Logging/Downhole measurements strategy

Downhole measurements during Expedition 336 will focus on characterizing crustal physical properties and defining structural and lithologic boundaries as a function of depth. In addition, wireline logging data can be compared to results of laboratory analyses of discrete samples and should help delineate alteration patterns, fracture densities, and structural orientations and determine how these correlate with fluid flow. These measurements will complement core measurements by determining the thickness and structure of lithologic units in intervals where core recovery is poor. These logs will be also critical for both shipboard hydrologic (packer) tests as well as for the precise depth placement of the CORK experiments.

Wireline logging

Wireline tool strings will be deployed at Sites 395, NP-1, and NP-2 (Table T3). Logging time estimates for each site are given in Table T3. These logs will provide measurements including temperature, natural gamma ray, density, porosity, resistivity, sonic velocity, and microresistivity. Descriptions of the wireline tools and their applications are available at​TOOLS_LABS/​index.html.

In Hole 395A, we intend to deploy an adapted triple combination (ATC) tool string. The ATC will include probes to measure natural gamma ray (Hostile Environment Natural Gamma Ray Sonde [HNGS]) and temperature (Modular Temperature Tool [MTT]). Additionally, we hope to add the Deep Exploration Biosphere Investigative Tool (DEBI-t) to this tool string. This tool is currently being developed to image the natural fluorescence of microbial communities exposed on the borehole wall.

At Sites NP-1 and NP-2, the first tool string deployed in the logged hole will be the triple combination (triple combo) tool string, which consists of several probes that record measurements of the penetrated formations and measure natural gamma radiation (HNGS), density (Hostile Environment Litho-Density Sonde [HLDS]), porosity (Accelerator Porosity Sonde [APS]), formation resistivity (Dual Induction Tool [DIT]), and borehole diameter. These measurements will be used for characterization of stratigraphic sequences, assessment of alteration, and reconstruction of the volcanic stratigraphy. Depending on borehole conditions, the Formation MicroScanner (FMS)-sonic tool string (composed of the Dipole Sonic Imager [DSI] and HNGS) will be run. The FMS-sonic tool string will provide high-resolution borehole images of lithostratigraphic sequences and boundaries, geographically oriented fractures, and structural features that could be related to present-day fluid flow and stress state. These images can also be used for reconstruction of the volcanic stratigraphy and reorientation of core pieces. The General Purpose Inclinometry Tool (GPIT) will be deployed with the image tool to collect accelerometer and magnetometer data, which will allow orientation of the images and provide information about borehole geometry. The DSI measurements will include compressional and shear wave forms as well as cross-dipole shear wave velocities measured at different azimuths. These types of measurements can be used to determine preferred mineral and/or fracture orientations, fracture densities, and paleostress directions. The velocity and density downhole measurements can also be used for constructing synthetic seismograms and tying the core and log measurements to regional seismic reflection data. In addition, if the DEBI-t is fully developed and successfully run as part of the ATC in Hole 395A and time permits, we hope to deploy it at Sites NP-1 and/or NP-2.