Patent attributes
A system and method of reverse stage cementing in which flow into a casing string from an annulus between the casing string and wellbore walls is pressure dependent; the flow is blocked after stage completion. The flow enters the casing string through a cementing sub integrally formed in the casing string. A flapper valve is in a sidewall of the cementing sub that opens when pressure in the annulus reaches a threshold value, and remains open until the annulus pressure falls below the threshold value. Flapper valve actuation is controlled by a hinge spring that is calibrated to open and close the flapper valve based on the annulus pressure. Also in the cementing sub is a sleeve that is positioned behind the flapper valve after the reverse stage cementing is completed. Sleeve actuation is timed to allow adequate time for the flapper valve to return to the closed position.
