How does the JOIDES Resolution take cores?
One of the goals of the deep sea drilling program is to be able to drill in water depths that exceed the limits of what oil and gas companies attempt. In the 1980s, drill ship was able to core the seafloor using "riserless drilling" which was not used by the oil and gas industry at the time. A riser is a large diameter pipe that connects the Blowout Preventer (BOP) on the seafloor to the floating drill rig. The riser is used to pump drilling mud to the bit and circulate out cuttings. The IODP "riserless drilling" does not use a BOP on the seafloor; instead the program used seawater as a drilling fluid, and cuttings circulate out of the deep ocean hole and are deposited onto the seafloor without creating biohazards. One major advance is the ability of the JOIDES Resolution drill ship to maintain its floating position using motor thrusters and mitigate motion due to ocean heave and current.
Until technological advances were invented to compensate for ship motion, it was very difficult to log the deep ocean boreholes after coring. Logging and drilling research for IODP is done today from the Lamont Doherty Earth Observatory in Palisades New York, and the benefits spread to the oil and gas industry. This includes research into using riserless wells in ultra deep water, and reentry of older wells. Open hole in the seafloor after core recovery is used for down hole observation using seismometers in earthquake prone areas like Japan and eastern Pacific Ocean. The borehole cavities are also monitored for extended periods of time for geochemical changes, fluids, and formation temperature. Lamont Doherty research has advanced the IODP logging capabilities by using (LWD) Logging While Drilling and capturing logs all the way to the seafloor, and in geophone logging for shear wave information.
Let’s look at the deep ocean cores
Dr. Jeff Fox took us on a tour of the IODP core storage facility which was just down the hall from his office at Texas A&M. The drilling program has drilled 1700 boreholes all over the world. The Gulf Coast Repository (GCR), located at Texas A&M houses cores collected by ODP and IODP from the Pacific and Indian Oceans core from other storage locations that are being transferred here. These cores are used to study paleontology, climate change, gas/methane hydrates and the biosphere, life in the oceans and physics of heat transfer. As Dr. Fox opened the door to the core storage facility a cold air blast reminded us the cores are permanently stored at 40 degree F. He pulled open a 30 foot core box and we observed that cores were stored in plastic and paper boxes, rather than in wood boxes like oil cores. The ODP sediment cores they were thinner than petroleum cores, an inch or so across, and stored in their original 31-foot long sections. Actually only half the original core is permanently archived. The other half of each core is sacrificed for scientific study and sampled into bags and sent out around the world for testing and study. While we talked, curatorial specialist Rachel Culberson was taking samples from white core. This core was a Turonian aged, calcareous, vitreous tuff from the eastern Indian Ocean. Dr. Fox said the core lab has distributed over 2 million samples to scientists all over the world and that scientists can request samples using the internet website----.
Scientists needed for deep ocean research
How about these job requirements for work on the JOIDES Resolution: Core Description. Macroscopic visual description, microscopic and entry into database. Measure physical property data on a split core including color reflectance, magnetic susceptibility, and digital images. Interpretation of depositional processes, X-ray diffraction and geochemistry. Stratigraphic correlation: work with real time coring information and use magnetic readings, gamma ray and gamma ray attenuation for logging after coring is completed. Biostratigraphy: sampling cuttings from coring and taking samples from the core to do nannofossils and diatom identification. Fossils are use to assess paleo-water depths. Magnetostratigraphy: measure core for paleomagnetism and absolute orientation of deformation structures. Organic geochemistry: monitor cores for hydrocarbons, conduct analysis on water in pores inside the core. Down hole logging: Lamont Doherty sends scientists to implement the open hole logging program. Seismic site surveys are also done and vertical seismic profiling.
This is Part I of the Guest Night Feature presentation. Click here to read Part II.