Gravel pack service tool back pressure valve

An apparatus comprising:

• a service tool configured to be deployed in a wellbore as part of a managed pressure drilling operation of the wellbore, wherein an outer annulus is defined between a wall of the wellbore and a work string that includes the service tool, a drill pipe, and a lower completion, the service tool comprising,
• a crossover port;
• a ball seat configured to receive a ball from uphole such that after receipt of the ball a pressure is exceeded from a fluid flow to cause at least one shear pin to shear such that the service tool is to stroke down to create a fluid communication path for proppant to be pumped through the crossover port and a return back through an inner annulus, as part of gravel packing;
• and
• a valve positioned configured to maintain a back side pressure in the outer annulus without pressurizing the work string.

A system comprising:

• a work string to be deployed downhole in a wellbore wherein an annulus is defined between a wall of the wellbore and the work string, the work string comprising,
• a drill pipe;
• a lower completion;
• and
• a service tool configured to be coupled below the drill pipe as part of a managed pressure drilling operation of the wellbore the service tool comprising,
• a crossover port;
• and
• a valve to be positioned below the crossover port and within the service tool, wherein the valve is configured to maintain a back side pressure in the annulus without pressurizing the work string.