Exploratory Borehole Drilling

What is Exploratory borehole drilling?

Exploratory borehole drilling is an important step in Geoexchange Suitability Assessments (GSA’s) which involves drilling a strategically placed borehole, known as an exploratory borehole, usually at one or more of the furthest points of the proposed geoexchange system design that allows engineers to evaluate site-specific ground conditions for a future geoexchange system.

Geoexchange Suitability Assessments are multi-step programs that evaluate the suitability of geoexchange systems at a particular site. They involve evaluating site-specific conditions to determine available site-specific options for geoexchange solutions.

There are a few different ways in which geoexchange systems can exchange heat with the ground to heat and cool buildings. One option is a Closed-Loop Vertical (V – GHX) system which involves a network of boreholes that are drilled into the ground at a typical depth of 50m to 250m. Once a network of boreholes is completed, heat transfer fluid will be circulated through the boreholes.

When a finished building is connected to this network, these pipes will allow the building to be cooled in the summer by transferring and storing the building’s heat into the ground. In the winter, this system will return to the heat stored in the ground and harness it to warm the building. The ground’s year-round moderate temperature will allow this heating and cooling system to operate at high efficiencies, leveraging every unit of electricity purchased and reducing carbon emissions while lowering the building’s heating and cooling costs. 

If the results from exploratory borehole drilling look promising, the process of designing and implementing a full scale geoexchange heating and cooling system can accelerate!

Exploratory borehole drilling: An exciting step in Geoexchange Suitability Assessments

1. Evaluation of ground thermal properties

Upon the completion of drilling an exploratory borehole, location-specific ground thermal properties can be evaluated, such as ground thermal conductivity – the ground’s ability to transmit heat – and  the passive ground temperatures along the length of the borehole. These properties significantly effect the performance of a geoexchange system, so measuring them before a design is finalized enables the design team to fine-tune geoexchange field sizing. This helps ensure that the client will only buy as much installed Ground Heat Exchanger (GHX) capacity as is required to right-size the system.

2. Construction cost management through mitigation of contractor risk

Exploratory boreholes provide site-specific information about drilling conditions to prospective contractors that was previously unavailable. This significantly reduces the risks for contractors who might be interested in working on the project. In fact, it is common for the contractor who drills the exploratory boreholes to submit a bid for the project when the complete GHX construction package goes to Tender.  

By documenting and sharing a description of conditions encountered below ground and the rate of drill progress observed during the drilling of exploratory boreholes, Falcon’s design team provides valuable, pertinent information to contractors during the bidding process. This has proven to be an effective method to mitigate contractor risk. With less risk, contractors often choose to bid the work more aggressively, resulting in savings for the client. 

Incorporating exploratory boreholes into the final GHX system

On top of leveraging every dollar spent on exploratory borehole drilling in the above ways, Falcon’s design team also makes every effort to incorporate the exploratory boreholes into their design of the final GHX. When an exploratory borehole is incorporated into the final GHX, it displaces one borehole required by the completed system. This is the quiet power of carefully prescribed exploratory borehole drilling – when an exploratory borehole is successfully integrated into a final GHX, its net effect is an almost negligible increase in effort and cost within the construction of the completed GHX.  

Despite this low cost, exploratory boreholes offer powerful insights into site specific conditions at a critical project stage, allowing designers to tailor the designed system capacity to suit while also helping to reduce construction costs through mitigation of contractor risk.  

All that benefit for minimal additional cost and effort? Now, that’s savings!