US 4,302,757 A · Bore telemetry channel of increased capacity

Abstract

Apparatus and method for signaling within a drill hole without disturbing an ongoing drilling operation. High data rates are achieved by using phase and/or amplitude modulation techniques which enable information transfer rates well in excess of the data bit rates being transmitted. The modulation technique provides a multi-level signal which makes optimum use of the amplitude/phase space available. The ability of the invention to substantially increase the carrying capacity of the communication channel is based upon the dispersive characteristics of electromagnetic propagation in a bore hole, wherein the lower frequencies propagate at a slower velocity, and with less attenuation than the higher frequencies. The relative effects of losses over the path length and the added signal-to-noise ratio required for the modulation techniques disclosed in this invention are balanced against each other in such a manner that data rates otherwise achievable only at higher frequencies can be obtained at lower frequencies with a net increase in usable path lengths for equivalent available signal powers and data rates. In accordance with this invention the number of signal states, e.g. phase levels and amplitude levels, for a given signal frequency are selected so as to maximize either the signal path length for a given carrying capacity of the signal channel, or the carrying capacity of the channel for a given path length.

Claims28

Dependent claims

A telemetry system for electromagnetic communication of input digital data of a first number base between a first and a second point spaced along the length of a borehole on a conductive member disposed in the borehole of a dispersive medium and making contact with the earth comprising:

transmitter means electrically coupled to said conduction member at said first point, for transmitting low frequency, narrow bandwidth electrical signals of a second number base along said member, said transmitter means including means for generating two or more mutually orthogonal carrier frequencies and multi-level modulation means responsive to data values for modulating said two or more carrier frequencies;
said electrical signals second number base being higher than said input data first number base;
and
receiver means electrically coupled to said conductive member at said second point, including demodulation means for receiving said electrical signals.

1 more element

A digital telemetry system for communicating digital data between spaced apart first and second locations along the length of an elongated borehole extending into the dispersive medium of the earth and containing an elongated conductive member therewithin, said system comprising:

an electromagnetic signal transmitter adapted for disposition at said first location for transmitting low frequency, narrow bandwidth electromagnetic signals from said first location to said second location;
said signal transmitter including
(a) digital data formatting means adapted to receive input binary-valued bit representing signals and to provide two groups of multiple-valued multiple-bit representing digital data signals corresponding thereto,
(b) first digital-to-analog conversion means connected to receive a first group of said multiple-valued multiple-bit representing digital data signals and to produce a first analog output signal uniquely representative thereof,
(c) second digital-to-analog conversion means connected to receive a second group of said multiple-valued multiple-bit representing digital data signals and to produce a second analog output signal uniquely representative thereof,
(d) carrier signal generation means for generating two mutually orthogonal carrier frequency signals,
(e) first modulation means for modulating one of said carrier frequency signals by said first analog output signal, thus producing a first modulated carrier signal,
(f) second modulation means for modulating the other one of said carrier frequency signals by said second analog output signal thus producing a second modulated carrier signal, and
(g) combined transmitter driving means connected to combine said first and second modulated carrier signals into a single low frequency, narrow bandwidth electrical signal for generating said electromagnetic signals;
and
an electromagnetic signal receiver means adapted for disposition at said second location for receiving said electromagnetic signals including means for converting them into two demodulated analog signals, means for converting such analog signals into two corresponding groups of multiple-valued multiple-bit representing digital data signals and means for combining such groups into binary-valued bit-representing digital data signals substantially identical in data value to those originally received by said signal transmitter.

8 more elements

A signal transmitter for use in communicating electromagnetic signals between spaced apart first and second locations along the length of an elongated borehole extending into the dispersive medium of the earth and containing an elongated conductive member therein, said transmitter comprising:

(a) digital data formatting means adapted to receive input binary-valued bit representing signals and to provide two groups of multiple-valued multiple-bit representing digital data signals corresponding thereto,
(b) first digital-to-analog conversion means connected to receive a first group of said multiple-valued multiple-bit representing digital data signals and to produce a first analog output signal uniquely representative thereof,
(c) second digital-to-analog conversion means connected to receive a second group of said multiple-valued multiple-bit representing digital data signals and to produce a second analog output signal uniquely representative thereof,
(d) carrier signal generation means for generating two mutually orthogonal carrier frequency signals,
(e) first modulation means for modulating one of said carrier frequency signals by said first analog output signal, thus producing a first modulated carrier signal,
(f) second modulation means for modulating the other one of said carrier frequency signals by said second analog output signal thus producing a second modulated carrier signal, and
(g) combined transmitter driving means connected to combine said first and second modulated carrier signals into a single low frequency, narrow bandwidth electrical signal for generating said electromagnetic signals.

4 more elements

Dependencies are inferred from the claim text.

Bore telemetry channel of increased capacity

Life of this patent

Bore telemetry channel of increased capacity

Life of this patent

Abstract

Claims28