Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B44/00—Automatic control systems specially adapted for drilling operations, i.e. self-operating systems which function to carry out or modify a drilling operation without intervention of a human operator, e.g. computer-controlled drilling systems; Systems specially adapted for monitoring a plurality of drilling variables or conditions

Definitions

• the present invention relates to a method and to a system for controlling vibrations in a drilling system.
• Drilling of an oil or gas wellbore is typically done by rotary drilling.
• the wellbore may include vertical sections and/or sections deviating from
• Rotary drilling generally employs a drill string including a drill bit at its downhole end.
• the drill string typically includes drill pipe sections which are mutually connected by threaded couplings.
• a drive system located at or near surface may provide torque to the drill string to rotate the drill string to extend the borehole.
• the drive system may include, for example, a top drive or a rotary table.
• the drill string transmits the rotational motion to the drill bit.
• the drill string also provides weight on bit and may transmit drilling fluid to the drill bit.
• the drill string may be several kilometres long, e.g. exceeding 5 or 10 km, the drill string may have a very large length to diameter ratio. As a result, the drill string behaves as a rotational spring and can be twisted several turns during drilling. Different modes of vibration may occur during drilling, e.g. rotational, lateral and/or longitudinal (axial) vibrations, possibly causing alternating slip-stick motions of the drill string or the drill bit relative to the borehole wall. Such vibrations are due to, for example, fluctuating bit- rock interactions and pressure pulses in the drilling fluid generated by the mud pumps.
• a drill string can often be regarded as a torsional pendulum wherein the top of the drill string rotates with a substantially constant angular velocity, whereas the drill bit performs a rotation with varying angular velocity.
• the varying angular velocity can have a constant part and a
• Maintaining rotation of the drill string at surface builds up torque and eventually causes the drill bit to come loose and to suddenly rotate again, typically leading to a downhole angular velocity being much higher than the angular velocity at surface, typically more than twice the speed of the nominal speed of the motor at surface, e.g. a top drive or rotary table.
• the downhole angular velocity is dampened again whereafter the process is repeated, causing an oscillating behaviour of the lower part of the drill string. This phenomenon is known as stick-slip.
• control methods and systems have been applied in the art to control the speed of the drive system such that the rotational speed variations of the drill bit are dampened or prevented.
• EP-B-443689 whereby the energy flow through the drive system of the drilling assembly is controlled to be between selected limits, the energy flow being definable as the product of an across-variable and a through- variable.
• the speed fluctuations are reduced by measuring at least one of the variables and adjusting the other variable in response to the measurement.
• EP-B-1114240 it is pointed out that the control system disclosed in EP-B-443689 can be represented by a combination of a rotational spring and a rotational damper associated with the drive system. To obtain optimal damping, the spring constant of the spring and the damping constant of the damper are to be tuned to optimal values, whereby the rotational stiffness of the drill string plays an important role in tuning to such optimal values. To aid this tuning, EP-B-1114240
• WO 2010/063982 discloses a method and system for dampening stick-slip operations, wherein the rotational speed is controlled using a PI controller that is tuned such that the drilling mechanism absorbs torsional energy at or near the stick-slip frequency.
• the method can also comprise the step of estimating a bit speed, which is the instantaneous rotational speed of a bottom-hole assembly.
• the bit speed is displayed at a driller's graphical interface and is regarded as a useful optional feature to help the driller visualize what is happening downhole.
• the Doris publication uses a dynamic rotor system, including an upper disc connected to the motor (the top drive) and a lower disc connected to the bit. Inputs to the model are the angular position (phase) and the speed (first derivative of the phase) of both the upper disc and the lower disc. For the model to provide accurate results, the speed and phase of the lower disc will have to be measured using a downhole sensor.
• vibration damping which relies on downhole sensors to measure motions of the drill string.
• angular position and speed of the downhole disc i.e. typically the drill bit.
• measurement of angular position and rotational speed may for instance be measured using a two-dimensional gravity sensor.
• the phase accuracy is often lost.
• the exact initial angular position of the drill bit is not known, which implies there is always an uncertainty or error in the measurement of the angular displacement of the bit.
• the drill string system is a non-linear system, for instance due to the friction, and exhibits multiple steady state solutions for the same excitation input, this error can drive the system in one or the other solution.
• a steady state solution for instance, is constant rotational velocity at the top drive and stick-slip behaviour at the bit.
• Another steady state solution for instance, is constant rotational velocity at the top drive and at the bit. Again, this is also due to the low data transmission rate as explained above .
• a method of controlling vibrations in a drilling system including an elongate body extending from surface into a borehole formed in an earth formation and a drive system for rotating the elongate body by providing a drive torque to the elongate body, the method comprising:
• the invention also relates to a control system for controlling vibrations in a drilling system, the drilling system including an elongate body extending from surface into a borehole formed in an earth formation and a drive system for rotating the elongate body by providing a drive torque to the elongate body, the control system comprising:
• an operating device for operating the drilling system to provide a drive torque to the elongate body, and for determining a system parameter that relates to an uphole parameter of the drilling system
• computer means for applying the model to determine a modeled system parameter that corresponds to said system parameter, for determining a difference between the system parameter and the modeled system parameter, for updating the model in dependence of said difference thereby obtaining an updated model, for determining from the updated model at least one modeled parameter of rotational motion, and for adjusting the drive torque in dependence of each modeled parameter of rotational motion so as to control vibrations of the elongate body.
• the model can include high system modes as many as required to simulate the drilling system accurately for the control purposes. It is robust in terms of model inaccuracies due to changes in the interaction between the rock formation and the drill bit or the drill string (frictional changes, damping changes, etc) .
• the controller provides information to the drive system to adjust the drive torque in order to avoid undesirable drill string vibrations. The adjusted drive torque results in a winding/unwinding of the drill string able to eliminate the stick-slip vibrations of the bottom-hole assembly .
• said uphole parameter of the drilling system relates to an uphole torque in the drilling system.
• An example of a parameter related to uphole torque can be a torque parameter provided by a rotary drive coupled to an uphole end of the elongate body, for example as available in modern top drives.
• a parameter related to uphole torque can be a torque parameter, such as torque, measured at an uphole position of the elongate body.
• said uphole parameter of the drilling system suitably relates to torque (T) in the elongate body at or near the earth's surface.
• said model of the drilling system includes a modelled torsional stiffness (k em ) of the elongate body, and wherein said drilling parameter comprises a ratio of said torque (T) over said modelled torsional stiffness (k 6m ) .
• said modeled system parameter relates to a modeled difference between an uphole rotational position of the elongate body and a downhole rotational position of the elongate body.
• said uphole parameter of the drilling system is a first uphole parameter
• step (c) comprises applying the model using an input parameter relating to a second uphole parameter of the drilling system.
• the drive system comprises a rotary drive coupled to an uphole end of the elongate body, and wherein said second uphole parameter is or comprises torque (T m ) provided by the rotary drive to said uphole end of the elongate body.
• T m torque
• the model suitably includes at least one modeled state parameter and wherein step (e) comprises adding to each modeled state parameter the product of said difference and a respective gain factor pertaining to the modeled state parameter.
• each modeled state parameter relates to a modeled parameter of rotational motion of the elongate body.
• said at least one modeled state parameter is selected from a modeled difference between an uphole angular velocity and a downhole angular velocity of the elongate body, a modeled uphole angular acceleration of the elongate body, and a modeled downhole angular
• step (b) comprises obtaining a state observer in which the model is included, the state observer further including a gain module for calculating each said gain factor.
• said at least one modeled parameter of rotational motion includes at least one of a modeled difference between an uphole rotational position and a downhole rotational position of the elongate body, a modeled uphole angular velocity of the elongate body, and a modeled downhole angular velocity of the elongate body.
• uphole may refer to locations within, for example, 200 m from the earth surface or from a drilling rig used in the method of the invention.
• the earth surface is formed by the seabed.
• downhole may refer to locations within, for example, 200 m from the lower end of the elongate body.
• the elongate body comprises a drill string having a drill bit at its downhole end.
• Figure 1 schematically shows a drilling system to be controlled by a preferred embodiment of the method and control system of the invention
• FIG. 2A schematically shows an embodiment of the control system in modular form
• Figure 2B shows a schematic representation of an embodiment of the control system of the invention
• FIGS 3a, 3b, 3c, 4a, 4b and 4c schematically show various results achieved using the method and control system of the invention.
• like reference numerals relate to like components.
• Fig. 1 shows a drilling system 1 including a drill string 2 extending from surface into a borehole (not shown) formed in an earth formation.
• the drill string 2 can be several thousand meters in length, and therefore behaves as a torsional spring.
• a drive system 4 is arranged at surface to rotate the drill string 2 in the borehole by providing a drive torque to the drill string 2.
• the drive system generally includes a motor arranged to drive a rotary table or a top drive (not shown) .
• the drill string 2 typically includes a downhole end part 6.
• Said downhole end part may include a bottom hole assembly (BHA) 6 including a drill collar having an increased weight which provides the necessary weight on bit during drilling.
• Top drive may imply a drive system which rotates an upper end of the drill string.
• Upper end implies the end at surface, i.e. near the location where the drill string is suspended from a drilling rig.
• Reference sign 7 represents torque resistance T u of the upper part of the drill string, e.g. due to
• Reference sign 8 represents torque
• T m drive torque provided by the drive system 4 to the drill string 2;
• V voltage input to a motor (not shown) of the drive system 4
• ⁇ torque in the drill string 2 as determined at or near the earth surface
• arrow 9 refers to the parameters ⁇ ⁇ , ⁇ ⁇ , ⁇ ⁇ , arrow 10 refers to the parameter T m , and arrow
• subscript "u" refers to an uphole position, preferably at or near the surface of the earth, and the subscript “1” refers to a downhole
• a bar above a symbol indicates a modelled parameter.
• a dot above a symbol refers to a single time derivative, i.e. a single dot indicates a velocity, and a double dot indicates acceleration.
• ⁇ ⁇ refers to a parameter of a state observer.
• Angular velocity is also referred to as rotational velocity.
• Uphole parameters of the drilling system 1 are determined at or near surface for use in the method of the invention. At or near surface implies that accurate measurements can be obtained using high-frequency sensors. High-frequency is for instance exceeding 1 kHz, i.e. more than 1000 samples per second.
• One such uphole parameter relates to uphole torque ⁇ in the upper part of the drill string 2.
• the torque T m applied in a modern drive system or a parameter directly related to T m is often available as a digital parameter.
• ⁇ differs slightly from T m due to, for example, friction in the drive system itself and/or higher-frequency contributions that may not be transmitted between the drive system and the drill string.
• the drive system 4 includes a rotary table, such difference also can be due to transmission losses.
• uphole torque ⁇ or a parameter directly related to ⁇ can be determined for example by measuring, e.g. by a torque sensor at a location at or near the earth surface. Further uphole parameters can be measured by suitable sensors.
• Uphole rotary velocity 0 U or a related parameter may also be measured by a sensor at or near surface.
• Such related parameter is for example a period of one rotation of the drill string 2 at an uphole position. The period of rotation is directly related to and representative of angular velocity.
• Fig. 2A shows a block diagram of a control system for controlling vibrations in the drilling system 1.
• the control system comprises a state observer 14 for
• the state observer 14 may use measurements of the input and the output of the drilling system 1.
• the state observer 14 includes a mathematical model 16 of the drilling system and a gain module 18 for updating the model 16.
• the gain module may use input and output measurements of the drilling system 1.
• the model 16 may typically be implemented in a computer system running software, e.g. written in Matlab. It is known in the art how to build a model for a given drill string, and for the drill string in the borehole.
• the model 16 can be a simple two degree-of-freedom (DOF) model, e.g. similar to the one used in section 6.2.2. of the Doris publication.
• DOF degree-of-freedom
• the model can also be a more complex multi degree-of- freedom model.
• the control system further comprises a controller 20 arranged to control a motor 22 that drives the drill string 2.
• the state observer 14 may receive an input signal 24 representing Tm.
• said motor torque Tm is available to the driller, as it may be derived from the current drawn by the top drive.
• Input signal 24 may also include ⁇ .
• the model 16 provides output signals 28, 30, 32 representing respective parameters ⁇ ⁇ , 9 l , 9 l . ⁇ ⁇ , are supplied to both the gain module 18 and the controller 20.
• ⁇ ⁇ is supplied to the controller 20.
• the controller 20 also receives an input signal 34 representing parameter 6 U and an input signal 36 representing parameters ⁇ ,6 U - ⁇ ⁇ .
• reference sign 38 represents voltage V supplied to motor 22, reference sign 40
• reference sign 42 represents a gain vector L supplied by gain module 18 to model 16.
• T may be input to the observer.
• the observer output comprises ⁇ ⁇ , ⁇ ⁇ ⁇ ⁇ .
• controller gain The controller output is -u which is input back into the motor.
• the motor adapts T m by -u and supplies the adjusted torque to the drill string 2.
• the equations of motions of the drilling system 1 are governed by two inertias J u ,J t , a spring flexibility k e , two frictional torques T fu , T fl , and torque input from the motor T m .
• J u is rotational inertia of the top drive and part of the drill string
• J 1 is rotational inertia of the Bottom-Hole-Assembly (BHA) and the remaining part of the drill-pipe.
• k e is rotational stiffness of the drill string. represents torque resistance in torsional motion of the upper part of the drill string (e.g.
• T cu (e u ) T su +AT su -sgn(0 u ) + b l ⁇ ,, + Abdition
• ⁇ ⁇ ( ⁇ ⁇ ) ⁇ ⁇ +( ⁇ ⁇ - ⁇ 1) - ⁇ ⁇ + b, ' ⁇ , (8) wherein :
• T cu ⁇ T su ⁇ T su r K , Ab u , T cl , T d , b t are constant parameters governed by frictional torque in the upper part of the drill string, such as in the drive system, and in the Bottom-Hole-Assembly. Example values of these parameters are presented in Table 1 at the end of this section.
• the torque ⁇ in the drill string 2 at or near surface is:
• T k e -(0 tt -0,) .
• the torque ⁇ can be derived from the current in the motor 22, and in practice it is always available to the drill-string operator.
• Equations (9), (10) below are a copy of equations (1), (2) however with some disturbances included in the
• T flm are model values of respective parameters k e , J u , J l ,T fu ,T fl .
• T fum and T flm have the same structure as T fu and T fl respectively.
• the parameters of the frictional forces of the model that are different from those of the drilling system are T sum (instead of
• ⁇ ⁇ , l 2 , l 3 can be computed.
• the goal of the observer is to derive estimates of the drilling system states that are as close as possible to the real drill-string system's states.
• a set of linear matrix inequalities (LMIs) is to be solved, for example using the software Matlab and in particular the Matlab toolbox LMI-tool. The procedure to derive these LMIs is described in the Doris publication.
• Formulas (9) and (10) may be used to derive either (0 U eq - ⁇ ⁇ eq ) , i.e. the output of the model 16 or (# fashion, ⁇ 3 ⁇ 4 - , i.e. the output of the
• ⁇ d ueq -0 leq may be derived.
• a measured value for 0 ueq may be included, for instance provided by sensor 54.
• k l ,k 2 ,k 3 are constants calculated according to the control theory of the Doris publication using the model (9), (10). Example values of these parameters are
• Formula (14) provides a correction factor to the torque.
• the corrected torque Tc applied to the drill string, after the adjustment is for instance:
• Fig. 2B shows a schematic flow scheme, representing the above described control system of the invention in an alternative form.
• a driller 50 operates a drilling rig (not shown) comprising the drive system 22.
• the driller 50 sets the voltage input V by signal 38 to the drive system 22.
• the drive system 22 will try to rotate the drill string 2 of the drilling system 1 at a reference rotation Q ref .
• the reference rotation Q ref is set by the driller, by signal 38.
• the equilibrium rotary speed at surface ⁇ and downhole would be equal to the set reference rotation Q ref :
• the drive system 22 To rotate the drill string, the drive system 22 provides a motor torque Tm to the drilling system 1. In response to the received motor torque Tm, the drill string and drill bit of the drilling system 1 will rotate. A resulting output vector y may include rotary position and rotary speed both at surface and downhole. However, in the system of the invention, downhole components of the output vector y of the drilling system may be disregarded. Only one or more uphole components, which can be accurately measured, are required. Downhole measurements are
• a measured torque value for instance the motor torque Tm, may be provided to the model 16 and to the model gain module 18. See signals 24.
• the model In response to receiving the motor torque Tm, the model provides a model output vector y m .
• Said model output vector y m may comprise angular position and rotary speed both at surface and downhole respectively.
• the signal 52 may also comprise the value of ( ⁇ ⁇ - ⁇ ⁇ ), which is available due to the relation thereof to the torque ⁇ in the drill string 2 at or near surface:
• the torque ⁇ can be derived from the current in the drive system 22.
• T is available to the operator 50. Otherwise, T can be measured accurately at or near the connection between the drive system 22 and the drill string 2.
• the value of (0 U eq — ⁇ 1 eq ) may thus be derived from the torque value when the drilling system operates at
• the value ( ⁇ ⁇ - ⁇ ⁇ ) may be provided to the control module 20 via signal 52.
• the contol module 20 may calculate the value ( ⁇ ⁇ - ⁇ 1 ) using the torque T as provided by the drive system.
• the model module 16 may be provided with any suitable model of the drilling system 1. Using the input signal 24, which comprises the motor torque Tm, the model module provides the model output vector y m .
• 0) lm and ⁇ are both
• the modelled rotary positions ⁇ ,, ⁇ at surface and downhole respectively may be provided to a model gain module 18. See signal 56.
• the model gain module provides the gain vector L to the model module 16. See signal 58.
• the model module 16 uses the gain vector L to improve the parameters of the model, and consequently to improve the output vector y m .
• control module 20 which preferably have been adjusted and improved using the input of the gain module 18, are provided to control module 20. See signal 60.
• the control module 20 uses the available inputs
• the torque correction factor u is provided to the drive system 22, which substracts said factor u from the motor torque T m , to arrive at a corrected torque value T c :
• the reference frequency Q ref as set by the driller 50 is not affected by the above correction. Rather, the correction is applied to adjust the torque that the drive system applies to the drill string to arrive at said ⁇ ⁇ £ .
• Figs. 3a-c showing results for the drill string 2, the model 16 and the observer 14, whereby the controller 20 is de-activated in order to illustrate convergence of the drill string states as determined by the model 16 and the observer 14 to the real drill string states.
• Figs. 4a-c showing results whereby the controller 20 is activated.
• the control system operates in closed-loop with the drilling system so as to dampen stick-slip behaviour of the drill string 2.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Geology (AREA)
• Mining & Mineral Resources (AREA)
• Physics & Mathematics (AREA)
• Environmental & Geological Engineering (AREA)
• Fluid Mechanics (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Earth Drilling (AREA)
• Feedback Control In General (AREA)

Priority Applications (1)

Applications Claiming Priority (3)

Publications (1)

Family

ID=47216292

Family Applications (1)

Country Status (4)

Families Citing this family (15)

Family Cites Families (14)

• 2012
  • 2012-11-22 US US14/360,109 patent/US20140318865A1/en not_active Abandoned
  • 2012-11-22 WO PCT/EP2012/073322 patent/WO2013076184A2/en active Application Filing
  • 2012-11-22 CA CA2856004A patent/CA2856004A1/en not_active Abandoned
  • 2012-11-22 EP EP12788552.3A patent/EP2783070A2/de not_active Withdrawn

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events