Patent Publication Number: US-7712223-B2

Title: Apparatus for azimuth measurements using gyro sensors

Description:
FIELD OF THE INVENTION 
   The present invention relates to apparatuses for azimuth measurements using gyro sensors in downhole. More particularly, the invention relates to apparatuses for azimuth measurements with gyro sensors in open-holes or cased-holes during oilfield operations such as wellbore drilling operations and wireline logging operations. 
   BACKGROUND OF THE INVENTION 
   In recent wellbore drilling operations, the drilling is mostly performed in highly deviated and horizontal wellbores. To drill a wellbore as planned prior to drilling, it is important to monitor an inclination of the wellbore and continually determine the position and direction of the drilling tool during drilling. For this monitoring, azimuth with respect to drilling direction and then an axis of the drilling tool is one of important information during drilling. The azimuth can be measured by utilizing some sensors such as a gyro sensor installed in the drilling tool during drilling. In wireline logging operations, a logging tool is conveyed into a wellbore after the wellbore has been drilled. The gyro sensor is used to measure azimuth with respect to the direction of the logging tool. 
   To improve accuracy and efficiency of the azimuth measurements, a plurality of gyro sensors with each input axis orthogonal to each other may be used. In this combination of the gyro sensors, each gyro sensor is rotated about its rotation axis perpendicular to the input axis. The drive unit for rotating the gyro sensors is configured so as to rotate the gyro sensors stably while maintaining a predetermined angular relationship between the input axes of gyro sensors. In practical point of view, the gyro sensors and the drive unit are installed in relatively narrow space in the foregoing drilling tool and wireline logging tool. Therefore, there is a need for a compact apparatus for azimuth measurements using gyro sensors that can allow the gyro sensors to be stably rotated in cooperation with each other even if such gyro sensors are used, for example, in oilfield and any other harsh environment. 
   BRIEF SUMMARY OF THE INVENTION 
   In consequence of the background discussed above, and other factors that are known in the field of oil exploration and development, apparatuses for azimuth measurements using gyro sensors in downhole are provided. In one aspect of the present invention, an apparatus for azimuth measurements comprises an elongated housing, a plurality of gyro sensors, each of the gyro sensors having an input axis for angular velocity measurements, spherical sensor holders arranged along the longitudinal direction of the housing, at least one motor for driving the sensor holders, a transmission mechanism for transmitting a rotation force from the motor to each of the sensor holders and a controller for controlling a rotation of the motor. Each of the sensor holders has one of the gyro sensors and is rotatable about a rotation axis so as to change the orientation of the input axis of the gyro sensor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings illustrate preferred embodiments of the present invention and are a part of the specification. Together with the following description, the drawings demonstrate and explain principles of the present invention. 
       FIG. 1  shows a partial cross-sectional plan view of a sensor apparatus for azimuth measurements in an embodiment according to the present invention; 
       FIG. 2  shows a perspective view of an example of the sensor holder; 
       FIG. 3  shows an explanatory view of a transmission mechanism of the sensor apparatus; 
       FIG. 4  shows an explanatory view of an example of internal structure of a sensor holder; 
       FIGS. 5A and 5B  show explanatory views of an example of electrical interconnection between a gyro sensor and a data processing unit; 
       FIG. 6  shows an explanatory view of another example of electrical interconnection between a gyro sensor and a data processing unit; 
       FIGS. 7A and 7B  show explanatory views of yet another example of electrical interconnection between a gyro sensor and a data processing unit; 
       FIG. 8  shows an explanatory view of an example of a heat insulation layer between a motor and sensor holders; 
       FIG. 9  shows an explanatory view of an example of a heat release layer between a motor and an internal surface of a housing; 
       FIG. 10  shows an explanatory view of an example of a thermal mass and a heat pipe thermally connecting between the thermal mass and a motor; 
       FIGS. 11A and 11B  show explanatory views of an example of a mechanical stopper for stopping rotation of a sensor holder; 
       FIGS. 12A and 12B  show explanatory views of an example of a clump mechanism for clumping a sensor holder; 
       FIG. 13  shows a block diagram of electric system of the sensor apparatus; 
       FIG. 14  shows a flow chart of an example of control of the motor and the clump mechanism; and 
       FIG. 15  shows a partial cross-sectional plan view of a sensor apparatus for azimuth measurements in another embodiment according to the present invention. 
   

   DETAILED DESCRIPTION 
   Illustrative embodiments and aspects of the present disclosure are described below. In the interest of clarity, not all features of an actual implementation are described in the specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, that will vary from one implementation to another. Moreover, it will be appreciated that such development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having benefit of the disclosure herein. 
     FIG. 1  shows a partial cross-sectional plan view of a sensor apparatus for azimuth measurements in one embodiment according to the present invention. The sensor apparatus  10  comprises an elongated housing  100 , three gyro sensors  210 ,  220 ,  230 , three sensor holders  310 ,  320 ,  330  arranged along the longitudinal direction of the housing  100 , a motor  400  for driving the sensor holders  310 ,  320 ,  330 , a transmission mechanism for transmitting a rotation force from the motor  400  to each of the sensor holders  310 ,  320 ,  330  and a controller  500  for controlling a rotation of the motor  400 . The controller  500  is configured to be a part of an electrical system  800  including peripheral circuits. The housing  100  is mostly cylindrical in shape and may be made from heat conductive metal such as stainless steel. Other elements of the sensor apparatus  10  are arranged in the housing  100 . Various types of motors such as a synchronous motor (for example, a stepper motor) or an induction motor can be used as the motor  400 . 
     FIG. 2  shows a perspective view of an example of the sensor holder. Each body  312 ,  322 ,  332  of the sensor holders  310 ,  320 ,  330  is mostly spherical in shape and includes a corresponding gyro sensor inside. An input axis for angular velocity measurements is defined in each of the gyro sensors  210 ,  220 ,  230 . Each of the sensor holders  310 ,  320 ,  330  is rotatable about a rotation axis so as to change the orientation of the input axis of the gyro sensor. Both ends of the rotation shafts of the sensor holder are supported with bearings in the housing  100 . The second sensor holder  320  has a helical gear  451  attached along the great circle on an outer surface of the second sensor holder  320  as shown in  FIG. 2 . The third sensor holder  330  has a helical gear  452  attached along the great circle on an outer surface of the third sensor holder  330 . The two helical gears  451 ,  452  are jointed to each other in a crossing manner at a contacting position of the sensor holders  320 ,  330  so that the rotation force is transferred from the second sensor holder to the third sensor holder. 
     FIG. 3  shows an explanatory view of the transmission mechanism of the sensor apparatus  10 . The transmission mechanism comprises a reduction gear unit  430 , an intermediate transmission mechanism  440  and a pair of the helical gears  451 ,  452 . The reduction gear unit  430  includes four spur gears  431 ,  432 ,  433 ,  434 , and transmits a rotation force from a rotation shaft  401  of the motor  400  to a rotation shaft  311  of the first sensor holder  310  with a predetermined reduction ratio (e.g. 1:5 or 1:10). The intermediate transmission mechanism  440  includes a pair of miter gears  441 ,  442  having conically shaped teeth faces, an idle shaft  443  and spur gears  444 , 445 . The idle shaft  443  has the miter gears  442  at one end and the spur gear  444  at an opposite end. The idle shaft  443  is arranged to be orthogonal to the rotation shaft  311  of the first sensor holder  310  and parallel to the rotation shaft  321  of the second sensor holder  320 . The miter gear  441  is fixed at an end of the rotation shaft  311  of the first sensor holder  310  and another miter gear  442  is fixed on the end of the idle shaft  443 . The conically shaped teeth faces of the miter gears  441 ,  442  are coupled with each other so as to transmit a rotation force of the rotation shaft  311  to the idle shaft  443  with rotation axes of the both shafts  331 ,  443  orthogonal to each other. The spur gear  444  is fixed at an opposite end of the idle shaft  443  and the spur gear  445  is fixed on a rotation shaft  321  of the second sensor holder  320 . Rotation force of the idle shaft  443  is transmitted to the rotation shaft  321  of the second sensor holder  320  through the spur gears  444 ,  445 . 
   By aforementioned combination of the motor  400  and the transmission mechanism, the gyro sensors  210 ,  220 ,  230  together with the sensor holders  310 ,  320 ,  330  can be stably rotated in cooperation with each other as shown in  FIG. 3 . When the motor  400  rotates in a rotation direction indicated by the arrow R 1 , the sensor holder  310  with the first gyro sensor  210  rotates in a rotation direction indicated by the arrow R 2  at an angular rate reduced by the reduction gear unit  430 . Accordingly, the input axis of the first gyro sensor  210  can be aligned to an arbitrary orientation parallel to an XY plane with respect to an orthogonal coordinates defined in  FIG. 3 . When the sensor holder  310  rotates, the rotation force is transmitted the rotation shaft  311  to the rotation shaft  321  through the intermediate transmission mechanism  440  with the idle shaft  443  rotating in a rotation direction indicated by the arrow R 3 . Then, the sensor holder  320  with the second gyro sensor  220  rotates in a rotation direction indicated by the arrow R 4 . Accordingly, the input axis of the second gyro sensor  220  can be aligned to an arbitrary orientation parallel to a ZX plane. When the sensor holder  320  rotates, the rotation force is transmitted to the sensor holder  330  by the pair of helical gears  451 ,  452  and the sensor holder  330  with the third gyro sensor  230  rotates in a rotation direction indicated by the arrow R 5 . Accordingly, the input axis of the third gyro sensor  230  can be aligned to an arbitrary orientation parallel to a YZ plane. 
   For azimuth measurements, two or three orthogonal accelerometers may be preferably provided in the sensor apparatus  10 . The accelerometers are used to determine a horizontal plane on which an earth rate vector determined by the gyro sensors. The accelerometers may be either conventional Q-flex types or MEMS type accelerometers. 
   A rotation angle sensor  410  may be preferably provided in order to detect a rotation angle position of a rotation shaft  401  of the motor  400  or an output shaft of the reduction gear unit  430  (i.e. the rotation shaft  311  of the first sensor holder  310 ). Various types of rotation angle sensors such as a mechanical or optical encoder can be used as the rotation angle sensor  410 . By using the detected rotation angle position, the angular orientation of each input axis of the gyro sensors  210 ,  220 ,  230  can be identified. This monitoring the angular rotation position allows the sensor apparatus  10  to return each gyro sensor at a home position and set each input axis of the gyro sensors aligned to a predetermined home angular orientation, whenever the system power is turned on. In addition, it is important to monitoring the angular rotation position during the azimuth measurement for reliability of the sensor apparatus. 
     FIG. 4  shows an explanatory view of an example of internal structure of a sensor holder. Each of the sensor holders  310 ,  320 ,  330  has some hollow space inside. For example, the first sensor holder has a gyro sensor  210  and electrical circuit boards  215 ,  216  supported by spacers  313  inside as shown in  FIG. 4 . The gyro sensor  210  and electrical circuit boards  215 ,  216  are connected by electrical wirings  314 . There are some hollow space between the gyro sensor  210 , the electrical circuit boards  215 ,  216  and the electrical wirings  314  in the sensor holder  310 . The hollow space may be filled with insulating and heat-resisting material such as silicone resin to prevent electronic components on the electrical circuit boards  215 ,  216  from dropping out. A heat-resisting material may be preferably used for filling the hollow space. 
     FIGS. 5A and 5B  show explanatory views of examples of electrical interconnection between the gyro sensor and the data processing unit  600  in the electric system  800 . An electrical wiring  316  may be led out from the electrical circuit board in the sensor holder  310  via a side through hole  311   a  of the rotation shaft  311  as shown in  FIG. 5A . The electrical wiring  316  also may be led out via a hole  312   a  made on spherical surface of the sensor holder body  312  as shown in  FIG. 5B . The electrical wiring  316  is wound around the outer surface of the rotation shaft  311  or the sensor holder body  312  for making a margin of wiring before rotating the sensor holder  310 . 
     FIG. 6  shows an explanatory view of another example of the electrical interconnection. This connection may be suitable for the second and third sensor holders  320 ,  330 . An electrical wiring  326  may be led out from the electrical circuit board in the sensor holder  320  via an axial through hole  321   a  of the rotation shaft  321  supported with bearings  110  as shown in  FIG. 6 . 
     FIGS. 7A and 7B  show explanatory views of yet another example of the electrical interconnection. Two electrical wirings  316  from the data processing unit  600  and the electrical circuit board in the sensor holder may be connected via a combination of a ring-shaped slip-electrode member  317  and a contact electrode member  318 . The slip-electrode member  317  is attached on flat portion  312   b  of the outer surface of the sensor holder body  312  and has a plurality of ring-shaped slip-electrodes  317   a . The contact electrode member  318  is fixed in the housing  100  and has a plurality of contact pins  318   a  corresponding to the slip-electrodes  317   a . The corresponding slip-electrode  317   a  and contact pin  318   a  are kept contact to each other during rotating the sensor holder  310 . 
   The electrical communication between the electrical circuit board and the data processing unit  600  may be performed by a short-distance wireless communication. 
     FIG. 8  shows an explanatory view of an example of a heat insulation layer between the motor  400  and sensor holders. The heat insulation layer  102  may be inserted between the motor  400  and a support member  101  fixed to the housing  100  to avoid heat flow from the motor  400  to the sensor holders. A heat-resisting material such as polyimide resin may be used for the heat insulation layer. 
     FIG. 9  shows an explanatory view of an example of a heat release layer between a motor and an internal surface of a housing. The heat release layer  103  may be inserted into a hollow space around the motor  400 . A heat conductive material such as metal or a thermally conductive high performance resin may be used for the heat release layer  103 . 
     FIG. 10  shows an explanatory view of an example of a thermal mass and a heat pipe thermally connecting between the thermal mass and a motor. The heat release layer  103  may be connected to a thermal mass  104  with a heat pipe  105  to release heat from the motor  400  efficiently. The thermal mass  104  may be made of metal such as aluminum or copper and may be located at an end position apart from the sensor holders. 
     FIGS. 11A and 11B  show explanatory views of an example of a mechanical stopper for stopping rotation of a sensor holder. At least one of the sensor holders may be provided with the mechanical stopper to prevent the sensor holder from rotating more than a predetermined rotation angle. For example, the mechanical stopper may be configured by using a pin member  319  fixed on flat portion  332   b  of the outer surface of the sensor holder body  330  and a guide member  106  having a ring-shaped guide groove  106   a . The ring-shaped guide groove  106   a  has a partition plate portion  106   b  at a predetermined position for stopping the pin member  319 . When rotating the sensor holder  330 , the top portion of the pin member  319  moves along the ring-shaped guide groove  106   a  by a rotation angle of almost 360 degrees as shown by an arrow in  FIG. 11B  and the movement of the pin member  319  is blocked by the partition plate portion  106   b . Touch sensors may be attached on the side-wall surfaces of the partition plate portion  106   b  for detecting the arrival timing of the pin member  319  to the blocked position. The detected result may be used for controlling an electrical supply to the motor  400 . 
     FIG. 12  shows an explanatory view of an example of a clump mechanism for clumping a sensor holder. The clump mechanism may be configured to clump at least one of the sensor holders when a power supply to the motor  400  is turned off. The third sensor holder  330  may be preferably clumped by the clump mechanism as shown in  FIGS. 12A and 12B . The clump mechanism may be configured by using a solenoid  460  fixed on a support member of the housing  100 , a movable member  461  with an elastic pressing part  462 , a guide member  108  for guiding the movable member  461  in a central open cavity, a spring  463  for biasing the movable member  461  to set apart from the sensor holder  330 . The guide member  108  is fixed to the inner surface of the housing  100 . A movable shaft  460   a  of the solenoid  460  is inserted into a coupling hole of the movable member  461 . When the solenoid  460  is turned off, the movable member  461  is biased to move at a non-clumping position by the spring  463  as shown in  FIG. 12A . When the solenoid  460  is turned on, the movable shaft  460   a  of the solenoid  460  depresses the movable member  461  against the biasing of spring  463  and the movable member  461  is moved at a clumping position as shown in  FIG. 12B . At the clumping position, the elastic pressing part  462  included in the movable member  461  depresses the outer surface of helical gear  452  attached on the sensor holder  330 . Accordingly, the sensor holder  330  and other sensor holders  310 ,  320  mechanically coupled with the sensor holder  330  are clumped during the power supply to the motor  400  is turned off. 
     FIG. 13  shows a block diagram of an electric system  800  of the sensor apparatus  10 . 
   The electrical system  800  includes the motor  400 , the controller  500 , a data processing unit  600  and a power supply unit  700 . The data processing unit  600  includes a computer having a processor  601  and a memory  602 . The memory  602  stores a program having instructions for the azimuth measurements. 
     FIG. 14  shows an example of a flow chart of data processing for azimuth measurements by using the sensor apparatus  10  with the three orthogonal axis gyro sensors. The input axes of the gyro sensors are orthogonal to each other. At least one program having instructions for the data processing is stored in the memory  602  of the data processing unit  600 . The sensor apparatus  10  is stationary located at an azimuth measuring position in downhole before azimuth measurements. The data processing for azimuth measurements may be performed as described in the specification of U.S. Provisional Patent Application No. 61/053,646, which is incorporated herein by reference. 
   In the data processing for azimuth measurements of  FIG. 14 , a first data from each of the gyro sensors with an input axis aligned to a first angular orientation)(0° is acquired (S 1001 ). After acquiring the first data, a second data from each of the gyro sensors with the input axis aligned to a second angular orientation)(180° opposite to the first angular orientation is acquired (S 1002 ). After acquiring the second data, a third data from each of the gyro sensors with the input axis aligned to the original first angular orientation)(0° (S 1003 ). An earth rate component at the first angular orientation is determined (S 1004 ) by following steps of: 
   (i) obtaining an average Ω (0°)     —     2  between the first data Ω (0°)     —     1  and the third data Ω (0°)     —     3 , 
   (ii) determining the earth rate component Ω E  subtracting the second data Ω (180°)     —     2  from the average Ω (0°)     —     2  and dividing the difference by two. 
   The acquisition of the three data and the determination of the earth rate component for each of the gyro sensors are repeated at a plurality of discrete target angular orientations on each of the sensor rotation planes (S 1005 ). A sinusoidal curve (Ω i =A cos θ i +B sin θ i ) is fit to the earth rate components at the discrete target angular orientations on each of the sensor rotation plane and the fitting parameters A and B are determined (S 1006 ). Components of an earth rate vector with respect to a predetermined orthogonal sensor coordinates are determined based on based on a result of the sinusoidal curve fitting (S 1007 ). 
   Based on a set of data from the gyro sensors with the input axes aligned to the common angular orientation (for example a angular orientation along one of orthogonal axes (x, y, z)), a ratio of sensitivity of a pair of the gyro sensors is determined (S 1008 ). The orthogonal earth rate components corrected based on the ratio of sensitivity to eliminate scale factor error between the gyro sensors (S 1009 ). 
   In parallel with data processing for the orthogonal earth rate components of an earth rate vector, a gravity direction with respect to the orthogonal sensor coordinates is determined based on acceleration data of gravity acquired with the accelerometers (S 1010 ). A north direction is determined by projecting the earth rate vector onto a horizontal plane perpendicular to the gravity direction (S 1011 ). Finally, an azimuth of a target direction on the horizontal plane is determined based on the north direction (S 1012 ). 
   There is a trade-off between dynamic range and resolution of the gyro sensor. If we focus on only azimuth measurements, the dynamic range may be reduced. The dynamic range may be set so as to cover not only the earth rate but also bias drift due to environmental temperature change. 
   There are many variety types of gyro sensors  210 ,  220 ,  230  used for the azimuth measurements including a MEMS gyro sensor. Among the variety types of gyro sensors, a MEMS gyro sensor of ring oscillating type may be preferably used in terms of the accuracy, measurement robustness in environmental vibration conditions. 
   In order to reduce noise in wires from a sensor peripheral circuit of a sensor apparatus including at least one gyro sensor, the sensor peripheral circuit may be configured to dispose an analog circuit portion of the sensor peripheral circuit as close as to the gyro sensor and to output only digital signals to the wires. For this configuration, the analog circuit portion may be included together with the gyro sensor head on a flipped stage of the driving mechanism and flipped or rotated together with the sensor head. 
   The drive mechanism of the sensor apparatus may be configured with separate motors. Each separate motor may drive each gyro sensor directly without a gearbox. Rotation angle sensors are provided in order to detect rotation angle positions of rotation axes of the motors, respectively. The drive mechanism with separate motors may be used to minimize angle errors due to back lash of the gear box in the sensor apparatus with relatively wide physical space for installation. 
   Any gyro sensor has more or less temperature sensitivity in its output. Especially downhole condition in oilfield temperature is changing. Some pre-calibration of the gyro sensor output against temperature using equation for temperature compensation with at least one coefficient may be performed before azimuth measurement in downhole. The coefficient obtained by the pre-calibration may be used to compensate the sensor output by monitoring temperature with a temperature sensor in the sensor part and/or the peripheral circuit. This kind of temperature compensation may be also performed for output data of the accelerometers. The temperature sensors can be installed on the gyro sensor and its analog circuit. The compensation is conducted to compensate temperature dependency of scale factor, bias and misalignment using pre-calibration coefficients of the temperature dependency of each item. 
   Each output of three-orthogonal axis gyro sensors, three-orthogonal axis accelerometers, and temperature sensors for the gyro sensors and accelerometers is input into the data processing unit. The data processing of the output data may be conducted by a digital signal processing unit (DSP) or a field programmable gate array (FPGA). 
   The power unit may be configured with a battery. The use of battery has an advantage in MWD and LWD applications, where no electric power is supplied through the cables of MWD and LWD tools. 
   The sensor apparatus may be installed in a downhole tool. When the Z-axis defined as parallel to a tool axis of the downhole tool is almost vertical, azimuth cannot be defined because of no projection of the Z-axis onto the horizontal plane. Instead of the Z-axis, the projection of other alternative axis onto the horizontal plane may be used to determine an angle from the north direction. The alternative axis may be defined so as to be normal to a reference face on side surface, which is called tool face. The direction of the tool face is determined with gyro sensors and accelerometers in the manner explained above during the tool is under a stationary condition. Once the tool starts moving in downhole, an additional gyro sensor installed in the tool monitors the tool rotation about Z-axis. The additional gyro sensor with an input axis parallel to a tool axis defined in the tool having the gyro sensors for azimuth measurements may be useful to monitor the tool rotation. Dynamic range of the added gyro sensor is large enough to cover the maximum angular rate of the tool rotation. Angular rate output of the additional gyro sensor is integrated to calculate rotation angles of the tool. 
   In a limited inclination range, it is possible to use only two orthogonal axis gyro sensors for azimuth measurements. In this case, the sensor apparatus  10  includes only two sets of sensor holders and orthogonal axis gyro sensors as shown in  FIG. 15 . 
   While the techniques have been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will be appreciate that other embodiments can be devised which do not depart from the scope of the techniques as disclosed herein. For example, the techniques are applicable to mechanical gyro sensors and optical gyro sensors (e.g. laser gyros and optical fiber gyros) or any other gyro sensors.