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Directional core drilling (DCD) and horizontal directional drilling (HDD) are two different drilling techniques. We often get the question «does Aziwell do horizontal drilling directional», and the easy answer is «no». We specialize in directional core drilling, and therefore, we want to highlight the difference between the two methods and show what separates them in terms of technology and uses.
What is directional core drilling (DCD)?
Directional core drilling is a drilling technique that drills bores or wells along a curved path to reach a specific target. Therefore, directional drilling provides access to underground areas that are not accessible through conventional drilling with minimal disturbance to the surface. DCD is primarily used for mineral exploration and geological analysis, with a main purpose of collecting high-quality core samples to understand the value of the mineral deposits.
Also read: What is diamond core drilling?
What is horizontal directional drilling (HDD)?
Horizontal directional drilling (HDD) is another form of directional drilling, and while it can drill along curved paths as well, which can be necessary to make adjustments and hit targets, it is mostly commonly used to drill long pathways over long distances. Therefore, HDD is considered a trenchless construction method used to install underground utilities with minimal surface disruption. HDD is widely used for infrastructure projects and for laying energy lines, for example when installing pipelines or cables.
Directional core drilling (DCD) technology
The purpose of directional core drilling is to steer the hole to target, with core recovery. As such, the technology employed needs to allow for coring at the same time as steering. To execute operations, one uses a directional core drilling tool which consists of several elements that enable the directional, curved drilling.
Elements of a directional core drilling tool
- Cylindrical diamond bits are used to cut rock cores.
- Core barrels are used to store the core, which are recovered by wireline.
- Wedges can be employed to deviate the borehole from vertical to a controlled angle, but newer technology such as the Azidrill are seeing increasing use.
- Survey tools such as gyros and magnetic single/multi-shot instruments) are used to track the borehole trajectory.
- Drilling fluid (mud or water) circulates to cool the bit, stabilize the hole, and clean the hole from cuttings.
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Horizontal directional drilling (HDD) technology
HDD is used to drill horizontally or nearly horizontally over long distances, mainly for infrastructure projects. It depends on some essential technological features to operate functionally, which is explained in the following section.
How does horizontal directional drilling work?
- Starts with a pilot bore drilled using a steerable drill head and tracked with surface-based walk-over locating systems or wireline steering tools.
- Steering is achieved by bent sub/housing and directional control of the drill head, often guided by real-time location tracking.
- Once the pilot hole is complete, it is enlarged with reamers to accommodate the pipe or conduit.
- Uses drilling mud (bentonite-based slurry) extensively for lubrication, hole stability, and transporting cuttings.
Directional core drilling (DCD) uses
Exploration of mineral deposits
Directional core drilling is primarily used in mineral exploration, where it allows geologists to sample ore bodies from multiple points. By drilling directionally, it becomes possible to trace the shape, orientation, and thickness of complex mineralized zones without relying solely on multiple vertical holes. This improves efficiency and provides a more accurate picture of the deposit.
Structural geology and geotechnical analysis
Core samples offer detailed insight into geological structures such as faults, fractures, bedding planes, and folding. Directional drilling makes it possible to intersect these features at different angles, giving engineers and geologists a better understanding of rock mechanics and ground stability which is critical for mines, tunnels, and large civil engineering projects.
Resource estimation and modeling
High-quality core samples obtained through directional drilling are essential for building accurate 3D geological and resource models. By targeting specific parts of the ore body, geologists can reduce uncertainty in grade distribution, continuity, and tonnage estimates. This leads to better mine planning, improved extraction methods, and more reliable resource/reserve classifications.
Reducing drilling costs and disturbance
Instead of drilling multiple surface holes, directional core drilling allows multiple branches to be drilled from a single mother hole. This significantly reduces costs and surface disturbance, which is particularly valuable in sensitive environments, urban areas, or offshore projects where minimizing impact is a priority.
Follow-up on specific targets
When exploration results or geophysical surveys identify promising anomalies, directional core drilling makes it possible to precisely target those areas. By adjusting the trajectory, drillers can intersect specific mineralized zones or high-grade pockets with great accuracy.
Horizontal directional drilling (HDD) uses
Utility installation
Horizontal directional drilling is widely used to install underground utilities such as water mains, sewer lines, natural gas pipelines, electrical conduits, and fiber optic cables. Because the drilling process avoids open trenches, it allows these systems to be placed safely underground with minimal disruption to the surrounding environment and infrastructure.
Crossings under obstacles
One of the biggest advantages of HDD is its ability to create underground passages beneath natural and man-made obstacles. It enables pipelines and cables to cross rivers, streams, highways, railways, and even dense urban areas without interrupting surface activity or damaging the structures above.
Environmental and social benefits
Compared to traditional excavation, HDD leaves a far smaller footprint on the environment. By drilling beneath sensitive areas such as wetlands, forests, or urban green spaces, it prevents habitat destruction, reduces erosion, and limits noise and dust. It also minimizes disruption to nearby communities, keeping roads open and neighborhoods undisturbed.
Energy and renewables
The energy sector relies heavily on HDD for installing pipelines that transport oil, natural gas, and hydrogen. It is also used to lay underground cables for renewable energy projects, such as wind farms and solar plants, ensuring efficient connections to substations and grids. Additionally, HDD can support geothermal energy systems by installing horizontal loops beneath the ground.
Municipal and civil engineering
In cities, HDD plays an important role in expanding and modernizing municipal infrastructure. It allows for the installation and replacement of water supply networks, stormwater drains, and sewage systems without digging up busy streets. This makes it valuable for projects in densely populated areas where open trenching would cause significant disruption.
Specialized applications
Beyond common utility projects, HDD has specialized uses such as installing offshore pipelines and communication cables beneath the seabed. It is also being explored for emerging technologies like hydrogen transport and underground energy storage. In emergency situations, HDD can provide a rapid and effective way to install or restore critical utilities without major surface works.
Summary
Directional core drilling is a great tool for exploring and retrieving information about mineral deposits, aiming to collect data on what is underground. Horizontal directional drilling is a method for installing infrastructures underground along a path that does not harm the surface.
HDD depends on a trenchless technology that enables operators to avoid creating large and disruptive trenches in the ground. Similarly, DCD creates one mother hole, a single starting point for the drilling, which does not disturb the surface unnecessarily. This enables the drilling of multiple paths while also reducing overall drilling costs.
In short, both these types of directional drilling differ in applications, goals, and outcomes.
