Previous   |    Next

doi:10.2204/iodp.sp.345.2012

Wireline logging

Wireline logs will be recorded at every site to measure the in situ physical properties of the formation and to complement the incomplete core recovery that is typical of basement drilling and expected in this challenging drilling environment. These data will help define the thickness of lithologic units, characterize alteration patterns, or estimate fracture density. They will also be crucial to characterize the local structure and provide orientation to structural features observed on the cores. The data from the wireline logging will be integrated with measurements on the core in order to pin individual core pieces to a specific wireline depth, to geographically orient the core pieces, and to constrain to the extent possible the characteristics of the uncored intervals.

Two logging strings will be used:

1. The triple combination (triple combo) tool string will include the High Resolution Laterolog Array (HRLA), which measures the resistivity of the formation; the Accelerator Porosity Sonde (APS), which measures porosity; the Hostile Environment Litho-Density Sonde (HLDS), which measures density; and the Hostile Environment Natural Gamma Ray Sonde (HNGS), which measures spectral gamma radiation and the contributions of uranium, thorium, and potassium. The caliper of the HLDS will measure the size of the hole that will allow an assessment of the quality of the data and the hole conditions for the following string.

2. The FMS-sonic tool string is composed of the Dipole Sonic Imager (DSI), which measures sonic velocity, and the FMS, which provides microresistivity images of the borehole wall. As part of the FMS, the General Purpose Inclinometry Tool (GPIT) includes a three-axis accelerometer and a three-axis magnetometer to monitor tool motion and provide orientation for the images of the surrounding structure. In addition to the shear and compressional velocity of the formation, the DSI uses two orthogonal dipole sources to measure acoustic anisotropy that can be used to determine preferred mineral and/or fracture orientations, fracture densities, and stress directions. Stoneley waveforms will also be recorded that could help identify fractures and constrain the permeability around the borehole.

A potential additional logging tool string with the Magnetic Susceptibility Sonde (MSS) and the multisensor Magnetometer Module (MMM) may be available. These two tools are in development and testing is planned prior to Expedition 345. If the tests are successful, these tools will be available for the expedition. If time allows, they could be deployed to investigate the in situ magnetic properties of the crust recovered at Hess Deep.

All of the wireline tools and their applications are described at iodp.ldeo.columbia.edu/TOOLS_LABS/index.html.

Top of page   |    Previous   |    Next