Float valve assembly for drilling and workover operations

A well system, comprising:

• a tubular string positioned in a wellbore drilled into a subterranean zone and comprising a plurality of tubular segments and a central bore;
• and
• a float valve assembly configured to be positioned within the central bore, the float valve assembly comprising:
• a valve main body comprising:
• an outer surface substantially cylindrical in shape;
• a valve flow passage defined in part by an inner surface of the valve main body and configured to be fluidically connected to the central bore;
• and
• a circumferential inner sealing surface formed on a portion of the inner body surface;
• and
• a plunger positioned within the valve main body and axially moveable therein, the plunger comprising:
• a circular base;
• a seal ring disposed circumferentially about the circular base;
• and
• a plunger main body disposed on the circular base, a surface of the plunger main body comprising a plurality of substantially flat lateral faces forming a pyramid;
• and wherein:
• the plunger is biased, by a spring, towards a closed position in which at least a portion of the seal ring is in contact with the circumferential inner sealing surface, thereby preventing a flow of fluid in an uphole direction through the valve flow passage;
• the plunger is configured to, in response to a fluid pressure in a downhole direction overcoming a biasing force of the spring, move to an open position in which the seal ring is not in contact with the circumferential inner sealing surface, thereby permitting a flow of fluid in a downhole direction through the valve flow passage;
• and
• a hydrophilic nano-coating comprising particles with sizes of between 1 and 100 nanometers is disposed on at least a portion of the surface of the plunger main body.

A method comprising:

• (a) positioning a float valve assembly within a central bore of a tubular string, the float valve assembly comprising:
• a valve main body comprising:
• an outer surface substantially cylindrical in shape;
• a valve flow passage defined in part by an inner surface of the valve main body and configured to be fluidically connected to the central bore;
• and
• a circumferential inner sealing surface formed on a portion of the inner body surface;
• and
• a plunger positioned within the valve main body and axially moveable therein, the plunger comprising:
• a circular base;
• a seal ring disposed circumferentially about the circular base;
• and
• a plunger main body disposed on the circular base, a surface of the plunger main body comprising a plurality of substantially flat lateral faces forming a pyramid;
• and wherein:
• the plunger is biased, by a spring, towards a closed position in which at least a portion of the seal ring is in contact with the circumferential inner sealing surface, thereby preventing a flow of fluid in an uphole direction through the valve flow passage;
• and
• a hydrophilic nano-coating comprising particles with sizes of between 1 and 100 nanometers is disposed on at least a portion of the surface of the plunger main body;
• (b) lowering the tubular string into a wellbore drilled into a subterranean zone;
• (c) sufficiently increasing a fluid pressure of the fluids in the tubular string uphole of the float valve assembly to overcome a biasing force of the spring, thereby causing the plunger to move to an open position in which the seal ring is not in contact with the circumferential inner sealing surface;
• and
• (d) flowing a fluid in a downhole direction through the valve flow passage.