REV97788 - Laserfiche WebLink

Home Browse Search

Application for Technical Revision to MLRB Permit 80-47 Page 3 of 7 To prepare for the conductive fracture experiments, a few fracture pretests will be performed to assess the direction of the fractures. These fracture pretests will be performed at three or more locations inside the commercial mine entries. An environmentally benign grout will be pumped into these fracture pretests, and the resultant fracture geometries will be probed with borehole cameras and observation holes. The holes for the conductive fracture tests may be drilled parallel to the cliff face (15° east of north) or may be drilled in a direction designed to intersect a natural fracture or `joint" (these are dominantly 69° east of north). They will be set back from the cliff face far enough to prevent fracturing and fluid escape through the cliff face. This set back distance is likely to be 50 to 200 feet. A hole may or may not have a casing cemented along its length. If it is cased, most of the casing will be a nonconductive material so that electrical current runs through the fracture and not through the casing. The casing will be perforated prior to fracturing. The fracture will be created by pumping a slurry of an inert material, such as calcined coke, in water (which may contain a viscosifier such as a benign polymer gel) into the hole at a pressure sufficient to break the rock. A material safety data sheet for the specific material(s) used will be provided to DRMS prior to fracturing operations. The fracture volume is likely to be 20-40 cubic feet, so the slurry will probably be made up in one or more relatively small tanks of 10-15 barrels. The pumps will also be relatively small compared to standazd hydraulic fracture job pumping equipment. After the fracture has been formed, two electrical connections will be made. The connection near the entry of the hole will probably utilize the conductive metal casing in that end of the hole. The connection at the other end may be accomplished by drilling a second hole from the Mahogany Zone face at the mine bench that will intersect the fracture. During and subsequent to the hydraulic fracture creation, geophysical sensing will be used to map, as accurately as possible, the position of the fractures. During fracture creation, passive seismic monitoring with geophones stationed in and around the mine will be used to map the fracture in three dimensions. Active seismic surveys using low energy (hand-held hammer) sources will also be used to locate the fracture after it is created. A fracture map will then be created to aid the experimentation effort. After the fracture has been created, connected and mapped, observation holes will be drilled both parallel and normal to the fracture. Instrumentation may be cemented in these holes or they may be left open to facilitate continuous logging with temperature and/or electrical sensors. Sufficient monitoring holes will be drilled to provide accurate information on electrical and thermal results.