drillhole

A drillhole, often written drill hole, is a hole created by drilling into the subsurface with a drill rig. Drillholes are used for geological exploration, mineral or hydrocarbon resource delineation, groundwater assessment, environmental monitoring, and construction or dewatering applications.

There are several types of drillholes. Exploration drillholes are intended to sample and characterize subsurface rocks. Core drilling uses a hollow core barrel to retrieve continuous cylindrical samples, while non-core drilling collects rock fragments. Blind or blast holes are drilled for mining and blasting, and production or monitoring wells provide access to fluids or gauge conditions in the subsurface. Common drilling methods include rotary drilling, diamond core drilling, and percussion or air/mud drilling; diamond core drilling yields intact cores for detailed analysis.

Equipment and procedures vary by purpose. A drill rig, drill string, and bits are standard, with core barrels and casings used for core or groundwater drilling. Surface casing and cementing may be employed to protect aquifers. In mining, holes are often drilled to precise diameters and depths for blasting, ore sampling, or dilution testing, while environmental projects emphasize sampling intervals and well integrity.

Data and interpretation rely on collar surveys, depth records, and downhole measurements (inclination and azimuth). Core logging, sample assays, and geological logging inform models of rock type, mineralization, and structure. Safety, environmental protection, and regulatory compliance guide drillhole abandonment, including sealing and plugging to prevent contamination or subsurface hazards.