Technical field The present invention relates to a downhole device, e.g. a downhole logging device, having a housing enclosing electronics for use in a downhole tool. In a second aspect, the present invention relates to a downhole tool comprising the downhole device. In a third aspect, the present invention relates to a method of running a downhole tool comprising the downhole device. In a fourth aspect, the present invention relates to a program for operating the downhole device. State of the art

Downhole tools that are provided in a drillstring are generally rented by suppliers to drilling operators. These downhole tools are submitted to severe constraints of pressure, temperature and vibration. Usually, drilling operators tend to drill a wellbore as fast as possible, which often results in damage on equipments like mud motors, bearings seals, rotors or stators included in a drill string. Positive displacement mud motors comprise a stator having a bore provided with lobes, generally made of elastomer or rubber, in which is eccentrically inserted a metallic helical rotor. Drilling fluid is circulated through the bore and the flow of fluid transmits power which drives the rotor to rotate within the stator. Lot of friction forces and involved that result, after a certain time of use of the motor, in local wear of the stator's lobes. When the motor has been used and is taken off from the drillstring, the stator has to be inspected before it can be sent to another client.

It is estimated that mud motors should be returned to the supplier for inspection and maintenance after 100 to 125 hours of drilling. When the downhole tool gets back to the supplier, the supplier knows neither the exact time for which the mud motor has been used nor under which conditions it has been used. Once a downhole tool has been used, the supplier may not be in a good position to guaranty good quality of the tool to the next drilling operator. Despite inspection of the mud motor, since the stator is a long tubular element, some hidden defects can sometimes be overlooked. Some components of the mud motor have a limited lifetime under certain conditions and it would be useful for the provider to know how long and under which conditions the tool has been already run, in order to assess if maintenance of the tool is necessary or not and to communicate to the next drilling operator the accurate limit of use time before maintenance of the mud motor.

There is a need for a downhole device adapted for recording accurately the time of use of a downhole tool and the history of the forces applied on the downhole tool during its operation. There is a further need for a downhole device adapted for monitoring and/or controlling on time a tool element comprised in the downhole tool.

Summary of the invention

According to a first aspect of the invention, a downhole device (e.g. a downhole data logging device) comprises a housing configured for enclosing electronics, preferably measurement and logging electronics, for use in a downhole tool, the housing comprising: a housing sleeve having a longitudinal bore therein, the longitudinal extending between a first end and a second end of the housing sleeve; a chassis dimensioned to be inserted into the longitudinal bore, the chassis being configured to maintain the electronics in a fixed position relative to the chassis, a first cap for sealing the first end; and a second cap for sealing the second end; the shapes of the chassis and at least one of the first and second caps being adapted to each other to mechanically engage with each other in a single relative position. Preferably, the chassis comprises a first mating part and the first cap has a second, preferably complementary, mating part, both the first and second mating parts being configured to mechanically engage with each other and to prevent, through the engagement, rotation of the chassis relative to the first cap.

Preferably, the first and second caps are fixed on the housing sleeve in a fluid-tight manner. Preferably, the downhole device comprises O-rings between the chassis and the housing sleeve for cushioning the chassis within the housing sleeve.

Preferably, the chassis has a first end and a second end opposite to the first end and comprises at least one venting channel extending from the first end to the second end.

Preferably, the housing is configured to fit within a pocket of a downhole tool and has a third mating part shaped for mechanically engaging with a second mating part provided on the pocket and for preventing, through the engagement, rotation of the downhole device within the pocket.

Preferably, the electronics comprise an elongated printed circuit board and, when in use, a battery. Preferably, the electronics comprise at least one measurement device, a real time clock, a memory and a processor, the processor being configured to receive signals coming from the measurement device, converting the signals into digital data and recording the data into the memory.

Preferably, at least one of the measurement devices is an accelerometer for measuring vibrations of the downhole tool.

Preferably, at least one of the measurement devices is a thermocouple.

Preferably, the electronics comprise a low G accelerometer adapted to measure vibrations resulting from the operation of the downhole tool.

Preferably, the electronics comprise a first low G accelerometer adapted to measure vibrations along an the longitudinal axis of the downhole tool, and a second low G accelerometer adapted to measure vibrations along an axis perpendicular to the longitudinal axis of the downhole tool.

Preferably, the electronics comprise a high G accelerometer adapted to measure accelerations resulting from shocks encountered by the downhole tool.

Preferably, the electronics comprise a first high G accelerometer adapted to record vibrations along a first axis of the downhole tool and a second high G accelerometer adapted to record vibrations along a second axis perpendicular to the first axis of the downhole tool.

Preferably, the electronics comprise a magnetic probe.

A second preferred aspect of the invention relates to a downhole tool having a body provided with a pocket, the pocket being shaped for receiving and maintaining in a single position a downhole device as described hereinabove, the downhole tool further comprising a cover for closing the pocket and protecting the downhole device. A device for keeping the downhole device mechanically constrained within the pocket, e.g. a spring, may be provided.

Preferably, the downhole tool comprises a rotor, the downhole device comprising a magnetic probe, the rotor comprising a magnet located in proximity of the magnetic probe such that the speed of the rotor can be recorded as a function of time.

A third preferred aspect of the invention relates to a method of running a downhole tool. The method comprises: using a downhole tool equipped with a downhole device as described hereinabove in wellbore construction;

- and examining data recorded by the downhole device; and Preferably, based on the data, maintenance and/or replacement of the downhole tool is scheduled.

According to a fourth aspect, the invention relates to a program for a processor of a downhole device to be inserted into a downhole tool. The program contains instructions, which, when executed by the processor, cause the processor to interact with one or more measurement devices (possibly to control them), receiving measurement signals from the measurement devices and to record the measurement signals as digital data in memory. In particular, the program instructions cause the processor to start recording the measurements signals only after at least one of the measurement signals has continuously remained either above or below a predetermined threshold during a minimum time. Preferably, the program instructions cause the processor to interrupt the recording of the measurements signals only after at least one of the measurement signals has continuously remained either above or below a further predetermined threshold during a further minimum time.

Brief description of the drawings

Figure 1 shows an exploded view from a first side of a downhole device according to an embodiment of the present invention.

Figure 2 shows an exploded view of the downhole device of figure 1 from the opposite side and an exploded view of a downhole tool comprising such downhole device.

Figure 3 shows a portion of a pocket on a downhole tool according to the present invention.

Figure 4 shows a schematic view of an embodiment of electronics for a downhole device according to the present invention.

Figure 5 shows a schematic longitudinal cross-sectional view of an embodiment of a downhole tool according to the present invention.

Detailed description of possible embodiments of the present invention

Figure 1 presents an exploded view of a downhole device 100 according to an embodiment of the present invention. The downhole device 100 has a housing enclosing electronics (such as e.g. a printed circuit board) for use in a downhole tool. The housing comprises: a housing sleeve 1 having a longitudinal bore extending between a first end 5 and a second end 6;

a chassis 2 inserted within the housing sleeve 1 and adapted for firmly maintaining the electronics in a single position,

a first cap 3 for closing the first end 5 and; a second cap 4 for closing the second end 6; wherein the chassis 2 has one first mating part 7 and one of the first cap and the second cap has a second mating part 8, both the first mating part 7 and second mating parts 8 being adapted for mating together and preventing rotation of the chassis 2 within the housing, and for ensuring alignment in a certain longitudinal plane of the housing sleeve 1. In other words, the first and second mating parts 7, 8 serve as indexing means that position the chassis 2 at one precise angle relative to the housing sleeve 1.

Preferably, the chassis 2 has two opposite ends 9, 10 wherein a first end 9 provides the first mating part 7. The first mating part 7 of the chassis 2 can be a socket and the second mating part of the first cap a pin 8, or conversely. Socket 7 and pin 8 have a shape adapted for maintaining the chassis 2 in a single position. Both mating parts have a cross section adapted for preventing rotation of the chassis relative to the first cap. The second cap 4 has preferably no mating part with the chassis. The second cap may comprise a cylindrical recess 17 for inserting a spring 16 destined to cushion the chassis 2 and to push it against the first cap 3 and thereby to keep the socket 7 and pin 8 engaged with each other.

The downhole device of the present invention is destined to be submitted to high pressures within the downhole. Electronics that cannot withstand those elevated pressures thus have to be confined in a fluid-tight container the interior of which is kept at a substantially lower pressure (e.g. at substantially atmospheric pressure). Therefore, after fixation of electronics on the chassis, and insertion of the assembly of the chassis and the electronics within the housing sleeve 1, the first and second caps 3, 4 are tightly fixed on the housing sleeve. Preferably, the first cap 3 and the second cap 4 have male threads 18, 19 that are screwed into female threads provided on the opposite ends of the housing sleeve 1. More preferably, the first cap 3 and second cap 4 are provided with a circular ledge 23, 24 located between the base of the cap and the threads for inserting an O-ring (not represented). More preferably, a further circular ledge is provided between each end of the housing sleeve and the respective female thread for receiving the CD- ring provided on the respective cap and providing an efficient sealing. In a preferred embodiment of the invention, the housing sleeve is cylindrical, such a shape being adapted for withstanding elevated pressure gradients. Preferably, the housing sleeve is made of a high strength, stainless and nonmagnetic material, such as for example nitrogen strengthened austenitic stainless steel, preferably containing between 1% and 4% of silicon. Preferably, the caps are made of beryllium copper alloy which is a further nonmagnetic material adapted for preventing galling of the threads sliding on threads of the housing sleeve. Preferably, the chassis is made of anodized aluminum with increased corrosion resistance and with a nonconductive surface, which can maintain electronics.

The outer diameter of the chassis 2 is slightly smaller than the diameter of the bore in the housing sleeve 1, allowing the chassis 2 to be inserted and removed from the housing sleeve without, however, offering too much clearance. Preferably, the chassis comprises one or more circumferential grooves, i.e. sections wherein the outer diameter of the chassis is recessed from the inner diameter of the housing sleeve, for example by 1 to 2 mm. Those sections are provided with O-rings a, b, c that cushion the chassis 2 within the housing sleeve 1 and that hinder axial movement of the chassis 2 within the housing sleeve

1. Preferably, such circumferential grooves are provided nearby both ends and the middle of the chassis 2. Preferably, the chassis 2 comprises a first compartment 14 for receiving electronics, such as e.g. a printed circuit board 12 which is fixed on the chassis 2 for example by means of screws 20. More preferably, the chassis 2 further comprises a second compartment 15 for inserting a battery 13 which can be secured within the second compartment for example by clips or by the flexibility of the walls of the second compartment 15 or by a spring holding the battery within the second compartment. A passage for wires is provided in the partition that separates the first and second compartment for connecting the battery 13 to the printed circuit board 12.

Preferably, the printed circuit board 12 is elongated and is disposed with the battery 13 along the same axis within the chassis 2.

As will be appreciated, the elongated shape of the downhole device 100 provides sufficient room for integration of an elongated printed circuit board 104 comprising more electronic components and of a longer lifetime battery 13. The battery 13 is advantageously selected from long lifetime batteries, such as lithium batteries, preferably lithium thionyl chloride batteries. Also, an elongated downhole device as described hereinabove can be more easily integrated within the body of a downhole tool such as a collar or a positive displacement motor 200. While assembling the downhole device, it is preferable to rotate as little as possible the chassis 2 within the housing sleeve 1 in order to avoid, as much as possible, deformation of chassis 2, which comprises the sensitive electronics that shouldn't be twisted. In a preferred method for assembling the downhole device 100, the first cap 3 comprising the second mating part 8 is first screwed with its O-ring on a first threaded end 5 of the housing sleeve 1. Then, the chassis 2 on which are fixed the electronics is inserted within the housing sleeve with an orientation such that the first mating part 7 provided on the chassis can mate with the second mating part 8 provided on the first cap 3. Preferably, the chassis 2 comprises venting channels 11 extending from the first end 9 to the second end 10 of the chassis. Those venting channels 11 permit the evacuation of air from the interior of the housing sleeve 1 when the chassis 2 is being inserted and thus avoid that one has to work against the a pressure increase in the interior. Once the chassis 2 in fully inserted, the second cap 4 is tightly screwed on the second end 6 of the housing sleeve

2. Preferably, a high load spring 16 is provided between the second end 10 of the chassis and the second cap 4 for preventing longitudinal movement of the chassis 2 within the housing sleeve 1.

Especially if rotation of the chassis 2 during insertion cannot be avoided, the O-rings provided on the chassis 2 may be lubricated with a lubricant in order to avoid damaging the O-rings. Preferably, the lubricant is nonconductive, whereby short-circuit would be avoided if the lubricant should enter in contact with part of the electronics.

As illustrated in Figure 2, according to a preferred embodiment of the invention, the second end 10 of the chassis 2 comprises a female connecting thread 25 for connecting a tool to the chassis 2 that facilitates installation of the chassis 2 in and/or removal of the chassis 2 from the housing sleeve 1.

Figure 2 illustrates a partially exploded view of a section of a downhole tool 200, for example a section of a downhole motor, with an exploded view of the downhole device 100.

Preferably, the downhole tool 200 comprises a body 207 with an axial bore 208, in which a drilling fluid is able to flow. The downhole tool 200 may comprise an actuated member (not shown) like a mandrel or a rotor actuated hydraulically, mechanically or electrically. Alternatively, the downhole tool may be a collar adjacent to a downhole tool comprising an actuated member like a mandrel or a rotor actuated hydraulically, mechanically or electrically.

Once the downhole device 100 is assembled, it may be inserted in a pocket 201 (see Figures 2 and 3) provided on the downhole tool 200 destined to be included in a drill string. Preferably, the housing of the downhole device 100 is designed to fit within the pocket 201 and comprises a mating part 21 mating with a second mating part 205 provided on the pocket 201. Mating parts 21 and 205 are shaped so as to prevent rotation of the downhole device 100 within the pocket 200. The mating part 21 of the housing may be provided on the housing sleeve 1 or preferably on one of the caps 3 and 4. In figures 1 and 2, the mating part 21 is provided on the first cap 3 as a polygonal pin 21 fitting within a female socket 205 provided in the pocket 201 of the downhole tool 200. It is preferred that the mating part 8 blocking the chassis 2 against rotation relative to the housing sleeve 1 and the mating part 21 blocking the housing sleeve against rotation relative to the body 207 are provided on one and the same housing component (i.e. on the first cap 3, the housing sleeve 1 or the second cap 4). The reason for this is that one can precisely define the position of the chassis 2 (and the electronics contained therein) relative to the body 207 of the downhole tool. If the mating parts 8 and 21 were provided on different housing components, the slightest misalignment of these components with respect to the planned configuration leads to an imprecisely defined position of the electronics relative to the downhole tool. A device (for example a spring 212) to keep bias the downhole device mechanically constrained within the pocket, e.g. against the female socket 205, , is provided. When the downhole device 100 is inserted within the pocket 201 of the downhole tool, a cover plate 202 may be fixed on the downhole tool 200 for closing the pocket 205. Preferably, the cover plate 202 is fastened on the downhole tool 200 by screws 203 engaging in counterbores 206. For preventing loosening of the screws 203 due to vibrations, means for maintaining the screws 203 are provided. For instance such means for maintaining the screws may comprise snap rings 204 arranged in grooves (not shown for clarity) provided in the counterbores 206. Figure 4 schematically illustrates a printed circuit board 12 for being secured within the chassis 2. The printed circuit board 12 carries electronic components comprising at least one measurement device, a real time clock 108, a memory 105 and a processor 104. The processor 104 is programmed for recording data collected by the measurement device and for storing values into the memory. After use of the downhole tool, the stored values can be read from the memory, decoded and the actual tool operating time, and possibly other operating parameters, can be derived therefrom. The measurement device is adapted for transmitting a signal to the processor 104. Preferably, the processor 104 is programmed to start recording a signal induced by the operation of the downhole tool 200 after a predetermined time during which the signal amplitude received by the processor 104 exceeds a predetermined value threshold.

In an embodiment of the invention, the downhole device is used for recording the conditions of operation of a downhole tool 200, e.g. a positive displacement motor, as a function of elapsed time. Circulation of a drilling fluid through a positive displacement motor drives the rotor into eccentric motion, which causes continuous low-amplitude vibrations that can be measured by a low-G accelerometer. Therefore, if the measurement device comprises a low-G accelerometer 101, the signal versus time can be recorded by the processor and converted into corresponding digital data stored into the memory 105. It is therefore possible to know when and for how long the tool has been operated.

In an embodiment of the invention, the electronics thus comprise a low G accelerometer 101 adapted to measure low-amplitude vibrations resulting from the operation of the downhole tool. In the case of a positive displacement motor, the vibration amplitude depends on the design of the positive displacement motor and on the flow of fluid passing there through. For calibrating the downhole device, in particular, for determining the range of vibration amplitudes that are indicative of operation of the positive displacement motor, a calibration curve showing the vibration amplitude for different working flow rates of fluid passing through the downhole tool can be realized. The processor 104 on the printed circuit is configured to start logging the operating conditions and recording the time of use of the downhole tool if the measured vibration amplitude lies within the predefined window of vibration amplitudes determined during calibration for a certain minimum time.

According to a preferred embodiment of the invention, illustrated in Figure 4, the electronics comprise a first low G accelerometer lOlx adapted to measure vibrations along the axis of the downhole tool ("X-axis"), and a second low G accelerometer lOly adapted to measure vibrations along an axis ("Y- axis") perpendicular to the axis of the downhole tool 200.

For example, the low G accelerometer 101 is adapted to measure vibration amplitudes ranging from -1.5G to +1.5G (1 G = 9.81 m/s ² ). Typically, the amplitude of vibrations of the downhole tool during operation oscillates within a range of values of comprised for example between -0.7G and +0.7G for a certain flow of drilling fluid. Alternatively, or in combination with the preceding embodiments, the electronics of the downhole device may comprise a magnetic field probe 106. The magnetic field probe 106 registers the earth magnetic field as a function of the time provided by the real time clock. The signal from the magnetic field probe 106 stored in the memory provides information on the orientation of the downhole tool and the path of drilled wellbore. Advantageously, a magnet is provided in a nonmagnetic section of the rotor 210 of a positive displacement motor 200, such that the magnetic field probe 106 produces a signal which provides information on the speed of rotation of the rotor 210 as a function of time.

According to a preferred embodiment of the invention, the downhole device further comprises a medium G accelerometer 103 adapted to measure vibration amplitudes of "medium" magnitude, ranging for example from -18G to +18G. Preferably, the medium G accelerometer is oriented on the printed circuit board so as to be able to take measurements along the X-axis.

According to yet a further preferred embodiment of the invention, the downhole device comprises a high G accelerometer adapted to measure vibrations resulting from possible shocks encountered by the downhole tool such as for example a shock resulting from activation of a jar, and for recording such events in the memory. For example, the high G accelerometer may be adapted to measure vibration amplitudes ranging from -50G to +50G.

Preferably, the downhole device 100 comprises a first high G accelerometer 102x disposed on the printed circuit board in such a way as to be able to measure vibrations along the X-axis of the downhole tool and a second high G accelerometer 102y disposed on the printed circuit board in such a way as to be able to measure vibrations along the Y-axis.

According to a second aspect, the present invention relates to a downhole tool 200 having a body 207 comprising: a bore 208 in which a drilling fluid is able to flow,

a pocket 201 shaped for receiving a logging device 100 as described hereinabove;

- the said downhole device 100;

a cover plate 202 for maintaining and protecting the downhole device 100 within the pocket 201.

Preferably, the downhole tool 200 further comprises an actuated member like a mandrel or a rotor 210 actuated hydraulically, mechanically or electrically. A schematic embodiment of a downhole tool is represented in Figure 5. The downhole tool 200 comprises a positive displacement motor comprising an eccentric helical rotor 210 within a stator 209, both rotor 210 and stator 209 comprising a plurality of lobes.

According to a third aspect, the present invention relates to a method of managing the use of a downhole tool 200, wherein: a downhole device 100 according to the first aspect of the present invention is provided in a downhole tool 200;

the downhole tool 200 is used for drilling a wellbore;

data recorded by the downhole device 100 are examined;

- based on the data, maintenance or replacement of the downhole tool is scheduled.

According to a fourth aspect, the invention relates to a program of a processor of a downhole device to be inserted into a downhole tool. The program, when carried out by the processor, causes the processor to interact with one or more measurement devices, in particular to control operation of the one or more measurement devices and to receive measurement signals from them. The program further causes the processor to record the measurements signals and to store the signals in machine-readable form in a memory. Preferably, the program implements a hysteresis in the sense that it causes the processor to start logging the measurement signals only after at least one of the measurement signals has remained within a predefined first window of values during a predefined first minimum time period. Similarly, the program is preferably configured to cause the processor to stop logging after at least one or a predefined group of measurement signals have remained outside a predefined second window of values for a certain second minimum time period. It should be understood that the first and second windows may be equal or different. Furthermore, also the first and second time periods may be equal or different.

Preferably, the data recorded by the downhole device are examined when the downhole tool 200 is removed back at the surface of the wellbore. The data stored in the memory 105 are readable by computer means and provide information on the conditions of use of the downhole tool during the time it has remained in the wellbore. For example, the temperature, the direction of the tool, the rotational speed of the rotor, the rotational speed of the tool body, any shock experienced by the downhole tool can be extracted as a function of the time during which the downhole tool was in the wellbore. That information can be used for determining the inclination of the wellbore that has been drilled and for characterizing the wellbore. The information provided is also useful for determining how much time and under which conditions the downhole tool has been operated in order to plan maintenance of the downhole tool.