Downhole cementing system

A wellbore cementing method comprising the steps of:

• (a) coupling a choke element to a float collar;
• (b) coupling the float collar between two adjacent joints of casing;
• (c) lowering the casing and the float collar into a borehole;
• (d) at all points during which step (c) is being performed, at least substantially blocking upward fluid flow through the float collar;
• (e) charging cement to an upper end of the casing so that the cement falls downward towards the float collar;
• and
• (f) contacting the cement with the choke element so that the velocity of the cement exiting the float collar is less that it would have been had step (a) not been performed.

A downhole choke couplable between to adjacent joints of wellbore casing, said choke comprising:

• a tubular body defining a fluid passageway;
• a seat coupled to the tubular body and defining a seat orifice, said seat orifice being in fluid communication with the fluid passageway;
• a choke element coupled to the seat and defining a choke orifice, said choke element operable to at least partially inhibit fluid flow through the seat orifice in a first flow direction;
• and
• a check valve coupled to the seat and operable to at least substantially block fluid flow through the seat orifice in a second flow direction generally opposite the first flow direction.

A wellbore which has been readied for cementing, said wellbore comprising:

• a borehole wall defining a generally downwardly extending borehole;
• a casing string at least substantially disposed in the borehole and at least substantially fixed relative to the borehole wall, said casing string presenting upper and lower ends and defining a fluid passageway;
• and
• a cement choke coupled to the casing string below the upper end, said cement choke presenting a flow restricting surface operable to at least partially inhibit the downward flow of cement through the fluid passageway,
• said fluid passageway above the choke primarily containing gas-phase fluids.