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 well drilling method can include transporting a pressure optimization unit to a rig site, the pressure optimization unit including a choke manifold, a control system which automatically controls operation of the choke manifold, and a flowmeter which measures flow of drilling fluid through the choke manifold, and then interconnecting the pressure optimization unit to rig drilling equipment. A pressure optimization unit for use with a well drilling system can include a choke manifold, a control system which automatically controls operation of the choke manifold, and a flowmeter which measures flow of drilling fluid through the choke manifold. The choke manifold, control system and flowmeter may be incorporated into a same conveyance which transports the pressure optimization unit to a rig site.

Abstract: A well drilling method can include transporting a pressure optimization unit to a rig site, the pressure optimization unit including a choke manifold, a control system which automatically controls operation of the choke manifold, and a flowmeter which measures flow of drilling fluid through the choke manifold, and then interconnecting the pressure optimization unit to rig drilling equipment. A pressure optimization unit for use with a well drilling system can include a choke manifold, a control system which automatically controls operation of the choke manifold, and a flowmeter which measures flow of drilling fluid through the choke manifold. The choke manifold, control system and flowmeter may be incorporated into a same conveyance which transports the pressure optimization unit to a rig site.

Abstract: A well drilling system for use with a drilling fluid pump includes a flow control device regulating flow from the pump to a drill string interior; and another flow control device regulating flow through a line in communication with an annulus. Flow is simultaneously permitted through the flow control devices. A method of maintaining a desired bottom hole pressure includes dividing drilling fluid flow between a line in communication with a drill string interior and a line in communication with an annulus; the flow dividing step including permitting flow through a flow control device interconnected between a pump and the drill string interior; and the flow dividing step including permitting flow through another flow control device interconnected between the pump and the annulus, while flow is permitted through the first flow control device.

Abstract: A method of controlling pressure in a wellbore can include placing a barrier substance in the wellbore while a fluid is present in the wellbore, and flowing another fluid into the wellbore while the first fluid and the barrier substance are in the wellbore. The first and second fluids may have different densities. Another method can include circulating a fluid through a tubular string and an annulus formed between the tubular string and the wellbore, then partially withdrawing the tubular string from the wellbore, then placing a barrier substance in the wellbore, then partially withdrawing the tubular string from the wellbore and then flowing another fluid into the wellbore. A well system can include at least two fluids in a wellbore, the fluids having different densities, and a barrier substance separating the fluids.

Abstract: A method of controlling pressure in a wellbore can include placing a barrier substance in the wellbore while a fluid is present in the wellbore, and flowing another fluid into the wellbore while the first fluid and the barrier substance are in the wellbore. The first and second fluids may have different densities. Another method can include circulating a fluid through a tubular string and an annulus formed between the tubular string and the wellbore, then partially withdrawing the tubular string from the wellbore, then placing a barrier substance in the wellbore, then partially withdrawing the tubular string from the wellbore and then flowing another fluid into the wellbore. A well system can include at least two fluids in a wellbore, the fluids having different densities, and a barrier substance separating the fluids.

Abstract: A method of controlling pressure in a wellbore can include determining a real time wellbore pressure PwbRT1 at a pressure sensor in the wellbore, calculating hydrostatic pressure Ph1 at the pressure sensor, determining a real time annulus pressure PaRT, calculating friction pressure Pf due at least to circulation of the fluid through the wellbore and depth in the wellbore, calculating a friction pressure correction factor CFPf1 equal to (PwbRT1?Ph1?PaRT)/Pf, and controlling operation of a pressure control device, based on the friction pressure correction factor CFPf1. The method can further include determining a desired wellbore pressure PwbD1 at the pressure sensor, calculating an annulus pressure setpoint PaSP1 equal to PwbD1?Ph1?(Pf*CFPf1), and adjusting the pressure control device as needed to maintain PaRT equal to PaSP1.

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 of controlling pressure in a wellbore can include placing a barrier substance in the wellbore while a fluid is present in the wellbore, and flowing another fluid into the wellbore while the first fluid and the barrier substance are in the wellbore. The first and second fluids may have different densities. Another method can include circulating a fluid through a tubular string and an annulus formed between the tubular string and the wellbore, then partially withdrawing the tubular string from the wellbore, then placing a barrier substance in the wellbore, then partially withdrawing the tubular string from the wellbore and then flowing another fluid into the wellbore. A well system can include at least two fluids in a wellbore, the fluids having different densities, and a barrier substance separating the fluids.

Abstract: A method of controlling pressure in a wellbore can include determining a real time wellbore pressure PwbRT1 at a pressure sensor in the wellbore, calculating hydrostatic pressure Ph1 at the pressure sensor, determining a real time annulus pressure PaRT, calculating friction pressure Pf due at least to circulation of the fluid through the wellbore and depth in the wellbore, calculating a friction pressure correction factor CFPf1 equal to (PwbRT1?Ph1?PaRT)/Pf, and controlling operation of a pressure control device, based on the friction pressure correction factor CFPf1. The method can further include determining a desired wellbore pressure PwbD1 at the pressure sensor, calculating an annulus pressure setpoint PaSP1 equal to PwbD1?Ph1?(Pf*CFPf1), and adjusting the pressure control device as needed to maintain PaRT equal to PaSP1.

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 method of controlling pressure in a wellbore can include placing a barrier substance in the wellbore while a fluid is present in the wellbore, and flowing another fluid into the wellbore while the first fluid and the barrier substance are in the wellbore. The first and second fluids may have different densities. Another method can include circulating a fluid through a tubular string and an annulus formed between the tubular string and the wellbore, then partially withdrawing the tubular string from the wellbore, then placing a barrier substance in the wellbore, then partially withdrawing the tubular string from the wellbore and then flowing another fluid into the wellbore. A well system can include at least two fluids in a wellbore, the fluids having different densities, and a barrier substance separating the fluids.

Abstract: A well drilling system for use with a drilling fluid pump includes a flow control device regulating flow from the pump to a drill string interior; and another flow control device regulating flow through a line in communication with an annulus. Flow is simultaneously permitted through the flow control devices. A method of maintaining a desired bottom hole pressure includes dividing drilling fluid flow between a line in communication with a drill string interior and a line in communication with an annulus; the flow dividing step including permitting flow through a flow control device interconnected between a pump and the drill string interior; and the flow dividing step including permitting flow through another flow control device interconnected between the pump and the annulus, while flow is permitted through the first flow control device.

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.