Horizontal Drilling for Electrical Resistance Heating

Aggressive removal of dense non-aqueous liquid (DNAPL) phase tetrachloroethylene (PCE) and trichloroethylene (TCE) under an active manufacturing

Welding the black steel casing for the horizontal ERH system and horizontal SVE

facility is the objective of an electrical resistance heating (ERH) system that was installed using horizontal drilling.  Placement of electrical resistance heating electrodes within horizontal carbon steel pipe overcame concerns about traditional, vertically installed electrodes at the site:

1. Drilling inside of the active facility would generate dust and cause vibration that would interfere with the precision machining and manufacturing work performed in the building,
2. The labyrinthine distribution of multiple milling machines of many different shapes and sizes would interfere with vertical drilling work to install the ERH electrodes under the building,
3. Interruption of the non-stop, 24-hour-a-day production schedule was unacceptable to the owners of the operation, who were not responsible for the plume beneath the building because it emanated from a neighboring former drycleaning facility, and
4. A grid of vertical ERH electrodes would severely limit placement options for a horizontal soil vapor extraction (SVE) system that was required in order to prevent vapors generated by the ERH system from entering the indoor air of the manufacturing facility.

Horizontal drilling was used to allow the 24-hour production schedule to continue and to avoid the labyrinthine of milling machines in this active facility.

The Horizontal Solution to ERH Electrode Placement

Electrical resistance heating electrodes are distributed in the subsurface to create a network of triangular electrode groupings in cross section.  The purpose of such a configuration is to optimize the distribution of heat across the target zone, from top to bottom.  One set of electrodes is placed at a shallow horizon within the target zone, and another set is placed at a deep horizon.  Shallow and deep electrodes are staggered, so that they don’t overlie each other.

Vertically the target zone reaches from 2 to 15 feet below ground surface (bgs), but horizontally it spans a 17,000 square foot area of the building.  Electrodes are placed at only two different elevations, but multiple electrodes are placed along a given horizontal traverse.  Installing electrodes within horizontal casings is therefore much more efficient than installing them in vertical casings.  The flexibility of shifting electrodes within a horizontal casing that extends 200 feet across the building is an additional benefit of using horizontal drilling to install the electrodes.  This flexibility will allow the electrical resistance heating to be optimized in the course of its operation, as some portions of the target zone remediate more quickly than others.

Hybrid ERH and horizontal SVE Wells

The shallow ERH pipes served double duty as horizontal soil vapor extraction (SVE) wells.  Alternating sections of the pipe were slotted for SVE, or solid for ERH.  This configuration avoided the logistical problem of threading SVE wells into the network of ERH electrodes.

Horizontal Electrode Pipe Installation

Heavy, rigid black steel casing with 6-inch diameter was used for installing the ERH system. Directional Technologies employed both blind and entry-exit installation methods for the horizontal ERH system.  Each black steel casing was welded onto the casing string as it advanced into the wellbore.  See the illustration at the top of this article.  The shallow wells were only 3 feet below the building slab, so the drilling method was adapted to minimize communication through cracks in the foundation.  A grout seal was emplaced around the pipe where it crossed below the building foundation in order to prevent short-circuiting of the horizontal SVE system.  Installation of the deep wells 14 feet bgs in weathered sandstone and gravel formation was challenging because of the weight and limited flexibility of the black steel casing.  In completing the ERH casing under the manufacturing facility, Directional Technologies Inc.  brought to bear its 20 years of experience directionally drilling in every form of soil, sediment or igneous and metamorphic rock.

Round-the-clock site operations using sensitive milling equipment continued unabated by the directional drilling work in yet another example of Directional Technologies’ tradition of partnering with consultants and site owners/operators to ensure successful and unobtrusive remedial system operation.

Contact Directional Technologies, Inc.
Horizontal Directional Drilling Services
Kathy Sequino
ksequino@directionaltech.com
203-294-9200

THE “STRAIGHT SKINNY” ON BENTONITE-BASED DRILLING MUDS AND THEIR STANDARD PRACTICE USE IN THE HORIZONTAL WELL INDUSTRY

Let’s make our point up front: 1) bentonite-based drilling fluid is NOT bad for horizontal well projects; 2) it does not damage the formation; 3) it is a naturally occurring clay material that is mined; and 4) it does flush easily/adequately during horizontal well development. Most remediation professionals have designed and/or installed vertical wells at one time or another during their careers. After advancing the boring, setting the screen/riser and sand pack, the vertical driller usually pours dry bentonite chips or pellets into the annular space between the vertical well and formation. The vertical driller then adds water to hydrate the bentonite, creating a very effective seal as the bentonite swells (or “yields”).

Why are we discussing a topic that is common knowledge/practice to most remediation professionals? Because some people who claim to be experts at installing horizontal wells assert that bentonite-based drilling fluids damage the formation and cannot be adequately flushed from the annular space during development. These are false assertions that distort what actually happens when bentonite-based drilling fluid is used. These false assertions feed off of most remediation professional’s real-world experience when dry bentonite is intentionally hydrated in situ to create a seal in a vertical monitoring well. In other words, an attempt is being made to make you think that because straight bentonite hydrated in situ makes a great seal, it does the same thing when used in a drilling fluid when installing a horizontal well.

The argument turns on the fact that: 1)bentonite-based drilling fluid is hydrated ex situ and yields prior to commencing directional drilling; and 2) bentonite is a component of the directional drilling mud system, not the sole component.

Horizontal Well mud pit

A “seal” is never formed by bentonite in a horizontal well and in addition Directional Technologies, Inc. uses a proprietary process to develop the horizontal wells based on years of field experience in the oil field, the utility industry and the environmental industry. This development process results in fully functional horizontal wells.

The same horizontal remediation well professionals that criticize bentonite-based drilling mud also advocate the use of “bio-polymer” drilling muds. These are manmade products based on gaur gums and vegetable products that biodegrade after use to various types of sugars that purportedly “jump start” the bioremediation process by supplying nutrients to naturally occurring bacteria. The problem with this is that the sugars tend to enhance undesirable bacteria that can create slime that damages the formation.

Directional Technologies, Inc. develops and formulates-specific drilling fluid programs for each horizontal remediation well we install. We do not use a one-dimensional, “one-size-fits-all” drilling program. There is both a science and an art to creating the optimal drilling fluid program for each horizontal well installation. It is imperative that the selected directional drilling fluid(s) build the bore path to: 1) prevent formation damage; 2) enable safe cost efficient directional drilling/horizontal well installation; and 3) prevent bio-fouling.

Stay tuned for additional technical communications regarding the horizontal well installation process or contact us at 1-877-788-4HRW or drilling@directionaltech.com to further discuss your possible horizontal remediation system.