Abstract: A method of mitigating undesired pressure variations in a wellbore due to movement of a well tool string in a well can include selectively decreasing and increasing fluid communication between sections of a wellbore on opposite sides of at least one well tool in the well tool string, the fluid communication being increased in response to detecting a threshold movement of the well tool string relative to the wellbore. A well tool string can include a well tool connected in the well tool string, and having an enlarged outer dimension relative to adjacent sections of the well tool string, a flow passage extending between the well tool's opposite ends, a sensor, and at least one flow control device which selectively permits and prevents fluid communication between the opposite ends via the flow passage, in response to an output of the sensor indicative of movement of the well tool string.

Abstract: A method of mitigating undesired pressure variations in a wellbore due to movement of a well tool string in a well can include selectively decreasing and increasing fluid communication between sections of a wellbore on opposite sides of at least one well tool in the well tool string, the fluid communication being increased in response to detecting a threshold movement of the well tool string relative to the wellbore. A well tool string can include a well tool connected in the well tool string, and having an enlarged outer dimension relative to adjacent sections of the well tool string, a flow passage extending between the well tool's opposite ends, a sensor, and at least one flow control device which selectively permits and prevents fluid communication between the opposite ends via the flow passage, in response to an output of the sensor indicative of movement of the well tool string.

Abstract: A method of mitigating undesired pressure variations can include flowing fluid between wellbore sections, thereby mitigating a pressure differential due to drill string movement, and the fluid flowing between the wellbore sections via a bypass passage extending through a drilling motor. A drill string can include a drilling motor, a bypass passage in the drilling motor, a sensor, and a flow control device configured to selectively increase and decrease fluid communication between opposite ends of the drilling motor via the bypass passage, in response to an output of the sensor indicative of drill string movement. A method of mitigating undesired pressure variations in a wellbore due to drill string movement can include selectively preventing and permitting fluid communication between wellbore sections on opposite sides of a drilling motor, the fluid communication being permitted in response to detecting a threshold drill string movement.

Abstract: A method of controlling pressure in a wellbore can include determining a desired position for a choke, the determining being based on a Cv curve for the choke, and adjusting the choke to the desired position, thereby producing a desired backpressure. A wellbore drilling system can include a choke which variably restricts flow of fluid from the wellbore, and a control system which compares actual and desired wellbore pressures and, in response to a difference between the actual and desired wellbore pressures, adjusts the choke to a predetermined position which corresponds to a desired Cv of the choke. A method of controlling pressure in a wellbore can include comparing an actual wellbore pressure to a desired wellbore pressure and, in response to a difference between the actual and desired wellbore pressures, adjusting a choke to a predetermined position, the predetermined position corresponding to a desired Cv of the choke.

Abstract: A well drilling system can include a hydraulics model which determines a modeled fluid friction pressure and a calibration factor applied to the modeled friction pressure, and a flow control device which is automatically controlled in response to a change in the calibration factor. A well drilling method can include drilling a wellbore, a fluid circulating through the wellbore during the drilling, determining a calibration factor which is applied to a modeled fluid friction pressure, and controlling the drilling based at least in part on a change in the calibration factor.

Abstract: A method of maintaining a desired temperature at a location in a well can include adjusting fluid circulation parameters, thereby reducing a difference between an actual temperature at the location and the desired temperature. A well system can include at least one sensor, an output of the sensor being used for determining a temperature at a location in a well, and a hydraulics model which determines a desired change in fluid circulation through the well, in response to the temperature at the location being different from a desired temperature at the location. Another method of maintaining a desired temperature at a location in a well can include adjusting a density, solids content and/or flow rate of a fluid circulated through the well, thereby urging a temperature at the location toward the desired temperature.

Abstract: A drilling method includes assigning values to behaviors of drilling parameters during a drilling operation; forming multiple parameter signatures, each of the parameter signatures comprising a respective combination of the values; comparing the parameter signatures to multiple event signatures, each of the event signatures being indicative of a respective drilling event; and controlling the drilling operation in response to at least a partial match resulting from comparing the parameter signatures to the event signatures.

Abstract: A well drilling method can include detecting a drilling event by comparing a parameter signature generated during drilling to an event signature indicative of the drilling event, and automatically controlling a drilling operation in response to at least a partial match resulting from comparing the parameter signature to the event signature. A well drilling system can include a control system which compares a parameter signature for a drilling operation to an event signature indicative of a drilling event, and a controller which controls the drilling operation automatically in response to the drilling event being indicated by at least a partial match between the parameter signature and the event signature.

Abstract: A method of controlling pressure in a well can include transmitting an instruction to change flow through an annulus formed radially between a drill string and a wellbore, and adjusting a pressure setpoint in response to the transmitting. A well drilling system can include a flow control device which varies flow through a drill string, and a control system which changes a pressure setpoint in response to an instruction for the flow control device to change the flow through the drill string. A method of controlling pressure in a well can include transmitting an instruction to divert flow from a drill string, and adjusting a pressure setpoint in response to the transmitting.

Abstract: Well pressure control is integrated in real time with geomechanics determinations made during drilling. A well drilling method includes updating determinations of properties of a formation surrounding a wellbore in real time as the wellbore is being drilled; and controlling wellbore pressure in real time as the wellbore is being drilled, in response to the updated determinations of the formation properties. Another well drilling method includes obtaining sensor measurements in a well drilling system in real time as a wellbore is being drilled; transmitting the sensor measurements to a control system in real time; the control system determining in real time properties of a formation surrounding the wellbore based on the sensor measurements, and the control system transmitting in real time a pressure setpoint to a controller; and the controller controlling operation of at least one flow control device, thereby influencing a well pressure toward the pressure setpoint.

Abstract: A well control method can include removing from a wellbore an undesired influx from a formation into the wellbore, determining a desired pressure profile in real time with a hydraulics model, and automatically operating a flow choking device while removing the undesired influx from the wellbore, thereby influencing an actual pressure profile toward the desired pressure profile. Another well control method can include removing out of a wellbore an undesired influx from a formation into the wellbore, determining a desired wellbore pressure with a hydraulics model, the desired wellbore pressure preventing further influx into the wellbore while removing the undesired influx from the wellbore, and automatically operating a flow choking device while removing the undesired influx from the wellbore, thereby influencing an actual wellbore pressure toward the desired wellbore pressure.

Abstract: A method for controlling a downhole pressure during drilling comprises continually sensing in real-time at least one real-time fluid property of an input fluid to a well and of a return fluid from the well. A wellhead setpoint pressure is calculated in real-time that results in a predetermined downhole pressure at a predetermined location in the well, where the calculation based, at least in part, on the at least one continually sensed real-time fluid property. The flow of the return fluid is controllably regulated to maintain the calculated wellhead setpoint pressure.

Abstract: A method of mitigating undesired pressure variations in a wellbore due to movement of a well tool string in a well can include selectively decreasing and increasing fluid communication between sections of a wellbore on opposite sides of at least one well tool in the well tool string, the fluid communication being increased in response to detecting a threshold movement of the well tool string relative to the wellbore. A well tool string can include a well tool connected in the well tool string, and having an enlarged outer dimension relative to adjacent sections of the well tool string, a flow passage extending between the well tool's opposite ends, a sensor, and at least one flow control device which selectively permits and prevents fluid communication between the opposite ends via the flow passage, in response to an output of the sensor indicative of movement of the well tool string.

Abstract: A method of mitigating undesired pressure variations can include flowing fluid between wellbore sections, thereby mitigating a pressure differential due to drill string movement, and the fluid flowing between the wellbore sections via a bypass passage extending through a drilling motor. A drill string can include a drilling motor, a bypass passage in the drilling motor, a sensor, and a flow control device configured to selectively increase and decrease fluid communication between opposite ends of the drilling motor via the bypass passage, in response to an output of the sensor indicative of drill string movement. A method of mitigating undesired pressure variations in a wellbore due to drill string movement can include selectively preventing and permitting fluid communication between wellbore sections on opposite sides of a drilling motor, the fluid communication being permitted in response to detecting a threshold drill string movement.

Abstract: A method of controlling pressure in a wellbore can include determining a desired position for a choke, the determining being based on a Cv curve for the choke, and adjusting the choke to the desired position, thereby producing a desired backpressure. A wellbore drilling system can include a choke which variably restricts flow of fluid from the wellbore, and a control system which compares actual and desired wellbore pressures and, in response to a difference between the actual and desired wellbore pressures, adjusts the choke to a predetermined position which corresponds to a desired Cv of the choke. A method of controlling pressure in a wellbore can include comparing an actual wellbore pressure to a desired wellbore pressure and, in response to a difference between the actual and desired wellbore pressures, adjusting a choke to a predetermined position, the predetermined position corresponding to a desired Cv of the choke.

Abstract: A method of providing substantially continuous circulation of fluid through a drill string and an annulus can include sealing off the annulus from atmosphere, regulating flow of the fluid from the annulus, thereby controlling pressure in the wellbore, and diverting flow of the fluid from a pump to an uppermost connector of the drill string and an inlet extending in a sidewall of the drill string, the regulating and the diverting being performed concurrently. A pressure and flow control system can include one or more flow control devices which divert flow from a pump to a valve which selectively permits and prevents communication between an uppermost connector of the drill string and a flow passage extending longitudinally through the drill string, and to a valve which selectively permits and prevents communication between the flow passage and an inlet extending in a sidewall of the drill string.

Abstract: A well drilling method can include sensing at least one of audio and optical signals, generating a parameter signature during a drilling operation, the parameter signature being based at least in part on the sensing, and detecting a drilling event by comparing the parameter signature to an event signature indicative of the drilling event. A well drilling system can include a control system which compares a parameter signature for a drilling operation to an event signature indicative of a drilling event, the parameter signature being based at least in part on an output of at least one audio and/or optical sensor, and a controller which controls the drilling operation in response to the drilling event being indicated by at least a partial match between the parameter signature and the event signature.

Abstract: A method of controlling pressure in a wellbore can include determining a desired well pressure setpoint, adding an offset to the setpoint in response to an actual well pressure deviating from the setpoint by a predetermined amount, and adjusting a flow control device, thereby influencing the actual well pressure toward the setpoint plus the offset. A well system can include a flow control device which variably restricts flow from a wellbore, and a control system which determines a desired well pressure setpoint, compares the setpoint to an actual well pressure, and adds an offset to the setpoint in response to a predetermined amount of deviation between the setpoint and the actual well pressure, whereby the control system adjusts the flow control device, and thereby influences the actual well pressure toward the setpoint plus the offset.

Abstract: A method of segregating flowable materials in conjunction with a subterranean well can include segregating flowable cement from a fluid by placing a flowable barrier substance between the cement and the fluid, and the barrier substance substantially preventing displacement of the cement by force of gravity through the barrier substance and into the fluid. Another method of segregating flowable materials can include flowing a barrier substance into a wellbore above a fluid already in the wellbore, and then flowing cement into the wellbore above the barrier substance. A system for use in conjunction with a subterranean well can include a flowable cement isolated from a fluid by a flowable barrier substance positioned between the cement and the fluid, whereby the barrier substance substantially prevents displacement of the cement by force of gravity through the barrier substance and into the fluid.

Abstract: A method for controlling a downhole pressure during drilling comprises continually sensing in real-time at least one real-time fluid property of an input fluid to a well and of a return fluid from the well. A wellhead setpoint pressure is calculated in real-time that results in a predetermined downhole pressure at a predetermined location in the well, where the calculation based, at least in part, on the at least one continually sensed real-time fluid property. The flow of the return fluid is controllably regulated to maintain the calculated wellhead setpoint pressure.