Telemetry Method for Cable-Drilled Boreholes and Method for Carrying It Out

This application is a national phase of PCT/EP92/02043 filed Sep. 4, 1992 and based, in turn, on German national application P4129709.1 filed Sep. 6, 1991 under the International Convention.

The invention relates to a telemetry method for cable-drilled boreholes as well as an apparatus for carrying out the method.

The publication "Horizontal Well Logging by `Symphor` (Eighth European Formation Evaluation Symposium, London, 1983) describes a borehole-logging method and the corresponding apparatus particularly directed at logging horizontal or slant boreholes by a logging probe on the end of the drill string and a logging cable extending between the drill string and logging cart on the surface and movable by a cable winch. The logging probe comprises a massive rod mechanically and electrically connected with the cable shoe and to which a coupling rod is connected which is connected behind the logging tools. The probe furthermore has a coupling housing for connection to the drill string and a protective housing for the logging tools and having an aperture. With this telemetry method and with the corresponding apparatus there is the disadvantage that the logging probe is fixed on the drill string so that the drill string must be taken apart before every logging in order to take the bit off the lower end of the drill string and to install the logging probe there.

Furthermore from "Efficiently log and perforate 60.degree.+ wells with coiled tubing" (World Oil, July 1987, pp. 32, 33, and 35) a method and a telemetry apparatus are known wherein instead of the drill string a special windable hose is used with a special hose winch and on whose end a logging probe, for example a gamma-ray probe, is connected as a locating probe for casing joints or as an acoustic sound for checking the annular cement joints between the casing and the surrounding rock. With this telemetry method and the apparatus for carrying it out it is possible to do a quick check of such bores after the derrick has been removed. On the other hand it is disadvantageous that one must use a special winch and a special hose string in order to make the necessary loggings.

It is an object of the invention to provide an improved telemetry method for cable-drilled boreholes. wherein the logging probe can be changed without dismantling the drill string. Yet another object of the invention is to provide an apparatus for carrying out the method according to the invention.

Still another object is to provide a telemetry method.

The telemetry method according to the invention for cable-drilled boreholes and the corresponding apparatus are ideal for geophysical loggings of strongly inclined bores. With this new telemetry concept, which is based on the method according to the invention having the step of independently functioning logging probe which is jetted into the drill string and projecting sensors forwardly out of the drill bit, there is no necessity to dismantle the drill string so that the effort and time necessary for making the loggings can be substantially reduced. During the logging procedure itself there is no need for a cable connection so that no expensive side apertures in the drill string are necessary. Since the logging probe is mounted inside the string, there is no way to lose it.

Even when the logging probe is switched it is no longer necessary to dismantle the string completely since each logging probe, similar to a solid core tube, can be taken rapidly by means of the core-tube grab out of the drill string whereupon with equal speed a new logging probe can be jetted into place. Use of the method of the invention eliminates problems when making the loggings because one can make loggings immediately after drilling without having to pull out the drill string. The outside diameter of the logging probe corresponds to that of a cable tube and can be easily secured via the inner-tube head to the core-tube coupling.

The jetting system in the inner-tube head of the logging probe and in the pickup probe allows wireless (inductive) communication from the surface location with the microprocessor of the logging probe. To this end the logging cable of the pickup probe is connected to a laptop PC or portable personal computer on the surface in order to initialize the logging probe before beginning the loggings and to synchronize it with the laptop PC.

The logging probe is then able in a fixed time, e.g. 1/10 sec, to take loggings and write them in its semiconductor memory of at least 1 megabyte capacity. Before the actual logging procedure, which takes place with dismantling of the string, the pickup probe is taken out of the borehole to protect the logging cable from damage.

Preferably with each logging the depth change is ascertained with a logging wheel which is provided on the surface at the string and thereafter it is written by the laptop PC in a data file. Once the loggings are complete the logging probe is recovered by the core-tube grab, is opened, and is read by the laptop PC. Simultaneously the loggings are correlated with the time information and a depth-data file is produced which can be printed out there on a printer.

If necessary the loggings can be interrupted and by jetting of the pickup probe the logging probe can be checked. In limited circumstances the loggings are read by the pickup probe directly and transmitted to the laptop PC.

The above and other features, objects and advantages will become more readily apparent from the following description references being made to the following accompanying drawing, in which:

FIG. 1 is a schematic representation of a telemetry method for cable-drilled boreholes as well as a method for carrying out the method according to the invention;

FIG. 2 is a schematic representation of a wireless logging and pickup probe unit;

FIG. 3 is a schematic representation of a length-logging device;

FIG. 4 is a schematic representation of a gamma-ray probe;

FIG. 5 is a schematic representation of a dip-meter probe; and

FIG. 6 is a schematic representation of a gyroscopic probe working both as a logging probe and as a pickup probe.

FIG. 1 shows, to illustrate principles of the telemetry method of the invention as well as the apparatus for carrying out the method, a probe 1 according to the invention in a deflected portion 43 of a borehole 12 as well as a pickup probe 2 working therewith and in a well string 3 that is in the borehole 12, 43. The probe 1 is conveyed to its logging location in the region of a drill bit 5 by the drilling mud. The pickup probe 2 is still in the upright portion of the borehole 12. It is also driven by the drilling mud along the string 3 until it is in a working position directly behind the logging probe 1. The pickup probe 2 is mounted on a borehole-logging cable 4 that is braked on paying out and tensioned on drawing in by a logging-cable pulley 13. The logging-cable pulley 13 is shown in the schematic drawing adjacent a derrick 14. The borehole logging cable 4 is connected in this embodiment to a logging cart 42 in which is mounted a laptop PC 7 with a register 41, a data processor 44, a memory 45, a printer 15, and a battery 28 as energy source. The logging probe 1 and pickup probe 2 are connected wirelessly to each other in the working position by means of a soft-magnet core 21 and two induction spools 9 (logging probe 1) and 10 (pickup probe 2) seen in FIG. 2. The self-powered logging probe 1 has a sensor 47 which can reach through a logging aperture in the bit 5 for direct mechanical contact with the floor and walls of the borehole 12, 43 in order to collect loggings, for example about the composition of the subsurface, the borehole walls, and the borehole diameter 38.

FIG. 2 shows the logging probe 1 and the pickup probe 2 interengaged to form a logging and transmitting unit in a data-transmission position. This drawing also shows the general construction of the logging probe 1 and pickup probe 2. The logging probe 1 has a longing-probe housing 30 holding a logging element 16, a power-source battery 17, a data processor 18, a data memory 19, as well as a serial data transfer device 20. The logging-probe housing 30 is behind the logging sensor 47 that during logging projects from the logging aperture of the bit 5. The rear end of the logging probe 1 carries an inner-tube head 11 which is connectable via a core-tube coupling 6 for fixing the logging probe 1 in the drill string 3 or on the bit 5. The side of the logging-probe housing 30 opposite the bit 5 centrally carries a soft-magnet core 21. The fixed magnet end 21a is surrounded by windings of an induction coil 9 whose connections 48 and 49 lead to the serial data transmitter 20. The soft-magnet core 21 extends with its free end 21b past the inner-tube head 11. In the transmission position the free magnet end 21b is surrounded by a coil part 23 in which the induction coil 10 of the pickup probe 2 is mounted. The coil part 23 is mounted on a cable head 22 in which the end of the borehole-logging cable 4 is fixed. Two terminals 50 and 51 of the induction coil 10 are connected via the cable head 22 with the borehole-logging cable 4. In the illustrated arrangement a wireless data transmission from the laptop PC 7 to the logging probe 1 is facilitated in order to initialize it and to synchronize it with the laptop PC 7. Finally the logging probe 1 is able to receive logging data and store it in the data memory 19. The pickup probe 2 can then be pulled by the logging-cable winch 13 out of the borehole 12, 43. The logging data is read as the bore string 3 is pulled out of the borehole 12, 43. Differentiated pulses of an RS232 protocol are used. Normally with an RS232 protocol the sent and received data are exchanged over two separate channels. Here it is necessary to transmit the data at different times over one channel.

As the logging data is being read the borehole depth is determined. This is done by the depth-logging device shown in FIG. 3. Engaged laterally with the uppermost string of the logging string 3 is a depth-logging wheel 8 whose rotations are outputted by a pulse generator 24 through a logging line 27 to a pulse counter 25 which is connected via a transmission circuit 29 to the laptop PC 7. Since the laptop PC 7 and the logging probe 1 work synchronously, all of the collected data can be combined, that is the logging data can be associated with the depth it was taken at.

It is possible for example to use a gamma-ray probe 1a as the logging probe 1, which is shown schematically in FIG. 4. The logging-probe housing 30 holds a sodium-iodide crystal 31 and an electron-multiplying tube 32 to which is connected a voltage converter 33 that is used to obtain the logging data. These are fed via a data processor 18 to the data memory 19 from which they can be read by the serial date transmitter 20. A battery 17 is the power source. Although radioactive loggings are also possible through the drilling string, loggings not influenced by the drill string are obtained by the solution whereby a radioactive emitter is used first and the gamma-ray probe 1a is used as a density probe. The sensor system of the radioactive logging can be monitored well and the exceptional logging data are minimal. With a 1 megabyte memory in the gamma-ray probe 1a one can take loggings for more than 24 hours.

The logging probe 1 can furthermore be for example a dip-meter probe 1b as shown in FIG. 5. Its housing 30 has a tip potentiometer 34 and an electronic analog circuit 35 acting as data-logging device which receives the reflections of ultrasonic signals that are emitted by an ultrasonic oscillator 37 which is connected to the probe housing 30. Furthermore the probe housing 30 holds a battery 17 as current source as well as a data processor 18, a data memory 19, and a serial data transmitter 20. The dip-meter probe 1b serves to determine the position of layer boundaries and fissures. Several fixed ultrasound oscillators 37 log by sonic echo-sounding techniques the amplitude and running time without contact. The ultra-sound pulses are diffused by the fissures and layer boundaries and are reflected with lessened intensity from the borehole wall.

These amplitude values can be subjected to successive evaluation and display methods as is known for electrical dip meters. The sum of all the ultrasound pulse times represents the borehole diameter 38 whose value is stored as a further value along with the amplitude. The orientation value is taken from the electrical tip potentiometer 34 and determines in which position relative to the roll axis of the dip-meter probe the ultrasonic oscillator 37 is oriented. This ensures a simple up/down orientation.

For final location of layers and fissures the loggings are then correlated with the travel and position of the borehole 12, 43 which is done with a gyroscopic probe which is described below.

By selection of another probe program when initialized the dip-meter probe 1b can also be used as a diameter probe. In contrast to the dip-meter action the diameter values are stored. The exact diameter values are of significance in combination with the density loggings from the gamma-ray probe 1a (gamma-gamma).

In addition the dip-meter probe 1b can make volume loggings of the borehole 12. To this end on assembly of the string 3 the dip-meter probe 1b is locked in place and the depth is logged by means of the depth-meter wheel 8 and the laptop PC 7. The dip-meter probe 1b allows highly accurate loggings to be made with a resolution of as little as 1 mm.

As shown in FIG. 6 the logging probe 1 can be a gyroscopic probe which is used alone or with another of the logging probes 1 and 1a or 1b to determine the loggings of interest. The probe housing 30 of the gyroscopic probe 1c is a gyroscopic module 39 and if necessary is integrated with an additional sensor 40 as logging derive. The gyroscopic probe 1c determines the path of the borehole 12, 43 and the position of the deepest part of the borehole with an accuracy of 1 m in 1000 m depth. It is lowered by the borehole-logging cable 4a into the drill string 3 and continuously logs the travel and position of the borehole 12, 43. When inclined greatly it can be propelled forward by a piston. While logging, the data are transmitted to the logging cart 42 and there are stored in the register unit 41. The additional sensor 40 allows one to simultaneously determine the position of the tube joints of the drill string 3. As with the logging probes 1a and 1b the housing 30 of the gyroscopic probe 1c holds a battery 17 for supplying current as well as a data processor, a data memory, and a serial data transmitter.