Method for transmitting digital data between a bottom hole assembly and a surface assembly of a drilling rig

Abstract

Method for transmitting digital data between a bottom hole assembly and a surface assembly of a drilling rig, wherein at least one of the bottom hole assembly and the surface assembly comprises a transmitting transducer actuatable to generate acoustic waves propagating in a drilling fluid and the other of the bottom hole assembly and the surface assembly comprises a receiving transducer configured to detect acoustic waves, comprising the following steps : processing in sequence the data by means of convolutional coding, an interleaving operation and at least one spread spectrum modulation technique, obtaining a processed digital signal; - converting the processed digital signal into an analog signal; - actuating the transmitting transducer in such a way as to generate, in the drilling fluid, acoustic waves that correspond to the analogue signal; receiving the analog signal through the receiving transducer; converting the analog signal into a received digital signal; - processing in sequence the digital signal received by means of at least one demodulation technique, one "de- interleaving" operation and one convolutional decoding, obtaining the received data.

Description

[0001] METHOD FOR TRANSMITTING DIGITAL DATA BETWEEN A BOTTOM

[0002] HOLE ASSEMBLY AND A SURFACE ASSEMBLY OF A DRILLING RIG

[0003] The present invention relates to a method for transmitting digital data between a bottom hole assembly and a surface as sembly of a drilling rig suitable , for example , for drilling a hydrocarbon well .

[0004] In the field of hydrocarbon extraction, the need for controlling and commanding in real-time from the surface the drilling operations that are carried out deep at the bottom of a bore hole has long been known . As a result , each drilling rig usually comprises a bottom hole assembly ( or BHA) which, in addition to the drilling tools required to drill the rock, also compri ses a plurality of sensors configured to collect several parameters relating to the progress of drilling operations and the characteristics of the geological formations being drilled (measurements that generally are better known as "measurement while drilling", or MWD, and " logging while drilling" , or LWD) . Purely by way of example , the parameters col lected may concern the inclination and direction of the drilling, the operation of the bottom hole assembly, the pressure and temperature measured in the bottom hole environment , or the reflection of seismic waves speci fically emitted to identi fy the structure and characteristics of the geological formations being drilled .

[0005] The data collected by the sensors of the bottom hole assembly, in digital format , are then transmitted to a surface assembly of the rig ( installed at the so-called stand-pipe ) to be analysed and interpreted by the operators , so that drilling operations can be adapted in real time to the actual conditions that characterise the bottom hole environment moment by moment , in order to minimise the risks to the safety of the rig and reduce the overall time and cost required to complete the drilling .

[0006] A commonly used method for transmitting data from the bottom hole assembly to the surface assembly, and vice versa, is represented by the so-called mud-pulse telemetry or MPT . This solution involves converting the digital data to be transmitted into pressure pulses to be propagated in the drilling mud flowing along the drill string that extends along the well between the bottom hole assembly and the surface assembly; to this end, the pulses are generated by means of a special servo-valve immersed in the drilling mud and actuatable to modulate the flow of the mud itsel f , and are picked up by means of a pressure detector that is also immersed in the drilling mud .

[0007] Mud-pulse telemetry, however, currently allows to transmit data at a maximum rate of 15 bits per second ( 15 bps ) , although the transmission rate is usually between 3 bps and 8 bps . This rate severely limits the maximum drilling rate in the rig (better known as rate of penetration, or ROP ) , because i f drilling occurs too fast compared to the rate at which the data is made available to the operators , it is not possible to perform a correct analysis and interpretation of the data in real time , and therefore not enough information is available to safely proceed with penetration .

[0008] An alternative method for transmitting data between the bottom hole assembly and the surface assembly involves using transmission cables installed along the entire length of the drill string to connect the bottom hole assembly to the surface assembly . However, this solution ( also known as "wired drill pipe technology" ) , while granting a high enough transmission rate to allow a satis factory drilling rate , is extremely expensive and requires specially dedicated equipment (bottom hole assembly, drill string, etc . ) .

[0009] Another alternative method involves propagating electromagnetic waves through the geological formations surrounding the well . However, this solution ( also known as "EM telemetry" ) is only used in on-shore bore holes of limited depth, due to the attenuation that electromagnetic waves inevitably undergo as they propagate through geological formations ; moreover, this solution is characterised by a data transmission rate that is not much higher than that of mud-pulse telemetry, and is relatively expensive .

[0010] Another alternative method involves propagating elastic waves along the metal wall of the drill string . However, this solution is characterised by a data transmission rate not much higher than that of mud-pulse telemetry, and only allows one-way data transmission .

[0011] WO 2016 / 134143 Al discloses a method for transmitting data from a downhole location to a location at the surface of the earth, including modulating the data using of fset quadrature phase shi ft keying and smooth transitions between phase shi fts to produce a series of two-bit symbols . WO 2020 / 263270 Al discloses an acoustic communications network including acoustic modems that exchange messages on tubing deployed in a wellbore by generating messages in the multicarrier communication system wherein the modulation on each subcarrier includes phase shi ft keying (ASK or QPSK) . US 2019 / 242250 Al discloses a communication method comprising : applying a forward error correction code to data , assigning the FEC-encoded data into a plurality of sub-channels , modulating the data from each of the plurality of subchannels into a corresponding one of a plurality of subbands , and concurrently transmitting the data from the plurality of sub-bands onto a banded communication channel .

[0012] The obj ect of the present invention is to overcome the above-mentioned drawbacks , and in particular to enable a two-way transmission of data between the bottom hole assembly and the surface assembly, enabling the rig to safely achieve a high drilling rate .

[0013] A further obj ect of the present invention is to provide a method for transmitting data between the bottom hole assembly and surface assembly that is applicable also through standard equipment , at relatively low cost . These and other results are obtained according to the present invention by a method according to claim 1 , and an apparatus according to claim 12 .

[0014] Further features of the invention are the subj ect matter of the dependent claims .

[0015] The present invention will now be described, by means of a non-limiting illustrative example , according to preferred embodiments thereof , with reference to the figures in the attached drawings , wherein :

[0016] - Figure 1 is a schematic view of a drilling rig to which a data transmission method according to the present invention is applicable ;

[0017] - Figure 2 is a schematic representation of the data transmission method according to the present invention; - Figure 3 is a schematic view of a surface assembly or bottom hole assembly of a drilling rig to which a data transmission method according to the present invention is applicable .

[0018] With reference to Figure 1 , 100 denotes a drilling rig, or drilling borehole , used in particular for the extraction of hydrocarbons from underground .

[0019] The borehole 100 comprises first of all a bottom hole assembly 101 comprising in turn drilling tools for drilling the rock and a plurality of sensors configured to collect parameters relating to the progress of drilling operations and the characteristics of the geological formations being drilled .

[0020] The rig 100 further comprises a surface assembly 102 configured to receive and / or transmit data from and / or to the bottom hole assembly 101 . In fact , at least one of the bottom hole assembly 101 and the surface assembly 102 comprises a transmitting transducer 106 (visible in Figure 3 ) configured to transmit data, while the other of the bottom hole assembly 101 and the surface assembly 102 comprises a receiving transducer 107 (visible in Figure 3 ) configured to receive data transmitted by the transmitting transducer 106. Preferably, however, both the bottom hole assembly 101 and the surface assembly 102 comprise both a transmitting transducer 106 and a receiving transducer 107 , so that communication between the assemblies 101 , 102 is bi-directional ; for example , data transmitted by the bottom hole assembly 101 and received by the surface assembly 102 may correspond to data collected by the sensors of the bottom hole as sembly 101 that are transmitted to the surface assembly 102 to be processed and viewed by an operator, while data transmitted by the surface assembly 102 and received by the bottom hole assembly 101 may correspond to command signals transmitted to the bottom hole assembly 101 to command the operations of the drilling tools .

[0021] Alternatively, both the bottom hole assembly 101 and the surface assembly 102 may comprise transceiver transducers , which may alternatively operate as either transmitting transducers 106 or receiving transducers 107 .

[0022] The borehole 100 further comprises a drill string 103 that extends deep between the surface assembly 102 and the bottom hole assembly 101 . The drill string 103 defines a pipe through which a drilling fluid ( such as a drilling mud) can flow from the surface to the bottom hole fed by a dedicated pump 104 , and then rise to the surface by flowing through the outer wall of the drill string 103 and the wall of the bore hole 100 . As is well known, the circulation of drilling fluid makes it possible , among other things , to remove cuttings produced by drilling operations , seal and stabilise the wall of the bore hole 100 , and feed, lubricate and cool the drilling tools .

[0023] In particular, the transmitting transducer 106 is housed in the drill string 103 , preferably immersed in the drilling fluid, and is actuatable to generate acoustic waves propagating in the drilling fluid flowing along the drill string 103 ; the receiving transducer 107 is also housed in the drill string 103 and is preferably immersed in the drilling fluid, and is configured to detect acoustic waves generated by the transmitting transducer 106 propagating in the drilling fluid . It is thereby possible to transmit data from the transmitting transducer 106 to the receiving transducer 107 , i . e . from the bottom hole assembly 101 to the surface assembly 102 and / or vice versa .

[0024] Preferably, the transmitting transducer 106 and the receiving transducer 107 consist of electro-acoustic transducers , such as electro-acoustic transducers based on moving magnets . Each of these electro-acoustic transducers with moving magnets comprises a plurality of electrical windings defining a cylindrical channel along which at least one magnet is movable and to which a membrane , that is in contact with the drilling fluid, is connected; in the transmission process , a predefined alternating electric current circulates in the windings , creating a magnetic field in the cylindrical channel which induces the alternating movement of the magnet and the movement of the membrane , thus generating acoustic waves in the drilling fluid in contact therewith; in the receiving process , on the other hand, the acoustic waves in the drilling fluid induce a movement of the membrane and the magnet connected thereto , inducing an electric current in the windings which can be detected and associated with the acoustic waves . This solution makes it possible to transmit and receive acoustic waves in a fairly wide frequency band, between 500 Hertz and 5000 Hertz , even under high pressure and high temperature conditions that are typical of the bottom hole environment .

[0025] However, the transmitting transducer 106 and the receiving transducer 107 may also consist of other types of electro-acoustic transducers , in any case capable of operating in the frequency band between 500 Hertz and 5000 Hertz . For example , each electro-acoustic transducer may comprise a piezoelectric transducing element ( e . g . , a piezo-ceramic stack) to which a membrane , that is in contact with the drilling fluid, is connected; in the transmission process , a predefined alternating electrical voltage is applied to the ends of the piezoelectric transducing element , causing a timevarying deformation and causing the movement of the membrane connected thereto , so as to generate acoustic waves in the drilling fluid in contact therewith; in the receiving process , on the other hand, acoustic waves in the drilling fluid cause a movement of the membrane and a deformation of the piezoelectric transducing element connected thereto , inducing a variable voltage at the ends of the piezoelectric element which can be detected and associated with the acoustic waves .

[0026] Alternatively, the transmitting transducer 106 may comprise a servo-valve immersed in the drilling fluid, which, when actuated, modulates the flow of the dri lling fluid itsel f and generates acoustic waves therein, and the receiving transducer 107 may comprise a pressure detector configured to pick up the acoustic waves generated in the drilling fluid by the servo-valve . This solution makes it possible to transmit and receive acoustic waves at a frequency of at least 100 Hertz . With reference to Figure 3 , the bottom hole assembly 101 and the surface assembly 102 also comprise the electronic equipment required to apply the data transmission method described below . In particular, a transmission processing unit 108 is associated with the transmitting transducer 106 , and a receiving proces sing unit 109 is associated with the receiving transducer 107 : these processing units 108 , 109 , preferably associated with corresponding memory units 110 , are configured to apply the data transmission method described below .

[0027] The rig 100 may also comprise an intermediate transducer system 105 housed in the drill string 103 between the bottom hole assembly 101 and the surface assembly 102 , and configured to receive data from the transmitting transducer 106 and to forward or re-transmit it to the receiving transducer 107 . This intermediate transducer system 105 makes it possible to transmit data safely and minimising errors even when the distance between the bottom hole assembly 101 and the surface assembly 102 is considerable and also makes it possible to monitor the bore hole 100 at intermediate depths .

[0028] With reference to Figure 2 , 1 overall denotes a data transmission method according to the present invention . The data 10 are initially in digital format and, as described above , may correspond to the parameters collected by the sensors of the bottom hole assembly 101 or to the command signals transmitted to the bottom hole assembly 101 to command the operations of the digging means .

[0029] The data 10 are initially processed by the transmission processing unit 108 using "convolutional coding" 11 . Preferably, "convolutional coding" 11 consists of a convolutional forward error correction ( or FEC ) coding : in fact , this solution, compared, for example , to the alternative "block code" solution, requires relatively simple algorithms , makes it possible to transmit more useful data with the same amount of overall transmitted data, makes it possible to reduce transmission latency and limits the negative impact of any clusters of consecutive errors (better known as "burst errors" ) . The data 10 are then further processed by the transmission processing unit 108 by means of an interleaving operation 12 . This solution, in fact , further limits the negative impact of any burst errors . The data 10 is then further proces sed by the transmission processor 108 using one or more spread spectrum modulation techniques . This solution, in fact , guarantees a reliable communication channel even in the presence of a very low signal-to-noise ratio , or even i f the signal has a lower amplitude than the noise .

[0030] More particularly, preferably, the data 10 is processed by the transmission processing unit 108 us ing a " frequency-shi ft keying" modulation 13 ( also known as FSK modulation) and a frequency-hopping spread spectrum technique 14 ( also known as FHSS technique ) . FSK modulation 13 , in fact , makes it possible to limit errors caused by channel distortions . FHSS technique 14 , on the other hand, consists of varying the transmission frequency at regular intervals according to a predetermined sequence , and increases the reliability of the communication channel , limiting data 10 degradation even in the absence of intermediate transducers 105 .

[0031] Preferably, a synchronisation preamble 15 is then added to the data processed using the FHSS technique 14 , by the transmission processing unit 108 . This solution, in fact , subsequently makes it possible to identi fy the correct instant to start processing the received signal ( synchronisation operation) .

[0032] A processed digital signal is thus obtained, which is converted into an analogue signal 17 by the transmi ssion processing unit 108 using a digital-to-analog converter 16 . The transmitting transducer 106 is then actuated by the transmission processing unit 108 to transmit the analog signal 17 by generating acoustic waves in the drilling fluid that correspond to the analog signal 17 .

[0033] The analog signal 17 is then received by the receiving transducer 107 , and is converted by the receiving processing unit 109 into a digital signal received by means of an analog-to-digital converter 18 .

[0034] The synchronisation preamble 19 from the receiving processing unit 109 is then removed from the received digital signal , i f present , once synchronisation has been carried out .

[0035] The received digital signal is then processed by the receiving processing unit 109 using a demodulation technique . I f data 10 was processed using a FSK modulation 13 and a FHSS technique 14 , the digital signal received is processed using a " frequency-hopping despreading" technique 20 and a " frequency-shi ft keying" demodulation 21 .

[0036] The received digital signal is then processed by the receiving proces sing unit 109 by means of a "deinterleaving" operation 22 , and by means of convolutional decoding 23 . Preferably, convolutional decoding 23 comprises a Viterbi algorithm . This results in received data 24 .

[0037] In case the transmitting transducer 106 and the receiving transducer 107 consist of electro-acoustic transducers , the data 10 are preferably processed in sequence by the transmission processing unit 108 by means of :

[0038] - a convolutional coding 11 characterised by a first rate of between 1 : 2 and 7 : 8 , preferably of 1 : 2 ; a binary " frequency-shi ft keying" modulation 13 , characterised by a first symbol period of between 2 milliseconds and 8 milliseconds, preferably of 5 milliseconds, and by two first characteristic frequencies differing by a value of between 100 Hertz and 500 Hertz, preferably of 200 Hertz;

[0039] - a "frequency-hopping spread spectrum" technique 14 characterised by three first carrier frequencies of between 1000 Hertz and 5000 Hertz, preferably of 2000 Hertz, 3000 Hertz and 4000 Hertz, and a first hop period of between half and twice the first symbol period, preferably equal to the first symbol period.

[0040] Preferably, moreover, convolutional coding 11 is characterised in this case by a memory length of 7 bits, and a generator matrix G defined on the basis of a timedelay operator D such as:

[0041] In case, on the other hand, the transmitting transducer

[0042] 106 comprises a servo-valve and the receiving transducer

[0043] 107 comprises a pressure detector, the data 10 are preferably processed in sequence by the transmission processing unit 108 by means of:

[0044] - a convolutional coding 11 characterised by a second rate of between 1:2 and 7:8, preferably of 1:2; a binary "frequency-shift keying" modulation 13, characterised by a second symbol period of between 2 milliseconds and 8 milliseconds, preferably of 5 milliseconds, and two second characteristic frequencies differing by a value of between 40 Hertz and 80 Hertz, preferably of 60 Hertz;

[0045] - a "frequency-hopping spread spectrum" technique 14 characterised by three second carrier frequencies of between 10 Hertz and 100 Hertz , preferably of 50 Hertz , 60 Hertz and 70 Hertz , and a second hop period between the second symbol period and five times the second symbol period, preferably equal to the second symbol period . In this second case , the Applicant was able to ascertain that FSK modulation of the "continuous phase" type , i . e . such as to guarantee continuity between the waveforms associated with two consecutive bits , makes it possible to improve performance .

[0046] In both cases , in the preferred embodiment j ust described, the data transmission can reach a transmission rate of at least 100 bits per second, while limiting transmission errors and creating a particularly "robust" communication channel . Such a transmission rate allows the rig 100 to safely achieve a satis factory drilling rate . Furthermore , the necessary equipment is easy to obtain and relatively cheap, as it can be similar to the one required to implement "mud-pulse" telemetry . The method j ust described can also be applied i f the surface assembly 102 comprises a device for the dri lling fluid recirculation . This device is actuated during the replacement operations of drilling pipes ( or the addition or removal of some of the drilling pipes ) to ensure the circulation of drilling fluid in the drill string 103 even at such times . The method according to the present invention can also be applied by the equipment ( in particular the valves ) of this device , enabling ef ficient and safe data transmission between the surface assembly 102 and the bottom hole assembly 101 .

[0047] The present invention has been described, by way of nonlimiting example , according to preferred embodiments , but it is to be understood that changes and / or modi fications may be made by the person skilled in the art , without departing from the relative scope of protection, as defined in the appended claims .

Claims

CLAIMS1) Method (1) for transmitting digital data (10) between a bottom hole assembly (101) and a surface assembly (102) of a drilling rig (100) , wherein at least one of the bottom hole assembly (101) and the surface assembly (102) comprises a transmitting transducer (106) actuatable to generate acoustic waves propagating in a drilling fluid, and the other of the bottom hole assembly (101) and the surface assembly (102) comprises a receiving transducer (107) configured to detect acoustic waves, comprising the following steps:- processing in sequence the data (10) by means of convolutional coding (11) , an interleaving operation (12) and at least one spread spectrum modulation technique (13, 14) , obtaining a processed digital signal ; converting the processed digital signal into an analogue signal (17) ;- actuating the transmitting transducer (106) in such a way as to generate, in the drilling fluid, acoustic waves that correspond to the analogue signal (17) ;- receiving the analog signal (17) through the receiving transducer (107) ;- converting the analog signal (17) into a received digital signal;- processing in sequence the digital signal received by means of at least one demodulation technique (20, 21) , a de-interleaving operation (22) and a convolutional decoding (23) , obtaining the received data (24) .2) Method (1) according to claim 1, wherein the at least one spread spectrum modulation technique (13, 14) comprises a frequency-shift keying modulation (13) anda frequency-hopping spread spectrum technique (14) , and wherein the at least one demodulation technique (20, 21) comprises a frequency-shift keying demodulation (21) and a frequency-hopping despreading technique (22) , respectively .3) Method (1) according to any one of the preceding claims, wherein a synchronisation preamble is added (15) to the processed digital signal before being converted into analogue signal (17) , and the synchronisation preamble is removed (19) from the received digital signal before being processed.4) Method (1) according to any one of the preceding claims, wherein the convolutional decoding (23) comprises a Viterbi algorithm.5) Method (1) according to any one of the preceding claims, wherein the transmitting transducer (106) and the receiving transducer (107) consist of electroacoustic transducers, preferably comprising respective moving magnets and / or respective piezoelectric transducing elements.6) Method (1) according to claim 5, wherein data (10) are processed in sequence by:- a convolutional coding (11) characterised by a first rate of between 1:2 and 7:8, preferably of 1:2; a binary frequency-shift keying modulation (13) characterised by a first symbol period of between 2 milliseconds and 8 milliseconds, preferably of 5 milliseconds, and by two first characteristic frequencies differing by a value of between 100 Hertz and 500 Hertz, preferably of 200 Hertz;- a frequency-hopping spread spectrum technique (14) characterised by three first carrier frequencies ofbetween 1000 Hertz and 5000 Hertz, preferably of 2000 Hertz, 3000 Hertz and 4000 Hertz, and by a first hop period of between half and twice the first symbol period, preferably equal to the first symbol period.7) Method (1) according to any one of claims 1 to 4, wherein the transmitting transducer (106) comprises a servo-valve and the receiving transducer (107) comprises a pressure detector.8) Method (1) according to claim 7, wherein data are processed in sequence by:- a convolutional coding (11) characterised by a second rate of between 1:2 and 7:8, preferably of 1:2; a binary frequency-shift keying modulation (13) characterised by a second symbol period of between 2 milliseconds and 8 milliseconds, preferably of 5 milliseconds, and by two second characteristic frequencies differing by a value of between 40 Hertz and 80 Hertz, preferably of 60 Hertz;- a frequency-hopping spread spectrum technique (14) characterised by three second carrier frequencies of between 10 Hertz and 100 Hertz, preferably of 50 Hertz, 60 Hertz and 70 Hertz, and a second hop period between the second symbol period and five times the second symbol period, preferably equal to the second symbol period.9) Method (1) according to any one of the preceding claims, wherein the transmitting transducer (106) and the receiving transducer (107) are housed within a drill string (103) of the rig (100) , wherein the drilling fluid flows in the drilling string (103) .10) Method (1) according to claim 9, wherein the analog signal (17) is received and retransmitted to the receiving transducer (107) by an intermediate transducersystem (105) housed within the drilling string (103) between the transmitting transducer (106) and the receiving transducer (107) .11) Method (1) according to any one of the preceding claims, wherein the bottom hole assembly (101) and the surface assembly (102) comprise a bottom hole transceiver transducer and a surface transceiver transducer respectively configured to operate as both transmitting transducers (106) and receiving transducers (107) .12) Apparatus for digital data transmission (10) between a bottom hole assembly (101) and a surface assembly (102) of a drilling rig (100) , comprising:- a transmitting transducer (106) comprised in at least one of the bottom hole assembly (101) and the surface assembly (102) and actuatable to generate acoustic waves propagating in a drilling fluid;- a transmission processing unit (108) associated with the transmitting transducer (106) and configured for:- processing in sequence the data (10) by means of convolutional coding (11) , an interleaving operation (12) and at least one spread spectrum modulation technique (13, 14) , obtaining a processed digital signal;- converting the processed digital signal into an analog signal (17) ;- actuating the transmitting transducer (106) in such a way as to generate, in the drilling fluid, acoustic waves that correspond to the analog signal (17) ;- a receiving transducer (107) comprised in the other of the bottom hole assembly (101) and the surface assembly(102) and configured to detect acoustic waves corresponding to the analog signal (17) ;- a receiving processing unit (109) associated with the receiving transducer (107) and configured for: - converting the analog signal (17) into a received digital signal; processing in sequence the digital signal received by means of at least one demodulation technique (20, 21) , a de-interleaving operation (22) and a convolutional decoding (23) , obtaining the received data (24) .

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