By Kyle Carlton, PG, Senior Geologist, Directional Technologies
The limitations of angled wells leave many environmental consultants frustrated. Angled drilling has its place for gaining access under some types surface infrastructure but using horizontal wells instead of angled wells provides significant advantages regarding entry angles, steerable bore paths, and horizontal coverage of the target areas beneath buildings, roadways, runways, and other areas difficult to access.
Access:
The primary reason environmental professionals require angled wells or horizontal wells is access. Directly accessing and installing remediation wells into contamination under buildings, utilities, roadways, runways, wetlands, or rivers can greatly expedite site cleanup. Access to contaminated soil or groundwater beneath surface obstructions can be reached using directional drilling or angled drilling for installation of remediation wells.
While both directional drilling and angled drilling can be performed beneath surface obstructions, the equipment, drilling procedures, and final wells are quite different.
Directional drilling is performed by horizontal directional drilling rigs, which begin borings at shallow angle entries of approximately 10 – 15 degrees from horizontal. The directional drill bit allows for steering and changes to the bore path so that the boring can be navigated to a target area and come to a horizontal position for installation of a horizontal well.
Angled drilling is typically done with sonic, direct push, or hollow-stem-auger drill rigs, at entry angles greater than 45 degrees. Directional control is not capable with these drilling methods, and the bore path is straight, follows the angle of entry, and does not curve. Wells installed with these methods are angled, matching the initial angle and direction of the bore.
Horizontal Wells vs. Angled Wells:
As with the drilling and installation methods, the horizontal wells differ significantly from angled wells in construction and function. Horizontal wells typically target a soil horizon where contamination may be spreading laterally within a plane such as the soil/groundwater interface or on top of a confining layer. Horizontal well screens can be engineered for long screened sections of 500 feet or more to target large plumes.
Angled Wells typically are designed, constructed, and operated like vertical remediation wells.
Limitations of Angled Wells:
Angled wells used for remediation can be successful; however, are highly limited in their ability to access large areas beneath surface obstructions. Additionally, because the angle is so steep (>45 degrees), angled well screen cannot be installed horizontally, which limits the ability of the angled well to target horizontal plumes.
Advantages of Horizontal Wells:
While accessing contamination beneath surface obstructions has been the primary focus of this discussion, it is important to know that horizontal wells provide several more advantages than just gaining access.
1) Remediation of Large Areas
2) More Screen Contact with Contaminate Plume
3) Normal Business Activities Continue During Remediation