A method for controlling a well being drilled into a subterranean formation 14, said method comprising the steps of,
- turning a tubular drill string (20) that extends into a borehole (12), said tubular drill string having an upper end (24) and a lower end (22) and a drill bit (26) disposed at said lower end,
- stopping said turning of said tubular drill string when a fluid influx is detected entering said borehole,
- closing a blow-out preventer (32), said blow-out preventer arranged and designed to close said borehole from atmosphere only at a time when said drill bit is stationary,
- operating a fluid pump (40) to pump a fluid from a surface fluid reservoir (42) through a fluid injection line (48), into and through said tubular drill string, out said drill bit and into a borehole annulus (18), said borehole annulus created between an outer diameter of said tubular drill string and an inner diameter of said borehole by said turning of said drill string and said drill bit in said borehole,
- operating a flow control device (70) disposed in a choke line (56), said choke line coupled between said borehole annulus and said surface fluid reservoir and arranged and designed to permit fluid communication therebetween in cooperation with said flow control device while said blow-out preventer closes said borehole from atmosphere, said fluid injection line, said tubular drill string, said borehole annulus, and said choke line defining a fluid flow path through said borehole,
- measuring actual outlet flow rate of fluid flowing through said choke line while said borehole is closed from atmosphere using an outlet flow measurement device (50) disposed in said choke line and arranged and designed to generate a signal Fout(t) representative of actual choke line fluid flow rate as a function of time (t),
- measuring actual outlet pressure in said choke line while said borehole is closed from atmosphere using an outlet pressure measurement device (64) disposed in said choke line and arranged and designed to generate a signal Pout(t) representative of actual choke line pressure as a function of time (t),
- transmitting said actual outlet flow rate signal Fout(t) and said actual outlet pressure signal Pout(t) to a central control unit (80), said central control unit arranged and designed to receive said signals, to determine a formation fracture pressure, to determine a formation pore pressure, to generate a signal Pann(t) representative of pressure at a well bore depth as a function of time (t), and to generate a signal FC(t) representative of choke line flow rate required as a function of time (t) to maintain said signal Pann(t) below said formation fracture pressure and above said formation pore pressure,
- receiving said signal Fout(t) and said signal Pout(t) in said central control unit,
- using said central control unit to determine said formation fracture pressure as a function of said signals Fout(t) and Pout(t),
- using said central control unit to determine said formation pore pressure as a function of said signals Fout(t) and Pout(t),
- using said central control unit to generate said signal Pann(t).
- using said central control unit to generate said signal FC(t),
- transmitting said signal FC(t) to said flow control device, said flow control device arranged and designed to receive said signal FC(t),
- receiving said signal FC(t) in said flow control device, said flow control device further arranged and designed to control fluid flow through said choke line in response to said signal FC(t), and
- adjusting said flow control device in response to said signal FC(t) to control choke line fluid flow rate to maintain said signal Pann(t) below said formation fracture pressure and above said formation pore pressure.