Fracture permeability investigations using a heat-pulse flowmeter

Abstract

The search for a suitable geologic medium for containing radioactive wastes has raised new interest in the hydrology of fractured rocks. Borehole geophysics can identify fracture systems and even locate saturated fractures, however, it is difficult to locate flow paths based on this information. In most cases, the flow rate is far below the range of conventional flowmeters. A borehole flowmeter was developed that can measure flow rates between 0.04 1/min (0.01 gpm) and 2 1/min (0.5 gpm). The flowmeter operates by measuring the travel time of a heat-pulse advected by flow in the borehole. The flowmeter was used to locate fractures conducting flow in granite near Oracle, Arizona, and in a welded tuff formation near Superior, Arizona. The information provided by the flowmeter allows the accurate positioning of test equipment in future research and has helped investigators to better understand flowfield conditions during tests.