Patent Publication Number: US-6216789-B1

Title: Heave compensated wireline logging winch system and method of use

Description:
BACKGROUND 
     This invention relates generally to computer-controlled winch systems for wireline logging. More particularly, the invention is a computer-controlled heave compensation wireline logging winch system that compensates for the effects of wave motion on floating installations performing wireline logging. 
     Wireline logging is the process by which oil or gas wells are surveyed to determine their geological, pertrophysical or geophysical properties using electronic measuring instruments conveyed into the wellbore by means of an armored steel cable, known as a wireline cable. The wireline cable is stored on a winch drum, which provides the mechanism by which it is lowered into the well via a series of sheave wheels to ensure proper alignment. The measurements made by downhole instruments secured to the wireline cable are transmitted back to a data acquisition computer located at the surface through electrical conductors in the wireline cable. Electrical, acoustical, nuclear and imaging tools are used to stimulate the formations and fluids within the wellbore and the electronic measuring instruments then measure the response of the formations and fluids. A device mounted close to the cable drum at the surface determines the depth at which these measurements are recorded. This device measures cable movement into and out of the well and is known as the depth system. The wireline well log contains the record of the series of measurements of the formations and fluids found in the wellbore with respect to the location within the borehole at which measurements are made. The raw measurements are often presented in the form of an x-y graph with the location where the measurement is made recorded on the y-axis and the measurement itself recorded on the x-axis. The location where the measurement is made is called the depth. It is a measure of the distance between a reference position, usually located somewhere on the surface above the well, and the location within the borehole following the path of the borehole. 
     The accuracy and quality of the wireline logging data obtained from such an arrangement is dependent on the smooth movement of the wireline cable and the downhole logging tools that extend from the wireline cable at a known and controlled speed, along with the precise determination of the depth at which the wireline logging measurements are made. Depth may be calculated by measuring the amount of cable spooled off or on the winch and may be adjusted for conditions in the borehole and characteristics of the cable. One cable characteristic that may be adjusted for is cable stretch, which is a function of temperature, pressure, tension and length of the cable. 
     For a fixed wireline setup, such as a land drilling rig or fixed offshore platform, the measurement of depth and cable speed is relatively straightforward. This is because the variables in the system can be measured and accounted for. On a land rig or fixed drilling rig, there is a fixed distance between a reference point at the surface of the well itself and the winch. Because the distance is fixed, it may be automatically adjusted out of the depth calculation. However, when the winch is installed on a floating vessel, which may typically be a semisubmersible rig, drill ship or barge, the movement of the rig itself due to tidal or wave motion effects is not taken into account by conventional wireline logging systems. In a floating vessel installation, the distance between the reference point at the surface of the well and the winch is not fixed and the distance changes with respect to the tide and waves. If ignored, the vertical component of this motion, relative to the wellbore, will have an adverse affect on the indexing and analysis of the log data. The movement of the wireline cable and the downhole logging tools induced by the movement of the rig, drillship or barge will not be measured. This same problem occurs if the rig is fixed, but the wireline winch is located on a floating tender. 
     Other systems have attempted to minimize the effects of wave motion on wireline logging data. The system is often compensated in such a way as to keep the wireline set-up fixed with respect to a known reference datum, usually the sea floor. This is normally achieved by interfacing with the drilling rig&#39;s compensation system, and using it to anchor the wireline rig to the fixed datum. A compensation device, usually in the crown of the rig, attempts to hold the cable distance constant using an electro-hydraulic device. This system is limited in its precision and the range of motion over which it can compensate since it relies on a passive compensation system designed for very heavy drill pipe strings and uses steel ropes to anchor the wireline upper sheave wheel to the seabed. The wireline acquisition system then assumes that the setup is not changing and is fixed. This type of system is high maintenance and expensive. Alternatively, an electromechanical compensation device can be inserted between the winch and the upper sheave wheel to be used for well logging only. Since well logging is done somewhat infrequently, this device is often idle. In both of these types of systems, no corrections are made for any errors induced by incomplete heave compensation. 
     SUMMARY 
     The present invention solves the problem of wave motion on wireline logging data firstly by physically compensating for vertical motion (heave) at the wireline winch and secondly, by calculating and recording any errors in that physical compensation so that the true depth at which a wireline log data measurement is made is recorded, along with the wireline well log measurement. Both the physical compensation system and the recording of errors in that physical compensation system utilize information on the physical movement of the rig itself, obtained from a motion reference unit (MRU). An electrically controlled wireline winch provides for the physical heave compensation. The wireline winch is fixed to the rig structure itself with no external compensation system connected. The movement of the wireline cable due to heave is measured by the MRU and is compensated for by the winch with a corresponding change in motion and/or direction of the wireline cable. This ensures that the wireline logging data is acquired at a constant, known speed. Any error in this compensation is detected by the depth system within a data acquisition computer located at the surface, recorded and may be used to adjust the true depth at which the wireline log measurements are being recorded. 
     The present invention comprises a system and method for compensating for the vertical motion of a floating vessel having a winch control means for receiving vessel vertical motion data and logging tool speed set points and a wireline winch means for raising and lowering a wireline cable within a wellbore, connected to the winch control means and comprising a winch motor for attaching to and rotatably moving a cable drum, the wireline cable having at least one logging measurement tool attached to an end of the wireline cable extending from the cable drum. The winch control means combines the vertical motion data and logging tool speed set points to produce a winch motor control signal for controlling the rotatable movement of the cable drum so as to cause the wireline cable to achieve movement within the wellbore at a controlled speed, which may be substantially constant, independent of vessel vertical motion. The system can also compensate for the vertical motion of a floating vessel using a winch control means for receiving vessel vertical motion data and logging tool tension set points and a wireline winch means for raising and lowering a wireline cable within a wellbore, connected to the winch control means and comprising a winch motor for attaching to and rotatably moving a cable drum, the wireline cable having at least one logging measurement tool attached to an end of the wireline cable extending from the cable drum. The winch control means combines the vertical motion data and logging tool tension set points to produce a winch motor control signal for controlling the rotatable movement of the cable drum so as to cause the wireline cable to achieve movement within the wellbore at a controlled speed, which may be substantially constant, independent of vessel vertical motion. Alternatively, logging tool speed and tension set points can be simultaneously used together with the vessel vertical motion to produce a winch motor control signal. The winch motor control signal comprises a RPM value and a torque value. Producing a winch motor control signal by the winch control means may occur in real time. 
     The system further comprises a depth computing means for receiving the vessel vertical motion data and measured wireline cable motion data and for calculating a heave compensation depth error by combining the measured wireline cable motion data and the vessel vertical motion data. The vertical motion data comprises vessel vertical position, speed and acceleration. The heave compensation depth error is saved together with logging measurement tool data from the logging measurement tools. The depth error may be used to compensate a depth measurement of the logging measurement tool data. 
     The system further comprises an alarm generation means for producing an alarm signal when the logging tool is about to enter a position above the wellbore and a heave compensation mode is activated or when a heave compensation mode of operation should be activated. The alarm signals are displayed on an operator display console connected to the depth computing means. At least operator control and display means for entering operator commands, displaying winch system status and providing feedback to an operator of heave compensation status is provided. 
     The present invention comprises a computer program for calculating a heave compensation depth error value comprising receiving measured speed from a first cable movement measuring device and converting the measured speed into a physical distance. A wheel wear correction, a heave compensation amount and a crank compensation amount pending are applied to produce a first net motion increment. A slip detection correction is applied to the first net motion increment and the net motion increment is converted into a first depth value. The process is repeated for receiving measured speed from a second cable movement measuring device and a second depth value is determined. The first depth value or the second depth value that is most advanced in cable motion direction is then selected. The selected depth value is saved together with logging measurement tool data. It may be used to compensate a depth measurement of the logging measurement 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings where: 
     FIG. 1 is a diagram showing the heave compensated wireline logging winch system mounted on a floating vessel. 
     FIG. 2 is a diagram of the winch of FIG.  1 . 
     FIG. 3 is a block diagram of the physical heave compensation system and the physical correction made by the winch. 
     FIG. 4 is a system block diagram of the heave compensation wireline logging winch system. 
     FIG. 5 is a network architecture diagram of the wireline winch controller with system and operator interfaces. 
     FIG. 6 shows the layout of a typical wireline winch logging status display. 
     FIG. 7 shows a hardware/software block diagram of the depth measurement processing. 
     FIG. 8 is a flowchart of the alarm generation function of the depth measurement system. 
     FIG. 9 shows a control flow diagram of the winch operation in manual mode. 
     FIG. 10 shows a control flow diagram of the winch operation in cruise mode. 
     FIG. 11 shows a flow control diagram of the winch operation in heave compensated mode. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing the heave compensated wireline logging winch system mounted on a floating rig. The system may also be mounted on various types of floating vessels or submersible vessels that may be used to perform wireline logging. FIG. 2 is a diagram of the winch  10  of FIG.  1 . Referring now to FIGS. 1 and 2, the winch  10  is mounted on a winch skid  11  located on the floating rig  13 . A winch controller  14 , adjacent or remotely connected to the winch  10  provides the commands to control the action of the winch  10  and thereby control the vertical movement of the wireline cable  15  within the well  21 . The winch skid  11  is able to receive a cable drum  22 , which can be a large or small drum using either a heptacable or monocable setup. Logging tools  20  are attached to one end of the wireline cable  15 . A wireline computer  16  interfaces with the winch controller  14 . A cable movement measuring device  12 , which measures cable speed and tension as the cable exits the cable drum  22 , is gimbal mounted and located just outside the winch  10  and comprises two wheels located side by side with the wireline cable  15  running between the wheels. The cable movement measuring device may comprise one device or two devices. If there are two devices, one usually measures cable speed and another cable tension. As the wireline cable  15  moves, the cable movement measuring device measures the amount and direction of wheel rotation electronically. An upper sheave wheel  17  and lower sheave wheel  18  are used to align the wireline cable  15  with the well and the winch. A motion reference unit (MRU)  19  located near the wireline cable  15  provides measured vertical position, speed and acceleration of the floating rig  13  at the derrick floor and provides that information to the winch controller  14 , which uses the information along with measurement data from the cable movement measuring device  12  to control the winch  10  and physically compensate for vertical motion on the wireline cable  15  by changing the speed and/or direction of the wireline cable  15  motion. The winch controller  14  also provides the vertical motion information to the wireline computer  16 . The wireline computer  16  uses the vertical motion information and the measurement data from the cable movement measuring device  12  to detect any errors in the physical compensation and to record the true depth at which the wireline log measurements are taken. 
     FIG. 3 is a block diagram of the physical heave compensation system and the physical correction made by the winch. The motion reference unit (MRU)  30  detects vertical motion of the drilling platform, which is used by the winch controller  31  and the wireline computer depth measurement processing  32 . Based on the vertical motion, the winch controller  31  calculates the necessary changes in the winch motor  34  speed and direction to keep the wireline cable  37  and the wireline logging tool  36  at a constant or controlled speed while being lowered or raised in the wellbore. The winch controller  31  sends a command to change speed and direction to the winch motor drive  33 , which in turn controls the winch motor  34 . The cable movement measuring device (CMMD)  35  measures cable motion and tension of the wireline cable  37  as it exits the winch drum. This measurement takes into account the amount of correction physically applied to the wireline cable  37  and the measurement is sent to the wireline computer  32 . The depth measurement system within the wireline computer detects any error in this compensation by comparing the actual vertical motion as measured by the MRU  30  with the physical correction made by the winch. Any error in the physical compensation may be used to adjust the true depth at which the measurements are being recorded. 
     Turning now to FIG. 4, a system block diagram of the heave compensation wireline logging winch system is shown. The winch controller  40  comprises a programmable logic controller (PLC)  41  and a winch motor drive  42 , which may be a variable speed drive. The winch controller  40  computes the parameters for accurately controlling the motion of the wireline winch  46 . The motion of the winch is achieved through the winch motor drive  42  and motor  43 , which are connected using an electrical cable. Using the winch motor characteristics and a winch motor model, the winch motor drive  42  can accurately control the winch motor  43  using the motor frequency and voltage. An encoder mounted on the motor shaft is connected to the winch motor drive so that increased precision may be achieved. The winch remote I/O  44  communicates with the PLC  41 . The winch remote I/O  44  collects information and sends commands to ancillary systems on the winch such as the brakes, steering, oscillating, light, operator backup control panel (BCT)  48  and general alarms. The motion reference unit  47  provides the vertical information about the floating rig or vessel to the winch controller  40  which is forwarded to the depth measurement system  54  processing in the wireline computer  53 . The winch controller  40  uses the vertical information (which comprises position, speed and acceleration) to calculate the necessary physical compensation in motor  43  speed and direction to keep the wireline cable  55  and the wireline logging tool  50  at a constant speed. The depth measuring system  54  within the wireline computer  53  accepts the measured cable speed and tension from the cable movement measuring device  49 . Using the vertical position from the MRU  47 , through the gateway controller computer  52 , and the measured cable speed and tension, the depth measuring system  54  computes any error in the physical compensation to calculate the logging depth at which the wireline logging measurements are made, which is then recorded by the wireline logging software. This information is sent back to the winch controller  40  through the gateway controller  52  which provides the interface between the depth measurement system  54  and the PLC  41 . Commands from the operator are input from a winch control panel and display human machine interface (HMI)  51 , which contains operator controls and displays. The HMI  51  may also be used to control other functions for different rig processes such as drilling or pumping. Depending on the various modes of operations, the winch controller  40  with its PLC  41  processes wireline computer  53  and motion reference unit  47  information and operator commands from the HMI  51  to determine the required motor  43  speed and torque and sends this information to the winch motor drive  42  for execution. The winch motor drive  42 , which may be a variable speed, alternating current motor drive, receives RPM/torque commands and generates the required electrical signals for controlling the winch motor  43 . The winch motor drive  42  has its own built-in sensors for RPM (with a tachometer mounted on the motor) and torque. It exchanges the start/stop and brake on/off status with the PLC  41 . The winch controller  40  then energizes the brake accordingly through the winch remote I/O  44 . The winch devices  46  are electric and electro-pneumatic components that control braking, oscillating, spooling and other winch functions. These components are activated through the winch remote I/Os  44 . An operator backup panel human machine interface (HMI)  48  is used for backup control and allows the operator to perform a reduced set of operator commands. The operator backup panel HMI  48  can be used in place of the winch control panel, when for example, the operator interface HMI  51  is being used to control other functions for different rig processes. The operator panel HMI  48  is linked to the winch controller via the winch remote I/Os  44 . The depth measuring system  54  interfaces with an alarm and control display  56  for displaying alarm and control status information to an operator. 
     The cable drum  45  can be a large or small drum with either heptacable or monocable. The cable drum  45  can have a flange diameter between about thirty inches and sixty inches and a cable length maximum capacity of about 40,000 ft. depending on the cable flange diameter and cable diameter. The cable drum  45  may be equipped with a one and one half inch pitch sprocket (between about 72 and 80 teeth), pillow blocks and a brake band surface on both sides of the cable drum  45 . In normal mode (not wave compensated), with a 140 kVA (110 kW) variable speed drive and depending upon the type and size of the cable drum, the winch allows for the delivery of a maximum cable speed of about 54,000 ft/hr and a minimum cable speed of about 42 ft/hr and a maximum pull on line of 26,100 lbs. 
     Turning now to FIG. 5, a network architecture diagram of the wireline winch controller with system and operator interfaces is shown. The winch controller programmable logic controller (PLC)  60  communicates with the winch controller/winch motor drive  61 , the gateway controller computer  62 , winch remote I/O (WRIO)  63  and motion reference unit one (MRU  1 )  75  and motion reference unit two (MRU  2 )  76  via a communication bus  66 . There may be one or more motion reference unit devices to provide estimated linear acceleration, estimated relative position and estimated linear velocity in the vertical axis. The winch motor drive  61  is connected to the winch motor located in the winch  74 . The winch remote I/O  63  interfaces with the operator backup control panel (BCT)  72  and sends operator commands from the operator backup control panel (BCT)  72  to the winch controller PLC  60 . The gateway computer  62  interfaces with the wireline computer  69  which contains a front end controller (FEC)  67 , depth measurement system  68  and measurement processing (SEC)  70 . The cable movement measuring device  73  sends cable speed and tension to the depth measurement system  68 . The depth measurement system sends alarm and winch control data directly to the alarm and control display  78 . The same information sent to the alarm and control display  78  is also sent to the gateway controller  62 . The gateway controller  62  reformats this data as necessary and sends it to be displayed on the winch control panel and display HMI  77  via the winch controller programmable logic controller (PLC)  60 . Logging tool  80  measurements are sent to the SEC  70  within the wireline computer  69 . The SEC  70  combines the output of the depth measurement system and the wireline logging measurements and sends that information to be recorded. The winch controller PLC  60  is electrically connected to the electrical control room input/output  71 . The winch controller PLC  60  communicates with the winch control panel and display HMI  77  via a communication bus  79 . The winch  74  can be controlled from several locations including the winch control panel and display HMI  77  and the operator backup control panel (BCT)  72 . The PLC  60  communicates with the winch control panel and display HMI  77  and sends winch control status and parameters along with error messages. 
     FIG. 6 shows the layout of a typical wireline winch logging status display. There is a winch wireline cable speed display area  100 , a logging tool depth area  101 , an auxiliary display area  102 , a cable tension display area  103 , a magnetic mark display area  104  and a menu display area  105 . The display also contains a dialog window  106  and alarm icons  107 . 
     FIG. 7 shows a hardware/software block diagram of the depth measurement processing. The cable movement measuring device (CMMD)  12  of FIG. 2 is gimbal mounted just outside the winch and is fixed in the roll axis. A wireline cable  15  is secured between two integrated depth measuring wheels  120  and  121  by means of cable guides and spring loaded rollers. On each wheel is a rotary encoder  122 , 123  that measure the amount and direction of rotation, where two times IT times the radius of each of the measuring wheels  120 ,  121  equals the amount of cable motion. Redundancy of measurement is provided because each of the encoders  120 ,  121  separately measures the amount and direction of rotation and the measurements from each CMMD measuring wheel  120 ,  121  are processed in parallel. First, the measurements from the measuring wheels  120 ,  121  comprising raw quadrature data are received by the quadrature pulse decoders  124 , 125  and are converted into incremental or decremental counts which are fed into motion accumulators  126 , 127 , where one detectable motion of the measuring wheels  120 ,  121  corresponds to one accumulator count. Next, the software begins motion processing  128 ,  129 . The accumulator counts, which correspond to motion increments or decrements over a sample period of time, are converted to a physical distance. Wheel correction for each wheel  128 ,  129 , heave amount  131  (as measured by the MRU) and crank compensation  132  are applied, as necessary. Wheel correction  129 ,  130  compensates for changes in measuring wheel wear since as the measuring wheels are used the wheels wear so the radius of the wheel changes and a corresponding wheel correction must be applied. If a crank amount is pending  132 , it is applied during the motion processing. Crank is a manual adjustment to the wireline cable that the winch engineer can enter to mechanically emulate a clutch assembly that was present in early winch systems. The engineer sets the amount of crank (change in the amount of wireline cable) and the electronics feed in the change to the winch uniformly and slowly over some period of cable motion. If heave compensation mode is selected, a heave measurement  131  that has been obtained from a motion reference unit is also applied. The output of the motion processing function  128 ,  129  is the net motion increment and cable speed. The net motion increment is calculated by subtracting the heave amount from the measured cable motion, where the measured cable motion is the logging tool motion plus the actual heave compensation applied by the winch control. Any cable slip detection and correction  135  is added to the net motion increment and the result is converted to depth in the encoder depth accumulators  133 ,  134 . In the multiplexor  136 , an algorithm is used to choose the best of the two estimates from both measuring wheels  120 ,  121  based on the measurement most advanced in direction of the wireline motion. The measured depth is then output to the logging system for recording, to the operator displays and to an alarm generation function. 
     FIG. 8 is a flowchart of the alarm generation function of the depth measurement system  150 . An alarm is set  156  when the well logging tool is outside the transition region and the winch is not in the appropriate mode. A transition region is a designated length of the well in which it is safe for the heave motion compensation to be either on or off. When heave motion compensation is off and the tool is stopped the tool does not move with respect to the rig, but does move with respect to the well and the sea bed. With heave motion compensation on, the tool moves with respect to the rig, but is stationary with respect to the formations in the well. Outsider of the transition region towards the surface, heave motion compensation should be turned off so that the tool may be safely handled on the rig floor. Outside the transition region, towards the bottom of the well, heave motion compensation should be turned on so that the tool motion, with respect to the formations in the well, is not affected by the rig motion. If the tool is above the transition region  151  and heave compensation is on  152 , an alarm is set  156 . If the tool is above the transition regions  151  and heave compensations  152  is off, the alarm is cleared  155 . If the tool is below the transition region  153  and heave compensation is off  154 , an alarm is set  156 . If the tool is below the transition region  153  and heave compensation is active  154 , the alarm is cleared  155 . The alarm may then be displayed on the alarm and control display and may also be available for display on the winch control panel and display HMI. 
     The winch may be operated in three modes of operation: manual mode (FIG.  9 ), cruise mode (FIG. 10) and heave compensated mode (FIG.  11 ). 
     FIG. 9 shows a control flow diagram of the winch operation in manual mode. In this mode, the operator manually adjusts the RPM and torque set points at the operator interface to obtain the required cable speed and tension  160 . The RPM/torque  161  is sent to the winch controller  162 , which scales the RPM/torque commands  163  and sends them to the winch motor drive  164  which in turn sends the RPM/torque commands  165  to the winch motor  166 . The winch controller  162  contains a drum revolution counter that gives the number of motor revolutions and therefore the number of drum revolutions. When cable speed and depth are received from the FEC, a comparison is made for each drum revolution to compute the relationship between depth and drum revolutions and between cable speed and motor RPM. When cable speed and depth are no longer received, the relationship is used to calculate an estimated cable speed and tool depth. When cable tension is received from the FEC, a comparison is made for each drum revolution to compute the relationship between the cable tension and the winch motor torque. When cable tension is no longer received, the relationship is used to calculate an estimated cable tension. 
     FIG. 10 shows a control flow diagram of the winch operation in cruise mode. In cruise mode, the operator at the operator interface  170  inputs cable speed and cable tension commands  171 . The measured cable speed and cable tension  172  is computed by the front end controller (FEC) within depth measurement system  173  using cable movement measuring device  179  measured cable motion and tension  180  and is transmitted to the winch controller. Using the cable speed and tension  171  input by the operator and the measured cable speed and tension  172 , the winch controller  174  calculates and scales RPM/torque commands  175  and sends them to the winch motor drive  176 , which in turn sends the RPM/torque commands to the winch motor  178 . 
     FIG. 11 shows a flow control diagram of the winch operation in heave compensated mode. In heave compensated mode, the operator at the operator interface  200  inputs cable speed and cable tension commands  201 , which are transmitted to the winch controller  204 . The motion reference unit (MRU)  202  provides vertical vessel motion  203 , which is also used by the winch controller  204 . The measured cable speed and cable tension  205  is calculated by the front end controller within depth measurement system  206  using cable movement measuring device  211  measured cable motion and tension  212  and is transmitted to the winch controller. Using the cable speed and tension  201  input by the operator, the vertical vessel motion  203  from the MRU  202  and the measured cable speed and tension  205 , the winch controller  204  calculates and scales RPM/torque commands  207  and sends them to the winch motor drive  208 , which in turn sends the RPM/torque commands  209  to the winch motor  210 . The winch controller  204  contains a drum revolution counter that gives the number of motor revolutions and therefore the number of drum revolutions. When cable speed and depth are received from the FEC  206 , a comparison is made for each drum revolution to compute the relationship between depth and drum revolutions and between cable speed and motor RPM. When cable speed and depth are no longer received, the relationship is used to calculate an estimated cable speed and tool depth. When cable tension is received from the FEC  206 , a comparison is made for each drum revolution to compute the relationship between the cable tension and the winch motor torque. When cable tension is no longer received, the relationship is used to calculate an estimated cable tension. 
     Although the present invention has been described in detail with reference to certain preferred embodiments, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments herein.