The Lugeon test, also known as a packer test, is used to determine the permeability of subsurface rock. It involves injecting a measured amount of water into a packer-isolated section of a borehole at set intervals. The pressure of the water entering the subsurface is predetermined and controlled in regular intervals. Once the system reaches a quasi-stable state, water pressure at the outlet is monitored.
The process begins by isolating a section, typically up to 5 meters long, from the rest of the borehole using rubber packers. During the descent, the packer is not in contact with the borehole walls. After initial positioning, the drilling equipment is lowered into the deeper parts of the borehole, causing the packer to expand and press against the borehole walls. Once the packer is correctly positioned, water is pumped under pressure through the drill pipes, packer body, and perforated pipe. Depending on the hydraulic conductivity of that rock section, the water infiltrates to varying degrees.
The Lugeon test is typically conducted in five steps. In each step, a constant water pressure is applied for 10 minutes or until steady flow is achieved. During the test, flow and pressure data are recorded every minute. Flow data may be registered as either volume or flux, depending on the flow meter. The first step usually involves a low water pressure, followed by an increase in the second step, with flow data recorded for the next 10 minutes or until equilibrium is reached (when flow ceases to be turbulent). This step is repeated until the maximum pressure is determined. Once maximum pressure is established, it is gradually reduced to the initial level in equal intervals. The resulting data are used to construct a pressure curve. The test generally includes three or two steps. Based on the recorded data and pressure curve, the rock's hydraulic conductivity, or permeability coefficient, is calculated.