Measurement-while-drilling system

Abstract: A measurement-while-drilling system (2) for measuring data at the bottom part of a well (1), in real time, by means of a sonde (30). The sonde (30) is arranged so that it can be mechanically and electronically connected to or separated from a first drill pipe (11A) so that it can be retrieved by wireline whenever necessary, whereas the measuring sensors are located in a lower connecting pipe (20) near the bit (13). Data received by these sensors is transmitted to the sonde (30) via an electromagnetic coupling. Within the sonde (30), the electric signals received from the sensors are altered to mud pressure signals for transmission of the data to the earth's surface. The electricity for the sensors and the sonde can be obtained by respective mud driven generators, one of which is located in the sonde (30), the other in the lower connecting pipe (20).

Description: The present invention relates to drilling equipment and in particular to equipment used to collect data at the bottom of a borehole which is drilled for petroleum wells, geothermal wells or gas wells, or for the investigation of earthquakes or geology. Such a borehole is drilled using a drill string comprising a plurality of cylindrical drill pipe sections which are connected to each other and provided with a bit at the lower end. The drilled rock and soil are discharged in drill mud which is continuously fed down through the inside of the drill string from the surface. The drill mud flows out through the bit at the bottom of the borehole and flows up to the surface between the outside of the drill string and the inside of the borehole. In the case of the borehole reaching the depth of 5000m below the ground, the temperature and pressure of the drill mud are greatly influenced by geothermal conditions and depth related pressure variations. In such equipment it is necessary to detect data related to the torque and load applied to the bit in real time. For collecting the data, several sensors are mounted inside the drill pipe near the bit. A main part of the conventional measurement while drilling equipment to collect such data sensed by these sensors is provided inside of the lower end of the drill string. The casing which covers the main part of the measurement while drilling equipment is therefore required to be well sealed so as to function in the drill mud at the above-mentioned high temperatures and pressures. To provide such sealing and the electrical connection to the sensor, the drill string section where the main part of the measurement while drilling equipment and the sensors are housed is firmly connected to other digging pipe sections. However, as the main part of the measurement while drilling equipment cannot be separated from the drill string, even if the temperature down the borehole becomes high, it is impossible to pull only the measurement while drilling equipment to the surface in order to prevent breakdown. Hence, the equipment can be damaged by heat and cannot subsequently be re-used. Another type of equipment which is capable of being separated from the drill string has been invented, but in this system it is difficult to provide an electrical connection to the bit torque and load sensors at high temperature and under high pressure. It is therefore necessary to record the collected data. Neither of the above measurement while drilling equipments can collect data representing torque and load applied to the bit during drilling in real time. The present invention aims to collect the data from the drill pipe in real time. The example shown in Fig. 2 of WO-A-90/14497 discloses a measurement while drilling equipment for collecting data at the bottom of a borehole, the equipment comprising a drill bit attached to the lower end of a drill string comprising first and second drill string sections, the second drill pipe section being adjacent to the drill bit; means for pumping drill mud through the drill string; a plurality of sensors provided in the second drill pipe section, each sensor being arranged to collect the data at the bottom of the borehole; and a coupler capable of connecting a sonde with the sensors so that the data collected by the sensors can be transmitted to the surface by the sonde; and according to the present invention, such an equipment is characterised in that a sonde mechanically connectable to and separable from the first drill pipe section; the coupler comprises a primary annular coil provided in the second drill pipe section, and secondary annular coil which surrounds an outer peripheral portion of the sonde; and in that the coils are arranged so that when the sonde is mechanically connected to the first drill pipe section, the secondary annular coil fits within and is at the same level as the primary annular coil to establish an electromagnetic coupling between the sonde and the sensors. The electricmagnetic coupling formed between the sonde and the sensor inserted in the digging pipes may be provided with sealing structure which can withstand the high temperatures and pressures of the drill mud. When it is expected that the temperature at the bottom-hole part is higher than the temperature which can be withstood by the sonde, and in order to prevent damage, the sonde is pulled to the surface. In the drawings: Figure 1 is a diagrammatic sectional view which shows the whole structure of the excavation equipment including equipment according to a preferable embodiment of the present invention; Figure 2 is a sectional view which shows the measurement while drilling equipment; Figure 3 is an enlarged sectional view of the part of the equipment shown in Fig. 2 in a connected condition; Figure 4 is a sectional view along the line IV-IV in Fig. 3; Figure 5 is an enlarged sectional view showing a part of the equipment in a separated condition; and Figure 6 is a diagram which shows the structure of the electric circuit for the measurement while drilling equipment. Figure 1 shows the whole structure of the drilling equipment 10 according to the present embodiment. This drilling equipment 10 is equipped with a drill string 12 consisting of a plurality of interconnected steel pipes 11, and a bit 13 which is attached to the lower end of the drill string 12. The drilling of the borehole 1 is caused by the rotation of the bit 13, as the steel pipes 11 are progressively added to the drill string 12. The drilling equipment 10 has a drilling rig 14, inside of which is provided a winch to lift the drill string 12, an apparatus to add or separate the steel pipes 11, and a driving apparatus to rotate the drill string 12. To the left of the drilling rig 14 as shown in Figure 1 are provided a drill mud tank 15 and a drill mud pump 16 which has an outlet connected to the upper end of the drill string 12, so that the drill mud is pumped inside the drill string 12. After flowing out of the bit 13, the drill mud picks up pieces of rock and sand cut by the bit 13. The drill mud is of a suitable composition to carry the cut pieces of drilled rock and sand to the surface. Measurement while driving equipment 2 is provided to collect necessary information at the bottom of the borehole 1 by being mounted in the lower end of the drill string 12. The measurement while drilling equipment 2 processes the collected data from an electrical signal to a pressure signal of the drill mud, and then sends it to the surface. The measurement while drilling equipment 2 has a connecting pipe 20 which contains several sensors and connects the drill string 12 to the bit 13, and a sonde 30 which collects the data from the sensors and sends it to the surface. Data processing equipment 4 is located inside an operation room 3 next to the drilling rig 14 to process the data collected by the measurement while drilling equipment 2. The data processing equipment 4 has a signal receiver set, which can receive the pressure signal of the drill mud which is transmitted through the drill mud after being emitted from the measurement while drilling equipment. Figure 2 is an enlarged view of the measurement while drilling equipment 2 attached to the lower end of the drill string 12. As is shown in Figure 2, a steel pipe 11A containing the sonde 30, the connecting pipe 20, and the bit 13 are connected to the end of the drill string 12 in this order. The steel pipe 11A has a supporting member 17 in one end 30H, to retain the sonde 30 in place. Female screw threads are provided in both ends of the connecting pipe 20 to receive a male screw thread formed on the end of the steel pipe 11A and a male screw thread formed on the base end of the bit 13 respectively, to connect the steel pipe 11A to the bit 13 through the connecting pipe 20. A plurality of cavities 21 are provided within the wall of the connecting pipe 20. In the cavities 21 are provided a first sensor 22 to detect the torque on the bit 13, a second sensor 23 to detect the load, a third sensor 24 to detect the temperature at the bottom part of the borehole 1, and a fourth sensor 25 to detect the pressure. An A/D converter 26 converts the analog signals from the sensors 22 - 25 into digital signals. Upper and lower turbine blades 27, 28 are mounted in the connecting pipe 20 so as to be rotatable by the flow of drill mud caused by drill mud pump 16. The lower turbine blade 27 has the role of driving a generator 29 which supplies electricity to a transmission circuit 60. The upper turbine blade 28 is used to drive a generator which is not shown but is preferably in the lower part 30H of the sonde 30 to provide the electric power required by the sonde 30, and in particular by a receiving circuit 70. The generator for the sonde 30 can be driven by the upper turbine blade 28 via a shaft 31 which is coupled into a hollow 28A which is axially aligned with the central axis in the turbine blade 28. The sonde 30 has a cylindrical shape which is a little thinner than the inner diameter of the drill string 12 so that it can be guided to the bottom the borehole 1 under its weight as it is lowered into the drill string 12 from the surface, and to allow free flow of the drill mud between the inside of the drill string 12 and the sonde 30. The head of the sonde 30 is provided with a shaft 31 which has a smaller diameter than, and is coaxial with the rest of the sonde, and is arranged to rotate freely. The end of the shaft 31 is securely inserted into the hollow 28A of the turbine blade 28 mounted inside the connecting pipe 20. The sonde 30 has a centralizer 32 comprising four plate springs each bent into an arc and which are evenly circumferentially spaced. The central part of each plate spring 32A is urged into contact with the inside of the steel pipe 11A, so that the central axis of the sonde 30 is aligned with the central axis of the steel pipes 11, 11A. The centralizer 32 ensures that the shaft 31 of sonde 30 automatically locates in the hollow 28A of the connecting pipe 20 when it reaches the bottom of the borehole. When the shaft 31 locates in the hollow 28A, the connection between the connecting pipe 20 and the sonde 30 is completed. At the tail part 30T of the sonde 30, that is, the end remote from the drill bit 13, the sonde 30 has a pulse valve 33 to limit the flow rate of the drill mud, and an upwardly extending fishing neck 34. The pulse valve 33 is a part of a positive mud pulse generator which sends various data to the surface by changing the pressure of the drill mud by opening or shutting the valve. The fishing neck 34 is provided to engage the end of a wireline suspended from the surface. When the wireline which engages the fishing neck 34 is winched up, the sonde 30 is separated from the connecting pipe 20, and is raised inside the drill string 12 to the surface. In Figures 3-5, an electromagnetic coupler 40 is shown which electrically connects the connecting pipe 20 and the sonde 30. The coupler 40 contains a primary coil 41 mounted in the connecting pipe 20 and a secondary coil 51 mounted to the sonde 30. The primary coil 41 has an annular shape which enables the shaft 31 of the sonde 30 to be inserted thereinto, and is fitted within a supporting member 42 fixed near to the upper end of the connecting pipe 20. The supporting member 42 has a plurality of arms 43 which extend radially from a hub 44, the inner diameter of which is almost the same as that of the primary coil 41. The hub 44 is formed with a groove 45 into which the primary coil 41 is fitted. The opening of the groove 45 is sealed by an annular member 46 made of non-magnetic material, such as aluminum or heat resistant synthetic resin. There is a passage 47 between the hub 44 and the inner circumference of the connecting pipe 20 to allow the flow of drill mud. The secondary coil 51 is an annular coil with an outside diameter which is almost the same as that of the shaft 31 of the sonde 30, and which is fitted in a circumferential groove 52 in the shaft 31. The groove 52 is formed at a position in which, when the sonde is installed, the groove faces the primary coil 41 mounted in the connecting pipe 20. Thus when the sonde 30 is connected to the connecting pipe 20, the secondary coil 51 is positioned within the primary coil 41. The opening of the groove 52 is sealed with an annular member 53 made of aluminum or non-magnetic matter such as heat resistant synthetic resin. In Figure 6, the main structure of an electric circuit 5 for the measurement while drilling equipment is shown. The electric circuit 5 comprises a transmission circuit 60 mounted in the connecting pipe 20 and a receiving circuit 70 mounted in the sonde 30. The two circuits are electrically connected by the above explained electromagnetic coupler 40. The transmission circuit 60 is equipped with a signal processing portion 61 to convert the respective analogue signals from the sensors 22-25 into digital signals after they have been amplified, and a multiplexing portion 62 to send the digital signals with a high frequency carrier to the receiving circuit 70 after multiplying the signals. Each converter 61A-61D for converting the analogue signals from each sensor into respective digital signals after amplifying them is equipped with a signal processing portion 61. The first converter 61A processes the signal from the torque sensor 22. The first converter 61A has an amplifier 63A for amplifying the signal from a bridge which includes the torque sensor 22, and an A/D converter 64A to convert this signal into a digital signal. The second converter 61B processes signals from the bit load sensor 23. The second converter 61B has an amplifier for amplifying a signal from a second bridge and an A/D converter. The third converter 61C processes signals from the temperature sensor 24 and has an amplifier 63C to amplify signals from the temperature sensor 24, and an A/D converter 64C to convert the analogue signal to a digital signal. The fourth converter 61D processes signals from the pressure sensor 25 and has an amplifier and an A/D converter similar to those in the third converter 61C. The multiplexing portion 62 multiplexes the digital signals output from the above-mentioned converters 61A-61D using a time-division system. The multiplexing portion 62 has a multiplexer 62A which selects one of the various outputs from the converters 61A-61D at a fixed cycle and then sends that signal to be controlled. A FM modulator 62B modulates the frequency of the output from the multiplexer 62A, and a driver 62C amplifies the weak signals output from the FM modulator 62B so that they are strong enough to be transmitted via the electromagnetic coupler 40. A power source circuit 65 electrically connected to the generator 29 is contained in the transmission circuit 60. The receiving circuit 70 is provided to demultiplex the data signal and convert them back to analogue signals. The receiving circuit 70 has a signal resolving portion 71 to demultiplex the signals from the transmission circuit 60 into the data signals for each sensor 22-25, and a D/A converter 72 to convert the digital signals back into analogue signals. The signal resolving portion 71 has a high frequency amplifier 73 to amplify the signals received by the electromagnetic coupler 40, a FM demodulator 74 to demodulate the signals modulated in the transmission circuit 60 and to separate the data signals and the control signals, a de-multiplexer 75 to divide the multiplexed data signals into an output corresponding to each detected signal, and a control circuit 76 to synchronize the de-multiplexer 75 with the multiplexer 62A in the transmission circuit 60 upon receipt of control signals from the FM demodulator 74. The converter portion 72 comprises four converters 77A-77D corresponding to respective sensors 22-25. Each converter 77A-77D is provided to convert the digital signals resolved in the demultiplexer 75 into analogue signals. Each of the converters 77A-77D comprises a D/A converter and an operation amplifier. The analogue data signals output from each converter 77A-77D are input to drill mud pulse transmission equipment which is not shown in drawings. Also, a power source circuit 78 connected to the generator 29 is also provided with the receiving circuit 70 similar to the above-mentioned transmission circuit 60. Therefore, in the present embodiment, when the sonde 30 is run in through the drill string 12, the sonde 30 is connected mechanically to the connecting pipe 20, in such a way that the sonde 30 and the sensors 22-25 are electrically connected. In this condition, the sonde 30 receives data regarding torque load etc. applied to the bit 13, during the drilling and transmits it as it is collected. At the surface, the transmitted data is monitored by the data processing equipment 4. Also, when the temperature at the bottom of the borehole 1 exceeds that which can be tolerated by the sonde 30, and there is a fear of damaging the sonde 30, the sonde 30 can be prevented from being damaged by pulling it to the surface after separating it from the connecting pipe 20. Since the connecting pipe 20 is electrically connected to the sonde 30 through the electromagnetic coupler 40, even if both the primary coil 41 and the secondary coil 51 of the electromagnetic coupler 40 are sealed, the electric connection can be conducted without mechanical contact between the coils. Thus, as long as the connection between the sonde 30 and the connecting pipe 20 is maintained, the data from the sensors is collected in real time. Also, when sonde 30 is likely to be damaged by the high temperature and pressure of the drill mud, it can be separated from the connecting pipe 20 and pulled to the surface. As the sonde 30 can be retrieved using the fishing neck 34, the sonde 30 can be re-used. Moreover, because the sonde 30 is equipped with the centralizer 32, it can be lowered without guidance and is automatically aligned with the central axis of the connecting pipe 20. This allows the sonde 30 and connecting pipe 20 be connected mechanically with the primary coil 41 and the secondary coil 51 of the electromagnetic coupler 40 automatically in alignment. That is, the sonde 30 achieves the mechanical and electrical connection to the connecting pipe 20 without having to be specially orientated. Also, because the turbine blades 27 and 28 are provided inside the connecting pipe 20 and because electricity is generated both in the connecting pipe 20 and the sonde 30, the connecting pipe 20 and the sonde 30 can get electricity just from the flow of the drill mud. Unlike measurement while drilling equipment using a battery, the sonde 30 can be left down the borehole 1 for a long time. Moreover, because the signals received and sent in the electromagnetic coupler 40 are digital signals modulated into FM, the signals received by the sonde 30 have very little noise, reducing the chance of errors in the data collected in the sonde 30. The measurement while drilling equipment 2 can be provided with sensors other than the described sensors 22-25. For example, additional sensors could include an azimuth sensor and a stratum ratio resistance sensor. Also, the shape of the two turbine blades 27 and 28 is not limited to the shape shown in Fig. 2, but could be any turbine shape. The power supplier of the measurement while drilling equipment is not limited to the generator but could instead be a battery. Although, in this case, the sonde 30 cannot be expected to be left down the borehole 1 for a long time, since the mechanism for the generator is not needed, the whole structure of the equipment can be simplified. The communication method from the sonde 30 to the data processing equipment 4 on the surface is not limited to the mud pulse method using the pulse valve 33, but could instead be a sound method using a sound radiator which can send supersonic waves.

Claims: A measurement while drilling equipment for collecting data at the bottom of a borehole (1), the equipment comprising a drill bit (13) attached to the lower end of a drill string (12) comprising first (11A) and second (20) drill pipe sections, the second drill pipe section being adjacent to the drill bit; means for pumping drill mud through the drill string; a plurality of sensors (22,23,24,25) provided in the second drill pipe section (20), each sensor being arranged to collect the data at the bottom of the borehole (1); and a coupler (40) capable of connecting a sonde (30) with the sensors (22,23,24,25) so that the data collected by the sensors can be transmitted to the surface by the sonde; characterised by a sonde (30) mechanically connectable to and separable from the first drill pipe section (11A); in that the coupler comprises a primary annular coil (41) provided in the second drill pipe section (20), and a secondary annular coil (51) which surrounds an outer peripheral portion of the sonde (30); and in that the coils (41,51) are arranged so that when the sonde (30) is mechanically connected to the first drill pipe section (llA), the secondary annular coil (51) fits within and is at the same level as the primary annular coil (41) to establish an electromagnetic coupling between the sonde (30) and the sensors (22,23,24,25). A measurement while drilling equipment according to claim 1, wherein the sonde (30) has a centralizer (32) which allows the sonde to be aligned with a central axis of the drill string (12). A measurement while drilling equipment according to claim 2, wherein the centralizer comprises four axially extending plate springs (32A). A measurement while drilling equipment according to any one of the preceding claims, wherein the sonde (30) is provided at its upper end with a fishing neck (34) by means of which it can be gripped so that it can be pulled to the surface. A measurement while drilling equipment according to any one of the preceding claims, wherein the sonde (30) includes a pulse valve (33) to change the pressure of the drill mud. A measurement while drilling equipment according to any one of the preceding claims, wherein the lower part of the sonde (30) contains a first generator which is arranged to be driven by a turbine blade (28) which is provided in the drill string (12) and is capable of being rotated by the drill mud. A measurement while drilling equipment according to claim 6, wherein the sensors (22,23,24,25) are supplied by a second generator (29), which is arranged to be driven by a turbine blade (27) which is capable of being rotated by the drill mud. A measurement while drilling equipment according to any one of the preceding claims, wherein the secondary coil (51) is rotatable. A measurement while drilling equipment according to any one of the preceding claims, wherein the primary coil (41) receives a signal from a signal processing portion which converts respective analogue signals from the sensors into digital signals, and a multiplexing portion which multiplexes the digital signals and subsequently combines the signals with a high frequency carrier; and wherein the signals received by the secondary coil (51) are fed to a signal resolving portion to resolve multiplexed signals into data signals, and a D/A converter. A measurement while drilling equipment according to any one of the preceding claims, wherein both coils (41,51) are sealed and do not, in use, directly contact one another.

Inventors: HOSONO KAZUHO C O AKISHIMA LAB, YUASA HAJIME C O AKISHIMA LAB, HOSONO, KAZUHO C/O AKISHIMA LAB. (MITSUI ZOSEN)INC, YUASA, HAJIME, C/O AKISHIMA LAB. (MITSUI ZOSEN)INC
Applicants: AKISHIMA LAB MITSUI ZOSEN INC, AKISHIMA LABORATORIES (MITSUI ZOSEN) INC.
Application year: 1992
Main classification: E21B47
IPC codes: E21B44, E21B47