Once all of the modeling, treatability studies, and design work have been completed, it’s on to the next step for TerraTherm and time to mobilize our staff, resources, and equipment to the field to install the thermal wellfield. This is an essential task that must be done precisely in order to ensure thermal success. It does not matter how well the site was modeled or designed; if the installation is not done correctly it can lead to issues with thermal treatment operations and potentially jeopardize the success of the project.
Plan of Attack:
When the wellfield layout has been finalized, a plan of attack is formulated regarding the methods that will be used to install the thermal wellfield. The following questions need to be answered:
- What type of drilling method will be used (sonic, auger, direct push)?;
- What are the Contaminants of Concern (COCs)?;
- Are there any access concerns (low ceilings, tight wellfield, close neighbors)?;
- How many of each type of well (Heater wells, Vapor Extraction, Multi-Phase Extraction wells)?;
- Are there utilities in the wellfield?; and
- Will bedrock be encountered?
When developing a drilling schedule it is important to work your way out of the wellfield and not “paint yourself into a corner.” By doing so, and carefully ensuring that no wells are missed during installation, the risk of potentially damaging wells that have already been installed is greatly reduced. Hitting wells during installation is never a good thing and it can lead to re-drilling the entire well.
Installation of the heater cans can be tricky depending on the length of the can. When installing cans, precautions must be used in order to ensure the integrity of the can is maintained as well as the safety of employees onsite.
Currently, TerraTherm’s preferred drilling method is the use of sonic rigs, although we continue to explore other methods. These rigs are very versatile, produce less drill cuttings, and limit the potential exposure of contaminants to the onsite workers. This system uses casing that is advanced along with the core barrel. In this method the casing is pushed first (usually in five or ten foot increments) essentially sealing the hole. Then the core barrel is sent down to clear the hole. This procedure is repeated until the desired depth is reached, and reduces the amount of drill cuttings that are produced, thereby helping to protect the drillers from potential contaminated vapors.
Knowing and paying attention to the COCs is highly important because it can affect the safety of the workers and also affect the schedule, e.g., if the level of personal protective equipment (PPE) needs to be increased. When drilling, one must be diligent to follow the TerraTherm site specific Health and Safety Plan (HASP) to ensure the safety of everyone onsite during wellfield installation.
Things to Watch Out For
Wells cannot always be placed exactly where they are originally designated on the map for various reasons. Aboveground or underground utilities may be encountered that can prevent a well from being installed in the desired location. If the well is near a building and the rig cannot gain the required access, the well location may need to be changed. If and when a well relocation occurs, it is important to keep in mind the overall goal, which is to heat the entire target treatment zone up to the desired treatment temperature. In these instances, the Construction Manager onsite, along with the Project Engineer need to work together to adjust well locations to avoid the obstruction while not having a negative effect on the temperature goals.
Also during the drilling installation it is important to pay attention to the soil make up and confirm that it matches the parameters that served as the basis for the thermal design. If there are differences (an example being if a clay layer is thicker than expected and interferes with a planned steam injection screen interval) it is much easier to address them during installation and make the necessary changes than it is to wait and have to make the changes during operations (e.g., drilling new wells). By paying attention during the installation, time and money can be saved.
Drilling and installation of the wellfield is a very important event that can contribute to the overall success of a thermal project or, on the other hand, be the cause of potential issues and even failure if corners are cut and the installation was not done correctly.
If you would like to ask about this topic, please do not hesitate to contact me at firstname.lastname@example.org. Also for other drillers in the industry, what are the methods that you use to achieve results without having issues? Feel free to leave a comment in the comment section below and don’t forget to sign up for more related posts in the future!