Most HDD contractors will tell you they prefer constructing double-ended well designs over “blind” horizontal wells (single-ended construction). This preference stems from the fact that pushing on pipe presents many more challenges than pulling.
Additionally, a reamer strategically placed in front of the pull-head ensures the borehole is fully opened when pulling back a well during double-ended construction. Blind horizontal well construction is much more prone to issues stemming from borehole collapse.
A challenging formation might hinder or even completely prevent blind horizontal well construction. However even in ideal drilling conditions, a long enough of a bore profile presents an increasing likelihood of collapse issues.
Many years ago, Ellingson developed their knock-off bit technology to address the challenges of blind horizontal well installation, particularly for long well profiles and/or loose soil conditions. The patented technology involves a steerable, expendable drill bit that allows well construction through the inside of the drill pipe. The drill pipe acts as a protective casing which mitigates the issues of borehole collapse. This method also reduces side friction and bowing of the well screena and casing during the installation process.
Ellingson successfully used the knock-off system to install record length blind horizontal wells, and they continue to address challenging sites with the technology.
Locating technology proved to be the biggest challenge to overcome with the knock-off method. Standard steering tools house the electronics inside the drill pipe. However, the knock-off requires an open drill pipe for the full length of the drill string.
Without giving too much away, the patented knock off tool design pushed the steering electronics to the outside of the drill pipe, leaving a full diameter open throat to allow the well materials to pass through.
Previously, compatible steering systems included walkover only. Occasionally, site-specific requirements might require an even more robust steering technology such as a wire line or solid-state gyroscope.
For many years, the knock-off system precluded the use of wireline or gyroscopic steering tools. However, Ellingson worked extensively with steering contractor SharewellHDD on the problem. The team eventually developed a removable gyro steering technology compatible with the knock-off system.
Since developing this advanced knock-off system, Ellingson has installed several long blind remediation wells where site-specific conditions precluded the use of walkover steering systems.
Most recently Ellingson used the tool at a former manufacturing site in Southern California. The design included single-ended air sparge wells installed to a total vertical depth of approx. 40ft BGS. The blind horizontal wells involved total installation lengths of over 1000ft with multiple screen intervals.
A compressed project schedule required an extensive amount of simultaneous construction activity across the site, limiting Ellingson crews’ access to the ground surface along the borepath. Rather than interfere with ongoing operations by using walkover steering, Ellingson deployed the recently developed knock-off tool with the gyroscopic steering option.
These long, blind horizontal wells will play a crucial role in the accelerated cleanup of this exciting brownfield development project.
Tags: blind horizontal wells, difficult access, directional drilling, environmental HDD, gyroscopic steering, horizontal sparge wells, horizontal wells, innovative technology, knock-off bit, wireline steering