons.
• Inaccessibility due to the surface being a populated area, mountain, or protected land.
• Oil and gas may be dispersed in separate pockets, which complicates extraction.
• Reservoirs are often located beneath salt domes or fault planes, increasing technical risks.
• Irregular patterns of the reservoir, such as bars and deep troughs, may further complicate access.
• Horizontal directional drilling can be used to extend access offshore or under lakes at lower costs.

As the quest for large reservoirs becomes increasingly challenging, the role of directional drilling gains prominence, making it essential in modern resource extraction.

Another application of directional drilling arises in situations involving uncontrolled wells. In cases of blowouts, creating a secondary control well may become necessary to intercept and securely cap the original well.

The effectiveness of this method heavily depends on underground pressure. In certain scenarios, a relief well can help manage pressure while control fluids are introduced to secure the original well.

How do the engineers know where the end of the drill is?

Due to the inability to visualize hundreds of meters underground, engineers depend on advanced technology to track progress. Directional drilling involves systematic surveying, with data sent back every 10-150 meters to ensure adherence to the intended well path.

Directional drilling employs sophisticated software integrated with multiple measurements taken by sensors in the drill bit. This process, alongside mud loggers using logging while drilling (LWD) technologies, offers comprehensive insights into the drilling process. Each segment of the drill—including collars and motors—provides vital data about actual drilling conditions.

Surface electromagnetic sensors contribute to monitoring drill bit progress, facilitating real-time adjustments to maintain the desired trajectory even in challenging scenarios.

How can the drill make a turn?

The mechanics behind directional drilling involve downhole drilling motors, which allow the drill bit to pivot in directions other than the conventional 180-degree vertical. Technologies like turbodrills and rotary steering drills are commonly utilized in scenarios that require deviation.

The drill string can be adjusted through mechanisms such as high-pressure jetting or whipstocks that redirect drill paths by positioning a wedge at the desired depth before resuming drilling at the new angle.

Sensors within the drill bit can relay critical information regarding weight and rotational speed to aid trajectory adjustments. Steerable drill pipes also feature bends near the bit, permitting operators to navigate towards the intended direction.

Equipment used:

Specialized drill bits enhance performance while reducing failure rates. For instance, Schlumberger offers directional PDC drill bits tailored for various rotary steerable systems.

Mud Motors. Positioned near the drill bit, these motors facilitate directional changes by utilizing fluid pressure to guide drilling at the proper angle until the trajectory is verified.

Rotary Steerable Systems (RSS). This system permits simultaneous drilling and steering, which is paramount for accessing previously unreachable formations.

Bottom Hole Assembly (BHA) consists of bent configurations for efficient directional drilling.

Multi-Shot cameras provide consistent monitoring through time-lapse imagery regularly transmitted to surface control systems.

Custom whipstocks designed for downhole motors allow continuous drilling without removal.

Networked or wired pipe solutions like National Oilwell Varco’s Intelliserve system offer live data transmission from downhole sensors to surface operations.

These innovations exemplify the specialized gear necessary for effective directional drilling, complemented by three-dimensional measurement systems previously discussed.

Wellbore stability considerations

The stability and integrity of the wellbore remain critical in directional drilling. Faced with complex challenges, engineers must manage additional stressors when drilling deep or around bends. The smaller size of downhole motors plays a crucial role while navigating tough geological conditions.

Directional drilling increases friction and imbalances in pressure; if well integrity is compromised, it may lead to equipment failures or blockages, necessitating expensive re-drilling efforts in different directions. Modern advancements have equipped complications with high-pressure, high-temperature (HP/HT) conditions in mind, enabling effective management during such intricate operations.

Directional well planning

Computer simulation programs are indispensable in plotting well paths. By utilizing 2D and 3D modeling tools, geoscientists receive visuals of the proposed drilling trajectories, informed by experience and real-time data from MWD instruments.

Horizontal Directional Drilling

Directional drilling comprises various styles, notably multilateral drilling, which features multiple lateral offshoots, and extended reach drilling characterized by long wellbores. Horizontal directional drilling stands out as among the earliest and often debated methods used in resource exploration.

Land leases enable access to specific territories; however, there have been instances where tension arises from drillers tapping into adjacent regions without appropriate agreements. While the industry possesses regulations to mitigate legal disputes, horizontal drilling often occurs for legitimate reasons, whether to navigate environmental constraints or to optimize resource extraction in complex geological fields.