Abstract: An improved system for measuring dielectric properties of fluids in an oil well, utilizing the well casing as a waveguide for certain electromagnetic signals. A production logging tool in accordance with the invention includes a cylindrical mandrel sheathed by a housing. Transmitting and receiving coils are contained in annular grooves defined in the mandrel. In operation, the tool is suspended by a wireline logging cable within the casing of a producing well. The transmitting coils generate magnetic fields and azimuthal electric fields, which induce voltages in the receiving coils. These voltages are affected by the dielectric properties of fluids in the casing, and the voltages may be interpreted to determine dielectric properties such as water resistivity, dielectric permittivity, water hold-up, water cut, and water salinity.

Abstract: In an MWD system, a mandrel for connection to the drill bit is set forth which supports shallow, intermediate and deep measuring resistivity systems. By transmitting upwardly and downwardly in alternate fashion, and receiving the transmitted signal at pairs of receiver coils, transmitted signal phase shift and attenuation are measured. A method of measuring is set forth which includes making resistivity measurements close to the drill bit at increasing ranges from the borehole so that formation resistivity prior to fluid invasion is obtained. Measurements are thus provided of formation resistivity before, during and after fluid invasion. The method also accommodates formations which have a relative dip angle with respect to the well borehole.

Abstract: The present system is directed to an improved dipmeter system including plural sensors on isolated pads around a sonde. An independent output is formed from each of the sensor pads, and each output is provided to its own adjustable high pass filter. The several high pass filters delete low frequency constituents in the sensor signals. Then, the signals are provided to a dipmeter computer to determine depth with greater accuracy. As a variation, the high pass filters can be selectively adjusted to provide an adjustable frequency for the filters, and one version utilizes the derivative of the dipmeter signal as a function of velocity or time.

Abstract: The transmitter and receiver coils (35,40) in an electromagnetic dipmeter (10) are separated by a finite spacing (L) to remove borehole positional effects. Dip and strike are then determined with the same methods available for zero spacing devices by pulsing the transmitter signal.

Abstract: A coil array which is installed on a MWD drill collar for use in a resistivity logging system. The drill collar is provided with upper and lower coil support rings. These are toroids which support individual coil segments, and are connected by suitable magnetic shorting bars. The coil segments and shorting bars inscribe a specified solid angle or azimuthal extent. By connecting the outputs of the several coils through a combining circuit, the coils on a single coil form can be connected in series additive, or subtractive relationship. Through the use of two such coil forms with aligned coils on each, an azimuthally oriented window is thereby defined. By proper switching multiple azimuthally oriented windows can be made operative so that there is an azimuthal orientation to the current flow pattern relative to the MWD resistivity logging tool.

Abstract: High resolution induction logs (28) are obtained through borehole casing (15) by magnetically saturating the casing (15), logging with a tool (10) having different transmitter (35a, 35b)-to-receiver (40) coil spacings, and determining the formation (30) conductivities as a function of the coil spacings, coil frequency, and phase difference between the signals at these spacings. The logging is preferably done at an intermediate frequency which gives good resolution but is little affected by the saturated casing.

Abstract: A second receiver coil system (45a,45b) at right angles to the primary receiver coil system (40) in an induction logging tool (10) detects the skewness in the logging tool field pattern caused by the presence of assymmetrical formation structures (30). This skew signal, which provides a composite measure of the asymmetry of the formation structures (30), can be used to correct for horns produced in formation conductivity logs when the logging tool sonde (14) traverses interfaces between dipping beds. The skew signal can also be used to determine the dip and strike angles between such dipping beds.