Method and core barrel apparatus for obtaining and retrieving

Abstract

Core barrel apparatus and a method for obtaining and retrieving sealed core samples of subterranean formations are disclosed. The core barrel apparatus comprises inner and outer core barrels. The upper portion of the outer core barrel is adapted to be connected to a drill string. A core bit for cutting a core sample is mounted on the lower portion of the outer core barrels. The inner core barrel comprises a sample chamber for receiving a core sample as it is formed at the bottom of a bore hole and an expansion chamber for receiving sample fluids. The sample chamber and expansion chamber are selectively connected to one another. The expansion chamber is sealed closed while the sample is being cut and received within the sample chamber. The lower portion of the sample chamber adjacent the core bit is sealed by a flap-valve which includes a flexible flap member. The flexible flap member is deflected from its normal form of a flat disc into a semi-cylindrical form and stored adjacent to the inner circumference of the sample chamber while the sample is being cut. Once the core sample is within the sample chamber, the flap member is permitted to spring into its flat disc form and extend across the opening in the lower portion of the sample chamber in order to seal the core sample within the chamber. Thereafter the expansion chamber is opened to the sample chamber. As the apparatus is raised toward the surface and the pressure within the bore hole decreases, the expansion chamber expands in response to the pressure of the fluid within it and thereby maintains the pressure within the expansion chamber at or relatively near the bore hole pressure.