Ole Bernt Lile

Estimating groundwater flow velocity from changes in contact resistance during a saltwater tracer experiment

Abstract The contact resistance of a current electrode is the potential measured at the surface of the electrode divided by the current strength and is a function of the resistivities and geometry of the formations surrounding the current electrode. The equation describing the contact resistance of a half sphere electrode shows that the resistivity of the formation immediately surrounding the electrode dominates the size of the contact resistance. Measurements of the contact resistance of a current electrode over time can then be used to estimate changes in the formation resistivity close to the electrode over time. The formation resistivity is directly related to the pore fluid conductivity, which again, is related to the concentration of a conducting solute. Existing solute flow theory can be used to relate the change in concentration with time of a solute to the groundwater flow velocity, hence the measurements of contact resistance can be used to estimate a groundwater flow velocity. Hydrogeologists use the rate of dilution of a tracer injected into a borehole, monitored by water samples, to calculate the groundwater flow velocity. At Haslemoen, Norway, the exponential decay of the inverse contact resistance during a tracer experiment was used for estimating the velocity. A sodium-chloride solute slug of 0.5 m3 was injected into the groundwater at 4 m depth through a well in which there was installed a short iron bar electrode, reaching from the surface to just below the groundwater table. The well was cased with a plastic tube so that only the lowermost part of the iron bar electrode was in contact with the surrounding formation. The inverse contact resistance of the electrode was monitored every 2 h over approximately 600 h, showing an exponential decay by time. Fitting of an exponential function to the data gave the groundwater velocity parameter equal to approximately 0.26 m/day, a number which was in satisfactory agreement with velocity estimations using other methods.

Self potential anomaly over a sulphide conductor tested for use as a current source

Abstract A minus 420 mV self potential anomaly over a sulphide deposit was tested as current source. Two lead electrodes were dug into the ground, one at the place where the negative peak value was found and the other one in a nearby bog. The electrodes were connected through variable load resistances ranging from 1 MΩ to 1 Ω and the voltage drop over the resistances was measured. The current strength through each load resistance which was applied was then calculated. The electrode groundings were then salted with sodium chloride and measurements following the same procedure were repeated after 3 days. The electrodes were then short-circuited for 4 days and the same type of measurements were then carried out. It is concluded that the SP voltage over the two electrodes behaves like an ordinary battery source. A maximum power of 130 μW could be extracted with a voltage drop of 175 mV over a load resistance of 250 Ω.

Monitoring of a tracer experiment with electrical resistivity at Haslemoen, Hedmark County, Norway

Electrical resistivity measurements can be used in tracer studies to monitor the movement of an injected saltwater pulse (Bevc and Morrison 1991, Karous 1989, White 1988). A tracer experiment was conducted in the unconfined, sand-silt groundwater aquifer at Haslemoen in Hedmark County, Norway. In the study area, groundwater flows mainly towards the south, with a velocity of approximately 0.2 m/day. Depth to groundwater level is approximately 2.5 m.

Characterising curing cement slurries by permeability, tensile strength and shrinkage

This work was carried out to obtain more knowledge about the transition period of curing oil well cements. The results show that the curing characteristics are a function of temperature and that there is a correlation between shrinkage and cement content. The paper also introduces a new mechanism for gas migration and discusses how the studied parameters can be used to predict gas migration.