Method and apparatus for taking an undisturbed core sample

The invention is a coring device which has features to seal off from the well fluids prior to taking of the specimen. The apparatus can be hydraulically or pneumatically actuated to move an inner string which is connected to a core barrel. Prior to moving the core barrel, an outer tube is sealingly pushed into the formation. Once the outer tube has been set into the formation, the inner tube drives the core barrel into the formation, leaving behind a rabbit. A clam shell is located at the forward end which stays open as the core barrel is driven into the formation and closes as the core barrel is withdrawn into the outer tube to retain the core. The pneumatic or hydraulic pressure continues to be applied to the inner string as the core barrel is withdrawn into the outer tube. Upon full retraction of the core barrel into the outer tube, a ball valve is actuated to seal off the core barrel. At that time, the hydraulic or pneumatic pressure is removed and the apparatus is pulled to the surface. The core barrel has a venting feature to allow any gas in the core barrel to escape as the core barrel fills with the core sample.