Combination well casing pressure relief and kill valve apparatus

Abstract

In a subterranean well having a production tubing string outwardly circumscribed by a brine-filled casing annulus, a specially designed combination casing pressure relief and kill valve is supported within a side pocket mandrel installed in the production tubing, the valve having inlet ports communicated with the casing annulus. During an initial production phase of the well, when the casing annulus/production tubing pressure differential reaches a first pressure differential set point of the valve due to a brine temperature increase, a pressure relief portion of the valve opens to admit a relatively low flow rate of annulus brine to the tubing string, thereby relieving the annulus pressure, and then closes to reseal the annulus. When it later becomes necessary to temporarily kill the well, kill fluid is pumped into the casing annulus. As the annulus pressure increases, the first valve set point is reached and the pressure relief portion of the valve opens. However, the flow rate of annulus fluid discharged from the valve into the production tubing is considerably less than the flow rate of kill fluid being pumped into the casing annulus. Accordingly, the fluid pressure differential between the casing annulus and the production tubing rises to a second, higher pressure differential set point of the valve. When this occurs, a kill portion of the valve permanently opens to admit kill fluid into the production tubing at a considerably higher flow rate than the pressure relief outflow rate of the valve.