Abstract:
The invention comprises real-time down-hole intelligent communication based on the characterization of signal attenuation caused by a coaxial cable used as a communication medium and by frequency response changes of the electronic components of the transmitters and receivers, generated by the down-hole operating environment. The invention relates to a method for the real-time characterization of the attenuation response of a two-way communication system using a coaxial cable, consisting in: generating test tones for the real-time characterization of the attenuation response of a two-way communication system in the transmission and reception bands, measuring the signals received, estimating noise and the ratio to the communication signal, comparing with reference responses, adjusting the transmission and reception frequencies in order to maintain the communication with the maximum signal-to-noise ratio. The invention also relates to an adaptive two-way transmitter/receiver system for communication using coaxial cable as a link means, formed by: a transmitter with automatic adjustment of the operating band by means of the real-time characterization of the attenuation response of a two-way communication system. The invention further relates to adjustable filtering and coupling devices for optimizing the transmission and reception bands, and a control module capable of measuring the transmission and reception attenuation responses.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This Application is a 371 of PCT/MX2013/000112 filed on Sep. 25, 2013 which, in turn, claimed the priority of Mexican Patent Application No. MX/a/2012/013691 filed on Nov. 14, 2012, both applications are incorporated herein by reference. 
     SCOPE OF THE INVENTION AND BACKGROUND 
     Down-hole measurement of thermodynamic and geophysical parameters, increasingly deep and hot, of oil reserves is a cardinal factor for proper extraction. Measurement of these parameters is performed using tools that are designed specifically to endure the adverse environments of these applications. Some important parameters provided by these tools are temperature, pressure, flow rate, and vibrations, among others. The records of these parameters are useful for the characterization of reserves, since these tools are in direct contact with the formation thereof. 
     The depth of oil wells increases gradually and nowadays, in some cases, it exceeds 7000 m. Consequently, at those depths it is possible to obtain high-temperature and high-pressure conditions. Temperatures may exceed 200° C. and pressures may exceed 20,000 psi. It is considered high temperature above 150° C. and high pressure above 10 000 psi. 
     The measurement and recording of the characteristics of oil reserves has driven the design and implementation of measuring tools with specialized electronics and innovative communications systems. The challenges of communication systems, in these hostile environments, which lead to obtaining very poor signal-to-noise ratios (SNR), include noise interference, cable attenuation, and thermal drift of passive electronic components, among others. 
     The state of practice is integrated by technologies that use cable connections for communications and power transmission. Various communication techniques have been described, for example: 
     U.S. Pat. No. 4,107,644 describes a system and method to digitally transmit down-hole measurement information; signal transmission via cable is performed on baseband (without modulation) by means of a synchronization system with phase encoding. However, the intelligent communication system presented here does not have the electronic circuits or the method for real-time characterization of the attenuation response of a bidirectional communications system using coaxial cable as linking medium, adjustment of transmission and reception frequencies to maintain communication with the maximum signal-to-noise ratio, and comparison with reference attenuation responses. 
     U.S. Pat. No. 4,355,310 describes a communications system for down-hole data capture that uses bidirectional communication with universal interconnection and addressing, which recognizes the control instruction from devices based on that addressing. However, unlike the intelligent communication system presented herein, this patent does not have the electronic circuits or the method for real-time characterization of the attenuation response of a bidirectional communications system using coaxial cable as linking medium, adjustment of transmission and reception frequencies to maintain communication with the maximum signal-to-noise ratio, and comparison with reference attenuation responses. 
     U.S. Pat. No. 4,415,895 describes a data transmission system that uses bidirectional transmission-reception by means of modulation by PCM-pulse encoding. However, this patent does not consider the electronic circuits or the Method for real-time characterization of the attenuation response of a bidirectional communications system using coaxial cable as linking medium, adjustment of transmission and reception frequencies to maintain communication with the maximum signal-to-noise ratio, and comparison with reference attenuation responses. 
     U.S. Pat. No. 5,838,727 describes a device and a method to transmit and receive digital data over a bandpass channel. It comprises a method and a device for transmission and reception combining amplitude modulation with QAM-phase modulation. However, this patent does not consider the electronic circuits or the method for real-time characterization of the attenuation response of a bidirectional communications system using coaxial cable as linking medium, adjustment of transmission and reception frequencies to maintain communication with the maximum signal-to-noise ratio, and comparison with reference attenuation responses. 
     Patent US 2010/0052940 uses switched power line communication at frequencies greater than 400 kHz, and the transmission of communication signals is sent at low frequency, which causes switched power transmission not to interfere with communication. However, unlike the intelligent communication system presented herein, this patent does not have the electronic circuits or the method for real-time characterization of the attenuation response of a bidirectional communications system using coaxial cable as linking medium, adjustment of transmission and reception frequencies to maintain communication with the maximum signal-to-noise ratio, and comparison with reference attenuation responses. 
     The aforementioned patents do not consider adaptive bidirectional transmission-reception equipment for communication using coaxial cable as linking medium, with a transmitter having operating-band automatic adjustment based on real-time frequency response of the communication link and the assessment of the signal-to-noise ratio for data transmission, the use of adjustable coupling and filtering devices for transmission and reception bands, a control module capable of measuring attenuation responses in transmission and reception to determine operating frequencies, and an intelligent receiver with operating-band automatic adjustment capability that best fits to modulation techniques in data transmission and reception. 
     In addition, the aforementioned patents do not deal with a method for real-time characterization of the attenuation response of a bidirectional communications system using coaxial cable as linking medium, by the generation of sweep signals by test tones or time-domain narrow pulse signals with known wide spectrum to characterize bands of interest covering transmission and reception bands, processing and measurement of received signals, comparison with reference responses, adjustment of transmission and reception frequencies to maintain communication with the maximum signal-to-noise ratio. 
     SUMMARY OF THE INVENTION 
     The purpose of this invention is a down-hole, real-time, intelligent communications system based on the characterization of signal attenuation in a communication link whose features are affected by temperature variations in the communication medium, which consists of a coaxial cable as linking medium and electronic modules that perform the transmission and reception functions. 
     The method for real-time characterization of the attenuation response of a bidirectional communication system using coaxial cable as linking medium, consists of: the measurement of the real-time frequency response of the communication link and the assessment of the signal-to-noise ratio for data transmission, the use of adjustable coupling and filtering devices of the transmission and reception bands, a control module capable of measuring the attenuation responses in transmission and reception and of determining the operating frequencies, and an intelligent receiver with operating-band automatic adjustment capability that best fits to the modulation technique in data transmission and reception. 
     It is, also, the purpose of this invention the development of the method and the implementation of the electronic circuit, for: Down-hole, real-time, intelligent communication based on the characterization of the signal attenuation caused by a mono-conductor cable and electronic modules that perform the transmission and reception functions. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram of the entire system for temperature and pressure measurement in oil wells. Where  11  is a mobile unit,  13  is a cable,  16  is a measuring device,  17  is a tractor equipment,  18  is the down hole,  12  is a spinning reel,  14  is a mechanical crane jib, and  15  is the wellhead. 
         FIG. 2  is a close-up to the temperature and pressure measuring system. Where  11  is a mobile unit,  100  is a computer,  50  is an acquisition and control module,  40  is a PLC (power-line communication) transmitter module,  30  is a PLC receiver,  20  is a power source,  16  is a measurement module,  66  is a sensing module,  90  is a processing unit,  70  is a transmitter,  60  is a receiver,  80  is a power supply,  17  is a tractor module. 
         FIG. 3  shows the functional block diagram of the intelligent communication system. Where  11  is a surface measurement module,  16  is a well measurement system,  17  is a tractor equipment,  13  is a coaxial cable,  20  is a high-voltage power supply,  22  is a power line source,  80  is a down-hole high-voltage reducing source and  88  is a down-hole high-voltage and high-power reducing source,  30  is a PLC receiver,  40  is a PLC transmitter module,  50  is an acquisition and control module,  100  is a computer,  21 ,  31 , and  41  are filtering modules,  110  is a storage module,  90  is a processing unit,  66  is a sensing module,  61 ,  71 , and  81  are filtering modules,  60  is a receiver,  70  is a transmitter, and  125  is an RS-485 transceiver module. 
         FIG. 4  Locking trap frequency response. Where Fc A is the central frequency of the transmission carrier signal from surface to down hole and BW A is the bandwidth of such signal. The solid line indicates the frequency response of the filter at 20° C. and the dotted line represents the frequency response of the filter at 200° C. The y-axis indicates the magnitude in decibels and the x-axis represents the frequency in Hertz. 
         FIG. 5  Frequency response of band rejection filters in transmission and reception. Where Fc A is the central frequency of the transmission carrier signal from surface to down hole, BW A is the bandwidth of such signal, Fc B is the central frequency of the transmission carrier signal from down hole to surface, BW B is the bandwidth of such signal. The solid line indicates the frequency response of the filter at 20° C. and the dotted line represents the frequency response of the filter at 200° C. The y-axis indicates the magnitude in decibels and the x-axis represents the frequency in Hertz. 
         FIG. 6  Overexposure of frequency responses of coupling filters in transmission and reception, as well as the frequency response of a high-pass filter contained in the filtering modules. 
         FIG. 7  Flow chart of the intelligent communication method. 
         FIG. 8  Example of time-domain test signal. 
         FIG. 9  Example of signal response for frequency-domain test. 
         FIG. 10  Down-hole control and processing block. Where  90  is the down-hole control and processing block,  340  is the PLC-receiving digital block,  330  is the PLC-transmitting digital block,  350  is the storage digital block,  300  is the core processing digital block,  320  is the measurement digital block, and  310  is the UART transceiver digital block. 
         FIG. 11  PLC-receiving digital block. Where  340  is the PLC-receiving digital block,  400  is an analogue-to-digital converter (ADC),  410  is a digital filter block,  420  is a demodulator block, and  430  is a data link and message detection block. 
         FIG. 12  PLC-transmitting digital block. Where  330  is the PLC-transmitting digital block,  500  is a message building and segmentation block, and  520  is a signal synthesizer block. 
         FIG. 13  Acquisition and control module. Where  50  is the acquisition and control module,  650  is a digital storage block,  640  is a PLC-receiving digital block,  630  is a PLC-transmitting digital block,  660  is a PLC-receiving filter digital control block,  600  is a core processing digital block, and  610  is a power supply digital control block. 
         FIG. 14  Surface PLC-receiving digital block. Where  640  is the PLC-receiving digital block,  700  is an analogue-to-digital converter (ADC),  710  is a digital filter block,  720  is a demodulating block, and  730  is a data link and message detection block. 
         FIG. 15  Surface module PLC-transmitting digital block. Where  630  is the PLC-transmitting digital block,  800  is a message building and segmentation block, and  820  is a signal synthesizer block. 
         FIG. 16  Surface module PLC-receiving digital block. Where  900  is an adjustable bandpass filter block,  910  is a central frequency control block,  920  is a low-noise amplifier (LNA), and  930  is a signal-conditioning block. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The method for real-time characterization of the attenuation response of a bidirectional communications system using a coaxial cable as linking medium is described below. 
       FIG. 1  shows the diagram of the entire system for temperature and pressure measurement in oil wells; it consists of a mobile unit  11  to house the measurement, control, power supply, and communications equipment, which is connected to and communicated by means of a cable  13  with the measuring equipment  16 , which in turn is connected to the tractor equipment  17  that descends to the down hole  18 , the cable is gradually released by a spinning reel  12  and assisted by the mechanical crane jib  14  to make the transition from the horizontal outlet of the reel to the vertical inlet into the well  15 . 
       FIG. 2  shows a close-up to the measuring system for temperature and pressure, and other physical parameters, where it is shown that inside the mobile unit  11  the following are indicated as outstanding elements: a computer  100 , connected to an acquisition and control module  50 , to a PLC-transmitting module  40  (power-line communication), to a PLC receiver  30 , which is connected to a power source  20 , where the PLC-transmission  40  and PLC-reception  30  modules and the source  20  connect to the cable by means of a coupling unit to cable  13 , which in turn connects to the measurement module  16 , comprised by a sensing module  66 , a processing unit  90 , a transmitter  70  and a receiver  60 , the measurement module  16  connects and communicates to the tractor module  17  by means of an RS-485 transceiver (recommended standard transceiver)  125 . 
       FIG. 3  shows the block functional diagram of the intelligent communication system, which can be divided into the surface measurement module  11  and the down-hole measurement module  16 , where both modules  11  and  16  are interconnected by cable  13 . The surface module consists of a power source  22  that supplies power to modules  30 ,  40 ,  50 , and  100  that are part of  11 , and a source  20  to provide the energy needed in the down hole module  16 , by means of cable  13 , and feeds the voltage-conditioning module, source  80 , which supplies power to modules  70 ,  60 ,  90  and  110 , the source module  20  also feeds the voltage-conditioning module, source  88  to energize the tractor module  17 . The operation of the intelligent communication system consists of the transmitter Ts  30  and receiver Rs  40  on the surface linked by cable  13  with receiver Rf  60  and Tf  70  down hole. Conditioning required to maintain the signal levels both in transmission and in reception is performed by the filtering modules  21 ,  31 ,  41  of the surface end and modules  61 ,  71 , and  81  on the down hole end, and their role is the following: when transmitter  30  sends a signal at the frequency Ts, receiver  60  must receive it with minimum attenuation and receiver  40  must receive the minimum signal (maximum attenuation) for not interfering with the communication channel between the transmitter  70  and the receiver  40 . Power sources without conditioning show very low impedance for communication signals, and therefore it is required to insert locking traps to ensure low attenuation of transmission and reception signals in both ways of the bidirectional communication link between  30  and  60  and between  70  and  40 , for this modules  21  and  81  show high impedance in communication frequencies. 
       FIG. 4  shows an example of the frequency response of  31 ,  41 ,  61 , and  71 ,  FIG. 5  shows the response of  21  and  81 . The shift of the frequency response shown in  FIG. 4  is representative of the behavior of the frequency responses of modules  61  and  71 , when subjected to different temperatures. Where the solid line represents the filter operation at room temperature with FcA as its central frequency and BWA as its bandwidth; on the other hand, the dotted line corresponds to the shift caused by thermal drift. Also, the shift of the frequency response shown in  FIG. 5  is representative of the behavior of the frequency responses of module  21 , when subjected to different temperatures. In both cases, the shift occurs when the operating temperature changes within the range of 20 to 200 degrees Celsius. Follow-up of these changes, automatically, is part of the intelligent communication that is the purpose of this patent. 
       FIG. 6  illustrates the overlapping of frequency responses of the filtering modules described in  FIGS. 4 and 5  at the transmission FcA and reception FcB frequencies with BWA and BWB bandwidths, respectively. 
     The acquisition and control module  50  performs characterization procedures of modules  20 ,  30 , and  40 , defines the power and frequency of transmission for the transmitter  30 , and defines the sensitivity for the receiver  40 , encodes the communication messages and decides about the operating central frequency to be used; it also controls the display and storage of information in the computer  100 . The processing unit  90  performs characterization procedures of modules  60 ,  70 , and  80 , defines the power and frequency of transmission for the transmitter  70 , and defines the sensitivity for the receiver  60 , encodes the communication messages and in coordination with  50 , adjusts the operating frequencies for transmission and reception, it detects and scales the measurement signals of the sensing module  66 . Module  90 , down hole, controls information storage in the storage module  110 ; likewise, module  50 , on surface, controls information storage in module  100 . The communications scheme in based on sending commands in the form of messages from the surface module  11  to the down hole module  16 , which executes the instructions and sends a response message to the surface module  11 . Command messages may contain execution requests from a set of functions comprising information requests related to the measurement of pressure and temperature variables, the execution of movement of the tractor  17 , modification of operating parameters, and synchronization of the characterization procedure of the communication medium. 
     The preferred method for real-time characterization of the communication medium is presented with the flow chart of  FIG. 7 ; the method starts with the delivery of a message that contains a characterization instruction or command of the communication medium from the surface module  11  to the down hole module  16 , which prepares its control module  90  to capture the wide-spectrum test signal, which is sent by the surface module  11 . The test signal that travels through the entire communication medium from the surface module  11  to the down hole module  16 , is acquired and stored for further processing by the control module  90  of the down hole module  16 . Then the surface module  11  stops the transmission of the wide-spectrum test signal to give the opportunity to the down hole module  16  to capture the floor noise signal that is present, which is also stored for further processing. 
     In the following step, the surface module  11  prepares its acquisition and control module  50  to capture the wide-spectrum test signal that will be sent from the down hole module  16 . The down-hole module  16  sends the test signal, which travels through the entire communications medium from the down hole, to the surface. The received signal is stored for further processing by the acquisition and control module  50 . Then, the down-hole module  16  stops sending the wide-spectrum test signal for the surface module  11  to be able to capture the background noise signal and also store it for further processing. 
     In the following step the surface  11  and down-hole  16  modules perform the processing of the signals that were captured in real time by means of their acquisition and control modules  50  and  90 , respectively. Processing involves obtaining the Fast Fourier Transform (FFT) of the wide-spectrum and floor noise test signals. Each one generates as a result a data vector that indicates the magnitude of the signals as a function of their frequency. Both data vectors obtained by the control module  90  of the down-hole module  16  are analyzed to find the frequency of reception with the best signal-to-noise ratio, which is sent to the surface module  11  as a response message. 
     The surface module  11  performs the same procedure using the data vectors obtained by its control module  50  to determine the frequency of transmission with the best signal-to-noise ratio from the down-hole module  16  to the surface module  11 . 
     As a next step, the surface module  11  sends a message with a communication parameter re-configuration instruction or command to the down-hole module  11 . This message tells the down-hole module the new transmission and reception frequencies to be used. Then the control module  90  of the down hole module  16  re-assigns the values of the coefficients associated to the digital filtering block of  FIG. 12 . Additionally, values are assigned to the demodulation parameters of  FIG. 13  and to the modulation parameters of  FIG. 15  of the new frequencies indicated in the message from the surface module  11 . While carrying out this task, the down-hole module  16  sends a response message to the surface module  11  that confirms the change in parameters of the communication blocks of  FIGS. 12, 13, and 15 . 
     On the other hand, the surface module  11 , through its acquisition and control module  50 , adjusts its digital filter blocks from  FIG. 17 , its demodulating block from  FIG. 18 , and its modulating block from  FIG. 20  to the new frequencies. 
     The preferred method for real-time characterization of the communication medium shown in  FIG. 7 , is not limited and may be considered a complement while keeping a record of the adjustment of transmission and reception parameters as a function of frequency and temperature, so that the beginning of operation of the communications system may have as alternatives the startup with parameters at room temperature, last parameters used in measurement, or automatic adjustment according to a table of parameters stored in previous measurement or calibration runs. 
     The control and processing block  90 , shown in  FIG. 10 , is composed of the PLC-receiving digital block  340 , the PLC-transmitting digital block  330 , the measurement digital block  320 , the storage digital block  350 , the UART (Universal asynchronous transceiver) transceiver digital block  310 , and the central processing digital block  300 . The analog signal coming from the receiving module  60  is shown at the input of the PLC-receiving digital block, which is connected to the central processing digital block to process the command messages coming from the surface module  11 . The central processing digital block  300  connects to the measurement digital block  320  to capture the physical parameters of the measurement block  66 , it is connected to the UART transceiver digital block  310  to transmit commands and receive responses from the tractor  17  by means of the RS-485 module  125 . It is also connected to a PLC-transmitting digital block to communicate the results to the surface module. 
     The PLC-receiving digital block from  FIG. 11  is composed of an analogue-to-digital converter (ADC)  400 , a digital filter block  410 , a demodulating block  420 , a data link and message detection block  430 . The ADC  400  receives the analog signal coming from the PLC-receiving module  60 , the ADC  400  converts such analog signal to a digital representation, which is the input to the digital filter block  410  that limits the band to the reception frequency spectrum, the output of the digital filter is connected to a demodulating block  420 , which retrieves the digital frame of the command messages, where the digital frame is sent to the data link and message detection block  430  that sends the retrieved information to the central processing digital block  300 . 
     The PLC-transmitting digital block from  FIG. 12  is composed of a message-building and segmentation block  500  and a synthesizing block (DAC)  520 . The message-building and data segmentation block  500  receives the information coming from the central processing digital block  300 , encodes and segments the message, whose segments are delivered to the signal-synthesizing module  520 , which delivers a transmission-band modulated analog signal to the transmitting module  70 . 
     The acquisition and control module  50 , shown in  FIG. 13 , is composed of the PLC-receiving digital block  640 , the PLC-transmitting digital block  630 , the display and storage digital block  650 , the PLC-receiver filter control digital block  660 , and the central processing digital block  600 . The analog signal coming from the receiving module  40  is present at the input of the PLC-receiving digital block  640 , which is connected to the control and processing block  600  to process response messages from the down hole module  16 . The control and processing block  600  is connected to the display and storage block  650  to display and store the physical parameters measured by the down-hole module  16 . Also, it is connected to a PLC-transmitting digital block  630  to send command messages to the down-hole module  16 . The central processing digital block  600  is connected to the PLC-receiver filter control digital block  660  to adjust the frequency response of the PLC receiver  30  as a function of the transmission response of the down-hole module  16 . 
     The PLC-transmitting digital block  640  from  FIG. 14  is composed of an analogue-to-digital converter (ADC)  700 , a digital filter block  710 , a demodulating block  720 , a data link and message detection block  730 . The ADC  700  receives the analog signal coming from the receiving module  40 , where the ADC  700  converts such analog signal to a digital representation, which is the input to the digital filter block  710  that limits the band to the reception frequency spectrum, the output of the digital filter  710  is connected to a demodulating block  720 , which retrieves the digital frame of the command messages, where the digital frame is transferred to the data link and message detection block  730  that sends the retrieved information to the processing and control block  600 . 
     The PLC-transmitting digital block  630  from  FIG. 15  is composed of a message building and segmentation block  800 , and a signal-synthesizing block based on a DAC  820 . The message-building and data segmentation block  800  receives the information coming from the processing and control block  600 , encodes and segments the message, whose segments are delivered to the signal-synthesizing module  820 , which delivers a transmission-band modulated analog signal to the PLC-transmitting module  30 . 
     The surface receiving module  40 , illustrated in  FIG. 16  is composed of an adjustable bandpass filter block  900 , a central frequency control block  910 , a low-noise amplifier (LNA)  920 , and a signal-conditioning block  930 . The adjustable bandpass filter block  900  receives the communications signal coming from the down-hole module  16 , filters it in frequency according to the frequency adjustment coming from the central frequency control block  910 , which receives the frequency adjustment value from the acquisition and control module  50 . The adjustable bandpass filter block  900  delivers the processed communication signal to the low-noise amplifier block (LNA)  920 , which amplifies the amplitude attenuated signal to the levels required by the signal-conditioning block  930 , which scales the signals and couples the output impedance to deliver the communications signal to the PLC-receiving digital module  640 .