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doi:10.2204/iodp.proc.342.101.2014

Preliminary scientific assessment: MDHDS sea trials

In situ pore pressure was directly measured at Site U1402. Pore pressure was 7.536 MPa, just slightly above hydrostatic pressure. This is the first in situ pressure measurement made on the Atlantic margin in ocean drilling, and it confirms previous indirect pressure estimates. Accelerometer data collected within the T2P’s electronic housing showed perfect decoupling from the drill string. We now have a dependable method to deploy pore pressure penetrometers successfully, which will allow the rapid measurement of in situ pressure in sediment. This new capability opens an exciting range of future science for the drilling program.

The MDHDS performed well and successfully emplaced a penetrometer with full decoupling and without bending the tip. The T2P penetrometer successfully measured in situ pressure and temperature. The ERS performed acceptably; however, the tool can overlatch, which resulted in dropping the MDHDS in one instance at Site U1402. Real-time data were acquired through the tethered system, but problems with the tether associated with drill string pressurization suggest that this component (real-time telemetry with a tether) is not ready for regular shipboard use.

The following decisions were made based on shipboard results and subsequent shore-based discussions between the MDHDS development team and the USIO. The MDHDS will undergo minor modifications before certification for shipboard deployment. The decision to remove the real-time telemetry tether allows a decrease in diameter of the MDHDS inner barrel subassembly, which provides space to install a larger, stronger spring in the MDHDS latching mechanism. This will make the inner barrel subassembly stronger and will reduce the risk of the MDHDS latch failing to release at depth. These modifications are currently being completed by Pettigrew Engineering. The T2P penetrometer successfully measured in situ pressure and temperature and will be certified by the USIO. The ERS performed acceptably yet will need additional modifications prior to regular shipboard deployment. The primary issue to address is overlatching, which can be resolved by installing a mechanical stop on the latching mechanism. A secondary but important issue to address is the ERS motors, which tend to leak (and leak more at depth) and need slight electrical modifications to ensure proper functionality during deployment. These modifications are currently being made by Stress Engineering with funding from IODP-Management International, Inc. The ERS is not ready to be adopted. A successful deployment of the Simple Cabled Instrument for Measuring Properties In Situ will be the bar for acceptance of the ERS.

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