Method of determining invaded formation properties including resistivity dielectric constant and zone diameter

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Attention is now directed jointly to FIGS.
1 and 2 which show a sonde supported logging tool in accordance with the present disclosure.
The logging tool is constructed with the circuitry shown in FIG.
2 incorporated in the tool.
The sonde has the several antennas defined in FIG.
1.
The sonde is thus indicated by the numeral 10 and is defined by a surrounding outer housing 11 which is supported on a logging cable 12.
The logging cable enables retrieval of the sonde as it is pulled upwardly in an open borehole, that is, a well that has been uncased.
The borehole is identified by the numeral 13.
The logging cable 12 passes over a sheave 14 and is stored in multiple turns on a drum 15.
The logging cable is connected by various conductors extending through the cable from the sonde 11 to data processing equipment 16 and the data is output to a recorder 17.
This sheave is connected with a mechanical or electrical depth measuring system 18 and provides measurements to the recorder 17 so that the data obtained from the logging sequence is recorded as a function of depth in the well borehole.
Details relating to construction of the several antennas will be given later.
It is sufficient for present purposes to describe the antenna system by referencing six antennas.
There are two receiving antennas and four transmitting antennas.
All six antennas are contructed in the same fashion and have the form of solenoid coils supported on a mandrel common to all the antennas.
More will be noted regarding that hereinafter.
Of importance at this juncture is the fact that the system includes receiver antennas 20 and 21 which are spaced from one another to thereby define a mid-point between the two antennas which is the symmetrical mid-point.
That is, the antennas positioned above the mid-point provide a mirror image to the antennas below that point.
In that sense, the antennas 20 and 21 are said to be equally spaced from the mid-point.
One acceptable measurement is five inches each from the mid-point, or a total span of 10 inches between the antennas 20 and 21