The When and Why of HDD Intersects
Horizontal directional drill (HDD) intersect methodology has been utilized since the early 2000s. It has only grown more prevalent as the industry matures and as larger, longer and more complicated HDDs are completed.
What Is an Intersect?
An HDD intersect is when two pilot holes are drilled from opposite ends of a crossing and meet somewhere in the middle. This creates a single pilot hole from one side to the other. This methodology requires two full HDD rig spreads. Therefore, it can double the amount of equipment required on site for the crossing. It adds complexity and cost to an HDD. However, it can be a large benefit or even a necessity for successful completion of certain crossings.
When and Why Are Intersects Used?
There are many cases in which an intersect methodology is a benefit. The most prevalent reasons for completing an intersect are the following.
Long Crossings
As drills get longer, friction along the drill pipe from the soil or rock around it will also increase. If excessive levels of friction build up along the drill pipe, it can lead to difficulty in making forward progress. This is due to not being able to put enough pressure on the bit to progress it forward, or to accurately steer it. Therefore, the achievable length of pilot hole can be essentially doubled with the use of an intersect methodology. Each string of drill-pipe would only need to complete around half of the total pilot hole length.
For this reason, many HDDs in excess of 5,000 ft (1,500 m) will utilize an intersect methodology. This minimizes the risk of not successfully completing the pilot hole. Aside from the friction consideration, intersects can also assist with schedule on long crossings. It can cut the pilot hole phase schedule in half.
In some cases it may even reduce total pilot schedule by more, since there is significantly less time required to trip the full pilot assembly out from the end of the drilled hole back to surface when required for tool changes, wireline breaks, and/or tripping for annular pressure or hole cleaning purposes.
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