Exploratory Drilling

Overview of Coal Exploration Drilling

Coal exploration drilling collects information that provides an understanding of the in-place coal resource, including the thickness and depth of the coal seams, whether the seams are flat lying or sloping and the presence of any faults that may offset the coal. It is also important to determine the quality of the coal and how the quality varies over the project area, as well as vertically within the coal seam.

Big Metal Coal exploratory drillingFor thermal coal utilized in power plants, important quality parameters include percentage of moisture, percentage of ash, Btu (energy) per pound and percentage of sulfur. Other important quality parameters are ash fusion temperatures to project behavior of the coal ash in the power plant boiler, the chemical makeup of the ash including sodium oxide content and naturally occurring trace element concentrations.

Depending on the location and geologic conditions various types of drill rigs are used for exploration. In the Powder River Basin, coal exploration drill rigs are typically truck mounted with a mast that is laid down on the bed of the truck during transport between holes. These are similar to water well drilling rigs.

Data will be collected on coal within the Big Metal project area by drilling holes from the surface through the coal seams. The holes will be approximately 6-inches in diameter. Most of the holes will be less than 400-feet in depth with maximum depth of about 650-feet.

A geologist will be present during the drilling to log and describe the characteristics of the materials encountered as the drilling advances. In most of the exploration holes, 3-inch diameter continuous cores will be collected through the full thickness of the coal seams. These cores will be divided into a number of samples from the top to bottom of the seam and are described and placed in sealed, plastic sleeves for transport to the coal-quality laboratory, where they are analyzed. When the drill hole is completed, a down hole geophysical log, or “electric log” is run on each hole. The geophysical log provides information on coal seam depth and thickness and characteristics of the overburden strata.

Representative core samples of the overburden overlying the coal seams will be collected for testing of material strengths. This will to provide information for future pit designs. A few holes will also be drilled for monitoring ground water levels.

Following completion of drilling at each location the drill site is reclaimed. The Bureau of Land Management in coordination with the Bureau of Indian Affairs (BIA) and the Crow Tribal Historic Preservation Office (THPO) provide the pre-inspection, periodic and post inspection of each drill site as well as access to the drill site. During the pre-inspection cultural surveys for exploration several archeological artifacts and sites have been identified. These sites have been avoided by relocating access roads and drill sites. The small disturbed area is raked and seeded and the drill hole is filled with bentonite from the bottom of the hole to near the surface. A cement plug is placed from the top of bentonite to the surface.

For more information, click here to view the press release from the ceremony marking the beginning of the Big Metal Exploratory Drilling Program.