Safety valve apparatus for downhole pressure transmission systems

Abstract

Safety valve apparatus for a pressure telemetry system utilizing a small diameter tubing conveying pressure from a downhole pressure chamber to the surface, the system pressurized with a monitoring gas, is presented. A check valve assembly is placed along the fluid flow path having a check valve with an operating member. The operating member moves to a sealed position by floating on an activating fluid. The operating member must be of low effective specific gravity to float on wellbore hydrocarbon fluids, either liquid or gas. Consequently, in one preferred embodiment, the check valve operating member is a hollow dart which retains the monitoring gas inside the hollow portion, thereby effectively reducing its specific gravity such that it will float on the activating fluid. The activating fluid is a fluid can be hydrocarbon wellbore liquid or gas, completion, stimulation or other injected liquids or gases or an activating liquid or gas stored in a separate chamber in fluid communication with the check valve chamber.