The Ocean Drilling Program IV: Deep water coring technology-Past, present, and future

Using the technology developed during 15 years of the highly successful Deep Sea Drilling Project (DSDP), the Ocean Drilling Program (ODP) is continuing to pursue both the scientific objectives of recovering core samples from beneath the world's oceans and the technical objectives of advancing the state-of-the-art of deep water coring. The wide variety of wireline coring tools developed during DSDP (1968-1983) which are still in use include a standard Rotary Core Barrel (RCB), a through-the-bit Extended Core Barrel (XCB) and a Pressure Core Barrel (PCB) for recovering cores at in situ pressures up to 5000 psi. All of these are variations of rotary coring done in conjunction with TCI roller cone core bits. Non-rotary coring tools and downhole instruments have included three generations of hydraulic piston corers for use in recovering undisturbed cores in unconsolidated sediments. The most recent version, the Advanced Piston Corer (APC), is about half as mechanically complex as its predecessors, yet delivers 76% greater coring thrust. Magnetic azimuth orientation for each piston core is available utilizing an Eastman multishot tool. A miniaturized electronic temperature measuring instrument can be used with the APC or a combined Heat Flow/Pore Water Sampler tool can be deployed in soft formations. Current ODP tool developments include a wireline retrievable hard rock coring tool, driven by a 3-3/4 inch diameter mud-motor. A sea floor structure to stabilize a hollow rotor 9-1/2 inch PDM mudmotor is being developed to start holes on hard rock with little or no sediment cover. Possibilities for future tool developments include: hydraulic sidewall samplers for hard rock or soft formations; in situ gas sampling in soft sediments; wireline retrievable downhole geotechnical instruments; a vibracorer to recover loose sands; and "smart" core barrels with the ability to interpret and adjust for changes in coring parameters.