Abstract: Backflow prevention assemblies and methods for downhole systems having outer strings and inner strings include a housing defining a cavity and being part of the outer string, a flow tube disposed between the inner string and the outer string movable axially within the outer string, and a backflow prevention structure having a flapper and a seal seat, the flapper biased toward a closed position and maintained in an open position by the flow tube. The flapper is housed within the cavity when in the open position and the flapper and seal seat form a fluid seal to prevent fluid flow into or through the flow tube when in the closed position. When the flow tube is moved from a first position that maintains the flapper in the open position to a second position, the backflow prevention structure operates to close the flapper and seal the backflow prevention structure.

Abstract: Backflow prevention assemblies and methods for downhole systems having outer strings and inner strings include a housing defining a cavity and being part of the outer string, a flow tube disposed between the inner string and the outer string movable axially within the outer string, and a backflow prevention structure having a flapper and a seal seat, the flapper biased toward a closed position and maintained in an open position by the flow tube. The flapper is housed within the cavity when in the open position and the flapper and seal seat form a fluid seal to prevent fluid flow into or through the flow tube when in the closed position. When the flow tube is moved from a first position that maintains the flapper in the open position to a second position, the backflow prevention structure operates to close the flapper and seal the backflow prevention structure.