Abstract: A circulating valve is provided for connection into the tubing string of a well for establishing selective flow of fluid between the tubing string and the well casing. The circulating valve incorporates a valve body which is adapted for connection into the tubing string of the well, which body defines a flow passage in registry with the flow passage of the tubing string. A valve seat is provided on the valve body and an outlet opening is defined downstream of the valve seat which is of sufficiently restricted dimension to permit opening of the valve at a particular injection pressure and to permit maintenance of the valve open condition by means of a pressure lower than the valve opening injection pressure.

Abstract: A circulating sub is provided which is adapted for connection in a production tubing string of a flowing well and which defines a flow passage through which production fluid is enabled to flow. The body structure of the sub defines an equalizing port in communication with the annulus between the tubing and casing of the well, which port is normally closed by means of a sleeve valve. An actuating plug is dropped through the production tubing after shutting in the well and descends to the level of the circulating sub where it seats on the closed valve. Application of fluid pressure through the tubing develops sufficient pressure differential across the valve and plug to force the valve to its open position to thus communicate the tubing and annulus for pressure equalization. The plug member incorporates a check valve which permits accurate balancing of kill fluid to well pressure to thus permit emergency killing of the well without causing damage to the production formation.