Oman Drilling Project Phase 2 Slimline Borehole Geophysics : Rock Parameters

In winter 2017-18, the Oman Drilling Project (OmanDP) drilled seven holes at two sites in the Samail ophiolite in the southern Samail and Tayin massifs. 1700 m of igneous and metamorphic rock cores were recovered from five holes (CM1A, CM2B, BA1B, BA3A and BA4A). In addition, drill cuttings were obtained from four rotary holes CM1B, CM2A, BA1C and BA1D). A comprehensive slimline borehole geophysical survey was conducted in all the OmanDP Phase 2 boreholes shortly after drilling in March and April 2018. In-kind support was provided from the Ministry of Regional Municipalities and Water Resources of Oman, Public Authority of Mining, Sultan Qaboos University and the German University of Technology.

Geophysical wireline logs were collected in most of the holes from slimline borehole logging equipment were provided and run by the Centre National de la Recherche Scientifique (CNRS) from Geosciences Montpellier, using logging trucks from the Ministry of Regional Municipalities and Water Resources. Electrical resistivity (dual laterolog resistivity, LLd and LLs), spectral gamma ray (K, U, and Th contents), magnetic susceptibility, total natural gamma ray, full waveform sonic (Vp and Vs), optical and acoustic borehole wall imaging were recorded to image rock properties, along with borehole fluid parameters and caliper (borehole diameter). Unfortunately, incomplete wireline logs are available for all holes at the CM site and in BA1C due to borehole obstructions.

With data recorded as part of oceanic scientific drilling over the past 35 years in the upper oceanic crust (particularly Holes DSDP/ODP 395A, 504B and 735B, plus Holes 1156D and 1309D) plus that obtained in 2017 as part of Phase 1 of OmanDP, a complete section of petrophysical data is now available for the entire oceanic crust and underlying mantle. This includes seismic velocities (Vp and Vs), electrical resistivity, magnetic susceptibility, natural gamma , as well as oriented images of fracturing cut but the borehole surface. Results from the slimline geophysical survey including preliminary log analysis will be presented for each OmanDP Phase 2 borehole.