Horizontal Directional Drilling

Why HDD engineering technology is valuable

The technique allows for non-straight bores, meaning drills are able to navigate obstacles such as geological formations, and penetrate hydrocarbon reservoirs in an effective and more environmentally friendly way. HDD expands possibilities and routes for accessing oil and gas in the earth. It allows for multiple down holes to be drilled from the same rig, which minimises surface disturbance and environmental impact, miles deep into the earth. In oilfields with multiple dispersed deposits for example, a large radius is able to be tapped, which maximises the usage and investment in the rig. HDD technology, by its nature, has allowed for drilling at an angle, which usually results in more of a single hydrocarbon reservoir being explored, as reservoirs tend to form horizontally instead of vertically (i.e. between formations).

Making the inaccessible, accessible

Horizontal Directional Drilling within the oil and gas industry has expanded opportunities by allowing the industry to overcome common obstacles and barriers. Some of these problems that HDD surmounts include: 

• Hard rock. Previous to HDD technology, a layer of tough rock (e.g. granite ) between the surface and the reservoir, would block drilling. HDD allows the industry to avoid or bore through this obstacle. 

• Surface obstacles. HDD allows for reservoirs to be tapped at an extreme angle, and rigs no longer must be placed directly above the site being tapped. This means that reservoirs trapped underneath towns, mountains or areas of Special Scientific Interest (SSI) are now accessible. 

• Drilling in ground underneath bodies of water. HDD allows for a cheaper and easier way to tap reservoirs that are trapped under lakes for example, as they are able to drill from dry land at an angle. 

• Salt domes. Many deposits are found below salt domes or fault planes, which is a technically difficult environment and has an increased technical risk for the driller. HDD allows drillers to avoid salt domes, as well as allowing for a reduction in pressure on equipment near fault lines. 

• Irregular reservoirs. As fewer large reservoirs now exist, reservoirs that are connected in an irregular pattern (such as in a series of bars and deep troughs) are much more common, which makes HDD even more crucial. 

When overcoming these obstacles, safety is paramount for all involved. Meeting the requirements of industry Standards is important to ensure a safe and sustainable venture. Standards oil and gas drillers should be familiar with include the I.S. EN 16228 Standards. This drilling and foundation equipment safety Standard is broken down into 7 parts, and is highly recommended for all HDD projects. 

PART 1: Common requirements

PART 2: Mobile drill rigs for civil and geotechnical engineering, quarrying and mining 

PART 3: Horizontal directional drilling equipment (HDD)

PART 4: Foundation equipment

PART 5: Diaphragm walling equipment

PART 6: Jetting, grouting and injection equipment

PART 7: Interchangeable auxiliary equipment

Crucial bits

One of most important parts of a rig comes down to the type of bit being used. There are many types of bits used in the oil and gas industry, depending on what sort of ground needs to be penetrated. Tricone bits however are the most common. This type of bit has a head that is in three parts/cones. These three cones rotate, working inside each other with each row of it's cutting teeth. It works not by digging or scraping, but by repeated applying pressure to hundreds of contact points per second. The weight of the teeth of the bit rotating creates tiny fractures in the rock. The rock then breaks away into fragments called cuttings. The cuttings must then be removed for the drilling process to progress. This is where drilling fluid plays a critical role.

When using advanced bits in horizontal directional drilling, I.S. EN ISO 10407-2:2008 Petroleum and natural gas industries - Rotary drilling equipment is useful, as it describes the required inspection for each level of inspection and procedures for the inspection and testing of used drill stem elements.

Drilling Fluid

In most cases, drilling fluid is made of water and a type of inert clay called bentonite. This drilling mixture continuously circulates through the drill string, to the bit and back to the surfaces, and serves several purposes. The fluid helps lubricate the drill pipe and cool it, while the clay in the fluid creates a seal along the wall of the hole, which helps maintain the structure. The clay also improves the water suspension properties, making it easier to lift and transport the cutting to the surface (like a conveyor belt made of liquid). At the surface, the used liquid is cleaned and the cuttings removed, and the liquid is then reused. 

Two important Standards for drilling fluids include I.S. EN ISO 13500:2008 Petroleum and natural gas industries - Drilling fluid materials and EN ISO 10769:2011 Clay geosynthetic barriers - Determination of water absorption of bentonite.