Determining gas content stratigraphies in ODP cores
Project Manager: Bill Ussler
Lead Scientist: Charlie Paull
Lead Engineer: Paul McGill

Our continuing objective is to develop a bore hole tool that is capable of determining the spatial variation in the amount of gas contained in continental margin sediments. We are developing and testing sensors to measure temperature, pressure, and electrical conductivity (TPC) inside the standard the Ocean Drilling Program (ODP) advanced piston corer (APC). These sensors are being placed on the face of the piston and monitor temperature, pressure and electrical conductivity variations that occur during core recovery. Gas hydrate decomposition, gas exsolution, and gas expansion occur during core recovery and should affect the temperature, pressure and electrical conductivity within the coring system especially as gas is released from the core. While gas related thermal and pressure effects have been observed on freshly recovered cores, the process has never been systematically monitored. Because each individual core is exposed to nearly the same conditions, anomalies within an individual core and between successive cores should reflect the variations in the amount of gas that was initially within the core.

This is a joint project with the ODP group at Texas A & M University (TAMU). ODP-TAMU is responsible for developing and testing the hardware and data collection software necessary to implement the TPC sensor package. MBARI is responsible for developing the TPC sensor package through internal and NSF funding.

A working prototype was field-tested downhole on ODP Leg 195 (4 March 2001 to 2 May 2001) in a particularly harsh drilling environment with generally positive results. This test demonstrated that the electronics design and board layout is robust for downhole use, the battery pack is of sufficient capacity, and that the mechanical package does not leak and is suitable for rapid swap-out from the coring string.

Further work is necessary before a final version of the tool can be constructed. These tasks include: (1) modifying control and data logging software to account for component changes and improved ease of use in the field; (2) calibration of the sensors; (3) selection of a faster response thermistor package that has mechanical properties suitable for downhole use. When this is accomplished, we have to assist the engineers at ODP in the fabrication of the final tools and provide documentation.

We have requested that ODP use the TPC tool during drilling off the Peru Margin in 2002 (ODP Leg 201) and plan to apply as shore-based participants in this drilling leg. This will begin the final phase of this project that includes the analysis of scientific data obtained by the TPC tool.