Maintaining Dynamic Friction in a Wellbore Through Harmonic Rotary Oscillations

Abstract

Techniques are disclosed which acts to maintain a drillstring in dynamic friction during geo-steering operations when the drillstring is not rotating. Embodiments of the invention include a drilling system having a drillstring coupled to a top drive or a kelly, and a method of estimating a frictional torque along the drillstring to compute an oscillatory rotary input to the top drive or the kelly based on an input period or amplitude received at a human machine interface. A rotary control signal based on the oscillatory rotary input is transmitted to the top drive or the kelly via a variable-frequency drive (VFD) motor control system. The drillstring can be further coupled to a sensor and the feedback from the sensor can be monitored for proper operation to adjust the oscillatory rotary input during the geo-steering operations.

1 . A method for imparting a harmonic rotary oscillation to a drillstring during a wellbore construction process, comprising the steps of:
 determining an estimate of a torsional friction along a drillstring of a drilling system to determine a desired amplitude of a rotary oscillatory motion based at least partially on drilling parameters comprising an oscillatory period or frequency transmitted to at least one motor coupled to the drilling system;   generating a rotary control signal based at least partially on the desired amplitude of the rotary oscillatory motion when the drilling system is activated;   transmitting the rotary control signal to the at least one motor via a variable-frequency drive (VFD); and   monitoring the drilling system to determine whether a bottom hole assembly (BHA) of the drilling system remains stationary, the BHA coupled to the drillstring.   
     
     
         2 . The method of  claim 1 , further comprising the steps of:
 reducing the desired amplitude of the rotary oscillatory motion upon detecting that the BHA is not stationary; and   transmitting a new rotary control signal based at least partially on the reduced amplitude of the rotary oscillatory motion.   
     
     
         3 . The method of  claim 1 , wherein the determining comprises the steps of:
 prescribing the rotary control signal to the drilling system starting from the drillstring when the BHA is stationary;   sensing recorded torque from the drillstring of the drilling system; and   recording a maximum torque sensed during a predetermined time period to determine an estimate of the torsional friction along the drillstring.   
     
     
         4 . The method of  claim 1 , further comprising the steps of:
 obtaining the torsional friction from a lookup table comprising data from a generated model of the drilling system based at least partially on a set of downhole measurements and the drilling parameters of the drilling system.   
     
     
         5 . The method of  claim 1 , wherein the monitoring comprises the steps of:
 monitoring rotations per minute (RPM) and torque of the drillstring.   
     
     
         6 . The method of  claim 1 , wherein the oscillatory period or the frequency is manually input by a remote human operator. 
     
     
         7 . The method of  claim 1 , wherein the oscillatory period or the frequency is automatically input via an automatic system. 
     
     
         8 . The method of  claim 1 , further comprising the steps of:
 determining an equivalent twist stored within the drillstring, the equivalent twist based at least partially on the torsional friction along the drillstring.   
     
     
         9 . A drilling system for wellbore construction, comprising:
 a drillstring comprising a drill bit coupled to a bottom-hole-assembly (BHA);   a top drive coupled to a surface end of the drillstring, wherein the top drive is configured to rotate the drillstring upon receiving an input signal from a controller; and   one or more sensors coupled to the drillstring and the controller, wherein the one or more sensors is configured to detect rotation or torque in the drillstring.   
     
     
         10 . The system of  claim 9 , wherein the controller comprises one or more nontransitory storage mediums configured to provide stored code segments, the one or more nontransitory storage mediums coupled to one or more processors, each configured to execute the code segments and causing the one or more processors to:
 receive a desired oscillatory period or frequency;   compute an amplitude of oscillation based at least partially on an estimated torsional friction and the oscillatory period or the frequency;   transmit a rotary control signal to the top drive, the rotary control signal based at least partially on the amplitude of oscillation;   receive torque and realized rotations per minute (RPM) of the drillstring from the one or more sensors; and   determine whether the BHA is stationary.   
     
     
         11 . The system of  claim 10 , wherein the one or more processors is further configured to transmit the rotary control signal based at least partially on feedback received from the one or more sensors. 
     
     
         12 . The system of  claim 10 , wherein the torsional friction is validated via the controller. 
     
     
         13 . The system of  claim 10 , wherein the one or more processors is further configured to provide a human machine interface (HMI). 
     
     
         14 . The system of  claim 9 , wherein the one or more sensors is operable to provide real-time downhole conditions and downhole drilling characteristics, the downhole conditions comprising formation resistivity, permeability, and the downhole drilling characteristics comprising a rate of rotation of the drill bit, a torque-on-bit (TOB), and a weight on the bit (WOB). 
     
     
         15 . The system of  claim 10 , wherein the one or more processors is further configured to receive a user-defined surface quill orientation and transmit the rotary control signal based at least partially on feedback received from the one or more sensors in order to achieve the user-defined surface quill orientation. 
     
     
         16 . The system of  claim 9 , wherein the one or more sensors is coupled to measurement while drilling (MWD) tools and/or logging while drilling (LWD) tools. 
     
     
         17 . The system of  claim 9 , further comprising a bent housing motor assembly coupled to the drill bit, wherein an angular position of the bent housing motor can be altered to allow geo-steering operations. 
     
     
         18 . One or more non-transitory computer-readable media storing computer-executable instructions that upon execution cause one or more processors to perform acts comprising:
 estimating a torsional friction along a drillstring of a drilling system to determine an amplitude of a rotary oscillatory motion based at least partially on an oscillatory period or frequency;   transmitting a rotary control signal to the drilling system based at least partially on the amplitude of the rotary oscillatory motion when the drilling system is activated;   monitoring rotations per minute (RPM) and torque of the drilling system to determine whether a bottom hole assembly (BHA) coupled to the drillstring of the drilling system remains stationary; and   reducing the amplitude of the rotary oscillatory motion upon determining that the BHA is not stationary.   
     
     
         19 . The one or more non-transitory computer-readable media of  claim 18 , wherein the acts further comprise:
 validating the torsional friction, the torsional friction derived from a lookup table comprising data from a generated model of the drilling system based at least partially on a set of downhole measurements and the drilling parameters of the drilling system, the downhole measurements obtained from one or more sensors coupled to the drillstring.   
     
     
         20 . The one or more non-transitory computer-readable media of  claim 18 , wherein the transmitting comprises:
 transmitting the rotary control signal to a top drive coupled to the drillstring to impart torque and rotation to the drillstring, wherein torque and rotation imparted on the drillstring is transferred to the BHA and a drill bit coupled to the drill string, causing both to rotate.