High speed downhole communications network having point to multi-point orthogonal frequency division multiplexing

• US 6,580,751 B1
• Filed: 02/01/2000
• Issued: 06/17/2003
• Est. Priority Date: 02/01/2000
• Status: Expired due to Term

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Inventors: Minear, John W., Gardner, Wallace R.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Fan, Chieh M.
• Application Number:
  US09/496,077
• Time in Patent Office: 1,232 Days
• Field of Search: 375/222, 375/225, 375/231, 375/260, 375/356, 375/362, 375/354, 375/257, 375/258, 370/431, 370/480, 370/508, 367/25, 166/250.1
• US Class Current: 375/222
• CPC Class Codes: G01V 1/22 Transmitting seismic signals to recording or processing apparatus
• CPC Class Codes: G01V 11/002 Details, e.g. power supply systems for logging instruments, transmitting or recording data, specially adapted for well logging, also if the prospecting method is irrelevant means for transmitting well survey signals E21B47/12; signal transmission systems in general G08C; transmission in general H04B
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems

Abstract

A method and related apparatus for high speed digital data conmunications from multiple distributed modems to a single central modem or a common transmission medium. In one embodiment, multiple downhole modems, with each modem associated with a geophone, transmit data to a surface modem over a single transmission medium. In a second embodiment, multiple transmission mediums are used and a plurality of downhole modems associated with geophones communicate to the surface modem over the downhole modem'"'"'s respective transmission medium.

Claims

1. A method comprising:

synchronizing data transmissions on a common transmission medium from a plurality of subsurface modems to a single surface modem, with each subsurface modem broadcasting in a corresponding frame period a sub-frame of discrete frequencies to create a super-frame for receipt by the surface modem in a single frame period, wherein the super-frame includes all the discrete frequencies in a band of frequencies during that frame period;

the synchronizing taking place on substantially all the subsurface modems before the broadcasting of any one of the plurality of subsurface modems by

calculating a phase delay for each subsurface modem;

delaying in time an initial sub-frame transmission of each subsurface modem proportionate to each subsurface modem'"'"'s calculated phase delay parameter;

thereby

synchronizing arrival at said surface modem of each of the sub-frames sent by the subsurface modems to create a substantially synchronized super-frame.

3. The method as defined in claim 1 wherein delaying in time the transmission of each subsurface modem further comprises programming each subsurface modem with each subsurface modem'"'"'s respective phase delay parameter.

2. A method comprising;

synchronizing data transmissions on a common transmission medium from a plurality of known subsurface modems to a single snrfae modem, with each subsurface modem broadcasting in a corresponding frame period a sub-frame of discrete fequencies to create super-frame for receipt by the surface modem in a single frame period, wherein the super-frame includes all the discrete frequencies in a band of fequencies during that frame period;

the synchronizing taking place before the broadcasting by

calculating a phase delay for each subsurface modem, comprising;

sending a timing signal from the surface modem to each subsurface modem during a training phase;

returning the timing signal from each subsurface modem to the surface modem; and

calculating said phase delay for each subsurface modem based on the round trip time of the timing signal for each subsurface modem;

delaying in time an initial sub-frame transmission of each subsurface modem proportionate to each subsurface modem'"'"'s calculated phase delay parameter;

thereby

synchronizing arrival at said surface modem of each of the sub-frames sent by the subsurface modems to create a substantally synchronized super-frame.

4. A method comprising:

synchronizing data transmissions on a common transmission medium from a plurality of known subsurface modems to a single surface modem, with each subsurface modem broadcasting in a corresponding frame period a sub-frame of discrete frequencies to create a super-frame for receipt by the surface modem in a sngle frame period, wherein the super-frame includes all the discrete frequencies in a band of frequencies during that frame period;

the synchronizing taking place before the broadcasting by

calculating a phase delay for each subsurface modem;

delaying in time an initial sub-frame transmission of each subsurface moderm proportionate to each subsurface modem'"'"'s calculated phase delay parameter comprising;

broadcasting a continuous timing signal by said surface modem; and

transmitting data in each frame period with each frame period having a frequency of said continuous timing signal and said transmitting by each subsurface modem initially delayed in time such that each sub-frame transmitted by each subsurface modem has a phase relationship proportional to each subsurface modem'"'"'s calculated phase delay;

synchronizing arrival at said surface modem of eah of the sub-frames sent by the subsurface modems to create a substantially synchronized super-frame.

5. A method of high speed digital data communications from multiple distributed modems to a single central modem over a common transmission medium, the method comprising:

dividing an available bandwidth of the common transmission medium into discrete frequency sub-channels;

analyzing a data transmission rate for each of the discrete frequency sub-channels;

allocating at least one of said discrete frequency sub-channels to each of said distributed modems;

creating a super-frame of transmitted data by having each of said distributed modems transmit only in their respective allocated sub-channels such that each distributed modem creates a sub-frame of the overall super-frame and all the distributed modems transmitting simultaneously in a frame period create the super-frame; and

wherein creating the super-frame further comprises creating a cyclic prefix and a cyclic suffix by allowing only one of said distributed modems to transmit at least one of a cyclic prefix and cyclic suffix in addition to data transmision in its respective allocated sub-channels.

6. A structure for high data rate communication in seismic detection systems, comprising:

a surface modem adapted to receive data in super-frames that include discrete frequencies within a range of frequencies;

a plurality of known subsurface modems adapted to transmit data in super-frames to said surface modem over a common transmission medium;

each of said subsurface modems associated with a down hole measurement device, each down hole measurement device adapted to take readings and create measurement data;

said surface modem adapted to calculate a phase delay representing a propagation time for each of the plurality of subsurface modems, said surface modem adapted to communicate the respective phase delay to each of the plurality of subsurface modems over the common transmission medium;

each of the plurality of subsurface modems adapted to delay the transmission of its respective measurement data based on the phase delay such that each sub-frame data transmission from each of the subsurface modems arrives at the surface modem substantially simultaneously; and

each of said subsurface modems further adapted to transmit its respective measurement data over the common transmission medium to the surface modem with each transmission from each subsurface modem being on a distinct subset of the discrete frequencies in the range of frequencies.

7. The structure as defined in claim 6 wherein the common transmission medium further comprises a twisted pair cable.

8. The structure as defined in claim 6 wherein each down hole measurement device associated with each subsurface modem further comprises a three axis seismic sensor.

9. The structure as defined in claim 6 further comprising:

multiple common transmission mediums with each common transmission medium coupling a plurality of subsurface modems; and

said surface modem adapted to communicate to and receive data from each of said subsurface modems over each subsurface modem'"'"'s respective common transmission medium.

10. The structure as defined in claim 9 wherein the multiple common transmission mediums each comprise a twisted pair cable.

11. The structure as defined in claim 10 wherein the multiple twisted pair cables forming the multiple common transmission mediums are bundled within a single cable jacket.

12. The structure as defined in claim 10 wherein there are five twisted pair cables.

13. The structure as defined in claim 9 wherein each down hole measurement device associated with each subsurface modem further comprises a three axis seismic sensor.

14. A method of simultaneous communication from multiple subsurface modems to a surface modem through a common transmission medium comprising:

coupling each of said subsurface modems to said common transmission medium; and

within each subsurface modem

driving a first conductor of said common transmission medium with a secondary winding of a transformer;

driving a second conductor of said common transmission medium with a secondary winding of the transformer, and wherein the secondary winding driving the first conductor and the secondary winding driving the second conductor are different windings; and

thereby

mixing the transmitted signals of each of the multiple subsurface modems to create a composite signal received by said surface modem.

15. The method as defined in claim 14 wherein coupling each subsurface modem and driving conductors of the common transmission medium by each subsurface modem further comprises coupling by use of a transformer having a single primary winding and two secondary windings, said secondary windings arranged and constructed such that each secondary winding has induced upon it a voltage of like amplitude and frequency as between the two windings, but differing by 180°

in phase relationship.