Small hole well logging sonde and system with transmitter and receiver assemblies

A well logging sonde has an outer diameter of 1-11/16 inches or less and includes a transmitter coil and at least two receiver coils. The coils are contained in a coil housing. A transmitter circuit provides a signal for energizing the transmitter coil to develop an electromagnetic field in an earth formation. A transmitter case contains the transmitter circuit and is mechanically connected to the coil housing so that the transmitter provides the signal to the transmitter coil which develops the corresponding electromagnetic field in the earth formation. A receiver circuit receives signals from the receiver coils resulting from the reception of electromagnetic energy from the electromagnetic field after passage through the earth formation. The receiver circuit provides a signal representative of at least one characteristic of the earth formation in accordance with the signals from the receiver coils. The receiver circuit is housed in a receiver case which is mechanically connected to the coil housing in a manner so that the receiver coils provide their signals to the receiver means. A cable connector is mechanically connected to a well logging cable so as to electrically connect the receiver circuit to at least one conductor in the well logging cable.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to monitoring instruments in general and, 
more particularly, to a well logging sonde and system. 
2. Summary of the Invention 
A well logging sonde having an outer diameter of 1-11/16 inches or less 
includes a passive element housing adapted to be physically and 
electrically connected to other members of the sonde, a transmitter case, 
a receiver case, and a cable connector. The passive element houses a 
transmitter coil and two receiver coils in a predetermined spatial 
relationship to each other. The transmitter case contains a transmitter 
circuit which provides a signal to energize the transmitter coil so as to 
develop an electromagnetic field in an earth formation. The receiver case 
contains a receiver circuit which receives signals from the receiver coils 
resulting from the reception of electromagnetic energy from the 
electromagnetic field after passage through the earth formation and 
provides a signal representative of at least one characteristic of the 
earth formation in accordance with the signals from the receiver coils. 
The cable connector includes an output connector adapted to be physically 
and electrically connected to a well logging cable so that a signal 
appearing at the output connector is provided to the cable. The cable 
connector is also adapted to be and is physically connected to the 
receiver case in a manner so as to provide the signal from the receiver 
circuit to the output connector. 
The objects and advantages of the invention will appear more fully 
hereinafter from a consideration of the detailed description which 
follows, taken together with the accompanying drawings wherein one 
embodiment of the invention is illustrated by way of example. It is to be 
expressly understood, however, that the drawings are for illustration 
purposes only and are not to be construed as defining the limits of the 
invention.

DESCRIPTION OF THE INVENTION 
Some of the world's largest oil fields have many open hole producing wells 
which contain a small diameter production or "kill string" tubing through 
which logging tools must pass before reaching the open hole interval. The 
present invention is a slim hole resistivity well logging tool which is 
capable of logging wells containing tubing as small as two inches in 
internal diameter. Logging these wells with standard 35/8" resistivity 
sondes requires the tubing to be pulled, at great expense. 
Referring to FIG. 1, a logging sonde 1 is 1-11/16" in diameter. A 
transmitter 5 provides an alternating current signal at a predetermined 
frequency preferably that of 2 megahertz to a transmitter coil 7. 
Transmitter coil 7 transmits electrical energy into the earth formation. 
Receiver coils 10 and 11 are spaced 25 and 37 inches, respectively, from 
transmitter coil 7. Receiver coils 10 and 11 receive electrical energy 
that has passed through the earth's formation and provides corresponding 
alternating current signals to a receiver 14. 
Referring now to FIG. 2, transmitter 5 includes an oscillator 18 providing 
a signal to a buffer amplifier 20 which in turn provides the signal to a 
power output amplifier shown as output 22. A typical power output would be 
in the order of 2 watts. The two megahertz signal emitted by coil 7 causes 
an electromagnetic field to propagate through the surrounding formation 
and this field is detected sequentially by receiver coils 10 and 11. The 
time lag or phase angle between the two signals detected at coils 10 and 
11 is inversely proportional to the resistivity of the surrounding 
formation. 
Coils 10, 11 provide signals to balanced mixers 26 and 28, respectively, 
which also receives a signal from a local oscillator 30 having a 
predetermined frequency of about 1.998 megahertz. Balanced mixers 26, 28 
provide IF signals at a predetermined frequency, preferably about 2 
kilohertz, to IF amplifiers 32 and 33, respectively, which, in turn 
provide IF signals to voltage controlled oscillators 34 and 35, 
respectively. Oscillator 34 provides an FM carrier frequency of 72 
kilohertz, while oscillator 26 provides an FM carrier frequency of 26 
kilohertz. The resulting signal from oscillator 35 is provided to a low 
pass filter 39 which in turn provides a signal to a cable driver 40 which 
also receives a resulting signal from oscillator 34. Cable driver 40 
provides an output signal to a capacitor 43 to a single filament type well 
logging cable 45. 
At the surface the signal from cable 45 passes through a DC blocking 
capacitor 48 and is communicated to amplifiers 50, 51. Amplifiers 50, 51 
provide amplified signals to a high pass filter 54 and to a low pass 
filter 55, respectively. Filters 54, 55 provide signals to automatic gain 
control amplifiers 57 and 58, respectively, which in turn provide 
amplifier signals to phase lock loop demodulators 60 and 61, respectively. 
The outputs from demodulators 60, 61 are provided to active filters 64 and 
65, respectively. Filters 64, 65 provide the signals corresponding in 
frequency to the original 2 kilohertz signals provided by mixers 26 and 
28, respectively. The signals from filters 64, 65 are provided to a phase 
computer 68, or any other type of phase determining means, which provides 
a signal corresponding to the phase difference between the signals from 
filters 64 and 65, which in turn correspond to the resistivity of the 
formation. Phase computer 68 provides a signal to an analog-to-digital 
converter 70 which provides corresponding digital signals to a digital 
read-out 75 for immediate viewing and to a programmable memory 76. Memory 
76 converts the digital phase signals into digital logrithmic resistivity 
digital signals and provides them to a digital-to-analog converter 80. 
Converter 80 provides a corresponding analog signal to a recorder 81. 
Referring now to FIG. 3, logging sonde 1 includes a cable adaptor sub 100 
having external threads and an internal passageway. Mounted within cable 
adaptor sub 100 is a feed through connector 104, having a wire 107 
connected to one end. A connector mounting plate 112 is affixed to cable 
adaptor sub 100 by screws and has mounted thereon one part of a coaxial 
connector 114 which is electrically connected to wire 107. A receiver 
electronic case 119 is threaded onto cable adaptor sub 100 with sealant 
being accomplished by o-rings 120. 
A connector mounting plate 123, having a mating part of coaxial connector 
114 mounted thereon is located within receiver electronic case 119. An 
electronic mounting plate 126 is separated from connector mounting plate 
123 by spacer rods 127. Mounting plates 126 has a channel 130 in it for 
the passage of wire (not shown) from connector 114. A second electronic 
mounting plate 133 is also located within receiver electronic case 119 and 
has a heat sink plate 134 mounted thereon. Spacing rods 128 provide 
strengthening features to the mounting plates 126, 133. An over voltage 
protection zener 138 is mounted to electronic mounting plate 133. 
Referring now to FIG. 4, receiver electronic case 119 also includes 
electronic mounting plates 142 separated from electronic mounting plate 
133 by spacer rods 145. Electronic mounting plate 147 cooperates with 
electronic mounting plate 142 and is separated therefrom by spacer rods 
150, to support a receiver electronics board 154, affixed thereto. An 
electronic mounting plate 155 is used in conjunction with electronic 
mounting plate 147 to mount two receiver electronic boards 158, 160. 
Spacer rods 162 are used to provide rigidity between mounting plates 147, 
155. 
Receiver electronic case 119 also includes connector mounting plates 163, 
164 mounted therein with mounting plate 163 being separated from 
electronics mounting plates 155 by spacer rods 168. A receiver coil 
connector 170 has one portion mounted on mounting plate 163 and its mating 
portion mounted on mounting plate 164. A guide pin 172 is mounted on 
mounting plate 164 and slides into a hole in mounting plate 163 to 
facilitate the connection of mating parts of connector 170. 
It should be noted at this time that threaded rod, such as rod 176, is 
mounted at one end of each spacer rod which passes through a clearance 
hole in the various mounting plates to be threaded into the next spacer 
rod to give even more rigidity. 
A mounting plate 180 is effectively affixed internal to receiver electronic 
case 119, by screws, to spacer rods 183. Mounting plate 180 is used to 
facilitate physical connection of a metal insert 186, having a channel 
187, which is threaded into receiver electronics case 119 and further 
affixed thereto by the use of screws passing through mounting plate 180 
and into metal insert 186. Again, sealant of receiver electronic base 119 
is accomplished by o-rings 120. 
Referring now to FIGS. 5 and 6, a metal insert 186 has a wire channel 187 
and grooves 198. An epoxy glass spacer 194 is connected to metal insert 
186 utilizing epoxy, grooves 198 and screws. A fiberglass covering 200 is 
wrapped around epoxy glass spacer 194, and other elements as hereinafter 
explained, after the physical construction and connections of those 
elements have taken place. A coil and shield assembly 206 which may be of 
the type disclosed and described in U.S. application Ser. No. 191,094 
filed on Sept. 26, 1980, which is assigned to Texaco Inc., assignee of the 
present invention, is affixed to epoxy glass spacer 194 by screws. Another 
epoxy glass spacer 212 is also physically connected to a receiver coil and 
shield assembly 206 by screws. A second receiver and shield coil assembly 
216 is also affixed to epoxy glass spacer 212. As can be seen epoxy glass 
spacer 212 has a wire channel 218. Receiver coil and shield assembly 212 
is similar to receiver coil and shield assembly 206 with the slight 
difference being that assembly 206 has more passage space for wires than 
assembly 212. An epoxy glass spacer rod 224 is affixed to one end of the 
receiver coil and shield assembly 212 by screws. 
Referring to FIGS. 7 and 8, the other end of epoxy glass spacer 224 has a 
transmitter coil and shield assembly 229 attached to it by screws. 
Electronic coil and shield assembly 229 is similar to assembly 206 and 212 
except that it is longer and the coil form is larger in diameter. Assembly 
229 also includes a wire channel 233. Another epoxy glass spacer 240 is 
affixed to the other end of coil and shield assembly 229 by screws. Spacer 
240 has a wire passageway 244 and grooves 198. 
A metal insert 248 is in effect glued to the epoxy glass spacer 240 by 
epoxy cement in grooves 198. Metal insert 248 has a wire passageway 250. 
It should be noted that the fiberglass covering 200 reaches from metal 
insert 186 to metal insert 248. 
An electronic case 255 is threaded onto metal insert 248 with sealing being 
accomplished by o-rings 120. A brass mounting 259 is part of transmitter 
electronics case 255 and is affixed thereto by screws which pass through 
and are screwed into spacer rods 264. Spacer rods 264 are physically 
connected to electronics mounting plate 270 which cooperates with 
electronics mounting plate 275, shown in FIG. 9, in having transmitter 
circuit board 278 affixed thereto. Again, rigidity is accomplished using 
spacer rods 222. 
Still referring to FIG. 9, transmitter electronics case 255 has internal 
threads at its other end that is the end by electronic mounting plate 275 
in which a bottom plug 280 is screwed into it. Again sealant is 
accomplished by o-rings 120. 
Referring now to FIG. 10 which is a cross-sectional view taken in the 
direction of the arrows along the lines marked 10--10 in FIG. 4, there is 
shown the receiver electronic case 119, spacer rods 162, receiver 
electronics boards 158 and 160, electronics mounting plate 155 with wire 
passage holes 284 and 286. 
Referring now to FIG. 11, there is shown the end view of receiver and coil 
and shield assembly 206, along line 11--11 in the direction of the arrows, 
having fiberglass covering 200, having a clearance hole 290 for the long 
space receiver coil coax, a clearance hole 292 for the transmitter power 
wire passageway and a clearance hole 294 for the short space receiver coil 
output coaxial. 
Referring now to FIG. 12, there is shown another cross-sectional view of 
receiver coil and shield assembly 206 along line 12--12 in the direction 
of the arrows having the fiberglass covering 200, epoxy glass shield 
supports 300, a coax passageway hole 304, a power wire passageway hole 
306, a receiver coil 308 and silicon rubber filler 312. 
Referring now to FIG. 13, there is shown a cross-sectional view of the 
connection between receiver coil and shield assembly 216 and epoxy glass 
spacer 224 along the line 13--13 in the direction of the arrows. Also 
shown are fiber glass covering 200 and wire passageway 226. 
The present invention is a slim hole well logging tool for logging wells 
without the removal of tubing in the wells.