Patent Publication Number: US-6912177-B2

Title: Transmission of data in boreholes

Description:
This application is a continuation of prior application Ser. No. 08/813,104 filed on Mar. 7, 1997 now abandoned, which is a continuation of application Ser. No. 08/687,907 filed Jul. 30, 1996 now abandoned, which is a continuation of application Ser. No. 08/544,666 filed on Oct. 18, 1995 now abandoned, which is a continuation of application Ser. No. 08/030,309 filed May 7, 1993 now abandoned. 

   This invention relates to a method of and apparatus for transmitting date in boreholes such an oil wells. 
   To optimise the efficiency both of the detection of oil reserves and the recovery of these reserves, it is important to obtain as much detailed information as possible about the ambient environmental conditions at the bass of an oil well. This information is obtained by a variety of sensors located at the base of a well when required. The information obtained by the sensors may be transmitted to the surface of an open well using sonic waves which propagate through the drilling mud. 
   However, this method may only be employed during drilling when sufficient hydraulic power is available to generate the signal at the base of the well. During well testing and production this power source is not available and a valve or plug may be inserted in the well resulting in there being no direct fluid path through the centre of the well from the base of the well to the surface. 
   One situation to which this particularly applies is in shut-in testing where a shut-in valve is included in the well. A test generally consists of flowing the well, thus drawing down the well pressure, and then suddenly stopping the flow by closing the shut-in valve. Information regarding the potential of the reservoir can be derived from examination of the ensuing pressure rite/time characteristic, requiring a pressure gauge beneath the valve. The shut-in is best done down-hole rather than at the surface, to avoid well-bore storage effects which are difficult to compensate for. 
   It is possible to adapt valves to produce a hydraulic or electrical path through the valve to enable the transmission of signals from a sensor below the valve to a receiver above the valve. The path through the valve terminates in a connector which is suitable for connection to the receiver, the receiver in turn being connected via a cable to the surface of the well. However, this system is extremely difficult to operate as the small connector on the surface of the valve is extremely difficult to contact with the receiver and a considerable length of time is taken to make a suitable connection. 
   Accordingly, the present invention provides a method of transmitting data in a borehole, the method comprising providing an electric signal representative of the data to be transmitted, converting said electric signal into a sonic signal, propagating said sonic signal along an elongate member, and processing the sonic signal for onward transmission. 
   The processing of the sonic signal may for example be at the surface, or it may be downhole by retransmission or it may be by electronic data storage for later pick-up. 
   In another aspect, the invention provides apparatus for transmitting data in a borehole, the apparatus comprising a transmitter and a receiver; the transmitter including means for converting data parameters into an electric signal and first transducer means responsive to said electric signal to generate an acoustic signal, the first transducer means being adapted for physical coupling to an elongate member extending along the borehole whereby the acoustic signal is propagated in said elongate member; the receiver comprising second transducer means adapted for physical coupling to said elongate member to produce an electrical output corresponding to said acoustic signal, and signal processing means connected to receive said output and operative to process the data into a condition for onward transmission. 

   
     An embodiment of the invention will now be described, by way of example only, with reference to the drawings, in which: 
       FIG. 1  is a schematic cross-sectional side view of apparatus in accordance with the invention in use in a well; 
       FIG. 2  is a block diagram of a transmitter forming part of  FIG. 1 ; 
       FIG. 3  is a block diagram of a receiver forming part of  FIG. 1 ; and 
       FIG. 4  is a block diagram of an alternative form of receiver. 
   

   Referring to  FIG. 1 , a drill stem  1  in sealed to a well bore  23  by a packer  2 , leaving an annulus  3  to contain mud and well control fluid. Any production fluids will pass up the centre of the drill stem  1  via a shut-in valve  4 . The present embodiment utilizes the invention to pass data relating to the fluid pressure in the drill stem bore  24  below the shut-in valve  4  to a location above it. 
   A transmitter designated generally at  6  is positioned in an external recess  25  of the drill stem  1 . The transmitter  6  is powered by a battery  7  and includes a pressure transducer  9  communicating with a lower bore  24  via a port  8 . The analog pressure signal generated by the transducer  9  passes to an electronics module  10  in which it is digitized and serially encoded for transmission by a carrier frequency, suitably of 2-10 kHz. The resulting bursts of carrier are applied to a magnetostrictive transducer  11  comprising a coil formed around a core whose ends are rigidly fixed to the drill stem  1  at axially spaced locations. The digitally coded data is thus transformed into a longitudinal sonic wave in the drill stem  1 . 
   A receiver generally designated at  12  is housed in an external recess  2  of the drill stem  1  at a location above the shut-in valve  4 . The receiver  12  comprises a filter  13  and transducer  14  connected to an electronics module  15  powered by a battery  17 . 
   The output of the electronics module  15  drives a signal coil  16 . 
   The filter  13  is a mechanical band-pass filter tuned to the data carrier frequency, and serves to remove some of the acoustic noise in the drill stem  1  which could otherwise swamp the electronics. The transducer  14  is a piezoelectric element. The filter  13  and transducer  14  are mechanically coupled in series, and the combination is rigidly mounted at its ends to the drill stem  1 , aligned with the longitudinal axis of the latter. Thus, the transducer  14  provides an electrical output representative of the sonic data signal. 
   A preferred method of retrieving the data is to store it in memory in the electronics module  15 , for retrieval at a convenient time by a pick-up tool  5 . This avoids the problems inherent in providing a real-time data path along the whole length of the well. The pick-up tool  5  is lowered on a cable or wireline  22  to locate in a nipple  18  which causes the signal in the receiver  16  to be aligned with a coil  19  in the pick-up tool  3 . The coils  16  and  19  are then inductively coupled, allowing the data to be transferred to the pick-up tool  5  serially on a suitable carrier wave to the pick-up tool  5 . 
   The pick-up tool  5  includes an electronics package  20  which is arranged to send a transmit command to the receiver  12  when the tool  5  is seated on the nipple  18 . The electronics package  20  may be arranged to decode and store the data if the tool is on wireline, or to re-transmit the data if the tool is on cable. In the latter case, power may be supplied to the tool via the cable; otherwise, power is derived from an internal battery  21 . 
   Referring now to  FIG. 2 , the transmitter electronics module  10  in the present embodiment comprises a signal conditioning circuit  30 , a digitizing and encoding circuit  31 , and a current driver  32 . The details of these circuits do not form part of the present invention, and suitable circuitry will be readily apparent to those skilled in the art. The transducer  11  has a coil  33  connected to the current driver  32  and formed round a core schematically indicated at  34 , suitably, the core is a laminated rod of nickel of about 25 mm diameter. The length of the rod is chosen to suit the desired sonic frequency which is suitably in the range 100 Hz to 10 kHz, preferably 2-6 kHz. 
   In the receiver, an seen in  FIG. 3 , the electronics module  15  comprises in series as passive band-pass filter  35 , an active band-pass filter  36 , and a phase-locked loop  37  supplying clean data signals to a decoder  38 . The decoded data is stored in memory  39 . When a pick-up tool  5  is positioned and activated, carrier frequency induced in the signal coil  16  in detected at  40  to enable control logic  41  to read data from memory  39  for transmission via encoder  42 , current driver  43 , and the signal coil  16 . 
   The alternative receiver shown in  FIG. 4  uses a similar mechanical filter  13 , transducer  14 , and electronic filter  35  and  36 . In this case, however, the filtered date signal is not stored but is used to contact a current driver  44  driving a magnetostrictive transducer  45  for sonic re-transmission further along the drill stem. 
   Thus, the invention enables data to be transferred by sonic transmission past a valve or the like and then further handled by (a) storage in memory for later retrieval, (b) real-time transmission electrically by cable, or (c) sonic re-transmission. 
   Modifications way be made within the scope of the invention. For example, the transmitter transducer may impart a torsional, rather than a longitudinal, sonic vibration to the drill stem. Transducers of other than magnetostrictive type may be used, such as piezoelectric crystals or polymers. 
   Although described with particular reference to shut-in testing in producing wells, the invention may be applied to any situation where a borehole is obstructed. The medium for sonic transmission need not be a drill stem but could, for instance, be casing or other tubular.