BohrlochResistivitätslogs

BohrlochResistivitätslogs, often referred to as resistivity logs, are geophysical well logging tools used in the oil and gas industry, as well as in hydrogeology and mining. They measure the electrical resistivity of the subsurface formations surrounding a borehole. Different rock types and fluids within the pore spaces of these formations have distinct electrical properties. Porous rocks saturated with saline groundwater or oil generally have low resistivity, while dense, impermeable rocks like granite or anhydrite tend to have high resistivity. Hydrocarbons, such as oil and natural gas, are highly resistive compared to water.

The fundamental principle behind resistivity logging involves introducing electrical current into the formation and measuring the resulting voltage drop. By applying Ohm's Law (R = V/I), the resistivity can be calculated. Various configurations of electrodes are used to focus the current and voltage measurements at different depths and to correct for borehole effects, such as the mud filtrate invasion. Common types include focused logs like the laterolog and induction log. Laterologs are effective in formations with conductive drilling fluids, while induction logs are better suited for non-conductive fluids.

The interpretation of resistivity logs provides crucial information about lithology, the presence and saturation of hydrocarbons, and the extent of water encroachment. Anomalously high resistivity can indicate the presence of oil or gas. Low resistivity in a porous formation typically signifies water saturation, the salinity of which can also be estimated. These logs are often used in conjunction with other well logs, such as gamma ray logs or neutron logs, to create a more comprehensive understanding of the subsurface geological environment.